SEQUENCE STRATIGRAPHIC FEATURES OF THE UPPER ORDOVICIAN IN EAST TARIM BASIN

Based upon the seismic, drilling, wireline logging data and others from various data sources, this paper studied the sequence stratigraphy and sedimentary facies of the Upper Ordovician in East Tarim Basin. The results suggest that the Upper Ordovician deposits consist of one 2nd-order sequence and three 3rd-order sequences, SQ1, SQ2 and SQ3 from bottom to top. The sequence of SQ1 is a transgressive system tract, consisting of deep basin sediments and turbidites. The sequence SQ2 can be further divided into three system tracts, i.e. the LST, TST and HST. The LST consists of shelf edge deltas upon a regression background. The TST is resulted from a fast transgression stage, in which prevailed marine mudstone sedimentation. The HST consists of high stand shoreface deposits. The SQ3 sequence is dominated by shallow marine sedimentation, characterized mainly by deltaic and shoreface sediments. Sequence stratigraphy and sedimentation of the region are controlled by the joint action of tectonic movement, sediment supply and eustatic fluctuation. In the sequence of SQ1, there developed high quality source rocks. The SQ2 sequence is considered a potential reservoir and the SQ3 sequence has been proved a good reservoir for petroleum accumulation.