A5: IAPETAN RIFT‒PASSIVE MARGIN TRANSITION IN NE LAURENTIA AND EUSTATIC CONTROL ON CONTINENTAL SLOPE OXYGENATION, TACONIC SLATE COLORS, AND EARLY PALEOZOIC CLIMATE
Ed Landing
New York State Museum
222 Madison Avenue
Albany, NY 12230
ed.landing@nysed.gov
Mark Webster
Department of the Geophysical Sciences
University of Chicago
5734 South Ellis Avenue
Chicago, IL 60637
mwebster@geosci,uchicago.edu
INTRODUCTION
This excursion along the eastern margin of the New York Promontory was prepared for the combined meeting of the New England Intercollegiate Geological Conference and the New York State Geological Association (October 2018). Parts of this guide have been modified from reports by EL and MW and are so indicated. There are two purposes of the trip:
(1) The oldest rocks of the Taconic allochthon (originally deposited on the east Laurentian margin of the Iapetus Ocean and at least 75 km east of its present location) and coeval shelf margin rocks in the Green Mountain anticlinorium (not seen on this trip) indicate a surprisingly late persistence or rejuvenation of Iapetan rifting. Although Iapetan rifting began in the later Ediacaran, the oldest record of sedimentary rocks deposited on the middle Proterozoic basement of the Grenvillian orogen in NE Laurentia is late Early Cambrian, with immature sandstone (arkose) deposition continuing well into the Middle Cambrian in the eastern Ottawa-Bonnechere aulacogen (Landing et al., 2009, In press; Figure 1).
(2) The second purpose of this trip emphasizes the relationship of major eustatic changes to macroscale alternations in oxygenation on the east Laurentian continental slope as exhibited in the Lower Paleozoic of the Taconic allochthon. One take away from the trip is that formation-level, type 1 depositional sequences on the Cambrian‒Ordovician shelf of eastern Laurentia are reflected by macroscale color alternations on the continental slope. Major eustatic rises and marine onlap of the cratons led to an increase in global insolation as reflective subaerial continental regions areas were inundated by shallow marine seas. These epeiric seas served as a heat sink, warmed the World Ocean, increased a key greenhouse gas (water vapor), all of which led to global temperature rise. Additional effects of high global temperatures include a decrease in storminess with decreased latitudinal temperature gradient as well as major intervals of deposition of organic-rich muds on the continental slope. Increased organic-rich mudstone deposition followed on the slope from the greater thickness and intensity of the mid-water low oxygen zone and in shallow shelf water with decreased oxygen solubility. Thus, high eustatic levels and consequent high global temperatures correlate with carbon sequestration and are the backdrop of the fossil fuel industries. This temperature increase is unrelated to changes in pCO2 or other greenhouse gasses, and is termed “global hyperwarming” (Landing, 2002, 2007, 2012). “Global hyperwarming” is also pertinent to global climate in the near future with accelerated global warming with eustatic rise due to the melting of ice on land in the high mountains, Greenland and other North Atlantic islands, and Antarctica. (modified from Landing et al., 2007, p. 25)

A5: IAPETAN RIFT‒PASSIVE MARGIN TRANSITION IN NE LAURENTIA AND EUSTATIC CONTROL ON CONTINENTAL SLOPE OXYGENATION, TACONIC SLATE COLORS, AND EARLY PALEOZOIC CLIMATE

Small road cuts in Grenvillian Proterozoic gneiss

First view of high ridges in Taconic
allochthon
At crest of low rise at south end of Proterozoic of French Mountain, note first view of high ridges in Taconic
allochthon directly in front of vehicles.

Pass Queenbury Country Club on left.
Underlying less resistant Cambrian-Lower Ordovician explains lack of relief.

Low road cuts on left (North) in Grenvillian
Low road cuts on left (North) in Grenvillian at south end Sugar Loaf Proterozoic inlier.

Low road cuts in Grenvillian inlier east of Hadlock Pond fault.

N-S-trending ridges in Taconic allochthon
Clear crest of hill and see spectacular view (if weather is clear) of N-S-trending ridges in Taconic allochthon across pastures developed on glacial outwash.

View to left (NE) of last ridge of Adirondacks
View to left (NE) of last ridge of Adirondacks east of Welch Hollow fault. East slope is nonconformity surface with lower Upper Cambrian Potsdam Formation eroded off.

Cross bridge over small creek
Cross bridge over small creek with medium-massively bedded dolomitic limestone and replacement dolostone. The locally oolitic, thrombolitic, intraclast pebble facies exposed here are more suggestive of the Upper Cambrian Little Falls Formation, rather than the Lower Ordovician Tribes Hill Formation (e.g., "Fort Edward Dolostone" [abandoned by Landing, 2003, 2012] as mapped by Fisher, 1984).

Pass ca. 1.0 mile of roadcuts in Proterozoic Hague gneiss
Pass ca. 1.0 mile of roadcuts in Proterozoic Hague gneiss on block uplifted by Welch Hollow fault.

STOP 1. Middle Proterozoic‒Cambrian Nonconformity
and Relationship of Thin Lower Paleozoic Shelf Succession to Continental Slope Oxygenation and Paleoclimate.
The stop shows several meters of east-dipping, medium–coarse grained, slightly dolomitic, brownish-weathering quartz arenite of the Potsdam Formation (Keeseville Member) with a basal quartz pebble conglomerate nonconformably overlying middle Proterozoic Hague gneiss. We are about 7 m below an upper Middle Cambrian trilobite-bearing horizon higher in the Keeseville with Crepicephalus, Komaspidella, and Lonchocephalus (Flower, 1964, p. 156; Landing et al., 2007, Stop 1.4).
This photogenic locality records the absence of ca. 600 million years of Earth history at this planar nonconformity. Further north in the Lake Champlain lowlands as the south flank of the Ottawa-Bonnechere aulacogen (OBa) is approached, the non-fossiliferous, feldspathic, often fluviatile facies of the lower Potsdam Formation (Ausable Member) appears under the Keeseville (Figures 1, 3). The oldest Paleozoic unit on the Grenville orogen in the OBa of northeastern New York and Adjacent Quebec is the Altona Formation―a thin (to 84 m-thick) heterolithic unit under the Ausable that includes lower wave-deposited feldspathic sandstones and red mudstones and a higher subtidal red-mudstone and sandstone with hydrothermal dolostones (compare Landing et al., 2009, In press, with Lowe et al., 2017, 2018; Figure 3).
Stop 1 emphasizes that the Lower Paleozoic of the eastern New York shelf is very thin by comparison with Great Basin and southern Canadian Rockies sequences (i.e., 100s of meters vs. several thousand meters). The ridge crest to the east is capped by the upper Little Falls Formation and only ca. 200 m of upper Middle‒Upper Cambrian overlies the Grenvillian basement. Thin Lower Paleozoic successions occur in this region of New York and Vermont due to its location on the slowly subsiding New York Promontory rift-margin of Laurentia (Thomas, 1977; Williams, 1978). For this reason, this passive margin can be expected to record Early Paleozoic eustatic changes as type 1 erosive sequence boundaries (e.g., Landing et al., 2003A). For example, the Cambrian–Ordovician boundary is a type 1 sequence boundary everywhere on the New York and western Vermont shelf and across most of the Laurentian platform except parts of the Great Basin and Southern Oklahoma aulacogen (Landing, 1988A; Landing et al., 1996, 2003, In press).
The Crepicephalus Chron (a “Chron” is the age of a biostratigraphic “Zone”) is a time in the late Middle Cambrian in which epeiric seas covered almost all of Laurentia except for the Trans-Continental Arch (e.g., Lochman-Balk, 1971), as well as major parts of other paleocontinents. Such an interval of high eustatic levels and high global insolation would have corresponded to a time of global hyperwarming, to d/a conditions on the Laurentian continental slope (i.e., part of the Hatch Hill Formation; Figure 3), and the probability of off-shelf transport of Potsdam sands and their deposition as part of the Hatch Hill lithofacies as seen at Stop 7. (modified from Landing et al., 2007, p. 30)

Rte 4 follows the Proterozoic–Cambrian nonconformity.
Rte 4 roughly follows a topographic break corresponding to the Proterozoic–Cambrian nonconformity.

