Occurrence of the marker dinoflagellate cyst Apectodinium in Narsapur Well-I, Krishna-Godavari Basin, India

Abstract

The morphology and taxonomy of the two dinoflagellate cyst taxa viz., Fibrocysta variabilis and Fibrocysts sp., described by Mehrotra and Sarjeant (1987) from the subsurface conventional core samples collected at 2703-2706 m (cc10) and 3621-3624 m (cc13) depths of Narsapur Well-1. Krishna-Godavari Basin, are discussed and reassessed. The two species are found to be the junior synonyms of Apectodinium paniculatum (Costa & Downie) Lentin & Williams 1977 and Apectodinium quinquelatum (Williams & Downie) Lentin & Williams 1981, respectively. A few other specimens comparable to A. paniculatum and A. augustum have also been described. The stratigraphic significance of the reported Apectodinium species is discussed. It is suggested that the dinoflagellate cyst assemblage at sample depth 2703-2706 is the latest Paleocene- ?earliest Eocene in age. The occurrence of Apectodinium species in infra-trappean sample at 3621-3624 m depth, dated as Maastrichtian by Mehrotra and Sarjeant (1987), indicates that this level is not older than the Late Palaeocene in age. This creates an anomalous situation because the youngest infra-trappean sediments at 3336-3339 m depth (cc 12), on planktonic formainiferal data, are dated to be latest Maastrichtian. This discrepancy creates doubt over the slide/sample numbering which needs conformation. Palaeoenvironmental significance of Apectodinium is discussed. A restudy of dinoflagellate cyst biostratigraphy of Narsapur Well-1 is recommended.