In search of the inland Carnian Pluvial Event: Middle-Upper Triassic transition profile and U-Pb isotopic dating in the Yanchang Formation in Ordos Basin, China

The Carnian Pluvial Event (CPE) in the early Late Triassic is a global climate change. The CPE is not only recorded in the ocean but also on the continent. It has been well-documented in the marine environments in Tethys and boreal areas. However, it is less reported for the terrestrial. As a global precipitation event, the CPE on the supercontinent Pangaea is related directly to the sudden increase in argillaceous transportation in the marine carbonate platform. Here, we report a chronological study of the Yunmeng profile in south-eastern Ordos Basin, China where the continuous lacustrine deposits developed with several tuff interlayers. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb isotopic dating of zircons from three bentonite samples show weighted mean ages of 234.1 +/- 2.4 Ma, 234.8 +/- 2.1 Ma, and 236.0 +/- 1.7 Ma, respectively. Based on the review of isotopic dating, sedimentary and palaeontological characteristics of the Triassic Yanchang Formation, the Middle and Upper Triassic boundary is located at the bottom of Chang 7 oil layer (YC7) in the Yanchang Formation at the Yunmeng profile in the Ordos Basin. Therefore, the Yunmeng profile provides a potential case for understanding the inland CPE and might link the terrestrial and oceanic systems in the Carnian.