Climate changes as recorded in stable carbon isotopic compositions of the Late Jurassic marine sedimentary succession in the Qiangtang Basin, Northern Tibet

Abstract

The Jurassic oceanographic and climatic evolution is considered to be related to the breakup of Pangaea. As a crucial component of the carbon cycle, atmospheric CO2 concentration (pCO2) has been postulated as a main driver for climate change during the Jurassic, and concomitant changes in paleo-oceanographic conditions occurred as a result. In this study, we present a high-resolution organic matter (kerogen) carbon isotope dataset (δ13Ckerogen) from Upper Jurassic marine sedimentary rocks in the Qiangtang Basin, Tibet. The δ13Ckerogen result contains a genuine record concerning the response of the eastern Tethys to exogenic carbon cycle perturbations in both marine and atmospheric reservoirs and is also consistent with the high-resolution bulk carbonate and organic matter carbon-isotope records from the Atlantic and western Tethys. The relative fractionation of carbon isotopes in organic matter vs. carbonate species, defined as Δ13C (δ13Ccarb-δ13Ckerogen), and the secular trend of atmospheric pCO2 over the Late Jurassic that is calculated from the high-resolution δ13Ckerogen values indicate a cold Callovian-Oxfordian transition, a long-term increasing but fluctuating Kimmeridgian and a prominent early Tithonian cooling event (ETCE). The pronounced temperature plateau during the late Kimmeridgian-early Tithonian was contemporaneous with the occurrence of major magmatic events during the Late Jurassic, while the ETCE has been possibly attributed to major changes in oceanic circulation patterns. Additionally, reconstructed atmospheric pCO2 values show very small differences to values using phytane- and stomatal density-based pCO2 calculations, providing an alternative estimate for accurate identification of the paleoclimatic framework of this enigmatic interval in the Mesozoic.