Mapeamento e carcterização dos depósitos em subsuperfície do setor meridional da Planície Costeira Sul de Santa Catarina

Na Planície Costeira Sul de Santa Catarina, entre o rio Mampituba e o norte da lagoa do Sombrio encontram-se depósitos costeiros gerados por transgressões e regressões da linha de costa no Quaternário. Em termos evolutivos os sistemas deposicionais costeiros são semelhantes aos encontrados na Planície Costeira do Rio Grande do Sul. Este estudo tem como objetivos o mapeamento das feições geológicas e geomorfológicas presentes e a caracterização da estratigrafia dos depósitos sedimentares em subsuperfície. Para tanto, foram integrados dados de Sensoriamento Remoto, de Geomorfologia, de Geofísica (radar de penetração do solo - GPR) e de mapas geológicos pré-existentes. Partindo da premissa que as curvas de variação relativa do nível do mar possam diferenciar depósitos pleistocênicos de holocênicos foram integradas ferramentas que auxiliaram identificar estas unidades. Nas seções obtidas com o GPR foram identificadas estruturas de sistemas deposicionais progradantes, gerados em ambientes subaquosos. Através desses dados foi possível propor um paleonível do mar a partir de estruturas sedimentares identificadas nos depósitos em subsuperfície. De acordo com os dados altimétricos, geofísicos e geomorfológicos nenhum evento transgressivo com cotas relativas ao último máximo transgressivo pleistocênico foi identificado no setor leste da lagoa do Sombrio. Dessa forma, a área de estudo foi caracterizada como um sistema costeiro holocênico progradacional, formado por um paleocampo de dunas recobrindo parte dos cordões litorâneos regressivos (foredune ridges) e por um campo de dunas transgressivo (transgressive dunefield) junto à linha de costa.In the south of Santa Catarina Coastal Plain, between the Mampituba river and north Sombrio lagoon are coastal deposits generated by transgressions and regressions of the shoreline in the Quaternary. In evolutionary terms the coastal depositional systems are similar to those found in the of Rio Grande do Sul coastal plain. This study aims to map the geological and geomorphological features present the characterization of the stratigraphy of the sedimentary subsurface. Therefore, data were integrated Remote Sensing of Geomorphology, Geophysics (ground penetrating radar - GPR) and geological maps pre-existing. Assuming that the curves of relative variation in sea level can differentiate Pleistocene to Holocene deposits have been integrated tools that helped identify these units. In sections obtained from the GPR were identified structures of prograding depositional systems, generated in subaqueous environments. Through these data it was possible to propose a palaeo-sea level from structures identified in the sedimentary deposits in the subsurface. According to the altimetric data, geophysical and geomorphological transgressive event with no quotas for the last Pleistocene transgressive maximum was identified in the eastern sector of the Sombrio lagoon. Thus, the study area was characterized as a coastal Holocene progradational system, consisting of a palaeodune covering of the foredune ridges and a transgressive dunefield along the coastline

Holocene sea-level changes in southern Brazil based on high-resolution radar stratigraphy

This paper focuses on high-resolution coastal stratigraphy data, which were revealed by the Ground Penetrating Radar (GPR) system. Surveys performed with GPR on the surface of prograded barriers reveal patterns of reflections that allow the interpretation of the geometry and stratigraphy of coastal deposits in a continuous mode. At the Curumim prograded barrier in southern Brazil (29 300 S–49 530 W), a two-dimensional transverse GPR survey revealed, with high precision, a serial of contacts between aeolian deposits of relict foredunes and relict beach deposits that have a strong correlation with sea level. In a 4 km GPR profile, a total of 24 of these contacts were identified. The high accurate spatial positioning of the contacts combined with Optical Stimulated Luminescence dating resulted in the first confident sea-level curve that tells the history of sea-level changes during the last 7 ka on the southernmost sector of the Brazilian coast. The curve shows that sea-level was still rising before 6 ka BP, with a maximum level of 1.9 m reached close to 5 ka BP; after that, sea-level started to falling slowly until around 4 ka BP when fall accelerated

Process control in the geneses and evolution of a lagoon-barrier system inside of the patos lagoon, south of Brazil

