Sedimentary Stratigraphic Structure And Provenance Environmental Evolution In The North Yellow Sea During The Late Quaternary

The North Yellow Sea (NYS) can be regarded as a typical key area for studyingsedimentary stratigraphy and paleoenvironment during the late Quaternary because of itsunique Geographic, geological, hydrologic bankgrounds. The research of sedimentarystratigraphic framework and environmental evolution in NYS during the late Quaternary notonly contributes to understanding the geological evolutionary history in the shelf area of theeastern China Seas and enriching the regional response theory to global change, but alsoprovides scientific evidences for revealing the significance of small-medium size rivers andcoastal mud areas to land-sea interaction at the marginal sea and understanding themechanism of land-sea interaction in the study area.In this paper, throuth a comparison between4916km high-resolution subbottomseismic profiles, and sedimentary characteristics of the core DLC70-2with the longest lengthand highest recovery rate by far in NYS, the stratigraphic framework in the study area sincethe late Quaternary (MIS6) will be precisely disclosed. In addition, by a geochemical analysisof rare earth element (REE), which will be compared with the sedimentary characteristics ofcore DLC70-2from the central of NYS and three piston cores in the Liaodong Peninsulasoutheast coastal mud area, the provenance environmental evolution in the midwest area ofNYS and their responses to the global sea-level fluctuations since the Late Quaternary will berevealed.High-resolution seismic profiles are divided into ten major regionally continuous todiscontinuous seismic bounding surfaces, which are designated T0、T1、T2、T3、T4、T5、T6、T7、T8、T9in descending stratigraphic order. Meanwhile, a total of ten seismic sequenceunits (SU11、SU12、SU2、SU3、SU41、SU42、SU51、SU52、SU53、SU6) are identified amongthe seismic surfaces. The contrastive analysis between sedimentary characteristics of coreDLC70-2(compared with previous cores NYS-101and NYS-102) and core-passing seismicprofile in NYS shows that stratigraphic units in the cores are confidently correlated withseismic units in the profiles, that is ten stratigraphic units (DU11、DU12、DU2、DU3、DU41、DU42、DU51、DU52、DU53、DU6) in the study area during late Quaternary correspond to tenseismic units (SU11、SU12、SU2、SU3、SU41、SU42、SU51、SU52、SU53、SU6), respectively.Strata formation and sedimentary sedimentary environment changes in the study area since MIS6are strongly controlled by sea-level fluctuations. There exists three majorsedimentary cycles. Most of the relative continuous successions were formed in threehighstand sea-level stages of MIS5to the early period of MIS4, the early-middle period ofMIS3and MIS1, which correspond to coastal-shallow sea facies, coastal-estuary facies,coastal-shallow sea facies respectively and regarded as Transgressive System Tract andHighstand System Tract. Major erosions and hiatuses happened in three lowstand sea-levelstages of MIS6, the late period of MIS4, MIS2, corresponding to fluvial-estuary filling facies,estuary filling facies, estuary filling and floodplains facies respectively and regarded as thesame period deposit with Lowstand System Tract.The vertical variations of REE compositions in core DLC70-2are relativelycomplicated and formed in different stages. The REE complication is mainly controlled bysource rocks and influenced by granularity. Furthermore, Fe-Mn oxides, Chemical Weatheringalso exert some influence on the REE composition. However, the effects of biogenouscarbonate and heavy minerals are not significant. The result of provenance discriminationexhibits that the sediments deposited at the stages of the late period of MIS6(69.23-60.72m)and the late period of MIS4(35.00-38.90m) are mainly derived from Yalu River and DayangRiver, the sediments at the stages of the late period of MIS5(60.72-48.90m) and since thelate period of MIS4(35.00-0m) mainly deriving from Yellow River, whereas the sediments atthe stages of the middle period of MIS6(70.60-69.23m) and the middle-late period of MIS5(38.90-48.90m) are jointly influenced by Yellow River, Yalu River and Dayang River, theeffects of Yangtze River and Korean Peninsula rivers being not clear. The sea-level fluctuationand estuary change of Yellow River are regarded as a dominated factor of provenancevariations and sedimentary fluxes in the study area since late Quaternary.AMS14C age data together with lithology analysis suggest that the hard clay in thecentral area of NYS was formed about12563to10330cal yr BP, in the similar period withthe peat layer of the NYS deposited in different sedimentary environment, which is highlycoincident with the age of the Younger Dryas event that was the most significant cold climaticevent during the last deglacial warming and occurred between12.9~11.6ka. The coincidenceindicates that the formation of hard clay in the central NYS possibly related to the YoungerDryas event.The high abundance of freshwater algae (Concentricystis and Pediastrum) andTypha indicates that the hard clay is a freshwater deposit. The presence ofChenopodiaceae-Artemisia in the hard clay indicates that the study area was occasionally affected by seawater during the formation of hard clay. Dinoflagellate occurs in increasingabundance in the upper and lower section of hard clay suggesting the study area had growingmarine influence during the early and late stage of the formation of hard clay. The reciprocalvariation law between freshwater algae and land-flora shows that the hard clay was formed inseveral stages. The sporo-pollen assemblages (Artemisia-Typha-Pinus-Poaceae-Monoletesand Pinus-Artemisia-Poaceae-Monoletes-Typha) from hard clay show that the study area wasin a cold and humid environment during the formation of hard clay, and characterized bymeadow present in the riverine wetlands with coniferous and broadleaved mixed forest.High-resolution shallow sub-bottom profiles reveal a prominent moundy low-anglebidirectional (landward and seaward) progradational mud clinoform deposit distributedalongshore off the southeast coast of Liaodong Peninsula, which is up to14m in thicknessand thins seaward and landward to less than2m. The clinoform deposit occurs about180to300km away from the Yalu River mouth between the northeast of the Dalian Bay andsouthwest of the Changshan Islands at a depth of20–40m. The mud deposit represents aHolocene Highstand System Tract sequence formed after the sea-level highstand at6.5ka andis mainly derived from Yalu River and Dayang River. The resuspension, transportation anddeposition of the sediments off the southeast coastal area of Liaodong Peninsula is mostlycontrolled by marine processes, such as tides, waves and the LCC.The paleoenvironment evolution in the Liaodong Peninsula coastal mud area sinceLGM is largely dominated by sea-level changes and sediment supply. The peat layer, formedabout10383to10396cal yr BP, is different from the peat layer related to the Younger Dryasevent in NYS, which results from a few stagnated periods of sea level existed betweenMWP-1B event and MWP-1C event.