Articles
7 June 2022

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

Publication: Geological Society, London, Special Publications
Volume 58
Pages 233 - 257

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.

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Published In

cover image Geological Society, London, Special Publications
Geological Society, London, Special Publications
Volume 581991
Pages: 233 - 257

History

Published in print: 1991
Published online: 7 June 2022

Authors

Affiliations

Gordon C. Baird
State University of New York, College at Fredonia, Department of Geosciences, FredoniaNew York 14063, USA
Carlton E. Brett
University of Rochester, Department of Geological SciencesRochester, New York 14627, USA

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