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Growth response of a deep-water ferromanganese crust to evolution of the Neogene Indian Ocean

A deep-water ferromanganese crust from a Central Indian Ocean seamount dated previously by 10 Be and 230 Th excess was studied for compositional and textural variations that occurred throughout its growth history. The 10 Be/ 9 Be dated interval (upper 32 mm) yields an uniform growth rate of 2.8±0.1...

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Published in:Marine geology 2000-01, Vol.162 (2), p.529-540
Main Authors: Banakar, Virupaxa K, Hein, James R
Format: Article
Language:English
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Summary:A deep-water ferromanganese crust from a Central Indian Ocean seamount dated previously by 10 Be and 230 Th excess was studied for compositional and textural variations that occurred throughout its growth history. The 10 Be/ 9 Be dated interval (upper 32 mm) yields an uniform growth rate of 2.8±0.1 mm/Ma [Frank, M., O'Nions, R.K., 1998. Sources of Pb for Indian Ocean ferromanganese crusts: a record of Himalayan erosion. Earth Planet. Sci. Lett., 158, pp. 121–130.] which gives an extrapolated age of ∼26 Ma for the base of the crust at 72 mm and is comparable to the maximum age derived from the Co-model based growth rate estimates. This study shows that Fe–Mn oxyhydroxide precipitation did not occur from the time of emplacement of the seamount during the Eocene (∼53 Ma) until the late Oligocene (∼26 Ma). This paucity probably was the result of a nearly overlapping palaeo-CCD and palaeo-depth of crust formation, increased early Eocene productivity, instability and reworking of the surface rocks on the flanks of the seamount, and lack of oxic deep-water in the nascent Indian Ocean. Crust accretion began (older zone) with the formation of isolated cusps of Fe–Mn oxide during a time of high detritus influx, probably due to the early-Miocene intense erosion associated with maximum exhumation of the Himalayas (op. cit.). This cuspate textured zone extends from 72 mm to 42 mm representing the early-Miocene period. Intense polar cooling and increased mixing of deep and intermediate waters at the close of the Oligocene might have led to the increased oxygenation of the bottom-water in the basin. A considerable expansion in the vertical distance between the seafloor depth and the CCD during the early Miocene in addition to the influx of oxygenated bottom-water likely initiated Fe–Mn crust formation. Pillar structure characterises the younger zone, which extends from 40 mm to the surface of the crust, i.e., ∼15 Ma to Present. This zone is characterised by >25% higher content of oxide-bound elements than in the older zone, possibly corresponding to further increased oxygenation of bottom-waters, increased stability of the seamount slope, and gradually reduced input of continental detritus from the erosion of the Himalayas. Middle Miocene Antarctic glaciation, which peaked ∼12–13 Ma ago, increased the oxic bottom-water influx to the basin resulting in accretion of the crust with low detritus. Therefore, the younger crust started to accrete in response to a shift in botto
ISSN:0025-3227
1872-6151
DOI:10.1016/S0025-3227(99)00077-8