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The AAPG/Datapages Combined Publications Database

Williston Basin Symposium

Abstract

SKGS-AAPG

Eighth International Williston Basin Symposium, October 19, 20, and 21, 1998 (SP13)

Pages 58 - 68

DEVELOPING A SEQUENCE STRATIGRAPHIC FRAMEWORK FOR THE LATE DEVONIAN CHATTANOOGA SHALE OF THE SOUTHEASTERN U.S.A.: RELEVANCE FOR THE BAKKEN SHALE

JÜRGEN SCHIEBER, Department of Geology, The University of Texas at Arlington, Arlington, Texas 76019

ABSTRACT

The Late Devonian Chattanooga Shale of Tennessee and Kentucky is in most areas a thin black shale fewer than 10 m thick. It is a distal equivalent to the almost 3000 m thick Catskill strata, and encompasses most of the Frasnian and Fammenian succession.

Although originally thought of as a continuously, though slowly, deposited deep water shale unit, the Chattanooga Shale shows internal erosion surfaces at various scales as well as storm deposits. These features suggest comparatively shallow water deposition (tens of metres water depth), and a stratigraphic record with numerous hiatuses of various duration. A number of erosion surfaces are laterally extensive and can be traced through the entire outcrop area (over distances of as much as 300 km). Erosion surfaces of this type are considered sequence boundaries sensu Vail, and tracing them has made it possible to subdivide the Chattanooga Shale into as many as 14 sequences.

These sequence boundaries are very subtle. The following features are indicative of their presence in a given outcrop: 1) sandy, silty, or pyritic lag deposits up to several centimetres thick; 2) sharp-based shale beds; 3) low-angle truncation of shale beds; 4) scoured surfaces; and 5) soft-sediment deformation in underlying shales. Tracing erosion surfaces from outcrop to outcrop is based on a combination of: 1) petrographic matching of lag deposits; 2) the petrography and microfabrics of individual shale packages; 3) conodont data; and 4) gamma-ray surveys.

Collection of additional conodont data and extension of this stratigraphic framework to adjacent areas may eventually lead to a comprehensive stratigraphic framework for the entire Late Devonian black shale complex of the eastern United States. Comparison between distal and proximal successions may allow differentiation of truly eustatic events from those due to tectonism and sedimentation.

The lower Bakken is of Late Devonian age and is probably equivalent to the upper half of the Gassaway Member of the Chattanooga succession. Cursory examination of drill core has shown lag deposits and evidence of erosional gaps. These features could be physical evidence of sequence boundaries that are traceable through careful examination of cores in conjunction with geophysical logs.

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