Grenville gneiss and intersection with Rte 22 on right
Road cuts along Rte 22 east of Comstock State Prison are important sections through conodont-, cephalopod-, trilobite-bearing Lower Ordovician Tribes Hill (=“Great Meadows Formation”, abandoned), Rochdale (=“Fort Anne Formation”, abandoned), and Fort Cassin formations (Landing et al., 1988B, 2003, 2012, Appendix 2).

Dip slope at 10-12 O'Clock is nonconformity surface on Proterozoic.

Hill directly in front (North) of vehicle is Skene Mountain in Whitehall.
This rock under this hill corresponds to the entire terminal Middle-Upper Cambrian of the Lake Champlain Lowlands.

STOP 2. Potsdam Formation Roadcut.
Ca. 30 m of upper Potsdam (Keeseville Member) siliceous and dolomitic quartz arenite are exposed in the Whitehall area. Whitehall east of the Champlain Canal is on the Proterozoic, and the canal is cut in Potsdam sandstone (Figure 5). Herring-bone cross sets, dolomitic quartz arenite pebbles at the base of small channels/dunes, and U-shaped Diplocraterion burrows point to tide influenced, high energy Potsdam facies at Stop 1. The upper Middle Cambrian Potsdam is overlain by lower Upper Cambrian dolomitic quartz arenites and quartzose dolostones of the Galway Formation higher on Skene Mountain (=“Ticonderoga Formation,” term abandoned, also mistakenly termed “Theresa Formation” in reports on eastern New York; Landing et al., 2003, In press). The top of Skene Mountain is upper, but not uppermost, Little Falls Formation limestone (Landing et al., 2010). (after Landing et al., 2007, p. 31)

Pass cuts in Potsdam Formation on the right

STOP 3. Crossman Quarry - Upper Cambrian Little Falls Formation.
NO HAMMERS! The eastern end of the quarry (Figure 5) shows ca. 18 m of medium- to massively bedded oolitic, stromatolitic, and thrombolitic limestones with 4 m of overlying calcareous quartz arenite. This shallow carbonate platform facies, represents Fisher’s (1977) undefined “Warner Hill Limestone” member of the middle “Whitehall Formation” (abandoned designations). As commonly seen in Cambrian‒ Ordovician carbonate platform successions in eastern New York, hydrothermal dolomitization likely during the Late Ordovician Taconian orogeny has led to abrupt lateral and vertical changes from limestones with well preserved primary structures to dolostones without primary structures is seen in the Little Falls Formation at Stop 3 (see Collins-Wait and Lowenstein, 1994; Landing et al., 1996; Landing, 2007). The limestones are increasingly dolomitized with the loss of primary features in the western part of the quarry. In the western quarry, neomorphic dolostones predominate and have been termed the “Skene Dolostone” (Wheeler, 1941) sensu Fisher (1977, 1984). These sucrosic “Skene” dolostones comprise the road cut opposite the western end of the quarry. Long term weathering of these dolostones yields buff-colored blocks that are present in the talus at the west end of Crossman quarry.
Well preserved primary carbonate structures appear in the middle part of the quarry. A photogenic block with a large, gray thrombolite capped by laminated thin, greenish weathering limestones with chert lenses and small SH-V stromatolites lies at the base of the cliff in mid-quarry.
A biostratigraphically important Late Cambrian trilobite assemblage appears ca. 3.5 m above the base of the eastern quarry wall (Taylor and Halley, 1974). A meter above this, the major trilobite replacement (biomere) that marks the Laurentian Upper, but not uppermost, Cambrian Sunwaptan Stage‒Ibexian Series boundary is located at a lithofacies break that includes an intraclast pebble-ooid packstone bed (with the biomere boundary), an overlying quartz arenite, and a distinctive bed with SH-V and LLH-V stromatolites (Landing et al., 2010). Above this, a biofacies dominated by snails and other mollusks with rare trilobites and sparse euconodonts occurs in a thrombolite-dominated succession to the top of the quarry, and indicates a restricted, relatively near-shore environment (e.g., Westrop et al., 1995).
One purpose of Stop 3 is to show the lithology of non-dolomitized Upper Cambrian limestones of the Little Falls Limestone (“=Whitehall Formation,” abandoned term; Landing et al., 2003A) for comparison with lithofacies of the overlying Tribes Hill Formation at Stop 4.
The second purpose of Stop 3 is to show the lithology of an extensive carbonate platform facies that extended in the Late Cambrian from eastern Laurentia and lenses out in coeval siliciclastic-dominated deposits of the Upper Mississippi Valley in western Wisconsin and Minnesota and passes west through the Black Hills and into western Laurentia. As the Late Cambrian was a time of particularly extensive epeiric seas and consequent global warming (e.g., Landing, 2010, 2011, 2012), it was also a time in which black shale deposits as those of the Hatch Hill Formation developed on the east Laurentian slope (Stop 7, 8). (modified from Landing, 2002, p. B6-7; Landing et al., 2007, p. 33, 34).

Ridges to the East
The first ridge to the east is the local top of the Cambrian‒Ordovician passive margin carbonate platform (Middle Ordovician Providence Island Dolostone). A thrust relationship suggestive of the Champlain thrust further north brings the Potsdam Formation and younger Cambrian–Middle Ordovician units onto the Providence Island Dolostone. The second ridge to the east is the front of the Taconic allochthon, which overrides synorogenic, lower Upper Ordovician “Snake Hill Formation” flysch and Forbes Hill mélange (Fisher, 1984).

Cross east end of Skene Mountain.

