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Ductile duplexes as potential natural gas plays: an example from the Appalachian thrust belt in Georgia, USA

By
Brian S. Cook
Brian S. Cook
1
University of Kentucky
,
Department of Earth and Environmental Sciences, 101 Slone Building, Lexington, Kentucky 40506
,
USA
2
Southwestern Energy Company
,
2350 N. Sam Houston Pkwy E. Ste. 125, Houston, Texas 77032
,
USA
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William A. Thomas
William A. Thomas
1
University of Kentucky
,
Department of Earth and Environmental Sciences, 101 Slone Building, Lexington, Kentucky 40506
,
USA
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Published:
January 01, 2010

Abstract

In a well-defined small-scale recess in the Appalachian thrust belt in northwestern Georgia (USA), two distinct regional strike directions intersect at c. 50°. Fault intersections and interference folds enable tracing of both structural strikes. Around the recess, tectonically thickened weak stratigraphic layers – shales of the Cambrian Conasauga Formation – accommodated ductile deformation associated with the folding and faulting of the overlying Cambrian–Ordovician regional competent layer. The structures in the competent layer are analogous to those over ductile duplexes documented along strike to the SW in Alabama, where gas production has been established from the deformed shale. The analogy with structures in Alabama suggests a ductile duplex and natural gas potential within the recess in Georgia.

The tectonic thickening of the weak-layer shales is evident in palinspastically restored cross sections, which demonstrate a nearly 100% increase in volume over the restored state cross sections. The dominant cause of the surplus shale volume is likely pre-thrusting deposition of thick shale in a basement graben that was later inverted. The volume balance of the ductile duplex is critical for palinspastic reconstruction of the recess, and for the kinematic history and mechanics of the ductile duplex.

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Contents

Geological Society, London, Special Publications

Hydrocarbons in Contractional Belts

G. P. Goffey
G. P. Goffey
PA Resources UK Ltd, UK
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J. Craig
J. Craig
Eni Exploration and Production Division, Italy
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T. Needham
T. Needham
Needham Geoscience Ltd, UK
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R. Scott
R. Scott
CASP, University of Cambridge, UK
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Geological Society of London
Volume
348
ISBN electronic:
9781862395961
Publication date:
January 01, 2010

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