Terrestrial records of the Early Cretaceous paleoclimate changes in the Liupanshan Basin, NW China: Evidence from sedimentology and geochemistry

Abstract

Abstract The Early Cretaceous paleoclimate has significant influence on global ecosystem and abundant clues were recorded in both marine and terrestrial sediments. However, much less studies were conducted on the terrestrial strata than the marine strata, leading to the significance of the Early Cretaceous paleoclimate in terrestrial systems is currently unclear. In this study, we present the terrestrial sedimentary characteristics and geochemical data of the upper member of the Lower Cretaceous Liupanshan Group (Liwaxia, Madongshan and Naijiahe formations) in the Liupanshan Basin (North China) and revealed the evolution of paleoenvironment and paleoclimate recorded in the terrestrial lake. The results show that the total REE concentrations of samples from these formations range from 79.94 to 195.54 ppm, 76.94 to 162.37 ppm, and 30.06 to 205.78 ppm, respectively. All samples display obvious negative Eu anomaly and negligible Ce anomaly with the enrichment of LREE and depletion of HREE. These mudstones were rich in Na2O, TFe2O3 and several trace elements (e.g., Ba, Sr, and Rb) and depleted in other elements (e.g., Al2O3, CaO, Th, Zr, and Hf,). The major element composition and other geochemical indicators (e.g., CIA) indicate that the collected mudstones have experienced weak weathering during transportation. Based on the geochemical characteristics, the source of the Liwaxia-Naijiahe Formation has a felsic provenance, derived from the predominantly acidic magmatic rocks in the Qinling-Qilian Orogenic Belt. Multiple geochemical indicators show that the Liwaxia Formation was deposited in a semiarid-arid, anoxic, and low-moderate salinity environment, while the Madongshan-Naijiahe Formation were deposited an arid, anoxic, and high salinity environment. As a typical terrestrial salified lake in North China, the salinization of the sedimentary water bodies and the formation of black shales in the Madongshan-Naijiahe Formation might be related to an oceanic anoxic event in the hothouse climate in the Early Cretaceous.