Micropaleontology And Sedimentary Environment Of Upper Cretaceous In Laiyang Basin,Shandong Province

A lot of dinosaur fossils have been unearthed from the Red Cliff Group and King Kong Port Group of upper cretaceous Wang Group in Laiyang Basin,Shandong.However,previous studies focus on the micropaleontology of the lower cretaceous and there are relatively few studies on micropaleontology fossils.In the paper,according to the species identification of ostracod fossils,shield pore type,shield development situation,shape size of shell surface cellular,dominant species,water medium and preservation conditions of valve,sedimentary environment restoration was conducted on Red Cliff Group and King Kong Port Group by combining with geochemical characteristics including trace elements and rare earth elements determined by ICP-MS.Based on the research result,the dominant species of ostracoda were Mongolocypris porrecta Su,Mongolocypris distributa Stankeritch,Cyclocypris valida Yuan,Cypridea cavernosa Galeeva and Cypridea cuboida Ye:the dominant species of gastropod were Parhydrobia minina Pan,Hydrobia langxiensis Pan,Hydeobia anhuiensis Pan,Hydrobia datangensis Yu,Hydeobia sp1,Parateinostoma turriculatum Yu et Zhang,Gyraulus sp.1 and Gyraulus sp.3.In terms of geochemistry,all the values of SLREE/SHREE,(La/Yb)N,(Ce/Yb)N,(La/Sm)N and(Gd/Yb)N reflected that there were huge differences between light rare earth elements and heavy rare earth elements,and that it was continental sedimentary environment.Sr/Ba,B/Ga,B,Sr/Cu,V/Cr,Ni/Co,Eu/Eu*,Ce/Ce*and other environmental evaluation indexes showed that the samples in both groups were all oxidized environments;only a few samples in different indexes were oxygen-poor environments or hypoxic environments;the sedimentary facies were all freshwater continental sediments.By combing with them,the sediment of gastropod fossils was inverted.A new understanding about the Hydrobia and Parhydrobia,which were always considered as the representatives of brackified water environment by predecessors was obtained.Moreover,it was found that they could survive in fresh water,and that other Valvata,ypsobia,Gyraulus and Proauricula lived in the fresh water shallow lake,lakeside and river sedimentary environment.To sum up,Red Cliff Group in Laiyang Basin is river and lake(dominated by shallow lake)facies sedimentary environment,with hot and humid climate during sedimentary period,while King Kong Port Group has more humid climate during sedimentary period and lakes there are dominated by lakeside.