Upper Silurian to Middle Devonian Stratigraphy and ...

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I New York State Geological Survey, The State Education Department. " Department of ..... cut at the western edge of Sharon Springs, and the unit is absent at ...

Upper Silurian to Middle Devonian

Stratigraphy and Depositional Controls,

East-Central New York

Edwin J. Anderson, Carlton E. BreW, Donald W. Fisher', Peter W. Good~in', Gerry J. Kloc", Ed Landing', and Richard H. Lindemann"' , Department of Geology, Temple University , Department of Geological Sciences, The University of Rochester , I Lindenwald Court, Kinderhook I New York State Geological Survey, The State Education Department " Department of Geology, Skidmore College

stone and related carbonates. Continued siliciclastic deposition and accumulation ofthe earlier portion ofthe Hamilton Group allowed aggradation and shoaling that permitted the appearance of diverse benthic faunas in the Mount Marion Formation (upper Marcellus equiva­ lent). The Mount Marion also shows near-shore deposi­ tional features on the seaward margin of rivers draining the rising Acadian highlands to the east.

SUMMARY (EL) The field trip is designed to provide an overview of the stratigraphy, paleoenvironments, and depositional con­ trols of the uppermost Silurian through the Middle De­ vonian in the essentially flat-lying terrane to the,south­ west of Albany, New York. Several topics will be emphasized on the trip: (l)The uppermost Silurian through lower Lower Devonian (Helderberg Group) rep­ resents a natural lithological grouping as a long-term transgressive-regressive cycle. All major facies (forma­ tions and members) are significantly time-transgressive and most fossils are facies-associated in the Helderberg Group. However, Helderbergian stratigraphy appears to be divisible into meter-scale, sharply bounded, shoaling upward cycles that are regionally extensive between major facies belts. These shoaling upward cycles are a type of punctuated aggradational cycle (PAC) that results from geologically instantaneous deepening fol­ lowed by aggradation to base level. PAC's offer the poten­ tial of finely resolved time correlation. (2)The upper Lower Devonian (Tristates Group: Oriskany-Esopus­ Carlisle Center-Schoharie) represents, or at least has the characters of a major transgressive-regressive coup­ let. (3)The base of the Middle Devonian (Onondaga Limestone), as in many other regions of eastern and midwestern North America, is disconformable with un­ derlying units and represents a significant unconform­ ity within the Kaskaskia Sequence. The Onondaga Limestone represents, from base to top, a progressively deepening sequence with analogues to the Helderberg Group: Edgecliff Member (with reefs) =Coeymans, Ne­ drow + Moorehouse = Kalkberg, Seneca=New Scot­ land), (4)Onondaga Limestone (Seneca) deposition is fol­ lowed by the progressive westerly flood of clastics from the rising Acadian mountain building interval. The ini­ tial siliciclastics of the marine Hamilton Group are black shales of the lower part of the Marcellus Forma­ tion that reflect widespread anoxic bottom waters. A short term regressive event during the lower portion of the Marcellus is recorded by the Cherry Valley Lime­

INTRODUCTION (EL) The area of the field trip lies on the northeastern mar­ gin of the Allegheny Plateau (Figure 1). Silurian and Devonian units are essentially unaffected by Acadian and Alleghenian tectonism (see, however, Stop 3) and dip gently toward the south-southwest into the Appala­ chian Basin. These Middle Paleozoic units rise as an es­ carpment and low range of mountains above the Mo­ hawk River Valley lowlands to the north. The underlying Middle to Upper Ordovician siliciclastics (Schenectady and Frankfort shales and sandstones) are more readily eroded than the Helderberg and Onondaga carbonates that form escarpments in the region. Th-e rounded hills to the south of the Onondaga Escarpment are underlain by shales and thin bedded sandstones of the Marcellus Formation and may be regarded as foot­ hills of the Catskill Mountains to the south. PRE·DEVONIAN STRATIGRAPHY (DWF, EL) Directly beneath the Early Devonian Manlius strata of this region are the Late Silurian Rondout and Bray­ man Formations, respectively. The Rondout is divisible into an upper Chrysler Dolostone Member and a lower Cobleskill Limestone Member; the two are vertically gradational. The Cobleskill contains diagnostic Late Si­ lurian fossils, foremost of which is the "chain" coral Cys· tihalysites. Relatively high energy environments are in­ dicated by circumrotational (e.g. "cannonball") stromatoporoids in the Cobleskill Limestone at Stop' 7. The Chrysler has not yielded diagnostic fossils for age

