The Paleoclimate Evolution In Northern Liaodong Bay Since Late Pleistocene To Early Holocene

Northern Liaodong Bay is located in the northern part of the Bohai Sea.It has been greatly influenced by land-sea interaction since late Quaternary,and has experienced multiple climate evolutions and coastal changes,which make it one of the most climate evolution sensitive regions.Study on sedimentary environment evolution of Northern Liaodong Bay will help develop a better understanding on the region's geological evolution history from Late Pleistocene to Early Holocene,and help reestablish the paleoclimatic evolution during this history,thus to provide scientific proofs for analyzing and predicting climate changes in the future.Based on clay mineral tests for LZK06 hole sediments,grain size analysis and optical stimulated luminescence dating,framework of chronological age for Northern Liaodong Bay from Late Pleistocene to Early Holocene is established,and sedimentary environment evolution is investigated.Besides,through paleoclimatic alternative indicators such as illite crystallinity and characteristics of clay mineral assemblages etc.,comparisons of responses to climate changes for different alternative indicators are made,and process of paleoclimatic evolution for Northern Liaodong Bay from Late Pleistocene to Early Holocene is reestablished.Below are some conclusions from this study:1.Chronological framework for LZK06 hole is established based on comparisons between stratum and original age from optically stimulated luminescence.This study also calculates the rate of sedimentation,and finds that the rate of sedimentation can be separated into five stages.2.Based on grain size characteristic and lithology of LZK06 hole core,and combined with research in published literatures,this study separates the sample into four sedimentary units,that is,U1 land facies(river facies),U2 land facies(lake facies),U3 land facies(lake facies)and U4 marine facies(Intertidal zone facies).The sequence of sedimentary environment evolution is river facies,lake facies,shallow sea facies.3.Based on X-ray diffraction,this study finds that clay minerals in this region are mainly montmorillonite and illite,among them montmorillonite content is the highest,and then illite;chlorite and kaolinite contents are relatively low.Clay mineral assemblages are montmorillonite—illite—chlorite—kaolinite.4.Ratios of clay mineral assemblages and crystallinity of illite can both be paleoclimatic alternative indicators and reflect the paleoclimate.Based on analysis of climate change trend indicated by characteristics of clay mineral assemblages and illite crystallinity,the paleoclimatic evolution for this sample can be separated into three stages: the first stage(19.0-17.4m)is second sub-interglacial of wurm glacial stage,the second stage(17.4-15.8m)is the pleniglacial,and the third stage(15.8-13.7m)is the last deglacial.5.The paleoclimatic environment evolution process of Northern Liaodong Bay from Late Pleistocene to Early Holocene fit well with processes in typical regions showed in published literatures.Among them the two cold events in second stage correspond to H2 and H1 event,the third stage has five temperature and humidity changing stages,which correspond to Oldest Dryas,Bolling,Older Dryas,Allerod and Younger Dryas.