STOP 4. Rte. 4 - Lower Ordovician (Upper Lower Tremadocian) Tribes Hill Fm.
Stop at east end of high, whitish weathering road cut in Tribes Hill Formation. Although dominated by dolostone, this cut is only 0.3 km south on strike of identical, but non-dolomitized strata with well preserved primary depositional structures in the Tristates quarry (see Landing et al., 2003A; Kröger and Landing, 2007; for conodonts, trilobites, and cephalopods). Key stratigraphic divisions (Sprakers, Van Wie, and Wolf Hollow members) of the Tribes Hill Formation will be pointed out from the south side of Rte 4; only the uppermost Tribes Hill Formation (Canyon Road Member, highstand facies) is missing in the Rte 4 road cut, as well as in the Tristates quarry.
This east-dipping section brackets most of the Tribes Hill Formation (=“Great Meadows Formation,” abandoned, of Fisher and Mazzulo, 1976, and “Spellman Formation,” abandoned, of Fisher, 1968). Well preserved, dark grey limestones with primary structures in the Tristates quarry just 0.2 mi. to the north (see Landing, 2002, Stop 5; Landing et al., 2003), are replaced directly along strike by hydrothermal, whitish dolostones at Stop 4. As detailed by Landing et al. (1996, 2003a, 2012) and Landing and Westrop (2006), the Tribes Hill Formation, with a uniform succession of four lithologically distinctive members, can be recognized in outcrops over about 12,000 square kilometers from Dutchess County, SE New York, through the lower Mohawk River valley of east-central New York, and north through the Lake Champlain lowlands. Just north of the New York-Quebec line near Ste-Clotilde, the Tribes Hill Formation has been termed the “Ste-Clotilde Member” (Landing et al., In press).
With exception of the Great Basin and the Southern Oklahoma aulacogen, the Cambrian‒Ordovician boundary is an unconformity across the Laurentian craton (Landing, 1988, 2012; Landing et al., In press). Early, but not earliest, Ordovician (i.e., late early Tremadocian) eustatic rise led to the Stonehenge transgression (Taylor et al., 1992) across Laurentia with carbonate platform deposits reaching the Upper Mississippi Valley (Oneota Dolostone) and the Rocky Mountains (e.g., Manitou Formation). These onlap units form a type 1 depositional sequence, are about the same age, and have Rossodus manitouensis Zone conodonts. This depositional sequence unconformity is the contact of the Upper Cambrian Little Falls Formation and Tribes Hill, with some localities showing channels up to 2.0 m deep that are filled with Upper Cambrian carbonate blocks (Landing et al., 2003A).
Rossodus manitouensis Zone conodonts have been recovered from most outcrops of the Schaghticoke d/a interval in continental slope sequences in NE Laurentia (e.g., Landing et al., 1986). This means that the extensive deposits of the Stonehenge transgression correspond to intense continental slope d/a conditions, as would be expected by the global hyperwarming model (Figures 3, 4).
The three lower members of the Tribes Hill Formation are exposed at Stop 4 (Figure 7). These include the thinner bedded, silty, locally intraclast-rich limestones (now dolomitized) of the Sprakers Member (which includes Fisher and Mazullo’s, 1976, “Winchell Creek Siltstone,” abandoned).
The most interesting unit of the Tribes Hill is the Van Wie Member. Although the Van Wie is never more than about 1.5 m in thickness, it occurs throughout the outcrop belt of the Tribes Hill. In all sections where it is exposed, it invariably has a basal intraclast conglomerate (to 25 cm in thickness) and a middle, thinner intraclast bed. These beds are perfect time-markers and seem to represent major storm beds in a time when dark shale appears in the Tribes Hill Formation. The Van Wie Member is composed only of black shale to the south in Dutchess County (Landing et al., 2003A). To the north and west, the shale lightens and has more limestone/dolomitized limestone beds (e.g., Landing et al., 1996), as at Stop 4. This presence of organic rich shale and the indication of d/a conditions on the NE Laurentian shelf also corresponds to the global hyperwarming model which predicts increased preservation (not increased production) of organic material in hot, oxygen-poor epeiric seas.
The Wolf Hollow Member (Fisher, 1954; = “Fort Edward Dolostone member” of Fisher and Mazullo, 1976; =“Kingsbury Limestone,” abandoned of Fisher, 1984, Appendix 2) occurs above the Van Wie at the Rte 4 cut and is characterized by massive thrombolite buildups in all outcrop areas of the Tribes Hill Formation. These huge thrombolites can be seen in the upper part of the Rte 4 cut.
The highstand facies of the Tribes Hill is the Canyon Road Member (Landing et al., 1996). The Canyon Road features lower ooid wackestones and mollusk-rich carbonates above the Wolf Hollow thrombolites. Higher strata include sparsely fossiliferous carbonates with planar stromatolites and molds of gypsum and anhydrite crystals and nodules of the upper Canyon Road Member. However, the Canyon Road is absent in the Rte 4 and nearby Tristates quarry sections (Figure 5).

Low ridge in front of the vehicles is the front of the Taconic overthrust.

Cemetery on right is on Taconic mélange
Pass cemetery on right which is on Taconic mélange under the Taconic master thrust.

STOP 5. Taconic Overthrust.
Note low brownish outcrops on left (north) side of road. Stop on right side of road at top of low hill.
NO HAMMERS! This is primarily a stop for geological perspective as well as one of the best localities to photograph the base of the Taconic master thrust.
The sheared brownish sandstone at the east end of the roadcut is the upper Lower Cambrian Bomoseen Formation, which here forms the westernmost edge of the Giddings Brook slice. The ca. 2.0 m of thin bedded, gray weathering, dark gray, fossiliferous limestone under the Bomoseen is a block of Upper Ordovician Glen Falls Limestone (Trenton Group, global Katian Stage) in what has been called the Forbes Hill mélange (Zen, 1961; Fisher, 1984).
A look to the west shows just how “compact” the geology of eastern New York is (Figure 1). As noted above, the Proterozoic basement of the Adirondack Mountains massif is analogous to the Black Hills in South Dakota; the block faulted, uplifted Proterozoic‒Ordovician shelf succession in the southern Lake Champlain lowlands to the front of the Rocky Mountains; and the Taconic overthrust succession to the Nevada thrust belt.

Upper Cambrian part of the Hatch Hill Formation
The cross road is in the Upper Cambrian part of the Hatch Hill Formation, with EL having found disarticulated olenid trilobites in a thin limestone bed on the east side of Rte. 21. This trilobite locality is ca. 50 m North of the intersection. After the intersection, drive South on strike along roadcuts in interbedded black shale and reddish (pyritic and dolomitic) weathering sandstone of anoxic/highly dysoxic Hatch Hill Formation (upper Lower Cambrian‒ lowest Ordovician)

Hatch Hill Formation in road cut on right.
After crossing creek at curve in road, pass more Hatch Hill Formation in road cut on right. After this point, the road swings east and crosses a large westerly overturned syncline in the Giddings Brook slice.

Lower Ordovician Deep Kill Formation
Greenish gray roadcut of Lower Ordovician Deep Kill Formation (“Poultney Formation” in many reports, abandoned designation, Landing, 2012).

OVERTURNED upper Lower Cambrian Browns Pond Formation.
Drive south past low road cuts in black slates and thin sandsones in east-dipping, OVERTURNED upper Lower Cambrian Browns Pond Formation.

Overlook of Browns Pond to south.

Browns Pond Formation
Pass low roadcuts on east and west sides of Holcombville Road. These overgrown cuts comprise the upper part of the type section of the Browns Pond Formation of Kidd et al. in Fisher (1984), The southerly cut on the east side of the road includes black shale with thin, laminated sandstones that are almost devoid of fossils with exception of a large looping epichnial trace fossil. The northerly cut on the west side of the road is a carbonate clast debris flow (Holcombville Member of Landing et al., Submitted) that forms the top of the Browns Pond Formation from Washington Co. to Dutchess County 160 km to the south. The pasture further west is underlain by slaty green mudstones of the Middle Granville Formation. These strata (Stop 3B and 3C of Rowley et al. (1979), Stop 8 of Landing, 2002, Stop 6.2 of Landing et al., 2007) will be better seen at Stop 6.

