The Paleoenvironmental Significance Of Characteristic Of Element Geochemistry In Sediments

Xihu sag is one of the most composing cell of ZheDong depression in the shief basin of East China Sea, whose characteristic is huge sediment in Eocene and Miocene.In the end of Eocene YuQuan tectonic movement ended the faulting period and uplifted Xihu sag to be exposed to denudation.At the beginning of Oligocene Xihu sag turned to depression period and deposit mostly by terrestrial stratum, meanwhile the center of sediment transfer to the Westnorth. LongJing tectonic movement,which occurred in the end of Miocene,made this area suffer extrusion and form anticlinal structure and reverse fault.Xihu sag suffer erosion which the Northern far more than the sourthern.On the basis of systemically analysed the evolvement of construction and the rule of distribution laws under the sequence stratigraphy , especially focused on the characteristic of hydrocarbon source rock in two wells, we discussed the situation of hydrocarbon source rock's development in Hugang Formation of Oligocene and Pinghu Formation of Eocene as well as the trait of organic matter abundance and style during the different sedimentary facies environment. Moreover we pointed out that organic matter abundance is controlled by sedimentary environment and redox conditions.Our research focused on the vertical variation of trace element in the Palaeogene sediment of some wells in Xihu sag,such as the change of boron,gallium,strotium's content and the corresponding relationship with sedimentary facies. The research showed that trace element gallium,strotium,barium can be used distinguish the river—delta facies environment and boron can indicate lake basin facies environment in Xihu sag. Ancording to exceptional change of boron content ,which appeared in the Huagang Formation of correlational well's Palaeogene sediment ,we identify out the biggest Sea-slooding during the period of Huagang Formation sediment.