Terrane rafting enhanced by contemporaneous climatic amelioration as a mechanism of vicariance: Permian marine biogeography of the Shan‐Thai terrane in Southeast Asia

Abstract

A model of tectonic vicariance and its effects on marine biogeography is proposed to predict changes in marine provinciality that may result when a terrane drifts from one major lithospheric plate to another, over a relatively short period of geological time. The model is employed to explain observed changes in marine provinciality of the Shan‐Thai terrane, in Southeast Asia, through the Permian. A succession of three broad biogeographical stages is recognised, consisting of an early Early Permian (Asselian‐Early Sakmarian) Gondwanan stage, a mid‐Permian transitional (Late Sakmarian to Midian/Maokouan) stage of mixed faunas constituting the Sibumasu Province, and the final Late Permian (Wujiapingian to Changxingian) Cathaysian stage. The tectonic vicariance scenario could not, on its own, account for marked changes in marine provinciality of the Shan‐Thai terrane, especially the seemingly abrupt transformation from a fauna of characteristic Gondwanan type to a mixed fauna, at the Early to Late Sakmarian boundary. Consequently, climatic amelioration is invoked to complement the tectonic interpretation. Together, these factors explain the warming effect demonstrated by Permian biogeographical and lithological data of the Shan‐Thai terrane. This seems to have resulted firstly from separation of the Shan‐Thai terrane from northern Gondwana, followed by continued northward drift, on which contemporaneous climatic amelioration was superimposed in the Late Sakmarian and thereafter.

Keywords:

• Vicariance biogeography
• Permian
• Brachiopoda
• Shan‐Thai terrane