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Figure 1 Generalized localities of field trip. determination, and it is uncertain whether this unit in the field trip area should be referred to the latest Silu­ rian or earliest Devonian. It is placed in the uppermost Silurian in Figure 2. The underlying Brayman Shale has yielded Late Silurian fossils, (Fisher and Rickard, 1953, p.8) establishing a Pridolian age. Except for the subtidal coral-bearing rocks, these Upper Silurian units were formed in shallow hypersaline waters largely within the supratidal and intertidal zones. North from the Cherry Valley region (Stops 1, 2), tTp­ per Silurian strata rest unconformably on peneplained Upper Ordovician Frankfort gray shales and argilla­ ceous siltstones which, in turn, rest on Utica black shale. Successively beneath the Utica are thin Middle Ordovician Trenton and Black River limestones. These limestones (not everywhere the same) rest unconform­ ably on Lower Ordovician Tribes Hill dolostones and do­ lomitic limestones and the Upper Cambrian to lowest Ordovician Little Falls Dolostone. Unconformably be­ neath these Early Paleozoic strata are Proterozoic rocks metamorphosed during the Grenville Orogeny 1,100­ 975 million years ago. The Cambrian and Ordovician carbonates represent shallow water supratidal, interti­ dal, and subtidal deposits on an ancient continental shelf; the Ordovician pelites are basinal deposits formed some 450 miHion years ago, on this downwarped shelf during the Taconic Orogeny. About 450 m (ca. 1500 ft) of Ordovician and Cambrian strata lie between the Silu­ rian and Proterozoic rocks.

The Thacher Limestone is a very light gray" to white weathering, dark gray to black, thin to thick bedded, fine to medium-grained limestone with rare calcareous shale interbeds and rare crossbedding in a few coarser beds. The thin bedded lime mudstones (ribbon lime­ stones) and blocky, medium bedded layers break with a conchoid"ll fracture. Fossils are abundant but only a few species are represented. Stromatoporoid reefs and baf­ fles are locally present at the top of the Thacher Mem­ ber. The tentaculitid Tentaculites gyracanthus and the ostracode Hermannina alta are ubiquitous in the ribbon strata, together with rare edrioasteroids (Postibula' n.sp.), scarce bryozoans, and common spiriferid brachio­ pods (Howellella uanuxemi); low- and high-spired gastro­ pods are more common in the reefs and bames. The Thacher represents at least three different envi­ ronments each characterized by specific physical and or­ ganic traits; supratidal, intertidal, and proximal subti­ dal. Clearing of marine waters from the hypersaline Rondout sea permitted a more diverse and abundant life to pervade the Manlius sea.

Coeymans Limestone The Coeymans Limestone is a medium- to thick­ bedded, medium to coarse-grained, fossil fragment lime­ stone. Bedding contacts are irregular and sty lolitic. The formation has a moderately diverse fauna characterized by the pentamerid brachiopod Gypidula coeymansis, meristellid and uncinulid brachipods, and crinoidal and cystoidal debris. The westwardly thickening Coeymans (Ravena Member-Rickard, 1962, p. 65-68) splits along the Judd's Falls Valley into a lower Dayville

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Figure 3 A. General model of the Hypothesis of Punctuated Aggradational Cycles. Each PAC is bounded by surfaces of abrupt change to deeper facies. Facies changes within a PAC are gradational. At a larger scale, shallowing and deepening se­ quences consist entirely of PACs pro­ duced during periods of aggradation punctuated by deepening events. B. Analysis of the dynamics involved in the development of a PAC. 114

