CARBON ISOTOPE SHIFT ACROSS THE GUADALUPIAN-LOPINGIAN (MIDDLE-LATE PERMIAN) BOUNDARY IN MID-SUPEROCEAN

The Middle to Upper Permian shallow marine carbonates in the Kamura area, Kyushu (SW Japan), was derived primarily from an ancient mid-oceanic atoll complex on seamount in Panthalassa and later incorporated as an allochthnous block in the Jurassic accretionary complex in Japan. A clear biotic turnover of fusulines from the Capitanian (Late Guadalupian) Lepidolina-dominant assemblage to Wuchiapingian (Early Lopingian) Codonofusiellla-Reichelina-dominant one was recently recognized within this limestone block. Between the extinction horizon of the Capitanian fusulines and the first appearance daum of Wuchiapingian ones, there is a ca. 10 m thick barren interval that probably represents a period of harsh environment in shallow mid-ocean. Detailed chemostratigraphic analysis of this section clarified a nearly 2 permil negative shift in carbonate carbon isotope ratio in this barren interval immediately below the fusuline-based Guadalupian-Lopingian boundary and another 1 permil drop in the lowermost Wuhiapingian. This signature suggests that a remarkable change may have occurred in bio-productivity and bio-diversity of the shallow mid-Panthalassa across the Guadalupian-Lopingian boundary. The occurrence of thin felsic tuff at the G-L boundary supports a possible causal link between the felsic volcanism and mass extinction.