Paleoceanographic and paleoclimatic history of the Somali Basin during the Pliocene-Pleistocene; multivariate analyses of benthic foraminifera from DSDP Site 241 (Leg 25)

Abstract

This study quantitatively examines benthic foraminifera (X25p.m) from 40 Pliocene-Pleistocene samples from Deep Sea Drilling Project (DSDP) Site 241, Somali Basin. R-mode factor and Q-mode cluster analyses of the 26 highest ranked species define five significant factor assemblages and five clusters reflecting different environmental characteristics in the Plio-Pleistocene sequence. Assemblage 1, consisting of Bulimina marginata, Nonionella japonicum, Cassidulina carinata, and Uvigerina proboscidea, reflects high flux of organic matter from high surface productivity and dominates Custer 11. Eggerella bradyi, Melonis pompilioides, and Oridorsalis umbonatus constitute Assemblage 2, which is inferred to reflect intermediate flux of relatively degraded organic matter (Cluster IV). Assemblage 3, characterized by Cibicides wuellerstorj and Epistominella exigua, coincides with Cluster I. This assemblage indicates increased oxygenation and strongly pulsed food supply. Assemblage 4, marked by Loxostomum karrerianum (=Bolivina karrerianum), Trifarina angulosa and Bolivina spathulata,corresponds to Cluster I11 and suggests an oxygen-deficient, organic carbon-rich environment. The principal species of Assemblage 5 is Nuttallides umbonifera, with Astrononion umbilicatulum and Epistominella exigua as secondary species. This assemblage, which corresponds to Cluster V, suggests low food, high oxygen and increased bottom water corrosiveness. Mean test diameters of the planktic foraminifer Orbulina universa were used to interpret sea-surface temperature history a t Site 241. Based on earlier observations that a positive correlation exists between the mean test diameter of 0. universa and surface water temperature, several intervals of cool and warm sea-surface temperatures have been interpreted in the Pleistocene. The Pliocene surface water temperatures were less variable than those of the Pleistocene, indicating increased monsoonal activity in the younger interval.

Late Pliocene climate variability on Milankovitch to millennial time scales: A high-resolution study of MIS100 from the Mediterranean

“…From a perspective of trophic and oxygenation state of bottom waters, the behaviour of Trifarina angulosa and Bolivina pseudoplicata is quoted by Verhallen (1991) as intermediate between opportunistic and equilibrium. For T. angulosa a relation with high (Gupta, 1997;Harloff and Mackensen, 1997) as well as with low organic flux rates (Mackensen et al, 1995) is documented. G. orbicularis is mentioned as an opportunistic taxon requiring ventilated bottom waters (Jorissen et al, 1992).…”

“…6). Noncostate buliminids are mentioned in relation to finegrained substrates and elevated productivity and/or lowered bottom-water oxygenation (Mackensen et al, 1993;Fariduddin and Loubere, 1997;Gupta, 1997;Jannink et al, 1998;Jian et al, 1999;Hayward et al, 2002). Shackleton et al, 1995) and are, therefore, interpreted to represent dominantly obliquity-controlled variations in global ice volume.…”

South Equatorial Current (SEC) driven changes at DSDP Site 237, Central Indian Ocean, during the Plio-Pleistocene: Evidence from Benthic Foraminifera and Stable Isotopes

“…2). Information on Recent benthic foraminifera was used to interpret the environments of these biofacies as shown in Table 3 (Corliss, 1979;1983;Gooday, 1994;Smart et al, 1994;Hermelin and Shimmield, 1995;Mackensen et al, 1995;Jannink et al, 1998;Loubere, 1998;Gupta, 1997;1999;Gupta and Thomas, 1999;Loubere and Fariduddin, 1999;Kurbjeweit et al, 2000;Ohkushi et al, 2000). The five biofacies are plotted along with the stable isotope values and inferred environments in Fig.…”

“…During the NE monsoon season, the overall productivity of the northern Indian Ocean is low (Krey, 1973). The effect of the Indian monsoon can be seen on marine fauna and flora in the geological record as far south as 178S in the eastern Indian Ocean and almost the same latitude in the western Indian Ocean (Gupta, 1997;Gupta et al, 2004). The deep water masses in the northern Indian Ocean (north of 108N) are mainly of northern Indian origin since the northward advection of intermediate-deep watermasses of southern origin is blocked by the Hydrochemical front at 108S (Tchernia, 1980;Dickens and Owen, 1999).…”

“…Numerous studies on living and dead benthic foraminifera have indicated that their distributions are closely tied to the organic carbon flux (Miller and Lohmann, 1982;Caralp, 1984;Jorissen et al, 1992;Gooday, 1993;Thomas and Gooday, 1996;Altenbach et al, 1999;Gupta and Thomas, 1999;Wollenburg and Kuhnt, 2000;Smart, 2002). However, some benthic faunal assemblages have been found associated more closely with the oxygen level of the ambient water (Hermelin and Shimmield, 1990;Bernhard, 1992;Miao and Thunell, 1993;Gooday, 1994;Wells et al, 1994;Gupta, 1997;Jannink et al, 1998). Murray (2001) argued that benthic foraminifera have the potential to serve as proxies for very low values of oxygen.…”