HELDERBERG GROUP

meters thick) shallowing-upward cycles (PACs) sepa­ rated by surfaces of abrupt change to deeper and envi­

ronmentally disjunct facies (Figure 3). These surfaces are created by geologically instantaneous, basin-wide, relative base-level rises; deposition occurs during the in­ tervening periods of relative base-level stability. Base­ level fluctuations occur with periodicities in the Mi­ lankovitch band and thus result in a small-scale pattern of allogenic cycles that provide a genetic framework for paleoenvironmental interpretation and detailed ba­ sinwide physical event correlation. A basic tenet of the PAC hypothesis is that the shallowing-upward motif on the scale of a few meters of thickness is pervasive throughout the stratigraphic record. The hypothesis predicts that PACs exist in rocks representing all environments in which a rapid base­ level rise can directly or indirectly influence deposi­ tional processes. Thus, fluvial, deltaic, tidal, shelf, slope, turbiditic fan, and basinal clastic environments as well as the full spectrum of marine carbonate environments should produce deposits that display the PAC motif. Not only are PACs expected in all sedimentary environ­ ments, but PACs are also basinwide rock units that may be traced laterally through the deposits of a variety of co-existing environments. Theoretically, PACs termi­ nate at the lateral limit of all contiguous depositional sites affected by a specific position of sea-level. There­ fore, a particular PAC will be defined by different sedi­ mentologic evidence at different places in the basin. A new and different environmental spectrum is created by each deepening event and modified by aggradation dur­ ing periods of base-level stability (Goodwin and Ander­ son, 1985). The thickness of carbonate cycles such as PACs is de­ pendent on the interaction of a number of variables. From analyses of facies within PACs (Figure 3 B) we are able to demonstrate that PAC thickness and thickness of facies within PACs are also dependent on the magnitude of punctuation events, topography inherited from the previous cycle, environmentally controlled sedimenta­ tion rates and gradual base-level change either from tec­ tonic subsidence or eustasy. Given adequate sedimenta­ tion rates, thick PACs will be produced following large punctuation events. Gradual base-level rise produces over-thickened facies within PACs because sedimenta­ tion keeps pace with subsidence or eustatic rise. PACs will be thinner over inherited topographic highs and thicker over low-areas. In all cases, supply of sediment is a factor in PAC thickness; in deeper environments oflow carbonate productivity PACs tend to be thin. These and other variables have been incorporated in computer modeling of synthetic carbonate cycles (Read and oth­ ers,1986). In these experiments Read and others have demonstrated that thickness and facies structure in synthetic cycles can be determined by amplitude and

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Figure 7 Chronostratigraphic correlation ofthe Onondaga Formation throughout New York State. Hori­ zontal dimension not to scale. Adapted from Oliver and others (1969) and Rickard (1975). named coral assemblage zone (8 of Oliver and Sorauf, 1981), both of which place the Seneca in the Cazenovian Stage. These fossils firmly establish the Onondaga Edgecliff Member as the lowermost Middle Devonian unit in New York State relative to the North American stages. However, Onondaga corals and brachiopods are geographically restricted t.o North America, a condition which precludes direct correlation with the Eifelian Stage of Europe. Cephalopods do little to facilitate this correlation. Foordites cf. buttsi from the Nedrow Mem­ ber (Oliver, 1956b; House, 1962) suggests an Eifelian age. However, House (1981) notes that Foordites is a long-ranging genus, and that European zonal taxa are not known from the Onondaga. Furthermore, Foordites has not been reported from the Edgecliff and cannot lend its support to interpretation of an Eifelian age for the lowermost Onondaga member. The International Union of Geological Sciences re­ cently ratified the decision of the Subcommission on De­ vonian Stratigraphy to establish the base of the Middle Devonian Series and the Eifelian Stage at the first oc­ currence of the conodont Polygnathus costatus partitus (Ziegler and Klapper, 1985). The subspecies partitus is

nately a coarse crinoidal sand (packstones and grain­ stones); the fauna is dominated by fenestrate bryozoans and Atrypa reticularis, and the unit is abruptly overlain by the Marcellus Shale. Additional detail is provided in the trip log description of Stop 2. Correl~tion of the Onondaga Limestone

The biostratigraphic basis for correlation of the Onon­ daga Formation, particularly the Edgecliff Member, to the standard biozones and stages of Europe reads like a "who-done-it?" with the last few pages missing. Brachio­ pod and coral faunas have long served to place the for­ mation at the base of the Middle Devonian Series (Rick­ ard' 1975). Dutro (1981) reports that the Edgecliff Member coincides with the base of the Frimbrispirifer diuaricatus Subzone of the Amphigenia Assemblage Zone which marks the base of the Southwoodian (= Up­ per Onesquethawan) Stage. Similarly, Oliver and So­ rauf (1981) state that the Edgecliff base coincides with the base of the Acinophyllum segreatum Assemblage Zone and the bottom of the Southwoodian Stage. High in the formation, the Seneca Member is within the Paras­ pirifer acuminatus Assemblage Zone as well as an un­ 121

