Sedimentological signatures and identification of Paleocene sedimentary facies in the Lishui Sag, East China Sea Shelf Basin

Abstract

The Lishui Sag is on the southwest margin of the East China Sea Shelf Basin (ECSSB), which is located on the continental shelf of the East China Sea. The analysis of sedimentological signatures is based on 217 m (712 ft) of Paleocene cores showing a wide variety of lithofacies, sedimentary structures, ichnological data, seismic data, and log data. Eight lithofacies, nine typical ichnofabrics, and four ichnofacies combined with petrological, geophysical, and bioturbation information were identified as the key sedimentary facies characteristics for identifying three sedimentary systems in the study area. Eleven sedimentological facies are present in the three sedimentary systems: foreshore, upper shoreface, lower to middle shoreface, offshore transition, proximal fan delta front, distal fan delta front, wave-dominated delta front sand bar, wave-dominated delta front sand sheet, interbar, tide-influenced distributary channel, and tide-influenced interdistributary bay facies. The three sedimentary systems that were identified are fan delta, wave-influenced delta, and tide facies. Fan delta deposits are present in the southwest and northeast of the sag, with subaqueous fan delta front deposits dominating, whereas farther seaward successions are characterized by distal fan delta front deposits that are intensely bioturbated. Wave-dominated deltaic deposits occur mostly in the western and middle parts, where fluvial discharge in the delta front and prodelta have been repeatedly reworked by waves and formed some isolated bars distributed perpendicular to the source; these deposits are sparsely to intensely bioturbated. Tide facies develop locally and have been identified as distributary channels and interdistributary bay facies.