STOP 6. Late Early Cambrian Anoxic‒Oxic‒Anoxic Macroscale Alternations.
Stop at entrance to small newly reactivated quarry on west side of road. This stop consists of two parts. Do not descend into the quarry.
A sharp black‒green mudstone transition (Browns Pond‒Middle Granville formation contact; see Figure 3) is exposed at the top of the steep ramp that descends into the quarry. The Holcombville Member consists of thin limestones interbedded with black shale and capped by a massive calcareous sandstone debris flow at the top of the ramp. These strata are replaced ca. 50 m north along strike by fossiliferous, bedded turbiditic limestones that show fracturing and incipient transition into a debris flow. The second part of this stop is an examination of the abundant trace fossils in oxic facies of the Middle Granville Formation. Bedding surfaces of the Middle Granville Formation are present on large blocks of green and red slate at the south end of the Holcombville quarry and in the hillock of scrap slate on the east side of the road. These bedding surfaces occur because of the local bedding plane-parallel cleavage. These bedding surfaces are crowded with shallow trace fossils that range up to several centimeters in diameter.
Browns Pond Formation and Holcombville Member
The Holcombville Road quarry is an overturned section. It begins with 2.0 m of black siliciclastic mudstones with light gray, nodular lime mudstones. The black mudstones are capped by a 30–40 cm-thick, white weathering, light gray, conglomeratic pack- to grainstone composed of limestone sand–small intraclast pebbles and trilobite fragments with black phosphatic sand grains.
This ca. 2.4 m of section is the type locality of the Holcombville Member of the Browns Pond Formation (proposed in Landing et al., Submitted). This is the top of the Browns Pond Formation and the end of the late Early Cambrian Browns Pond d/a macroscale interval on the east Laurentian continental slope (Landing and Bartowski, 1996; Figure 3). The 30–40 cm-thick limestone thickens to 2.0 m about 50 m to the north where weathered cracks on the top surface of the unit show initial fracturing and formation of a debris flow. Micro- and macrofaunal elements of the lower Elliptocephala asaphoides assemblage (Lochman, 1956; Bird and Rasetti, 1968; Landing and Bartowski, 1996) occur in this top member of the Browns Pond Formation (E. Landing and M. Webster, unpub. data).
Middle Granville Formation
A very abrupt change into the gray-green mudstones of the Middle Granville Formation takes place right at the top of the 30–40 cm-thick limestone clast debris flow. The lower part of this greenish macroscale interval formed by the Middle Granville Formation has several beds of nodular lime mudstone. A thin limestone clast debris flow (less than 1.0 m-thick), which may be visible if the water level is low, is composed of slumped fragments of these nodular limestones. All of the thin Middle Granville Slate is exposed in the quarry. Several beds of purple slate in the Middle Granville Formation are present higher in the quarry.
Hatch Hill Formation.
A transitional interval from the Middle Granville Formation into the Hatch Hill Formation is seen in the west wall of the quarry, where the Middle Granville changes color into a grayish hue. Black, pyritiferous mudstones of the lower Hatch Hill Formation [i.e., the Hatch Hill interval, or terminal Lower Cambrian–lowest Ordovician dysoxic/anoxic macroscale interval (Landing et al., 2002)] appear ca. 5 m higher. Finally, beds of dolomitic quartz arenite characteristic of the Hatch Hill Formation are found not more than 10 m stratigraphically above the west wall of the quarry.
Middle Granville Slate and Middle Granville oxic interval (MGOI) (15 minutes)
Trace fossils Trace fossils are abundant in the red and green mudstones of the Middle Granville Formation. The crude retaining wall composed of large slate slabs at the south end of the Holcombville Road quarry and the large large pile of brownish red and minor green slate on the east side of the road came from the Holcombville Road quarry.
If the light is good, dense Planolites and large grazing traces up to 2 cm-wide can be seen on many of the bedding plane-parallel cleavage surfaces of the green and reddish slate. The abundance of burrows, which led to the general absence of primary depositional structures in the slate, and its reddish color (produced by traces of ferric iron) are consistent with deposition of the Middle Granville Slate under a more oxygenated slope-water mass than the underlying Browns Pond Formation. Evidence for skeletalized metazoans is not present in the reddish, purple, and green mudstones of the Middle Granville Formation. Either these metazoans were not present on the bottom, or their calcareous remains were dissolved away during diagenesis.
MGOI Landing et al. (2002) noted that the uppermost Lower Cambrian (upper but not uppermost Olenellus Zone) on the New York and Québec portions of the eastern Laurentian slope is composed of red and green siliciclastic mudstones. Unfortunately, Landing (2007, also Landing et al., 2007) equated this interval of improved oxygenation of slope waters with the presumed lowered sea-levels, cooler climates, and deeper circulation of oxygenated surface waters during Palmer and James’ (1971) Hawke Bay regression. Subsequent sea-level rise and the re-establishment of dysaerobic slope facies (e.g., Hatch Hill Formation and Hatch Hill dysoxic/anoxic interval) took place in the terminal Early Cambrian (Landing et al., 2002).
This interpretation has been re-evaluated with the obvious fact that the lower Elliptocephals asaphoides assemblage of the upper Browns Pond and Middle Granville formations is not terminal Lower Cambrian (upper Dyeran Stage in Laurentia) but is best regarded as middle Dyeran. Thus, it is older than the “Hawke Bay regression” and the improved slope oxygenation represented by the Middle Granville Formation is now called the Middle Granville Oxic Interval (MGOI, Landing et al., Submitted; Figure 3). In the course of this re-evaluation, Landing et al. (Submitted) questioned the existence of a global “Hawke Bay regressive interval,” restricted the “Hawke Bay” to its type area in NE Laurentia, and regarded it as epeirogenic in origin. They concluded that units such as the Hatch Hill Formation really reflect shore-line derived sand transport from Laurentia at a time of slowly rising sea levels that led to a global hyperwarming interval. In short, Early–Middle Cambrian boundary interval eustatic rise and climate amelioration led the development of a poorly oxygenated (hot) continental shelf in such widely separated areas as northern Vermont (Parker Slate) and eastern California (Mule Springs Formation) (Landing and Bartowski, 1996). (text modified from Landing et al., 2007, p. 64)

