Using carbonate Zn and conodont Sr isotopes to link marine productivity and chemical weathering intensity changes during the Permian-Triassic transition

Abstract

The end-Permian mass extinction (EPME), the greatest biodiversity crisis since the Cambrian Explosion, was followed by a protracted and complex recovery. Intensified continental weathering and fluctuating primary productivity, under conditions of hyperwarming, characterized both the EPME and the subsequent protracted marine biotic recovery. However, detailed reconstructions of changes in weathering and productivity during the Permian-Triassic transition have not been achieved yet, leaving uncertainty regarding the nature of environmental controls during the extinction and recovery intervals. To address this issue, we apply a novel multi-proxy framework centered on the coupled use of carbonate zinc (δ⁶⁶Zn_carb) and conodont strontium (⁸⁷Sr/⁸⁶Sr_conodont) isotopes. We investigate the environmental sensitivity of this paired system using a high-resolution dataset from the Guryul Ravine section (Indian Kashmir), integrating δ⁶⁶Zn_carb, ⁸⁷Sr/⁸⁶Sr_conodont, δ¹³C_org, and bulk-rock geochemistry across the Permian-Triassic boundary. Elevated chemical index of alteration (CIA) and ⁸⁷Sr/⁸⁶Sr_conodont values in the uppermost Permian record enhanced weathering that likely boosted marine productivity and caused anoxia. Elevated δ⁶⁶Zn_carb coupled with declining ⁸⁷Sr/⁸⁶Sr_conodont in the lowermost Triassic (H. parvus Zone) suggests reduced weathering inputs following the EPME. A subsequent rapid ⁸⁷Sr/⁸⁶Sr rise (above I. staeschei Zone) marks renewed weathering and nutrient input, driving high productivity (high δ⁶⁶Zn_carb, positive δ¹³C_org) and a second anoxic episode. A negative excursion in δ⁶⁶Zn_carb coupled with rising ⁸⁷Sr/⁸⁶Sr_conodont at the Griesbachian-Dienerian boundary indicates strong weathering but low marine productivity. The amelioration of nutrient limitations during the Dienerian, indicated by a positive δ⁶⁶Zn_carb excursion, was potentially driven by declining seawater temperatures and weakened oceanic anoxia. This study establishes the Zn-Sr isotope pair as a robust tracer for deconvolving weathering-productivity dynamics and demonstrates the close relationships between global climate, weathering fluxes, and ocean-redox conditions that were pivotal in driving the EPME and shaping the subsequent Early Triassic marine biotic recovery. In particular, our findings reveal the Dienerian to have been a transient phase of environmental and ecological amelioration during the Early Triassic, setting the stage for the subsequent development of complex Mesozoic marine ecosystems.