Paper No. 68-1
Presentation Time: 1:30 PM
HOW LARGE IGNEOUS PROVINCES AFFECT CLIMATE AND SOMETIMES CAUSE EXTINCTIONS
LIPs can have a significant climatic effect as monitored by sedimentary isotopic compositions that record seawater composition, and numerous LIPs are temporally correlated with extinction events. Literature on the links between LIPs and catastrophic climatic change is rapidly expanding. Improved U-Pb dating (with better than 0.1 Ma resolution in the Phanerozoic; e.g. Burgess, Blackburn & others) is confirming the long-proposed extinction-LIP link (e.g. Courtillot, Rampino & others). The most dramatic climatic effect is global warming due to greenhouse-gases from LIPs. Subsequent cooling (and even global glaciations) can be caused by CO2 drawdown by weathering of LIP-related basalts. Environmental effects associated with LIPs also include oceanic anoxia, sea level changes, etc., and all these effects and their interactions can be displayed as a complex flow chart (e.g. Wignall). Notably, the size of a LIP is not the only important factor. Also contributing to climatic/extinction effects are the abundance of LIP-produced pyroclastic material and volatile fluxes that reach the stratosphere and in particular the role of super-eruptions (e.g. Self). Another effect is the type of host terrane; while flood basalt degassing (CO2, SO2, etc) is important, there is also a significant amount of these gases (but also including ozone-destroying halocarbons) released from volatile-rich sedimentary rocks (e.g. evaporites and coal horizons) heated by LIP intrusives (e.g. Svensen & others). Feedbacks are important; such as global warming leading to destabilization of clathrates, consequent release of further greenhouse gases, and greater global warming. An important global terrane effect is the surface extent of basalts at the time, and the portion which is at low latitudes, factors which increase the efficiency of the CO2 drawdown (and global cooling) through weathering. In addition, the climatic changes will be affected by the paleogeography (the distribution of continents and their mountains) and wind and ocean current patterns present at the time of LIP emplacement. In the broadest sense LIPs can affect shifts between Icehouse, Greenhouse and Hothouse climatic states (e.g. Kidder & Worsley). However, the specific effects, their severity, and their time sequencing will be specific to each LIP.