Geochemical and palynological records of rapid climatic change from the early to late Aptian: evidence from the Jiaolai Basin, eastern China

Abstract

The Laiyang Group in the Jiaolai Basin, eastern China, contains Lower Cretaceous continental river and lake deposits that provide a complete record of the evolution of the paleoclimate in the Laiyang area from the early to late Aptian. This study used novel chemical weathering indices and palynological data for Lower Cretaceous mudstone in the Laiyang Group coupled with existing geochemical data, clay mineralogy and plant fossil record to reconstruct the geochemical weathering conditions and paleoclimatic evolution of the Jiaolai Basin over this period. Four distinctive episodes of paleoclimatic change were identified, with one linked to an extremely dry–hot climatic event correlated with the Oceanic Anoxia Event (OAE)1a. During Stage 1, strong chemical weathering was correlated with a relatively warm–humid climate during the early Aptian but the intensity of chemical weathering tended to decrease with an increasingly dry and hot climate. In contrast, Stage 2 was characterised by stable conditions with weak chemical weathering and an extremely dry, hot climate during the early and middle Aptian. The presence of organic-rich black shale and the associated distribution of organic carbon isotope values verified that the extremely dry–hot climate during this stage was related to OAE 1a. Stage 3 was a transitional period extending through the middle and late Aptian during which the climate became relatively warm and humid, triggering increases in chemical weathering. Finally, Stage 4 during the late Aptian was characterised by a return to high chemical weathering rates and a warmer climate. Notably, the paleoclimatic changes in the Aptian period indicated by the geochemical record of the Jiaolai Basin are synchronous with those indicated by marine records. The results of this study provide a reference for further study of this climatic event in terrestrial systems within the context of the greenhouse climate in the Cretaceous. KEY POINTS Geochemical and palynological records of rapid climatic change are preserved in lower to upper Aptian terrestrial sediments in eastern China. Chemical weathering in inland east Asia during OAE 1a first increased, then decreased and then increased again. Terrestrial vegetation responded to global climate change during the early Aptian period in eastern China.