Abstract: Radioisotopic age determinations targeted at key stratigraphic successions worldwide continue to refine the geological timescale with increasing precision and accuracy and to unravel the tempo of global geological, palaeoclimatic and palaeobiotic processes that have shaped our planet. The last decade has witnessed significant progress in the calibration of the Permian Period through integrated stratigraphic, palaeontological and high-precision geochronological investigations. These studies have largely focused on the Cisuralian and Lopingian stages, particularly the end-Permian mass extinction, whereas much of the Guadalupian and its associated events remain inadequately calibrated. A compilation of the high-precision U–Pb geochronology generated in the past ten years yields ages of 298.92±0.19 Ma for the onset of the Permian, 293.52±0.17 Ma for the base-Sakmarian, 290.10±0.14 Ma for the base-Artinskian, 272.95±0.11 Ma for the Cisuralian–Guadalupian boundary, 265.22±0.34 Ma for the base-Capitanian, 254.14±0.12 Ma for the base-Changhsingian and 251.90±0.10 Ma for the Permian–Triassic boundary. Extension of modern astrochronological methods to the Palaeozoic Era presents new opportunities for broader stratigraphic correlations and enhanced calibration of the Permian timescale. Supplementary material: Table S1 (U–Pb data) is available at https://doi.org/10.6084/m9.figshare.c.3917425

The temporal link between mass extinctions and large igneous provinces is well known. Here, we examine this link by focusing on the potential climatic effects of large igneous province eruptions during several extinction crises that show the best correlation with mass volcanism: the Frasnian-Famennian (Late Devonian), Capitanian (Middle Permian), end-Permian, end-Triassic, and Toarcian (Early Jurassic) extinctions. It is clear that there is no direct correlation between total volume of lava and extinction magnitude because there is always sufficient recovery time between individual eruptions to negate any cumulative effect of successive flood basalt eruptions. Instead, the environmental and climatic damage must be attributed to single-pulse gas effusions. It is notable that the best-constrained examples of death-by-volcanism record the main extinction pulse at the onset of (often explosive) volcanism (e.g., the Capitanian, end-Permian, and end-Triassic examples), suggesting that the rapid injection of vast quantities of volcanic gas (CO 2 and SO 2 ) is the trigger for a truly major biotic catastrophe. Warming and marine anoxia feature in many extinction scenarios, indicating that the ability of a large igneous province to induce these proximal killers (from CO 2 emissions and thermogenic greenhouse gases) is the single most important factor governing its lethality. Intriguingly, many voluminous large igneous province eruptions, especially those of the Cretaceous oceanic plateaus, are not associated with significant extinction losses. This suggests that the link between the two phenomena may be controlled by a range of factors, including continental configuration, the latitude, volume, rate, and duration of eruption, its style and setting (continental vs. oceanic), the preexisting climate state, and the resilience of the extant biota to change.

There are at least a dozen Phanerozoic continental flood basalts and oceanic plateaus (large igneous provinces) that roughly obey a “rule of two times one million” (volume of extruded lava of one million cubic kilometers and duration of volcanic activity ~1 m.y.). The correlation between large igneous province ages and mass extinctions (and oceanic anoxia events) is excellent, but quantitative scenarios are still wanting. We hypothesize that the temporal sequences of extrusions determine the severity of extinction: Volcanic pulses separated by thousands of years allow the ocean-atmosphere system time to recover, whereas large volcanic pulses occurring in a shorter sequence may result in a runaway effect and cause a mass extinction. Detailed flow-by-flow magnetic stratigraphies of thick sections have identified directional groups (sequences of superimposed lava flows with the same paleomagnetic direction that cooled in a time too short to record secular variation). With help of this simple tool, many single eruptive events with a volume larger than 1000 km 3 , some in excess of 10,000 km 3 , emplaced in possibly less than a decade, have been identified. We review this evidence, mainly for the following flood basalt provinces: Columbia, Brito-Arctic, Deccan, Karoo-Ferrar, Central Atlantic magmatic province, and Siberian Traps. Large igneous province volcanism occurs in a highly discontinuous way, on embedded time scales, on the order of 10 m.y., 1 m.y., 100 k.y., and 10 yr. This provides constraints for models of plume-lithosphere interaction and magma production. A next step is to model the consequences of massive injection of gases that can be derived from these time and duration estimates. Early attempts are reviewed in a companion paper in this volume.