INVESTIGATING THE CONIACIAN-SANTONIAN IN THE SONGLIAO BASIN AND POSSIBLE LINKS TO OCEANIC ANOXIC EVENT 3

The terrestrial response to carbon cycle perturbations during the Cretaceous is largely undetermined. However, the Songliao Basin (northeast China) preserves the record of a long-lived lake system allowing investigation of mid-latitude terrestrial responses to major ocean-climate perturbations, such as the Cretaceous Oceanic Anoxic Events (OAEs). A major challenge in evaluating synchronous environmental change between marine and terrestrial realms is chronostratigraphic uncertainty due to limited biostratigraphic control. Recently published astrochronologies and U-Pb age determinations reduce age uncertainty for the Late Cretaceous Qingshankou and Yaojia Formations, and permit preliminary interpretation of chemostratigraphic data from the Songliao Basin in a global context. In this study we investigate the terrestrial response and hydrologic evolution of the Songliao Basin system during the OAE 3 interval (~88 to 86.5 Ma) from the SK-1 (S) core by: (1) modeling oxygen isotope and trace element variations in ostracod valves; and (2) presenting a new δ¹³C record from lacustrine organic matter to compare to the existing ostracod δ¹³C record and marine δ¹³C records. The modeling approach uses a system of total differential equations describing variations in measured δ¹⁸O, Sr/Ca, and Mg/Ca as a function of temperature, runoff and evaporation for a terminally draining lake system. The ostracod valve δ¹³C record exhibits a broad ~+2.5 ‰ excursion, hypothesized to define OAE 3, followed by a sharp ~-4 ‰ decrease. During and after the putative OAE 3 we find two warming events of 3 to 5°C accompanied by sustained ~10% increase in lake size over the interval. Previous workers have suggested that OAE 3 was limited to the Western Hemisphere; however, our modeling and chemostratigraphic data suggest that OAE 3 is recorded in the Songliao Basin. Preliminary comparison of astronomically tuned δ¹³C curves from the Western Interior Basin and astronomically tuned OAE 3 ostracod δ¹³C data in the Songliao Basin indicates a 0.5 to 1 Myr lag in the peak δ¹³C excursion and warming in the Songliao Basin. Future work comparing existing ostracod and new organic matter δ¹³C records will provide further information linking Songliao Basin to the Northern Hemisphere response to the OAE 3 carbon cycle perturbation.