Causally Linked Redox Changes and Invertebrate Extinctions Through the Permian-Triassic Transition in an Inner-Shelf Basin Section of South China

The Permian-Triassic mass extinction (PTME) represents the most severe biotic crisis in Earth's history. While the timing, pacing, and environmental triggers of this event have been extensively documented in shallow marine environments, the extinction dynamics and underlying causes within deep-water settings remain poorly understood. To address this critical gap, we present a first integrated paleobiological and geochemical study of deep-sea sediments spanning the crisis interval from the Rencunping section in the South China Block. We synthesized high-resolution radiolarian species richness data with multiple geochemical proxies, applying linear sedimentation rate conversions to establish precise timestamps. Utilizing advanced Vector Autoregression (VAR) modeling and Granger causality tests on stationary time-series data, we quantitatively assessed the causal relationships between physical environmental drivers and their impacts on deep-marine biodiversity. Unexpectedly, our quantitative analyses reveal a fundamentally decoupled extinction timeline between shallow and deep marine ecosystems. We identify an initial extinction pulse in the deep sea during the upper Clarkina yini zone, indicating that the deep-water extinction peak occurred approximately 198 kyr earlier than the major extinction horizon on shallow carbonate platforms. Furthermore, severe environmental stress, specifically widespread deep-water anoxia, was initiated even earlier, during the middle C. changxingensis zone, preceding the main PTME by ~750 kyr. Despite this early onset of environmental deterioration, major diversity loss was significantly delayed. We propose that transitory, episodic upwelling, analogous to modern El Niño-like conditions, periodically oxygenated these waters and boosted marine productivity. This mechanism sustained high faunal diversity in the basin prior to the final ecosystem collapse. Our Granger causality analysis explicitly confirms that shifts in redox conditions served as the primary driver of deep-sea biodiversity decline. Ultimately, these findings demonstrate that the deep-water PTME was not an abrupt catastrophe, but rather the culmination of a protracted environmental and biological crisis.