Palaeoecological patterns within the dysaerobic biofacies: Examples from Devonian black shales of New York state

AbstractTwo regional composite sections in the Frasnian, Upper Devonian, of New York State result from graphic correlation of conodont species. The first extends from Frasnian conodont zones 3 to 7, the second from Frasnian zones 11 to 13c (we prefer this terminology to “Montagne Noire” or “MN” zonation as the zone-defining species occur throughout the Devonian tropics). Key beds, widely traceable bases of prominent black shales, have been used with only a few exceptions to position the lines of correlation (LOC) in the graphs. Other key beds, not used for positioning, fall exactly on the LOC supporting the hypothesis of their synchrony. Fifty-five conodont species in the New York regional composites are compared with their ranges in the global Frasnian Composite Standard proving no major discrepancies. The taxonomy ofAncyrodella nodosaUlrich and Bassler, widely misidentified in the past, has been clarified through restudy of the type specimens, resulting in its distinction fromA.hamataUlrich and Bassler (=A.buckeyensisStauffer). A new species ofPolygnathellusBassler, which is restricted to Frasnian Zone 4, is kept in open nomenclature because the rarity of specimens is insufficient to determine the extent of intraspecifc variation and whether one or two species are represented in our New York and Western Australian collections.

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Fossil communities of the upper Trenton Group (Ordovician) of New York State

Journal of Paleontology ◽

10.1017/s0022336000042967 ◽

1986 ◽

Vol 60 (4) ◽

pp. 805-824 ◽

Cited By ~ 20

Author(s):

Robert Titus

Keyword(s):

New York ◽

Carbonate Platform ◽

Group Structure ◽

New York State ◽

Black Shales ◽

Wave Dissipation ◽

York State ◽

Short Period ◽

Trenton Group ◽

Water Facies

During the late Trentonian the New York State region experienced gentle crustal subsidence which preceded the onset of the Hudson Valley phase of the Taconic Orogeny. The lower and middle Steuben Limestone represents several shallow-water facies: a protected shoal, a wave dissipation zone and a shallow shelf. Overlying strata of the upper Steuben and the Hillier limestones represent progressively deeper water facies. After a short period of uplift, which produced a minor unconformity, black shales began to bury the Trenton carbonate platform.Three fossil communities are found in the upper Trenton Group. Each had been present on the Trenton bank since it first formed. The Liospira Community existed on the shallow protected shoal facies of the Steuben Limestone. Its assemblages are dominated by brachiopods, gastropods, bryozoans, and crinoids. The Encrinurus Community was found in the wave dissipation zone and on the shelf facies. This diverse community was dominated by brachiopods, bryozoans, and crinoids. The Trematis Community is found in the deeper shelf deposits of the Hillier Limestone. It was a very heterogeneous community with brachiopods, crinoids, gastropods, trilobites, and conodonts all represented.These communities have now been traced through a minimum of eight million years of their history and it is now possible to evaluate their patterns of community evolution. At the species level these communities were quite changeable. Between 45% and 55% of the species which were present in the lower Trenton Group were replaced by the late Trentonian. Despite this changeover, the communities maintained a remarkably familiar look because there was great stability at higher taxonomic levels and the same proportions of brachiopods, bryozoans, crinoids, etc., were maintained throughout the Trentonian. Community trophic group structure also seems to have been quite stable throughout the Trentonian. If these patterns are representative, then these invertebrate communities appear to be genuinely stable entities. Evolution changes the cast of characters but the play is the same!

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