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

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/ m 2 /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.

High-Frequency Sequences in the Quaternary of Pelotas Basin (coastal plain): a record of degradational stacking as a function of longer-term base-level fall

“…The bottom of section A is interpreted as the limit with older deposits related to System III, representing both a sequence boundary and transgressive surface. In section B, lagoon margin is covered by two phases of aeolian deposits: one is related to the evolution of System III in a highstand systems tract context, while the other one is related to younger loess deposition related to System IV, described and dated (between 30 and 10 kyr) in the area by Lopes (2013) and Lopes et al (2016). In section A, a 14 C analysis determined the age of 8,320-8,070 cal yrs BP (Silva 2011).…”

On the presence of Megatherium Cuvier, 1796 (Xenarthra, Pilosa) in fossiliferous deposits of the Coastal Plain of Southern Brazil

“…On the other hand, the cyclic climate changes could have allowed for both species to inhabit the area only at distinct times. In southern South America, including the CPRS, there are also geological indicators of changes in terrestrial environments, with alternating warm-cold and dry-humid phases (Clapperton, 1993;Lopes et al, 2016;Lopes & Dillenburg, 2017). These changes were probably controlled by latitudinal shifts of climatic belts, accompanied by vegetation and faunal migrations.…”

“…Most of the assemblage consists of disarticulated and/or fragmented remains, but some articulated specimens have been found (Lopes & Ferigolo, 2015). The SVF is overlain by the loess deposits of the Cordão Formation (Lopes et al, 2016) and modern soils at the top.…”

Geocronologia De Eventos Deposicionais Associados Às Coberturas Superficiais Que Sustentam E Recobrem Níveis De Terraços Marinhos Pleistocênicos E Holocênicos No Litoral Sul De Santa Catarina (Sc)

“…Correlaciona-se estes materiais, que compõem dunas fósseis pedogenizadas na planície costeira de Araranguá, com depósitos eólicos do tipo loess identifi cados por Lopes et al (2016) no litoral sul do Estado do Rio Grande do Sul. Os autores desenvolveram proposta de nova unidade litoestratigráfi ca, denominada Formação Cordão, composta por silte fi no e muito fi no com areia e argila subordinadas, encontrada principalmente entre as barreiras costeiras pleistocênicas I, II e III, estando mais bem preservada no sistema laguna-barreira III.…”

“…-Datações por termoluminescência (TL) em areias costeiras do Rio Grande do Sul (Poupeau et al 1984e Dillenburg 1994; -Datações radiocarbônicas ( 14 C) em sambaquis já extintos (Mesodesma Mactroides e Donax Hanleyanus) encontrados na bacia hidrográfi ca do rio Araranguá (Duarte, 1995); em depósitos lagunares de barreira costeira vinculada ao sistema barreira-laguna IV (Travessas et al, 2005); em moluscos (Ostrea. Sp e T. plebeius) situados no contexto do afogamento da desembocadura do Arroio Chuí, extremo sul do Rio Grande do Sul (Caron, 2007); em registros palinológicos adjacentes a Lagoa de Sombrio, no sul de Santa Catarina (Cancelli, 2012); em registros palinológicos de matas paludiais e depósitos fl uviolagunares de materiais holocênicos no sul de Santa Catarina (Schneider, 2012); -Datações por Luminescência Opticamente Estimulada (LOE) em depósitos de loess na planície costeira sul do Estado do Rio Grande do Sul (Lopes et al 2016); em planície de cordões litorâneos arenosos de margem lagunar, na porção norte do litoral do Rio Grande do Sul (Bitencourt et al, 2017); em depósitos eólicos indiferenciados, lençol de areia e campo de dunas localizados nas bacias hidrográfi cas dos rios Araranguá e Uruçunga, litoral sul de Santa Catarina (Rodrigues, 2017); em coberturas superfi ciais de baixos terraços fl uviais, fl uviomarinhos e marinhos holocênicos na planície costeira da bacia hidrográfi ca do rio Araranguá (Rubira e Perez Filho, 2018).…”