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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Shelf Sands and Sandstones — Memoir 11, 1986
Pages 346-346
Symposium Abstracts: Paleoecology

Paleoecological Parameters for the Study of Shelf Sands and Sandstones: Abstract

George Farrow1

Abstract

Sediments of the inner and outer shelf may be distinguished by using fossils as indicators of different environments. Molluscan-dominated inner shelf and bryozoan/brachiopod-dominated outer shelf environments have been documented from Recent high-latitude seamounts, micro-continents and tectonically active shelves. These two belts may be extended back in time to Upper Paleozoic shelves, such as the Carboniferous of Kansas and the Devonian of New York State. Orientation and mode of preservation of shells is different in tide-dominated and storm-wave dominated settings. Resistate carbonate fractions are often dominated by serpulids in Recent tidal sand wave complexes and dominated by serpulids, belemnite guards and brachiopods in the Mesozoic. Storms, by contrast, may cause only one reworking event and shells may be well preserved. Benthic communities may be related to bed shear stress: the bivalves Modiolus and Glycymeris are typical of tide-dominated settings. Dead shells rarely move more than 5 km before becoming reduced to unrecognizable bioclastic carbonate. Shell debris from high-energy environments has few borings, whereas low-energy environments are characterized by much boring. Regional mapping of calcareous algae, algal borings and associated limpet grazing traces enables the photic zone to be determined. In the tropics the entire shelf (up to 200 m depth) may fall within the photic zone but high-latitude shelves have a photic limit of 30 to 40 m. This method has successfully indicated the depth of deposition of Lower Cretaceous shales from the North Sea Basin.


 

Acknowledgments and Associated Footnotes

1 Department of Geology, University of Glasgow, Glasgow, U.K.

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