A report on the Late Cretaceous-Early Palaeocene molluscs and echinoids from the Meghalaya shelf in the vicinity of the K-Pg Mass Extinction Boundary

A rich assemblage of molluscs (bivalves, gastropods, ammonites) and echinoids have been recorded from the Late Cretaceous-Early Palaeocene sediments of the Mahadek and Langpar formations of Meghalaya shelf, which preserve one of the best and most complete Cretaceous-Palaeogene (K-Pg) mass extinction boundary in India. The Mahadek and Langpar formations are mainly exposed in the southern part of the Meghalaya plateau and represent shelf sediments having contact with the Assam Meghalaya Gneissic Complex (AMGC), Sylhet Traps or the Shillong Group metasediments. A diverse fauna of 37 taxa has been recorded represented by 19 bivalve genera, 9 gastropod genera, 4 genera of ammonites, and 5 genera of echinoderms along with burrows (mainly Thalassinoides and a few Skolithos), shark tooth and serpulid worm tubes. Some of the invertebrate taxa are valuable biostratigraphic tools for regional and global correlation of many Upper Cretaceous successions in the world. The heteromorph ammonite assemblage of Nostoceras sp., Eubaculite sp., Glyptoxoceras sp., and Pachydiscus sp. have been recorded from the lower part of the Langpar Formation just below the K-Pg mass-extinction boundary and probably represent the last Indian representatives of the ammonites just before their extinction. Both epifaunal and infaunal organisms in almost equal abundance and wide diversity for palaeoecological consideration noted. The assemblage is dominantly cosmopolitan with few Tethyan, European and Indo-Pacific affinities analogous to many Upper Cretaceous sections.