Sediment Grain Size Controlling the Distribution of Foraminiferal Assemblage: A Case Study from Chandipur Coast, India

ABSTRACT The distribution of smaller benthic foraminifera is controlled by several biotic and abiotic factors. Nutrient supply and oxygen availability are the most commonly researched factors. However, the influence of sediment grain size is less studied and understood. Here, the relationship between sediment grain size and foraminiferal assemblage is studied from Chandipur Coast, India. Chandipur has various sub-environments within a relatively smaller area due to the presence of an estuary, a bar and a vast tidal flat. This, in turn, facilitated variation in grain size. Other than the qualitative correlation, statistical analyses like Principal Component Analysis (PCA), Q-Hierarchical Cluster Analysis (Q-HCA) and linear r (Pearson) correlation were performed to check the relation between foraminiferal assemblages. The total Foraminiferal number (N), Species richness (S) and Shannon index (H) are proportional to the percentage of mud content of the sediment. Few smaller benthic foraminifera like Ammonia tepida, Elphidium limpidum, Melonis sp., Melonis barleeanus, Ammonia bellaria, Elphidium clavatum, and Ammonia parkinsoniana are moderately to strongly correlated with the mud content (r> 0.5 = strong, r> 0.3 = moderate). Two dominant foraminifera, Rosalina bradyi (r=0.15) and Asterorotalia trispinosa (r=0.02), are not related to sediment grain size, but other factors like total organic carbon, river influx or epiphytic nature of the foraminifera may have controlled their abundance.