All

NYSGA 2008
New York State Geological Association
Twenty-Ninth Annual Meeting
Wellsville, N.Y. - May 9 - 12, 1957
Guidebook
for
Geology of S.W. Tier
Oil and Gas Fields
Oil Refining
Field Trips
Edited and Compiled
by
W. H. Young, Jr. and W. L. Kreidler

A2: A QUICK LOOK AT NEW YORK’S UNCONVENTIONAL GAS SHALES: SUMMARY AND ROAD LOG
Richard Nyahay
GASTEM USA
Montreal, Quebec
INTRODUCTION
The purpose of this trip is to take a look at the organic rich shales that are driving unconventional shale exploration in New York. These shales are the Devonian Marcellus and the Ordovician Utica. Over the last fifteen years Ver Straeten has worked on the Marcellus Formation and Brett, Baird, Mitchell, Jacobi, and Joy have worked on the Utica Group to determine new and improved correlations. These shales have joined the list of names such as the Barnett, Antrim, and Fayetteville to rejuvenate interest in organic rich shales for natural gas exploration
Technology has been able to make these highly impermeable shales that have long been considered nuisance gas in the past highly profitable. This then begs the question why are these shales highly productive? In order to answer this shales are being studied intensely across the nation. Of all the shales being studied the Barnett shale is the one everyone looks to use as the model. The Barnett shale exploration was inspired by the Eastern Gas Shale Project in the Appalachian Basin that took place during the late seventies and early nineteen eighties (Steward 2007).
The Utica Group is been divided into three formations, the Upper and Lower Indian Castle, the Dolgeville and the Flat Creek. The Dolgeville is coeval with the Rust and Steuben of the lower Trenton Group. The Flat Creek is coeval with the Denley of the Lower Trenton Group.
The Marcellus members we are interested in are the Chittenango, the Cherry Valley, and the Union Springs. Interestingly enough, the patterns of the Barnett, Lower Marcellus and Utica are similar. In the Barnett, the upper and lower shale units are separated by the Forestburgh Limestone. In the Lower Marcellus, the Chittenango, and the Union Springs are separated by the Cherry Valley Limestone. In the Utica Group, the Indian Castle and Flat Creek are separated by the ribbon limestones of the Dolgeville.
The deepening upward sequence that is evident within the Trenton Group and the overlying Utica Group was interpreted as a product of lithospheric flexure caused by the loading of the Laureantian margin during the Taconic Orogeny (Jacobi and Mitchell 2002). Numerous normal faults occur in the region and many underwent significant displacement during the deposition of the Trenton and Utica Groups as a consequence of the attempted subduction of the Laurentian margin (Jacobi and Mitchell 2002). Differential rates of subsidence across the region produced accommodation rates that increased by an order of magnitude from west to east. High rates of siliciclastic sediment supply and even higher subsidence rates resulted in thick deeper water succession to the eastern part of the study region (Joy, et al. 2000). The coeval Trenton Group succession in the west formed under conditions of moderate sediment supply and lower subsidence rates resulting in net shallowing in the upper succession (Joy, et al. 2000).
Baird and Brett (2002) noticed that both the Ordovician Indian Castle and Devonian Marcellus developed as onlap disconformities in a similar western cratonward side of a synorogenic foreland basin. These units record the transgressive drowning of a carbonate shelf with the ensuing establishment of a stratified dysoxic to anoxic bottom conditions.
The Dolgeville Formation formed as a short duration pulse of calciturbidites (Merthens 1988). The Dolgeville formation records a turbidite deposition on a subtidal slope well below fair weather base (Baird and Brett, 2002). The presumed source of the turbiditic carbonate was from the carbonate shelf to the north and west, storm energy as well as seismic activity disturbed sediments in the in the upper slope triggering gradient current and density flows( Baird and Brett 2002).
The Flat Creek Formation was formed as the basin deepened to the east, suggesting that differential tectonic subsidence was the dominant mechanism creating accommodation space (Joy, et al. 2000).
The Indian Castle Formation is divided into two units, the lower Indian Castle and the Upper Indian Castle separated by the Honey Hill disconformity (Baird & Brett 2002). It is overlain by the Schenectady and Frankfort formations and underlain by the carbonates of the Trenton to the west and the Dolgeville Formation to the east. The lower Indian Castle corresponds to the Climacograptus (Diplacanthograptus) spiniferous assemblage zone of graptolites and possibly to the lowermost Geniculograptus Pygmaeus Zone. The lower Indian Castle is hard blocky to sheety black shale with bundles of tabular impure limestone (Baird & Brett 2002). The upper Indian Castle corresponds to the Geniculograptus Pygmaeus Zone and is composed of fissile to platy shale that lack limestone beds (Baird and Brett 2002).
The Dolgeville Formation is distinctive unit that is composed of closely spaced rhythmic dark gray shale and calcisiltic ribbon limestones. The Dolgeville is overlain by the Thruway unconformity that bevel the soft sediment slumps and fault scars of the Dolgeville and is overlain further to the west by the onlapping upper Indian Castile and is underlain by the Flat Creek to the east of the Little Falls fault and lower Trenton Group carbonates west of the fault. The Dolgeville corresponds to the time range of Orthograptus ruedemmani assemblage zone of graptolites with only a very narrow segment of the basal Climacograptus (Diplacanthograptus) spiniferous assemblage near its top (Goldman, et al. 1994). Baird and Brett have traced the Dolgeville as far east as the Hoffman’s Fault. Goldman, et al. 1994 describe the Dolgeville as a thin to medium bedded tabular silty black micrite and interbedded black shales. In subsurface cores at the NYSGS core repository the Dolgeville will show a white weathering color that distinguishes them from the Flat Creek below and Indian Castle above.
The Flat Creek Formation rest disconformably over the Sugar River of the Trenton Group (Joy, et al. 2000) and is gradationally overlain by the Dolgeville Formation (Goldman et al. 1994). The Flat Creek corresponds to the the Corynoides Americanus graptolite Zone assemblage to 8 meters below the base of the Dolgeville where is corresponds to the Orthograptus ruedemmani assemblage zone (Goldman et al. 1994). The Flat Creek is a calcareous, laminated black shale with interbedded calcilutites.
The Chittenango is a jet black, very fissile shale, with no limestone beds as in the Union Springs. It is non-calcareous until the basal section near the top of the Cherry Valley.
The Cherry Valley is a black to brown argillaceous limestone that gives a petroleum odor when broken. It is divisible into two massive parts separated by a shaley limestone or shale containing limestone nodules, and pyrite.
The Union Springs is the basal Marcellus which is a black, pyritiferous, fissile, calcareous shale with concretions, and thin limestone layers.

A2: A QUICK LOOK AT NEW YORK’S UNCONVENTIONAL GAS SHALES: SUMMARY AND ROAD LOG

STOP 1. South Chuctanunda Creek and Rt. 5S Roadcut
This outcrop features the Flat Creek Formation. This shale can be further subdivided into a black fissile shale overlying a dark gray calcareous mudstone with black shale interbeds. A north trending vein displays a nearly vertical fault that might show possible lateral slip, with horizontal slickensides next to a clastic dike (Neptunian?) that strikes north. Could this be evidence of seismic activity that triggered the turbiditic flows of the Dolgeville? Vertical calcite veins cut the roadcut and strike nearly E-W. The roadcut as seen from the east shows a synclinal structure. Bentonite beds are can be easily picked out by their rusty colored weathering. The creek shows these E-W vertical calcite veins that show extensional horsetail features, breccias and possible small pull aparts. In the black fissile shale there is evidence of thrust faulting. Before Baird and Brett (2002), this outcrop could have been interpreted as Utica Shale undivided, but with the Dolgeville extended as far east as Hoffman's fault, this make this shale a good candidate to be the Flat Creek shale. Collections of graptolites would confirm this more correctly.

Dolgeville outcrop on both sides of the NYS Thruway

Black Canyon outcrop of Indian Castile to the S on ramps going E.

STOP 2. Paradise Road NYS Thruway Road Cut
This roadcut displays Lower Indian Castile Formation overlying the Dolgeville Formation separated by the Thruway unconformity. To the eastern end we see a normal fault, a splay of the Little Falls fault. Weathered bentonite beds outline the dark gray Lower Indian Castile showing the blocky limestone beds and indurated shales overlying the alternating tabular beds of dark gray to black limestone and shale with fold trains that have a west vergence. Following the weathered bentonite beds small sags can be seen in the Lower Indian Castile. A fault at the eastern end displays the Upper Indian Castile down dropped to the east against the Lower Indian Castile and Dolgeville formations. Notice the lack of weathered bentonite beds in the Upper Indian Castile. The Upper Indian Castile is a dark gray fissile shale. These laminations can be seen from the perch of the farm field we are standing on.

STOP 3. Otsquago Creek Outcrop
This creek cut shows the contact between the Dolgeville tabular alternating beds of limestone and shale overlying the Flat Creek black fissile shale . Calcite filled veins cut both the Flat Creek and Dolgeville Formations. The veins trend N 110° - 130° E and N 20 E forming a brick work pattern. The density of veins decreases away either side suggesting some type of fault activity. Beds dipping toward each other suggest a synclinal feature just around the bend of the creek.

STOP 4. Hallsville Road Outcrop
At this out crop we will examine the well laminated fissile gray to dark gray Upper Indian Castile. This lamination might be considered papery. This outcrop shows one tabular limestone bed that has a rusty weathering color outlining it. Walking further up the section we see just Upper Indian Castile with no tabular limestone beds.

STOP 5. Otsego County Rt. 54 or old Chestnut street outcrop
At this classic outcrop we will see the lower part of the Chittenango now renamed to the Oakta creek (VerStraten, et al. 1994). Underlying the Oakta Creek is the Cherry Valley Limestone, and the uppermost section of Union Springs. Talus covers intensely deformed sections with the Union springs that exhibit a small thrust fault that ramps up through the Cherry Valley (Bosworth, 1984). The Union Springs member is the richest organic shale in New York, TOC range can be as high as sixteen percent.

AB1:GEOLOGICAL RELATIONSHIPS OF THE ANORTHOSITE-MANGERITE-CHARNOCKITE-GRANITE (AMCG) SUITE AND RELATED ORE DEPOSITS
James McLelland
Colgate University
Hamilton, NY 13346
Introduction
The Adirondack Mountains represent a southwestern extension of the Grenville Province via the Thousand Islands – Frontenac Arch region of the St. Lawrence River (Fig. 1). The region is topographically divided into the Adirondack Highlands and Lowlands separated by the Carthage-Colton Mylonite Zone (CCMZ, Fig. 2). The former is underlain largely by orthogneisses metamorphosed to granulite facies and the latter by upper-amphibolite grade metasediments, notably marbles. Both sectors have experienced multiple deformations resulting in refolded major isoclines. Due to the complexity of the terrain, it was difficult to establish a reliable geologic history prior to the advent of U-Pb zircon geochronology. Silver (1969) pioneered a landmark study based on multigrain thermal ionization mass spectrometry (TIMS). His investigations indicated high-grade metamorphism at ca 1050 Ma and widespread intrusion of granitoids at ca 1120 Ma. These early analyses required very large zircon fractions (hundreds of mg.) and did not have the advantages of hand picking or air abrasion; hence, they represent mixed ages and serve only as rough guidelines. In the 1980's McLelland and Chiarenzelli initiated an investigation in which 30 representative samples were dated by multigrain, air-abraded TIMS methods (McLelland et al. 1982, McLelland and Chiarenzelli, 1990). Subsequently, these results have been extended by single grain TIMS and SHRIMP techniques and most of these are summarized in McLelland et al. (1996), McLelland et al. (2001), Wasteneys et al. (1999), and McLelland (2004) from which the first portion of this article has been derived. The picture that has emerged is one of a tripartite division of Adirondack geologic history, as summarized below.

AB1:Geological Relationships of the Anorthosite-Mangerite-Charnockite-Granite (AMCG) Suite and Related Ore Deposits

STOP 1. Roaring Brook on Giant Mt. (located near R, Fig. 4)
The valley of Roaring Brook on the southwestern slopes of Giant Mt provides some of the finest exposures of AMCG rocks in the Adirondacks. Over a distance of ∼1.5 km and a width of 50-100 m there occur an uncommon array of dikes, sheets and plutons of several generations and compositions that have intruded approximately parallel to the stream valley. A plausible interpretation of the association is that it represents a zone of weakness that repeatedly served as a magma conduit during the emplacement of the ca 1155 Ma AMCG suite.
From 1400' to 2000' the brook is underlain by a variety of anorthositic and gabbroic rocks. Near the lip of the high bridal veils falls the valley is defined by erosion of a diabase dike in the anorthosite. Slightly farther upstream a broad (∼3 m) irregular pyroxene-monzonite dike outcrops on the northwest bank, and clearly truncates magmatic flow foliation in the anorthosite. Coarse comb texture is visible along the dike's margins.
Proceed upstream past several plunge pools to a steep 3-10 m cliff face. A dark, meter-wide eroded and irregular dike of orthopyroxenite is exposed at the base of the waterfall. Erosion of the dike has resulted in the stream channel and can be followed 30-40 m upstream from the cliff edge. Orthopyroxene greatly dominates the mode (90%), but some clinopyroxene, magnetite-ilmenite, and plagioclase are also present. The orthopyroxene appear to be of orthocumulate origin with narrow adcumulate overgrowths. We speculate that the origin of the dike is the result of drainage of orthopyroxene cumulates into a fracture that opened at the base of magma chamber. Several xenoliths of anorthosite are present in the dike, and locally it exhibits soft margins with the country rock anorthosite. The Mg-numbers of the pyroxenes are high (Cpx-75, Opx-65) and suggest that the dike formed early in the fractionation history of the magma.
The smooth outcrop surfaces surrounding the orthopyroxenite dike are dominated by gabbroic anorthosite transitional to gabbro. Several stages in the magmatic history of the anorthosite are recorded by crosscutting relationships. The oldest anorthosite facies are coarse-grained rafts of blue-gray andesine-labradorite anorthosite corresponding to the Marcy facies. They occur as xenoliths within as xenoliths within a medium grained, subophitic, two-pyroxene gabbro that locally grades into norite. This, in turn, is crosscut by a fine-grained gabbroic anorthosite similar to the Whiteface facies. Elsewhere in the outcrop the sequence may be reversed and attests to multiple pulses of magma; however, the coarse grained rafts are always the oldest.
Returning to the trail and proceeding uphill, we cross Roaring Brook and ascend the summit trail to the 2260' (689 m) level. Here we leave the trail and scramble downhill to water-smoothed pavement outcrops in the brook valley. The outcrops expose a spectacular intrusion breccia consisting of rounded and angular blocks (10-30 cm on average) that include coarse, white anorthosite and glassy, pink garnetiferous anorthosite, but consist mostly of gray to black, medium to fine-grained, granular pyroxene-plagioclase assemblages. These are set in a medium grained groundmass ranging from gabbroic anorthosite to garnetiferous mangerite and ferrogabbro. These matrix rocks are highly mingled and difficult to separate without the aid of staining.
A number of dark inclusions exhibit narrow (∼0.5 cm), light colored layers. Traditionally these were interpreted as primary in origin and associated with a sedimentary or volcanoclastic origin (Kemp, 1921, deWaard, 1970, Mclelland et al., 1982). However, examination of stained slabs and thin sections reveals that the light layers are of syenitic composition whereas the dark layers consist of gabbro. It is common for the light, syenitic layers to be continuous with host rocks of the same composition. Moreover, the gabbroic layers contain acicular rods of orthopyroxene that, together with plagioclase, define a “fence-post” pattern (Fig. 5). The pyroxene-plagioclase layers are essentially gabbroic to dioritic in composition with sub-equal amounts of magnesian pyroxene and intermediate plagioclase. On the basis of chemistry and textures, we interpret the layered inclusions as igneous enclaves intruded by parallel veins of syenite and mangerite and incorporated into the mixtures of country rock magmas now constituting the breccia groundmass. The “fence-post” textures are identical to comb-textured pyroxenes in orbicular granites (McKinney, 1990) and provide compelling evidence for their igneous origin (Fig. 5).
The outcrops at Roaring Brook also contain numerous non-layered inclusions, and most of these are rich in magnesian clinopyroxene. They are interpreted as disrupted cumulates caught up by ascending AMCG magmas. None of these enclaves contain acicular pyroxene and exhibit coarse, interlocking grains. They are commonly associated with dark gray, relatively fine grained material of approximately dioritic composition and are thought to be cumulates from these magmas.
A number of the inclusions at Roaring Brook exhibit soft, lobate boundaries typical of magma commingling. Some of the anorthositic inclusions have especially well-developed borders of this sort. These features are attributed to the interaction and incomplete mixing of magmas ascending in the Roaring Brook conduit.

