Maria Luiza C.C. Rosa

Sequential opening and filling of cavities forming vesicles, amygdales and giant amethyst geodes in lavas from the southern Paraná volcanic province, Brazil and Uruguay

The opening and filling of cavities in rocks are the major processes related to the generation and sealing of porosity in ore deposits. This study documents three stages of opening and filling of vesicles and geodes in the basalts and rhyodacites of the southern Paraná volcanic province. Each step detailed here is actually part of a sequence of minor hydrothermal events. First, lava degassing at high temperature (1150°C) formed small (<4 cm) vesicles in the crusts of flow units. In sequence, these vesicles were partly to fully filled at low temperature (30–150°C) by hydrothermal minerals, particularly clays and zeolites; this process also sealed the porosity of the lava. Second, the injection of fluidized sand generated new cavities, which were partly filled with sand; the newly formed porosity was sealed by the low-temperature fluid. Third, intense alteration of the basalt or rhyodacite core into a claystone favoured the opening of small to giant protogeodes (0.1 mm to 4 m) by dissolution; cooling of the fluid led to the precipitation of hydrothermal minerals, particularly the spectacular amethyst, calcite, and gypsum-bearing geodes.

Natural and Anthropogenic Coastal System Comparison Using DSM from a Low Cost UAV Survey (Capão Novo, RS/Brazil)

ABSTRACT Scarelli, F.M.; Cantelli, L.; Barboza, E.G.; Rosa, M.L.C.C.; and Gabbianelli, G., 2016. Natural and Anthropogenic coastal system comparison using DSM from a low cost UAV survey (Capão Novo, RS/Brazil). In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1232 - 1236, ISSN 0749-0208. In many cases, unplanned urbanization is the main factor that causes a decrease in coastal resilience. This paper compares the differences between the anthropogenic and natural coastal zone, based on the morphological dune reconstruction, using a low cost UAV (unmanned aerial vehicle) survey and the photogrammetric reconstruction method. The study area is in the Northern Littoral of Rio Grande do Sul State, where the dunes have few man-changes and are adjacent to an anthropogenic zone with a highly modified beach/dune system. By photogrammetric reconstruction it was possible to obtain a high-resolution DSM (Digital Surface Model) and a high-resolution othophoto to analyse differences in morphology. Data acquired by UAVs are important to coastal managers and decision makers as they can collect high-resolution data and be used for Integrated Coastal Zone Management. Moreover this work propose a low cost method for obtaining a high-resolution data for researchers and local authorities.

Aeolian Deposition and Barrier Stratigraphy of the Transition Region between a Regressive and a Transgressive Barrier: an example from Southern Brazil

ABSTRACT Dillenburg, S.R., Barboza, E.G., Tomazelli, L.J., Rosa, M.L.C.C., Maciel, G.S., 2013. Aeolian Deposition and Barrier Stratigraphy of the Transition Region between a Regressive and a Transgressive Barrier: an example from Southern Brazil. The transition region between regressive and transgressive barriers on the northern and central coastal sectors of Rio Grande do Sul (RS) in southern Brazil is represented by a 170 km long stretch of coast where the barrier shows a general aggradational/stationary (a/s) behavior on a long term time scale. In this study, approximately 50 km of this transition region was analyzed at four sites: Tramandaí, Jardim do Éden, Cidreira and Dunas Altas. All barriers began forming around 7.8 - 7.2 ka. The northernmost site (Tramandaí) has a typical a/s stratigraphy, and barrier morphology is dominated by transgressive dunefields. Ten km to the south, at Jardim do Éden, the barrier shows a transgressive stratigraphy, and barrier morphology is also dominated by transgressive dunefields. At Tramandaí the maximum barrier height is around 4 m, with a maximum of 6 m, while at Jardim do Éden it averages 6 m, with a maximum of 11 m. Further to the south, 10 km from Jardim do Éden, the barrier at Cidreira shows a dominant transgressive stratigraphy developed in the last 7 ka, but with evidence of a relatively small regression (~600 m). Barrier height averages 10 m, reaching 20 m due to the existence here of a large transgressive dunefield. And finally, at around 30 km to the south of Cidreira, the a/s barrier of Dunas Altas occurs. Barrier morphology here is dominated by transgressive dunefields, with a surface height of around 8 m, but fronted by the largest and highest foredunes (around 8–10 m) in Rio Grande do Sul. The Dunas Altas coastline has regressed around 600 m in the last 7.8 ka. The Holocene barrier analyzed in this study, along a 50 km segment shows a general a/s behavior in the last 7.8 ka. The long time of a relatively stationary condition allowed the barrier to grow vertically by accumulation of aeolian deposits of at least four phases of transgressive dunefield development.

