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Systematics and Paleoecology of Norian (Late Triassic) Bivalves from a Tropical Island Arc: Wallowa Terrane, Oregon
- Cathryn R. Newton, Michael T. Whalen, Joel B. Thompson, Nienke Prins, David Delalla
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- Journal:
- Journal of Paleontology / Volume 61 / Issue S22 / July 1987
- Published online by Cambridge University Press:
- 11 August 2017, pp. 1-83
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Early Norian silicified bivalves from Hells Canyon in the Wallowa terrane of northeastern Oregon are part of a rich molluscan biota associated with a tropical island arc. The Hells Canyon locality preserves lenses of silicified shells formed as tempestites in a shallow subtidal carbonate environment. These shell assemblages are parautochthonous and reflect local, rather than long-distance, transport. Silicification at this locality involved small-scale replacement of original calcareous microstructures, or small-scale replacement of neomorphosed shells, without an intervening phase of moldic porosity. This incremental replacement of carbonate by silica contrasts markedly with void-filling silicification textures reported previously from silicified Permian bivalve assemblages.
The bivalve paleoecology of this site indicates a suspension feeding biota existing on and within the interstices of coral-spongiomorph thickets, and inhabiting laterally adjacent substrates of peloidal carbonate sand. The bivalve fauna is ecologically congruent with the reef-dwelling molluscs associated with Middle Triassic sponge-coral buildups in the Cassian Formation of the Dolomites (Fuersich and Wendt, 1977). Hells Canyon is a particularly important early Norian locality because of the diversity of substrate types and because the site includes many first occurrences of bivalves in the North American Cordillera. These first occurrences include the first documentation of the important epifaunal families Pectinidae and Terquemiidae in Triassic rocks of the North American Cordillera.
The large number of biogeographic and geochronologic range extensions discovered in this single tropical Norian biota indicates that use of literature-based range data for Late Triassic bivalves may be very hazardous. Many bivalve taxa formerly thought to have gone extinct in Karnian time have now been documented from Norian strata in this arc terrane. These range extensions, coupled with the high bivalve species richness of the Hells Canyon site, suggest that the Karnian mass extinction in several literature-based compilations may be an artifact of incomplete sampling. Even for the Norian, present compilations of molluscan extinction may have an unacceptably large artifactual component.
Thirty-five bivalve taxa from the Hells Canyon locality are discussed. Of these, seven are new: the mytilid Mysidiella cordillerana n. sp., the limacean Antiquilima vallieri n. sp., the true oyster Liostrea newelli n. sp., the pectinacean Crenamussium concentricum n. gen. and sp., the unioid Cardinioides josephus n. sp., the trigoniacean Erugonia canyonensis n. gen. and sp., and the carditacean Palaeocardita silberlingi n. sp.
Benthic invertebrates of a modern carbonate ramp: a preliminary survey
- Linda C. Ivany, Cathryn R. Newton, Henry T. Mullins
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- Journal:
- Journal of Paleontology / Volume 68 / Issue 3 / May 1994
- Published online by Cambridge University Press:
- 20 May 2016, pp. 417-433
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A preliminary survey of benthic invertebrates off central west Florida provides documentation of modern epifaunal communities on a low-gradient carbonate slope. Three large-scale biofacies occur in soft-sediment carbonate environments between 200 and 2,000 m: an Echinoderm biofacies (200–550 m) dominated by a diverse assemblage of echinoderms, gastropods, and decapod crustaceans; a Penaeid shrimp–conical mound biofacies (550–1,200 m) characterized by large bioturbation structures; and a Microbial mat biofacies (1,200–2,000 m) with only rare epifaunal invertebrates. A fourth, hard-substrate biofacies reflects the presence of localized Miocene and Pleistocene hardgrounds in water depths of 200–600 m. This illustrates that hard-substrate biofacies may be laterally correlative with soft-sediment biofacies in a slope setting, thus producing a mosaic of contrasting faunal associations. All four biofacies have low population densities, presumably as a consequence of relatively low surface productivity. All four biofacies also show biogeographic affinity with other faunas at intermediate depths in the Caribbean region. Depth-related faunal transitions on the west Florida slope correlate with substrate and current velocity. Decreasing species diversity and abundance and a biofacies transition from suspension-feeding to deposit-feeding assemblages correlate with increasing depth, a decrease in mean grain size, and an increase in organic content of the sediment. This biofacies model may provide a modern analogue for faunas of ancient low-gradient slopes such as those of Cretaceous “shelf-sea” chalks of northwestern Europe.