LATE DEVONIAN SEDIMENTARY EVOLUTION IN THE TARIM BASIN AND ITS MARGINS

Based on a lot of outcrops investigation,cores observation and well logs analysis,the Donghetang Formation is divided into the standard typeⅠsequence with a complete transgressive-regressive cycle.It corresponds to sedimentary strata of Ⅲ-grade sea-level cycles.It is composed of lowstand system tract(LST),transgressive system tract(TST) and highstand system tract(HST).The lowstand system tract is subaerial fluvial deposit system with limited distribution.The transgressive system tract is mainly composed of shore deposit controlled by tide.A series of shallowing and fining upward parasequences constitute the spanking parasequence group.The highstand system tract is mainly composed of wave-controlled shore deposit.A series of shallowing and thickening upward parasequences constitute the retrograding parasequence group.Additionally,there are alluvial fan,alluvial plain and fan delta deposition system in the basin edge.