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Anais da Academia Brasileira de Ciências

Print version ISSN 0001-3765On-line version ISSN 1678-2690

Abstract

LOPES, RENATO P.; DILLENBURG, SERGIO R.  and  SCHULTZ, CESAR L.. Cordão Formation: loess deposits in the southern coastal plain of the state of Rio Grande do Sul, Brazil. An. Acad. Bras. Ciênc. [online]. 2016, vol.88, n.4, pp.2143-2166. ISSN 0001-3765.  https://doi.org/10.1590/0001-3765201620150738.

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 pale-colored (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.

Keywords : Chuy Creek; coastal plain; Last glacial stage; Loess; Pleistocene.

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