Phanerozoic Time - the Palaeozoic and Mesozoic

These eras (which started some 545 Ma ago) are dominated by the presence of two supercontinents, Gondwanaland mainly in the south and Laurasia mainly in the north. Gondwanaland came into existence through several continental plate collisions associated with Cambro-Ordovician orogenesis: shallow inland seas covered parts of Gondwanaland until the Devonian and there was a distinct southern marine assemblage of fossils. Laurasia still comprised scattered small continents in the warm Tethyan sea until the late Palaeozoic, when they began to merge.

Soon after the Permo-Triassic Gondwana orogeny the new super-supercontinent, Pangea, was formed by the collision of Gondwanaland with the newly assembled Laurasia.

The palaeoclimate of Gondwanaland, and later, of early Pangea, was clearly zoned since glacial centres can be shown to have shifted as different parts of the continent drifted across the South Pole. When the Gondwanaland part finally drifted away from the South Pole and the landmass became larger with the formation of Pangea, the overall climate became warmer and drier. It was not until the break-up of Pangea at the end of the Permo-Triassic period some 250 million years ago and the eruption of basalts associated with rifts, that the formation of the Atlantic rift began at the margins of the present central Atlantic basin.

< P>During the Cretaceous, new Atlantic and Indian oceanic zones opened and rifting of micro continents from northern Africa developed with the widening of the Tethyan Sea. The destruction of the former Gondwanaland/ Pangea was completed about 100 million years ago: the last continental breaks were between Australia and Antarctica (in the late Cretaceous/early Tertiary) and South America and Antarctica (in the Miocene).

Young rifts between the newly separated continents first received non-marine clastic and evaporite sediments followed by deep marine sediments as the ocean basins widened. Shallow marine transgressions then flooded the adjacent cooling and subsiding passive continental margins.