Emeishan Basalts (SW China) and the 'end-Guadalupian' crisis: magnetobiostratigraphic constraints

Abstract

A magnetostratigraphic investigation of the Permian Emeishan LIP (large igneous province) was carried out on a composite section in Ebian County, close to the type area in Sichuan, SW China. The main succession of twelve flows (175 m thick) carries a normal polarity whilst the one reliable site from the overlying 30 m thick volcanic waning sequence is marked by a reverse polarity. The data enable a correlation to be proposed with an Emeishan Basalt sequence in western Guizhou, c. 400 km to the SE. From our knowledge of the geomagnetic field's reversal behaviour during the Permian, it suggests that the main lava pile along the eastern half of the Emeishan Basalt outcrop belt was erupted within a half to one million years. Using magnetobiostratigraphic data from the adjacent South China platform, the normal polarity magnetozone is correlated with the normal polarity chron associated with the upper part of the Maokou Limestones. Constrained by conodont data, the main Emei Basalts appear to be at least two biozones older (1-1.5 Ma) than the Mid-Late Permian boundary. It is possible, however, that the Emei Basalt waning zone sequence, which represents an explosive volcanic phase, might be coeval with the 'end-Guadalupian' biotic crisis. Thus arguments implicating Emei Basalt volcanism as the causal mechanism behind this major global event have to accommodate the new relative-age constraints.