THE STRONTIUM AND CARBON ISOTOPE STRATIPRAPHY ACROSS THE GUADALUPIAN-LOPINGIAN BOUNDARY OF THE MID-PANTHALASSAN PALEO-ATOLL LIMESTONE AT AKASAKA IN JAPAN

In order to clarify the mid-superoceanic environmental change across the Guadalupian-Lopingian boundary, isotope stratigraphy of Sr and C was analyzed in the Akasaka Limestone that consists of the Neoschwagerina Zone (Wordian), Yabeina Zone + barren interval (Capitanian), and the Codonofusiella-Reichelina Zone (Wuchiapingian). From the drilled core samples, ⁸⁷Sr/⁸⁶Sr ratio was measured for 38 horizons, and d¹³C_carb for 71 horizons. The ⁸⁷Sr/⁸⁶Sr values stayed extremely low around 0.7068 throughout the Yabeina Zone, started to rise rapidly at the disapperance level of Yabeina, and reached over 0.7074 in the Codonofusiella-Reichelina Zone. As to the Capitanian low value interval corresponding to the “Permian minimium”, the present study first confirmed the total duration of this interval to be over 3 m.y. The d¹³C_carb values stayed very high up to +5 permil from the uppermost Neoschwagerina Zone to the Yabeina Zone, started to decrease around the extinction horizon of large fusuline (Yabeina) and after fluctuating in the barren interval, dropped down to +2 permil by the G-LB. This implies that the high primary productivity during the Capitanian (Kamura event) collapsed around the G-L boundary. It is noteworthy that the end-Capitanian ⁸⁷Sr/⁸⁶Sr rise occurred almost simultaneously with the extinction of large fusuline and the onset of d¹³C_carb fluctuation. This suggests a possible link between non-biological causes and biological results in the latest Guadalupian world.