Paleoclimate Evolution and Elemental Geochemical Response during Middle Jurassic-Early Cretaceous in Tectonic Regime Transition Period in the North Yellow Sea Basin

The North Yellow Sea basin in the eastern part of the North China platform from the Middle Jurassic to the Early Cretaceous was influenced by the transformation from Paleo-Asian tectonic system to Marginal Pacific tectonic system, and its tectonic evolution experienced transformations of extension-compression-extension. The differences of tectonic systems are shown not only in the geotectonic properties and their geological effects, but also in the sedimentary characteristics of the basin, paleontology and paleoclimate. In this paper, the Middle Jurassic to Lower Cretaceous of the well X1 in the eastern depression of the North Yellow Sea basin is taken as the research object, and the paleoclimate evolution is studied by using the indication of mudstone element geochemical characteristics to paleoclimate, combined with basin sedimentary characteristics and paleobiological data. Research results show that, the longitudinal changes of Sr/Cu(2.12-34.10), Sr/Ba(0.16-1.60), Rb/Sr(0.13-1.23), Fe2O3/FeO(0.22-11.10), V/Cr(0.91-1.78), V/Sc(4.89-8.33), Ni/Co(1.14-3.85), δU(0.50-0.84), U/Th(0.11-0.24) from the Middle Jurassic to the Early Cretaceous reflect that the paleoclimate evolution experienced variations from warm and humid to whole humid, short dry and hot to dry and hot. The sediments experienced the main changes form dark fine-grained sediments to gray, gray interbedded with gray-green, gray and reddish brown interbedded fine sediments to gray coarse-grained sediments and reddish-brown and grayish-yellow fine-grained sediments. Paleontology experienced the process of abundance of hygrophilous plants-appearance of heat-loving plants-abundance of heat-loving plants. The results show that the North China platform drifted northward due to the influence of Paleo-Asian tectonic system and Marginal Pacific tectonic system. At the same time, the paleoclimate evolution of the North Yellow Sea basin underwent a dramatic change from the Middle Jurassic to the late Late Cretaceous; during the Middle Jurassic to the early Late Jurassic, it was dominated by warm and humid climate; from the late Late Jurassic to the early Early Cretaceous the whole climate was relatively wet, with a short dry and hot climate; from the middle Early Cretaceous to the late Early Cretaceous it was dry and hot climate. The paleoclimate in the North Yellow Sea basin has experienced the evolution from a warm and humid climate to dry and hot climate during the Middle Jurassic-the Early Cretaceous, which is a response to the transformation of two major Mesozoic tectonic regimes in the east of North China platform. © 2021, Editorial Department of Earth Science. All right reserved.