B6: EARLY PALEOZOIC SEA LEVELS AND CLIMATES: NEW EVIDENCE FROM THE EAST LAURENTIAN SHELF AND SLOPE
Ed Landing
New York State Museum
The State Education Department
Albany, NY 12230
INTRODUCTION
Purpose
Field studies undertaken in eastern New York in the early 1800s by Amos Eaton and others led to the birth of American geology (see review by Friedman, 1979). With this early work, geology continued as an important applied discipline, but it developed into an important intellectual and cultural activity that provided the first empirical explanations of physical and biotic change through earth's "deep time." Although almost two centuries have passed since Eaton's first work, "everything isn't known and decided" either about the geology of eastern New York or its significance in opening a window into "deep time." This field trip will illustrate recent published syntheses of eastern New York geology that help reconstruct Early Paleozoic sea-level and climate changes.

B6: EARLY PALEOZOIC SEA LEVELS AND CLIMATES: NEW EVIDENCE FROM THE EAST LAURENTIAN SHELF AND SLOPE

Small road cuts in Grenvillian Proterozoic at south end of village.

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" as mapped by Fisher, 1984).

STOP 1. LOWER ORDOVICIAN AT KANE FALLS: AGE AND LITHOSTRATIGRAPIDC REINTERPRETATIONS. (30 MINUTES).
A stratigraphic section for Kane Falls will be distributed on this field trip; this section is available in Landing et al. (2003, fig. 5).
Mazzullo (1974) and Fisher and Mazzullo (1976), respectively, termed the upper part of the Kane Falls sequence a "reference section" for the lower part of the lowest Ordovician "Cutting Formation" and "Great Meadows Formation" (abandoned designations). A planar-laminated silty dolostone 9.55-10.75 m above the base of this 23 m-thick section (Landing et al., 2003, fig. 5) at the top of the falls was regarded as a thin or condensed "Winchell Creek Siltstone" (abandoned term, now Sprakers Member of Tribes Hill Formation; Landing et al., 2002; see Appendix). This interpretation meant that Kane Falls is near the western feather-edge of this lowest "member" of the "Great Meadows" and that a disconformity separated the silty dolostone from the underlying "Whitehall Formation" (abandoned designation, now Little Falls Formation; Landing et al., 2003, see Appendix).
Re-investigation of the Kane Falls section (Landing et al., 2003) led to its re-interpretation. 1) There is no physical evidence for disconformity at the base of the silty dolostone. 2) The medium-gray thrombolitic dolostones and dolomitic limestones of the lower 9.55 m of the section do not resemble the light gray or white thrombolites of the upper Little Falls Formation ("Whitehall") at Steves Farm (Stop 6) or elsewhere in the Lake Champlain Lowlands. These medium-gray thrombolitic facies resemble those in the middle "Fort Ann Formation." 3) Diverse conodonts in the thrombolitic facies and rarer conodont elements in the higher laminated dolostones at Kane Falls are significantly younger than those from the Tribes Hill Formation (="Cutting"/Great Meadows," designations abandoned by Landing et al., 2003). The conodonts from Kane Falls are all referable to middle Lower Ordovician conodont Fauna D of Ethington and Clark (1971), and are comparable to those of the "Fort Ann Formation" elsewhere in the Lake Champlain lowlands.
The "moral" of this stop is the following: Mapping and stratigraphic syntheses on Lower Paleozoic carbonates on the New York Promontory require a combination of a detailed familiarity of lithofacies with adequate micro- and macro-fossil investigations to allow age discrimination of broadly similar carbonate platform units.

Cross onto uplifted (Proterozoic) block
Cross onto uplifted (Proterozoic) block of Welch Hollow Fault and pass by ca. 1 mile of Grenvillian road cuts.

