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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
David
A. Pivnik,2
Wayne P. Wilson,3 Martin L. Albertin3, Richard A.
Beck,4 and Margaret A. Stratton
1Manuscript received June 20, 1996; revised manuscript received
October 10, 1997; final acceptance April 23, 1998.
2Gulf of Suez Petroleum Co. (GUPCO), P.O. Box 4381, Houston,
Texas 77210.
3Amoco E & P Sector, P.O. Box 3092, Houston, Texas 77253.
4Department of Geology, Miami University, Oxford, Ohio 45056.
5Amoco Canada, Calgary, Alberta T2P 2H8, Canada.
We are indebted to the entire Amoco team that contributed to the exploration
effort in Pakistan. We wish, in particular, to thank Jeffrey Barndt and
the staff of Amoco Pakistan Exploration Company in Islamabad, and Javed
Khan, Ahmed Hussain, and Rashid Tahirkheli, who unselfishly shared the
incredible geology of their spectacular country with us. Potential-field
data processing was completed by Earthfields Technology, and interpretations
were assisted by Robert E. VanNieuwenhuise of PGS SERES Inc. Military protection
in the North-West Frontier Province was provided by the Khyber Rifles,
Tochi Rifles, and South Waziristan Scouts. Insightful reviews were provided
by M. Coward, R. Raynolds, K. Biddle, and an anonymous reviewer. Some graphics
were completed by David
Orchard and the staff of Manzanita Graphics, Houston,
Texas. Special mention is reserved for Michael J. Griffin, Ian R. Halliday,
and Robert F. Wilson for their initial consultations.
ABSTRACT
The acquisition, processing, and interpretation of reflection seismic,
gravity, and magnetic data, in conjunction with detailed geological mapping
throughout the Kohat Plateau, have resulted in a reinterpretation of the
structural style of this portion of the northern Pakistan foreland. Our
interpretation of the recently acquired geologic and geophysical data,
as well as a critical reevaluation of previously acquired data and regional
geology, indicates that the Kohat Plateau has undergone major episodes
of strike-slip faulting, basement-involved reverse faulting, and minor
thrust faulting consistent with transpressional tectonics. Our interpretation
contrasts with previous models that invoked only southward-directed thrust
faulting. The principal key to the reinterpretation of seismic data was
depth migration before stack (MBS) seismic processing, which was performed
on five seismic lines to resolve the structural geology. MBS-processed
seismic data show complex deformation and steep dips more accurately than
other methods, and allowed us to identify the high-amplitude structures
in the Kohat Plateau. Surface geological mapping in the Kohat Plateau and
adjacent areas indicates tight anticlines, consistent steep dips, horizontal
motion fabrics, and a conspicuous lack of low-angle thrust faults. Aeromagnetic
and gravity data indicate that Precambrian basement is involved in the
deformation. Modern seismicity indicates that faults mapped at the surface
and subsurface are dominated by strike-slip displacement. The Kohat Plateau
is located near the intersection of the transcurrent Chaman fault system,
a 1000-km-long system of north-south-striking sinistral strike-slip faults,
and east-west-striking contractual structures that form the grain of the
Himalayan mountain chain in this area of northwest Pakistan. Surface and
subsurface structures fit the expected regional patterns that result from
transpressional deformation in this complex zone of intersection. Our reinterpretation
has applicability to other deformed belts worldwide that exhibit analogous
characteristics and criteria of transpressional tectonics, but are interpreted
as being dominated by low-angle thrust tectonics.
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