Meandering fluvial system influencing the evolution of a Holocene regressive barrier in southern Brazil

ABSTRACT Biancini da Silva, A., Barboza, E.G., Rosa, M.L.C.C., Dillenburg, S.R., 2014. Meandering Fluvial System Influencing the Evolution of a Holocene Regressive Barrier in Southern Brazil. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 205–210, ISSN 0749-0208. A meandering fluvial system changes its course according to geological time, eroding rocks and pre-existing deposits and transporting large volumes of sediment to the coastal plains. Understanding the evolution of channels and paleochannels in regions showing coastal barriers and relating them to changes in sea level becomes extremely important to comprehend the factors that contribute to the behavior of coastal barriers. During the Holocene the barrier at Passo de Torres located northeast of the Mampituba River, along the southern coast of Santa Catarina state, prograded approximately 5.5 km. The barrier comprises both foredune ridges, which occur in the landward portion, and transgressive dune ridges, which occur seawards. One feature that stands out in the region is that the regressive barrier morphologies are truncated (eroded) by paleochannels and channels of a meandering fluvial system, which can be related to the dynamics of the Mampituba River. These paleochannels have elongated morphologies with SW – NE orientation and are up to 25 km long. With the purpose of characterizing the longer paleochannels, the geophysical method of ground penetrating radar (GPR) was used, associated with drill hole and radiocarbon dating. The GPR profile reveals continuous reflectors (± 5 m depth) with great contrast and lateral continuity for over 450 m. These represent an erosive surface, interpreted as the base of the fluvial channel. The granulometric results indicate that around 5 m, an increase in grain size (fine sand grading to medium sand) and the presence of several shells. These are very fragmented, characterizing a probable bedload transport. However, shells of the genus Donax sp. were collected intact with no signs of abrasion. This genus inhabits beach environments (specifically foreshore) and cannot survive in freshwater environments. These shells were incorporated to the bedload of the fluvial channel through an inlet, probably during storm surge events. These events carried beach sands, associated with shells (mainly Donax sp.), towards the continent, which were incorporated into the fluvial sediments. The dating of these species revealed an age between 5.6 – 5.4 cal ka. The ages obtained are consistent with the maximum sea level of the Postglacial Marine Transgression (PMT) in southern Brazil. Because these shells are exclusive to beach environments, dating allowed us to infer that this channel was active and had connection with the ocean at about 5.5 ka, concomitant with the maximum sea level of PMT.

Geological evolution and inundation hazard: an analysis through geotechnologies

ABSTRACT Rosa, M.L.C.C; Barboza, E.G.; Menegon, B.S.; Frota, P.C.; and Anoni, R.A.O., 2016. Geological evolution and inundation hazard: an analysis through geotechnologies. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1227 - 1231. Coconut Creek (Florida), ISSN 0749-0208. In the southern coastal plain of Rio Grande do Sul, southern Brazil, part of the city of Santa Vitória do Palmar was studied to analyze inundation hazard and its relation to geological evolution. Remote sensing, GNSS, total station surveys, laser scanning and photogrammetric reconstructions with a low cost UAV were combined and compared aiming at defining four main units with different levels of inundation susceptibility, which correspond to geological units of different ages. The allogenic factor related to the development of these units is sea level, which controls lagoon level, and determines that younger areas have higher inundation susceptibility. An autogenic control was also verified and is related to the dynamics of the lagoon system, where spits are higher and have a lower susceptibility when compared to the plains of the same age.

Ground Penetrating Radar applied to the Characterization of the Itapeva Dunefield, Torres, Brazil

ABSTRACT Rockett, G.C.; Barboza, E.G., and Rosa, M.L.C.C. 2016. Ground Penetrating Radar applied to the characterization of the Itapeva Dunefield, Torres, Brazil. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 323–327. Coconut Creek (Florida), ISSN 0749-0208. Subsurface data obtained from Ground Penetrating Radar (GPR) have been used in studies in various coastal plain environments. GPR applied to dune characterization and stratigraphy is well described in the literature, and enables the distinction between different depositional patterns and their delimitation. This study aimed to characterize the stratigraphy of the Itapeva dunefield, located at the municipality of Torres, north of the Rio Grande do Sul (Brasil) coastal plain, using subsurface data. This dunefield contains aeolian forms that differ from other dunefields in Rio Grande do Sul: namely, reversing dunes. The 150 and 400 MHz frequency antennas were used to collect subsurface data in dunes located in the central portion of the dunefield, with a linked GNSS system to obtain positional data. GPR data were processed, and the geospatial data were integrated to satellite images in a geographic information system. Results show that at least two different dune packages are present in the Itapeva dunefield, indicating two different depositional phases.