BREAKING BARRIERS AND BUILDING BRIDGES FOR THE PERMIAN WORLD: THE SIGNIFICANCE OF TRANSITIONAL BIOTAS AS GATEWAYS FOR PERMIAN GLOBAL CORRELATIONS

Biotic endemism at global scale has waxed and waned through time, primarily as a function of paleogeography, climate variability and evolution. At times of strong world-wide provincialism, biogeographic boundaries between regions usually are well defined and therefore tend to present themselves as pronounced biostratigraphic barriers across which correlation of biotas and sedimentary successions is extremely difficult to achieve. With the advance of isotope geochronology and paleomagnetism in recent decades, this problem has been alleviated to some extent; nevertheless, supplementary and/or alternative approaches therefore remain crucial for improving the resolution of global stratigraphic correlations. In this paper, the focus is drawn to the current Permian global chronostratigraphic scale with particular reference to the recent progress made by the SPS international working group on Permian global transitional biotas.

As has been widely acknowledged, the current, primarily conodont-based, Permian timescale has encountered considerable difficulties in its application to high paleolatitude areas/biotas, such as NE Siberia and eastern Australia, where no conodonts have been found. However, recent global effort by Permian biostratigraphers indicates that correlation between Gondwanan and Tethyan sequences and that between the Boreal and Tethyan sequences is still possible if “bridges” (or gateways) of biogeographically transitional nature between the biogeographic regions can be established. Two mains areas that qualify for serving as such “bridges” can be highlighted: West Yuunan of southwest China, and the South Primorye area of Far East Russia. The former contains a succession of mixed faunal horizons characterized by intermingling warm-water Cathaysian and temperate-water peri-Gondwanan elements, a critically important feature that helps correlate some horizons of the Guadalupian of South China with those of southern Tibet and eastern Australia. Similarly in South Primorye, there are stratigraphic sections that contain mixed Cathaysian and Arctic (Boreal) faunal elements, which can help align some Permian stratigraphic formations of Mongolia and Siberia with the Guadalupian of South China and North America.