CARBON ISOTOPE CHEMOSTRATIGRAPHY FROM MID-CRETACEOUS LACUSTRINE IN NW CHINA

Carbon isotope chemostratigraphy can be an efficient method to correlate continental and marine stratigraphic sections assuming geologically synchronous signals between these reservoirs. Carbon isotope excursions in the Cretaceous Period are associated with Oceanic Anoxic Events especially in Aptian-Albian These excursions were likely a result of carbon cycle perturbations and may have resulted in climate changes. The purpose of this project is to develop a carbon isotope profile for the Xinminpu Group at the Hanxia locality in Gansu province of China.

Two 30 meter sections of mudstones, shales, sandstones and conglomerates were collected approximately every 25 centimeters. These samples were crushed into powder form using mortar and pestles, decarbonated in 3M HCl, weighed to calculate the percentage of carbonate lost, crushed again, weighed in tin capsules, and combusted in a Costech 4010 Elemental Analyzer, which is connected to a Thermofinnigan Delta +XP isotope ratio mass spectrometer. Samples were corrected using in house and international standards and reported relative to VPDB.

The average d¹³C values from the Hanxia locality is -23.6 ‰ with a minimum of -26.1 ‰ and a maximum of -21.6 ‰. The carbon isotope curve is preliminarily correlated to the lower to middle Aptian, specifically carbon isotope segments C7 to C10. Additional analyses will be used to confirm or reject this hypothesis. If confirmed, these strata at the Hanxia locality may help elucidate potential climate change associated with these carbon isotope excursions.