THE TRIASSIC WORLD: PLATE TECTONICS, PALEOGEOGRAPHY, PALEOCLIMATE & PALEOBIOGEOGRAPHY

In order to tell the story of the Triassic, we present 24 plate tectonic, paleogeographic, paleoclimatic and paleobiogeographic reconstructions. The Triassic began with a catastrophic mass extinction caused by the eruption of the massive West Siberian LIP and ended with the eruption of the Central Atlantic Magmatic Province (CAMP). During the Triassic, the contiguous core continents of Pangea were emergent, while N. & S. China and Cimmeria, along the periphery of Pangea, were flooded by shallow seas. The global average temperature at the start of the Triassic was probably > 35˚ C, making it the hottest time period since the Archean. Temperatures cooled dramatically during the Triassic (to 20˚C ). During the earliest Triassic, central Pangea languished under intense and unrelenting heat that created a super-sized arid belt with equatorial temperatures exceeding 40˚C . During the last half of the Triassic, Pangea shifted 25˚northward. The northern hemisphere rotated under the North Pole bringing some relief to those regions while leaving the South Pole surrounded by open ocean. Polar temperatures were warm (North Pole 11˚C, South Pole 3˚C) when compared to modern values (North Pole -12˚C, South Pole -21˚C).

Triassic Pangea was surrounded by subduction zones that dipped beneath the supercontinent. The interior of Pangea was cross-cut by a system of SW-NE trending mountain ranges which marked late Paleozoic continent-continent collisions. During the Triassic, the PaleoTethys separated Cimmeria from the southern margin of Pangea. We have only a rudimentary understanding of the plate tectonic situation in the vast Panthalassic Ocean. Our speculative plate tectonic reconstructions, show a three-armed midocean rift system, migrating eastward across Panthallasa. The longest arm of this triple junction, the proto-Neotethyan ridge system was subducted northward beneath the newly accreted Cimmerian terranes during the latest Triassic. The subduction of this ridge system triggered Jurassic rifting along the entire margin of Indo-Australian Gondwana. The collision of Cimmeria and the subduction of the proto-Neotethyan midocean ridge may have also triggered the two most important plate tectonic events of the early Mesozoic: the formation of the Pacific plate and the breakup of Pangea.