SEQUENCE STRATIGRAPHY PATTERNS IN DIFFERENT ACCOMMODATION SPACE TECTONIC ZONES-IMPLICATION FOR THE MID-LOWER JURASSIC IN TURPAN DEPRESSION

High-resolution sequence stratigraphy was a binary division of time stratigraphic units which reflected changes of base-level cycles in stratigraphic records. Both strata structures and sedimentary characteristics were controlled by the dynamic system of base-level cycles accompanied by the variations of accommodation space. The key to the theory and technology of high-resolution sequence stratigraphy was to identify multi-order stratigraphic cycles which represented multi-order base-level cycles in stratigraphic records.

Turpan-Hami basin was in the eastern part of Sinkiang province, which was known the first Jurassic coal measures-related in China. Turpan depression was the main body of the Turpan-Hami basin which was a multi-cycle composite petroliferous basin composed of continental sediments of Mesozoic and Cenozoic, tectonically located in the southeast corner of Kazakhstan plate at the junction of Kazakhstan, Siberia and Tarim plates.

Five outcrops surrounding Turpan depression and typical wells of each tectonic unit were systematically investigated before re-recognizing the sedimentary sequence characters of Mid-Lower Jurassic based on high-resolution sequence stratigraphic theory, for the purpose of guiding stratigraphic and subtle reservoirs exploration.

The result shows that the stratigraphic sequences of the Mid-Lower Jurassic were divided into 5 third-order sequences (SQ1-SQ5), further subdivided 10 fourth level cycles (SC1-SC10). On the basis of analysis for sequence stratigraphy styles in different accommodation space and sedimentary backgrounds, it suggests that the sequence architectures of mid-lower Jurassic could be divided 3 different stages. SC1-SC5 which represented the sequence developmental model of gentle slope shallow water lake basin in low base level background, were characterized by deposited braided river, braided river delta and onshore shallow lake facies. SC6 and SC7 represented the shallow water lake basin sedimentary background, evolved from gentle slope shallow water lake basin environment to the sedimentary background of shallow lake basin with obvious paleo-geomorphic slope break. SC8-SC10 represented a set of fine-grained sediments formed in a relatively stable lake environment, which shows an obviously retro-gradational sequence.