Pre-Extinction Stress in the Salt Range: Wordian Eustasy and its Role in the End-Guadalupian Crisis

The end-Guadalupian (Middle Permian) mass extinction represents a pivotal yet enigmatic event in Earth's history. Its drivers, often attributed to the emplacement of the Emeishan Large Igneous Province, are intensely debated, with proposed mechanisms ranging from volcanic outgassing to sea-level fluctuations and widespread marine anoxia. However, a critical lack of high-resolution, multi-proxy records from key paleo-tropical regions has hindered a unified model. This study presents a fully integrated dataset combining field sedimentology, microfacies analysis, and a comprehensive suite of major, trace, and rare earth element geochemistry from the Wordian carbonates of the Salt Range, Pakistan, a classic Neotethyan margin. Our data reveal a pronounced transgressive systems tract, marked by a shift from peritidal cycles to deeper-water carbonates. Crucially, geochemical proxies (e.g., Sr/Ca, Mn/Sr) confirm this sea-level rise was accompanied by a shift in oceanic chemical budgets. More significantly, we identify a pre-extinction perturbation in redox-sensitive trace elements (e.g., V/Cr, U/Th, Mo enrichment) and nutrient tracers (P, Ba), indicating a trend towards deoxygenation and increased nutrient loading in the Tethyan ocean during the Wordian. We interpret this coupled sedimentological-geochemical signal as a direct record of eustatic rise-driven oceanographic stagnation. The transgression likely flooded vast continental shelves, enhancing organic matter burial and fostering the development of stratified, anoxic water masses on a near-global scale. The synchronicity of this event with the onset of Emeishan volcanism suggests a powerful feedback mechanism: sea-level rise created the environmental context in which the effects of volcanism (e.g., nutrient runoff, greenhouse warming) were dramatically amplified. By providing a high-resolution record from the Tethyan gateway, this research places the Wordian of the Salt Range as a vital recorder of pre-extinction environmental deterioration. Our findings demonstrate that the stage for the end-Guadalupian catastrophe was set several million years earlier by oceanographic upheaval, forcing a re-evaluation of the extinction's triggers and providing a critical ancient analogue for modern sea-level rise and ocean deoxygenation.