Tectonically-induced icehouse-greenhouse climate oscillations during the transition from the Variscan to the Alpine cycle (Carboniferous to Triassic)

Abstract

Remarkable global climate oscillations were recorded during the timespan middle Carboniferous-Triassic, which allows definition of two cold (icehouse 1: middle Carboniferous; icehouse 2: early Permian) and two warm episodes (greenhouse 1: late Carboniferous-earliest Permian; greenhouse 2: middle Permian-Triassic). The tectonic evolution of the central Pangean realm from Variscan to late Variscan, and finally to early Alpine offers an explanation for these climate oscillations, in terms of mountain building, extensional collapse, rifting, epeirogeny, volcanism, erosion, and exhumation. The cold periods were associated with orogenic (icehouse 1) or epeirogenic (icehouse 2) movements leading to uplift and erosion, and therefore, to CO 2 output from the atmosphere. On the contrary, the warm periods were related to extension-related phenomena, such as volcanism, deep- and shallow-seated hydrothermal activity, unroofing of large-scale metamorphic core-complexes (greenhouse 1), or vast exhumation of coal and peat deposits and volcanism (greenhouse 2), all of them processes leading to massive input of CO 2 into the atmosphere, hence, to global warming.