STOP 2. PROTEROZOIC-TERMINAL MIDDLE CAMBRIAN NONCONFORMITY
STOP 2. PROTEROZOIC-TERMINAL MIDDLE CAMBRIAN NONCONFORMITY AND THIN LOWER PALEOZOIC SHELF SUCCESSION. (10 MINUTES). Approximately 4 m of east-dipping, medium-coarse grained, slightly dolomitic quartz arenite of the Potsdam Formation nonconformably overlie Grenvillian gneiss with east-dipping exfoliation surfaces. This photogenic locality records the absence of ca. 600 million years of earth history at this planar nonconformity. Flower (1964, p. 156) reported a trilobite fauna (presently unillustrated) approximately 5-6 m above the base of the Potsdam in this area, which he said includes a possible Crepicephalus with Komaspidella, and Lonchocephalus. Following the recent decision (January 2002) of the Cambrian Subcommission to define the base of the Upper Cambrian at the lowest occurrence of the agnostoid Glyptagnostus reticularus, this traditional "Upper Cambrian" Crepicephalus Zone assemblage must now be regarded as uppermost Middle Cambrian. This lower Potsdam Formation fauna indicates that the earliest marine onlap in this part of the Lake Champlain-Hudson River lowlands was terminal Middle Cambrian.
The purpose of this stop is to emphasize that the Lower Paleozoic of the eastern New York shelf is a relatively thin succession by comparison with Great Basin and southern Canadian Rockies sequences (i.e., hundreds of meters vs. several thousand meters). The ridge crest directly to the east is underlain by the upper Little Falls Formation and indicates that only ca. 200 m of Upper Cambrian is present above the Grenvillian. Thin Lower Paleozoic successions occur in this region of New York and Vermont (e.g., Palmer, 1971) 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., 2003). Two of these type 1 sequence boundaries will be viewed in the course of this trip.

Topographic break corresponding to the the Proterozoic-Cambrian nonconformity.
Note that Rte 4 roughly follows a topographic break corresponding to the the Proterozoic-Cambrian nonconformity.

Pass cuts in Grenville gneisses

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.

Continue north through Whitehall along the foot of Skene Mountain.

STOP 3. POTSDAM FORMATION ROADCUT. (10 MINUTES).
Approximately 30 m of Potsdam Formation siliceous quartz arenites and dolomitic quartz arenite are exposed in the Whitehall area. The village of Whitehall east of the Champlain Canal lies on the Proterozoic nonconformity, and the canal is excavated in Potsdam Formation sandstones. Herring-bone cross sets, dolomitic quartz arenite pebbles at the base of Small channels/dunes, and U-shaped Diplocraterion burrows all point to tidally influenced, higher energy deposition of the Potsdam. The Potsdam is overlain by lower Upper Cambrian dolomitic quartz arenites and quartzose dolostones of the Galway Formation (="Ticonderoga Formation," designation abandoned; Landing et al., 2003, see Appendix) higher on Skene Mountain.

Cuts in Potsdam Formation immediately on the right.

STOP 4. CROSSMAN QUARRY: UPPER CAMBRIAN LIITLE FALLS FORMATION.
The eastern end of the quarry 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, which represents Fisher's (1977) undefined "Warner Hill Limestone" member of the middle "Whitehall Formation" (abandoned designation), is increasingly dolomitized and neomorphic with the loss of primary features, in the western part of the quarry, where it is laterally transitional into the "Skene Dolostone" (Wheeler, 1941) sensu Fisher (1977, 1984). Although a biostratigraphically useful Late Cambrian trilobite assemblage appears ca. 3.5 m above the base of the eastern quarry wall (Taylor and Halley, 1974), snails and other mollusks are the dominant macrofauna! elements in this sequence, and indicate a restricted, relatively near-shore biofacies (e.g., Westrop et al., 1995).
The purpose of Stop 4 is to show the lithology of non-dolomitized Upper Cambrian limestones of the Little Falls Limestone ("=Whitehall Formation," abandoned term; Landing et al., 2003, and Appendix) for comparison with lithofacies of the overlying Tribes Hill Formation at Stop 5. The dolomitic limestones at the west end of Crossman Quarry and at Steves Farm and Comstock (Stops 6 and 7) were likely produced by the movement of hydrothermal fluids during burial with the Taconic orogeny (e.g., Collins-Wait and Lowenstein, 1994).

