Some observations on an atypical planktic foraminifer from the Middle Eocene of Kutch, India

Abstract. An atypical planktic foraminifer having close resemblance with Orbulinoides Blow & Saito, 1968 is recorded from a lignite mine section in Kutch, western India. It is practically indistinguishable from Orbulinoides under optical microscope due to general similarities in chamber morphology, coiling mode, aperture number and character, but differs in wall texture when observed under scanning electron microscope (SEM). The wall is characterized by pores of variable size and irregularly distributed pustules unlike the spinose wall of normal Orbulinoides. Based on the SEM micrographs some specialist opinion suggested that the taxon might be a benthic foraminifer. The morphological features of the studied foraminifera are, however, distinctly different from benthic foraminifera with a planktic stage. The associated larger benthic foraminifera correlate the section with the carbonates of Middle Eocene (Bartonian) age in the adjoining areas of Kutch. The accompanying foraminiferal assemblage suggests a near-shore, brackish-water, semi-enclosed depositional environment. It is suggested that the aberrant wall texture was possibly due to environmental stress developed in the restricted basin. Due to incongruous wall texture and to its occurrence as the only planktic foraminifera in the section, the nomenclature of the reported foraminifera is kept open.