(1) Serra GeoConsulting LLC, Bellaire, TX
ABSTRACT: Trap Styles in a Multi-Detachment Fold and Thrust Belt, Tarim Basin, Western China
The Tarim Basin in western China is one of several microplates which together comprise the Asian continent. Deformation produced by successive south-to-north accretion of these microplates to the Siberian craton is recorded in a series of intervening orogenic belts.
One such belt is the 1000km-long deformed northern margin of the Tarim Basin, which includes the 250km-long Kuche Fold and Thrust Belt (KFTB). The KFTB deforms a 12km-thick Mesozoic and Tertiary section of terrigenous clastics, coals, and evaporites (halite and anhydrite) deposited in near-shore, alluvial, and lacustrine settings. The section is divided into two major tectonostratigraphic units by regional detachments in lower Triassic shales and a base-Tertiary salt horizon. A Miocene salt is the locus of another detachment in the eastern part of the belt. There is often profound geometric disharmony between structures above the salt detachments and those below. Supra-salt folds are box-shaped, with varying sense of vergence from fold to fold and along strike on a single structure.
Principal reservoirs in the KFTB are Cretaceous and Lower Tertiary sandstones. Gas-prone source rocks are Triassic and Jurassic coals and lacustrine shales. Primary seals are Lower Tertiary and Miocene salt horizons. Recent exploration efforts for sub-salt traps by PetroChina and other companies have partly overcome problems of accurately imaging complex sub-salt structures and drilling through salt into highly overpressured sections. One 6-8Tcf field has been discovered, and at least two more with potentially similar reserves are being tested.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.