The Junggar basin is one of the largest oil
producing areas in China, and contains Upper Permian lacustrine oil shales
with some of the greatest hydrocarbon potental in the world. In this study,
we present the diagenetic characteristics of Permian-Triassic sandstones
from the southern Junggar basin and evaluate their reservoir potential.
The uppermost Permian and Lower Triassic
Cangfanggou Group in the southern Junggar basin is characterized by alternating
fluvial and lacustrine deposits, whereas the Middle-Upper Triassic Xiaoquangou
Group was deposited predominantly in a lacustrine environment; fluvial
and deltaic sedimentation was subordinate. The sandstones of the Cangfanggou
and Xiaoquangou groups are volcanic litharenites. Their detrital modes
and textures of volcanic fragments suggest a primarily andesitic/basaltic
Early diagenesis of the sandstones is characterized
by nonferroan calcite cementation, grain-coating, pore-lining clay minerals,
and the initial dissolution of detrital grains. Authigenic quartz; pore-filling
phyllosilicates; pore-filling, grain-replacive zeolites; albitized detrital
plagioclase; authigenic K-feldspar;
1997. The American Association of Petroleum Geologists. All rights reserved.
received April 15, 1996; revised manuscript received November 4, 1996;
final acceptance May 2, 1997.
of Earth Sciences, University of Western Ontario, London, Ontario, N6A
of Geosciences, Queen's University of Belfast, Belfast BT7 1NN, United
work was done at the Queen's University of Belfast with funding from Exxon,
BHP, Mobil, and ITOTAL, which we gratefully acknowledge. The Karamay Institute
of Petroleum Exploration and Development generously provided borehole samples.
Geng Ansong at the Institute of Geochemistry (Guangzhou), Academia Sinica,
and Zhou Yisheng at the Xinjiang Institute of Petroleum are thanked for
assistance with field work and for valuable discussions. Special thanks
go to the staff of the Electron Microscopy Unit at the Queen's University
of Belfast. We also thank A. H. Ruffell and S. R. Lawrence for their constructive
comments on an earlier version of the manuscript. Stable isotope analysis
and ongoing research concerning the Junggar basin at the University of
Western Ontario have been supported by the Natural Science and Engineering
Research Council of Canada. The manuscript benefited substantially from
critical commentary by Kevin T. Biddle, Suzanne Kairo, W. R. Kaiser, and
an anonymous reviewer.