Moluscos holocênicos em sedimentos lagunares associados à barreira arenosa da Pinheira-Guarda-Gamboa, Santa Catarina: implicações paleoambientais

This paper documents the occurrence of mollusk carbonate fossils in sediments of the backbarrier of the Pinheira-Guarda- -Gamboa beaches, Santa Catarina Coastal Plain, southern Brazil, in which five species of gastropods and nine of bivalves were recognized. Among the bivalves, four species were articulated, Ostrea equestris, Anomalocardia brasiliana, Lucina pectinata and Tagelus plebeius, and the last three were found in life position. Radiocarbon datings were performed on articulate and life position specimens: Lucina pectinata, indicating a conventional age of 5.260 ± 30 years BP. (calibrate age 5.620 - 5.440), Tagelus plebeius, 5.620 ± 30 years BP. (calibrate age 6.000 - 5.840) and Ostrea equestris articulate, 5.410 ± 30 years BP. (calibrate age 5.805 - 5.580), indicating the material in the middle Holocene. The topographic data gathered with precision equipment established that the top of the outcrop is 2 m above the relative sea-level. The fossil association suggests lagoon-estuarine environment subsequently filled in response to a lowering of the sea level.Este trabalho documenta a ocorrência de moluscos fósseis carbonáticos em sedimentos da retrobarreira das praias da Pinheira-Guarda-Gamboa, Planície Costeira de Santa Catarina, sul do Brasil, onde foram reconhecidas cinco espécies de gastrópodes e nove de bivalves. Dentre os bivalves, identificaram-se quatro espécies articuladas, Ostrea equestris, Anomalocardia brasiliana, Lucina pectinata e Tagelus plebeius, as três últimas registradas em posição de vida. Datações radiocarbônicas foram realizadas em espécimes articulados e em posição de vida: Lucina pectinata apontando idades convencionais de 5.260 ± 30 anos AP (idade calibrada 5.620 - 5.440), Tagelus plebeius, 5.620 ± 30 anos AP (idade calibrada 6.000 - 5.840) e Ostrea equestris apenas articulado, 5.410 ± 30 anos AP (idade calibrada 5.805 - 5.580), posicionando o material no Holoceno médio. O dado topográfico com equipamento de precisão estabeleceu que o topo do afloramento encontra- -se a 2 m acima do nível relativo atual do mar. A associação indica um ambiente lagunar-estuarino, posteriormente colmatado como resposta ao rebaixamento do nível do mar

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 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

The sea-level highstand correlated to marine isotope stage (MIS) 7 in the coastal plain of the state of Rio Grande do Sul, Brazil

The coastal plain of the state of Rio Grande do Sul, in southern Brazil, includes four barrier-lagoon depositional systems formed by successive Quaternary sea-level highstands that were correlated to marine isotope stages (MIS) 11, 9, 5 and 1, despite the scarcity of absolute ages. This study describes a sea-level highstand older than MIS 5, based on the stratigraphy, ages and fossils of the shallow marine facies found in coastal barrier (Barrier II). This facies outcrops along the banks of Chuí Creek, it is composed of fine, well-sorted quartz sand and contains ichnofossils Ophiomorpha nodosa and Rosselia sp., and molluscan shells. The sedimentary record indicates coastal aggradation followed by sea-level fall and progradation of the coastline. Thermoluminescence (TL) and electron spin resonance (ESR) ages from sediments and fossil shells point to an age of ∼220 ka for the end of this marine transgression, thus correlating it to MIS 7 (substage 7e). Altimetric data point to a maximum amplitude of about 10 meters above present-day mean sea-level, but tectonic processes may be involved. Paleoceanographic conditions at the time of the highstand and correlations with other deposits in the Brazilian coasts are also discussed