Advances in Earth Science
Xiangdong LI. Current Situation of Combined-flow Deposition for Sedimentary Characteristic Series and Its Theory Frame Work[J]. Advances in Earth Science, 2021, 36(4): 375-389.
Combined flows belong to the interaction between different flows， common with both a unidirectional and an oscillatory component， which were first investigated in flume experiments associated with sedimentology. Deposits of combined flows have great significance in the study of sedimentology in a complex hydrodynamic system， which includes the main evidence for the interaction between different sedimentary flows in rocks. Here we review the deposits of combined-flow from three sections based on present literatures： bed configurations and series of vertical sequences； sedimentary effects of flow and series of cross-bedding structures； and sole marks on muddy substrate. The characteristics of combined-flow deposits are controlled by velocities of unidirectional and oscillatory flow， therefore both the bed configurations and related laminated structures have a continuous variation from symmetric to asymmetric form， and become more asymmetric as the unidirectional flow velocity increases. The vertical sequence is between the vertical stratification produced by suspension of purely unidirectional flow and oscillatory flow， and Bouma sequence and tempestite sequence are their end-member cases， respectively. Although the combined-flow deposits are mainly composed of silt and fine-grained sand， some special granular fabric is produced in coarser particles such as plate-like intraclasts. Different spectrum of sole surfaces on muddy substrate is also formed among bed side sedimentary structures because of the variable velocities （including magnitude and superposition direction） of unidirectional and oscillatory flows. Therefore， in the future research area of combined-flow deposits， sedimentary processes research of the interaction of unidirectional and oscillatory flows should be paid much attention， rather than sedimentary mode research for traditional sedimentology based on the various sedimentary environment.