196 / 2019-06-13 20:21:24

The Study of Sedimentary Evolution Characteristics of Longshore Current-Dominated Lake Delta in the Second Member to the Middle Part of the Third Member of Paleogene Shahejie Formation in Gubei sub-sa

longshore current,delta,wavy sedimentary structures,sedimentary evolution,Gubei sub-sag

Longshore Currents gradually become the one of the most significant factors in terms of the sedimentary evolution of delta. Longshore Current-Dominated Lake Delta was developed in south nose-like structures in Gubei sub-sag of Zhanhua Sag during Es2 and the middle part of Es3. This paper aim to intensively analyse the sedimentary evolution characteristics with the research area making full use of the cores and granularity materials combining with the logging data and seismic methods. The results show that the research delta mainly developed in the south ramps of the lake, while the delta front subfacies became the main region of sand bodies reservoir facies with limited prodelta. According to the observation and analysis of cores as well as grain size characteristics, massive amounts of wavy sedimentary structures with some coastal sand dams were confirmed in delta front subfacies sandy body, which has migrated laterally by virtue of intensive hydrodynamic condition. The logging data and the development of sedimentary system also illustrate the crucial effects from longshore currents. Longshore current-dominated delta in study area features the asymmetry shape and the front sand dam. During the middle part of Es3 to Es2, the delta almost ceased to extend towards lake basin due to the longshore currents in spite of the sufficient source supply. In conclusion, longshore currents serve as the vital factor in terms of the evolution of delta sand body and delta facies. The results of this paper will be conducive to guide the exploration and essential to the paleogeomorphy and paleowind restoration.