Latest Maastrichtian palaeoclimatic and depositional environmental perturbations, a record from Micula prinsii Zone of Meghalaya, northeastern India

Abstract

A significant latest Maastrichtian calcareous nannofossil assemblage is recorded from the exposed section near Syndai Village, Meghalaya. A total of twenty two samples from sedimentary succession consisting of shales and sandy shales, calcareous at places, were studied; out of which ten samples were found productive in terms of calcareous nannofossils recovery. The presence of Micula prinsii in all the productive samples along with the other latest Maastrichtian nanno taxa suggests that the assemblage belongs to Micula prinsii Zone and well correlates with the CC26b Zone of Perch Nielsen and UC20dTP Zone of Burnett which are an amalgamation of old and new biozonation schemes from a range of palaeolatitudes and biogeographic provinces from both oceanic and shelf palaeoenvironments. Micula prinsii Perch–Nielsen, the latest Maastrichtian marker all over the globe, is recorded from both deep–sea sections and shelf areas. It is most evolved form of the genus Micula and got extinct just before K–Pg boundary. The Micula prinsii Zone is marked by the first occurrence of Micula prinsii to the last occurrence of unreworked, non–survivor Cretaceous taxa. In the present study, cluster analysis envisaged the palaeodepositional environmental changes within the Micula prinsii Zone in northeastern India. In the lower part of the section, the abundance of Micula concava and Micula staurophora with the increased numbers of Watznaueria barnesiae indicates environmentally stressful conditions with low productivity in surface water. However, in the upper part the increased numbers of Calculites obscurus with the decrease in Micula concava and Micula staurophora abundance indicates relatively increased productivity in surface water in marginal marine depositional environment.