The Early Permian fossil record of Gondwana and its relationship to deglaciation : a review

Deglaciation sequences of Early Permian age in Gondwana have until now been distinguished mainly on lithological criteria by reference to climate-sensitive lithologies and associated geochemistry; whereas identification on biotic criteria such as vegetational or faunal change has not been employed. Present palaeontological data, which are widely- scattered geographically and of different stratigraphic scales and resolutions, show diversity increase from glacial conditions to post-glacial conditions. Amongst the marine fauna, a cold-water fauna consisting of bivalves such as Eurydesma and Deltopecten, and brachiopods such as Lyonia and Trigonotreta, were established in the earliest post-glacial marine transgressions. Above this is a more diverse, increasingly warmer, temperate fauna, including brachiopods, bryozoans, bivalves, cephalopods, gastropods, conularids, fusulinids, small foraminifers, asterozoans, blastoids and crinoids. The polynomorph succession shows change from monosaccate pollen assemblages, associated with fern spores, to more diverse assemblages with common non-taeniate bisaccate pollen. In Oman, where this has been studied in greatest detail, the upland saw changes from a glacial monosaccate pollen-producing flora to a warmer climate bisaccate pollen-producing flora; while in the terrestrial lowlands, a parallel change occurred from a glacial fern flora to a warmer climate colpate pollen-producing and lycopsid lowland flora. The sedimentary organic matter of the associated clastic rocks shows a decreasing δ13C trend believed to reflect palaeoatmospheric change due to post-glacial global warming. Early Permian farfield isotope studies, compiled by other workers, from brachiopods from the southern Urals, show a δ 18O decline of 2.5‰ in the Early Permian (Asselian to Artinskian) and stable δ13C values of around +4.3‰ in the same period. This farfield evidence is in part consistent with palaeontological data since the most likely cause for the decline in δ18O is the return of isotopically light waters to the oceans from melting of glaciers at high latitudes.