Paleoclimate variation during the Cretaceous revealed by geochemical and mineralogical analyses from continental sediments in northern Vietnam

Severe aridification has been recognized in low-latitude areas of Southeast Asia during the mid-Cretaceous; however, previous studies mainly focused on continental interior basins. Here, we investigate Cretaceous continental sediments from northern Vietnam, located in the Southeast Asian continental margin, where a precise study has not been conducted. The geochemical and mineralogical characteristics of mudstones collected from the Ban Hang and Yen Chau formations revealed fluctuations in climate conditions in northern Vietnam, including a slight humidification from the Early to mid-Cretaceous and aridification in the Late Cretaceous. Northern Vietnam is considered to have experienced a temperate semi-arid climate in the Early Cretaceous but shifted to a hot and sub-humid environment in the mid-Cretaceous and then returned to arid conditions in the late Period. The results indicate that the coastal area of Southeast Asia was more humid than the inland due to its proximity to the proto-Pacific Ocean. We also detected an increase in humidity in the coastal area during the mid-Cretaceous, contrasting with the inland regions where extreme aridification progressed. This contrasting paleoclimate regime was probably established by the isolation of coastal and inland areas by the tectonic re-configuration of the Southeast Asian continent. During the Cretaceous, closure of the Meso-Tethys Ocean and collisional tectonics generated a coastal mountain range, which caused the orogenic rain-shadow effects, i.e., increased precipitation in the coastal area and intensified desertification in the inland area. The present contribution indicates that the Cretaceous paleoclimate conditions in Southeast Asia were primarily constrained by the regional geographical background rather than the global climate system.