Late Palaeozoic biogeography of East Asia and palaeontological constraints on plate tectonic reconstructions

Abstract

Biogeographical patterns of late Palaeozoic rugose coral genera are analysed for the Lower Carboniferous (Visean), early Lower Permian (Asselian/Sakmarian), late Lower Permian (Qixian) and early Upper Permian (Maokoan) of East Asia. Boundaries to the biotic regions are defined to coincide with tectonically significant suture zones to test rival hypotheses about the plate tectonic reconstruction of that region. Three numerical techniques are employed to cluster areas on the basis of shared endemic taxa; parsimony analysis of endemism, principal coordinates analysis and single linkage cluster analysis. Geographical variation in overall diversity is also considered. These results are compared with empirically derived patterns based on other groups of organisms. Major conclusions from this work are as follows, (i) During the Carboniferous and early Permian, the Cathaysian region (North and South China Blocks, Tarim Terrane, Kunlun Terrane, Qiangtang Terrane) formed one cohesive biotic region lying tropically or subtropically; it did not start to fragment until the Upper Permian, (ii) This region was biotically isolated from Central Asia at least during the Carboniferous and Lower Permian, (iii) The southern boundary to the Cathaysian region does not coincide with a single suture zone through time, nor is it sharply defined. Instead there appears to be a gradual faunal impoverishment southwards across the Tibetan Plateau. This implies that faunal ranges are controlled only by the prevailing global climatic regime and not by a geographical barrier, (iv) The Lhasa and Himalaya Terranes shared a similar fauna until the mid-Permian, when a marked faunal disjunction developed coincident with the Zangbo Suture, (v) For terrestrial floras, the barrier to biotic exchange between the North China Block and Angaraland started to break down in the late Permian. It follows that no major oceanic break (‘Palaeotethys’) can be recognized within the Cathaysian region during the late Palaeozoic on palaeontological evidence. This region then formed an integral part of the Gondwanaland craton, extending up into broadly tropical latitudes, and did not become separated from it until the late Lower Permian. The Tienshan-Yinshan Suture is the most likely site of ‘Palaeotethys’, which appears to have occupied a broadly equatorial latitude. Combined with evidence on the ages of the various Asian sutures, this raises significant problems for those who demand a large ocean in their Carboniferous to early Permian palaeogeographical reconstructions of this region.