Upper Pliocene heterozoan assemblage from the Guitar Formation of Car Nicobar Island, India: palaeoecological implications and taphonomic signatures

摘要

The upper Pliocene Guitar Formation outcrops in Car Nicobar Island, a near-pristine locality of the Andaman-Nicobar Group of Islands, India. Tropical-subtropical photozoan and cool-water heterozoan assemblages have been broadly studied up to now, but little is known about the tropical heterozoans that require deeper analysis. The major objectives of the current assessment pertaining to the Guitar Formation are evaluation of biotic diversity, palaeoecological processes governing the depositional environment and general taphonomic signatures. The carbonate sediments rich in algal and benthic foraminiferal assemblages are dominated by lithophylloids and nummulitids, respectively. Secondary biotic constituents are corals, barnacles, bryozoans, echinoderms, molluscs and gastropods. In particular, a reefal environment is indicated after a thorough examination of the heterozoan assemblages including relative abundance of the algalforaminiferal taxa. The results indicate that carbonate sedimentation occurred in warm, tropical waters under mesooligotrophic conditions and shallow to mildly deeper bathymetric levels ranging close to or below the fair-weather wave base.