First SHRIMP U-Pb zircon ages of the potash-bearing Mengyejing Formation, Simao Basin, southwestern Yunnan, China

High temperatures and arid climates were extensive throughout the Tethyan domain during the mid-Cretaceous, and thus greatest volumes of evaporites were deposited and widely distributed. The Mengyejing Formation, which contains the only pre-Quaternary potash salt deposit in China, is thought to be genetically related to the Late Cretaceous Maha Sarakham Formation in the Khorat Basin. The age of the. Mengyejing Formation has been a subject of debate and controversy and was previously interpreted as Paleocene in age mainly based on a few palynology and ostracoda fossils. In this paper, we report U-Pb sensitive high-resolution ion microprobe (SHRIMP) ages between 100 Ma to 110 Ma for the first time from the tuff beds interbedded with gypsum units and siltstones from the upper part of the Mengyejing Formation in the Simao Basin, southwestern Yunnan. This age indicates that the age of the Mengyejing Formation is likely Albian to Cenomanian providing precise geochronological constraint for the age of the Mengyejing Formation in the Simao Basin, which is consistent with the age of the Maha Sarakham Formation. Combined with marine origin of delta S-34 values for gypsum units in the Mengyejing Formation, the ages indicate that marine incursions from the Neo-Tethyan Ocean in the mid-Cretaceous were caused by global high sea level. However, the stratigraphic succession of the Mengyejing Formation cannot be well correlated with those of the Maha Sarakham Formation caused by marine incursion and tectonic inversion in the mid-Cretaceous. (C) 2014 Elsevier Ltd. All rights reserved.