Paleobiogeography of the Permian Neo-Tethys Shores

Abstract

The Permian was a period of marked climate change and plate tectonic reconfiguration. Climate changed from glacial conditions at the dawn of the period to warm conditions in the Middle Permian. The Cimmerian terranes migrated from southern Gondwanan paleolatitudes in the Early Permian to subequatorial paleolatitudes by the Middle-Late Permian as the result of the opening of the Neo-Tethys Ocean. This opening was asymmetrical, with higher seafloor spreading rates for the central Cimmerian terranes (central Afghanistan, Pakistan Karakoram) than for the western terranes (Iran), and it took place contemporaneously with the transformation of Pangea from an Irvingian B to a Wegenerian Atype configuration. During this Early to Middle Permian tectono-climatic transition, bioprovincial patterns evolved rapidly across the southern and northern margins of the opening Neo-Tethys Ocean, as testified by the rich fossil record. Here we place climate-sensitive biotic associations on paleomagnetically based paleogeographic reconstructions of the Gondwanan margin and the Cimmerian blocks for the Early and Middle Permian and use them to reconstruct the evolution of oceanic circulation patterns, latitudinal thermal gradients, and biogeography in this time interval. We show that, in the Early Permian, the tropical Gondwanan margin and the western Cimmerian terranes benefited from a warm subtropical surface current gyre, which was confined to low latitudes. At the same time at higher southern latitudes, the central Cimmerian terranes were affected by cold surface currents promoted by the Gondwanan ice caps that distributed cold biota toward the tropics. These results suggest that low latitude sea surface temperature did not undergo significant cooling during the Gondwanan glaciation and that there was a steep thermal gradient between the compressed tropical belt and the expanded cold high latitude belt. This situation changed abruptly in the Middle Permian with the creation of current gyres in the newly opened Neo-Tethys Ocean that arranged biotic associations in distinct bioprovinces. Wordian brachiopods from the western Cimmerian terranes contain a significant proportion of Gondwanan taxa some of which are restricted to the Gondwanan margin (Tunisia, Turkey, Oman). Coeval brachiopods from central Cimmerian terranes are instead different and pertain to a separate, low-latitude bioprovince supporting the paleomagnetically derived differential drift of Cimmerian terranes.