STOP 2. Split Rock Falls (located near 40, Fig. 5)
The roadcut across from the parking area provides good evidence for multiple intrusions of anorthositic and gabbroic rock. The dominant rock type is gabbroic anorthosite that encloses numerous xenoliths of the anorthositic suite. Subophitic textures are preserved in some of the more gabbroic xenoliths. Garnetiferous gabbro truncates foliation in some xenoliths and has, itself, a different foliations. It is thought that many of the foliations are magmatic in origin. A late mafic facies similar to that at Woolen Mill disrupts all earlier rock types. Late mafic dikes (Phanerozoic?) with well-developed slickensides cut all other lithologies.

STOP 3. Elizabethtown anorthositic gabbro
Although most of the outcrop is highly altered, it affords the opportunity to see the effects of Ottawan deformation on AMCG rocks that are situated near the outer margins of the Marcy Massif. Most of the outcrop consists of somewhat gneissic anorthositic gabbro. Some small calcsilicate inclusions consist of grossularite, diopside, and wollastonite. Large cm-scale garnets appear to truncate foliation and may have grown under static conditions. Large black clots of hornblende contain remnant pyroxene cores and may represent deformed, metamorphosed giant pyroxenes.

STOP 4. Woolen Mills Anorthosite and Ferrogabbro (located near 40, Fig.4
The large roadcut shows anorthosite intruded by a dark, reddish-brown, fine-grained rock known as the Woolen Mill Gabbro (1154 ± 9 Ma) for the mill that once existed in the stream across the road. It is a clinopyroxene-garnet-oligoclase granulite with considerable opaque oxides and apatite and minor K-feldspar and quartz. Prior to metamorphism, the granulite was a late ferrodiorite representing residual mafic liquids filter-pressed from the anorthosite. The outcrop was used by deWaard (1965) to establish his clinopyroxene-garnet subfacies of the granulite facies that marks the transition to higher pressures, garnet granulites, and ultimately the eclogite facies.
Across the road from the granulite, a variety of anorthositic rocks (1155 ± 8 Ma) are exposed in the streambed. At the west end of the water-polished outcrops, Woolen Mill gabbro clearly intrudes the anorthosite. However, note an inclusion of gabbro in the anorthosite indicative of coeval relationships. Note the “block structure” where blocks of earlier anorthosite have been broken up and intruded by later magmatic pulses.

2: CHEMICAL WEATHERING AND CALCIUM DEPLETION IN ADIRONDACK SOILS
Richard April
Dept. of Geology
Colgate University
Hamilton, NY 13346
rapril@mail.colgate.edu
Michele Hluchy
Division of Geology and Environmental Studies
Alfred University
Alfred, NY 14802
fhluchy@alfred.edu
INTRODUCTION
Acid Rain and the Adirondack Mountains
The term 'acid rain' was first coined in 1872 in Air and Rain: The Beginnings of Chemical Climatology, a book published by Angus Smith, an English chemist, who was the first to systematically analyze the chemistry of precipitation in industrialized Britain. The effects of acidic deposition on aquatic and terrestrial ecosystems have been studied intensively since the late 1960's and early 1970's, first in Scandinavia, then in Europe, and eventually in the U.S when acid rain emerged as an important ecological issue (Oden, 1968; Likens et al., 1972).
The Adirondack Mountains receive elevated inputs of sulfur and nitrogen in the form of acid deposition. The acid emissions that cause acid deposition began in the late 19th century and increased well into the 20th century, peaking in the 1970's. Annual emissions of sulfur dioxide in the U. S., for example, peaked in 1973 at 28.8 million metric tons. By 2003, following implementation of the Clean Air Act Amendments (CAAA) of 1970 and passage of Title IV of the Acid Deposition Control Program by Congress in 1990, sulfur dioxide emissions had decreased 50%, to 14.3 million tons.
Prevailing winds from the west carry pollutants emitted in the Midwest, mainly from coal-burning electric utilities, over the northeastern United States and Canada. Precipitation in the Adirondacks averages 100 – 150 cm/yr, with about 30% falling as snow (Johannes et al. 1985). This large quantity of precipitation results in high acid loadings. H+ deposition averaged about 500 eq/ha/yr over the Adirondacks in the early 1990s, but decreased to about 300 eq/ha/yr by 2002. Average deposition of H+ and SO4-2 in the Adirondacks has been declining over the past few decades due to significant decreases in SO2 emissions. Average annual pH values of precipitation have risen over this period from about 4.2 to 4.5. Because precipitation amounts decrease from the western to eastern Adirondacks due to orographic effects, H+ deposition decreases by about 10% across the mountain range, a distance of about 150 km (Charles 1991, Driscoll et al. 2003). There has been no significant change in nitrogen deposition during this same period because CAAA legislation did not specify limits for NOx emissions (Driscoll et al. 2001).
Cumulative and lingering effects of over a century of acid rain has led to renewed interest in determining whether terrestrial and aquatic ecosystems in the Adirondacks are showing signs of recovery (i.e., to more natural states, although “natural” is oftentimes difficult to determine because of two centuries of anthropogenic perturbations and lack of historical data). In these studies detailed knowledge of the geology, hydrogeology and geochemistry of the Adirondacks plays a critical role. For example, recent studies of the terrestrial system have shown that base cation depletion in soils, particularly low levels of available calcium in forested watersheds, negatively impacts forest health and the ability of surface waters to recover from acid inputs (c.f. DeHayes et al. 1999, Lawrence et al. 1995, 1999). Because Spodosols (a predominant soil type in the Adirondacks) naturally have low base saturation, leaching of base cations by acidic inputs exacerbates an already fragile balance between nutrient supply for vegetation and organisms that live on or within the forest floor and replenishment of these nutrient cations by litter decay and mineral weathering. Adirondack soils consist mainly of the primary minerals quartz, K- and Na-rich feldspar, and muscovite (April and Newton 1983, April et al. 1986), all of which are highly resistant to chemical weathering. Minerals such as Ca-rich plagioclase, biotite, hornblende, diopside, garnet and calcite are much less abundant in these soils, but they are more susceptible to chemical weathering and therefore can provide base cations to exchange sites at rates comparable with depletion rates accelerated by acidic deposition (April and Newton 1992).
The effects of acid deposition on aquatic systems in the Adirondack Mountains have been studied intensively since the 1970's. Findings show that the acidification status of streams and lakes is strongly influenced by the geology and hydrology of watersheds. Deposition input quantity and quality, the mineralogy and depth of surficial materials, the hydrological properties of soils, groundwater flow paths, wetland processes, snowmelt, etc., all contribute to the final chemical composition of surface waters.

2: CHEMICAL WEATHERING AND CALCIUM DEPLETION IN ADIRONDACK SOILS

Note “outcrops” of glacial outwash sand on the left.

STOP 1. Town of Webb “Site 10”
Note: If you wish to return to this area, permission must be obtained from the Town of Webb supervisor. During the fall months, this land is leased to a hunting club and is generally inaccessible to the public until the winter season, when the trails are re-opened for snowmobiling.
At this site, we will walk a few hundred meters into the woods to dig a soil pit and view monitoring and collection equipment used to study soil and soil moisture. This site is part of an NSF-funded research project studying calcium depletion in Adirondack watersheds exposed to acid precipitation – the “site 10” designation is our own internal label. Soils here, as in most of the Adirondacks, are typical spodosols. In this area, soils are developed on a sandy outwash material, which could be seen in roadside “outcrops” as we traveled from Old Forge into the site. Few cobbles or boulders are encountered when digging soil pits in this area.
As part of the research project, a 50-meter diameter circular area on one side of the small stream flowing through the site was treated 3 times with 0.75 tonnes (each time) of powdered limestone and an identically-sized untreated area on the opposite side of the stream was used as a control. Soil and soil moisture chemistry has been monitored at this site since 2005. Figures 5 and 6 show soil pH and exchangeable calcium with depth over time before and after application of powdered limestone. As expected, additions of calcium carbonate raised the soil pH in the upper horizons and, over time, that effect is being translated lower into the soil profile. Similarly, exchangeable calcium is increased in the upper horizons of the soils treated with powdered limestone, although that increase is only seen down to about 15 cm, even 3 years after the first application of calcium carbonate.

STOP 2. Moss Lake Trailhead
We will take a short walk here to the shore of Moss Lake and take a reading of water pH. The south side of the Moss Lake watershed consists of thick sand-covered bedrock and much of the north side has a thinner cover of till and bedrock close to the surface. Flow paths of water moving through the soils and underlying materials determine how well buffered the incoming acid precipitation becomes and therefore affects the lake pH. At this location, we will also view the Moss Lake National Atmospheric Deposition Program data collection site (site NY29 – Fig. 7). Precipitation pH for the past few years is shown in Figure 8.

STOP 3. Covewood
Note: This land is private property and permission must be obtained from the owners of Covewood Lodge.
On the north shore of Big Moose Lake, Covewood Lodge and surrounding property presents a somewhat different surface material than previous stops. The surficial material upon which soil are developed in this area is a thinner, bouldery till, as is evident just by looking at the surrounding landscape. Numerous cobbles and boulders are encountered when excavating soil pits around here. Depth to the saturated zone is shallower here and soils are often wetter than at Town of Webb Site 10 or Moss Lake.
The owner of Covewood Lodge uses spring water (groundwater) to supply his lodge and cabins. Several years ago, he determined that the water was very acidic (below pH of 4) and he has attempted several different methods for neutralizing the acidity. We will look at one or two these devices as well as view monitoring equipment we have set up in this area as part of the aforementioned research project.
Covewood is one of the sites where powdered limestone was applied in 2005, 2006 and 2007. Exchangeable calcium in the soils is shown in Figure 9 below. As at Town of Webb Site 10, the data show that exchangeable calcium in the soil has increased down to a depth of about 10 cm due to the addition of calcium carbonate. We have not seen any effect of the limestone additions on the groundwater yet.

Pass Windfall Pond trailhead on the right.
We will not take the trail to Windfall Pond, but it is a nice walk. The trail passes over the outlet of Windfall Pond. The Windfall Pond watershed contains some calcium carbonate rock, which acts to buffer acidic precipitation. Outlet pH values are generally higher here than in other streams in the Big Moose area because of this buffering effect.

4: DEGLACIAL HISTORY OF THE UPPER HUDSON REGION
David J. De Simone
Rensselaer Polytechnic Institute
Jonsson-Rowland Science Center
Troy, NY 12180
and
De Simone Geoscience Investigations
957 Babcock Lake Road
Petersburg, NY 12138
Robert G. LaFleur
SPECTRA
19 British American Blvd.
Latham, NY 12110
INTRODUCTION
The Hudson River descends from the Adirondack Mountains through a beautiful gorge and empties into the northern Hudson lowland onto a diverse complex of ice contact, glaciofluvial and glaciolacustrine sediments. Early workers such as Ogilvie (1902), Woodworth (1905), Miller (1914, 1925), Fairchild (1917), Stoller (1922), Chadwick (1928) and others posed early explanations and some interesting contrasts for the diverse suite of glacial deposits. All provided a solid context for future workers. Readvance hypotheses were a popular paradigm in the 1960's and 1970's when Connally & Sirkin (1969, 1971) hypothesized a major readvance of the Hudson-Champlain (H-C) ice lobe through much of the northern Hudson region. De Simone (2008) recently proposed this Luzerne readvance lacks strong evidence for its occurrence and should be abandoned. This trip will address concerns over the proposed Luzerne readvance hypothesis and present an alternative interpretation of the stratigraphy of the Luzerne Mountain gorge. The interpretation is based upon a synthesis of past descriptions of the Corinth Road exposures combined with insights from borehole data analyzed from a site in the western portion of the gorge.
The southern Champlain and northern Hudson lowlands contained a continuum of glaciolacustrine lakes that fronted the retreating H-C lobe as the ice front melted back during the late Wisconsinan. Woodworth (1905) recognized the shared Quaker Springs (QS), Coveville (CV) and Fort Ann (FA) water levels in the two lowlands. Rayburn (2004), Rayburn et al., (2005, 2007) and Franzi et al., (2007) developed a modern chronology of deglacial events in the Champlain lowland building upon the classical work of Chapman (1937). They provide a valuable time frame for deglaciation and the sequence of Coveville and Fort Ann lake levels. De Simone (2006) recently extended their 4ft/mi tilted water planes into the northern Hudson lowland and found good agreement with major deltas for the Fort Ann, Coveville and earlier Quaker Springs and Albany II (ABII) lake levels, the latter confined to the Hudson Valley. This correlation appears to solve the old problem of aberrantly low tilts on Hudson Valley water planes that were a feature of regional syntheses for many decades (Woodworth 1905, LaFleur 1979, De Simone and LaFleur 1985, 1986, Dineen et al 1992). We'll discuss these lake levels, their ice margins and their outlets as we tour the H-C divide region.
Most recently, De Simone et al., (2008) present a summary of work in progress that adds to our understanding of the deglaciation of the H-C region. In this volume, Wall expands upon his earlier (Wall 1995) analysis of IroMohawk discharge; Miller discusses the implications of the Cohoes mastodon site for the Younger Dryas with new information based upon his earlier work (Miller and Griggs 2004); Rayburn contributed a revised water planes correlation and insights into QS in the southern Champlain Valley; and, Dineen presents data on the onset of Lake Quaker Springs incorporating earlier analysis (Dineen and Miller 2006).This trip will expand that synthesis to include the Lake George basin. We will visit some different sites than the FOP 2008 trip but will link our discussion thread into that synthesis.

1. Crown Point CV Delta:
Location: Crown Point quadrangle. Proceed along Rte 9N from north of Crown Point to the intersection with Street Road. The main entrance to this pit is on the west side of the road. However, if you loop back and turn west toward the town transfer station, there is another upper entrance to this pit. The main or lower entrance is preferred for easy parking of large vehicles. Note that you can drive up to the high level of the pit from below along the access road in the north face of the pit. It is a wide and safe route but not for a bus.
Parking: N 4861517, E 0625137, lower or main entrance parking area.
Ownership & permission: Gerald Huestis is the owner and the pit is operated by his 2 sons. Mr. Huestis does not need prior arrangement for access to his excavation but it is good to call and introduce yourself. 518-623-3671.
Description: The lower portion of the pit exposes the bottomset sand beds of the delta. The upper portion of the pit beautifully reveals the topset-forest contact at 525 ft within interbedded gravels with some sand. There is no ice contact deformation evident in the exposure and supports the notion this is an open water delta of the small brook exiting the Adirondacks. The valley wall portion of the Street Road delta has numerous kettles and suggests the delta buried recently stranded ice.
Discussion: Rayburn (2004) mapped Champlain Valley strandlines as far south as Ticonderoga, NY, and Brandon, VT. On the New York side of the valley, no strandlines higher than Lake Coveville were found; across the valley in Vermont, there are higher deltas in Brandon, VT. The highest one is Chapman's (1937) Forest Dale delta that was originally thought to be CV but it is better correlated with QS at 560-570 ft. The northern termination of QS strandlines perhaps at the Fernville kame moraine at the north end of Forest Dale suggest that this may have been the ice margin position when the lake dropped from QS to CV. It is interesting that there is no QS delta or obvious kame terrace above the Street Road delta. But, the vicinity is tightly constrained by the surrounding Adirondack Mountains where the brook spills out onto the lowland and there may have been little or no time passage between ice recession to the kettled area next to the valley wall and the drop from QS to CV.
However, south of the Street Road delta on the Ticonderoga and Putnam quadrangles, there are lake sediments that correlate to a higher lake and suggest the ice margin was near or at the Street Road delta at the time QS dropped to CV. Just north of the Street Road delta is are a complete series of well defined CV and FA strandlines in the upland west of the Town of Crown Point. Most of these strandlines were recognized by Connally and Cadwell (2002), but correlated to different levels than stated in Rayburn (2004). A small delta fan at 525 ft (161 m) is at the Coveville level. Terraces at 440 ft (135 m), 350 ft (108 m), and 185 ft (56 m), are at the highest Fort Ann, lowest Fort Ann, and highest Champlain Sea levels respectively (Rayburn, 2004). The Town of Crown Point is built on the highest Champlain Sea delta terrace. The foreset-topset contact in the Coveville level Street Road delta is at about 525 ft (161 m). These strandline measurements are in good agreement with the 0.70 m/km isostatic rebound estimate for the entire valley data set.
By projecting this rebound trend southward into the Hudson Valley we hope to unravel the earlier deglacial story hidden among the Lake Albany strandlines, lacustrine sediments, and ice marginal deposits.

