Gordon C. Baird

Distal sedimentation in a peripheral foreland basin: Ordovician black shales and associated flysch of the western Taconic foreland, New York State and Ontario

Black shale is characteristic of early siliciclastic fill along the distal (western) flank of the Middle to Late Ordovician Taconic peripheral foreland basin. This facies, referred to as the Utica black-shale magnafacies, includes at least five intervals bounded by unconformities and/or condensed beds. Each unit records a pulse of subsidence and subsequent siliciclastic sedimentation in the foreland basin. Progressive episodic shifts from carbonate to organic-rich mud deposition may be due to steepening and subsidence of the western carbonate ramp followed by onlap of axially dispersed sediment. In general, silt-poor, organic-rich mud was deposited on a subsided carbonate ramp that sloped eastward toward the nearest siliciclastic sediment source. This mud may have accumulated from the pelitic tails of axial fan turbidites derived from source areas to the east, and possibly the south. The resultant black shale does not necessarily represent the deepest part of the basin; the deepest part of the basin (the basin axis) contained coarser-grained, axial, submarine fan deposits. Throughout the later part of the Middle Ordovician and the first half of the Late Ordovician, the basin axis migrated westward over 100 km, yet the orientation of the axis and the basin margins were persistent. This basin orientation (generally parallel to the orogenic belt), along with the large-scale basin shape, resulted from a combination of deformational loading of the continental margin and progressive flexure in the foreland. Smaller-scale structural elements, normal fault-bounded basement blocks, were superposed on large-scale Taconic foreland-basin geometry. Abrupt shifts from carbonate ramp sedimentation to deeper-water, organic-rich mud deposition may reflect movement along these faults during the orogeny.

On the Origin and Significance of Pyrite Spheres in Devonian Black Shales of North America

ABSTRACT Devonian black shales deposited on the North American craton contain abundant Tasmanites cysts that are typically preserved as flattened circular discs on bedding planes. Work by the present authors shows that cysts can be preserved as pyrite-infill casts that are expressed as sand-size whole and geopetal half-spheres of pyrite. At the bases of thin black shale layers these occur in situ at many stratigraphic levels in the distal prodelta facies of the Catskill Delta complex of New York, as well as in laterally equivalent black shales in Tennessee and Kentucky. Reworked pyrite casts, usually dominated by whole spheres, form lenticular lag accumulations and hydraulic placers, together with plant debris and phosphatic particles (bone debris, conodonts). An earlier model for the formation of pyrite spheres in gas bubbles is rejected in favor of formation within uncompressed Tasmanites cysts. Direct observation of cyst cuticle in association with pyrite spheres suggests that localized bacterial sulfate reduction in Tasmanites interior voids led to formation of localized pyrite deposition, in a manner similar to that described from certain ammonoid chamber settings. Cyst fill commenced with formation of framboidal pyrite, followed by later diagenetic pyrite cementation between framboids. These fills show geopetal features and appear to have formed within the redox zone below the sediment-water interface. Although described here from the Upper Devonian, comparable pyrite textures are also known from Proterozoic, Cambrian, Ordovician, and Silurian sediments. They probably occur throughout the sedimentary record, and in mudstone successions they may prove to be an important source of sand-size grains in areas far removed from the basin margins. As such they may be important for detection of erosive events and strong bottom currents, and provide valuable information about the depositional history of mudstone successions.

Submarine erosion on the anoxic sea floor: stratinomic, palaeoenvironmental, and temporal significance of reworked pyritebone deposits

Abstract Numerous black (organic-rich) shale units in the Palaeozoic of North America are marked by discontinuities along their bases which are characterized by acid-insoluble lag concentrations of reworked pyrite, phosphatic debris, and siliceous material. These contacts, ranging in magnitude from widespread disconformities (typically marine flooding surfaces) to local, within-outcrop-scale, scour features, were produced by submarine erosion under anoxic to lower dysoxic conditions. Dissolution of carbonate debris under conditions of carbonate undersaturation and/or low pH in bottom waters, was generally complete. Hydraulic transport coupled with dissolution led to the formation of laterally discontinuous and current-sorted lenses of pyritic grains, fish bones, condonts, quartz sand, chert nodules, and glauconite. Lags of reworked pyritic tubes and small spherules are typical of finely interbedded black and green shale successions (‘zebra facies’) observed in the Upper Devonian (Famennian). Under anoxic conditions pyrite was chemically stable, while carbonate debris was not. Herein, we examine lag deposits associated with a variety of black-shale-roofed discontinuities ranging in age from Middle Ordovician to Mississippian. Possible erosion mechanisms for producing these discontinuities and associated lags include deep-stormwaves, density currents and internal waves. In each case erosion occurred following an interval of condensation associated with flooding surfaces, particularly those timed with the beginning of highstand intervals.

