Depositional Environments And Sequence Stratigraphy Of The Late Cambrian, Luxi Block, China

The Luxi Block is a geological subdivision of North China Block, which is located in southwest of Shandong Province, China. The Cambrian-Ordovician strata in Luxi Block are very continuous and well exposed. The upper Cambrian which consists of the uppermost part of the Gushan Formation and the whole Chaomidian Formation, comprises mostly carbonate deposits. Thirteen sedimentary facies were divided according to grainsize, sedimentary structures, texture, bed geometry and fossil contents. These 13 facies were, again, grouped into 5 facies associations (FA), i.e., FA1, FA2, FA3, FA4, and FA5, which represents outer-ramp, deep mid-ramp, shallow mid-ramp, bioclastic/oolitic shoal, and lagoon environment, respectively. The depositional environment of the late Cambrian in Luxi Block was interpreted as the storm-dominated carbonate ramp which includes outer-, mid-, and inner-ramp.Two third-order sequences were divided in the background of one second-order megasequence, both of which consist of transgressive systems tract and highstand systems tract. Upward-coarsening meter-scale cycles were interpreted as the forth-order sequences. The cycles themselves resulted from the basinward progradation of sediments, whereas the repetition of the cycles was probably the result of periodic trangressive events. Since North China Block is a stable caratonic basin, the main control of the transgressive events might have been the result of the eustasy.