Utility of sub-surface benthic foraminiferal assemblages to decipher the paleoenvironment of the north-west Kerala coast

Benthic foraminifera have proved to be reliable proxies for understanding paleoenvironmental changes or paleoclimatic changes in the past geological history of the Earth, especially since the Cambrian when these unicellular protozoans began to evolve. Since then, foraminifers have been recorded as fossils and their abundant occurrence in the fossil record has aided in understanding the past history of the Earth. Within the Holocene, this group of microfossils has proved to be of immense utility, as their assemblages could be utilized for understanding past environmental changes, as they are so sensitive to variations in such ecological parameters as pH, depth of the water column, salinity, dissolved oxygen content, nature of substrate calcium carbonate and organic contents, which are the primary controlling factors over their species populations and diversity. The study area is a part of Kannur District, Kerala, India, about 5–7 km from the present-day shoreline. Trench samples (sub-surface) at varying depths up to 3.6 m, at Karakkeezhu and Kuduvathala, yielded a benthic foraminiferal assemblage that is characteristic of modern estuarinelbrackish water environments. This assemblage, typified by the dominance of Ammonia beccarii (Linnaeus) and its associated species, is suggestive of a shallow, probably sheltered, tidal flat environment with a possible connection to the Arabian Sea ∼5,000 to 5,500 years B.P. as revealed by 14C dates of both mollusk shells and sediment samples. The study has thrown open some intriguing questions, particularly with regard to the complete absence of arenaceous, agglutinated forms (Suborder TEXTULARIINA) and the poor representation of calcareous, imperforate taxa (Suborder MILIOLINA).