559 / 2024-09-18 13:10:22
Exploring the driving mechanisms behind variations in 87Sr/86Sr ratios in Neoproterozoic-Cambrian oceans
Neoproterozoic-Cambrian oceans,,87Sr/86Sr ratios
Session 42 - Deep-time ocean and climate changes: insights from models and proxies
Abstract Accepted
Bo Ran / Chengdu University of Technology

The long-term trends in seawater strontium isotope ratios (87Sr/86Sr) hold significant implications for unraveling paleogeographic, paleoclimatic, and paleobiological evolutions across geological time scales. However, the intricate interplay of various geological processes, such as the breakup and assembly of supercontinents, orogeny, and volcanic eruptions, complicates the precise understanding of the mechanisms controlling the 87Sr/86Sr curve variations during the Neoproterozoic-Cambrian interval (700-500 Ma). To address this gap, we have assembled and analyzed 790 strontium isotope data from marine carbonates spanning this period, integrating them with temporal data from 89 global orogenic belts to gain deeper insights into the geological evolution during this era. The refined curve reveals a consistent upward trend in the seawater 87Sr/86Sr ratio between 700 and 500 Ma. When compared to orogenic data, we discern three phases governing the rise in 87Sr/86Sr ratios: Phase I (700-635 Ma), characterized by lower seawater 87Sr/86Sr ratios attributed to the breakup of the Rodinia supercontinent; Phase II (635-540 Ma), where the ratio steadily increased due to intense orogenic activities associated with the assembly of the Gondwana supercontinent; and Phase III (540-500 Ma), marked by a sustained rise driven by volcanic degassing, which augmented atmospheric CO2 concentrations, fostering warm-humid climates that intensified continental silicate weathering, subsequently elevating the seawater 87Sr/86Sr ratio. Based on this three-phase model of marine Sr isotope ratios, we hypothesize that the pre-Cambrian orogenic activities lay the foundation for the Cambrian Explosion. Subsequently, the convergence of East and West Gondwana, coupled with the Cambrian greenhouse climate, significantly intensified continental weathering, enhancing the influx of nutrients into the oceans, a process that may have directly catalyzed the Cambrian Explosion of life.