Taxonomy And Biostratigraphy Of Limnic Ostracoda(Crustacea) From The Nenjiang And Sifangtai Formations,Santonian-Campanian,Upper Cretaceous,Songliao Basin,Ne China

The typical "greenhouse climate" in Cretaceous provides a good record for earth's climate system operation and change under the conditions of greenhouse climate.So far,the understanding of Cretaceous terrestrial climatic change is limited(especially the Late Cretaceous),despite oceanic responds to Cretaceous climate change is relatively mature.China deposite massive lacustrine sediments throughout the Cretaceous,which contributes to Cretaceous terrestrial research.As one of the most complete and large-scale records of Cretaceous lacustrine sediments,preserving abundant ostracods fossil records,Songliao Basin is a perfect location for study Cretaceous climate and biology on the continent.The work materials collected from ZKY2-1 Well,southwest Songliao Basin,which is characterized by shallow burial and well-preserved fossils,are valuable for research.The sequences are composed of Nenjiang and Sifangtai Formation,yielding abundant ostracod records,which provide unique materials for the study of ostracods in the Late Cretaceous.The overestimation of diversity and endemicity of ostracods in previous works bring a few disputes and inaccuracies to ostracods' taxonomy and biostratigraphy.In current work,as a result of the abundant ostracod fossils from ZKY2-1 Well,some achievements as following:1)14 species belonging to 8 genus were recorded in detail: Scabriculocypris trapezoids,Ilyocyprimorpha netchaevae,Cypridea squalida,C.acclinia,C.cavernosa,C.ardua,C.lepida,Candona disjuncta,Lycopterocypris profunda,Mongolocypris magna,M.tera,Talicypridea obliquecostae,T.reticulata and Renicypris? Renalata.Among them,5 species are emended.2)the first discussion on sexual dimorphism in Cypridea acclinia and Candona disjuncta;the first study on the ontogeny of Ilyocyprimorpha netchaevae.3)On the basis of taxonomy,we emend 3 ostracod assemblages : 1.Lycopterocypris profunda-Talicypridea reticulata-Renicypris? renalata,2.Ilyocyprimorpha netchaevae-Scabriculocypris trapezoids,and 3.Mongolocypris magna-Cypridea ardua-Cypridea acclinia.4)The apparent transition of the composition between the Nenjiang and Sifangtai formations ostracod fauna,is consistent with an abrupt change in the paleoenvironment of Sonliao Basin during the lower Santonian-upper Campanian from deep lacustrine to fluvial and shallow lacustrine.