Mid-Cretaceous desert system in the Simao Basin, southwestern China, and its implications for sea-level change during a greenhouse climate

Abstract

Paleoclimatic indicators suggest that the mid-Cretaceous was one of the warmest intervals of the Phanerozoic. The period of the mid-Cretaceous “super-greenhouse” also experienced an equator-to-pole temperature gradient much lower than that of the present day, implying greater meridional heat transport by the atmosphere and/or oceans. However, reconstructions of Cretaceous atmospheric circulation have been hindered by a lack of relevant datasets based on reliable proxies or direct geological evidence. Aeolian deposits provide direct information about paleoclimate, as well as the direction and intensity of paleo-wind in the interiors of continents. Using petrologic and sedimentologic observations, this study reassesses the terrestrial deposits of the mid-Cretaceous Mangang Formation in the Simao Basin of southwestern China. Originally considered to be aqueous deposits, we reinterpret these strata as representing aeolian transport in a desert environment. We suggest that the development of aeolian deposits in the Mangang Formation (and coeval strata in adjacent basins) was a local response to the prevailing desert climate in the mid- to low-latitudes of the Northern Hemisphere during the mid-Cretaceous, which were dominated by subtropical high-pressure systems on a planetary scale. In addition, with the closure of the Mesotethys Ocean, the intermontane basins of the South China, Simao, and Indochina blocks became more isolated from atmospheric circulation. Bidirectional subduction of the Bangong-Nujiang oceanic crust and the Izanagi Plate beneath East Asia led to the development of Andean-type margins, which created a rain-shadow effect in continental East Asia. These factors caused the development of a tropical desert climate, characterized by aeolian dunes and evaporite deposition. We speculate that the severe depletion of groundwater reservoirs via the desertification of East Asia may represent a previously unrecognized trigger for short-term sea-level changes during the ice-free Cretaceous greenhouse interval.