HR: 11:00h
AN: OS22A-03    [Abstracts]
TI: Mineralogical contents of bottom sediments collected on the southeastern South American continental shelf
AU: * Campos, E J
EM: edmo@io.usp.br
AF: Instituto Oceanográfico da Universidade de São Paulo, Pça. do Oceanográfico, 191, São Paulo, SP 05508-120 Brazil
AU: Mukherjee, S
EM: swapnamukherjee1@rediffmail.com
AF: Geological Survey of India, 65L/1 Bose Pukur Road, Kolkata, 2442-2976 India
AU: Piola, A R
EM: apiola@hidro.gov.ar
AF: Servício de Hidrografia Naval, Rua Montes de Oca 1224, Buenos Aires, Argentina
AU: de Carvalho, F M
EM: flavio@ig.usp.br
AF: Instituto de Geociências da Universidade de São Paulo, Rua do Lago, São Paulo, SP 05508-900 Brazil
AB: The Plata River and the Patos-Mirim lagoon system discharge a considerable amount of fresh water onto the eastern South American continental shelf. This water, coming from a drainage basin which represent near 20% of the entire South American continent, brings to the sea a variety of suspended material which is ultimately deposited on the bottom, mainly in the shelf region. The study of mineralogical contents of continental borne constituents on the sea floor could reveal valuable information about changes in the environmental conditions in the drainage basin. In this paper we report results of a study of the mineralogical contents of bottom sediments sampled in the eastern South American shelf between 4°S and 25°S. The present work is the first of this kind in that region and is likely to provide valuable information for choosing sites for drilling core samples in future work. The results we obtained with X-Ray Diffraction and other analysis techniques show that the non-clay part of the sediment consists mainly of Quartz, Feldspar, Calcite and Hematite. In only one sample, Amphibole was detected with non-negligible concentration (~20%). Quartz abundance varied from about 20% to 30%, on the average. However, in three of the samples the concentration of this mineral was found in the order of 40%. The Feldspar concentration was found to be of 15-20%. Concentrations of the other two non-clay phases Calcite and Hematite, have some similarity. In the region of 37°S to 33°S, Calcite content varied from 15% to 20% and Hematite concentrations lied within 1-5%. From 29°S to 33°S, the concentration of Calcite was between 4-9% while for Hematite it was in the range of 0-2.5% only. The general concentration pattern of non-clay part was 50-70% for near-shore samples while for samples away from the shore, this value was of about 30-50%. It was also observed that, from 33°S to 28°S, the non-clay concentration presented a trend, decreasing northward, even near the shore line.
UR: http://www.labmon.io.usp.br
DE: 3022 Marine sediments--processes and transport
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 4219 Continental shelf processes
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly