| The impact of global change on human and society more and more obviously,makes people study on global change is more and more urgent,and so that the past study on climatic and environmental changes is one of the core contents of global change research.The Q uaternary is the most recent geological history of mankind,and it can provide a reliable basis for the prediction of future climate and environmental evolution by studying the changes of Quaternary paleoclimate.C hina loess paleosol records the history information of the paleoclimate and palaeoenvironment evolution in East Asia since the late Cenozoic.Compared with the Loess Plateau loess,the coastal loess in Shandong Province of eastern China has recorded the climatic and environmental cha nges and sea level changes on the orbital scale due to its special geographical location.Therefore,the study of loess in this area has special value for revealing the evolution of paleoclimate and paleoenvironment in the eastern coastal areas of C hina.In this study,we choose the BZ hole section of Beizhuang Village on Daheishan island which is located on the west of Miaodao islands as the research object.Based on the analysis of sedimentology and clay mineralogy and OSL methods to discuss the history o f environmental evolution in this area.Through this study,we get the following conclusions:(1)Four OSL samples at 50 cm,100 cm,150 cm and 200 cm deep were collected,the OSL age at the 50 cm depth on BZ hole section is 26.23 ± 4.92 ka belongs to the Late Pleistocene.Thus,Holocene loess and MIS 2 stage loess are not available on the very top of BZ hole section,which may be eroded or not deposited after the deposition.Through the analysis with other two loess sections in the same area(Xianjingyuan section and Miaodao stratigraphical section),we conclude that BZ hole loess mainly accumulated during the last interglacial time.Based on the comparison of OSL ages and the inference of sedimentary period,the strata of BZ hole section on Daheishan Island that can be determined three layer.Thus,0-50 cm on the section is a modern farming layer,top layer of 50~380 cm is paleosol corresponding to L1S1;layer 380 ~ 1220 cm is loess corresponding to L1L2;layer 1220 ~ 1610 cm is another paleosol corresponding to S1.(2)Through the analysis of grain size frequency curve,probability cumulative curve and grain size composition,it is concluded that BZ hole loess is a typical eolian sediment.The particle size frequency curve of BZ hole loess is distributed in three peaks.Compared with Luochuan loess,the lowest peak of the profile frequency distribution curve of BZ hole section coincides with the secondary peak of Luochuan loess.However,the BZ hole loess in the silt area more than a secondary peak,and than the Luochuan loess the highest peak right shift.The results showed that BZ hole loess particle is thicker than the Luochuan loess,at the same time,it showed that there are obvious differences between the two loess profiles in material source and formation environment.The composition of BZ hole loess grain size is dominated by silt,the average content of 60.1%,followed by the sand,the average value is 21.4%.Compared with Shandong and Luochuan loess,the mean grain size of BZ loess is coarse.Compared with the same region of the Nanchangshan Island loess,Tuoji Island loess and Beihuangcheng Island loess,the sand content in the grain size composition gradually increased from south to north,this suggests that the loess in the area may have nearby source material from the north direction.(3)The characteristics of grain size,magnetic susceptibility,chromaticity and clay mineral assemblage of BZ hole loess are analyzed and compared it with loess of Loess Plateau,the magnetic susceptibility of BZ hole loess is lower than that of Loess Plateau,and the clay mineral assemblage is different from the Loess Plateau,it is indicated that the BZ hole loess is different from the Loess Plateau loess in material source and sedimentary environment.Comprehensive analysis characteristics of the climatic indicators,BZ hole loess profile in the accumulation process experienced warm and humid to dry and then to cold and humid environment evolution.Layer 1610 ~ 1220 cm is S1 paleosol which is corresponding to MIS 5 stage,the climate is warm and humid,the weathering and soil forming effect was stronger,the paleosol layer is developing.Layer 1220 ~ 380 cm is L1L2 loess which is corresponding to MIS 4 stage,the climate is relatively dry and cold,for the development of loess layer.Layer 380 ~ 0 cm is L1S1 paleosol corresponding to MIS 3 stage,the climate is more humid and the pale soil layer is more developed.The profile accumulation process was accompanied by sea-level rise and decline,indicating the profile climate change and global climate fluctuations have good consistency,but that different sedimentary characteristics and provenance indicating that in the large climate environment background is basically the same,there are different in regional environment. |
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