Pangea; evolution of a supercontinent and its consequences for Earth's paleoclimate and sedimentary environments

During its life span from mid-Carboniferous (320 Ma) merger to mid-Jurassic (160 Ma) initial breakup, Pangea comprised two contrasting sedimentary provinces: (1) an emergent southern (Gondwanaland) province, with no more than 15% of the landmass covered by the sea, dominated by nonmarine facies, and (2) a submergent northern or Laurasian province, 25% or more covered by the sea, dominated by marine facies. This contrast arose from the unequal size of Pangea"s original components. The 100-million-km (super 2) area of Paleozoic Gondwanaland, which generated a large heat anomaly in and beneath the lithosphere, dwarfed the 30-million-km (super 2) area of Laurentia and was 10 times the size of the two Chinese microplates. Pangea inherited the contrast and maintained it by the growth of its own heat anomaly. Within this overarching factor that distinguished northern from southern Pangea, plate-tectonic forces modulated by the growth of the Pangean heat anomaly brought about a sedimentary/tectonic evolution that reflects the repetition of couplets of shortening and extension. Initial Variscan/Appalachian (325 to 290 Ma) and Kanimblan/Alice Springs (350 to 325 Ma) collisional shortening and uplift were followed at 290 Ma by Extension I The lithosphere underwent thermal subsidence in modes that depended on basement structure: Hot, newly formed orogenic basement subsided in volcanic rifts, whereas cratonic basement types were nonvolcanic; the cratonic Proterozoic foldbelts of the Zambezian terrain subsided in linear fault-bounded zones or rifts; cratonic nuclei of the Karoo terrain subsided in oval-shaped basins or sags. Subsequent Gondwanide/Indosinian (255 to 230 Ma) shortening and uplift were followed at 230 Ma by Extension II, mainly by rifting. Final dispersal started when continental rifting was superseded by seafloor spreading. Glaciation in the Gondwanaland province during the Pennsylvanian-Permian and coal-forming conditions during the Pennsylvanian in Euramerica and Permian in the Gondwanaland province and Asia were terminated by global warming that accompanied excessive venting of CO (sub 2) into the atmosphere during the eruption of the Permian/Triassic (approximately 250 Ma) Siberian Traps and other volcanics. The resulting gap in coal deposition lasted through the Early and Middle Triassic until the excessive CO (sub 2) was finally resorbed by the crust, at which time coal deposition resumed during the Late Triassic.