Coastal ecosystem responses to late stage Deccan Trap volcanism: the post K-T boundary (Danian) palynofacies of Mumbai (Bombay), west India

The Deccan Trap continental flood basalt eruptions of India occurred c. 67-63 Ma, thus spanning the Cretaceous-Tertiary, boundary (65 Ma). Deccan eruptions were coeval with an interval of profound global environmental and climatic changes and widespread extinctions, and this timing has sparked controversy regarding the relative influence of Deccan volcanism upon end-Cretaceous catastrophic events. If Deccan Trap activity was capable of affecting global ecosystems, evidence should be present in proximal Indian sedimentary facies and their palaeontological contents. The impact of late stage Deccan volcanism upon biota inhabiting Mumbai (Bombay) Island's post K-T boundary lagoonal systems is documented here. Sediments (of "intertrappeans") which accumulated within these lagoons are preserved between Trap lavas that characterise the closing stages of this flood basalt episode. Mumbai Island Formation intertrappean faunal and floral communities are conspicuously distinct from those common to many pre K-T boundary, late Maastrichtian intertrappeans across the Deccan province. The latter sedimentary intercalations mostly developed in cognate semiarid, palustrine ecosystems; by contrast. those around Mumbai evolved in peripheral marine settings, within subsiding continental margin basins unique to this late Deccan stage. and under an increasingly humid Danian climate. Geochemical analyses reveal that Mumbai sedimentation and diagenesis were intimately related to local explosive volcanic and regional intrusive activity at c. 65-63 Ma. Although tectonic and igneous events imprinted their signatures throughout these sedimentary formations. organisms usually sensitive to environmental perturbations, including frogs and turtles, thrived. Critically, palynofacies data demonstrate that, whilst plant material deposition was responsive to environmental shifts. there were no palpable declines in floral productivity following Mumbai pyroelastic discharges. Therefore. it is implausible that this late stage explosive volcanism influenced major ecosystem collapses globally. (C) 2004 Elsevier B.V. All rights reserved.