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The role of extensional tectonics in the generation of basaltic melt and eruption of continental flood basalts is controversial, and yet it remains crucial to understanding the origin and cause of these large-volume eruptions. Establishing the timing of lithospheric extension, continental rifting, and the onset of continental flood basalt volcanism is therefore of importance to petrogenetic models. Detailed mapping along the Mumbai coast, India, reveals three chemically distinct sets of dikes, which, together with high-precision [sup.40]Ar/[sup.39]Ar dating, demonstrate the temporal relationship between lithospheric extension and Deccan volcanism. The east-west extension evident along the west coast of India, which led to the separation of the Seychelles from the Indian plate, only began during the final phases of the basalt eruptions, and cannot have initiated the large-volume eruptions of the Deccan flood basalt province. doi: 10.1130/G31072.1

New magnetostratigraphic data from seven Western Ghats sections in the Deccan Volcanic Province are presented. These are combined with an established geochemically defined stratigraphy, and volcanological logs, to provide a correlated, chronological eruptive framework. We identify two magnetic polarities in five of the sections, and these are assigned to chrons 29r and 29n. Importantly, the reversal boundary represents an identifiable isochronous surface within the volcanic pile. This surface occurs at different elevations, as does the altitude of the geochemically defined formation boundary (i.e. Ambenali-Mahabaleshwar Fms), which defines a second isochronous surface. Inspection reveals significant differences in the number and thickness of lava units preserved between these two surfaces. This indicates that there was significant local topography (c. 80 m) across Deccan Volcanic Province lava fields during their development; an interpretation consistent with topographies observed across modern and historical examples (e.g. Hawaii, Iceland). These data also indicate that the geochemical stratigraphies of continental flood basalt provinces can mask local and sub-regional detail in lava stacking patterns when applied at smaller spatial scales (

Research from biological and geological sources has highlighted the role of volcanoes in the outgassing of P, and thermal fixation and subsequent atmospheric oxidation of N[O.sub.x] in volcanic environments. The impact of these nutrient fluxes on biological systems has been demonstrated on present-day Hawai'i, and here we consider the impact on the plant communities within a large igneous province (LIP). The Miocene Columbia River Basalt Province, the youngest LIP on Earth, contains many sedimentary interbeds between the flows of the major extrusive phase, and these interbeds preserve variable but often diverse palynofloras. By integration of palynofloral analysis with analysis of macronutrient levels in the interbeds it can be suggested that there may have been significantly elevated levels of P within the lava field proximal to the source vents, a distribution mirrored by Ca and Mg. Evidence for potential volcanogenic eutrophication is restricted to >[10.sup.3] year duration interbeds, contemporary with eruptive activity elsewhere in the LIP. The geochemistry and palynology of other interbeds demonstrate nutrient deficiency, with a potential route to nutrient sufficiency available from long-term symbiotic N-fixation. Elsewhere within the Columbia River Basalt Province, this process is short-circuited by the imput of felsic ash from the nearby Cascades Range of volcanoes.

The Deccan Volcanic Province is one of the world's largest continental flood basalt provinces, and derives additional importance because its eruptions (64-67 Ma) straddle the Cretaceous-Tertiary boundary. To better assess the environmental impact of Deccan volcanism, and its possible effect upon Cretaceous-Tertiary boundary biota, it is necessary to document the stratigraphy, chronology and volume of the eruptions. New chemostratigraphical data permit mapping of the SE Deccan. These data strengthen the likelihood that the Rajahmundry Traps of eastern India were originally fed by long-distance flows, and are an extension of the Main Deccan Volcanic Province. An east-west cross-section reveals a depression or 'moat' around the SE periphery of the Deccan Volcanic Province. This provided a site in which shallow lakes initially formed, and along which later lava eruptions became channelled and confined. Published palaeomagnetic data indicate that the lavas of the SE Deccan were erupted during Chron 29R, coeval with the Cretaceous-Tertiary boundary, and the chemostratigraphic data place the associated lake sediments (i.e. Lameta Group) beneath and within lavas of the Wai Subgroup. Finally, these new map data are combined with previous work to provide a quantitative estimate for the original Deccan Volcanic Province eruptive volume of c. 1.3 x [10.sup.6] [km.sup.3].

Globally, the Series 2 – Series 3 boundary of the Cambrian System coincides with a major carbon isotope excursion, sea-level changes and trilobite extinctions. Here we examine the sedimentology, sequence stratigraphy and carbon isotope record of this interval in the Cambrian strata (Durness Group) of NW Scotland. Carbonate carbon isotope data from the lower part of the Durness Group (Ghrudaidh Formation) show that the shallow-marine, Laurentian margin carbonates record two linked sea-level and carbon isotopic events. Whilst the carbon isotope excursions are not as pronounced as those expressed elsewhere, correlation with global records (Sauk I – Sauk II boundary and Olenellus biostratigraphic constraint) identifies them as representing the local expression of the ROECE and DICE. The upper part of the ROECE is recorded in the basal Ghrudaidh Formation whilst the DICE is seen around 30m above the base of this unit. Both carbon isotope excursions co-occur with surfaces interpreted to record regressive–transgressive events that produced amalgamated sequence boundaries and ravinement/flooding surfaces overlain by conglomerates of reworked intraclasts. The ROECE has been linked with redlichiid and olenellid trilobite extinctions, but in NW Scotland, Olenellus is found after the negative peak of the carbon isotope excursion but before sequence boundary formation. [ABSTRACT FROM PUBLISHER]