Middle Eocene calcareous Nannofossil Biostratigraphy and Taxonomy of onland Kutch Basin, western India

Abstract

Rich and diversified nannofossil assemblage comprising 110 species (13 new species and 8 new taxonomic combinations) and 4 calcareous dinoflagellates species are described from the type locality of Harudi Formation and Fulra Limestone Fonnation of Kutch Basin. The assemblage is dominated by the families Braarudosphaeraceae, Rhabdosphaeraceae and Calyptrosphaeraceae. All holococcolith genera except genus Peritrachelina are recorded in the assemblage. The assemblage is typically indicative of low-latitude, nearshore, shallow water environment and can be assigned to zone NP 17 Discoaster saipanensis Zone (Martini, 1971a emend. Rai, 1988). It also correlated with parts of both P 13 Orbulinoides beckmanni and P 14 Truncorotaloides rohri planktonic foraminifera Zones (Blow, 1969) and a part of D11 Dinoflagellate Zone (Costa & Manum in Vinken, 1988) of Bartonian age. Critical reappraisal of published fossil records including age diagnostic planktonic and larger foraminifera species and nannofossil data along with field observations of supratrappeans indicate, three discrete lithounits in ascending order viz., shale-marl-limestone upto terminal Fulra Limestone Formation. The proposed model questions the presence of marine sediments of Palaeocene, Lower Eocene and Lutetian age in onland Kutch Basin (Biswas & Raju, 1973; Biswas, 1992).