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Benthic foraminiferal assemblages from the eastern Weddell Sea between 68 and 73°S: Distribution, ecology and fossilization potential

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Mackensen, A. , Grobe, H. , Kuhn, G. and Fütterer, D. (1990): Benthic foraminiferal assemblages from the eastern Weddell Sea between 68 and 73°S: Distribution, ecology and fossilization potential , Marine micropaleontology, 16 , pp. 241-283 . doi: 10.1016/0377-8398(90)90006-8
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Abstract:

Surface sediment samples taken with a vented box corer from the eastern Weddell Sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content. The live fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Based on the dead assemblages, potential fossil assemblages were calculated to facilitate the analogy with late Neogene core material. Five distinct live assemblages inhabit the continental margin today. Six dead assemblages and five potential fossil assemblages, respectively, correspond to these biocoenoses.A predominantly calcareous live fauna dominated by Trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope. Below this, on the upper slope down to 2000 m water depth, the predominantly calcareous Bulimina aculeata assemblage coincides with the core of warm (>0°C) Weddell Deep Water and with fine and more organic-rich sediments. These calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment, which depends largely on the grain size distribution of the sediment and the fluxes of organic matter. Therefore, a still calcareous T. angulosa-dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope, whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by Martinottiella nodulosa, the characteristic arenaceous fossil remnant of the former predominantly calcareous live B. aculeata fauna.On a continental terrace between 2500 and 3500 m water depth Cribrostomoides subglobosus dominates the live fauna, but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by Oridorsalis umbonatus and Epistominella exigua comprises the dead assemblage and the potential fossil assemblage, respectively.On the lower continental slope, between the carbonate lysocline (3500 m) and the carbonate compensation depth (4000 m), tests of Nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna, which is associated with the lower part of the Antarctic Bottom Water (AABW). This corroborates earlier investigations suggesting a relationship between the carbonate-corrosiveness of water masses and the distribution of N. umbonifer. This is important for inferring paleo-routes and estimates of paleo-production rates of AABW during the Neogene.

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