LAUSR

Abstract Several conceptual models have been proposed on the tectono-sedimentary evolution of the Late Sinian to early Cambrian “aulacogen” in the central Sichuan Basin, China. However, none of them can adequately reconstruct 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 aulacogen in three dimensions using a stratigraphic forward modelling approach. Our model considers various geological processes including: changes of accommodation space, growth and erosion of carbonates, transportation and deposition of clastics, interactions between carbonates and clastics, and gravity flow deposition etc. The simulation has reconstructed the tectono-sedimentary evolution and indicates that: (1) the aulacogen started from a prototype small sag during the deposition of the Sinian Doushantuo Formation (Z1ds); (2) it began to expand progressively during the deposition of the Sinian Dengying Formation (Deng-2 and Deng-3 to Deng-4), and (3) the aulacogen was eventually filled up during the early Cambrian. The tectono-sedimentary evolution differs in the southern and central-northern parts of the study area, and also inside and outside of the aulacogen. The developing mechanism of the aulacogen 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 Sinian Deng-2 and Deng-3 periods. Slope to basinal facies were deposited with relatively slow rates. The depositional rate of the deep water sediments in the aulacogen could not catch up with the rate of tectonic subsidence. This had led the aulacogen to finally become “starved” and increasingly deepened with steep slopes developed on both flanks. In contrast, in the eastern part of the study area shallow water carbonates are persistently developed with relatively high growth or depositional rates, maintaining a shallow water depositional setting. Platform facies were well developed throughout the entire Dengying Formation depositional period, although the area experienced a similar tectonic evolution history as the central and western parts with a slower subsidence rate.