Catastrophic event characteristics of stratigraphic slope slumping accumulation: a case study of the Upper Triassic Nanshuba Formation in Baoshan area, western Yunnan Province

Researches on Upper Triassic Nanshuba Formation (T3n) in Baoshan area of Baoshan block are very insufficient. In the 1∶50000 Baoshan sheet, the 1∶200000 Fengqin sheet and the 1∶250000 Dali City sheet have been completed, which, however, mainly lay emphasis on the study of rock-strata and biostratigraphy. The data of the sedimentary environment are very few. Through regional geological survey of 1∶50000 Baoshan sheet and other seven sheets, the authors found a series of very important data of sedimentary facies, such as limestone slumping rock-block, downlap surface, hunger deposition, channel conglomerate, graded bedding, flysch rhythm and flute cast and groove cast at the upper Triassic Nanshuba Formation in Baoshan area. The authors hold that the sedimentary environment is a slope-basin environment. On the whole, that exist a set of turbidites, which include contemporaneous folds, contemporaneous faults, large amounts of slumping surfaces, various types of slumping fold, which constitute three relatively large-scale slumping zones. The stratigraphic characteristics of the sediments were formed by the triggering of earthquakes in a slope environment, and the profile structure is unreasonable, suggesting obviously a catastrophic event. In the limestone slump, rock block has strong hydrocarbon flavor, implying a good environment for oil generation and storage. Therefore, the restoration of the geographic environment of Upper Triassic Nanshuba Formation not only has very important significance for the development of sedimentology and stratigraphy but also is of remarkable practical importance in search for hydrocarbon source rocks.