Volcanically modulated micronutrient cycles in the mid-Proterozoic ocean

Abstract

Volcanic forcing of nutrient influxes into the ocean has been proposed as an important driver in punctuating the pervasive depression of oceanic productivity during the mid-Proterozoic, yet direct evidence linking these events remains scarce. Here, we present high-resolution zinc isotopic systematics from the well-studied Xiamaling Formation of the North China Craton (NCC), where mid-Proterozoic volcanism can be temporally correlated with the deposition of organic-rich sediments. Our results reveal coeval negative δ66Zn excursions and sedimentary zinc enrichments during episodes of either NCC volcanism or large igneous province activity, followed by positive δ66Zn excursions and concomitant high and/or moderate zinc enrichments. The observed decrease in δ66Zn values toward the continental range can most likely be explained by volcanism-induced intensification of continental weathering, which can enhance influxes of terrestrial-sourced Zn into the ocean. Following the culmination of volcanism, a gradual increase in δ66Zn indicates a mechanistic linkage between ocean nutrification and stimulated marine primary productivity, promoting the drawdown of organic-derived light zinc isotopes from marine inventories due to enhanced organic carbon burial. These findings help reconcile the temporal relationships between major mid-Proterozoic volcanic events and the widespread black shale deposition in the Nuna supercontinent, wherein volcanism-driven micronutrient feedbacks may have modulated Earth’s surficial evolution on billion-year time scales.