Tagasi otsingusse
Baird & Brett, 1991

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

Baird, G. C., Brett, C. E.
DOI
DOI10.1144/GSL.SP.1991.058.01.16
Aasta1991
AjakiriGeological Society, London, Special Publications
Köide58
Number1
Leheküljed233-257
Tüüpartikkel ajakirjas
Id10037

Abstrakt

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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