Top (Middle Ord. Providence Island Dolostone) of the carbonate platform.
The first ridge to the east is the top (Middle Ordovician Providence Island Dolostone) of the carbonate platform. 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 the synorogenic, Lower Upper Ordovician "Snake Hill Formation" (Fisher, 1984).

STOP 5. TRISTATES QUARRY: LOWEST ORDOVIClAN TRIBES HILL FORMATION.
A stratigraphic section for the Tristates Quarry will be distributed on this field trip; this section is available in Landing et al. (2003, fig. 4).
Landing et al. (2003) measured a 32 m section along the west and north walls of the old Tristates Quarry. The section is lithically identical to the middle part of the Comstock section (Stop 7) in showing: 1) thin- to medium-bedded, current cross-bedded, fine-grained dolomitic quartz arenite in the lower part of the section; 2) a thin (ca. 1.5 m) dark gray, pyritiferous, siltstone with a middle tempestite bed (note prominent rusty-weathering layer in the middle of the west wall); and 3) a higher interval with massive thrombolites to 2.9 m high. Landing et al. (2003) demonstrated that the conodonts from the Tristates Quarry indicate a precise correlation with the Tribes Hill Formation in the Mohawk River valley (see Landing et al., 1996). In addition, they described how intervals 1, 2, and 3 (above) in the Tristates Quarry correspond to the Sprakers, Van Wie, and Wolf Hollow Members of the Tribes Hill in the Mohawk valley-even down to the presence of a storm bed in the middle Van Wie Member and thrombolites in the Wolf Hollow. These data indicate that the Tribes Hill Formation is regionally extensive on the New York Promontory, where it comprises a deepening shoaling sequence (Landing, 1998) with the Van Wie indicating the deepest facies. Fisher and Mazzulo (1976) earlier referred this section to the "Great Meadows Formation" and recognized a lower "Winchell Creek Siltstone" member (units 1 and 2, above) and assigned the higher strata to Fisher's (1977) undefined "Fort Edward Dolostone." Somewhat later, Fisher (1984) separated the interval with prominent thrombolites (lower unit 3, above) as his "Kingsbury Limestone," but maintained "Fort Edward" for higher strata, thus creating an objective homonym for the undefined "Port Edward" (see Appendix).
In the course of Stop 5, note the large fallen blocks along the west wall that show sections through the massive hexagonal thrombolites. The inter-thrombolite lithology consists of echinoderm grainstone with ellesmeroceratoid cephalopods, orthid brachiopods, snails, and trilobites (Symphysurina and Hystricurus), and is the most unrestricted marine biofacies in the local Tribes Hill Formation. The abundance of snails and other mollusks increases higher through the quarry. Note also the lateral transitions along the north wall from limestones with well preserved primary fabrics and allochems into structureless, recrystallized dolostones, probably as a result of the hydrothermal activity noted at Stop 4.

Lower part (Sprakers Member) of Tribes Hill Formation.
Road cut on right (north) in fine--grained, dolomitic quartz arenites of lower part (Sprakers Member) of Tribes Hill Formation.