BIOFACIES RECURRENCE IN THE MIDDLE DEVONIAN OF NEW YORK STATE: AN EXAMPLE WITH IMPLICATIONS FOR EVOLUTIONARY PALEOECOLOGY

Abstract The diverse, well-preserved fauna of the Middle Devonian Hamilton Group of western New York has become an exemplar of long-term taxonomic and paleoecological stability and habitat tracking in response to sea-level change. Recent detailed, quantitative studies have challenged this view, suggesting instead a relatively low proportion of persistent lineages and recurrent biofacies sharing only the most abundant species; however, most studies have considered only limited geographic areas. As a result of shifting basin-forebulge positions and sedimentation patterns, analogous facies do not occur in every cycle of single geographic areas but show complex migration within the Appalachian Basin. Consequently, similarity of biofacies recurrence can only be fairly assessed by considering the most analogous facies wherever they occur across a major cross section of the basin. This paper evaluates patterns of biofacies recurrence based on samples from subsymmetrical cycles of dark-gray shale, calcareous mudstone, and argillaceous limestone. Low-sedimentation, depth-related biofacies, identified quantitatively using cluster analysis, recur symmetrically in single third-order regressive-transgressive cycles throughout the 5–6 myr duration of the Givetian Hamilton Group and Tully Formation at different geographic locations. Detrended correspondence analysis was used to recognize gradients of species and sample distribution both within and among depositional cycles; depth-related biofacies range from basinal, low-diversity leiorhynchid brachiopod– dominated associations to highly diverse coral-brachiopod (shallow subtidal) assemblages. This pattern is also comparable to the order of species-biofacies appearances in single, small-scale shallowing-upward cycles. In addition to similarities of species richness and guild structure, given biofacies show strong similarities of species composition. Low-diversity, high-dominance associations typical of deeper water biofacies show lower similarities (60%–75% species overlap), suggesting that they represent loosely structured aggregations of eurytopic taxa. Similarities are greatest in the diverse coral and brachiopod biofacies, for which most pairwise comparisons of samples throughout the Hamilton–Tully interval show >80% overlap in species composition and very strong similarity of richness and guild structures but not necessarily rank or relative abundance of taxa. Overall, these data suggest that gradients of species distribution in relation to environmental gradients, especially depth-related factors, were quite stable over several million years and that biofacies shifted in response to transgressive-regressive cycles. Such biofacies stability need not imply persistence of tightly integrated communities. Nonetheless, the long range of many species and maintenance of biotic gradients have important evolutionary implications—under relatively stable conditions, a majority of species track shifting habitats rather than adapt to changing local conditions.

Carbonate-shale cycles in the Middle Devonian of New York: An evaluation of models for the origin of limestones in terrigenous shelf sequences

Thin, widespread carbonate beds in the predominantly siliciclastic Hamilton Group (Middle Devonian) of New York appear to represent biogenic accumulations of winnowed, shallow (normal to storm wave base) shelf areas, rather than products of transgression-induced sediment starvation, as frequently assumed. In western New York, these fossiliferous limestones form the centers of subsymmetrical marine cyclothems. Carbonates are overlain and underlain by calcareous, gray to black, laminated shales, and they grade laterally into siltstones or sandstones that cap upward-coarsening sequences in central New York. Thus, the limestones appear to represent shallow-water facies of regressive hemicycles, instead of transgressive maxima, as argued by earlier workers.

