Abstract
The mid-Cretaceous Oceanic Anoxic Event 1d (OAE-1d) represents one of an important carbon cycle perturbations, yet its global correlation and driving mechanism remain debated. Here, we compare records from the Youxia section in the eastern Tethys with those from other globally distributed sections, integrating carbon isotope, Hg concentration, Hg isotope, Os isotope, and major- and trace-element data from representative OAE-1d records to investigate the global carbon-cycle perturbation and its forcing mechanism. During OAE-1d, the δ¹³C curve records four positive carbon-isotope excursions, designated as peaks a, b, c, and d, together with one negative excursion preceding peak a and two short-lived negative excursions between peaks a–b and b–c. These carbon-isotope features can be correlated with records from the western Tethys, North Atlantic, North Pacific, North America, and southern high latitudes in Australia, indicating that OAE-1d was a globally recognizable carbon-cycle perturbation with a cross-oceanic response. In the Youxia section, synchronous anomalies in Hg/TOC and Δ¹⁹⁹Hg occurred before the onset of OAE-1d. Combined with pre-OAE-1d sea-surface warming, elevated atmospheric pCO₂, and Hg enrichment and enhanced terrigenous input recorded at southern high-latitude Site U1513, these observations suggest that Central Kerguelen LIP volcanism may have been the primary trigger for OAE-1d. Meanwhile, Hg/TOC, Δ¹⁹⁹Hg, and Os isotope records indicate that the subsequent two negative carbon-isotope excursions may also have been linked to volcanic activity. Productivity and weathering proxies further suggest that nutrient delivery and productivity responses during OAE-1d were phased and regionally heterogeneous. Organic matter burial was therefore more likely controlled by enhanced runoff, increased terrigenous organic matter supply, strengthened water-column stratification, and improved preservation conditions. We propose that OAE-1d was a compound carbon-cycle perturbation triggered by Central Kerguelen LIP volcanism, maintained by multi-phase volcanic pulses, and amplified by coupled climate–weathering–ocean feedbacks.

Keywords: Oceanic Anoxic Event 1d (OAE 1d);Youxia section; Carbon isotope stratigraphy;Mercury isotopes ;Large igneous provinces