Road cut on right in massive dolostones of upper Little Falls Formation

STOP 6. STEVES FARM: AGE AND LITHOSTRATIGRAPHIC REVISIONS OF THE TERMINAL CAMBRIAN.
A stratigraphic section for the Steves Farm section will be distributed on this field trip; this section is available in Landing et al. (2003, fig. 4).
A carbonate-dominated, 85 m section was measured from the pasture 0.5 km west of Upper Turnpike and through gently east-dipping strata on the wooded north side of the 108 m (360 foot) hill at this stop (Landing et al., 2003). The section immediately south of the trailer has a massive white lime mudstone with lenses of high energy ooid grainstone and intraclast pebble-ooid grainstone and silicified gastropod conchs and black chert in the 40-59 m interval of the measured section. This limestone apparently corresponds to Flower's (1964) "Steves Farm Limestone" member of the Little Falls Formation (="Whitehall Formation," abandoned). A second 0.6 m-thick, massive white limestone with ellesmeroceratoid cephalopods and snails forms the highest exposed carbonate bed on the northern slope of the hill. This second limestone is Flower's (1964) Rathbunville Limestone member of the Little Falls Formation. Following a covered interval (13 m), fine-grained, dolomitic sandstone of the lowest Tribes Hill Formation appears as float near the hill crest.
The restricted marine, mollusk-rich, trilobite-poor Little Falls Formation at this section yields low diversity conodont faunas. The interval from the "Steves Farm" through Rathbunville Limestones is referable to the uppermost Cambrian Clavohamulus elongatus through C. hintzei Subzones of the Cordylodus proavus Zone s.s. (Landing et al. (2003).
With use of the lowest occurrence of the conodont lapetognathus fluctivagus Nicoll to define the base of the Ordovician globally (Webby, 1998), the conodonts from the Little Falls at Steves Farm and elsewhere in the Lake Champlain lowlands show that the Little Falls Formation does not extend into the lowest Ordovician. Earlier reports that assigned trilobite faunas with Missisquoia from the lower Little Falls Formation to the Ordovician (Taylor and Halley, 1974) or used the "Ordovician aspect" of molluscan faunas from the "Steves Farm" and Rathbunville Limestones (Flower, 1964; Fisher, 1984) are now superseded by this new global standard for definition of the base of the Ordovician. The conodonts illustrate that the ellesmeroceratoids from the "Steves Farm" and Rathbunville are Upper Cambrian and among the oldest cephalopods known in North America.
Clavohamulus hintzei Subzone (top Cordylodus proavus Zone s.s.) conodonts from the top of the Little Falls in the Lake Champlain lowlands are younger than the C. elongatus Subzone (middle C. proavus Zone s.s.) at the top of the Little Falls in the Mohawk Valley (Landing et al., 1996). In the Mohawk Valley, Mazullo and Fisher (1976) proposed a major hiatus between the Little Falls and Tribes Hill Formations and equated the lower Tribes Hill with the "Steves Farm"-Rathbunville Members of the "Whitehall" and assigned this interval to the lowest Ordovician. Correlated. However, these new conodont-based data show the top of the Little Falls is uppermost Cambrian across the New York Promontory and the sub-Tribes Hill hiatus shortens by only two conodont Subchrons in the Champlain Lowlands. The Cambrian-Ordovician boundary is further discussed at Stop 7.
The eustatic rise equated with deposition of the Tribes Hill Formation is equated with a middle-upper Tremadocian macroscale black mudstone-limestone in the Taconian allochthons of New York and Quebec (Stop 13).

Pass road cuts in "Fort Ann Formation."

