Quantitative palaeobiogeography of the Kungurian–Roadian brachiopod faunas in the Tethys: Implications of allometric drifting of Cimmerian blocks and opening of the Meso-Tethys Ocean

Abstract

Benthic faunas and their palaeobiogeographic affinities related to climate gradient can provide insightful information to unravel the tectonic histories of their hosted blocks if they moved across different latitude zones. In this study, three different quantitative analyses (network, cluster and non-metric multi-dimensional scaling analyses) are employed to carry out a palaeobiogeographic study of the Kungurian–Roadian brachiopod faunas of the Cimmerian blocks. A spin-glass algorithm that enables network community detection is here used for the first time and its six groups-partition is considered as the optimal solution. Two new palaeobiogeographic subprovinces, the Southern and Northern Cimmerian subprovinces in the Southern Transitional Zone, are first recognised besides the previously perceived Cathaysian, Transhimalayan, Westralian and Austrazean provinces. Based on distinct palaeobiogeographic discrepancies, it is suggested that the Lhasa, Tengchong and Irrawaddy blocks, constituting the main parts of the Southern Cimmerian Subprovince, were probably situated near the peri-Gondwanan region; whereas the South Qiangtang, Baoshan and Sibuma blocks of the Northern Cimmerian Subprovince probably were located in the temperate region of the southern hemisphere during the Cisuralian to Guadalupian transition. Such discrepancies in palaeobiogeographic affinitites between two continental slices imply that the Meso-Tethys Ocean had existed before the late Cisuralian and its present oceanic remnants are represented by the Bangong-Nujiang Suture Zone in central Tibet, the Gaoligongshan shear zone in western Yunnan and the Medial-Myanmar Suture Zone in southern Myanmar and Peninsula Thailand. Moreover, the Neo-Tethys Ocean had likely co-existed with the Meso-Tethys Ocean during that time. Given that all these blocks were attached to the northern peri-Gondwanan margin during the early Cisuralian, the Kungurian-Roadian faunal discrepancies among different continental slices with a distinct latitude gradient can be interpreted by the allometric northward drifting of the Cimmerian blocks, which led to the formation of the Meso-Tethys and Neo-Tethys oceans.