Revised stratigraphy of the Trenton Group in its type area, central New York State: sedimentology and tectonics of a Middle Ordovician shelf-to-basin succession

Abstract This paper presents new stratigraphic correlations of the middle and upper parts of the Trenton Group in the type area, near Trenton Falls, New York, based on detailed bed by bed matching, of all outcrop sections. This work, in conjunction with newly revised biostratigraphy and geochemical fingerprinting of K-bentonites, has been used to establish a high resolution chronology for these deposits. Our revised correlations reveal that published stratigraphic–geochronologic schemes are largely in error, resolve several long-standing dilemmas, and have important implications for interpreting sedimentological and tectonic history of the Taconic foreland basin. Key new conclusions/revisions include: (1) The lowermost part of the Trenton type section at Trenton Falls is laterally equivalent to the Rathbun Member of the Sugar River Limestone (lower Shermanian) in the Newport–Herkimer, New York area. (2) The medial Trenton (Denley Formation), dated primarily within the Corynoides americanus graptolite Zone, can be divided in ascending order into two distinctive units, the Poland, Russia members, each of which is further subdivisible into component shallowing-upward cycles and condensed beds. As such, the Poland is completely exposed at Trenton Gorge (contrary to assertions by previous authors) and is about 10.5 m-thick. At its type section, also Trenton Gorge, the overlying Russia Member, comprising four shallowing-upward cycles, extends upward from the Kuyahoora K-bentonites for about 24 m to its sharp upper contact with another distinctive and fingerprinted K-bentonite, the High Falls ash bed. (3) Both the Poland and Russia members thin southeastward from Trenton Falls and become condensed in downslope sections near Middleville. However, the Poland section then thickens and passes eastward into basinal dark gray shales (lower-medial part of the Flat Creek Formation) in central Mohawk Valley sections, whereas the Russia remains thin and relatively carbonate-rich throughout this area. (4) A third unit, the Rust Limestone is elevated to formation status and subdivided into members. The lower part of the Rust Formation (Mill Dam Member) thins dramatically to the southeast from about 12 m at Trenton Falls to 1.5–2 m in the Middleville–Herkimer area before thickening again into basinal black shale facies. (5) The upper Rust and Steuben formations (coarse skeletal pack-to grainstone facies) of the Trenton Falls area apparently thin by condensation into the Newport area before expanding again into turbiditic slope facies of the Dolgeville Formation (essentially corresponding to the Orthograptus ruedemanni graptolite zone) beginning in the Middleville–Herkimer area. The new correlations imply that the lower-middle Rust interval belongs to the Corynoides americanus graptolite Zone, and that the upper Rust–Steuben interval probably belongs in the O. ruedemanni Zone, rather than the Climacograptus spiniferus or even to the lower Geniculograptus pygmaeus Zone, as previously inferred. (6) The Dolgeville carbonate turbidite facies is found to extend eastward to the vicinity of the Hoffmans Fault, east of Amsterdam. (7) Slumped breccia-filled channels in shelf-margin facies of the upper Rust and Steuben limestones may have served as feeder conduits to submarine fans now represented by the Dolgeville Formation. These observations indicate that a sediment-starved east-facing submarine ramp was developed across the study area during Shermanian time. Regional lithospheric flexure coupled with westward retreat of the shelf, explains the distribution of condensed facies and discontinuities. The widespread distribution of many marker beds plus the observation of spectral facies gradations at many levels, suggests that submarine faulting was usually a minor process superimposed on larger-scale diastrophic and eustatic patterns.

Indian Castle Shale: late synorogenic siliciclastic succession in an evolving Middle to Late Ordovician foreland basin, eastern New York State

Abstract The thick, organic-rich, Indian Castle Shale, is a major component of the greater Utica Shale basinal facies succession associated with the Taconian Orogeny. Detailed correlations of numerous Indian Castle sections, presented herein, are based on physical matching of numerous altered ash layers (K-bentonites) coupled with use of submarine discontinuities and other distinctive beds. Several important trends are observed: first, the Dolgeville Formation extends eastward into the eastern Mohawk Valley region (Hoffmans Fault area) lithologically separating an older Utica division (Flat Creek Shale) from Indian Castle Shale proper. Second, Indian Castle Shale strata are observed to overlap the regional top-Dolgeville and post-Trenton disconformity towards the northwest. Third, the lower part, and possibly the upper part, of the Indian Castle succession is differentially thickened in the west-central Mohawk Valley region due to differential subsidence and syntectonic fault activity. Fourth, the lower part of the Indian Castle Shale succession in the central-to-eastern part of the Mohawk Valley region continues to thin slightly with little evidence for major eastward transition of Utica facies into turbiditic Schenectady deposits. Fifth, K-bentonitic beds, many displaying distinctive sedimentological features, are clustered in intervals of apparent Indian Castle stratigraphic condensation. Ashes also display an overall upward decrease in abundance within the Indian Castle Shale succession. These patterns indicate that Indian Castle deposition, influenced by lithospheric flexural processes, localized fault activity and eustatic fluctuations, occurred when the foreland basin was maximally developed. Indian Castle deposition was probably linked to a collisional tectophase of Taconian overthrusting.

