Thanetian–Ilerdian coralline algae and benthic foraminifera from northeast India: microfacies analysis and new insights into the Tethyan perspective

Abstract

Thanetian–Ilerdian carbonate deposits from the Lakadong Limestone in Assam Shelf, Meghalaya, northeast India, are studied with respect to microfacies distributions and controlling ecological factors on dominant biogenic components. Palaeoenvironmental implications are inferred following the detailed analysis of microfacies characterized by rich assemblages of coralline red algae and benthic foraminifera. The carbonate sediments have been interpreted as lagoonal to outer shelf facies. It is envisaged that the analysed benthic communities thrived in a meso-oligotrophic regime above the fair-weather wave base. The Lakadong Limestone constitutes a well-preserved record of Late Palaeocene–earliest Eocene shallow marine carbonate ecosystem and has high potential to decipher its response to an interval of distinct changes in climate and tectonic settings. The abundance of oligotrophic larger benthic foraminifera in the Lakadong Limestone is comparable to the foraminiferal assemblages of west Tethys. The phylogenetic changes (‘Larger Foraminiferal Turnover’, LFT) and subsequent rapid radiation of typical Eocene larger benthic foraminifera (Alveolina, Nummulites) usually observed in the west Tethys have also been observed in the upper part of the Lakadong Limestone. The eastward migration of Eocene foraminifera from the west coincided with the India-Asia collision and global warming events at the Palaeocene–Eocene boundary that may have produced a wide array of modifications in biogeography, seasonal run-offs and ocean circulation pathways. The data indicate that rapid rate of migration from west before the onset of geographic barriers and/or timely restoration of pan-Tethyan environmental conditions ensured the incidence of these forms in the earliest Eocene sediments.