PALAEOGEOGRAPHIC ENVIRONMENTAL EVOLUTION IN THE HUANGHE RIVER ESTUARY SINCE LATE PLEISTOCENE
晚更新世末期以来黄河口古地理环境的演变*

The palaeogeographic environmental evolution are studied and discussed by analyzing the CB20A Core obtained in the offshore area of the ancient Huanghe River estuary,including grain size analysis,detrital mineral analysis,palaeontological researches of foraminifera,ostracoda,lamellibranchia,gastropoda,pollen and spores,and megafossil plants,and ~(14)C dating as well.The palaeogeographic environmental evolution from the Late Pleistocene up to now can be divided mainly into 6 stages,i.e.the early stage of the last glaciation,the interglacial stage of the last glaciation,the late stage of the last glaciation,the early stage of the postglacial age,the middle stage of the postglacial age,and the late stage of the postglacial age.In those stages the palaeoclimates alternated along with the risings and fallings of the sea level,which are corresponding respectively to the shore-line invading and retreating.The landscape features also changedaccordingly from sea to land.In addition to the above 6 major stages,some short-term sea level risings or fallings are also observed.For example,the general climate was cold and the sea level fell during the early stage of the last glaciation.However a marine deposit sublayer indicating a warmer period has been found in the sediments corresponding to that stage,which reflects a sea level rising.Furthermore,although on the whole the climate was warm in the interglacial stage of the last glaciation,fossils evidence indicates a climate variation for that stage as follows:the lower part of the sediments was deposited in a sea marsh environment of a colder climate with a lower sea level;the middle layer of a warmer climate in a shallow-sea environment;and the upper layer in a tidal-flat environment with the lowest sea level.A similar climatic variation and sea level fluctuation existed also in the postglacial age.The data of the variations of palaeoclimate,sea level and shoreline obtained from the CB20A Core are helpful for studying palaeogeographic environmental evolution history of the estuary.This study can also be used as a scientific foundation for oil and gas exploitation in this area.