Tectono-stratigraphic evolution in the Paleocene Lishui Sag, East China Sea Shelf Basin

Abstract

The tectonic evolution of the Lishui Sag in the East China Sea Shelf Basin significantly influences its sequence stratigraphy. By integrating seismic reflections, well logs and core data, this study examines the quantitative activity of the Lingfeng fault, sequence framework and sequence architecture in the Lishui Sag. The Paleocene succession is divided into one second-order sequence (SSQ1), three third-order sequences (SQ1–SQ3) and nine system tracts, representing a complete syn-rift evolution consisting of initial syn-rift, rift climax and late syn-rift stages. The results indicate that the differential activity of the Lingfeng fault shapes the basin structure and controls the subsidence centre, leading to prominent variations in the spatial distribution and filling of the sequence stratigraphy during different tectonic stages. The initial syn-rift sequence (SQ1), characterised by a low activity of the segmented Lingfeng fault, is primarily found in isolated small sub-sags. The rift climax sequence (SQ2), with increasing displacement and longer segmented fault zones, exhibits a wedge-shaped filling pattern with substantial topographic elevation differences. The late syn-rift sequence (SQ3) shows a gradual decrease in tectonic activity and uniform filling, with all system tracts within the sequences fully developed. The sequence architecture of the hanging wall in the Lishui Sag can be classified into fault-scarp and fault-slope type, whereas the sequence architecture of the hanging wall dip-slope can be classified into sedimentary slope-break and faulted slope-break.