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Cordão Formation: loess deposits in the southern coastal plain of the state of Rio Grande do Sul, Brazil

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Cordão Formation: loess deposits in the southern coastal plain of the state of Rio Grande do Sul, Brazil

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Título Cordão Formation: loess deposits in the southern coastal plain of the state of Rio Grande do Sul, Brazil
Autor Lopes, Renato Pereira
Dillenburg, Sergio Rebello
Schultz, Cesar Leandro
Abstract Loess consists of silt-dominated sediments that cover ~10% of the Earth’s surface. In southern South America it occurs in Argentina, Bolivia, Paraguay and Uruguay, and its presence in southern Brazil was never studied in detail. Here is proposed a new lithostratigraphic unit, Cordão Formation, consisting of loess deposits in the southern Brazilian coastal plain. It consists of fine-very fine silt with subordinate sand and clay, found mostly in lowland areas between Pleistocene coastal barriers. These sediments are palecolored (10YR hue) and forms ~1,5-2,0 meter-thick stable vertical walls. The clay minerals include illite, smectite, interstratified illite/smectite and kaolinite, the coarser fraction is mostly quartz and plagioclase. Caliche and iron-manganese nodules are also present. The only fossils found so far are rodent teeth and a tooth of a camelid (Hemiauchenia paradoxa). Luminescence ages indicate that this loess was deposited in the latest Pleistocene, between ~30 and 10 kyrs ago, and its upper portion was modified by erosion and accumulation of clay and organic matter in the Holocene. The estimated accumulation rate was ~630 g/ m2/year. The probable source of this loess is the Pampean Aeolian System of Argentina and it would have been deposited by the increased aeolian processes of the last glacial.
Contido em Anais da Academia Brasileira de Ciências. Vol. 88, n.4 (Out./ Dez. 2016), p.2143-2166
Assunto Planície costeira
Pleistoceno
Rio Grande do Sul
Unidade lito-estratigrafica
[en] Chuy Creek
[en] Coastal plain
[en] Last glacial stage
[en] Loess
[en] Pleistocene
Origem Nacional
Tipo Artigo de periódico
URI http://hdl.handle.net/10183/171124
Arquivos Descrição Formato
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