The origin and geological evolution of a complex of a beach ridgeplain in the Feitoria lagoon-barrier, located on the western margin of the southern cell Patos lagoon, Brazil was influenced by the interactions between the alocyclic (climate change and relative sea level) and autocyclic (sediment supply, waves, longshore drift and storm surges) forcing. The study of this regressive beach ridgeplain included the analysis of orthophotos; topographic detail (PRO-XRS Trimble®-post-processed); and shallow geophysical data with Ground Penetrating Radar (GPR), 150, 200 and 400 MHz antennae, combined with facies analysis and radiocarbon dating (AMS) and Optically Stimulated Luminescence (OSL) from shallow borehole samples. The analysis of orthophotos allowed for the definition of at least nine morphologically distinct series of progradation, marked by truncations of progressive orientation changes. The integration of topographically corrected GPR data, sedimentary records, and geochronological data determined the beginning of the progradation occurred at 7.2 kaBP. At the beginning of progradation, the low tide terrace was at the height of 1.9m (EGM96) Above the Sea Current Level (ASCL). The swash zone was in the 2.5m, and the crest reached 4.3m ASCL. Currently, the low tide terrace quota is -0.4m, the swash zone to 0.3m and the crest reaches 2.1m ASCL. Among other factors, the fall of the lagoon base levels was associated with sea level fall during the Holocene regression. However, crest construction control is dependent on the lagoon base level oscillation, which in turn is controlled by the precipitation regime and storms surges. Moreover, these results suggest that the orientation of the ridges was controlled by changes in the internal lagoon hydrodynamics, due to the progressive narrowing of the lagoon connection with the open ocean

Geomorphological and stratigraphic evolution of a fluvial incision in the coastal plain and inner continental shelf in southern Brazil

This paper describes the evolution of a sector of the southern coastal plain of the Pelotas Basin, southern Brazil, between the last Pleistocene sea-level lowstand and the Holocene highstand, based on geomorphology and high-resolution stratigraphy. A fluvial drainage system associated with an incised valley developed during the Last Glacial Maximum (LGM) was identified. Two highresolution 2D and 2.5D geophysical profiles using Ground-Penetrating Radar (GPR) show a Pleistocene fluvial system's former path, starting close to its present mouth inside Mirim Lagoon crossing the coastal barriers and reaching the inner continental shelf, covering some 60 km across the coastal plain. During the LGM, with the sea-level at −120 to −130 m and the coastline positioned close to the shelf edge (distant 200 km from the present coastline), the fluvial system excavated a ~31.5-m deep channel. Two cores, 36 and 32 m long, show that the paleochannel was filled with sedimentary deposits after 19.4 ka BP, and the facies succession represents the transition from fluvial, to estuarine, to the coastal barrier, and finally to inner shelf depositional environments, generated by processes connected to LGM and the Postglacial Marine Transgression (PMT). The study region behaved as a sediment by-pass zone, connecting the adjacent coastal plain's inner portion with the inner continental shelf. The studied area presents an unusual record of the LGM at a coastal plain domain

Análise estratigráfica da barreira transgressiva holocênica na região da Lagoa do Sombrio, SC

Na Planície Costeira Sul de Santa Catarina, entre o rio Mampituba e o norte da lagoa do Sombrio encontram-se depósitos costeiros gerados por transgressões e regressões da linha de costa durante o Quaternário. A área de estudo situa-se em um suave embaiamento costeiro onde a barreira holocênica apresenta um comportamento progradacional. Contudo, dados de subsuperfície adquiridos através do método geofísico do GPR na porção mais interna deste setor, revelaram a presença de refletores inclinados no sentido do continente, evidenciando a fase retrogradacional da barreira holocênica. Estes refletores são interpretados como estratos sedimentares formados em ambiente subaquoso, correspondente à margem lagunar que progradou no sentido do continente. A inversão dos refletores no sentido do oceano corresponde à fase progradacional, sendo estes interpretados como estratos formados no pós-praia (backshore) e na zona de estirâncio (foreshore). As diferentes fácies reconhecidas em subsuperficie com o GPR foram caracterizadas com o auxilio de dois furos de sondagens SPT (Standard Penetration Test). Os dados obtidos nos testemunhos permitiram diferenciar aspectos como textura, cor, conteúdo fossilífero, teor de matéria orgânica e forma dos grãos. Os depósitos sedimentares relacionados à fase retrogradacional são representados por areias finas a muito finas, com a presença de até 34% de lama. Por outro lado, os depósitos relacionados à fase progradacional são compostos por areias finas sem contribuição significativa de lama. Por fim, a datação por radiocarbono de um fragmento de madeira, localizado na fácies interpretada como a margem lagunar, revelou que esta foi depositada há cerca de 8 ka AP, em um nível relativo do mar aproximadamente 7 m abaixo do atual. Esta margem, que progradou no sentido do continente, corresponde à fase retrogradacional (transgressiva) da barreira holocênica.In the Southern Santa Catarina Coastal Plain, between Mampituba river and the northern Sombrio lagoon, are present coastal deposits generated by shoreline transgressions and regressions during the Quaternary. The study area is situated on a gentle coastal embayment where the holocenic barrier has a progradational behavior. However, subsurface data acquired through the GPR in the innermost portion of this sector, revealed the presence of reflectors inclined landward, evidencing the retrogradational phase of the holocenic barrier. These reflectors are interpreted as sedimentary strata formed in subaqueous environment, corresponding to the margin lagoon which prograded landward. The reversal of reflectors basinward corresponds to the progradational phase, which is interpreted as backshore and foreshore strata. The facies recognized in subsurface with GPR were characterized with the aid of two SPT (Standard Penetration Test) drill holes. The core data allowed differentiate aspects such as texture, color, grain shape, fossil and organic matter content. Sedimentary deposits related to the retrogradational phase are represented by fine to very fine sand, with the presence of until 34% of mud. On the other hand, progradational deposits are composed of fine sand without significant mud content. Finally, the radiocarbon dating of a wood fragment, located in lagoon margin facies, showed that it was deposited at about 8 ka BP, in a mean sea level of around 7 m below the current level. This margin, which prograded landwards, corresponds to the retrogradational phase of the holocenic barrier (transgressive)

