Sedimentary characteristics and distribution of grain shoals in the Lower Cambrian Longwangmiao Formation of Sichuan Basin and its adjacent areas
Ma Teng1,2, Tan Xiucheng1,2,3, Li Ling1,2,3, Zeng Wei1,2,3, Jin Mindong1,2, Luo Bing4, Hong Haitao4, Yang Yu4
1 State Key Laboratory of Oil and Gas Reservoir Geology and Exploration,Southwest Petroleum University,Chengdu 610500, Sichuan 2 Sichuan Province Key Laboratory of Natural Gas Geology,Southwest Petroleum University,Chengdu 610500, Sichuan 3 The Sedimentary and Accumulation Department of Key Laboratory of Carbonate Reservoirs, PetroChina Southwest Petroleum University,Chengdu 610500, Sichuan 4 Institute of Petroleum Exploration and Exploitation,PetroChina Southwest Oil and Gasfield Company,Chengdu 610041, Sichuan
Abstract：Based on data from regional outcrops and wells,together with systematical observation and sampling for some outcrops and wells, it was found that grain shoals in the Lower Cambrian Longwangmiao Formation of Sichuan Basin and its adjacent areas are comprised of carbonate grainstone and crystallized carbonate grainstone.The grain shoals are dominated by unexposed shallow shoals, and mainly develop two types of vertical sequences including upward-shallowing and upward-deepening. In terms of the lateral occurrence of the grain shoals, those in the central Sichuan palaeouplift and the north of the central Guizhou palaeouplift are characterized by a large scale and stable and continuous stratigraphic distribution. In contrast, the shoals in other regions are mainly patched shoals with relatively small scales. Based on the reconstruction of the palaeogeographic pattern of the study area during the Longwangmiao Period, the water depth was shallower in the west and deeper in the east, the basin was surrounded by old lands from southwest, northwest and north, and one uplift was divided two depressions inside the basin. With respect to the lateral occurrence, the grainstones in highlands demonstrate a widely covering style of “five lines and one area”.Central Sichuan palaeouplift and the north of Central Guizhou palaeouplift are superior regions for grain shoals developing,and the sub-marine island chain in the northeast and southeast may be the potential locations for high-quality grain shoals. The development of the palaeouplift evidently had the dominating effects on the development of grain shoals and favorable reservoir sedimentary zone. The sub-level eustatic change influenced the vertical superimposed pattern and lateral continuity of the grain shoals.
Ma Teng,Tan Xiucheng,Li Ling et al. Sedimentary characteristics and distribution of grain shoals in the Lower Cambrian Longwangmiao Formation of Sichuan Basin and its adjacent areas[J]. JOPC, 2015, 17(2): 213-228.
