Guembelitria (foraminifera) in the upper cretaceous-lower paleocene succession of the Langpar Formation, India and its paleoenvironmental implication

Abstract

Guembelitria is an essential biotic component in the Late Cretaceous-Early Paleogene (K/Pg) marine successions to provide crucial information about the K/Pg boundary; however, it is not well studied in Indian subcontinent. Biostratigraphically well constrained K/Pg successions of Therriaghat and Mahadeo in the East Khasi Hills District, Meghalaya, India provided a scope to present a comprehensive account of the genus in the perspective of differences of opinion about its species. A total of six species including Guembelitria langparensis n. sp., are recognized and their stratigraphic distribution is recorded. A review of the taxonomic validity of the known species, an evaluation of the diverse concepts of Guembelitria cretacea Cushman, and semiquantitative analysis of the recovered species permitted their clustering into two morphogroups that had different ecology. Morphogroup I comprising Guembelitria cretacea, Guembelitria trifolia and Guembelitria langparensis n. sp., is characterized by flared and short spire tests that form a bioseries and thrived as surface floaters. Morphogroup II comprising Guembelitria irregularis, Guembelitria danica and Guembelitria sp a, possesses high spire, narrow tests that have morphological abnormalities and had preference for living in subsurface stressed environment. The occurrence of the species and accompanying other features like ratio of planktonic to benthic foraminifera (p/b), lithologic assemblage and incidence of phosphorite, are used to infer depositional environments and sea level changes during successive biozones of the sequence. The recognized Guembelitria events during the K/Pg transition are discussed with reference to world occurrences.