Stratigraphy of late Quaternary deposits in the mid-western North Yellow Sea

Abstract

The North Yellow Sea (NYS) is characterized by strong land-sea interaction and paleoenvironmental changes with sea-level fluctuations during the late Quaternary. However, large-time scale depositional stratigraphy in this area and its relationship with sea-level changes remain unresolved. Highresolution seismic profiles from NYS were subdivided into eleven seismic units (U1 to U11 in descending order). A 70.6-m-long borehole (DLC70-2) from localities on seismic profiles, analyzed for lithology, microfossil assemblages and geochronology, comprises eleven sedimentary units (D1 to D11 in descending order), which were clearly correlated with the eleven seismic units. These units constitute four distinctive sequences (SQ1 to SQ4 from top to bottom) bounded by three sequence boundaries (S3, S5 and S10) with obvious depositional hiatus, correlated with sea-level lowstands of MIS2, MIS4 and MIS6, respectively. The lowermost SQ4 below S10, has been identified only upper part of transgressive systems tract (TST) (D11, tidal flat facies in early MIS6). SQ3 overlying S10 consists of a set of lowstand systems tracts (LST) (D10, fluvial to incised-channel filling facies in late MIS6), TST and highstand systems tracts (HST) (D9 to D6, interactive deposits of neritic and littoral facies in MIS5 and early MIS4). SQ2 above S5 is composed of LST (D5, channel-filling facies in late MIS4) and TST (D4, littoral to estuary facies in early-middle MIS3), but lack of HST resulting from subaerial exposure and channel incising during the Last Glacial Maximum (LGM). The uppermost SQ1 overlying S3 comprises LST (D3, channel-filling to flooding plain or marsh facies in MIS2), Holocene TST (D2, littoral and tidal sand ridge facies) and HST (D1, neritic facies). The unusual depositional stratigraphy was largely dominated by sea-level fluctuations and the Bohai Strait topography. This study confirms that TSTs are relative continuous and widely distributed, while LSTs vary considerably in thickness and lateral extent since MIS6 in NYS.