CHARACTERISTICS AND GEOLOGIC SIGNIFICANCE OF CALCAREOUS NANOFOSSILS IN SEDIMENTS
OF TERRESTRIAL SALINIZED LAKES
Sun Zhencheng Yang Gelian Qiao Zizhen Yang Fan Li Dongming Jing Minchang
1College of Resources and Information, University of Petroleum,Beijing 100220
2Research Institute of Petroleum Exploration and Development of Qinghai Petroleum Corporation, Duihuang
Ten genera of calcareous nanofossils (Coccolithus,Reticulofenestra, Cyclicargolithus, Quadrum,Discoaster,Gephyrocapsa,Calcidiscus, Umbilicasphaera, Cotonocyclus, Watznaueria) have been found in 38 samples collected from 15 locations in Cenozoic—Recent sediments of terrestrial salinized lakes in northwest and northeast China by analysing 433 samples from 36 places. It was found that most of them were sedentary deposits and a few of them resediment ones. Hence, it is not appropriate to regard all the appearance of calcareous nanofossils as the evidence of marine faces or transgression. More evidences are needed. Characteristics of calcareous nanofossils in sediments of salinized lakes are as follows: low abundance and less smalquantity; low species and generic diversity; coexistence with terrestrial saline hydrobioses. Calcareous nanofossils found in Quaternary and present terrestrial salinized lakes are generally the common kinds in modern oceans. Reticulofenestra bisecta, which is an index fossil of marine faces in Middle Eocene—Oligocene, was found in core of Qixin Well 1 in upper part of Lower Ganchaigou formation (Middle –Upper Eocene) in Qigequan structure in Qaidm Basin. Some progresses have been achieved in correlation between marine and terrestrial strata, but it is far from correlation among series units.
