--> Abstract: Origin of Allocycles, Depositional Sequences, and System Tracts and Their Relationship, Lower-middle Jurassic, East of Jungar Basin, Northwest China, by R. Pu; #90925 (1999)

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PU RENHAI, Northwest University, Dept. of Geology, P.R. China

Abstract: Origin of Allocycles, Depositional Sequences, and System Tracts and Their Relationship, Lower-middle Jurassic, East of Jungar Basin, Northwest China

Lower-middle Jurassic, east Jungar Basin is composed of five 100-300m thick, basin-wide fining upward allocycles which are rightly depositional sequences bounded by unconformities seen on seismic profiles. The lower coarse parts of each allocycle, laterally consist of depositional systems of braided, meandering streams and swamps from present basin margin to its center, comprising low stand system tracts with Terrigenous supply from northern Klameili and southern Bogeda Mountain. The middle-upper fine parts of each allocycle, developed meandering stream and swamp systems throughout the present range of the basin, comprising the highstand system tract with terrigenous supply from Artai Mountain - a region much farther away in NE direction. Around the present basin margins - the pediment of Klameili and Bogeda Mountain do not exist coarse sediments, such as fan conglomerates of high stand system tract, which may have formed far outside today’s basin. The phenomena seemingly suggest that Jungar basin likely connected with its southern Tupan basin during high stand epoch and separated by Bogeda Mountain during low stand epoch.

Because the denudation volume of basin-surrounding mountains over an unconformity should equal the synchronous basin fill during low stand epoch, it can be deduced that Klameili Mountain might rise about 120-180m and Bogeda Mountain uplifted about 150-200m between two adjacent cycles.

Each of fluvial sequence lasts for as long as a marine supper-cycle (about 7-14 Ma). It seems not sea level change but tectonic movements that controlled the genesis and depositional architecture of a fluvial sequence and system tract.

AAPG Search and Discovery Article #90925©1999 AAPG Foundation Grants-in-Aid