Structure Characteristics And Its Petroleum Significance Of The Nima Basin, Central Tibet

The Tertiary Nima Basin located in Bangong-Nujiang suture zone in central Tibet,covers an area of about 3000km² and is closely similar to the nearby Lunpola Basin which commercial oils have been produced.As the finding of the bitumen,Nima Basin becoming one of the continental basins with oil and gas potential in Bangong-Nujiang suture zone.This study based on observing and analyzing on measured stratigraphic sections,and the structure phenomenon of the study area and nearby,combining with previous geological researches,focuses on exposed strata,formation thickness,lithology distribution,sedimentary characteristics and depositional environment,also focus on identifying the surface structural features,including a variety of tectonic deformation characteristics,scale,distribution and combination rules,also with magnetotelluric and 2D Seismic Profiling,come to the following conclusions:?1?the Cenozoic strata in the Nima Basin mainly from the Paleogene to Quaternary,Paleogene strata are the Paleocene-Eocene Niubao Formation(E_1-2n)and Oligocene Dingqinghu Formation?E₃d?,in addition,the Neogene strata outcropping in the north and south Depression.Paleogene strata of the southern Depression and northern Depression deposition is mainly dominated by fan delta and lacustrine,the thickness of the Oligocene Dingqinghu Formation?E₃d?is above 3000 meters.Sediment thickness in southern Depression of Nima basin is up to 5000 meters.Niubao source rocks are mainly limestone and dark shale,and mostly belonging to high-quality source rocks,but the source rocks in southern Depression and northern Depression are difference.Southern Depression are mainly marl source rocks,organic matter the abundance of,the total thickness of the medium-high quality source rocks is up to 125m,compared with the dark shale source rocks in the northern Depression,its thickness is thinner than southern,the total thickness approximately about 3m,but the abundance of organic matter is very high.?2?:base on the stratigraphic distribution,characteristics of magmatic rocks,metamorphism and deformation characteristics,Nima basin is divided into three primary tectonic units,the central uplift,the Jiaruo Co Depression?northern Depression?,and the Daze Co Depression?southern Depression?.The interpretation of the two-dimensional seismic profiles further confirmed this program.?3?:strata below the Neogene of the Nima basin were subjected to varying degrees of tectonic deformation,and multi-active,most Thrust faults,north-south trending Thrust development,Paleogene strata deposited in the northern and southern depression were folded and deformation,presumably in the end of Oligocene the basin has experienced a strong regional tectonic event associated with the subduction and collision between the Indian plate and the Asian plate.