STABLE ISOTOPIC ANALYSIS OF VERTEBRATE FOSSILS FROM THE EARLY CRETACEOUS HEKOU GROUP, GANSU PROVINCE CHINA

By analyzing stable isotopes of carbon and oxygen from vertebrate fossils, terrestrial climate and environment will be constrained for the early Cretaceous (Valanginian-Albian) Hekou Group from Gansu Province, China. Tooth enamel from Lanzhousaurus magnidens will be analyzed for δ¹⁸O_p, δ¹⁸O_co3 and δ¹³C _co3. These values will be used to calculate δ¹³C of diet which will in turn be used to estimate mean annual precipitation (MAP). δ¹⁸O_p will be used to determine drinking water source. δ¹⁸O of turtle shells and crocodilian tooth will be analyzed to determine the oxygen isotopic composition of meteoric water (δ¹⁸O_w). Calculated δ¹⁸O_w will be used in conjunction with measured fish δ¹⁸O_p to give the mean annual water temperature fish were living in.

The average δ¹³C_CO3 and δ¹⁸O_CO3 values for the Lanzhousaurus second dentary tooth are -6.06±0.35‰ VPDB and 24.32±1.24‰ VSMOW respectively. Phosphate δ¹⁸O averages for the second dentary and second maxillary tooth are 19.89±1.64‰ and 21.10±1.15‰ respectively. Crocodile tooth δ¹⁸O_p = 12.3±0.2‰ VSMOW, while the turtle shell δ¹⁸O_p = 13.0±0.4‰, and the fish scale δ¹⁸O_p = 16.0±1.1‰. Calculated δ¹⁸O_w values using crocodile and turtle δ¹⁸O_p yield meteoric water values from -8.9‰ (crocodile) to -9.2‰ (turtle). Using these water values and δ¹⁸O_p-fish, calculated water temperature in which the fishes, turtles, and crocodiles lived in ranges between 4.1to 5.2± 2.6°C, implying very cold water, which could imply bottom dwelling fish or that diagenesic alteration to phosphate. Using d¹³C_co3, estimated d¹³C_atm= -5.8‰ and a paleolatitude of 25°N, average MAP was 295.7 mm/year, implying an arid/semi-arid environment.

This study will contribute toward a better understanding of the paleoenviroment, paleoecology, and paleoclimate of the early Cretaceous mid-latitude of Asia.