Abstract:
Multivariate (Factor and Cluster) analyses of abyssal benthic foraminifera from 31 latest Miocene-Pleistocene samples from Deep Sea Drilling Project (DSDP) Site 236, west-central Indian Ocean (eastern Somali Basin) revealed significant changes. R-mode factor and Q-mode cluster analysis of 29 highest ranked species identify 5 environmentally significant assemblages and 5 clusters reflecting distinct environments of deposition. Cibicides refulgens, Ehrenbergina carinata, Cymbaloporetta squammosa, Bolivina pusilla, Astrononion umbilicatulum and Quinqueloculina weaveri mark assemblage 1. This assemblage, characterizing Cluster II, is inferred to reflect high flux of organic matter. Assemblage 2 of Bolivinita quadrilatera, Uvigerina proboscidea, Nonionella japonicum, Bolivina spathulata and Uvigerina porrecta, characterizes Cluster IV, suggesting low oxygen content and sustained flux of organic matter from high surface productivity. Cibicides bradyi, C. wuellerstorfi, Oridorsalis umbonatus and Melonis barleeanum typify Assemblage 3, which is indicative of intermediate flux of degraded organic matter characterizing Cluster I. Assemblage 4, marked by Reussella spinulosa, Astrononion umbilicatulum, Bolivina spathulata, Nonionella japonicum and Bolivina pusilla, corresponds to Cluster III and suggests low-oxygen and organic carbon rich environment. Nuttallides umbonifera, Pyrgo murrhina and Cibicides wuellerstorfi typify assemblage 5. This assemblage corresponds to Cluster V and indicates well-oxygenated, corrosive bottom water.