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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 1003

Last Page: 1004

Title: Sunbury Shale of Central Appalachian Basin--Depositional Model for Basinal Black Shales: ABSTRACT

Author(s): Victor Van Beuren, Wayne A. Pryor

Article Type: Meeting abstract


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A model for the deposition of basinal black shales and associated base-of-slope turbidites is established in the central Appalachian basin. The model is based on an outcrop and subsurface stratigraphic study of the thin, but extensive Lower Mississippian Sunbury black shale. This model is termed the Sunbury cycle and it provides an explanation for the geometrid relations observed between basinal black shales and laterally adjacent gray/green slope shales and siltstones.

Two genetic types of black shales are recognized--transgressive and regressive. The transgressive black shale is the basal unit that initiates the cycle. Characteristically thin and widespread, it was deposited in the anaerobic zone of a stratified water column. Its sharp basal contact represents the rapid migration of the anaerobic environment over base-of-slope and slope deposits. This is caused by an increase in the subsidence rate of the active basin, decrease of clastic influx, and a minor rise in sea level. The regressive black shale overlies the basal unit. It is thicker, more laterally restricted, and represents the distal facies of base-of-slope turbidites formed by a progressive increase of clastic influx and a decrease in the subsidence rate of the basin floor. The thick re ressive black shale and laterally adjacent non-black clastics represent facies of a continuous unit (base-of-slope turbidites) containing varying amounts of preserved organic material. The degree of organic preservation is the result of deposition in zones of varying oxygen content caused by the intersection of the stratified water column with the basin floor.

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