ANOMALIES IN ORGANIC CARBON CONCENTRATIONS AND ACCUMULATION RATES DURING THE PERMIAN-TRIASSIC BOUNDARY CRISIS: IMPLICATIONS FOR SEDIMENT FLUX AND MARINE PRODUCTIVITY CHANGES

Changes in marine primary productivity in conjunction with the Permian-Triassic boundary (PTB) crisis have been debated at length, with little resolution to date owing to a paucity of quantitative data. Herein, we report total organic carbon (TOC) concentrations and organic carbon accumulation rates (OCAR) for 33 PTB sections with a near-global distribution and consider their implications for changes in marine primary productivity rates during the end-Permian crisis. Many sections in South China exhibit abrupt declines in TOCs and OCARs from the Changhsingian (latest Permian) to the Griesbachian (earliest Triassic), a pattern not observed for PTB sections from any other region. This pattern cannot be explained through changes in sedimentation rates, sedimentary facies, or redox conditions, all of which would have favored higher (rather than lower) TOCs and OCARs during the Griesbachian. The most likely explanation is a collapse of marine primary productivity across the South China craton in conjunction with the end-Permian crisis that continued for an extended interval into the Early Triassic. The productivity crash as well as the coeval decimation of marine fauna coincided with deposition of the “boundary clay” at Meishan D, suggesting that both events were related to an explosive volcanic eruption of regional origin, the lethality of which may have been enhanced by climatic and environmental stresses induced by ongoing Siberian Traps flood basalt volcanism. Elsewhere globally, OCARs increased on average by ~7-8X from the Changhsingian to the Griesbachian, largely as a function of a concurrent increase in bulk accumulation rates. Radiometric dating uncertainties can account at most for only a fraction of this secular variation, which probably resulted mainly from an increase in subaerial weathering rates and elevated fluxes of detrital material to Early Triassic marine systems. Concurrent intensification of chemical weathering relative to physical weathering is likely to have increased the flux of nutrients to the global ocean, leading to enhanced marine primary productivity that contributed to the development of widespread oceanic anoxia.