HR: 0800h
AN: PP51B-0601    [Abstracts]
TI: A new model for the Toarcian global climate change: Explosive venting of greenhouse gases from metamorphic aureoles around sill complexes in the Karoo basin
AU: * Svensen, H
EM: hensven@fys.uio.no
AF: Physics of Geological Processes, Dept. of Physics, University of Oslo, PO Box 1048 Blindern, Oslo, 0316 Norway
AU: Planke, S
EM: planke@vbpr.no
AF: Volcanic Basin Petroleum Research, Forskningsparken, Gaustadalleen 21, Oslo, 0349 Norway
AU: Chevallier, L
EM: luc@geobell.org.za
AF: Council for Geoscience, PO Box 572, Bellville, 7535 South Africa
AU: Malthe-Sorenssen, A
EM: malthe@fys.uio.no
AF: Physics of Geological Processes, Dept. of Physics, University of Oslo, PO Box 1048 Blindern, Oslo, 0316 Norway
AU: Jamtveit, B
EM: bjorn.jamtveit@geo.uio.no
AF: Physics of Geological Processes, Dept. of Physics, University of Oslo, PO Box 1048 Blindern, Oslo, 0316 Norway
AU: Corfu, F
EM: fernando.corfu@geo.uio.no
AF: Department of Geosciences, University of Oslo, PO Box 1047 Blindern, Oslo, 0316 Norway
AB: Emplacement of voluminous intrusive complexes in organic-rich sedimentary basins may cause global climate change (e.g., intrusive volcanism in the NE Atlantic may have caused the Initial Eocene Thermal Maxima). The Karoo basin in South Africa was intruded by voluminous basaltic melts in the early Jurassic. Black organic-rich shale in the lower parts of the Karoo basin (the Ecca Group) were intruded by up to 130 m thick sub-horizontal magmatic sills, whereas dominantly saucer-shaped sills were emplaced in the overlying fluvial sedimentary sequences. The sills are associated with numerous hydrothermal vent complexes formed in a sub-aerial environment and deep-level breccia pipes. Field relations, borehole data, geochemistry, and geodynamic modeling show that both the deep pipes and the shallow hydrothermal vent complexes were formed as a consequence of pressure build-up in contact aureoles surrounding the sill intrusions. Analyses of shale from the metamorphic aureoles show that most of the organic carbon was lost during the heating event. The formed greenhouse gases (e.g., methane) were explosively released to the atmosphere through the pipes and the vent complexes. Mass balance calculations suggest that the volume of the released greenhouse gases were likely sufficient to initiate the Toarcian greenhouse. The causal relationship between the intrusive event and the Toarcian global warming is corroborated by new U-Pb zircon ages from a dolerite sill associated with breccia pipes in the Ecca Group, both occurring at about 183 Ma.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4930 Greenhouse gases
DE: 8424 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8135)
DE: 9611 Jurassic
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005