Delta development and channel incision during marine isotope stages 3 and 2 in the western South Yellow Sea

Approximately 4100km of high-resolution seismic profiles recently obtained from the western South Yellow Sea were subdivided into seven seismic units by six major seismic surfaces. Three sediment cores between 60 and 71m in length, obtained from localities on the seismic profile lines, were analyzed for sedimentary characteristics, clay mineral components, and benthic foraminiferal and ostracod assemblages and were also dated by AMS 14C and optically stimulated luminescence to document the environmental history of the region. Stratigraphic units in the cores were confidently correlated with seismic units in the profiles. Stratigraphic correlation among these three cores and the previous well-studied core QC 2 was facilitated by the cold-water deposits in marine isotope stage (MIS) 5. The three cores document the sedimentary sequence during the period from MIS 6 up to MIS 1. Strata formation and sedimentary environment changes since MIS 5 are strongly controlled by sea-level fluctuations. Most of the successions were formed in MIS 5, MIS 3, and MIS 1 with major erosions in MIS 4 and MIS 2. Particularly our data revealed the presence of a large delta active during MIS 3 (likely from the early stage of MIS 3 to about 40calkyr BP) that was subsequently affected by channel incision. The delta succession and incised-channel fills have a high concentration of smectite in their clay mineral components, suggesting that the paleo-Yellow River was the main contributor to the delta development and channel incision. The delta sequence has a coarsening-upward trend and consists of two seismic facies. The upper facies shows lateral alternations of chaotic and oblique or very low-angle reflectors, which correspond to sandy (proximal) delta-front and delta-plain facies, and the lower facies is characterized by seaward-dipping clinoforms, which correspond to muddy (distal) delta-front and prodelta facies. The top surface of the delta inclines very gently seaward, consistent with a deltaic development associated with the sea-level fall in MIS 3. The incised-channel system consists of two main channels with multiple tributaries in a dendritic pattern. The incised-channel fills begin with fluvial and then estuarine sediments, which are truncated by a transgressive ravinement surface and capped by transgressive deposits. The main incision channels have a terraced cross-sectional morphology, which is interpreted to reflect multiple episodes of sea-level fall during incision, presumably from the late MIS 3 to the Last Glacial Maximum.