The trace elements and rare earth elements in sedimentary rocks are highly sensitive to changes in the water medium of the sedimentary environment,and are of great significance to the study of the paleoenvironment,sediment source properties and tectonic background.Previous studies on the element geochemistry of the Dongtai Depression,North Jiangsu Basin(Subei Basin),are relatively weak,and the use of element geochemical data to explain the paleoenvironment and provenance is blank to now.Methods:The paper takes 20 mudstone samples from the 3rd Member of the Paleocene Funing Formation in Dongtai Depression as the research object,carries on the determination of trace elements and rare earth elements,and analyzes their geochemical characteristics and the geological significance revealed.Results and Conclusions:①Sr,Sr/Cu,Rb/Sr,Lan/Ybn indicate dry and hot climates,and Li,Sr,Ni,Ga,Sr/Ba indicate freshwater—brackish water environment.V/(V+Ni),V/Cr,Ni/Co,U/Th, andδCe indicate oxidation—weakly reducing water environment.The overall water environment is mainly freshwater,occasionally saltwater is injected into the basin, and local is brackish water.②Co/Th—La/Sc,La/Th—Hf discriminant diagrams and rare earth elements distribution patterns reflect the original sedimentary materials from the upper crust.③La—Th—Sc,Th—Co—Zr/10,and Th—Sc—Zr/10 discrimination diagrams generally reflect the tectonic setting of continental island arcs and active continental margins.The comparison results between the characteristics of the trace elements and rare earth elements in the sandstones of different structural backgrounds listed by Bhatia and the samples in the study area also reached the same conclusion.