Integrated Provenance Analysis of Fluvial Sandstones From the Middle Jurassic Shaximiao Formation in Western Sichuan Depression, China

Abstract

Western Sichuan Depression is a hotspot for petroleum exploration in Sichuan analogous foreland basin. Previous researches have agreed that Longmen Mountains which located in the west were the primary siliciclastic sediment suppliers of Western Sichuan Depression in the middle Jurassic Shaximiao period. However, in recent years, studies at more accurate levels showed that an amount of fluvial channels in the depression were parallel to the strike of Longmen Mountains. The confusions of sedimentary source-to-sink directions and fluvial channels' distribution hindered the exploration of oil and gas. Based on field outcrops observation, heavy mineral analysis, sandstone composition analysis and seismic slices analysis, this study identified two main sedimentary source directions in the middle section of Western Sichuan Depression. Utilizing outcrops observation, cores description and logging data analysis, the study described the fluvial channels' distribution in different times. At the western margin of the depression, controlled by tectonic movements of the middle section of Longmen Mountains, source-to-sink direction was perpendicular to the strike of the mountains, from northwest to southeast, forming alluvial fans and fluvial deposits. Meanwhile, in the northeast, meandering river channels whose source area located in the northern section of Longmen Mountains, flowed from northeast to southwest, paralleled to the strike of the mountains. These long meandering channels were the result of continual converging of sediments in smaller scales from different directions. After the two trends gathered in the central region of the depression, the fluvial channels turned south to the center of subsidence, forming delta and lake deposits. Due to the unsynchronized tectonic movements of different sections of Longmen Mountains and the relatively arid climatic environment, the amount and transport distance of sediments on the two main source directions kept changing, which resulted in different features of the fluvial channels' distribution in different times of Shaximiao Period.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015