STOP 7. Tanner Hill Road
Hatch Hill D/ Interval (Late Early Cambrian‒Earliest Ordovician) Through Early Late Ordovician Paleooceanographic Changes on the East Laurentian Slope(30 MINUTES).
OHM 2020: Locations are very confused and should certainly not be trusted along this road. Why such vague location data is used in 2018, when everyone has GPS in their phone, boggles the mind!
Park just before (east of) lowest exposed rocks on right (north) side of road. Walk uphill and examine east dipping (overturned) section in core of large syncline. Walk through section in Hatch Hill, Deep Kill, Indian River, and Mount Merino formations (Figure 3). Stop 7 ends just west of hill crest with reappearance of Indian River Formation red mudstones on west limb of syncline.
Hatch Hill Formation deposition.
Dolomitic quartz arenites; conglomeratic sandstones; and interbedded, minor dark gray and black siltstones and shales of the Hatch Hill Formation form the lowest part of the section. (Remember that the section is overturned.) The medium- to massively bedded, coarse, lensing, conglomeratic sandstones and conglomerates of the lowest part of this interval have typically been compared to submarine channel-fill deposits in reports on Taconic geology (e.g. Keith and Friedman, 1977, 1978; Friedman, 1979; Rowley et al., 1979). However, significant erosion at the base of purported channels and vertical stratigraphic successions characteristic of channels have never been described in the Taconic regions. These coarse-grained sandstones and conglomerates may simply be sand- and debris-sheets that originated at many places along the shelf–slope break and upper slope, and not from a persistent point source (submarine canyon head).
The sandstones of the Hatch Hill Formation become thinner-bedded and finer-grained higher in the section, and black mudstones become dominant. This entire interval with black mudstones up to an abrupt transition into the green-gray mudstones of the overlying Deep Kill Formation is the Hatch Hill Formation. The Hatch Hill records a long interval of persistent dysaerobic deposition on the east Laurentian continental slope (terminal Early Cambrian–lowest Ordovician [lowest Tremadocian] Hatch Hill dysoxic/anoxic interval) (see Landing, 1993; Landing et al., 2002).
However, the changes in relative oxygenation of slope waters through this long interval are admittedly poorly known at present. Indeed, the development of three important Upper Cambrian “Grand Cycles” on the northeastern Laurentian shelf (Chow and James, 1987) should have been accompanied by sea-level and climate fluctuations recorded by changes in relative oxygenation on the continental slope. One explanation for the lack of any apparent record for changes in relative oxygenation through this interval may be that the transport and deposition of the thick sandstones that characterize the lower Hatch Hill served to erode and obscure much of the record of relative oxygenation that is recorded elsewhere in the Taconic succession by mudstones of various colors. Even with a maximum estimated thickness of 200 m (Rowley et al., 1979), the 20 m.y. interval bracketed by the Hatch Hill Formation indicates that it is a condensed unit that may have a number of unconformities produced during the transport and deposition of thick sand sheets. These sand sheets may have been emplaced primarily during eustatic lows.
Sandstones disappear in the upper Hatch Hill in the Tanner Hill section. The upper Hatch Hill corresponds to the interval of earliest Ordovician d/a mudstone deposition that has been termed “Poultney A” (abandoned designation, Landing, 1988b) by Theokritoff (1959; Zen 1964).
Deep Kill Formation.
A sharp transition from the Hatch Hill Formation into the overlying green-gray mudstones of the Deep Kill Formation is present in the drainage ditch on the north side of Tanner Hill Road. Limited outcrop of the Deep Kill Formation likely explains the apparent absence of the black mudstone-limestone mesoscale intervals characteristic elsewhere of the formation (Figure 3).
Indian River Formation
The transition into the lowest synorogenic sediments of the Taconic allochthon is observable just west of the crest of the hill with the appearance of low outcrops of the red, thin (ca. 50 m) Indian River Slate. Fisher (1961) attributed the red color of the Indian River to off-slope transport of lateritic sediments produced on the platform during development of the Knox unconformity. However, the rapid development of bacterial films on sediment grains with their transport into marine regimes regularly leads during early burial to a grayish sediment color, and an alternative explanation for the color of the Indian River must be found.
Landing (1988b) noted three lines of evidence in proposing that the Indian River reflects very slow deposition on an oxygenated sea-floor and long sediment residence time at the sediment-water interface. These lines of evidence include: 1) occurrence of radiolarian cherts and thin volcanic ashes undiluted by background argillaceous sediment; 2) thorough burrow-homogenization of much of the unit; and 3) presence of large, up to 3 cm-wide burrowers that were active on a well-oxygenated bottom).
Indian River Formation: oldest synorogenic deposit of Taconic orogeny and its age
The cherty, red slaty mudstones of the Indian River Slate mark an important stage early in the Taconic orogeny. Landing et al. (1992) discussed comparable red mudstones in a number of orogens, where they always underlie green mudstones and higher flysch (e.g., Taconian allochthons from New York to western Newfoundland, southern Uplands of Scotland, Hercynian Rheinisches Schiefergebirge and Harz Mountains, and Jurassic of Japan).
These data suggest that red, cherty, oxygenated shales in collisional orogens reflect the following history: 1) passage of a peripheral bulge through passive margin successions; 2) consequent flexural uplift and restriction of sedimentation on the peripheral bulge to slowly deposited pelagic muds, radiolarian cherts, and thin volcanic ashes of the Indian River-type; and 4) final flexural down-warping and increased rates of deposition as sediment provenance changes to the emergent accretionary prism (initial cherty green mudstones of Mount Merino-type and overlying Austin Glen flysch). The transition into the green-dominated, synorogenic mudstones of the overlying Mount Merino and then into Austin Glen Formation flysch are present in the core of the Tanner Hill syncline north of the road.
The interpretation of the Indian River Formation as reflecting the first indication of the Taconian orogeny in continental slope facies seems also to explain why its color (red and minor green) is so distinct from other continental slope mudstones in the Taconics (Figure 3). Rather than being part of the “standard” black or green macroscale alternations that reflect eustatic and climate change by the hyperwarming model, the red color of this apparently condensed unit and presence of volcanic ashes suggest depositional controls associated with advance of the Taconic arc toward the Laurentian margin.
The age of the Indian River Formation can only be approximated because biostratigraphically useful fossils (e.g., graptolites, conodonts) have not been recovered from it―although it is possible that the radiolarians in the cherts (Ruedemann and Wilson, 1936) might allow correlation of the unit. Geochronologic dating of the ashes is certainly possible, although it has not been done.
The Indian River is likely upper Middle Ordovician (Darriwillian Stage). It is underlain by lower Middle Ordovician rocks (upper Dapingian Stage) of the Deep Kill Formation (Landing, 1976) and overlain by the lower Upper Ordovician (lower Sandbian Stage) Mount Merino Formation with Nemagraptus gracilis Zone graptolites (e.g., Berry, 1962).

STOP 8. Cambrian‒Ordovician Boundary Interval in Dysoxic-Anoxic Hatch Hill Formation
OHM 2020:Locations on this road are very confused. Landing 2007 Stop 6.4 is 1.4 miles from Holcombville road, whereas in this guidebook it is only 1.0 miles.
(Stop 6.4 of Landing et al., 2007)
Graptolite and conodont biostratigraphy
As discussed above, the Cambrian–Ordovician boundary is a type 1 sequence boundary/unconformity across most of the Laurentian craton. However, stratigraphically unbroken Cambrian‒Ordovician boundary intervals occur in successions marginal to NE Laurentia. This is the case in the upper Hatch Hill Formation in northern and southern localities in the Taconic allochthon (Landing, 1993). An understanding of the Cambrian–Ordovician boundary interval in the Taconics came from a re-examination of three supposed “Upper Cambrian” dendroid graptolite genera that had been repeatedly cited from Stop 8 (Berry, 1959, 1961; Bird and Rasetti, 1968; Fisher, 1984).
Examination of these specimens in the NYSM Paleontology Collection showed the assemblage was not Upper Cambrian because it is comprised exclusively of rhabdosomes of the earliest Tremadocian form Rhabdinopora flabelliformis praeparabola Erdtmann, 1982 (Landing, 1993). This monospecific, lowest Tremadocian dendroid assemblage was relocated in a shaly interval (42.9–43.4 m) near the top of this cut on Tanner Hill Road (Figure 22). Twelve samples were processed for conodonts, but only a sample at 22.8 m yielded conodont elements—an upper Sunwaptan Stage fauna [Eoconodontus notchpeakensis Zone with E. (E.) alisoniae Landing, 1983; E. (E.) notchpeakensis (Miller, 1969); Proconodontus muelleri Miller, 1969]. These limited biostratigraphic data indicate that the base of the Ordovician lies in the interval 22.8 to 42.9 m, an interval without any evident stratigraphic break or lithofacies change (Figure 8).
Lithostratigraphy and regional comparisons
The Stop 8 succession in the upper Hatch Hill Formation is dominated by thin- to medium-bedded dolomitic quartz arenites and dark gray silt shales with debris flows with pebble-sized dolomitic sandstone clasts. By comparison, bedded limestones and carbonate clast debris flows dominate the Cambrian–Ordovician boundary interval at a locality approximately 160 km south in the southern Taconics near Hudson, New York (Landing, 1993). As in the late Early Cambrian (Landing and Bartowski, 1996), southern localities in the Giddings Brook thrust seem to have occupied a somewhat higher position on the continental slope and have more prominent bedded limestones and carbonate clast debris flows (Landing, 1993).
The presence of black mudstones of the Hatch Hill d/a interval through the boundary interval obviously does not seem to follow the global hyperwarming model. Perhaps the explanation lies with erosion of boundary interval strata across most of the Laurentian craton with eustatic fall that was not latest Cambrian but earliest Ordovician.

