Buried channels under the northern Bohai Sea: Evidence for a great Bohai Paleolake during the late MIS3

Abstract

Buried channels are widespread on continental shelves and potentially record Quaternary glacial–interglacial environmental changes. The Bohai Sea, an epicontinental basin, is extraordinarily sensitive to such environmental changes, but the evolution of buried channels there remains poorly understood. Here, combined seismic and sedimentological data were used to investigate the evolution of buried channels in western Liaodong Bay, northern Bohai Sea. We identified over six sets of channels, up to 15 m thick and up to 4 km wide, at different horizons within a terrestrial bed formed during the late Marine Oxygen Isotope Stage (MIS) 3 between 35 and 30 kyr BP. Most of these channels are interpreted as incised valley systems of fluvial origin, with complex combinations of fill facies. They were truncated on their tops by transgressive ravinements, which formed during base-level rise. Our findings suggest that these incised valley systems formed and evolved over multiple cycles of incision/filling controlled by the alternation of subaerially exposed and drowned environments during the late MIS3, and the contemporaneous shoreline advanced and retreated repeatedly within our study area. Given that sea level during this period was ∼10–45 m lower than the buried channels in our study area, the evolution of the multiple channels appears to be dominated by lake level fluctuations rather than global eustasy. We hypothesize that during late MIS3, the Bohai Basin transformed into a great paleolake (>39000 km2) as a result of falling sea levels, separating it from the Pacific Ocean, which is also supported by the microfossils in a core collected from the more basinward location. Our stratigraphic evidence also suggests that lake level fluctuations were intensive and of different amplitudes (∼5 to >15 m), which is consistent with climate proxy records. These fluctuations in the paleolake level were presumably a response to and therefore could provide implications for reconstructing regional climate dynamics.