| Abstrakt: |
The most typical large-scale fan deltas developed in the Lower Triassic Baikouquan Formation on the western slope of Mahu Sag, Junggar Basin. Based on core observation, particle size, and composition analysis, combined with logging and drilling data, the sedimentary characteristics and evolution law of these large-scale lacustrine fan deltas were researched, and a sedimentary and evolutional model was established. The results showed that, during the depositional period of the Baikouquan formation, two large-scale fan deltas developed along the north slope of Mahu Sag, which had a distance of over 40 km. The fan delta facies can be divided into fan delta plain, fan delta front, and pro-delta subfacies, and further into 9 microfacies containing debris flow, braided channel, subaqueous debris flow, subaqueous distributary channel, etc.. These two fan deltas were gravelly, characterized by the interbeds of gravity-flow conglomerates, traction-flow conglomerates, and gravelly sandstone. The subaqueous distributary channels in the fan delta front environment reached nearly 20 km and always remained gravelly. Longitudinally, from the first member to the third member, these fan deltas retrograded continuously and showed a very clear sedimentary evolution law, during which the fan deltas were dominated by a fan delta plain environment during the deposition of the first member. However, they were dominated by a fan delta front environment during the deposition of the third member, which could still maintain large-scale fan deltas due to the long distances of gravelly subaqueous distributary channels. [ABSTRACT FROM AUTHOR] |