Host‐specific acrothoracid barnacles on Middle Devonian platyceratid gastropods

Borings, attributed to acrothoracic barnacles, occur on the platyceratid gastropod Naticonema lineatum (Conrad) from the Middle Devonian Hamilton Group of western New York and rarely in specimens as old as the Early Devonian. These latter are the oldest known acrothoracid borings are in the fossil record. The borings are consistently developed as laterally compressed, inequilateral pouches exclusively on these gastropods, commonly as dense infestations. Naticonema shells yielding borings typically occur associated with partially articulated qrinoid remains, and they are sometimes found attached to crinoids in a manner similar to coprophagous Platyceras. In addition to barnacle borings, Naticonema shells often bear thin encrustations of bryozoans which are usually perforated by these borings but sometimes also overgrow them. Barnacles bored live hosts; gastropods prevented shell penetration by producing cyst‐like secondary secretions of calcite beneath acrothoracid boreholes. The relative antiquity of thes...

Protosalvinia Dawson and Associated Conodonts of the Upper Trachytera Zone, Famennian, Upper Devonian, in the Eastern United States

Abstract Protosalvinia first occur in association with conodonts of the Upper trachytera Zone and below the Three Lick Bed in the Ohio Shale and the Ellicott Shale of the central and northern Appalachian Basin, as well as in the Clegg Creek Member of the New Albany Shale of the Illinois Basin. In the Chattanooga Shale of the southern Appalachian Basin, Protosalvinia are found no lower than the Upper marginifera Zone or associated with obviously reworked conodonts in the Middle expansa Zone. Regionally Protosalvinia are associated with a disconformity and may be found with conodonts of the Lower expansa Zone.

New perspectives on transitions between ecological-evolutionary subunits in the “type interval” for coordinated stasis

Abstract Northern Appalachian Basin deposits and associated fossils have served as exemplars for ecological-evolutionary investigations, and as the reference interval for the concept of coordinated stasis. Here, we examine faunal and environmental changes within the uppermost Hamilton and lowermost Genesee Groups of the late Middle Devonian succession of New York State. Dramatic diversity loss, faunal migrations, and ecological restructuring recognized in these strata have been used previously to define the end of the Hamilton ecological-evolutionary subunit, and, furthermore, these strata and corresponding faunal changes represent the type region for the global Taghanic Biocrisis. We present and analyze a new, high-resolution data set of post-Taghanic Genesee fossil assemblages, in which we recognize 11 biofacies corresponding to an onshore-offshore (depth) gradient. The Genesee Fauna shows an unexpectedly high taxonomic similarity to nearshore biofacies of the pre-Taghanic Hamilton Fauna, related to the persistence of siliciclastic-dominated nearshore settings through the Taghanic Biocrisis, whereas the onset of anoxic/dysoxic conditions typified offshore portions of the environmental gradient. The “Nearshore Refugium Model” of Erwin offers a possible explanation for the persistence of taxa through the biocrisis in nearshore settings. This constriction was followed by subsequent expansion of these residual taxa to offshore environments in relatively similar associations, as increased Acadian orogenic activity and resultant delta progradation increased habitable space offshore by decreasing the extent of deeper-water, oxygen-poor settings. Although taxonomic similarity was high between the Hamilton and Genesee Faunas, biofacies structure differed primarily because of tectonically driven physical transformations to the basin and associated biotic turnover. Nevertheless, the combination of high taxonomic persistence of Hamilton nearshore taxa and the introduction of relatively few new taxa in the Genesee Fauna resulted in a taxonomic holdover that was much higher than observed in the original formulation of coordinated stasis.