232 / 2022-03-22 15:35:19

Distributive Fluvial Systems in Permian-Triassic Mahu Depression, Junggar Basin: their recognition, configuration and evolution

distributive fluvial system, fluvial fan, sedimentary model, depositional system, Mahu depression, Junggar

The distributive fluvial system (DFS) means a radial channel and floodplain system which enters the sedimentary basin from an apex, there are several types of DFS developed in the Permian and Triassic stratigraphy of Mahu sag, Junggar basin.

This Study described the DFS and their evolution in Permian-Triassic Mahu Depression using the DFS theory and built the DFS models based core, logging and seismic interpretation. Quantitative scales of DFSs are calculated from the facies map and have been used for searching the transition of DFS in these stratigraphy. The results show that the Jiamuhe Formation in Mahu depression is characterized by the coexistence of volcanic rocks, pyroclastic rocks and clastic rocks, mainly developing small DFS as alluvial fan and fan delta depositional system. DFS in Fengcheng Formation, Xiazijie formation and Wuerhe formation are mainly of fluvial fan and alluvial fan with great variability due to lake level vibration. The Upper Wuerhe formation and Baikouquan formation dominated by coarse gravelly fluvial fan conglomerate, while the Karamay and Baijiantan formations developed sandy megafan and fluvial fan depositional system. With the basin’s tectonics transferred from pressure-flexure to flexure-depression stage, the DFSs changed gradually from smaller alluvial fan to larger fluvial fan and megafan, or from the fan delta to braided river delta and meandering river delta in their terminal facies.