The Evolution Of Silurian Structural Paleogemorphology And Sedimentology, The South Slope Of Tabei Uplift, Tarim Basin

Tabei Uplift, located in the northern Tarim Basin, is one of the first order structural units. Affected by regional tectonic movements, its framework of geomorphology was changing and dominated the development and distribution of stratigraphic sequence and depositional systems. Silurian became the most important target of finding stratigraphic and lithologic traps, because of its unique feature of geomorphology and its related sedimentology. It is significant for development and exploration of oilfield to analyze the control of paleo-structure and paleo-geomorphology on the depositional systems and the rule of the distribution of Silurian stratigraphic and lithologic traps.The main control on the distribution of Silurian marine sand and the development of favorable reservoir zone is impercipient, so it is difficult to reveal the patterns of the traps and the distribution of hydrocarbon. Guided by sequence stratigraphy, seismic sedimentology and seismic geomorphology, analyze the architecture of stratigraphic sequence and the types of depositional systems using cores, well logs and seismic data. The paleogeomorphology of the major depositional period of Silurian was recovered. The control of tectonic movement on the evolution of structural paleogeomorphology and sediment filling was discussed, and analyzed the impact of structural paleogeomorphology on the stratigraphic traps and predicted the favorable traps zone. The main results and achievement are as follows:（1） According to the analysis of the feature and the scale of unconformity surface, Silurian is a 2^nd-order sequence. There are five 3^nd -order unconformity surfaces in Silurian. They separated Silurian into four 3^nd-order sequence: SQ-Skp2, SQ-Skp1, SQ-Stt, SQ-Sym. SQ-Skp1 includes lowstand systems tract, transgressive systems tract and highstand systems tract, and others are composed of transgressive systems tract and highstand systems tract.（2） Back-stripping, residual thickness and the pattern of unconformity distribution were combined to rebuild the structural paleogeomorphology of every 3^nd-order sequence. The paleogeomorphology was divided into several units based on the characteristics of the distribution of slope. The units are: highland, highland slope, low-amplitude highland, low- amplitude sag and slope-sag.（3） Analyzed the patterns of unconformity and concluded a model: onlap and truncation unconformity develop on highland slope; parallel unconformity and conformity occur in low-amplitude highland and low-amplitude sag; slope-sag is the zone where onlap and truncation unconformity develop.（4） According to the control of paleogeom （?） the depositional systems, the pattern that how sedimentary facies developed in the geomorphology units was summarized: highland and highland slope often have forshore - upper shoreface and delta deposits; low-amplitude highland mainly deposits upper shoreface, while low-amplitude sag usually develop upper shoreface and lower shoreface; shelf and lower shoreface mostly distribute in slope-sag.（5） Combined the characteristics of structural paleogeomorphology and the distribution of sedimentary facies with the analysis of existing reservoir, suggested that highland slope and sag-slope are the region where traps of onlap and sand pinching out developed, low-amplitude highland is the favorable zone that structural and lithologic traps formed.