Sulfur and carbon isotopic systematics of Guadalupian-lopingian (Permian) mid-panthalassa: δ34S and δ13C profiles in accreted paleo-atoll carbonates in japan

Abstract

Immediately before the extinction of the end-Guadalupian (Middle Permian; ca 260 Ma), a significant change to the global carbon cycle occurred in the superocean Panthalassa, as indicated by a prominent positive δ13C excursion called the Kamura event. However, the causes of this event and its connection to the major extinction of marine invertebrates remain unclear. To understand the mutual relationships between these changes, we analyzed the sulfur isotope ratio of the carbonate-associated sulfate (CAS) and HCl-insoluble residue, as well as the carbon isotope ratio of bulk organic matter, for the Middle-Upper Permian carbonates of an accreted mid-oceanic paleo-atoll complex from Japan, where the Kamura event was first docu-mented. We detected the following unique aspects of the stable carbon and sulfur isotope records. First, the extremely high δ13C values of carbonate (δ13 Ccarb) over +5 ‰ during the Capitanian (late Guadalupian) were associated with large isotopic differences between carbonate and organic matter (Δ13 C = δ13 Ccarb − δ13 Corg). We infer that the Capitanian Kamura event reflected an unusually large amount of dis-solved organic matter in the expanded oxygen minimum zone at mid-depth. Second, the δ34S values of CAS (δ34 SCAS) were inversely correlated with the δ13 Ccarb values during the Capitanian to early Wuchiapingian (early Late Permian) interval. The Capi-tanian trend may have appeared under increased oceanic sulfate conditions, which were accelerated by intense volcanic outgassing. Bacterial sulfate reduction with increased sulfate concentrations in seawater may have stimulated the production of pyrite that may have incorporated iron in pre-existing iron hydroxide/oxide. This stimulated phosphorus release, which enhanced organic matter production and resulted in high δ13 Ccarb. Low δ34SCAS values under high sulfate concentrations were maintained and the continuous supply of sulfate cannot by explained only by the volcanic eruption of the Emeishan Trap, which has been proposed as a cause of the extinction. The Wuchiapingian δ34SCAS –δ13 Ccarb correlation, likely related to low sulfate concentration, may have been caused by the removal of oceanic sulfate through the massive evaporite deposition.