STOP 2. Dresden Station Subaqueous Fan:
Location: Putnam quadrangle along Rte 22.
Parking: N 4836666, E 0627970 at entrance to the pit.
Ownership & permission: Richard Dedrick Trucking & Excavating of Putnam Station, NY. Call Richard @ 518-547-8432.
Description: Striated and grooved bedrock ridges with steep flanks are capped with subaqueous fan gravel and sand beds that fine upward to lacustrine sand. The top of the deposit has been terraced at an elevation of 190ft, likely a FA terracing event. There is no till atop the bedrock.

STOP 3. Chapman's Potholes
Location: Fort Ann quadrangle on Flat Rock Road, a small loop of old Rte 4 between the H-C Canal and present Rte 4. The junction with Rte 4 is approximately 1.5 mi north of the Rte 4 – Rte 149 junction in Fort Ann Village. The road is between the village of Fort Ann and the Rte 22 junction north of the village.
Parking: N 4809487, E 0624274; park at the edge of the railroad tracks and proceed across the tracks and up onto the outcrop to the south. CAUTION ! Poison ivy and oak present.
Description: There is a pothole visible in the opposite wall of the canal. Also, there appear to be potholes present on the top of the outcrop in the brush near the south end of the outcrop and along the south face of the outcrop. These potholes have been largely covered by organic litter.
Location: Fort Ann quadrangle on the north side of Rte 4 approximately 0.4mi south from the junction with Flat Rock Road. This is a very heavily traveled 55mph passing zone along Rte 4 and CAUTION is urged!
Parking: N 4809022, E 0623199; park off the north side of the road where there is a little used turnoff into the grassy area.
Description: There are 4 large potholes visible in this outcrop of granitic gneiss. All are semi-circular in form and extend down below the present graded ground surface.
Discussion: Chapman (1937) described the location of numerous potholes along the Hudson-Champlain Canal north of the village of Fort Ann. These potholes have been interpreted to be the result of the outflow of Lake Fort Ann as that discharge passed through the primary Fort Edward channel of the Fort Ann outlet channels. More specifically, the potholes are concentrated in the area where the channel is constricted by the steep granitic gneiss flank of Battle Hill to the north and the predominantly carbonate bedrock platform to the south. Pothole formation has been attributed to mechanical abrasion by stream bed load into the rock bottom of a channel. Eddying in very powerful flow may be the mechanism of formation for the potholes observed in this Fort Ann outlet.

STOP 4. Glen Lake Kame Moraine – Kame Terrace
Location: Putnam Mountain quadrangle. Proceed approximately 2.8mi east on Rte 149 from the junction of Rte 9 and Rte 149, near I-87 Exit 20. Continue past the Bay Road junction east for an additional 1.4 mi to the Rte 9L junction. From this point, there are several gravel and sand excavations with access from Rte 149. The first is approximately 0.8 mi to the east with another smaller pit in sand another 0.1 mi east behind the self storage facility. Continue along Rte 149 from the Rte 9L junction a total of 1.6 mi to Patten Mills Road and turn south on this road. Proceed 0.8 mi to the entrance of the Jointa Galusha excavation. There is another excavation adjacent to the Washington County closed pit on Tripoli Road. This excavation can be accessed by continuing on Rte 149 to the next intersection with Tripoli Road on the south and Hadlock Pond Road on the north.
Parking: N 4805293, E 0613466 at the entrance gate. After checking in at the scales office, drive to the left and park before the sorting operation if it is busy or drive down to the edge of the pond at the bottom of the pit if there is no activity.
Ownership & permission: Jointa Galusha, John Davidson @ 5158-792-5029.
Description: Bedrock ridges in the pit trend approximately 070° and striations, although faint in the gray gneiss and black amphibolite, average 220° and range from 210-230°. So, the H-C ice lobe flowed subparallel to the orientation of the bedrock ridges in this area during at least the later thin ice stages.
In the bottom of the excavation, well sorted sand and well sorted gravel occur. The sand beds show some ripples and deformation likely the result of loading and de-watering of the sediment. Above, there are interbeds of gravel and sand. Some cobble gravel beds are free of matrix. Clast supported gravel beds might exhibit grading upward to sand beds. The sequence is repeated a few times in these thick beds. Near the top of the excavation, sand beds predominate and the sediment appears more lacustrine. Small dunes are evident on the top surface of the feature.
Discussion: The Glen Lake kame moraine-kame terrace is an extensive deposit that covers portions of 4 quadrangles – Putnam Mountain, Hudson Falls, Lake George and Glens Falls. The deposit is the most extensive ice marginal accumulation of sediment north of the Hudson-Mohawk confluence. Likely, the H-C lobe maintained a position here along its western-northern lateral margin while the front of the lobe and eastern margin retreated rapidly. This was possible due to the Glen Lake area being close to the ice source coming from the Champlain Valley. The long duration of the ice margin here would account for the extensive and thick accumulation of sediment.
The kame terrace generally tops at approximately 520-490 ft along its entire length of approximately 14 miles to the base of the Luzerne Mountains. It is a recessional moraine and there is no evidence of readvance observed within exposures as of this writing. It is very possible the deposition in this deposit was time transgressive with some portions of the moraine accumulating before other portions. However, the moraine is apparently graded to a persistent base level along what was the northern and western edge of the H-C lobe. An ice marginal lake may have persisted in the area of the kame moraine, a lake dammed by the ice and extending northward into the Lake George basin and adjacent basins. If true, then 500 ft would be an approximate maximum elevation of the highest level of Glacial Lake George.
Ice recession from the base of the Palmertown Range to the south allowed the GlacioHudson River to have its first access to the valley and it deposited the West Glens Falls open water delta into AB II. Eventual ice recession from the kame moraine allowed Glacial Lake George to lower and this outflow deposited the Oneida Corners fan delta into Lake Quaker Springs. Contemporaneously, the GlacioHudson River built its major Glens Falls delta into QS.
Ice margins (De Simone, 1985, De Simone & La Fleur, 1985, 1986) through this area are similar to those of Chadwick (1928) and La Fleur (1979).

STOP 5. Corinth Road Multiple Till Exposures
Location; Proceed west along Corinth Road from Exit 18 of I-87 approximately 3 miles, past the Queensbury sewage treatment plant on the south side of the road. Continue another 0.5 mile past roadside outcrops of bedrock at the foot of the Luzerne and Palmertown Mountains. As the road grade begins to rise, look for any of several parking areas along the north side of the road where the overburden exposures are visible. It's a good idea to drive all the way to the top of the hill, past the house on the bluff and note the highest exposure below the house. This is the Hartman terrace. You can turn around and return to a convenient pullout and park to examine the exposures.
Parking; The best parking area is about half of the way up the hill where there is a large pullout that still has crumbly asphalt and plenty of room.
Ownership and permission; You only require permission to access the bluff exposure below the house at the elevation of the Hartman terrace.
Description and Discussion; Please see the text for a thorough analysis of this site. Note that the exposures have been overgrown for many years and may not be in good shape at the time of your – or our – visit.

5: TRANSPRESSIONAL DEFORMATION IN TACONIC SLATES AND ITS RELATION TO BASEMENT ARCHITECTURE
Jean M. Crespi
Center for Integrative Geosciences
University of Connecticut
Storrs, Connecticut 06269
H. Ray Underwood
GeoDesign, Inc.
984 Southford Rd.
Middlebury, Connecticut 06762
The Taconic allochthon is a north-northeast-trending tectonostratigraphic unit in westernmost New England and easternmost New York State. The allochthon, which consists of Neoproterozoic rift clastics, Cambro- Ordovician slope-rise deposits, and Ordovician flysch, was emplaced during the Middle to Late Ordovician Taconic orogeny (Rowley and Kidd 1981, Stanley and Ratcliffe 1985, Karabinos et al. 1998). The strata were folded and cleaved during orogenesis. In the northern Giddings Brook thrust sheet, the penetrative deformation, low-grade metamorphism, and dominantly fine-grained nature of the strata resulted in the formation of slate that has been extensively quarried (Dale 1899).
Nearly thirty years ago, Rowley et al. (1979) led a field trip for the New York State Geological Association through part of the slate belt in the northern Giddings Brook thrust sheet. The mapping presented in that field guide and the bedrock geologic map of the Glens Falls-Whitehall region compiled by Fisher (1985) show that the folds and slaty cleavage in the section of the Giddings Brook thrust sheet between Granville/West Granville and Hampton Flats/East Whitehall are not parallel to the overall trend of the Taconic allochthon (Fig. 1). Although the allochthon trends north-northeast, the folds and slaty cleavage in this area trend north-northwest. The primary goal of this field trip is to examine evidence supporting the hypothesis that the strata in this area underwent transpressional deformation. The field trip (Fig. 2) will begin in the classic area mapped by Zen (1961) to the north of Hampton Flats where the folds and slaty cleavage trend north-northeast. Inspection of the style of deformation of the strata to the north of Hampton Flats will provide a framework for understanding that of the strata in the area between Granville/West Granville and Hampton Flats/East Whitehall. Continuation of the field trip to the south to examine the area of anomalously north-northwest-trending folds and slaty cleavage will include stops that permit discussion of not only transpression but also the magnitude of tectonic volume change in slate, which remains a controversial topic.

5: TRANSPRESSIONAL DEFORMATION IN TACONIC SLATES AND ITS RELATION TO BASEMENT ARCHITECTURE

STOP 1. Cedar Mountain Syncline
Park at entrance to abandoned quarry. Do not block driveway to house. Walk north along the path into the quarry. A path leads off to the right from the main path into the quarry. Continue along the main path and climb up slate pile on the east side to view quarry walls.
This is a well-known exposure of the Cedar Mountain syncline. The strata belong to the Cambrian Mettawee (Middle Granville) Slate Formation. The main cleavage in the strata is the slaty cleavage (S2), which is axial planar to the fold. The west wall of the quarry exposes both a profile view of the fold and a folded S0 plane with a well-expressed S0-S2 intersection lineation parallel to the fold axis. A crenulation cleavage (S3) is also present and is readily observed in blocks in the pile of waste slate.
The quarry lies in the transition region between Taconic rocks to the west, in which S2 is the dominant cleavage and S3 is either absent or only weakly developed, and Taconic rocks to the east, in which S3 is the dominant cleavage. Because S3 pervades the strata in the quarry, the exposure is not mapped as part of domain 1. Structural orientations, however, are consistent with this domain. Both the north-northeast trend of the fold axis and the shallow, approximately 25 E dip of S2 are characteristic of domain 1.
In addition to the fold and cleavages, reduction spots are a highlight of the exposure. The green spots can be ellipsoidal or irregular in shape. Reduction bands subparallel to S0 are also present.

STOP 2. Scotch Hill Syncline
Park temporarily in grassy area along side of road. Obtain permission from homeowner to park in the parking area of one of the houses. The outcrop is the large cliff face just to the east of Glen Lake.
This exposure of the Scotch Hill syncline is a frequent stop on field trips to the northern Taconic allochthon. Please do not hammer on the outcrop face and be on guard for poison ivy.
The folded strata belong to the Ordovician Poultney Formation. The exposure is mapped as part of domain 1 on the basis of the orientations of the fold axis and S2. Detailed information on the S2-related strain is not available because strain fringes have not been sampled. The north-northeast trend of the fold axis is shown by the S0-S2 intersection lineation, which is best observed on west-facing, vertical S0 surfaces on the short limb of the fold. The mean orientation of S2 is 025, 25E.
Two sets of veins can be observed on the outcrop face. Veins in one set intersect S0 at an angle to the S0-S2 intersection lineation, and veins in the other set intersect S0 parallel to the S0-S2 intersection lineation. Crosscutting relations are visible on both limbs of the fold and show that veins in the latter set are younger. These veins, which are coaxial with the fold, are interpreted to have formed in response to flexural folding. On the short limb of the fold, they display Z shapes. The vein asymmetry is not as clear on the long limb of the fold, but there is a very wide vein that displays an S shape. To observe this vein, go around the small shed and climb to the base of the exposure behind the shed. The top half of the vein is visible in the main outcrop face, and the bottom half is visible in the continuation of the exposure in front of the main outcrop face. Despite being pre folding, veins in the older set lie in nearly the same orientation on the long and short limbs of the fold. This is interpreted to be a result of rigid rotation of S0 combined with shearing within layering in opposite senses on the two limbs during flexural folding.

STOP 3. Cambrian Browns Pond Formation
Park along side of road.
There is an outcrop on the west side of the road. More illustrative outcrops are present to the east along either side of the Exit 3 off ramp from US 4.
These exposures of the Cambrian Browns Pond Formation lie on the long limb of the Scotch Hill syncline.
Data obtained from strain fringes have been used in combination with the orientation of outcrop-scale structural elements to place the exposures in domain 1.
Features observable in the exposures include calcite veins, which form two main sets. The veins that strike approximately north-south are more easily observed in the outcrops along the exit ramp, and the veins that strike approximately east-west are more easily observed in the outcrop along the road. Veins in both sets are deformed and are inferred to predate S2 formation. The thickness and orientation of the veins in the north-south striking set differ depending on whether the vein lies in limestone or slate. In relatively coherent beds of limestone, the veins are thick and about perpendicular to S0. In slate, the veins are thin and lie at a low angle to S2 as a result of rotation during S2 formation. Boudinage is visible in many of the veins in the slate layers. In contrast, veins in the east-west striking set are folded.

Lunch Stop

STOP 4. Cambrian Mettawee Slate Formation
Park along side of road.
The outcrop is on the north side of the road directly opposite a driveway. This is a small exposure of the Cambrian Mettawee (Middle Granville) Slate Formation within domain 2.
The outcrop lies on the long limb of a north-northwest-trending anticline. The Cambrian Browns Pond Formation is exposed to the north of the road and yields strain fringes that are curved in S2-parallel thin sections. This is one of three locations in domain 2 where evidence for triclinic strain symmetry has been found. The strain fringes also record flattening strain.
This stop is in the heart of domain 2, and the overall north-northwest-trending structural grain of domain 2 can be easily seen on Google Earth images of the area directly north of this stop. Although the images have not been analyzed in detail, the prominent lineaments are probably the Browns Pond Formation and sandstone layers in the Hatch Hill Formation.

STOP 5. Graptolite bearing Mount Merino Fm
Park along side of road.
One outcrop is on the east side of the road opposite the drained beaver pond, and the other is on the island in the drained beaver pond. The latter outcrop can be accessed using an ATV track at the south end of the pond.
Exposures along this road lie in the core of a syncline in domain 2 and provide excellent examples of deformed graptolites. The short limb of the fold is exposed in the outcrop along the road, and the core is exposed on the island in the drained beaver pond. The graptolite-bearing strata belong to the Ordovician Mount Merino Formation. The graptolites appear as white “films” on S0 surfaces because during S2 formation strain fringes developed adjacent to the periderm, which also fractured and infilled with fibrous material. At high magnification, chocolate-tablet structure can be seen in the periderm of graptolites from the exposure along the road. This contradicts evidence for prolate strain from measurements of the thecal spacing of the graptolites (Goldstein et al. 1998). The thecal spacing, which indicates large volume loss, is inferred to record the total strain undergone by the strata since deposition. Estimates of volume change using markers that record only the strain related to S2 formation support approximately constant-volume deformation.

STOP 6. Clastic Dikes and Sills
Park in small parking area on the east side of NY 22A.
The outcrop is directly opposite the parking area.
This road cut exposes the Ordovician Poultney Formation. The outcrop lies on the long limb of a northnorthwest- trending anticline in domain 2, and the strain fringes indicate triclinic strain symmetry and flattening strain. The outcrop provides good examples of clastic dikes and sills (?), which formed before lithification, and brittle faults, which formed after S2 formation. The clastic dikes lie at a high angle to S0 and S2 and are folded. Some of the sandstone layers may be clastic sills. The distance between two relatively thick sandstone layers, for example, changes, indicating that they are not parallel to S0. In addition, some sandstone layers do not show evidence for internal layering. The brittle faults are generally steeply dipping, and the direction and sense of slip along the faults are well shown by slickenfibers and steps. Normal and strike-slip motions are observed. Post-S2 faults with similar kinematics have been mapped in other exposures in domain 2.

