A review of the embedded time scales of flood basalt volcanism with special emphasis on dramatically short magmatic pulses

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 similar to 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.