STOP 9. Raceville: Early Middle Ordovician Dysoxic/Anoxic Interval
(Stop 11 of Landing, 2002)
This vertically dipping section shows a black mudstone-limestone, d/a macroscale alternation in the lower (northern) part of the section and overlying greenish-gray, siliciclastic mudstone without limestone intercalations. The ca. 2 m-thick interval of interbedded limestone and black mudstone is repeated three times in the northern half of the roadcut with the northernmost and central repetitions comprising a faulted antiform and the southern repetition fault bounded.
Most of the limestone in the lower part of the section consists of fine-grained, argillaceous lime mudstones that appears to have resulted from diagenetic remobilization of fine-grained carbonate and/or methanogenic production of nodular diagenetic carbonate. Acid dissolution of these limestones yields conodonts (e.g., Histiodella species) indicative of the highest (lower Middle Ordovician, lower Whiterockian) black mudstone-limestone macroscale alternation of the Deep Kill Formation (Landing et al., 1992; Landing, 2012; Figure 3). The climate maximum, eustatic high, and resultant interval of intensified dysaerobic slope water recorded by the Raceville cut is equated with earliest Middle Ordovician (Whiterockian) eustatic rise across Laurentia and with deposition of such units as the Providence Island Dolostone (Figure 3). (modified from Landing, 2002, p. B6-14)