6: MIDDLE ORDOVICIAN SECTION AT CROWN POINT PENINSULA
Charlotte Mehrtens
Department of Geology
University of Vermont
Burlington, VT 05405
charlotte.mehrtens@uvm.edu
Bruce Selleck
Colgate University
Hamilton, NY 13346
bselleck@mail.colgate.edu
The Chazy, Black River and Trenton Groups are a well studied sequence of fossiliferous limestones, dolostones and sandstones in the Champlain Valley of New York, Vermont and southern Quebec. These rocks record shallow water cyclic sedimentation in the foreland basin of Laurentia prior to and during the initial stages of the Taconic Orogeny. This field trip reviews the stratigraphy of these units, as well as the evidence for reconstructing depositional environments and cyclic sea level changes.
THE CROWN POINT HISTORICAL SITE
This field trip takes place at the scenic Crown Point Historical Site (Figure 1), a no-hammer, no-collecting locality. Approximately 120 meters of section is exposed in a combination of excavations, ridges and shoreline exposures that dip ∼8° northwest. The overall stratigraphy (Figure 2) from the Crown Point Formation (Chazy Group) to the Glens Falls Formation (Trenton Group) records the Middle Ordovician transgression seen throughout the Appalachians. Correlation of this stratigraphy exposed at Crown Point to the type Trenton in central New York State is provided by Prasopora spp. (Mehrtens and Barnett, 1979). Conodonts collected from strata to the north and east (Harris, pers. comm. and Harris, et al., 1995; Roscoe, 1973) provide additional age control. Detailed sedimentologic studies of these units have been published by Bechtel and Mehrtens (1995), Mehrtens and Cuffey (2003) and MacLean (1986) and Selleck (1988).

STOP 1. Redoubt
STOP 1. The Redoubt Approximately 6 meters of burrowed, slightly dolomitic, thin to medium bedded bioclastic packstone and grainstone is exposed at this stop. Some beds are relatively well-sorted grainstones with sharp bases which are interpreted as tempestites. The same interpretation is made for the grainstone intraclast-rich bed visible in the low ledge at the southeast corner of the ditch. Approximately 3 meters above the base of the section abundant Girvanella algal oncolites are common allochems. Nuclei of fossil fragments are visible within some oncolites. In other beds fossils are relative abundant, and are best seen on slightly weathered bedding surfaces. Trilobite fragments, brachiopods, bryozoans, pelmatozoan fragments, nautiloids and large Maclurites magnus are present (exterior shells and opercula). Dolomite occurs in along shaley seams and in burrow fill.
The relatively high faunal diversity, general bioturbation, and storm-related sedimentation all point to a low energy shallow subtidal environment at depths slightly below fair-weather wave base. The abundant algal oncolites and discrete calcareous algal fossils (e.g., Hedstromia spp.) suggest depths well within the photic zone. A possible modern analogue is found in the mixed mud and sand shelf to the west of the emergent tidal flats of Andros Island, Bahamas, as described by Purdy (1963).
We interpret the wavy, irregular dolomite laminae as the result of dolomitization of lime mud, followed by compaction and pressure solution of calcite that produced irregular clay and dolomite-rich stylocumulate seams. Preferential dolomitization of burrows is due to contrasts in permeability of burrow-fill versus burrow-matrix sediment. The burrow-fill material retained permeability longer during diagenesis and allowed more pervasive dolomitization. In similar facies exposed on Bullwagga Bay (the west shore of the Crown Point Peninsula), modular limestone with shaley dolostone seams and stringers are present. The limestone nodules appear to have been cemented prior to significant burial compaction, whereas the shaley dolostone material was compacted around the cemented limestone. The early-cement limestones were resistant to dolomitization. This sort of fabric selective dolomitization is common in the Chazy and Black River Groups throughout the Champlain Valley.

STOP 2. Ridge of outcrop running NE from entrance gate
WARNING: poison ivy is common along this ledge
Cross-stratified coarse bioclastic grainstones are well-exposed near the main gate along the entrance road and adjacent ridge. Nearly three meters of section form a prominent belt parallel to strike, extending from the entrance road to the main highway. Foreset cross-strata show bipolar dip directions. Angular quartz and felspar grains are concentrated in some laminae. The carbonate particles are dominantly sub-rounded abraded pelmatozoan plates with gastropod and brachiopod fragments. Large Maclurites fragments and grainstone intraclasts are present on the upper bedding surfaces of these ledges.
We propose that the environment of deposition of this facies was a shallow subtidal wave and current reworked bioclastic sand shoal. Active transport of abraded grains may have been accomplished by tidal currents (as suggested by the bi-directional cross-strata) or by storm-generated currents that produced complex, anastomosing patterns of cross-strata and intervening reactivation surfaces. The lack of burrowing and well-preserved whole-shell body fossils may be due to the inhospitable shifting sand substrate. A modern analogue for this environment would be the unstable sand shoals of the Bahamas Platform (Ball, 1967), as the scale and style of cross stratification are similar. Oxley and Kay (1959) report that similar strata in the northern Lake Champlain Valley are oolitic.

STOP 3. Low ledges adjacent to the entrance road (Picnic Pavilion ridge)
Approximately 50 meters north of Stop 2
Brown-weathering, slightly shaley dolostone exposed here contains lenses and stringers of fossiliferous lime packstone and wackestone. The fauna is similar to that at Stop 1, with trilobites, small brachiopods and Maclurites common. The environment of deposition is assumed to be similar to that of Stop 1, however lacking evidence of storm activity. Note that some of the fossils are almost entirely encased in dolomite, which is assumed to be of replacement origin here.

STOP 4. SE moat of Fort Crown Point
Approximately 3 meters of thickly laminated limestone and dolostone of the Valcour Formation are exposed in the southeast moat of the British Fort. The dominant facies here is alternating 0.5-2.0 cm thick laminae of limestone and dolostone, we term “ribbon rock.” The limestone ribbons are very fine-grained peloid grainstones or “calcisiltites” and appear blue-grey color on slightly weathered surfaces, and as indentations on more deeply weathered surfaces. The dolostone ribbons weather tan-brown in color, and consist of an interlocking mosaic of 20-300 micron dolomite crystals of replacement origin. Quartz silt grains are present in the dolostone ribbons, versus medium to fine-grained quartz sand in the limestone ribbons, suggesting the limestone horizons were slightly coarser-grained than the dolostone when deposited.
An erosional surface with 10 to 20 cm of relief is exposed near the base of the south wall of the moat (Figure 9). Similar erosional surfaces occur within this facies in other Chazy exposures in the Champlain Valley. We interpret these to represent micro-karstic solution surfaces on a tidal rock platform that developed during subaerial exposure of cemented limestone. Typically, the rock below the surface is mostly calcite limestone, suggesting that cementation and diagenetic stabilization of the limestone occurred prior to development of the erosional surfaces. Overlying rock horizons contain more dolomite. Maclurites shell hash can be found in pockets on the erosional surface. Dolomitized burrows cut across the limestone ribbons in some parts of the outcrop. Trough cross-strata filling low scour surfaces are also visible.
On the less weathered prominence on the SE corner of the moat, shallow scours containing brachiopod and gastropod debris can be seen. Intraclasts or pseudoclasts of limestone in dolostone are also present. Some “clasts” appear to be cored by dolomitized burrows.
We interpret the stratigraphy seen at this stop as representing a tidal flat to shallow subtidal facies. The alternating limestone/dolostone ribbon rock represents rhythms of slightly coarser-grained (limestone) and finer-grained (dolostone) sediment deposited on the lower reaches of a tidal flat, similar to the rhythmic bedding described by Reineck and Singh (1980) from the mud/sand tidal flats of the North Sea. These coarse-fine alternations might also reflect storm-related, ebb-surge deposition (Nelson, 1980). Early cementation of the slightly coarser-grained limestone ribbons made this lithology less susceptible to dolomitization, which affected the finer-grained muddy ribbons that became dolomitized. Variations in the intensity of burrowing is interpreted to reflect subtle differences in duration of subaerial exposure of the tidal flat and/or the extent of reworking by tidal currents. Limited in situ faunal diversity is to be expected in the tidal flat setting, where organisms are stressed by salinity fluctuations. The absence of mudcracks or evidence of evaporite minerals may indicate that only the lower portion of a humid climate tidal flat system is preserved here.

STOP 5. Parade Grounds near barracks.
As we enter the parade ground from the southwest corner of the moat, note the array of carbonate rocks used in construction of the barracks walls. Chazy, Black River and (rarely) Trenton lithologies can be identified. Restoration of the barracks began in 1916 and in 1976 the New York State Division for Historic Preservation undertook protection and stabilization of the ruins.
The low rock pavement just north of the barracks is within the upper part of the “ribbon rock” unit seen at Stop 4. Immediately up-section, cross-stratified grainstone beds are exposed. Coarse-grained quartz and feldspar sand is easily seen on weathered surfaces. Trough cross-strata and herringbone co-sets of planar-tabular cross-strata are visible on the vertical surfaces. Large, angular clasts of slightly dolomitic grainstone and Maclurites are present on bedding surfaces. We interpret this facies as representing a current-dominated sand shoal environment, similar to that seen at Stop 2.

STOP 6. West parade grounds
Bechtel and Mehrtens (1993) suggested that the sandstone unit in the westernmost parade ground is the basal sandstone of the Black River Group, an interpretation which differs from that of Speyer and Selleck (1988), who suggested that this unit was part of the underlying Chazy Group. In thin section this sandstone is a quartz arenite, very poorly sorted, and containing fewer lithic fragments and phosphatic fragments than stratigraphically lower Chazy sandstones. Visible at the very easternmost portion of this ridge is a buff-colored dolostone bed containing pockets of quartz sand (burrow infills?). These basal sandstone and dolostone lithologies are very similar to those described by Walker (1972) in his description of the Pamelia Formation at its type locality in north-central New York. Alternatively, placement of the sandstone unit within the Chazy Group is consistent with the common presence of coarse-grained quartz and feldspar sand within the Chazy at the Crown Point Preserve, whereas the siliciclastic material in the Black River Group at Crown Point is mainly silt and clay. Whatever the stratigraphic placement of the sandstones and dolostones here, it marks an interval when sands were transported from a nearby source area to this possible peri-tidal setting. This interval was followed by marine reworking of the sand and deposition of fine-grained limestone of the basal Black River Group.

STOP 7. Northeastern moat
WARNING: poison ivy is common along the base of this exposure
There is approximately one meter of covered interval between Stop 6 in the parade grounds and Stop 7 in the northeastern moat. Along this wall are exposed several meters of the lower Black River Group (Lowville Formation, House Creek Member) which in Vermont is termed the Orwell Limestone. At the base of this exposure a series of stylolitized gastropod-bearing (Liospira) wackestone beds are overlain by thicker beds of Phytopsis-burrowed aphanitic mudstones. This sequence can be interpreted as a shallowing-up cycle (SUC) consisting of subtidal overlain by peritidal lagoonal muds. Examine the sharp contact of the aphanitic mudstone with the overlying wackestones, a contact which in thin section appears to be a firmground (Bechtel, 1993). These SUCs also comprise the base of the Black River Group at other localities in the Champlain Valley. There are three motifs of repetitious bedding that occur in the Black River Group and the cycles seen here at the base are the the thickest, occurring at a macroscopic scale, interpreted to represent 4th order (10,000 to 100,000 years) or smaller cycles. Examination of Phytopsis burrows in thin section (Figure 10) reveals that many are filled with graded (fining-up) geopedal silt, evidence of cementation in the meteoric vadose zone.
Continuing up section, several thick packstone beds are exposed. More detailed examination of these beds reveals that they consist of alternating one to six centimeter thick intraclast and oncolite-rich packstone horizons interpreted as tempestites, interbedded with fossiliferous wackestone/packstone horizons. The tempestites consist of graded and crudely imbricated intraclasts and skeletal fragments. Note the nature of the upper and lower contacts of these horizons. The second common bedding motif in the Black River Group are these tempestite horizons interbedded with in situ fossiliferous muds.
The uppermost third of the outcrop appears to be a massive bed of limestone, however closer examination also reveals small scale cycles of alternating wackestone/packstone and grainstone, the third motif of bedding in the Black River strata. These cycles are characterized by a base of thinly laminated or cross laminated grainstone horizons 0.5 to 1 cm thick, overlain by fossiliferous wackestones and packstones. In thin section the bases of the grainstones can be identified as firmgrounds, recognizable by the truncations of allochems and cements present in the underlying mud (Figure 11).
The very top of this exposure (best seen at the next stop) exhibits a burrow mottled fabric with selected dolomitization of many burrows. Tetradium occurs in life position in these horizons.

STOP 8. East-west ridge across the service road
A black chert layer near the top of Stop 7 provides the correlation to Stop 8, the outcrop across the service road. The limestone beds on this ridge commonly consist of alternating wackestone/packstone and planar to cross laminated grainstone beds, as seen at Stop 7, however bedding plane exposures permit identification of many fossils in these, the most faunally diverse beds in the Black River Group. Specimens of gastropods (Liospira, Lophospira, Hormotoma), Lambeophyllum, Tetradium, stromatoporoids, the bivalve Cyrtodonta, the brachiopod Stromphomena sp. and cephalopods are recognizable. This ridge exposure is most notable for its bedding plane exposures of Tetradium and Lambeophyllum. It is interpreted as representing a wave baffle margin lithofacies similar to that described by Walker (1972) at the Black River type section.
The third cycle motif we recognize, laminated grainstone overlain by bioturbated wackestone, so common in this portion of the stratigraphy, are interpreted to represent smaller scale 4th order cycles, which could be the result of facies mosaicing and/or small scale base level changes.
There are at lest two distinct types of chert occurrences in the Black River Group. One, the infilling of horizontal burrows, is fabric selective. Chert also occurs less frequently as broad bedding plane parallel sheets. The uppermost chert horizon on this ridge, traceable down to the shoreline, is of this latter variety. Clearly, there was a significant source of silica available for chert formation, perhaps a combination of silica derived from sponges (Tetradium?) and bentonite alteration (the Ordovician sequence in the Champlain Valley is notorious for the paucity of bentonites compared to equivalent strata in central New York and southern Quebec, although Ryan, et al., 2007 have recently been successful in identifying altered bentonites in the Beekmantown Group in the Champlain Valley). In thin section the chert cross cuts all previous cements, including late fracture-filling calcite, and it is therefore the youngest form of diagenesis present in these rocks.

STOP 9. Quarry
STOP 9. Quarry to the north WARNING: be extremely careful around the quarry as the thick algal scum in the quarry water obscures where the grass ends and the quarry wall drops off.
The older weathered south walls of the quarry show, by color differentiation, two cycles. There are 3 to 4 cm thick beds of planar laminated skeletal and peloidal hash overlain by burrowed wackestones overlain by intraclast-rich horizons. These cycles represent our third motif of Black River bedding. Interbedded with these cycles are tempestite couplets of mudstone/wackestone and fossil hash layers in which brachiopod-rich layers are abundant. The abundant quarried blocks lying about provide the opportunity to look for cycles, and from these, topping directions.

STOP 10. Shoreline of eastern Bulwaga Bay
The uppermost horizons in the quarry can be traced down to the shoreline to the north where the uppermost Black River strata can be seen (Chaumont Formation). Shoreline bedding planes exhibit horizontal traces of Chondrites and opercula of Maclurites. There is a thin covered interval of approximately one meter to the basal beds of the Glens Falls Limestone of the Trenton Group. The Glens Falls is characterized by thin beds of nodular to wavy bedded wackestones, mudstones and rare grainstones. Bedding planes along the shoreline contain mostly Chondrites and Helmenthopsis burrows, however as one moves up section, recognizable fragments of Cryptolithus, Isotelus, orthid brachiopods, Stictopora, and Prasopora simulatrix can be found; the latter is important because it permits the correlation of the lower Glens Falls here in the Champlain Valley to the lower Denley Limestone at the Trenton type section in central New York (Mehrtens and Barnett, 1979).
MacLean (1986) interpreted the lithofacies of the basal Glens Falls visible here to represent sedimentation in a shallow subtidal environment periodically influenced by storm activity. In thin section the nodular and wavy bedded wackestones appear thoroughly bioturbated, a process which would influence and enhance subsequent differential compaction. Grainstone beds exhibit more planar bases with basal skeletal fragment lags or finely crushed debris of brachiopod, trilobite and crinoidal material and capped by carbonate mud. MacLean interpreted these as tempestite deposits. Moving further up section (in horizons not seen at Crown Point) the Glens Falls records progressively deepening conditions from the subtidal, storm influenced conditions seen here to bioclastic turbidites separated by autochthonous shale horizons. For those familiar with the lower Trenton Group localities in central New York State (ex., Rathbun Brook, City Brook, Inghams Mills), the paucity of fossiliferous bedding planes here at Crown Point is noteworthy. The overall fine grain size and ichnofauna suggest that bathymetry increased significantly and rapidly from the Black River into the Glens Falls, a transition that might reflect not only rising sea level but base level changes as well. The sedimentologic and faunal transitions from the Glens Falls to the overlying Cumberland Head Argillite and the Stony Point Shale are much more gradational than that of the Black River/Glens Falls contact.

