Deep-Water Origin of the Mesozoic Coal-Bearing Strata in Yanqi Basin, West China

H. Lu¹ and Z. Jiang^2
1University of Texas at Austin, Department of Geological Science, Austin, TX
²University of Petroleum, Department of Petroleum Exploration, China

Yanqi basin is located on the South Tianshan Mountain folded belt, west China. It is a newly discovered petroliferous intermontane basin with an area 13,000 km². The Basement is composed of pre- Mesozoic overlain by Triassic, Jurassic, Tertiary and Quaternary. The Jurassic system, a set of petrol-bearing coal-series strata, is considered to have main reservoir and source rocks. Much has been done on the sedimentary environment of coal-bearing strata and the model of coal’s origin, examples as formation from fluvial-alluvial plain, lake bay and shoal swamp, abandoned delta and fan-delta. Coal seams in these environments were originated from shallow water reducing swamps.

The study on the Jurassic sedimentary environment of Yanqi basin shows that there are lots of deep water sedimentary features in coalbearing beds which are inconsistent with the traditional standpoint of coal’s origin, deposited in shallow water. According to the basic principle of sedimentary geochemistry and geomathematics, two geochemical sections from Dongying Sag of Bohai Bay region and Turpan basins were selected as the standard models for deep-water rift-subsidence basin and shallow water coal measure basin, respectively. The discriminate analysis on inorganic element abundance has shown that the paleosedimentary environment of Jurassic in Yanqi basin was closer to the Dongying Sag, a rift-subsidence basin. This breaks free from the traditional standpoint of coal’s origin, and a new approach was made to build a distinctive model for coal’s accumulation.

AAPG Search and Discovery Article #90905©2001 AAPG Southwest Section Meeting, Dallas, Texas