Tectono-sedimentary evolution of the Late Ediacaran to early Cambrian trough in central Sichuan Basin, China: New insights from 3D stratigraphic forward modelling

摘要

Several conceptual models have been proposed on the tectono-sedimentary evolution of the Late Ediacaran to early Cambrian trough in the central Sichuan Basin, China. However, none of them has adequately accounted for the regional stratigraphic architecture, palaeogeography and sedimentary facies revealed by recent petroleum exploration in a quantitative manner. This study presents the first attempt to simulate the tectono-sedimentary evolution of the trough in three dimensions using a process-based stratigraphic forward modelling approach. The model simulates the tectono-sedimentary evolution and indicates that (1) the trough started from a prototype of small sag during the Early Ediacaran Doushantuo stage; (2) it began to expand progressively during the Late Ediacaran Dengying stage, and (3) the trough was eventually filled up in the early Cambrian. The tectonosedimentary evolution differs in the southern and central-northern parts of the study area, and also inside and outside of the trough. The developing mechanism of the trough is due primarily to a combination of regional extension, differential subsidence and especially differential carbonate growth or deposition. Differential subsidence and sea level changes resulted in relatively deep water in the central and western parts of the study area during the Deng-2 and Deng-3 deposition. Slope to basinal facies were deposited with relatively slow rates. The depositional rate of the deep-water sediments in the area could not catch up with the rate of tectonic subsidence. This had led the central and western parts of the study area to finally become "starved" and developed into a deep trough with steep slopes developed on both flanks of the trough. In contrast, in the eastern part of the study area shallow water carbonates were persistently developed with relatively high growth or depositional rates, maintaining a shallow-water carbonate depositional setting. Platform facies were well developed throughout the Dengying stage, although the area experienced a similar tectonic evolution history as the central and western parts with a slower subsidence rate. The new tectono-sedimentary model may offer some new insights for future hydrocarbon exploration in the Sichuan Basin.