7: GEOLOGY AND GEOCHRONOLOGY OF THE EASTERN ADIRONDACKS
James Mclelland and Martin Wong
Department Geology
Hamilton, New York, 13346
The eastern Adirondacks contain a wide variety of rock types, and this trip aims to visit representatives of the major lithologies. Stops include units recently dated by U-Pb geochronology including multi- and single grain TIMS and SHRIMP II analyses. The Adirondack Mountains represent a southwestern extension of the Grenville Province via the Thousand Islands – Frontenac Arch region of the St. Lawrence River (Fig. 1). The region is topographically divided into the Adirondack Highlands and Lowlands separated by the Carthage-Colton Mylonite Zone (CCMZ, Fig. 2). The former is underlain largely by orthogneisses metamorphosed to granulite facies and the latter by upper amphibolite grade metasediments, notably marbles. Both sectors have experienced multiple deformations resulting in refolded major isoclines. The tectonic history consists of a tripartite division, as summarized below and in figure 3. Broadly, the various lithologies fall into the following groups: 1300-1350 Ma tonalites and granodiorites; 1160-1150 Ma anorthosites, mangerites, charnockites, and granites (AMCG suite); 11000-1090 Hawkeye granite; and 1050-1040 Ma Lyon Mt Granite (LMG). The three major orogenic events associated with these are the Elzevirian (ca 1350-1220), the Shawinigan (1215-1160 Ma) and the Ottawan Orogenies (1090- 1045 Ma). The Elzevirian involves protracted outboard arc magmatism and accretion and was followed by the collisional Shawinigan Orogeny between Laurentia and the Adirondack Highlands – Green Mountain Terrane. The Ottawan was a Himalayan-type collision of Laurentia with Amazonia (?). Most of the metamorphic and structural effects present in the Adirondacks are the result of the Ottawan Orogeny, but Shawinigan and Elzevirian features can be recognized locally. Both the AMCG suite and the LMG are thought to be late- to post-tectonic manifestations of delamination of over thickened orogens.
Structurally, the eastern Adirondacks are dominated by the same large, recumbent fold-nappe structures (F2) as found in the southern Adirondacks (Figs. 2, 4, 5), and with fold axes oriented dominantly ∼E-W parallel to lineation. As in the southern Adirondacks, the fold-nappes are thought to have sheared-out lower limbs, but this has yet to be demonstrated on a map scale. At least two distinguishable upright fold events are superimposed on the nappes: F3 with shallow plunging ∼E-W axes and F4 with shallow-plunging NNE axes. All of three fold sets affect Hawkeye and older units, and thus must be of Ottawan age. This also the case with the strongly penetrative rock fabric, including strong ribbon lineations, that are present in these rocks and are associated with the large fold-nappes. Intense fabric and nappe structure are largely absent from the Lyon Mt Granite and this is interpreted to reflect its intrusion in late, post-nappe stages of the Ottawan. In the northern portion of the eastern Adirondacks the NNE, F4, folds become quite tight and have a strong lineation associated with them. This may be the result of rock sequences being squeezed between large, domical prongs of anorthosite. Finally, we note that there exists abundant local evidence of small isoclinal F1 folds that pre-date F2. These, and their associated fabrics, are thought to be pre-Ottawan in origin, and in a few cases this can be shown to be the case.
A dominant feature of the eastern Adirondacks is the great Marcy anorthosite massif that underlies almost all the High Peaks (Fig. 2). Over two-dozen zircon age determinations demonstrate that the anorthosite was emplaced at 1155 ±8 and that associated granitoids and coronitic metagabbros are coeval with it (Fig. 6). These relationships make it clear that thermal energy from the anorthosite had nothing to do with the regional granulite facies (ca 1050 Ma) that characterize the Adirondack Highlands and post-dates the AMCG suite by 60-100 million years. It is likely that most of the region experienced peak temperatures on the order of ∼750- 800o C and pressures of ∼8 Kbar. Based upon extensive isotope work by John Valley and his students, it appears most likely that this metamorphism proceeded under fluid-absent conditions (Valley et al., 1983). Note, however, that this does not exclude the presence of late, post-peak fluids associated with the emplacement of Lyon Mt Granite.
Recent investigations in the Adirondacks have demonstrated that emplacement of Lyon Mt. Granite accompanied extensional collapse of the Ottawan orogen and exhumation of the high-grade granulite core. The most complete study of this sort is that of Selleck et al. (2005) that utilized zircon geochronology to document that down-to-the-west displacement along the northwest dipping Carthage-Colton shear zone (CCZ, Fig. 2) was coeval with intrusion of Lyon Mt. Granite (Fig. 2) into the fault complex at ca 1045 Ma. It is thought that at peak Ottawan contraction the over thickened lithosphere experienced delamination by foundering, convective thermal erosion, or both. Following delamination of the dense lithospheric keel, the orogen rebounded and hot new asthenosphere moved to the crust-mantle interface and caused melting of deep crust to yield Lyon Mt. Granite. As the granite ascended into the crust it both lubricated and enhanced low-angle normal faults formed in response to increased topographic elevations and leading to orogen collapse. In such situations, it is not uncommon to find that collapse is quasi-symmetrical around the orogen core thus giving rise to a mega-gneiss dome or double-sided core complex such as the Shuswap complex. Given this, we have undertaken research aimed at establishing whether, or not, low-angle down-to-the-east normal faulting took place in the Adirondacks at ca 1045 Ma. Geological evidence is consistent with this proposition, and kinematic indicators related to the issue are described in Stop 9 of the Road Log where the authors present evidence supporting topside down-to-the- east displacement. Some of the more regional geological evidence is discussed below.
The Canada Lake isocline is a prominent feature of the southwestern Adirondacks (Fig. 7). The lithologies comprising it reappear to the east of Great Sacandaga Reservoir in the southeastern Adirondacks, but given the pattern of strikes and dips, there are only two ways of achieving the repetition: either by thrust faulting or normal faulting. Although there is remaining uncertainty, kinematic indicators tend to support the normal fault alternative. The fault trace consists of a distinctive belt of pegmatites and quartz veins that are locally mylonitic and stained by hydrothermal fluids. We propose that this belt represents the trace of a low angle (∼45°) normal fault whose projection is shown on figure 7. Coarse synkinematic pegmatites are common in, and near, the belt, and secondary muscovite occurs locally. To the east of the fault trace metapelites and ca 1300 Ma tonalites are common, whereas east of it they are not encountered. These issues are discussed in greater detail at stop 9.

7: GEOLOGY AND GEOCHRONOLOGY OF THE EASTERN ADIRONDACKS

Sulfidic staining on NNE fault in granite.

Exposure of hornblende granite on left.

Pegmatite on right.

Pass metagabbro

Hornblende granite on both sides.

Hornblende granite

Hornblende granite with metagabbro

Metagabbro, pegmatite, and metasediments on right.

STOP 1. Mega-Garnet Amphibolite. (20 Minutes).
STOP 1. The Poor Man's Gore Mt. (30 min) These exceptionally good roadcuts provide instructive observations regarding the origin of the famous megagarnets of Gore Mt. and dated at ∼1050 Ma. Although these garnets are smaller than the classic examples at Barton Mines, they occur in the same sort of coarse grained, almandine amphibolite and have the same sort of relationships as the former. Moreover, they are similar to 6-7 other occurrences scattered around the Adirondacks. Importantly, each of these, including Barton Mines, is characterized by its location along a fault zone characterized by pegmatites, quartz veins, and various other hydrothermal manifestations. We shall return to this key observation.
The protolith of the garnetiferous amphibolite is demonstrably a coronitic olivine gabbro of the type associated with the coeva1 ca. 1155 Ma massif anorthosites of the Adirondacks (Fig. 6). These anhydrous, silica undersaturated protoliths are commonly well preserved in pluton interiors. The timing of garnet corona formation has been dated at ∼1050 Ma, when the Adirondack Highlands were at upper amphibolite to granulite facies conditions (Basu, pers. comm., Connelly, 2005). Note that many garnets appear to be localized in trains that suggest that they formed along fractures.
Rims of coarse, black hornblendes that resemble reaction rims surround the large garnets. However, these are best accounted for as reaction “behinds”, i.e., as the original gabbroic composition reacted to form garnet at a given nucleation site, there was an excess of hornblende-forming components that accumulated into the rims. In gabbroic anorthosites the more feldspathic bulk composition results in lag deposits of white, plagioclase rims.
The northern contact of the amphibolite is defined by a very coarse, white pegmatite consisting of striated oligoclase, K-spar, quartz and hornblende is one many oligoclase-bearing pegmatites of the eastern Adirondacks that have been dated at ca, 1042 Ma and are related to ∼1050 Ma Lyon Mt. Granite. A narrow offshoot of the pegmatite crosscuts within the main body of the amphibolite. A highly deformed, ∼1155 Ma hornblende granite lies north of the pegmatite and is crosscut by quartz veins. Both the pegmatite and quartz veins manifest a locally abundant hydrothermal phase present at ∼1050 Ma. Just prior to this time the olivine metagabbros were at ∼ 700C and 10-20 km AND DRY. Fine-grained coronas may have been in the process of forming between olivine and plagioclase. At this point, a high angle fault developed and provided access for hydrothermal, pegmatitic differentiates of Lyon Mt Granite. As these fluid-rich materials encountered the olivine gabbro, hydrous solutions moved along fracture-related pathways and resulted in greatly enhanced mobility of chemical species at ∼700C. The result was the almandine amphibolite that we see today. The reason that such grain size is anomalous is that hydrous fluids are rarely present at these temperatures and depths. The model also explains the association of over a dozen other similar deposits, including Gore Mt, along pegmatite bearing faults.
The final chapter in this story concerns the presence of light colored clots of calcic plagioclase and orthopyroxene in the rock. These are associated with garnets and commonly develop as rims between hornblende and garnet or within pressure shadows associated with garnet. This assemblage is due to the reaction:
Garnet + Hornblende → Ca-Plagioclase + Orthopyroxene.
The entry of orthopyroxene marks passage into granulite facies conditions and cannot merely be due to “loss of water” since breaking down the reactant assemblage requires that its stability curve be exceeded to the high temperature side. Note that the plagioclase-orthopyroxene assemblage also occurs in what appear to be pressure shadows on the garnets and have an igneous appearance. Anatexis could have been promoted by dehydration reactions upon entering the granulite facies.

Quartz-sillimanite nodules in Lyon Mt Granite.

STOP 2. Ca 1050 Ma Lyon Mt Leucogranite. (30 Minutes).
The medium grained, pink leucogranite is characteristic of the main quartz-microperthite unit of Lyon Mt Granite that occurs in broad tracts along the perimeter of the Adirondack Highlands. The classic low-Ti Kiruna-type magnetite deposits of the Adirondacks are closely associated with the granite, either occurring within it or in rocks (commonly metacarbonates) immediately adjacent to it. Magnetite mineralization is accompanied by sodic alteration manifested by checkerboard albite and by quartz-albite (Ab98) replacements of the original quartz-microperthite rocks (McLelland et al., 2002). A total of 12 occurrences of Lyon Mt Granite from across the Adirondacks have been dated by U/Pb techniques including single and multigrain TIMS and SHRIMP II (Fig. 2). All of these fall into the interval 1050 ± 10 Ma (McLelland et al., 2001). The present roadcut was dated by single grain TIMS methods and yields an age of 1049 ± 2 Ma (Fig. 3). Staining of the roadcut reveals that it contains several sheets and layers of quartz-albite rock one of which is associated with a irregular veinlet of magnetite. Locally, quartz-sillimanite nodules are present in these rocks and are attributed to leaching by high temperature hydrothermal fluids (McLelland et al., 2002). Pegmatites and quartz veins are common. Oxygen isotope studies indicate that sodic alteration and magnetite deposition took place at relatively high temperatures of ca 650°C. The granite exhibits some deformation and grain-shape fabric, but it is very much less intense than that present in older rocks (cf. the ca 1155 Ma Hornblende granite at Stop 1).
Evidence from the Carthage-Colton Zone along the Highlands-Lowlands boundary demonstrates that the detachment normal faulting along that zone overlapped emplacement of the Lyon Mt. Granite in the zone. As discussed in Selleck et al (2005) the granite enhanced the faulting by providing lubrication and elevated fluid pressures.

Quartz-sillimanite nodules in Lyon Mt Granite included by Walton and deWaard in their "Basement Complex".

Metapelites assigned by Walton and deWaard to their "Older Paragneiss".

Marble, calcsilicate of Walton's "Paradox Lake Formation in near continuous outcrop for 2.6 miles.

Long roadcut of migmatitic metapelite
Long roadcut of migmatitic metapelite assigned by Walton to the "Treadway Mt Formation".

STOP 3. Deformed Migmatitic Metapelites (> 1300 Ma).
The southern and eastern Adirondack Highlands, as well as the Northwest Lowlands, contain significant thicknesses of dark garnet-biotite-quartz-oligoclase + sillimanite metapelite accompanied by white garnet bearing quartz-feldspar leucosome. McLelland and Husain (1986) interpreted the leucosomes as in situ anatectic products of the original rock and the dark fraction as restite. The presence of armored spinel, and rarely corundum, in the restite is consistent with this interpretation. In regions of low strain the leucosomes occur as crosscutting, anastomosing, irregular sheets, dikes, and veins of clearly coarse-grained pegmatitic material. As strain increases, the pegmatitic material gets pulled into psuedo-conformity, disrupted, and grain size reduced so as to yield porcelaneous layers that are commonly parallel but locally retain their original crosscutting configurations. In short, the apparent layering in these rocks is almost wholly tectonic and has nothing to do with original stratigraphic superposition. They are, in fact, mylonitized migmatites, of the variety referred to as “straight gneiss”. These metapelites are crosscut by the ca 1300 Ma tonalitic suite, and therefore pre-date or are penecontemporaneous with these rocks. Our interpretation is that their current reintegrated compositions are best accounted for by a greywacke-shale precursor, and that these were arc-related, flysch-type sediments approximately coeval with the Elzevirian tonalites. This would also help to explain the relative proximity between these lithologies.
The age of anatexis within the metapelites has been ascertained by SHRIMP II studies on zircons from leucosomes and restites in both the Highlands and Lowlands (Heumann et al, 2004, Bickford et al, 2008) and reveals cores of age ca 1340-1240 Ma and narrow metamorphic overgrowths of 1010-1040 Ma. Sandwiched between these are mantles with oscillatory zoning and ages of 1170-1180 Ma. We interpret these mantles as zircon grown during anatexis thus dating this event as Shawinigan. Within the southwestern Highlands, the absence of further significant anatexis during the granulite facies Ottawan Orogeny (1090-1030 Ma) is thought to be a consequence of earlier dehydration. Within the Lowlands, the absence of any Ottawan zircon is interpreted as a reflection that this terrane did not experience granulite facies conditions at ca 1090-1030 Ma. Significantly, east of the present locality, zircons exhibit both Shawinigan and Ottawan (ca 1050-1040 Ma) overgrowths, and the latter can be quite robust. We interpret this observation to reflect the introduction of fluids into the eastern Adirondacks late in the Ottawan Orogeny. Within the outcrop at this stop, the thick vein of coarse pegmatite shows excellent Ottawan overgrowths exhibiting excellent oscillatory zoning.
A second, highly deformed leucosome was also dated and yielded the same results. An important difference is that oxygen isotope values for zircons from the large, coarse vein suggest that it was not formed in situ whereas those in the highly deformed vein are consistent with an in situ origin, as is the case in all other metapelitic migmatites studied.
Both mafic and granitic sheets can be traced across the roadcut face and reveal the presence of fault offsets. Note that the name “Treadway Mt Formation” assigned to this unit by Walton suggests that it has stratigraphic characteristics and continuity. This assumption is no longer considered to be correct and is, at best, is a lithotectonic assignation.

Granite and gabbro.

Large isoclinal fold in quartzites and metapelitic rocks.

Undeformed gabbro.

STOP 4. Swede Mt Sequence (60 Minutes, Including Lunch).
The metasediments exposed along the Rt 8 at Swede Mt provide an exceptional opportunity to closely examine both the rocks and structure. At the southwestern end of the sequence (mile 47.9) a well-exposed isoclinal fold can be seen in the large roadcut on the south side of Rt 8. Folded units include marble, quartzite, sillimanite-garnet-quartz-feldspar (khondalite) gneiss, and rusty sulfidic Dixon Schist. The latter is thought to represent a sheared, altered, and graphitic variety of the khondalite. The fold axis trends ∼E-W at a low angle of plunge about the horizontal, and its axial plane, which dips from ∼50 degrees SW to horizontal, has been folded about upright E-W axial planes. The fold is typical of refolded isoclines in the Adirondacks. Similar rocks at Dresden Station, on the east side of Lake George, are intruded by a metagabbro dated at 1106 ± 7 Ma. At this locality the metagabbro truncates foliation and even individual garnet grains in the khondalite. These relations indicate that the khondalite was deposited and first metamorphosed in Elzevirian times. Early workers considered the khondalite to be a stratigraphic unit (Hague Gneiss or Spring Hill Pond Formation), but regional mapping suggests that individual units are continuous over distances of miles only. Both Dixon schist and the khondalite were mined for flake graphite during the early part of the century. The region around Swede Mt is known as the Dixon National Forest and the former mining hamlet of Graphite is located at mile 49.8. As Rt 8 is followed eastward, an undeformed dolerite dike is encountered. The dike strikes parallel to the highway and has caused brecciation and alteration of the country rock that consists principally of marble at this locality. At the top of the hill, and across from Swede Pond, a long roadcut exposes typical Adirondack marbles. At the eastern end of these exposures, a thick bed of quartzite is wrapped around the nose of an isoclinal fold. Note the linear features along its axis. Xenoliths of the quartzite occur in the metagabbro across the road.

