Lower Palaeozoic facies and faunas around Gondwana

Abstract

A new base map for the Lower Palaeozoic of the Gondwanan continental plate incorporates various modifications to older reconstructions. An analysis is attempted of faunas at various times through the Lower Palaeozoic, in particular the Lower Ordovician (Arenig-Llanvirn), the middle and late Ordovician (Caradoc-Ashgill) and the early Silurian (Llandovery). Regressions and transgressions are identified and ‘western’ and ‘eastern’ Gondwanan platform faunas identified in contrast to the deeper-water peri-Gondwanan marginal faunas. The effects of climatic variation, both with time and between contemporary areas, are reviewed, and are seen to be the chief controlling factor on platform faunas, with a cline from Boreal to tropical faunas alongside the Gondwanan palaeocontinent. The biogeographical relationships of deeper-water faunas were more complex: certain distinctive taxa may be found distributed widely around the perimeters of the continent, and other faunas have taxa in common with marginal faunas around other contemporary palaeocontinents. Some older-described faunas, particularly brachiopods, trilobites and graptolites, are freshly reviewed, and new faunal data from Libya, Turkey, and Iran are presented and figured.