STOP 7. COMSTOCK SECTION
COMSTOCK SECTION - BRACKETING THE CAMBRIAN-ORDOVICIAN BOUNDARY AND OVERLYING TRIBES HILL FORMATION. (40 MINUTES).
A stratigraphic section for the Comstock section will be distributed on this field trip; this section is available in Landing et al. (2003, fig. 4).
Stop 7 includes an examination of the roadcut on the north side of Rte 22, then continues along the low section in the shallow stream at the east end of the cut, crosses a long covered interval to the east across the pastures on the Scalaro farm, and then climbs the west slope of the 132 m ( 440 foot) hill to the ridge crest.
The roadcut on Rte 22 begins at the east border of Comstock village and exposes ca. 20 m of medium- to massively-bedded, gently-dipping (10° E), upper Little Falls Formation (="Whitehall") dolostone. In 1998, these sucrosic, locally evaporitic (note gypsum molds) dolostones were sharply overlain by a 30 cm bed of fine- to medium-bedded, brown-weathering, current cross-bedded, dolomitic sandstone of the basal Tribes Hill Formation (="Cutting/Great Meadows Formation") at the east end of the cut. Almost all of this dolomitic sandstone bed was collected as a conodont sample. This dolomitic sandstone-facies (Sprakers Member, ="Winchell Creek Siltstone," abandoned designation) is present as float immediately above the exposed Little Falls, is exposed in the shallow creek above the road cut, and apparently continues east under the covered interval in the pasture behind the Scalero family farmhouse. This facies re-appears at the foot of the ridge on the west side of the pasture at the base of the 132 m ridge, where it is overlain by ca. 1.5 m of gray siltstone with a middle storm-deposited sandtsone (Van Wie Member). Thicker-bedded, increasingly dolomitic sandstones continue upward to a cliff with several horizons of spectacular thrombolites with echinoderm grain- and packstone inter-head matrix (Wolf Hollow Member;= "Kingsbury Limestone"). Higher locally oolitic and overlying structureless (i.e., burrow-homogenized) white limestone (Canyon Road Member; = "Fort Edward" + "Smith Basin" Members of Fisher [1977] and Flower [1968b]) extend to the top of the Tribes Hill. The top of the Tribes Hill Formation forms the crest of the 132 m (440 foot) hill, and has a paleokarst surface with 30 cm of relief overlain infilled by arenaceous dolostone of the "Fort Ann Formation."
Conodonts from the Tribes Hill Formation comprise a low diversity, restricted marine assemblage that persists unchanged through the formation. This Rossodus manitouensis Zone assemblage is referable to the lowest Ordovician (middle-upper Tremadocian-equivalent), and shares no taxa either with the underlying Little Falls Formation or the overlying "Fort Ann Formation." The total replacement of the Upper Cambrian, upper Cordylodus proavus Zone fauna of the top Little Falls Dolostone (Stop 6) at the base of the Tribes Hill reflects the duration of the trans-Laurentian Cambrian-Ordovician boundary hiatus on the east Laurentian shelf. Similarly, the total replacement of the Tribes Hill Formation conodonts by Fauna D conodonts at the base of the "Fort Ann Formation" reflects the duration of the trans-Laurentian, intra-Lower Ordovician hiatus that occurs in the Tremadocian-Arenigian boundary interval.

Cross into Taconic allochthon.

Lower Cambrian Bomoseen Member (argillaceous lithic arenites).
Rocks immediately ahead are probably Lower Cambrian Bomoseen Member (argillaceous lithic arenites).

North Granville Slate.
Drive past slate scrap heap and quarry (on left, West) in North Granville Slate.

STOP 8. BROWNS POND
PALEO-OCEANOGRAPHIC CHANGES IN THE LATE EARLY CAMBRIAN. (15 MINUTES).
This section may be regarded as the "type locality" for the late Early Cambrian Browns Pond dysaerobic interval on the east Laurentian slope (Landing et al., 2002). The Browns Pond dysaerobic interval is recognized throughout the external thrusts of the Taconic allochthon in New York-Vermont and in Taconian Quebec (Figure 3).
This overturned section in the upper Browns Pond Formation shows several meters of dark gray, fine-grained sandstones and slates with thin (decimeter-thick), lensing, sandstone pebble debris flows on the east side of the cut. Small-scale current cross-bedding in the orange-weathering, dolomitic quartz arenites shows that the section is overturned. Although centimeter-wide grazing trails can be found on the top of some of the sandstone beds, burrows are rare, and fine lamination and other primary structures are not disturbed in these rocks. Rare burrows, absence of a shelly fauna, and dark gray (carbonaceous) sediments are all consistent with deposition under dysaerobic conditions (e.g., Sagemann et al., 1991).
The west side of the road cut is dominated by a thick limestone pebble to (rare) boulder clast debris flow with local dark argillaceous matrix. Trilobites, archaeocyathan, mollusk, and calcareous and phosphatic problematica of the lower Elliptocephala asaphoides assemblage (see Landing and Bartowski, 1996) appear in the limestone clasts at this locality (Theokritoff, 1964). None of these clasts show derivation from the carbonate platform, and they include nodular lime mudstones and bedded fossil packstones that are interpreted as allodapic clasts that accumulated as limestone on the upper slope. Pyrite-infilled and phosphate-replaced, calcareous conoidal fossils in these clasts (E. Landing, unpublished data) is consistent with the deposition/lithification of these limestones in a strongly dysaerobic environment that developed on the upper slope (see Landing and Bartowski, 1996; Landing et al.,2002).
Debris-flow conglomerate lenses are common as the cap unit of the Browns Pond Formation, and some have received local stratigraphic names (e.g., Ashley Hill Conglomerate in Landing, 1984). Locally, allodapic fossil hash packstones and decimeter-thick debris lenses are the cap unit of the Browns Pond (e.g., Landing and Bartowski, 1996). In either case, the conglomerates or bedded limestones are directly overlain by a green/green gray or locally purple or red siliciclastic mudstone unit in the Taconic allochthon. This black-green transition in the late Early Cambrian is seen here at Stop 8 immediately above the conglomerate with the abrupt transition into the lower green slates of the Middle Granville Slate. These green slates form low outcrops in the pasture to the west. Stop 10 further illustrates this interval of improved oxygenation on the east Laurentian slope and relates the improved oxygenation to the latest Early Cambrian Hawke Bay regression of Palmer and James (1979). Sea-level still-stand and progradation of the shelf margin or sea-level fall at the onset of the Hawke Bay regression are mechanisms to explain the carbonate clast debris flows and allodapic limestones at the top of Browns Pond dysaerobic facies.