Elephant rock.
Consists of leucocratic sillimanite-garnet-quartz-feldspar gneiss (khondalite).

Khondalite, Dixon Schist and graphite.
Trail on right side of road leads to old graphite mines.

Charnockite of the Ticonderoga Dome.

STOP 5. Classic Great Unconformity (10 Min)
This roadcut provides a classic exposure of flat-lying Potsdam sandstone (∼550 Ma) in profound angular unconformity with steeply dipping Proterozoic gneisses (ca. 1300-1050 Ma). A conglomeratic layer is developed at the base of the Potsdam, and zone of alteration is present along the unconformity.

STOP 6. Isoclinal Folds And Intrusion Breccia (30 Min)
Roadcuts on the west side of the highway expose excellent examples of Adirondack isoclinal folds developed in granitic gneiss of uncertain, but possibly ∼1150 Ma (AMCG) age. The fold axes are oriented almost E-W and plunge gently around the horizontal, which is common in the Adirondacks. However, the axial planes are vertical which is very unusual for Adirondack isoclinal folds, which are commonly recumbent. The upright axial planes appear to be the result of a late, upright anticlinal fold that has rotated recumbent isoclines to their present upright positions. In places the folded units appear to be crosscut by other granitic material. Towards the north end of the roadcut a deformed pegmatite fills a small reverse fault.
South from the folded outcrop a large roadcut exposes a series of intrusion breccias in which granites have disrupted amphibolites and other rocks. A number of crosscutting relationships can be seen. Many of the granitic rocks display minimal deformational fabric and are thought be Lyon Mt. Granite (see Table 1 for whole rock geochemical data). In any case, the intrusion breccia is one of the very few recognized outside of the anorthosite massifs. Its proximity to the upright isoclinal folds is considered to be significant but is not yet clearly understood.

Parking area with potable spring water

STOP 7. Dresden Station Roadcut (30 Min)
Large roadcuts on either side of the highway contain some of the best exposures seen anywhere in the Adirondacks. Lithologies include strongly foliated ferrodiorite at the south end of the western roadcut and an olivine metagabbro at the south end of the eastern roadcut. Also present are marbles, calcsilicates, garnet-sillimanite metasediments, and graphitic schist. Dips are everywhere steep to the south, and a strong subhorizontal E-W lineation is widely developed. Well-exposed isoclinal folds are present at several localities in the roadcuts. These features are described below.
a) The ferrodiorite belongs to a much larger mass of this rock that can be seen a few hundred feet south in the next roadcut. It is typical of late liquid fractionates of anorthosite, which it grades into to the west and uphill. The contact with quartzite at the south end of the roadcut is highly foliated and may represent a detachment surface. Elsewhere this structural horizon is associated with intense mylonitization.
b) A few tens of feet to the north an isoclinal fold is clearly visible and is cored by marbles.
c) The south end of the eastern roadcut passes through a dark metagabbro with a U-Pb zircon age of 1106 ± 7 Ma indicative of AMCG suite affinities (McLelland and Chiarenzelli, 1989, Aleinikoff, 2006 pers. comm.). The rock contains olivine and two pyroxenes with clinopyroxene exceeding orthopyroxene. The olivines are rimmed by orthopyroxene-clinopyroxene-garnet coronas and small grains of spinel clouded plagioclase. McLelland and Whitney (1980) have extensively described coronas of this type, and relevant reactions are given in their publications. The coronas are thought to have formed during granulite facies conditions characteristic of the Ottawan Orogeny. The northern contact of the metagabbro exhibits a good chill margin and adjacent garnet-sillimanite metapelite has undergone microscopically visible anatexis along the contact. Within the metagabbro good ophitic texture is well preserved and randomly oriented plagioclase laths are undeformed despite the fact that these rocks experienced the Ottawan Orogeny (1090-1030 Ma). Preservation of original, delicate igneous textures in the metagabbros is thought to be the result of their strength, low ductility, and anhydrous nature. The pristine nature of the chilled contact margin may reflect the fact that the local country rock had already been dehydrated. This possibility is manifested by relationships plainly displayed on the top surface of the roadcut where the metagabbro truncates strong linear (∼N-S) and planar fabrics in a garnet-sillimanite xenolith (?). It follows that the fabric is older than ca 1106 Ma and most likely represents Shawinigan (ca 1210-1160 Ma) penetrative deformation. This is one of the few examples of unequivocal pre-Ottawan fabrics in the Adirondack Highlands. Within the metagabbro, and exposed near the truncated contact, are planar surfaces that exhibit strong E-W lineation defined by elongate mineral grains. This lineation parallels Ottawan fabrics and is interpreted as due that that event. Across the highway, the metagabbro thins and is exposed at the top of the roadcut as a narrow (∼0.5 m) body hydrothermally altered mylonite surrounded by metasediments. This exposure may represent a fold nose or a neck resulting from attenuation. Whatever structure is involved is somewhat immaterial compared to the fact that at this locality the metagabbro exhibits mylonitic foliation and lineation parallel to regional and local Ottawan trends thus substantiating that the Ottawan Orogeny was strongly felt in the eastern Adirondack Highlands.
d) As one proceeds north at road level from the metagabbro contact, a series of metasediments are encountered. The first of these is the garnet-sillimanite (+ feldspar, quartz, and graphite) with a fabric orientation that now parallels E-W regional Ottawan structures. Presumably the fabric was originally formed in the Shawinigan but was rotated into parallelism by intense Ottawan tectonism. Note the manner in which the marbles have torn through other lithologies that now sit within them as tectonic “fish”. Beyond the marble unit, a schistose unit shows a sulfidic stain. Close inspection shows that these rocks represent highly fractured equivalents of the garnet-sillimanite unit with which it is commonly associated. It is also the horizon that was mined for graphite in the late 1800's and into the 20th century. The unit is known as the Dixon Schist; hence Dixon-Ticonderoga pencils. Presumably the fracturing provided pathways for fluids that deposited sulfides and perhaps graphite. Given the ductile nature of the Ottawan Orogeny, this fracturing must have been a late event in the geologic history of the area.
e) At the north end of the roadcut there are excellent exposures of the garnet-sillimanite unit with its distinctive, pea-size garnets. Although these garnets exhibit the pale-lavender color commonly associated with spessartine, there is very little of this molecule present and the garnets are dominantly almandine. Many garnets have spiral arms and almost all are zoned with clear rims and ilmenite-rich cores. This difference may be the result of Shawinigan vs. Ottawan growth.

STOP 8. Ca 1350 Ma Tonalite (15 Min.)
Within the Adirondacks, the ca 1350-1250 Ma suite of tonalitic to granodioritic rocks is restricted to the southern and easternmost regions (Fig.5). Identical lithologies and ages are found in the Green Mts., Vermont and in the western Central Metasedimentary Belt. Together this group is known as the Adirondack-Dysart-Green Mt suite. Its strongly calcalkaline signatures attest to its origin in within a group of composite, outboard arcs. The rocks themselves tend to be compositionally homogeneous and consist of approximately 25% quartz, 80% intermediate plagioclase (∼AN35), and 10% mafics. They are characterized by their gray color and the presence of disrupted amphibolite layers thought to be disrupted syn-emplacement gabbroic dikes.

STOP 9. Kinematic Indicators & Straight Gneiss (30 Mins)
This long outcrop provides some of the best exposures of mylonitic rocks and kinematic indicators in the Adirondacks. At its north end it exposes mylonitic metapelitic migmatites that are folded around E-W recumbent isoclinal axes that are visible only in minor folds. Upright, relatively open folds that are approximately coaxial with the E-W isoclines refold them. Down-dip ribbon lineations are readily apparent on foliation surfaces and trend ∼E-W. Zircons from leucosomes in these rocks have been dated at this locality and show Elzevirian cores, Shawinigan mantles, and Ottawan overgrowths, and are consistent with the fluxing of Ottawan anatexis by Ottawan fluids.
Towards the south end of the roadcut the mylonitic migmatites are intruded by pink megacrystic granite thought to be of AMCG (ca 1155 Ma) age. The granite is variably deformed into a L-S tectonite gneiss defined by elongate feldspar and quartz grains. Foliation in the gneiss generally dips gently SE (Figure 8), although in some areas, the foliation wraps around weakly deformed mafic boudins. Lineations trend SE, typically down dip of the foliation. The fabric in this granite is similar to those in the surrounding metapelite units. This granitic gneiss unit is important for understanding the late stage deformation of this region because it is younger than the surrounding metapelites and presumably did not experienced as complex a deformational history. Measurements of strained porphyroclasts in the granitic gneiss at this location generally indicate near plane strain (2D) deformation of the granite, although some samples fall into the constrictional field (Figure 9). We note that in some samples it was difficult to accurately measure strain because of high strain (S1:S3 ratios as high as 50:1), large grain sizes, and complex deformation. However, the best-constrained samples indicate plane strain. As such, we interpret this deformed zone as one that has experienced bulk plane strain after the intrusion of the megacrystic granite.
Strained feldspar porphyroclasts in this granitic gneiss also allow an excellent opportunity to assess the kinematics of this zone. An analysis of >100 tailed feldspar porphyroclasts indicates that ∼45% indicate a top-SE sense of shear (normal sense offset in current orientation) based on the asymmetry of sigma-type porphyroclasts (Figure 10), while 25% indicate a top-NW sense of shear (Kowalkoski et al., 2008). The remaining 30% of porphyroclasts with clear tails were symmetrical. When ranked for the confidence of the kinematic indicator, the top-SE sense of shear is even more dominant. These data could be interpreted in several ways. Given the predominance of top-SE kinematic indicators, this zone could be interpreted as a region of normal ductile shear that post-dates the emplacement of the granite (post 1155 Ma?). This extension may have overprinted early thrust displacement, which would explain the presence of top NW sense indicators, although it may be unlikely that early kinematic indicators would be preserved. Alternatively, the presence of both top–SE and NW as well as porphyroclasts with symmetrical tails could also be interpreted as a zone of pure shear that produced thinning and extension of the lower to middle crust.
Based on these preliminary studies, we hypothesize that the last stage of ductile deformation within this zone of the eastern Adirondacks involved extensional deformation, possibly along a SE-dipping normal detachment fault. It is possible that this extension was coeval with the NW-dipping ca 1045 Ma Carthage-Colton Zone that dropped the Lowlands down to the northwest and into juxtaposition with the Highlands. Ongoing geochronologic studies will provide new information of the timing of deformation in this zone. We also suggest that this eastern zone of extension may be an along-strike continuation of the Tawachiche Shear Zone in Quebec (Fig. 11) that dropped the Montauban-La Bostonaiss arc down to the east and into juxtaposition with the Morin Terrane (Nadeau et al, 1992, Corrigan and van Breemen, 1999, Bickford et al, 2008). The picture that emerges is one of late-stage orogen collapse affecting the Adirondack-Morin Terranes at the end of the Ottawan Orogeny. The collapse, which was accompanied by emplacement of Lyon Mt Granite, gave rise to a symmetrical core complex or gneiss dome on the scale and style of the Shuswap Complex.

STOP 10. Mylonitic Straight Gneiss (20 Min)
This roadcut contains excellent straight gneisses of several lithologies as well as some unusual rock types. Near its SE end are superb mylonitic straight gneisses of sillimanitic migmatitic metapelites. Pegmatites are in various stages of disruption. To the north these become interlayered with garnetiferous gabbroic anorthosite that closely resembles the metapelite leucosomes except for the presence of hornblende and coarser and more abundant garnets. Gabbroic layers are also present as well as a peculiar aluminous ultramafic that contains diaspore. A whole rock analysis yields SiO2 = 33%, Al2O3 = 17.5 %, Fe2O3 = 85 MgO = 24.32%, and CaO = 3%. Calcsilicates are found on both sides of the highway, but on the west side contain pods and layers of orange grossularite-diopside-wollastonite skarn. Nearby these is a discontinuous layer consisting of ∼80% red garnet. These types of lithologies are indicative the presence of fluids at high temperature.

Unconformity with Potsdam sandstone expos

8: GEOLOGY AND MINING HISTORY OF THE BARTON GARNET MINE, GORE MT. AND THE NL ILMENITE MINE, TAHAWUS, NY AND A REVIEW OF THE MACINTYRE IRON PLANTATION OF 1857
William M. Kelly
New York State Museum
3140 Cultural Education Center
Albany, NY 12230
Robert S. Darling
Department of Geology
SUNY, College at Cortland
Cortland, NY 13045
This field trip examines the geology and history of mining at two types of ore deposits, one a metal and one an industrial mineral. Both are strongly identified with the Adirondack Mountains of New York and both have histories that extend for more than a century. While mining activities began at both in the nineteenth century, only the Barton garnet mining venture has remained in continuous operation. Attempts, successful and unsuccessful, to exploit the ore at Tahawus occurred sporadically through the nineteenth and twentieth century. During this time the minerals that were the target and gangue at Tahawus essentially reversed roles.

8: GEOLOGY AND MINING HISTORY OF THE BARTON GARNET MINE, GORE MT. AND THE NL ILMENITE MINE, TAHAWUS, NY AND A REVIEW OF THE MACINTYRE IRON PLANTATION OF 1857

STOP 1. Barton Mines, Gore Mt. (1.5-2 hours)
Note: there is a charge of $1.00 – 2.00 per pound of material collected, payable at the mineral shop. There is also a charge to visit the mine as a tourist. The cost is usually reduced for school groups. This NYSGA trip will visit the No. 4 pit of the Gore Mt. mine. Visitors are normally escorted into the No. 1 pit, the earliest and lowest, which was developed in the garnet hornblendite. The No. 4 pit offers access to the olivine gabbro protolith of the ore in addition to the garnet ore per se. Proceeding down the access road on the north side of the pit takes the visitor across the contact zone between the protolith and the ore. In a matter of a few meters, the rock changes from altered olivine gabbro to garnet amphibolite. Garnets appear in the rock and increase in size and abundance over a very short distance. The texture and minerals of the olivine gabbro disappear. Description of the ore is presented in the text above. The opposite (south) side of the mine is in a “syenitic” gneiss, separated from the ore by a vertical fault. Minor granitic pegmatite occurs at the contact with the fault.

STOP 2. KRONOS Worldwide, Inc., Cheney Pond Deposit (1.5-2 hours)
At this stop, examine the large boulders that block the dirt roads on the east and west side of the main road. Both “gabbroic” (disseminated) and “anorthositic” (massive) ore types are displayed here. The massive ores contain xenoliths of anorthosite and xenocrysts of plagioclase derived from the anorthosite, attesting to the intrusive nature of this ore. Garnet reaction rims occur on both the xenoliths and xenocrysts. Deformed (sheared) and relatively undeformed representatives of the host rocks are present. Minerals are: blue-gray plagioclase (∼An45) megacrysts, white, fine grained plagioclase matrix (∼An 28), magnetite, ilmenite, garnet, amphibole and clinopyroxene. Sulfide mineralization is minor and late stage.
Walk (or drive) up the old haul road about 1km to the prospect pit developed in the Cheney Pond deposit. This is entirely disseminated ore. However, a great deal of “massive” ore of low grade has been hauled to this site to build the road so confusion regarding the exact source of the ore is possible. Sampling is recommended alone the haul road.
South of the top of the pit at Cheney Pond an overgrown logging road leads to the left into the woods. Follow this road about 75 m to a prospect pit, perhaps 7 meters across, on the right. This prospect was developed in nelsonite, although the identity of the apatite was not recognized when the pit was excavated.

STOP 3. Adirondack Iron and Steel Co. "New" Furnace (1 hour)
Please take only photographs at this stop. Do not take artifacts as souvenirs. Visible at the present time are the furnace stack, tuyere arches and tuyeres, casting arch, slag piles, and the entire contents of the wheel house with cross-heads, blowing tubs, and manifold more or less intact and in working position. Of the dam, wooden water wheel and casting house, little remains. Description given in text above.

