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Three Depositional Models of Deepwater Gravity Flow System of Late Ordovician in Tarim Basin, Western China

Liu, Jingyan; Lin, Chongsong; Jiang, Zaixing; Yang, Haijun; Song, Xiaoyong; Li, Hao; Fu, Chao

The Tarim Basin, located in western China, is a large sedimentary basin with a long geological evolution history stretching from the Sinian to the Neogene. An enormous deep-water gravity flow system up to 3000-5000 m thick developed during the Late Ordovician, with the great potential for forming large lithologic or stratigraphic oil/gas traps. However, the generally acknowledged poor reservoir conditions have caused oil/gas exploration to fall to a standstill. Integrated with lots of seismic data, well data and outcrop data analysis, this research focused on the study of sequence-depositional systems, paleo-geomorphology and paleo-geography, in an attempt to reveal the relationship between different types of deep-water gravity flow systems and paleo-geomorphology, tectonic backgrounds. The palaeo-geomorphology of deep water deposits in the Late Ordovician was reconstructed through erosion restoration and residual strata thickness obviously controlled the different depositional systems' distribution. Above the submerged platform and the 1st fault break slope of the Tazhong area, wide-shallow braided channels or tidal-river mixture channels developed. Carbonate breccia slump formed turbidite fan aprons along the marginal of the break slope. Deep U-shaped incised ditches developed at the edge of the Tabei Uplift. Large-scale turbidite fan aprons developed under the continental slope. Regional tectonic background analysis shows that the Tarim Basin experienced a recycled orogenic environment during the Middle-Late Ordovician, with compaction stress mainly stemming from the West Kunlun, the western section of East Kunlun at the southern edge of the basin, the Altun massif to the east of the basin, and the Kuluketage block at the northeastern margin of the basin, which provided a major source system. Three different deep-water gravity flow depositional models were constructed in this study, one for the each of the following areas: Tabei, Tazhong and Tadong. The Tazhong area tends to be a debris-flow-dominated setting with shallow, sandy channelized systems and controlled by multiple slopes; the Tabei area is a debris-flow-dominated setting with non-channelized or few U-shaped deep incised ditches filled with muddy debris; and the Tadong area features a typical submarine turbidite-dominated fan system. According to the models, the favorable reservoir sandbody and lithologic-stratigraphic oil/gas traps belts of the Late Ordovician Tarim Basin can be predicted.

 

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013