STOP 9. TANNER HILL SYNCLlNE
PALEO-OCEANOGRAPHIC CHANGES IN THE LATEST EARLY CAMBRIAN-MIDDLE ORDOVICIAN. (40 MINUTES).
The superb Tanner Hill section was first described by Rowley et al. (1979). The walk up hill crosses the overturned east limb of a large syncline.
Dolomitic quartz arenites and interbedded, minor dark gray and black siltstones and shales form the lowest part of the section. The coarse, lensing (apparently channelized), conglomeratic sandstones become thinner bedded and finer grained higher in the section, and black shales become dominant. This entire interval up to an abrupt transition into 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 [early Tremadocian] Hatch Hill dysaerobic 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 dysarobic mudstone deposition that has been termed "Poultney A" (abandoned designation, Landing, 1988b) by Theokritoff (1959; Zen 1964; see Appendix). A sharp transition from the Hatch Hill Formation into the lowest green-gray mudstones of the Deep Kill can be observed in the drainage ditch on the north side of Tanner Hill Road. Limited outcrop of the Deep Kin Formation likely explains the apparent absence of the black mudstone-limestone mesoscale intervals characteristic elsewhere of the formation (Stops 11, 13; Figure 3).
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 to grayish sediment color, and an alternative explanation for the color of the Indian River must be found. Landing (1988b) noted the multiple lines of evidence (e.g., occurrence of radiolarian cherts and thin volcanic ashes undiluted by background argillaceous sediment; thorough burrow-homogenization of much of the unit; presence of large, up to 3 cm-wide burrowers) 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. Cherty red slates are widespread in a number of orogens (e.g., in the Taconian allochthons from New York to western Newfoundland, southern Uplands of Scot1and, Hercynian Rheinisches Schiefergebirge and Hart Mountains, and Jurassic of Japan), where they always underlie green mudstones and higher flysch. These data suggest that red, cherty, oxygenated shales in overthrust belts reflect the following history: passage of a peripheral bulge through passive margin successions; consequent flexural uplift and restriction of sedimentation on the peripheral bulge to slowly deposited pelagic muds, radiolarian cherts. and thin volcanic ashes; and final flexural down-warping and increased rates of deposition as sediment provenance changes to the emergent accretionary prism. 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.

STOP 10. OXYGENATED MIDDLE GRANVILLE SLATE AND THE HAWKE BAY REGRESSION.
This stop serves to fill in the stratigraphic interval between the rocks of Stops 8 and 9. The large pile of brownish red and minor green slate of Middle Granville Slate on the east side of the road apparently came from the small flooded quarry on the west side of the road. If the light is good, dense Planolites traces can be seen on many of the bedding plane-parallel cleavage surfaces of the reddish slate, where they accompany large grazing traces up to 2 cm in width. 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.
Landing et al. (2002) noted that the uppermost Lower Cambrian (upper but not uppermost Olenellus Zone) on the New York and Quebec portions of the eastern Laurentian slope is composed of red and green siliciclastic mudstones. This interval of improved oxygenation of slope waters is equated 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 dysaerobic interval) took place in the terminal Early Cambrian. This Lower-Middle Cambrian boundary interval eustatic rise and climate amelioration led the actual movement of poorly oxygenated slope water onto the continental shelf in such widely separated areas as northern Vermont (Parker Slate) and eastern California (Mule Springs Formation) (Landing and Bartowski, 1996).