Análise estratigráfica da barreira transgressiva holocênica na região da Lagoa do Sombrio, SC

Na Planície Costeira Sul de Santa Catarina, entre o rio Mampituba e o norte da lagoa do Sombrio encontram-se depósitos costeiros gerados por transgressões e regressões da linha de costa durante o Quaternário. A área de estudo situa-se em um suave embaiamento costeiro onde a barreira holocênica apresenta um comportamento progradacional. Contudo, dados de subsuperfície adquiridos através do método geofísico do GPR na porção mais interna deste setor, revelaram a presença de refletores inclinados no sentido do continente, evidenciando a fase retrogradacional da barreira holocênica. Estes refletores são interpretados como estratos sedimentares formados em ambiente subaquoso, correspondente à margem lagunar que progradou no sentido do continente. A inversão dos refletores no sentido do oceano corresponde à fase progradacional, sendo estes interpretados como estratos formados no pós-praia (backshore) e na zona de estirâncio (foreshore). As diferentes fácies reconhecidas em subsuperficie com o GPR foram caracterizadas com o auxilio de dois furos de sondagens SPT (Standard Penetration Test). Os dados obtidos nos testemunhos permitiram diferenciar aspectos como textura, cor, conteúdo fossilífero, teor de matéria orgânica e forma dos grãos. Os depósitos sedimentares relacionados à fase retrogradacional são representados por areias finas a muito finas, com a presença de até 34% de lama. Por outro lado, os depósitos relacionados à fase progradacional são compostos por areias finas sem contribuição significativa de lama. Por fim, a datação por radiocarbono de um fragmento de madeira, localizado na fácies interpretada como a margem lagunar, revelou que esta foi depositada há cerca de 8 ka AP, em um nível relativo do mar aproximadamente 7 m abaixo do atual. Esta margem, que progradou no sentido do continente, corresponde à fase retrogradacional (transgressiva) da barreira holocênica.In the Southern Santa Catarina Coastal Plain, between Mampituba river and the northern Sombrio lagoon, are present coastal deposits generated by shoreline transgressions and regressions during the Quaternary. The study area is situated on a gentle coastal embayment where the holocenic barrier has a progradational behavior. However, subsurface data acquired through the GPR in the innermost portion of this sector, revealed the presence of reflectors inclined landward, evidencing the retrogradational phase of the holocenic barrier. These reflectors are interpreted as sedimentary strata formed in subaqueous environment, corresponding to the margin lagoon which prograded landward. The reversal of reflectors basinward corresponds to the progradational phase, which is interpreted as backshore and foreshore strata. The facies recognized in subsurface with GPR were characterized with the aid of two SPT (Standard Penetration Test) drill holes. The core data allowed differentiate aspects such as texture, color, grain shape, fossil and organic matter content. Sedimentary deposits related to the retrogradational phase are represented by fine to very fine sand, with the presence of until 34% of mud. On the other hand, progradational deposits are composed of fine sand without significant mud content. Finally, the radiocarbon dating of a wood fragment, located in lagoon margin facies, showed that it was deposited at about 8 ka BP, in a mean sea level of around 7 m below the current level. This margin, which prograded landwards, corresponds to the retrogradational phase of the holocenic barrier (transgressive)

A herança geológica, a geomorfologia e a estratigrafia da barreira complexa de Passo de Torres, Planície Costeira Sul-Catarinense