STOP 10. Best Exposed Taconic Section: Browns Pond and Bomoseen Formations on Mettawee River
OHM 2020: This is Lower Turnpike on Google Earth, not Upper
Cross single lane bridge on Mettawee River; park immediately north of the bridge. Walk east for ca. 0.6 km on dirt track that follows the Mettawee River. Descend to river bank at east side of ruins of a small mill(?) foundation. Stop 10 features an overturned (east-dipping), almost completely exposed section from the base of the Middle Granville through the Browns Pond Formation and down into the upper Bomoseen Formation. (Stop 5A of Rowley et al., 1979)
Overview
An exception to the limited outcrops typical of the Taconics is the almost completely exposed succession that extends along the Mettawee River. This is an overturned (ca. 30° E) Cambrian‒Ordovician succession in the Giddings Brook slice (Jacobi, 1977; Rowley et al., 1979). It was measured stratigraphically downward (i.e., upstream) from a horizon low in the Middle Granville Formation. Sample horizons are recorded as meters below the top of the section (e.g., Mett-neg 29.0; Figure 9).
The Lower Cambrian (Bomoseen‒base of Middle Granville formations; Figure 9) extends upstream from the falls over the Bomoseen Formation to 0.6 km east of the Upper Turnpike bridge. The Mettawee River section is on the SE margin of Theokritoff’s (1964) map area, but he mapped the interval between the Bomoseen and Hatch Hill formations as green and purple green slates, although an intervening black slate unit is prominent in this interval (Figure 3). Subsequently, Jacobi (1977; also Rowley et al., 1979) mapped this unit of black siliciclastic mudstone and limestone within the Bomoseen‒Hatch Hill interval.
This black unit is the Browns Pond Formation (Jacobi, 1977; Kidd et al. in Fisher, 1984). Recognition of the Browns Pond Formation as distinct from the lithologically similar, higher Hatch Hill is important for mapping purposes (Rowley et al, 1979; Fisher, 1984) and demonstrates that the two formations represent temporally distinct intervals of strong d/a on the east Laurentian continental slope. This has implications for regional and global geological and climatic history (Landing, 2000, 2007, 2012; 2013A, B).
The Mettawee River section received little early paleontological attention. Walcott (1912, p. 188, USNM locality 21a) reported a linguloid brachiopod and trilobites he identified as “Olenellus?”, “Ptychoparia sp.”, and “Microdiscus connexus (Walcott)” from a “limestone below the first fall of Mettawee River, above the North Granville bridge…” but did not illustrate the specimens and gave limited provenance information. Without modern study, Walcott’s (1912) identifications only indicate a Laurentian late Early Cambrian (Waucoban) age. This fauna could have come from any Lower Cambrian unit in the section as high as the lower Hatch Hill Formation (Figure 3).
The turbiditic limestones and thin debris flows at the top of the Browns Pond Formation (Holcombville Member of Landing et al., Submitted) earlier yielded the oldest acid-resistant microfossils from the southern Taconic allochthon (Landing and Bartowski, 1996). This suggested that older limestones and calcareous clast debris flows exposed through the Browns Pond and extending down into the upper Truthville Formation (Figures 3, 9) on the Mettawee River might have biostratigraphically significant faunas that could provide an upper age bracket on the origin of the east Laurentian passive margin in offshore facies, and also a bracket on the earliest d/a interval on the east Laurentian continental slope.
Lithofacies and sediment provenance
Most of the Browns Pond and Truthville formations on Mettawee River are a low energy facies of planar laminated mudstone and scattered mm-thick sandstones. The succession demonstrates for the first time that the Browns Pond is dominated by thin (cm- to several mm-thick), argillaceous lime mudstone-rich distal turbidites that may have sand- to rare granule-sized clasts of black lime mudstone. A near lack of trace fossils in the Browns Pond (noted below; also Landing, 2012) suggests the substrate was low in oxygen and metazoans were probably rare. The most abundant body fossils are echinoderm sclerites that comprise a few thin lenses and small ripples (to 1 cm-high) and were likely washed off the east Laurentian shelf or upper slope (horizons Mett-neg 112.5; -neg 62.5, -neg 28.5; Figure 9).
Decollement surfaces in the middle Browns Pond (Figure 9) suggest rapid deposition and easterly transport of weakly compacted mudstone. Weak compaction, soft mud at the sediment‒water interface, and low oxygen bottom waters that led to black, organic-rich mud deposition (Landing, 2012) with locally abundant pyrite (Figure 9) suggest that Browns Pond and Truthville shelly fossils are allochthonous (e.g., Thayer, 1983).
Carbonate clast debris flows occur in the Truthville and Browns Pond. The clasts are fine grained, dark colored, and laminated and were locally derived, and not from an Iapetus Ocean-facing shelf or upper slope. Thus, debris flows clasts in the Browns Pond and Truthville yield limited skeletal fossils.
As proposed earlier (Landing, 2007, 2012, 2013a, b), the succession of the Mudd Pond Member quartzite and late Early Cambrian age of the uppermost Browns Pond (Landing and Bartowski, 1996) suggest these units are the slope equivalent of the shelf Cheshire Formation (quartz sandstone tidalite) and Dunham Formation (now dolostone-dominated) (Figures 3, 9). This lithologic correlation and the soft, strongly d/a substrate of the Browns Pond would mean that the abundant, fine-grained carbonate component of bedded carbonates and secondarily transported debris flows came off the Dunham shelf (Figure 3) and that much of the fossil debris was similarly transported.
Trace fossils and bottom water oxygenation
Planolites burrows at the base of thin sandstones of the upper Bomoseen persist into the Truthville Formation where they appear at the base of a few thin sandstone laminae (Figure 9). The Browns Pond has rare trace fossils with a few Planolites at Mett-neg 71.6 to Mett-neg 82 m on bedding surfaces and in slabbed sections.
Most of the Browns Pond Formation lacks any traces, which is consistent with it’s interpretation as a strongly d/a facies (Landing, 2007, 2012, 2013A, B). The only large traces found in our study are black anastomosing forms limited to an interval of green weathering, medium grey mudstone (Mett-neg 55.0 to Mett-neg 56.5) that records a more oxic time on the sea floor (e.g., Landing, 2012). The large traces suggest Megagrapton Książkiewicz, 1968, a distinctive graphoglyptid known from large polygonal nets with common right angle branches (e.g., Książkiewicz, 1970). However, recent analysis of graphoglyptids (Fan et al., 2018) shows that Megagrapton actually has burrow segments intersecting at a variety of angles and thus allows a tentative assignment of the Browns Pond traces to “Megagrapton?” These large traces are not restricted to a bedding surface; they are endichnial and the product of a burrowing organism.
Ichnofossils of the Taconic allochthon have not received modern study, and the Browns Pond specimens can only be compared with the spartan original description and illustration of Fucoides flexuosus Emmons, 1844. They were compared with specimens in the NYSM Paleontology Collection that were collected from the “Cambrian roofing slates” in the vicinity of Middle Granville village that have been assigned to Emmon’s ichnospecies. Both the Browns Pond and Middle Granville specimens have been tentatively assigned to Megagrapton? flexuosus (Landing et al., Submitted). Walcott (1890, p. 603) complicated an understanding of Taconic Cambrian ichnofossils by synonymizing all previously named, elongate taxa with the thin (i.e., thread-like) looping trace Helminthoidichnites Fitch, 1850. This synonymy meant that the much wider looping traces of the genotype Gordia marinus Emmons, 1844, became H. marinus (Emmons, 1844). Walcott (1890, pl. 52) illustrated large and anastomosing traces comparable to those from Mettawee River as H. marinus?
Late Early Cambrian age of syn-rift and passive margin (Truthville‒lower Hatch Hill Formation)
A significant “younging” of the oldest units deposited along the margin of the New York Promontory (Figure 3) is indicated by re-evaluation (Landing et al., Submitted) of the biostratigraphic information on mineralogically immature, likely syn-rift deposits in the Taconic allochthon (i.e., Rensselaer and Bomoseen formations). In addition, small skeletalized faunas appear below and persist through the Browns Pond d/a interval to provide an upper age bracket (late Early Cambrian; middle Dyeran Age in Laurentia) on the rift‒ passive margin transition along the New York Promontory.
Reactivation of rifting or persistence of rifting into the late Early Cambrian (late Dyeran) and into the middle Middle Cambrian is suggested by the first marine transgression of the Ottawa-Bonnechere aulacogen and the coeval, on-strike subsidence of the Franklin Basin on the northwest Vermont shelf (Landing, 2007, 2012, 2013A, B; Landing et al., 2009, In press; Webster and Landing, 2016; Figure 1). The occurrence of Oldhamia-bearing trace fossil assemblages from the Rensselaer and Bomoseen formations comports with Dyeran and not Ediacaran or earliest Cambrian rifting and production and accumulation of immature sediments on the Iapetus-facing margin of the New York Promontory, as well as the Quebec Reentrant and Newfoundland Promontory. Recent study (Herbosch and Vaniers, 2011) shows that the trace fossil Oldhamia is biostratigraphically useful and not a form that could range even down into the Ediacaran. Indeed, Oldhamia is known worldwide from strata that are no older than the late Early Cambrian, and its occurrence in the Rensselaer and Truthville formations thus brackets the transition in NE Laurentia from a rifted margin in the late Early Cambrian in the Taconics of New York and Quebec (see Swett and Narbonne, 1993; Landing et al., Submitted) and western Newfoundland (Lindholm and Casey, 1990).
The trilobite Olenellus from the Cheshire Formation has been reported as the oldest body fossil on the northeast Laurentian passive margin (Osberg, 1969; Allen et al., 2010). However, Olenellus was actually reported to occur much below the Cheshire in chemically immature (syn-rift) arkoses at Clarksburg Mountain, northwest Massachusetts (Walcott, 1888). The Clarksburg Mountain rocks with purported Olenellus were mapped as “Cheshire” by Ratcliffe et al. (1993) with the “Cheshire” claimed to nonconformably overlie gneisses in southern Vermont and adjacent Massachusetts (e.g., Rankin et al., 1989; Hatcher, 2010; Allen et al., 2010). However, Walcott’s (1888) Olenellus report is from rocks that occur only ca. 30 m) above the nonconformity with middle Proterozoic gneisses. This occurrence in conglomeratic arkoses brought to the “Mendon Formation” (Brace, 1953, p. 33; Skehan, 1961), and now best assigned to the Pinnacle Formation (Landing, 2007, 2012, 2013a, b; Webster and Landing, 2016; Figure 3). Walcott’s (1888) supposed Olenellus specimen was never illustrated and a search of the USNM collections by MW did not lead to its recovery. Thus, a presently unidentified trilobite has been found in the oldest syn-rift sedimentary rocks on what became the NE Laurentian shelf, with the trilobite indicating a late Early Cambrian (Epoch 2) correlation comparable to that of the oldest known rocks (i.e., Rensselaer or Bomoseen formations) of the Taconic allochthon. This generalized correlation supports the conclusion that Iapetan rifting persisted or was re-established on the NE Laurentian margin in the late Early Cambrian.
Higher Mettawee River strata provide information on post-syn-rift deposits on the continental slope of NE Laurentia. The age of these deposits are provided by fossils from the Mettawee River section and other localities. The middle Dyeran Elliptocephala asaphoides assemblage spans the upper Browns Pond‒lower Hatch Hill formations. This assemblage brackets the d/a intervals known from these two formations and the more oxic strata of the Middle Granville Formation (Landing and Bartowski, 1996; Landing 2012; Figure 3). The Mettawee River section shows that small skeletalised taxa known from the E. asaphoides assemblage persist lower through the Browns Pond and into the relatively oxic facies of the upper Truthville Formation (Landing et al., Submitted).
The likely sediment source of the carbonate-rich Browns Pond Formation and its fossils was the Dunham Formation on the eastern shelf of the New York Promontory (Figure 3). This slope‒shelf correlation accords with correlation of the Mudd Pond Member quartzite with Cheshire Formation tidalites on the shelf (Landing, 2007, 2012). This correlation of shelf and continental slope units would make the lowest calcareous mudstones of the Browns Pond Formation equivalent to the shelf-margin Moosalamoo Phyllite that underlies the oldest NE Laurentian carbonate platform carbonates (Forestdale Marble; Figure 3).
These correlations mean that a significant amount of rift‒passive margin rocks on the NE Laurentian shelf (Pinnacle‒Dunham) and slope (Rensselaer‒Browns Pond) are lower and middle Dyeran. This remarkable history of events that took place in the earlier Dyeran is actually incomplete as the Middle Granville Formation (and Middle Granville Oxic Interval, or MGOI), its shelf-equivalent HST, and the lowermost Hatch Hill Formation, are all middle Dyeran (upper Elliptocephala asaphoides assemblage interval). Thus, reestablishment of reduced slope water circulation and deposition of dysoxic/anoxic mudstones of the lower Hatch Hill Formation beginning in the middle Dyeran in the Taconics of eastern New York and adjacent Vermont are significantly older than the upper Forteau and lower Hawke Bay formations (upper Dyeran) of western Newfoundland.
The MGOI is proposed as replacement for the earlier named “Hawke Bay Oxic Interval” in theTaconics by Landing (2012; “HBOI” abandoned by Landing et al., Submitted). Correlation of the lower Hawke Bay Formation in western Newfoundland as upper Dyeran means that it is the lower, but not lowermost, part of the lengthy Hatch Hill d/a interval (middle Dyeran to lowermost Ordovician; Landing 2012) that really correlates with the Hawke Bay Formation and “events” (Landing et al., Submitted). As concluded by the latter authors, the designation “Hawke Bay Events” (“HBE”) should probably be limited to NE Laurentia where a comparable rifting history that persisted into or was reinitiated in the late Early Cambrian along the Newfoundland and New York promontories and included similar, likely coeval, lower passive margin successions (Bradore‒Hawke Bay and Cheshire‒Monkton formations).
The paradigm that the Hawke Bay Events necessarily featured major eustatic regression and an interregionally extensive unconformity should be questioned as noted by Nielsen and Schovsbo (2015) who regarded the “Hawke Bay regression” in Baltica as an epeirogenetic event. Similarly, Knight et al. (2017) also suggested that the “type” Hawke Bay Event unit, the Hawke Bay Formation in western Newfoundland may also be the record epeirogenic activity, not eustatic changes. Indeed, available evidence can be used to interpret the Hawke Bay Formation not as a regressive sedimentary unit but as an HST lithosome. By this proposal, the Hawke Bay, and possibly Monkton Formation in NE Vermont, were deposited either during an interval of reduced rate of sea-level rise and development of a shallow-water siliciclastic by-pass shelf with significant offshore transport of shoreline-derived quartz sand (Landing et al., Submitted). The qualification “local epeirogenic uplift” is appropriate in NE Laurentia as approximately coeval (upper Dyeran‒Middle Cambrian) deposits of the Parker Formation in NW Vermont that are correlated with the Hawke Bay Formation record an abrupt and continuing epeirogenic foundering of the Franklin Basin and at least the eastern part of the Ottawa-Bonnechere aulocogen (Landing et al., 2009; Webster & Landing, 2016). (modified from Landing et al., Submitted)

West edge of Taconic Allochthon
The ridge to the left (east) of Rte 40 is formed of more resistant rocks at the western edge of the Taconian allochthon. The SSW trend of Rte 40 from this point to just north of Troy follows the front of the allochthon and edge of the Giddings Brook slice. Rte 40 meanders back and forth from the edge of the allochthon and onto erosionally less resistant, structurally underlying Upper Ordovician “Snake Hill” synorogenic flysch and wildflysch (see Landing et al., 2003b; English et al., 2006) and, in the area of Middle Falls, onto Lower and Middle Ordovician shelf carbonates.

