The Research Of Depositional System And Sequence Palaeogeography Of Xujiahe Formation Of Upper Triassic In Western Sichuan Depression

On the basis of research results of previous studies,make use of the wild outcrops, drilling cores, well logging, on the guiding of sedimentology and sequence stratigraphy theories,this paper study the Stratigraphic classification and contrast, characteristic of sedimentary system, characteristic and lithofacies paleogeographic of the of Upper Triassic Reservoirs in Western Sichuan Depression.Main contents and results are as follows:1.According to the wild outcrops,drilling cores,and relevant indoor analysis test, merging and dividing the stratigraphy of Upper Triassic Reservoirs in Western Sichuan Depression. and name unitedly Ma’antang and Xiaotangzi formation are named the first member of Xujiahe formation which is divided five sections and established the Sequence stratigraphic framework.2.Studies suggest that three depositional systems of Xujiahe Formation in Western Sichuan Depression has been recognized:Continental system group,Sea-land transition system group and marine systems group of groups,including seven depositional system.such as alluvial fan depositional system,river depositional system, lake delta depositional system, lake depositional system, marine delta depositional system,beach-barrier depositional system and Carbonate platform depositional system.Sedimentation mode has established of the Xujiahe Formation of Upper Triassic in Western Sichuan Depression.3.On the basis of stratigraphy and depositional system to study the sequence boundary characteristics,identify six kinds of sequence boundary and its material manifestations. The Xujiahe Formation can be divided into3tectonic sequences and6long-term stratigraphic cycles(third-order sequence).The characteristic of sequences is discussed Detailedly.4.Xujiahe Formation of Late Triassic tectonic sequence lithofacies-paleogeographic diagram is systematically created using the systems tracts of tectonic sequence as compilation unit in this dissertation. We used the systems tracts of the third-order sequence as the mapping unit to draw the sequence based lithofacies paleogeography map,in the Middle Part of Western Sichuan Depression. This paper demonstrats in details the characteristics of lithofacies paleogeography and their evolution during different sedimentary sequence developing period.