塔西南坳陷侏罗系的扇三角洲沉积

塔西南坳陷侏罗系广泛发育扇三角洲沉积。在论述沉积特征的基础上，确认本区的扇三角洲是一个典型的退积型层序。该层序三层结构明显，下部为扇三角洲平原，中部为扇三角洲前缘，上部为前扇三角洲。反映了该区在早中侏罗世时处于活动盆地边缘，湖水由浅变深，沉降速率大于沉积速率的特点。通常扇三角洲的形成受湖盆边界类型和源区距湖盆距离及古气候３个主要背景条件的约束，因此，本区的扇三角洲一般发育在源区距湖盆距离短，靠近山前植被不发育的地带。塔西南坳陷侏罗系生储盖组合发育齐全，湖相暗色泥岩为主要烃源岩，扇三角洲前缘砂体是较好的储集层，上白垩统和第三系膏泥岩则起着主要的封盖作用。本区侏罗系有着良好的油气勘探前景。

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

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.