Pollen Assemblage and Its Paleo-environmental Significance of JXC-1 Borehole in Northern Liaodong Bay,Bohai Sea
[Objective]In order to better understand the paleo-environment of Liaodong Bay since late Early Pleistocene,the palynology study of JXC-1 borehole was carried out.[Method]A total of 159 samples were selected from JXC-1 borehole sedimentary strata for pollen identification.Combined with the dating data,foraminifera abundance and grain size changes of the samples,pollen composition and content changes were analyzed.[Result]9 pollen zones were identified and the borehole pollen assemblages can reflect the vegetation features of the Liaodong Bay continental margin,in which the herbaceous pollen was absolutely dominant(above 60%)in the whole hole and was super representative,while the woody pollen was lowly representative.[Conclusion]Compared with the climate change process of glacial period and interglacial period,the characteristics of pollen assemblages since the late Early Pleistocene indicate that the paleoclimate in the study area alternated between cold dry and warm wet.Three transgressions have occurred in Liaodong Bay since the end of the Middle Pleistocene,which is consistent with the paleo-climate change indicated by pollen assemblages.In the MIS7 and MIS5,the proportion of broad-leaved tree species and Artemisia was relatively high,the foraminifera was also high,and the paleo-climate was warm,indicating that the study area was a shallow or coastal environment with relatively stable sedimentary dynamics.However,in the MIS6 and MIS4,the pollen concentration was very low and the paleo-climate was cold,indicating the terrestrial environment such as coastal lakes or swamps had relatively complex sedimentary dynamics.From the MIS3 to the Holocene(MIS1),the paleo-climate changed from cool and humid to warm and humid.The pollen assemblage in Holocene indicates the trend of temperature:first rising and then falling,which was obviously in response to sea level change.
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