The sedimentary record of the last glaciation in the western Bellingshausen Sea (West Antarctica): Implications for the interpretation of diamictons in a polar-marine setting

Upper Quaternary marine sediments recovered from the West Antarctic continental margin are characterized by a distinct lithological succession allowing the reconstruction of past environmental changes. Massive, homogenous diamictons were deposited elsewhere on the margin during the last glacial period, when grounded ice masses advanced across the shelf. Sedimentological investigations using a multi-proxy approach and examination of the margin topography suggest that during this time a deformation till and subsequently a glaciomarine till were deposited on the shelf, while glaciogenic debris flows were deposited on the slope and rise. The comparison of the clay mineral assemblages in the matrix of the diamictons with clay mineral assemblages of potential source areas reveals distinct pathways of grounded ice flow on the shelf. Lithogenic sandy muds overlying the diamictons were deposited by meltwater flows and/or marine currents on the shelf, and by turbidity currents and marine currents on the slope and rise, respectively. The sedimentation of the sandy muds denotes a deglaciation stage, when grounded ice started to retreat from the shelf, but semi-permanent sea-ice coverage still hampered biological productivity. Bioturbated, foraminifer-bearing sediments were deposited in a glaciomarine setting during the present interglacial period, when sea-ice cover was only seasonally present and a marine current related to the southern boundary of the Antarctic Circumpolar Current winnowed the seafloor on the outer shelf, slope and rise.

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