Continental weathering-phosphogenesis coupling across the ediacaran-cambrian transition, Southwestern China.

Abstract

Phosphorus, as a primary limiting element for ecosystem productivity, plays a pivotal role in regulating the redox state of the atmosphere-ocean system and climate change. Under-standing the coupling relationship between the phosphorus cycle and climate dynamics during geological history has long been a research challenge in Earth system science. Here we are primarily based on sedimentary profiles and rock samples from phosphate mining areas on the western margin of the Yangtze Plate. By analyzing multiple elemental geo-chemical proxies, it reconstructs the depositional environment and phosphorus enrichment mechanisms during the Meishucun Age of the Early Cambrian. Our results show that: (1) The total phosphorus flux from continental weathering is jointly controlled by tectonic activity and climate change. The intensity of tectonic activity affects the rate of rock erosion, which determines the total phosphorus flux, while climate influences the in-tensity of chemical weathering, which controls the proportion of reactive phosphorus; (2) During the Ediacaran-Cambrian (E-Ꞓ) transition, due to the continuous increase in atmospheric oxygen concentration, the Yangtze region experienced intense chemical weathering. Concomitant with the occurrence of a "Great Unconformity" at the Ediacaran/Cambrian boundary, weathering of continental (phosphorus-bearing) rocks constituted the primary source of phosphorus in the oceans; and (3) Upwelling transported particulate and dissolved phosphorus from the marine phosphorus reservoir to shallow-water environments, where physical concentration, biological processes and potential hydrothermal activity contributed to phosphorus enrichment to different extents, ultimately leading to the formation of high-grade phosphorites. Collectively, these findings highlight the complexity of marine phosphorus enrichment mechanisms in the Early Cambrian and provide additional constraints for understanding the coupling relationship between phosphorus burial and organic carbon burial.