STOP 11. RACEVILLE: EARLY MIDDLE ORDOVICIAN DYSAEROBIC INTERVAL.
This vertically dipping section shows a black mudstone-limestone mesoscale alternation in the lower (northern) part of the section and overlying greenish-gray, siliciclastic mudstone without limestone intercalations. Most of the limestone in the lower part of the section consist of fine-grained, argillaceous mudstone 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; Figure 3). The climate maximum, eustatic high, and resultant interval of intensified dysaerobic slope water recorded by the Raceville cut is equated with earliest Ordovician, Whiterockian eustatic rise across Laurentia and with deposition of such units as the Providence Island Dolostone (Figure 2).

Western edge of the Taconian allochthon.
The ridge to the left (east) of Rte 40 is formed of 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 overthrust. Rte 40 meanders back and forth from the edge of the allochthon and onto structurally underlying, Upper Ordovician "Snake Hill" synorogenic flysch and wild flysch, and, locally in the area of Middle Falls, onto Lower and Middle Ordovician shelf carbonates.

STOP 12. LOGAN CYCLES: MESOSCALE CYCLES IN THE MILANKOVITCH BAND.
This is one of the most accessible outcrops that shows the color alternations characteristic of Logan cycles (Landing and Benus, 1985; Landing et al., 1992) in the Lower-lower Middle Ordovician Deep Kill Formation.
The section lies at the leading edge of the Taconic allochthon and is structurally complex. It is overturned and dips ca. 70 degrees east dip. About four Logan cycles are present in this ca. 6 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 4). The uppermost part of the section (about at waist level) shows the highly burrowed, buff-weathering C-unit of a Logan cycle sharply overlain by black mudstones with thin sandstones (A-unit) of an overlying Logan cycle. Well preserved Logan cycles that extend through a completely exposed section through the Arenigian Series at Levis, Quebec, appear to have an average period of less than 100 k.y. (Landing et al., 1992). Logan cycles are evident as 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).

Continue to classic outcrop at Schaghticoke gorge on the Hoosic River.
If time is available, we will continue south on Rte 40 to examine the classic outcrop at Schaghticoke gorge on the Hoosic River. This structurally complex section features the black shale and limestone interval that records middle-late Tremadocian dysaerobia on the Laurentian continental slope from eastern New York to easternmost Quebec (Landing et al., 1992).

Note prominent Logan cycles in cut in Deep Kill Formation on left side of road.

The old Bald Mountain limestone quarry
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 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.

This is a good place to bring class trips
Note cut in vertical beds of lower Trenton Group limestones along east side of road and opposite wide dirt pulloff 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 south, the Proterozoic Grenvillian hills 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 but possibly early Middle Ordovician and referable to the Providence Island Dolostone).

STOP 13. SCHAGHTICOKE GORGE
LATE TREMADOCIAN DYSAEROBIC INTERVAL. ( 40 MIUTES).
This section appears to be a tectonically isolated slice at the leading edge of the Taconic allochthon. This type section of the lowest Ordovician "Schaghticoke Shale" (term abandoned; Landing, 1988b) features the structural duplication of a thin (ca. 4 m) black mudstone-limestone mesoscale alternation in greenish-gray slaty mudstones. These facies are referable to the lower Deep Kill Formation. 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 Quebec, but conodonts 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 black shale-limestone macroscale alternation exposed for 400 km along the south shore of the St.Lawrence River in Quebec (Landing et al., 1986). This interval of climate maximum and intensified dysaerobia on the Taconic continental slope is equated with the eustatic rise that led to deposition of the Tribes Hill Formation (Stops 5, 6).