Conodont zones and related ash beds through the Permian-Triassic Boundary in South China

Abstract

Six sections from diverse paleogeographic settings in South China provide a high-resolution succession of conodont zones and associated ash beds through the Permian-Triassic boundary. Acomplete succession of eight conodont zones and eight associated ash beds is recorded in the basin-filling sequences: in ascending order, the Clarkina yini Zone with top ash bed 1, the Clarkina meishanensis Zone and ash bed 2 within it, the Clarkina taylorae Zone with ash bed 3 at its base, the H. changxingensis-C. microcuspidata Zone with ash bed 4 at its base and ash bed 5 within it, the Hindeodus parvus Zone with top ash bed 6, the Isarcisella staeschei Zone and ash bed 7 within it, the Isarcisella isarcica Zone and ash bed 8 within it, and the Neogondolella krystyni Zone. In slope settings, ash bed 3 and the C. taylorae Zone are missing; whereas in the strata of the platform interior, the C. meishanensis Zone and associated ash beds 1 and 2 are also missing. This pattern indicates an unconformity that represents increasing missing section in increasingly shallower deposits. The Global Stratotype Section and Point for the base of the Triassic, at Meishan, China, is recognized as having been formed in a slope setting, with an unconformity at the base of Bed 25. The identification of these conodont zones in Iran indicates their applicability outside of South China.