Quantitative Study of the Early Cretaceous Paleoclimate in Beishan Area, Gansu Province: Based on C-O Isotope Analysis of Reptiles

In order to quantitatively study important paleoclimatic indicators such as paleotemperature and precipitation of early Cretaceous in Beishan area, Gansu Province, effective samples of dinosaurs' teeth, crocodiles' teeth and turtles' carapace were collected from the Lower Cretaceous in the Beishan area of the northeastern margin of the Jiuquan Basin. Bioapatite was extracted from tooth enamel and tortoiseshell samples by chemical experiments, the δ¹⁸O_P (‰, V-SMOW) of phosphate and the δ¹³C_C (‰, V-PDB) in apatite have been extracted and measured. The δ¹⁸O_P (‰, V-SMOW) of Iguanodon tooth enamel is between 14.627‰～22.137‰, the average value is 17.634‰; The δ¹⁸O_P (‰, V-SMOW) of ceratopsia tooth enamel is between 15.532‰～22.668‰, the average value is 18.225‰; The δ¹⁸O_P (‰, V-SMOW) of theropod tooth enamel is between 16.915‰～20.763‰, the average value is 18.925‰; The δ¹⁸O_P (‰, V-SMOW) of crocodiles' tooth enamel is 16.619‰; The δ¹⁸O_P (‰, V-SMOW) of turtles' carapace is between 15.106‰～16.627‰, the average value is 16.061‰. The δ¹³C_c (‰, V-PDB) of Iguanodon tooth enamel is between −6.477‰～−1.852‰, the average value is −5.274‰. The δ¹³C_c (‰, V-PDB) of ceratopsia tooth enamel is between −5.609‰～−2.495‰, the average value is −4.051‰. Based on oxygen isotope data, the annual average paleotemperature is calculated to be (19±3)℃, Based on carbon isotope data, the annual average precipitation is calculated to be (605 ± 151)mm/y, which indicates that the early Cretaceous in Jiuquan area had a warm temperate subtropical dry forest climate, mainly semi-arid to arid environment.