O sistema costeiro holocênico, estabelecido na porção emersa da Bacia de Pelotas – extremo sul da Margem Continental Brasileira –, possui setores contemporâneos com padrões de empilhamento opostos. As barreiras regressivas (progradacionais) ocorrem em embaiamentos da linha de costa, enquanto, as barreiras de natureza transgressiva (retrogradacionais) situam-se nas projeções costeiras. No embaiamento norte da Bacia de Pelotas, somente na barreira regressiva de Passo de Torres – situada entre o rio Mampituba e o extremo sul da lagoa do Caverá – se fazem presentes alinhamentos de cordões de dunas frontais (foredune ridges) bem desenvolvidos. No restante do embaiamento, lençóis de areias transgressivos (transgressive sand sheets), formados pela erosão parcial ou total dos cordões frontais, cobrem a morfologia das barreiras. Observa-se também que em certo ponto da progradação da barreira de Passo de Torres, o sistema eólico se desestabilizou e na sua morfologia lençóis de areias transgressivos cobrem os cordões frontais, igualmente como ocorre nas demais barreiras do embaiamento norte da Bacia de Pelotas. Desta forma, duas questões surgem: Por que unicamente na barreira de Passo de Torres, alinhamentos de cordões de dunas frontais ficaram preservados, enquanto que, nas demais barreiras do embaiamento os mesmos foram erodidos? E, além disso, por que em determinado momento da progradação da barreira, ocorreu uma desestabilização do sistema eólico (erosão) e os lençóis de areias transgressivos passam a dominar a morfologia da mesma? As hipóteses analisadas neste trabalho referem-se à influência do rio Mampituba, a mudanças climáticas e a herança geológica da topografia antecedente, ou seja, do substrato pleistocênico. Constatou-se que uma ação combinada destes fatores pode elucidar tais questões. Ressalta-se que uma inversão do comportamento do nível relativo do mar (uma elevação em torno de 2000 anos antes do presente) também foi analisada na tentativa de esclarecer o comportamento diferenciado da barreira de Passo de Torres. As hipóteses consideradas neste estudo foram avaliadas com base em análises geomorfológicas, estratigráficas, geocronológicas e batimétricas, através do emprego do sensoriamento remoto, de sistemas de posicionamento, do método geofísico do georradar, de sondagens (as quais se obtiveram materiais para datação) e cartas náuticas da Diretoria de Hidrografia e Navegação (DHN).The Holocene coastal system established in the onshore portion of the Pelotas Basin – the southern end of the Brazilian Continental Margin – has contemporary sectors with opposite stacking patterns. Regressive barriers (progradational) occur in shoreline embayments, while the transgressive barriers (retrogradational) are located in coastal projections. In the north embayment of the Pelotas Basin, only in the Passo de Torres regressive barrier – located between the Mampituba river and the southern end of the Caverá lagoon – there are alignments of well-developed foredune ridges. In other parts of the embayment, transgressive sand sheets, formed by partial or total erosion of the foredune ridges, cover the morphology of the barriers. It is also possible to observe that at a certain moment in the Holocene progradation of the Passo de Torres barrier, the aeolian system has been destabilized and in its morphology transgressive sand sheets cover the foredune ridges, the same that occurs in other barriers of the Pelotas Basin northern embayment. Thus, two questions arise: Why only in the Passo de Torres barrier, foredune ridges were preserved, while in the other barriers of the northern embayment they have been eroded? Furthermore, why at some point in barrier progradation, occurred destabilization of the aeolian system (erosion) and transgressive sand sheets start to dominate the barrier morphology? The hypotheses analyzed in this work are related to the influence of the Mampituba river, the climate change and geological inheritance of the antecedent topography, i.e., the Pleistocene substrate. The finding of this research shows that a combined action of these factors can elucidate these questions. It is noteworthy that a reversal of the relative sea-level behavior (rising around 2000 years before the present) was also evaluated in an attempt to explain the different behavior of the Passo de Torres barrier. The hypotheses suggested considered in this study were evaluated based on geomorphological, stratigraphic, geochronological and bathymetric analysis, using remote sensing, global positioning systems, the geophysical method of ground penetration radar (GPR), drill hole (of which was obtained material for dating) and nautical charts of the Directorate of Hydrography and Navigation (DHN)

Descrição de uma brecha-tufisítica espessartítica da região do Cerro Tupanci, Vila Nova do Sul, RS

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Descrição de uma brecha-tufisítica espessartítica da região do Cerro Tupanci, Vila Nova do Sul, RS

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