High road cut on left (east) is in overturned Deep Kill Formation.
The road cut shows repetitions of meter-scale Logan cycles that are relatively tectonized (faulted). Better preserved Logan cycles will be seen at Stop 11. This road cut is Stop 12 of Landing (2002).

STOP 11. Logan Cycles in the Deep Kill Formation: Mesoscale Cycles in the Milankovitch Band.
Stop on edge of Rte 40 close to ca. 10 m-high cut with prominent banded slaty mudstones (Logan cycles) on left (east) side of road. CAUTION! Traffic can be heavy so cross road after discussion only with care. No hammers on this superb locality, take pictures only. When examining road cut, stay close to the steel barrier or walk inside the barrier and hug the rocks.
This is one the most accessible and well preserved outcrops that shows the color and lithologic alternations characteristic of Logan cycles (Landing and Benus, 1985; Landing et al., 1992) in the Lower‒ lower Middle Ordovician Deep Kill Formation. NO HAMMERS AT THIS STOP!
The road cut lies close to the leading (west) edge of the Taconic allochthon and Giddings Brook slice. The section is overturned and dips gently to the east. The utility of Logan cycles (Figure 10) in geological field work is that the upward transition of muddy intervals provides tops-sense in successions that otherwise lack much in the way of primary structures. Thus, successions with ABCABC, BCBC, or ABABABCABC, etc. alternations can be invariably used to determine tops-sense in a “monotonous” mudstone or slate sequence because A-units form the base of tripartite Logan cycles and C-units form the top.
About six Logan cycles are present in this ca. 8 m-thick section. Most of the cycles are BC cycles, and lack the lower black mudstone that appears in many, but not all, Logan cycles (Figure 10). The buff-weathering, dolomitic C-intervals are often the thickest part of the Logan cycles at Stop 11 and grade imperceptibly down into greenish B-intervals. Several of the Logan cycles show the abrupt upward transition from the C-interval into the black mudstone (A-unit) of the overlying Logan cycle.
Well preserved Logan cycles that extend through a completely exposed section through the Floian Stage at the leading edge of the Taconian allochthon at Levís, Québec, appear to have an average duration of less than 100 k.y. (Landing et al., 1992). EL’s experience is that only the more proximal parts of Laurentian slope successions (i.e., the Levis area in Québec and the central and southern Giddings Brook slice in eastern New York) show Logan cycles, while more distal successions are comprised of completely oxic mudstones with green, purple, and red color.
Logan cycles should be seen as potentially economically significant as they comprise the dominant depositional motif in the deeper-water, organic-rich, Miocene petroleum source rocks on the southern margin of the Mediterranean (Landing et al., 1992). However, the rocks of the Giddings Brook slice record a much higher burial temperature, with euconodont elements typically opaque black in color and showing a C.A.I. (Color Alteration Index) of 4.0, which means that any organic materials have been transformed into graphite (e.g., Landing, 1976, 1993).

Pass by intersection with Bald Mountain Road on right.
The old Bald Mountain limestone quarry was developed in a giant block of white weathering, massive limestone with a mollusk-dominated fauna (e.g., Cushing and Ruedemann, 1914, p. 75–80). This macrofauna and conodonts (E. Landing, unpub. data) indicate a late Early Ordovician (Floian) age, and allows interpretation of the Bald Mountain limestone as a massively bedded block of Fort Cassin Formation torn off the outer carbonate platform by Taconian thrusting. The block lies under the Taconic master thrust in early Late Ordovician wildflysch (see Zen, 1967, p. 31, 32, 36).

Early Ordovician carbonate platform units
For the next several miles, Early Ordovician carbonate platform units under the Taconic allochthon are exposed in low cuts along the east side of Rte 40.

Note cut in vertical beds of lower Trenton Group
Note cut in vertical beds of lower Trenton Group (Upper Ordovician, Katian) limestones and thin interbedded black mudstones along east side of road and opposite wide dirt pull-off on west side of road. This is a good place to bring class trips, as it provides a panorama that includes the Devonian of the Catskill High Peaks to the southwest, the Proterozoic Grenvillian of the southernmost Adirondacks to the west, and the Lower Cambrian of the Taconic allochthon on the hill crest immediately east. In addition, the Upper Ordovician “Knox unconformity” can be investigated at the very north end of the outcrop. The “Knox unconformity” is seen at the contact of relatively proximal, brachiopod-dominated limestones of the Trenton Group with underlying, brown weathering dolostones (age presently undetermined, possibly early Middle Ordovician and referable to the Providence Island Dolostone).

STOP 12. Schaghticoke Gorge: Late Early Tremadocian Dysaerobic Interval.
Turn right on curve immediately after red brick church and park in Hoosick River overlook parking area. Until recently, the rocks in Schaghticoke gorge below the dam could be accessed by walking downslope under the Rte 40 bridge. Unfortunately, the response to drinking parties and a few drownings has meant that an iron fence has been put along the gorge, and this makes access difficult. What will be done for Stop 12 will be a photographic overlook downstream from the eastern part of the bridge. Two areas on the north bank and on the upstream side of the island in the middle of the Hoosick where black mudstones of the Schaghticoke dysoxic/anoxic interval crop out can be seen. After this, CAREFULLY cross the bridge roadway, and the same Schaghticoke d/a interval can be seen tectonically repeated several times from a viewpoint directly down from the NE end of the bridge.
(Stop 13 of Landing, 2002).
The section appears to comprise a tectonically isolated slice at the leading edge of the Taconic allochthon and Giddings Brook slice. This is the type section of the upper lower Tremadocian (Lower but not lowermost Ordovician) “Schaghticoke Shale” (term abandoned by Landing, 1988b, and grouped as the lowermost part of the Deep Kill Formation).
Schaghticoke gorge features the structural duplication of a thin (ca. 4 m) black mudstone-limestone macroscale alternation in greenish-gray slaty mudstones. Graptolites from the black mudstones (Ruedemann, 1903) are representative of the lower Ordovician Matane faunas known along the leading edges of the Taconian allochthons in Québec. Unfortunately conodonts from limestones in the Schaghticoke d/a interval in the Hoosick River gorge are limited to stratigraphically long-ranging protoconodonts (Landing, 1976; E. Landing unpublished data). The lithology of this middle–upper Tremadocian black shale-limestone macroscale alternation is remarkably similar to the coeval (based on graptolites) black shale-limestone macroscale alternation exposed for 400 km along the south shore of the St. Lawrence River in Québec and which yields Rossodus manitouensis Zone conodonts (Landing et al., 1986). The Schaghticoke d/a interval of climate maximum and intensified dysaerobia on the Taconic continental slope and elsewhere along the Laurentian margin (Landing, 2012) is equated with the eustatic rise and the Stonehenge transgression (Taylor et al., 1992) that led to deposition of the Tribes Hill Formation as a type 1 depositional sequence (Stop 4).

Most of route is on low-lying terrane developed on Late Ordovician Utica Fm
Most of route is on low-lying terrane developed on Late Ordovician Utica Formation (black mudstone with abundant graptolites). A few miles south of Lake George village, note road cuts in middle Proterozoic Grenvillian orogen (Adirondack basement).