Source-to-sink analysis in an Eocene rifted lacustrine basin margin of western Shaleitian Uplift area, offshore Bohai Bay Basin, eastern China

摘要

During the Eocene, the western Shaleitian Uplift and its adjacent sags constituted a source-to-sink (S2S) system on an active lacustrine basin margin with a steeply dipping boundary fault. We integrated a range of data types with subsurface observations from the western offshore Bohai Bay Basin (OBBB) that allowed us to quantify the size and classification of catchment-fluvial segments, and analyze the sedimentary architecture and sediment fluxes of the proximal fan-delta system. We then discovered quantitative coupling relationships among the parameters of ancient source-to-sink segments. Results show that in the study area the bedrock of the western Shaleitian Uplift is composed of Proterozoic migmatized granites or granites. On the basis of paleogeomorphology reconstruction, we established classification standards for multi-scale catchment units, divided the provenance into four third-order catchment units, obtained quantitative parameters of the catchment-unit area (A), catchment relief (R), and total sediment discharge (Q(s) calculated by BQART model) and then confirmed the scales and distribution (cross-sectional area, S-cs) of sediment-transport pathways. Furthermore, we analyzed tectonic subsidence, sediment-dispersal patterns, and sediment fluxes of fan-delta systems (Q(f)) using seismic sedimentology in the third member of the Eocene Shahejie Formation (Es-3). Finally, we used quantitative, multivariate, statistical analysis of the parameters involved in the source-to-sink segments to (1) show the proportional range between total sediment fluxes of fan delta (Q(f)) and sediment discharge (Q(s)) from catchment (largest rate of Q(f)/Q(s) in the lower part of Es-3, smallest rate of Q(f)/Q(s) in the middle part of Es-3, and the range from 30% to 70%) and (2) arrange the mainly controlled parameters in terms of their importance (i.e., rate of tectonic subsidence, catchment area, catchment relief, and cross-sectional area of sediment-transport pathway are listed in order of importance). This study can provide an effective way of quantifying and ordering the parameters important in that controlling a complex ancient source-to-sink system, thus helping to achieve an understanding of the process of tectono-sedimentary evolution on a rifted, lacustrine-basin margin.