Abstract
Sedimentary facies is the summation of all primary sedimentary features in a sedimentary unit, which is the product of sedimentation in a specific environment. It emphasizes the material performance of sediment formation conditions, including mineralogy, petrology, paleontology, geochemistry and geophysics. Therefore, it has unique sedimentary features in this environment. In this paper, the types and units of sedimentary facies which can reflect the basic characteristics and geometry of sedimentary system are established, and based on the comprehensive analysis of rock types, lithological assemblages, sedimentary structures, palaeontological assemblages and section structures, the sedimentary facies types of Xujiahe formation of Upper Triassic in the study area mainly include semi-arid flooded basin facies, delta facies, beach bar-lagoon system and lake facies, among which delta facies and beach bar-lagoon system are the main sedimentary facies types. Because sedimentary facies is the historical product of basin formation, evolution and extinction, it can not only reflect the formation conditions, temporal and spatial distribution and evolution law of related strata and rock types, but also be the basis for analyzing the nature and structural background of sedimentary basin. At the same time, the analysis of sedimentary facies is of great significance for understanding and analyzing the evolution history of basin and guiding the exploration and development of related oil and gas resources.
Highlights
Sichuan Basin is a multicycle sedimentary basin on the Yangtze block
In the middle and late late Late Triassic, Xichang, Panzhihua and Central Yunnan areas transformed into foreland basins, a large coal bearing sedimentary basin, the upper Yangtze sedimentary basin in the Late Triassic, is formed by connecting it with the "Sichuan Basin", covering an area of 10 × 104km2
During the sedimentary period of Xujiahe formation, Sichuan Basin was a large bay connected with the ocean only in the southwest
Summary
Sichuan Basin is a multicycle sedimentary basin on the Yangtze block. In the middle and late late Late Triassic, Xichang, Panzhihua and Central Yunnan areas transformed into foreland basins, a large coal bearing sedimentary basin, the upper Yangtze sedimentary basin in the Late Triassic, is formed by connecting it with the "Sichuan Basin", covering an area of 10 × 104km. The present "Sichuan Basin" is only a part of the upper Yangtze sedimentary basin in the Late Triassic. During the sedimentary period of Xujiahe formation, Sichuan Basin was a large bay connected with the ocean only in the southwest. During the sedimentary period of Xujiahe formation, the basin experienced three ups and downs, forming a sandwich structure between large open flow delta deposits and deep lake deposits. The second, fourth and sixth members of the Xujiahe formation are sandstone and conglomerate[1][2][3]
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