9: MINING HISTORY, MINERALOGY AND ORIGIN OF THE GNEISS (GRANITE)-HOSTED Fe-P-REE AND Fe OXIDE AND GABBRO-HOSTED Ti-Fe OXIDE DEPOSITS FROM THE MINEVILLE-PORT HENRY REGION, ESSEX COUNTY, NY
Marian Lupulescu
New York State Museum
Research and Collections
3140 CEC, Albany, NY
Email: mlupules@mail.nysed.gov
Joseph Pyle
Department of Earth and Environmental Sciences
Rensselaer Polytechnic Institute, Troy, NY
Email: pylej@rpi.edu
“…genesis of these important ore bodies in Northern New York may reach the conclusion that there is a hopeless disagreement among those who have studied these deposits” (Alling, 1925)
New York State was a significant supplier of iron ore used in developing the resources and industries of the United States through the first part of the 20th century. The most important regions with iron deposits in the Adirondack Mountains are the northwestern area extending from Jefferson County into St. Lawrence County that includes the Antwerp-Keene hematite belt (Sterling and Caledonia mines) and the Jayville and Clifton mines; the central region with the Benson mines (St. Lawrence County) and Tahawus (Essex County); and the northeastern region with the Mineville-Port Henry-Fisher Hill group of mines (Essex County), and Ausable and Lyon Mountain mines (Clinton County). The earliest discoveries and mining operations of iron ores in the Adirondack Mountains were in the northeastern part (Linney 1943).
Iron ore was mined on the northeastern side of the Adirondack Mountains between Lake Champlain and the Adirondacks as early as 1804 (Birkinbine 1890). At the end of the 19th century three main areas were mined for iron in this region: Mineville-Port Henry-Fisher Hill, Chateaugay Mine at Lyon Mountains and Crown Point. The Mineville-Port Henry-Fisher Hill mines were considered “to represent one of the greatest magnetite deposits in the world” at that time (Anderson and Jones 1945). The first record of mining in the Mineville-Port Henry was in 1775 at a location that later came to be called Cheever Mine (Farrell 1996), but the first lease reported for this mine has been given later in 1820 (Smock 1889). The Mineville-Port Henry Iron Mining District had a cyclical pattern of boom and bust in its long mining history that spanned over 150 years. The various mines were repeatedly opened and then shutdown only to be reopened later depending on world events, economic changes and ownership's interests.
The Mineville-Port Henry mines were important and continuous iron producers, but they were also known for their apatite by-product and for the beauty and specific forms of the magnetite crystals that can still be seen today in many museums.
In this field trip we will examine the mineral composition and texture of the iron ore, the characters of the country and host rocks, and the relationships between magnetite ore and the host rock from the Craig Harbor, Cheever, Pelfshire, Mineville (the waste dumps of the Clonan and Bonanza pits), and the Barton Hill mines (Essex County).

9: MINING HISTORY, MINERALOGY AND ORIGIN OF THE GNEISS (GRANITE)-HOSTED Fe-P-REE AND Fe OXIDE AND GABBRO-HOSTED Ti-Fe OXIDE DEPOSITS FROM THE MINEVILLE-PORT HENRY REGION, ESSEX COUNTY, NY

STOP 1. Craig Harbor Mine
200m. Stop 1a. Upper Cambrian limestones with layers of chert. Small vugs and veinlets with pyrite are along the chert layers. Vertical faults cut the limestones.
100 m. Stop 1b. Craig Harbor faultline scarp. Beautiful view of the Craig Harbot faultline scarp. On the southern side of the fault there are Ordovician limestones and on the northern side there are Precambrian rocks. Here, a gabbroic intrusion is overlain by a metasedimentary sequence containing gneisses and marbles with deformed inclusions of gneisses, calcsilicates, metagabbro and quartzites. A very good description of the outcrop is in McHone (1987). The faultline zone was mentioned first by Emmons (1842); he noted inclusions of high-temperature minerals in the marble and considered them of igneous origin. Wiener et al. (1984) and McHone (1987) considered the marble to overlie the Eagle Lake gneiss. Roden-Tice (2002) reported that a sample from the gneisses below the marble yielded apatite-fission-tracks (AFT) age of 123 Ma.
200 m. Stop 1c. Craig Harbor Mine. The ore-hosted metagabbro displays micro- to coarse-texture: the coronitic character is obvious in places. The metagabbro contains garnet, hastingsite, phlogopite, plagioclase (oligoclase), clinopyroxene and orthopyroxene. The magnetite-ilmenite ore is in a pyroxene hornblendite layer (intrusion?) in the gabbro. Narrow veins of pyrite cut the iron-titanium ore. Whitney and McLelland (1975) and McLelland and Whitney (1980) studied the coronitic gabbros across the Adirondacks and determined that this texture formed in the granulite facies conditions of 8 kb and 800° C.

STOP 2. Cheever ore body (Port Henry mines)
250 m. Stop 2a. There is a marble outcrop on the side of the Jeep road. The marble contains deformed inclusions of metapelites, calc-silicates and quartzites.
500 m. Stop 2b. On the left side of the road is the Witherbees-Sherman pit that opened the Cheever ore body. Fragments of felsic rocks with granitic to dioritic compositions containing layers of magnetite with sharp contact with the host are piled above the pit opening. Be careful and do not go very close to the rim. The gabbro outcrops on the right side of the road. Examine the texture, the mineral composition, the nature of the contact, and the gabbro outcrop.
500 m. Stop 2c. On the left side of the road there is a small mining work that opens the contact between the magnetite ore and the host rock. Examine the contact, the mineral composition of the ore, and the host rock. Coarse aggregates of amphiboles and clinopyroxenes are common in the ore.
250 m. Stop 2d. A large pit appears on the left side of the road. Take the left avoiding the pit and climb an easy slope on a deer trail heading north-north west. The trail goes between small pits and after 25 m you will reach a barbwire fence. Do not cross, just follow it along the trail. After 5 m another barbwire fence appears; go over and after 50 m you are at the Three Holes Mine. The host rock and the magnetite “layers” can be examined in the mine (the hanging wall and footwall are solid and there is no danger to going inside). Flash lights are not necessary because the Three Holes Mine was a very small operation and the day light is enough to help us to see the contact of the ore and to study the mineral composition of the ore and the host rock.

STOP 3. Pelfshire (Pilfshire) mines (pits)
The Pelfshire (Pilfshire) mines were mentioned by Smock (1889) and described by Kemp (1908). The ore and the host rock are similar to the Port Henry mines (Cheever ore body). The gabbro forms a ridge not far from the pits. The magnetite ore strikes north-south and dips 60° west; it is hosted by a felsic rock with transitions to more mafic compositions. Examine the characters of the gabbro, the host rock and the magnetite ore. The pits and dumps are the property of Rhodia Inc. (New Jersey). Ask for permission to visit and collect samples (Mr. Paul Tramblee of Mineville is the guardian of the property).

STOP 4. Mineville group of mines
We will examine the rocks from the waste dumps of the Clonan, Joker and Bonanza shafts. Large fragments of magnetite-apatite, magnetite-apatite-pyroxene, magnetite, and magnetite-pyroxene ore display interesting textures. Examine the mineral composition and the texture of the ore and the host rock. The dumps are the property of Rhodia Inc. (New Jersey). Ask for permission to visit and collect samples (Mr. Paul Tramblee of Mineville is the guardian of the property).

STOP 5. Barton Hill mines
The Barton Hill group of mines is located half mile to the northwest from Mineville. Half mile north of the Barton Hill group is the Fisher Hill mine (actually on and under the Moriah Shock Correctional Facility). Here, we will examine the host rock with gabbroic character, its fabrics and the large body of pegmatite with magnetite and allanite-Ce cutting the gabbroic rock. The Lover's Hole from the Barton Hill mines is the location where beautiful magnetite crystals came from at the end of the 19th century.

11:ORIGIN OF THE LEWIS WOLLASTONITE DEPOSIT
William H. Peck
Department of Geology
Hamilton NY 13346
Eve Bailey
NYCO Minerals Inc
P.O. Box 368
803 Mountain View Drive
Willsboro NY 12996
The Willsboro-Lewis mining district is a world-class wollastonite (CaSiO3) producer in the eastern Adirondack Mountains, where wollastonite skarn is associated with Mesoproterozoic anorthosite. This district has estimated reserves of about 6 million short tons (St) from the Lewis open pit, Fox Knoll (the underground mine), and Oak Hill, half of which are represented by the currently operating Lewis mine. NYCO's Willsboro, NY plant produced 58,000 St of finished product in 2007. Combined with another 60,000 St produced at its Mexican operations, NYCO supplies approximately ¼ of the world's wollastonite. Wollastonite and its association with clinopyroxene and garnet was first described from the mining district by Vanuxem (1822), and his chemical analysis may be the first of a mineral from the Adirondacks (Buddington 1977). Fieldwork by A.F. Buddington in 1936 and 1937 led to the recognition that wollastonite skarns formed between anorthosite plutons and carbonate country rocks (Buddington and Whitcomb 1941). Oxygen isotope studies (Valley and O'Neil 1982; Valley et al. 1990; Clechenko and Valley 2003) reveal the importance of heated meteoric water during anorthosite emplacement and formation of the wollastonite-clinopyroxene-garnet ores.
Mining in the Willsboro-Lewis mining district is ongoing at the Lewis mine, which has been in operation since 1983. Mining in the area was intermittent until the early 1953, when Cabot Corporation began wollastonite mining operations at the Willsboro mine for use as a ceramic base and filler (Olmsted et al. 1992; Whitney and Olmsted 1995). Underground mining at Willsboro began in 1960 and ended in 1982. Currently at Oak Hill, NYCO is in contract with Graymont Materials of Lewis to crush the caprock for aggregate applications, thus lowering the overall strip ratio. Wollastonite mining will commence in approximately six years, with an overlap in supply to the plant in Willsboro from both the Lewis and Oak Hill mines. At this time the Deerhead deposit has been deemed uneconomical for mining. Wollastonite from Lewis and NYCO's operation in Sonora, Mexico is primarily used for applications such as plastics & elastomers, paints & coatings, construction materials, friction and metallurgical products, and finally for conductive/anti-static purposes.

STOP 1. Field Trip to the Lewis Open Pit
The geology of the Lewis deposit is described by Whitney and Olmsted (1993), and Figure 4 shows the current open pit workings. The footwall to the ore zone is gabbroic anorthosite gneiss. The ore zone, which is on average 8-10 meters thick, is gneissic with alternating wollastonite and garnet+pyroxene layers. Garnetite is locally abundant near the contacts with plagioclase-bearing rocks, such as anorthosite. The ore zone and adjacent units strike E-W and dip 10-15° S or SW (Whitney and Olmsted 1993). Historically, the Lewis deposit was one continuous ore section that was up to 21 meters thick in some areas of the mine. As mining proceeded southward, the ore fingers out with layers of “interburden” amid the ore. The interburden zones can range from 0.3 meters to 9.0 meters thick which create a challenge to mining operations.

12: TIMING OF FLUID ALTERATION AND Fe MINERALIZATION IN THE LYON MOUNTAIN GRANITE: IMPLICATIONS FOR THE ORIGIN OF LOW-Ti MAGNETITE DEPOSITS
Peter M. Valley and John M. Hanchar
Department of Earth Sciences
Memorial University of Newfoundland,
St. John's, NL A1B 3X5 Canada
The Lyon Mountain granite (LMG), which crops out extensively in the northeastern Adirondack Highlands (Fig 1), is the host to numerous Kiruna type low-Ti magnetite deposits. The LMG experienced extreme metasomatic alteration by potassic- and sodic-rich fluids related to the Fe mineralization and during which time high field strength elements (HFSE) including Zr Y, U, and light and middle rare earth elements were highly mobilized during Fe mineralization.
This field trip will examine features associated with Fe mineralization, alkali metasomatism, the relative and absolute timing of the processes involved in the formation such deposits and the tectonic context in which these processes have occurred. Such processes are complicated and debate is encouraged.

STOP 1. Chateaugay Mine, Lyon Mountain, New York
The Chateaugay mine is one of a series of large open pit and underground mines in the Lyon Mountain area. Mining began in the town of Lyon Mountain in 1867. By the early 1950s 15,000,000 tons of ore had been taken from the Chateaugay mine (Postel, 1952). The Lyon Mountain mines closed in 1967. Much iron remains but removal is not cost effective compared with cheaper foreign sources.
The strike of the quarry is approximately SW. The footwall and hanging wall of the ore body are perfectly exposed on the SE and NW walls of the pit, respectively. The ore follows the general trend of the pit and the gneissic layering, but locally crosscuts the gneissic banding (Gallagher, 1937). The local structure here appears to be that of a monocline with dip increasing towards the hanging wall. Overall the ore bodies here occur as "cigar-shaped" shoots in the limbs and core of a synclinal structure that plunges to the NE (Postel, 1952). These NE plunging structures are sometimes mimicked on a smaller scale by mafic and magnetite layers when observed in overhanging ledges in the quarry wall. Locally the ore may pinch and swell and may be openly folded.
Magnetite is the constituent ore mineral and is associated with pyroxene skarn and pegmatite and locally apatite and quartz. Magnetite rims pyroxene at both the outcrop and thin section scale. Late amphibole and chlorite are also associated with the pyroxene.
New age data from U/Pb zircon dating of various samples from the LMG and associated rocks will be discussed doing the field trip but are not listed here as they are in the process of being published elsewhere in a peer reviewed journal.
Mylonite
On the SE wall of the mine is a mylonitic shear zone (Fig. 2). The shear zone appears approximately parallel to the gneissic layering of the granite. "In-place" measurement is not possible as the mylonite is exposed high in the footwall of the mine and is not easily accessible. Blocks of the mylonite, however, lay at the base of the wall. Mylonitization is accompanied by partial melting of the felsic component of the host rock. Thin sections from this mylonite show that Fe mineralization is contemporaneous with shearing (Fig 3). Mineralogically, the mylonite contains remnant perthitic feldspar and microcline. The matrix consists of fine-grained albite, quartz, calcite, "strings" of magnetite and minor apatite and titanite.
Migmatites
In the hanging wall, on the northwest wall of the quarry immediately opposite the mylonite, is an approximately meter wide zone of migmatization. Here, the felsic component of the rock has melted leaving behind the more competent mafic rock to be deformed in a brittle manner. In places leucosomes are clearly rimmed by mafic selvages indicating that melting took place relatively in-situ and that these zones of melting are not intrusions into the LMG. The migmatite zone continues along the quarry wall. The felsic portion of this rock consists of quartz and coarse microcline. The mafic portion is dominantly cpx with late amphibole. Sugary-textured microcline granite borders the migmatized zone consisting of quartz, microcline and clinopyroxene.
Localized migmatite zones may also be evidence for fluid pathways. If this is true and the fluids are related to Fe mineralization then these fluids must have been hot enough to melt the felsic component of the rock. Fluid temperature estimates between 675 and 565 °C were determined from quartz-magnetite δ18O fractionation elsewhere in the LMG (McLelland et al., 2002). Melting of granitic rocks in the presence of even small quantities of H2O may begin at 600 °C (Robertson and Wyllie, 1971). Experimental data for granitic melts in the presence of F show that melt may be present as low as 550 °C (Manning, 1981). The presence of fluorite and F bearing alteration minerals and the previous temperature estimates by McLelland in the LMG suggests that partial melting during fluid alteration is a reasonable assumption.
Ore
The quarry steps down ∼5 meters just beyond the migmatite locality. This step provides an excellent cross section view to the northeast of un-mined ore and the contact of the ore with the hanging wall and footwall (Fig.2). The ore here varies from "strings" or layers of "lean" ore to massive magnetite. The layers of magnetite in the "lean" ore are generally concordant with the gneissic fabric of the host, but locally these strings of magnetite are highly variable in orientation. Pegmatites containing amphibole and orange potassium feldspar are common near the edges of the ore as well as pyroxene skarn. There is a general transition from massive ore to layered magnetite + pyroxene skarn + pegmatite to barren granite (see below) to microcline granite with disseminated magnetite in the hanging wall (Fig.2). The contact of the ore with the footwall is not well exposed here. Further along in the quarry to the southwest a transition from ore to layered magnetite, to perthitic granite with pyroxene and disseminated magnetite occurs in the footwall. The ore commonly consists of magnetite, quartz, pyroxene and varying amounts of apatite and remnant perthitic feldspar.
"Barren" Granite
Disseminated magnetite is ubiquitous throughout the LMG. In the granite immediately adjacent to the ore body, however, there is commonly found a zone depleted in magnetite. These so-called "barren" zones are most likely a source for much of the magnetite in the ore body (the breakdown of Fe bearing pyroxene may be another). The barren zone can be traced along the length of the quarry just above the ore body and appears to be "sandwiched" between two zones of "lean" ore. There is possibly a second barren zone above the top "lean" ore but this is inaccessible and as such difficult to verify. The width of the barren zone is ∼2 meters in most places. Approximately 50m beyond where the floor of the quarry steps down is an easily accessible place to view the barren zone on the NW side of the quarry. The rock is dominated by microcline and quartz with essentially no ferromagnesian minerals. Remnant pyroxene where present, usually occurs as inclusions in "forest" green amphibole. Late albite crosscuts microcline and there is some Ca alteration as well in the form of calcite. These zones depleted in magnetite are common around most of the ore deposits in the LMG (Postel, 1952). At the Palmer Hill mine this zone is up to 150m wide (Hagner and Collins, 1967).
Crosscutting Dike
Approximately 250 meters from the entrance to the quarry, located on the northwest side of the quarry, is a dike that crosscuts the gneissic fabric of the granite. The dike consists of quartz, plagioclase, magnetite, and minor sulphide and is approximately one meter wide. The composition of the plagioclase is oligoclase (McLelland, 2001). We will discuss the U-Pb age of this dike and its implications for Fe mineralization and deformation of the ore and host granites. A number of cross-cutting pegmatitic dikes are present throughout the quarry and range from plagioclase rich to syenite pegmatites to granite pegmatite and younger cross-cutting diabase dikes. These dikes do crosscut the ore but seem closely related, exclusive of the diabase dikes, to the mineralization and fluid alteration based on their chemistry and mineralogy.
Possibly related to these pegmatitic dikes are miarolitic cavities that also truncate the layering in the ore and the granite. These cavities are often up to a meter long. One is said to be large enough for a man to stand in (Gallagher, 1937). These cavities may contain very large crystals of orthoclase more than a foot in length, quartz, titanite, apatite, aegerine/augite, amphibole and late nearly pure albite. It is not clear how these formed but for open spaces this large they could not have experienced much deformation. These cavities are difficult to find in the quarry but a number of them are present. One can be observed on the backside of an ore pillar at the southwest end of the quarry. It is associated with an orange granitic pegmatite dike that crosscuts the layering in the ore.
Ore Pillar
Most of the quarry we have walked through has been filled in after mining ceased for safety reasons. However at the far end of the quarry it is still possible to view a deeper section of the mine. Here, two ore pillars are still standing where it is possible to view the true thickness of the ore. Access is difficult due to the steep slope, but the pillars can be viewed from a distance. The massive ore is approximately 3 meters thick with lean ore above and below. You may also be able to observe the NE plunging lineation in the rocks that overhang the ore pillar as well as another crosscutting dike, the barren zone, and migmatite layer.
Another feature at the mine are discontinuous mafic layers. They consist of amphibole and/or biotite and plagioclase that take on a “salt and pepper” appearance. These mafic layers may exhibit gneissic banding internally and vary in thickness from a few centimeters to meters in width and are common throughout the LMG. During this study they were observed to be continuous beyond the limit of exposure. When exposures were better during active mining, these layers are reported to anastomose and pinch out, but can persist for over 100 meters (Gallagher, 1937).