the second in a lineage of three which are sequentially related as shown in Figure 8. Thus, the bottom of the patulus Zone is high in the Emsian Stage and the bot­ tom of the costatus Zone is well within the Eifelian. Klapper (1981) reports that the upper Nedrow beds at Cherry Valley yield both P. c. costatus and P. c. patulus, placing the member's top well within the partitus Zone (Figure 8). Noting this along with the fact that P. c. par­ titus is unknown from the Onondaga, Ziegler and Klap­ per (1985) suggest, with question marks, that the Edge­ cliff Member is within the patulus Zone and correlative to the Emsian Stage of the Lower Devonian Series. At the very least, this obfuscates the Lower·Middle Devo­ nian boundary in New York State and speaks for a "han­ dle with care" approach in transatlantic correlation of the North American stages which abut that boundary. To date the chronostratigraphic placement of the lower­ most Onondaga member remains uncertain.

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Cherry Valley is the youngest limestone in eastern New York State. The unit has been called the "Agoniatites Limestone" in the older literature because of the promi· nent cephalopod component of the fauna. The Union Springs Shale (Cooper, 1930) under the Cherry Valley is a fissile black shale with calcareous nodules and very limited and sparse benthic fauna in local, thin argilla­ ceous limestones. The Chittenango Shale (Cooper, 1930) overlies the Cherry Valley Limestone and is similar to the Union Springs but has exceedingly rare benthic fos­ sils. Simple, small conical calcareous tubes represent­ ing problematical organisms such as tentaculitids and styliolinids are more characteristic of these shales. Rapid accumulation of Acadian orogen-derived silici­ clastics allowed progradation of nearshore environ­ ments into eastern New York while more open marine conditions persisted through the Hamilton Group in central and western New York State. These marginal marine deposits are the Mount Marion Formation (Stop 8) in the excursion area and represent equivalents of the middle and upper portions of the Marcellus Formation (see Rickard, 1975).

Faunas, Stratigraphy and Depositional Environ­ ments of the Cherry Valley Limestone and Associ­ ated Carbonates (CEB, GK) partitus boundary

Figure 8 Vertical relationship of the Polygnathus costatus subspecies (from Ziegler and Klapper, 1985). HAMILTON GROUP STRATIGRAPHY (DWF, EL) The Hamilton Group is a siliciclastic-dominated se­ quence that reflects the influx of sediments derived from the rising Acadian orogen to the east. Only the lowest (Marcellus Formation and local coarse-grained equiva­ lents) formation of the four forma tions of the Hamil ton Group (see Cooper, 1930) will be investigated on this ex­ cursion. The Marcellus Formation is primarily black and grey shales and siltstones with rare thin black limestones in the excursion area. In general, both benthic and planktic fossils are rare in the dysaerobic to anoxic, deeper water facies of the Marcellus. The lower portion of the Marcellus is divisible into three members based on the abrupt appearance of the Cherry Valley Limestone and related carbonates within a black shale sequence (Stop 3). The light-grey to tan weathering, black fossil wacke- to packstone of the

The Union Springs-Cherry Valley sequence is pres­ ently considered to be oflatest Eifelian age based on the occurrence of the conodont Tortodus kockelianus kock­ elianus in the basal Cherry Valley Limestone in central New York (see Klapper, 1981). The so-called "Wernero­ cems" bed in the upper Union Springs shale has also yielded goniatites diagnostic of the la te Eifelian or earli­ est Givetian (House, 1981). The basal contact of the Union Springs is not exposed at Stop 3 (Figure 9) but nearby localities reveal· that the black shale sharply overlies the uppermost Onondaga with probable disconformity. The lowest portion of this roadcut exposes sparsely fossiliferous, sooty, black, fis­ sile Union Springs shale which is locally about 11·13 m thick. Two 20 cm-thick zones of "crumpled" slicken-sided and cleaved shale occur in the upper Union Springs. These intervals, which are under and overlain by undis­ turbed shales, have been interpreted as shear zones as­ sociated with a major decollement in the Marcellus that was produced during late phases of the Acadian or the Alleghanian orogeny

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