Permafrost in the Cretaceous supergreenhouse

During the archetypal supergreenhouse Cretaceous Earth, an active cryosphere with permafrost existed in Chinese plateau deserts (astrochonological age ca. 132.49–132.17 Ma). Permafrost wedges have been identified in three different outcrops of the Luohe Fm.  Most of the wedges are concentrated in two discrete horizons bounding three draa successions representing composite-wedge pseudomorphs. A late Pleistocene analogue for the Cretaceous aeolian–permafrost system of the Luohe Fm is provided by the composite wedges and sand wedges within aeolian dune deposits of the Kittigazuit Fm., Hadwen Island, NT, Canada. A modern analogue for these Cretaceous plateau cryospheric conditions is the aeolian–permafrost system we report from the Qiongkuai Lebashi Lake area, Xinjiang Uygur Autonomous Region, China. Significantly, Cretaceous plateau permafrost was coeval with marine cryospheric indicators in the Arctic and Australia, indicating a strong coupling of the ocean–atmosphere system. The Cretaceous permafrost contained a rich microbiome at subtropical palaeolatitude and 3–4 km palaeoaltitude, analogous to recent permafrost in the western Himalayas. Global permafrost thaw during the Cretaceous released significant volumes of greenhouse gases to the atmosphere as well as dissolved organic carbon (DOC) and other nutrients into watersheds, and marine waters affecting aquatic systems through carbon and nutrient additions. The contribution of permafrost thaw to the Cretaceous global C balance, including during oceanic anoxic events (OAE) will have to be determined in future research dealing with ocean–continental cryosphere coupling associated with events of cryosphere degradation in the aftermaths of supergreenhouse cold snaps. A mindset of persistent ice-free greenhouse conditions during the Cretaceous has stifled consideration of permafrost thaw as a contributor of C and nutrients to the palaeo-oceans and palaeo-atmosphere.