13: STRATIGRAPHY, SEDIMENTOLOGY AND DIAGENESIS OF THE POTSDAM FORMATION, SOUTHERN LAKE CHAMPLAIN VALLEY, NEW YORK
Bruce Selleck
The Cambrian Potsdam Formation is widely exposed on the periphery of the Adirondack massif in northern New York State and adjacent Ontario and Quebec. As the basal unit of the Paleozoic sequence over the cratonic interior of eastern Laurentia, its distribution and character are strongly controlled by the geometry of the pre-Potsdam erosional surface, and patterns of rift-related faulting of the Iapetean margin and sea-level change. In the northern Lake Champlain Valley, the Potsdam is characterized by a basal arkosic unit, the Ausable Member, which is overlain by marine quartz sandstones of the Keeseville Member (Fisher, 1977) Recent study of key exposures in the Lake Champlain Valley region (Landing, 2007) have more firmly established age relationships of the Keeseville and Ausable Members of the Potsdam. Landing (2007) has also documented the existence of a Middle Cambrian unit, the “Altona” Formation, which underlies the Ausable Member of the Potsdam Formation in the northern Lake Champlain region.
The Potsdam Formation is approximately time-equivalent to the Danby and Winooski Formation of western Vermont (Mehrtens and Butler, 1987; Landing, 2007). The Potsdam is thickest in the northern Champlain Valley and adjacent southern Quebec (∼250 meters), likely related to accumulation on the downthrown side of an Iapetan margin fault (Landing, 2007). In the area of this field trip, the total thickness reaches a maximum of 80 meters. A locally-developed basal arkosic unit may be correlative to the Ausable Member. The succeeding quartz-rich sandstones are referable to the Keeseville Member.
The Potsdam Formation acted as an aquifer for the transport of basinal brines and hydrothermal diagenetic fluids during burial. Significant diagenetic alteration of the original sediment has occurred, and the Proterozoic basement rocks beneath the Potsdam have been altered by hydrothermal fluids (Whitney and Davin, 1987). This alteration may be related to seismic pumping of fluids during Taconic (Late Ordovician), Acadian (Middle-Late Devonian) and/or Alleghanian (Carboniferous-Permian) tectonism on the Laurentian margin.
In the southern Lake Champlain Valley and Lake George Valley, the Potsdam records non-marine, tidal flat and nearshore marine depositional systems. This field trip will include exposures of a variety of sedimentary facies within the Potsdam Formation, and will also examine relationships with underlying Proterozoic basement and burial diagenetic and hydrothermal features within the sandstone and basement rock.

13 STRATIGRAPHY, SEDIMENTOLOGY AND DIAGENESIS OF THE POTSDAM FORMATION, SOUTHERN LAKE CHAMPLAIN VALLEY, NEW YORK

STOP 1. Lower cyclic unit of Keeseville Member, Potsdam Fm
The low outcrops by the roadside display gray-white quartz arenite of the lower cyclic unit of the Potsdam Formation with interbeds of reddish-brown dolomite and dolomitic sandstone. The quartz sandstone units are cross-laminated and trough cross-sets are present. The uppermost layer in the outcrop is comprised of domal stromatolites – algal accretionary structures – that formed in a shallow, muddy tidal pond. Modern stromatolites having this geometry are developed in coastal saline lagoons such as Lake Clifton in Western Australia. The stromatolitic laminations are very well preserved, and the grainy material between individual heads includes quartz sand and dolomitized bioclastic material. Coarse intraclast breccia is also found between individual heads. Note the coarsely crystalline calcite within the cores of some stromatolites. This may be a replacement of gypsum that grew as an evaporite mineral in the sediment that hosted the stromatolites.
Note the minor faults in the outcrop. Some of the patterns of faulting appear to mimic the major graben structure of Lake George and the boundary between the Adirondacks and Champlain Lowlands.

STOP 2. Proterozoic marble with Paleozoic dolomitization features
The roadcut on the east side of Route 22 displays dolomitized Proterozoic basement marble. Note the very coarse crystal size of the unaltered calcite marble and the pseudomorphic dolomite in the dolomitized portions. Graphite with the calcite marble is not altered in the dolomitized marble. The coarse dolomite crystals contain mm-scale voids that are sometimes partially filled with tiny 'saddle' dolomite rhombs, and terminated calcite and quartz crystals, which resemble miniature Herkimer 'diamonds'. Note the vertical fractures in the marble which served as conduits for the dolomitizing fluid. This is a good exposure to examine the effects of enhanced permeability, produced during the dolomitization process, on the development of a 'dolomitization front'. Alteration of calcsilicate minerals (clinopyroxene, brown phlogopite mica) in the dolomitized marble may have served as a source of magnesium for dolomitization. The relict altered minerals are now represented by chlorite and illite pseudomorphs. Pyritiferous, cherty, chlorite-bearing lithologies on the west side of the highway are also the result of hydrothermal alteration accompanying the dolomitization.
Saddle dolomite crystals within vugs in the dolomitized marble contain aqueous 2-phase fluid inclusions with homogenization temperatures of 160-210°C. Ice melt temperatures of these inclusions indicate salinity near halite saturation; similar high salinity inclusions are also found in sparry dolomite in the overlying Beekmantown Group carbonates (Collins-Waite, 1991). Stable isotopic analysis of the calcite and dolomite suggest interaction of the marble with dolomitizing fluids that were isotopically enriched relative to seawater, and that the fluids were strongly rock-buffered (Selleck, 1997).
The broad valley to the north of this road cut is underlain by Potsdam Formation; Stop 3 is visible approximately 2 km to the north along Route 22. The local geology suggests that the marble exposure here was close to the overlying Potsdam, and thus fluids within the Potsdam were readily available to invade the marble along vertical fractures. Enhancement of permeability within the marble by dolomitization increased the access of fluids to the basement rocks.

STOP 3. Lower Potsdam Sandstone at Firehouse Road
These road cuts expose the upper part of the basal arkosic unit, the succeeding lower stratified unit and the lower cyclic unit of the Potsdam Sandstone. We will examine the basal arkosic unit in more detail at Stop 5. The contact between the basal arkosic unit and the overlying lower stratified unit is well-displayed on both sides of the road. Note the abundant large clasts at the contact. This layer is interpreted as a lag deposit on a ravinement surface formed by the reworking of previously deposited gravel and sand by the encroaching marine shoreline during sea level rise. The immediately overlying marine sandstone contains rare mudcracks, best seen in the silty layers less than a meter above the contact. Rare vertical burrows are sometimes visible in outcrop, but common in slabbed samples of the sandstone 2-3 meters above the contact. Note the dominantly horizontal stratification and tabular foreset cross-stratification. Trough crosssets are also present. This facies is interpreted as a shallow subtidal foreshore deposit.
Continuing up-section at this outcrop, the base of the lower cyclic unit is marked by reappearance of coarse pebbly sandstone that documents shallowing to an intertidal depositional setting; availability of local Proterozoic basement source rocks is indicated by pebbles of vein quartz and feldspar. Well-developed bipolar cross lamination is clearly seen on vertical faces. The coarse pebbly sandstone intervals are capped by medium sandstones and carbonate beds at approximately one meter intervals. The carbonate beds consist of ferrroan dolomite with late calcite veinlets and vugs; and are interpreted as accumulations of carbonate mud on shallow upper intertidal flats. In other outcrops of this facies in the area, the carbonate beds contain stromatolites, mudcracks and intraclast breccia. Note the buckling and truncation of some of the carbonate beds. Sulfide mineralization is common in the carbonate, with pyrite, sphalerite and galena present. The dolomitization and sulfide mineralization are assumed to be related to the same hydrothermal event(s) which caused the dolomitization of marble seen at the last stop.

STOP 4. Upper Potsdam Sandstone at Firehouse Road
The upper part of the lower cyclic unit and the succeeding upper stratified unit of the Potsdam Sandstone are exposed in the outcrops on the west side of Route 22. Scattered low outcrops to the south allow for a nearly complete section to be constructed in these exposures. The lowest beds on the southern end of the roadcuts are dolomitic sandstones of the lower cyclic unit. A phosphate mineralized hardground with large burrows is developed at the top of these beds. This surface, interpreted as a sediment starvation interval that records the onset of a period of sea level rise, marks the contact between the lower cyclic unit and the upper stratified unit. The succeeding beds of the upper stratified unit consist of sandy dolomite, dolomitic shale and silty sandstone. The dolomite beds contain fragmentary lingulid brachiopods, dolomitized bioclasts, vertical and horizontal traces including Rusophycos and Teichichnus, intraclast breccias and wispy phosphatized surfaces. This interval is apparently correlative to the beds near Fort Ann, New York that have yielded a uppermost Middle Cambrian trilobite fauna. Diligent searching at this outcrop has not recovered identifiable trilobite remains, but it is a likely target for further study.
The upper stratified unit coarsens rapidly above the basal beds with coarse bipolar cross-stratified sands documenting storm or tidal current effects. Medium bedded sandstone with thin silty shale interbeds form the bulk of the exposures. Note the lensoid character of the bedding in the middle and upper portion of the outcrop. The uppermost part of the outcrop is thicker-bedded and slightly coarser sandstone. The upper stratified unit facies is interpreted as a lower shoreface and foreshore subtidal deposit, documenting a deepening event followed by shallowing. Exposures in the forested area immediately north and west of this outcrop are within the lower portion of the upper cyclic unit, and record further shallowing to tidal flat facies. We will not examine these exposures on this trip. Note the prominent fault-line scarp to the west and north of the highway. We will cross this fault as we proceed north to Stop 5.

STOP 5. Basal arkosic unit of the Potsdam Formation
The angular non-conformity separating banded Proterozoic calcsilicate gneiss and the basal arkosic unit of the Potsdam Formation is very well-displayed in road cuts on both sides of Route 22. The gneiss below was deformed in the Ottawan Orogeny, ca. 1050 Ma. The Potsdam here is ca. 520 Ma.
Medium to thick-bedded arkosic wacke, and arkosic arenite with abundant quartz and feldspar pebbles form the basal arkosic unit at this stop. Coarser lenses of pebble conglomerate occur discontinuously above the basal contact, and are sharply overlain by sandstone. These lenses represent an earlier phase of gravel deposition. The main body of sandstone contains normal and reverse graded beds. This facies was deposited by mass flow and sheet flood processes in a high-gradient fluvial system.
The gray-green color of the sandstone is due to iron-rich chlorite (25-29 wt. % total FeO). The chlorite formed as a diagenetic replacement of hornblende, garnet, biotite and plagioclase. Chlorite also occurs as an intergranular cement with quartz, K-feldspar and anatase. Chlorite occurs as tabular crystals within fluid inclusions in vein quartz at this outcrop, suggesting that the vein-mineralizing fluids were similar to those causing the general diagenetic alteration. Chemical data indicate that the diagenesis of the basal arkosic facies involved exportation of sodium, magnesium and calcium from the original sediment. This is consistent with petrographic observations, notably conversion of plagioclase, hornblende, biotite and garnet to Fe-chlorite. Chemical data also require importation of potassium and iron by diagenetic fluids.
The magnesium lost for the primary detrital minerals during burial diagenetic alteration may have served as a source of magnesium for dolomitization of underlying marble (Stop 2) and overlying marine carbonates (Stop 3). Similar Fe-chlorite alteration occurs in Proterozoic basement rocks and these could also have served as a source of magnesium for dolomitization. The widespread occurrence of these features in the vicinity of faults in this region suggest that seismic pumping of diagenetic/hydrothermal fluids was an important process during fluid alteration of the basement and overlying sedimentary strata. Other metals (Cu, Pb, Zn) in the original depositional minerals were also mobilized and exported via hydrothermal fluids, documented by scattered, non-economic occurrences of galena, sphalerite and chalcopyrite in the Potsdam Formation sandstones and in carbonates of the Beekmantown Group.
The diagenesis of the basal arkosic unit also resulted in precipitation of REE-bearing minerals. The yttrium phosphate mineral xenotime is found as scattered grains within authigenic chlorite and as authigenic overgrowths on detrital zircon grains. Monazite occurs as 'meshwork' replacement of detrital allanite and as overgrowths on detrital monazite grains. Thorite is present as detrital grains and micron-scale crystals within authigenic quartz. The source of the REE was the original sediment, which contained detrital grains of allanite, which is rather common in the adjacent Proterozoic granites and REE from breakdown of minerals such as garnet, ilmenite and magnetite. Detrital grains of ilmenite and magnetite in the basal arkosic unit are often altered to intergrowths of chlorite and anatase. Authigenic pyrite, sphalerite, galena and chalcopyrite are common in the green sandstones at this locality.
Collins-Waite (1991) reported fluid inclusions with 200-300° homogenization temperatures in vein quartz hosted by the sandstone at this locality. Fluids in the inclusions are halite-saturated. The quartz crystals hosting the inclusions show strong inclusion zoning patterns, suggesting a series of pulses of fluid flow and quartz crystal growth.

STOP 6. Potsdam Sandstone in Ticonderoga Village at LaChute River Falls
The upper stratified unit of the Potsdam Formation forms the water fall on the LaChute River in Ticonderoga Village. The hydroelectric plant excavations in the mid-1990's provided an opportunity to inspect the underlying carbonate-bearing lower cyclic unit. The overlying upper cyclic unit can be observed in scattered outcrops up slope to the north of the river exposures. Basal beds of the Galway Formation are present further up slope, near the road adjacent to Mt. Hope Cemetery. The sandstone slabs used in construction of the building at the hydroelectric site are from the upper stratified unit of the Potsdam. Note that some of these bear the trace fossil Protichnites.