Fan Delta Deposits in Jurassic in the Depression of the SW Tarim Basin

Key words: 
• depression of the SW Tarim Basin /
• Jurassic fan delta /
• a set of retrog radinging ression /
• lacustrine sequrnce /
• source-reservoir-cap rock assemblages

Abstract: Fan delta sediments is widely developed in Jurassic in the depression of the SW Tarim Basin. Based on analyses of sedimentary characteristics, the paper is lonsidered that fan delta is a typical set of retro-gradinging ression lacustrine sequence. Three-layer structre of the sequence is quite clear with prefan-delta plain in the lower part, fan-delta-front in the middle part and prefandelta in the upper part. It indicates that the region be in margin of active basin in Early-Middle Jurassic, in which lake changes form shallow to deep and rate of subsidence is more rapid that rate of sedimentaion. Generally peaking, the forming of fan delta be resericted by three main condition wuioth marginal type of lake basin, distance form provanance to lake basin and palaeoclimate, so fan delta usually develop in the region of short distance form provenance to lake basin and lacking plant near foreland. It has develped a complete source-reser-voir-cap rock assemblage in Jurassic in the depression of the SW Tarim basin. Dark mudstone of lake are main hydrocarbon source rocks, fandelta foront sand bodies are good resewoirs, and gypmudrock in Upper Cretaceous and Tertiary is good cover rock It has been proved that Jurassic have good potentials for exploration of oil and gas in this region.