Sequence stratigraphic characteristics of Triassic back-bulge zone in Tarim basin

In order to reveal the sequence stratigraphic characteristics of Triassic back-bulge zone in Tarim basin,the sequence stratigraphy and sedimentology was used to establish the sequence stratigraphic framework and reveal the sequence stratigraphic characteristics by comprehensive analysis of seismic data,well logging,cores and outcroppings.Besides,the study proposed the main controlling factors which influence third-order sequence development.The results show that Triassic can be divided into one tectonic sequence,three sequence sets and five three-order sequences.The boundary between each three-order sequence is abruptly contacted by thick sandstone and mudstone,with obvious scarp on logging and truncation on seismic profiles respectively.Internally,the lower part of each three-order sequence mainly consists of coarse delta sandstone or sandy conglomerate,while the upper part is composed of fine muddy deposits.On the whole,it shows a dual structure that changes from coarsing one to fining one.The episodic tectonic activities of foreland basin predominantly control the formation of such sequence structure.Simultaneously,the sediment supply influences its internal sedimentary characteristics and superimposed styles.And the climate affects not only the types of deposits,but also the sequence development through dominating raining and vegetation to cause lake level change.