Different integrated mechanisms drove the two pulses of the Late Ordovician mass extinction

Across the Ordovician–Silurian transition, the first large-scale extinction event in geological history, the Late Ordovician mass extinction (LOME), occurred. The LOME was a double-pulse event, and the two extinction pulses occurred in the late Katian – early Hirnantian (LOME-1) and middle Hirnantian (LOME-2). At present, the comprehensive driving mechanism of the two extinction pulses is still controversial. In this study, two cores (JY87 and JY143) from the middle Yangtze shelf in South China were selected as the research objects. Combined with previous research results, four main stressors, namely, volcanism, ocean redox, climate and nutrient supply, were analyzed. On this basis, the two-pulse driving mechanism of the LOME was comprehensively studied. The comprehensive mechanisms driving the two extinction pulses were different. During the LOME-1, the intensity of volcanism was relatively weak. Volcanic silicate weathering, high nutrients and long-term accumulation of high organic carbon burial flux may have jointly caused cold conditions and led to the expansion of the anoxic sulfide zone and enhancement of sulfidation. The cold conditions had less effect on deep-water benthos, but enhanced euxinia led to their extinction. In contrast, shallow-water benthos were less affected by the enhanced euxinia, but the cold conditions led to their extinction. During the LOME-2, a sudden and brief increase in volcanism that was extremely intense occurred, bringing in abundant nutrients and SO2, resulting in more widespread and long-lasting euxinia. This occurrence led to the extinction of benthos that survived during the LOME-1. •Four stressors that may lead to LOME, including volcanism, ocean redox, climate and nutrient supply, are analyzed.•During the LOME-1, the intensity of volcanism was relatively weak.•During the LOME-2, a sudden and brief increase in volcanism that was extremely intense occurred.•Both cooling and relatively widespread euxinia lead to the occurrence of the LOME-1.•More widespread and long-lasting euxinia lead to the occurrence of the LOME-2.