A rare foraminiferal assemblage with new species of Nummulites and Globigerina from the Eocene-Oligocene transition strata of Cambay Basin, India

A foraminiferal assemblage comprising Nummulites longilocula n. sp., Globigerina dinodensis n. sp., Turborotalia sp. A, Chiloguembelina aff. C. cubensis, Nonionella cf. N. wemmelensis and Nonionella aff. N. pauciloba has been recovered from a stratigraphic interval between the last occurrence of Turborotalia cerroazulensis s.l. and the first occurrence of Cassigerinella chipolensis in an apparently continuous sequence of calcareous sediments exposed near Dinod village in Cambay Basin, Gujarat, India. The assemblage also includes sparingly occurring Nummulites retiatus, radiate Nummulites spp., discoidal Pellatispira spp., calcareous nannofossils and radiolaria; furthermore, the assemblage is found to be occupying a stratigraphic position between the last appearance of Discocyclina and the first appearance of Nummulites fichteli. Planktonic foraminiferal zones P17-P18 have been clearly demarcated in the sequence. and the new assemblage clearly denotes a distinctive passage from the older zone to the younger; thus a provisional P17-P18 transition Zone with an age range of latest Eocene to earliest Oligocene is assigned to it. The distinctive features and the new foraminiferal species of this assemblage, seemingly in contrast with the standard zonal boundary character, are described, and their bearing on the nature of the Eocene-Oligocene boundary in the Cambay Basin sequence is discussed. The assemblage, with its new foraminiferal data, lends further credence to several analogous records of foraminiferal transition found in similar passage beds occurring elsewhere.