A 200,000-yr interval of extreme global warming marked the start of the Eocene epoch about 55 million years ago. Negative carbon- and oxygen-isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid (approximately 10,000 yr) input of isotopically depleted carbon. It has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change. Large-scale hydrate melting, however, requires a hitherto unknown triggering mechanism. Here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the Vøring and Møre basins in the Norwegian Sea. We propose that intrusion of voluminous mantle-derived melts in carbon-rich sedimentary strata in the northeast Atlantic may have caused an explosive release of methane--transported to the ocean or atmosphere through the vent complexes--close to the Palaeocene/Eocene boundary. Similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the Siberian Traps (approximately 250 million years ago) and the Karoo Igneous Province (approximately 183 million years ago).

Avoluminous magmatic complexw asemplaced int he Vøringa ndM øreb asins duringP aleocene/Eocenec ontinentalr iftinga ndb reak-up int he NE Atlantic.Thisintrusivee vent hashad asignificant impactondeformation,source-rock maturation andfluid flow inthe basins. Intrusivecomplexesandassociated hydrothermalv ent complexeshaveb eenm apped on aregional2 Dseismic dataset( c .1500 00 km) andon one large 3Dsurvey. The extent ofthe sill complexisatleast 800 00 km 2 ,withanestimated totalvolumeof0.9 to 2.8 £ 10 4 km 3 .The sheetintrusions aresaucer-shaped inu ndeformed basins egments. The widthso fthe saucers becomelargerw ithi ncreasinge mplacement depth.Morevaried intrusion geometriesaref oundi n structured basinsegments. Some734hydrothermalvent complexeshavebeenidentified,although itisestimated that2-3000 vent complexesarepresent int he basins. The vent complexesarelocated abovesills andwere formed asad irectconsequence ofthe intrusivee vent byexplosivee ruption ofg ases,liquidsandsediments, formingup to 11 kmwide craters atthe seafloor. The largest vent complexesarefoundinbasinsegments with deeps ills (3-9kmp alaeodepth). Moundsandseismic seepanomaliesl ocated abovethe hydrothermalv ent complexess uggest thatt he vent complexeshaveb eenr e-used for verticalfluid migration longa ftert heir formation. The intrusivee vent mainly tookplace just prior to,or during, the initialp haseofmassiveb reak-up volcanism (55.0-55.8Ma). Thereisalso evidence for aminor UpperPaleocenevolcanic event documented by the presence of20 vent complexest erminatingi nt he UpperPaleocenesequence andthe localp resence of extrusivevolcanic rockswithinthe Paleocenesequence.Volcanic processesanddeposits mayhaveastrongimpactonthe structureandgeodynamic development ofcontinentalmargins and associated sedimentary basins. The identification ofvolcanic deposits andthe evaluation oftheirimpacto nt he marginhistory are, thus,two important aspects ofpetroleum exploration of continentalrifted margins. Significant attention has,overt he past decade, beendevoted to studieso fe xtrusiveprocessesand deposits on volcanic rifted margins (e.g.Eldholm etal .1 989; Menzies etal. 2002; White etal .2 003). However,petroleum explorationists will commonly encounterintrusivec omplexes beforetheyencounterextrusivevolcanic rocksw hent heym ove from shallow-watert odeep-waterareas. Deep-waterexplorationists,therefore, need to know how to recognize, interpretand risk-evaluatei ntrusivec omplexes.The frontierVøringa ndM øreb asins off mid-Norwayare classicalexampleso fi ntruded volcanic basins located on arifted volcanic margin( e.g.Skogseid etal .1 992; Skogly 1998;Berndt etal .2 000; Brekke 2000; Gernigon etal .2 003). The volcanic activity inthesebasins wasassociated withLatePaleocenerifting andc ontinentalbreak-up int he NE Atlantic.Similarintrusive basinprovincesarelocated alongthe entireEuropeanNE Atlantic margin(e.g.Gibb &Kanaris-Sotiriou 1988;Bell &Butcher2002; Smallwood&Maresh2002) andonshoreincentral-east Greenland (e.g.Larsen&M arcussen1 992; Price etal .1 997).Sill comp...

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