Major Floral Turnover at Mahadeo-Langpar Formational Boundary above K/T Iridium Layer: Is it Facies Controlled?

The Um Sohryngkew river section at Therriaghat, Meghalaya, exposes Mahadeo (Maastrichtian) and Langpar (Danian) Formations extensively. The palynological investigation of the topmost Mahadeo and lowermost Langpar reveals an abrupt change in palynoflora at the formational boundary. The Maastrichtian index palynofossils viz. Azolla cretacea, Ariadnaesporites ariadnae, Mulleripollis bolpurensis etc. disappear at the uppermost Mahadeo. At the basal Langpar the assemblage is dominated by fungal and algal elements. On this basis the palynofacies turnover is demarcated within a 40 cm thick calcareous sandy shale underlain by the 3 cm thick highly carbonized shale. The palynological boundary corresponds with the lithological one demarcated by Pandey(1978, 1981), and is located 10 m above the foraminiferal, nannofossil, dinoflagellate boundary approximating the iridium rich level. The palynological data suggest no major catastrophic event at the iridium level with the major taxa continuing through. The major palynological break reported in this paper is at formational boundary and may be facies controlled as well.