Records of the influence of Deccan volcanism on contemporary sedimentary environments in Central India

Abstract

Deccan volcanism, with a duration of ˜5 Myr, represents a major continental flood basalt province in which ˜2 million km³ of lavas were formed. Such voluminous and rapid volcanism in Phanerozoic earth history has commonly been advanced as a cause for mass extinctions. Despite this significance, few studies have attempted to understand the influence of continental flood basalt volcanism on contemporary sedimentary environments. Thin sedimentary sequences associated with the Deccan volcanics, i.e. the infra- and inter-trappean sequences, offer an opportunity to assess the influence of Deccan volcanism on contemporary sedimentary environments in Central India. The Lameta Formation mainly constitutes a well-characterised regolith, regionally consisting of calcretes and palustrine facies, which may, in places, be associated with ephemeral sandy braided river and sheetflood facies. An assessment of the influence of Deccan volcanism on contemporary surficial environments reveals: (a) an input of basaltic degradational products in the basal fluvial facies of the Lameta Formation; (b) upward changes in facies assemblages from lacustrine/palustrine to subaerial dominated, followed eventually by burial by the first lavas locally; (c) significant changes in the palaeoflow characteristics of fluvial channel facies, respectively under and overlying the main calcareous regolith of the Lameta Formation; (d) that most freshwater lacustrine taxa survived the initial effects of the Deccan volcanism without undergoing any drastic change. In addition to the role of constructional topography resulting from lava emplacement and associated surface uplift, the mode of preservation of sedimentary packets significantly affects changes in the vertical motifs of coeval sedimentary sequences. Because of the problems of time-resolution on 10⁵-10⁶-year time scales in the continental infra- and inter-trappean sequences, detailed cause (volcanism)-effect (surficial environments) relationships at the event level are not well understood. Also, the lack of data from multiple stratigraphic levels of the inter-trappean beds precludes any serious assessment of the directions and rates of changes that took place in CO₂ concentrations of the palaeoatmospheres of that period (65±3 Myr).