Eduardo G. Barboza

Beach ridges, foredunes or transgressive dunefields? Definitions and an examination of the Torres to Tramandaí barrier system, Southern Brazil

Many prograded barriers and some dunefields in the world have been termed ‘beach ridge’ plains, but the actual genesis of the ‘ridges’ is often unknown. Use of the terms, berms, beach ridges and foredunes is also confusing in the literature because their definitions are highly variable and are commonly used interchangeably. Thus, the formation and definition of sand berms, beach ridges and foredunes is briefly reviewed. Beach ridges are re-defined as entirely wave formed deposits which are most commonly formed during high wave conditions and/or elevated water levels (e.g. storm surges). Foredunes are formed by aeolian sand deposition in vegetation on the backshore. Some dunefields in Brazil have been called beach ridge plains when they are, in fact, foredune plains, transgressive dunefields, or complex barriers (i.e. barriers comprising two types of dunes). The Holocene barrier extending from Torres to Tramandai in southern Brazil has been regarded as a beach ridge plain. The landforms of this Holocene barrier comprise wide, relatively linear, widely spaced (400–600m), shore parallel ridges on the landward half, and more closely spaced (80–400m), lobate and crescentic, discrete ridges on the seaward half. Low, rolling dunefields, sand sheets, nebkha fields and deflation plains occur between the ridges. The barrier is re-interpreted as a prograded, transgressive dunefield

Barrier evolution and placer formation at Bujuru southern Brazil

Abstract This paper demonstrates the link between the evolution of a coastal barrier in southern Brazil during the Late Holocene and the formation of a large volume of eolian disseminated heavy mineral deposits. Our data set is based on an earlier heavy mineral prospecting campaign (1991) and on 10 new shallow vibrocores, 2–5 m long. The model presented has three main steps of barrier evolution. The first step is the recycling of coastal plain deposits during the Postglacial Marine Transgression, which ended at 5.6 ka when heavy minerals were incorporated into beach and washover facies of a transgressive barrier. The second step is the shoreward retreat of the barrier, under a slow and small sea-level fall, during the last 5.6 ka. This second step eroded and recycled sediments from the Pleistocene substrate, which acted as an extra source of heavy minerals. Heavy minerals were concentrated in backshore deposits by wave action during barrier recession. The third step is the erosion and transport of backshore sands by onshore winds into an inter-barrier depression in the form of transgressive dune deposits. These deposits contain an average of 4.66±1.02% disseminated heavy minerals (1494 samples). This eolian placer deposit has started to form 1 ka ago and is still under formation.

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.

The strike-fed sandy coast of Southern Brazil

Abstract The Holocene barrier along the southern Brazilian coast is most likely the most continuous barrier structure in the world. This coast is characterized by a Holocene barrier extending for 760 km, interrupted by only six discontinuities, which are associated with narrow lagoonal inlets and river mouths. This coast is marked by a huge availability of sand, a gently sloping continental shelf, and incident waves of moderate to high energy. Together, these factors constitute ideal conditions for the formation of coastal barriers. During periods of low sea-levels, the continental shelf in front of the La Plata estuary was fed by immature fluvial sands delivered by the Paraná River, which were transported to the southern Brazilian coast by a predominantly northward littoral drift. Based on forecasts of sea-level rise, it will take decades or centuries for change to occur in the progradation of the regressive barriers along the coastal embayments. During the last centuries and millennia (Middle to Late Holocene), the evolution of this coast has been controlled by the variations in wave energy along the coast.

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.

Nearshore Dynamics and Holocene Evolution of the Coastal Barrier South of the Santa Marta Cape, Southern Brazil

ABSTRACT Oliveira, J.F.; Barboza, E.G., and Benavente, J., 2016. Nearshore Dynamics and Holocene Evolution of the Coastal Barrier South of the Santa Marta Cape, Southern 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. 437–441. Coconut Creek (Florida), ISSN 0749-0208. The emerged part of the Pelotas Basin extends about 800 km from the Polonio high (Uruguay) to the Florianópolis high (Santa Catarina state, southern Brazil). Since 6-5 ka B.P., the sea level has been dropping slowly, and the sediment balance is the principal factor that controls the actual barrier development. The Holocene barrier presents sectors of transgressive patterns that are usually located in coastal projections, while regressive sectors generally appear in the embayments. This work analyses the evolution of the barrier along a 30 km stretch of coast south of the Santa Marta Cape (Santa Catarina State), in the northernmost part of Pelotas Basin. The sub-superficial configuration of the barrier was characterized through Ground Penetrating Radar (GPR) profiles surveyed perpendicular to the coastline. In addition, an analysis of the nearshore wave propagation was carried out through SMC-Brasil (IHCantabria) to simulate the currents generated by breaking waves and the net sediment transport. The results show two different behaviors along the barrier system; the northern part with transgressive characteristics (dipping landward reflectors) and the southern part with regressive characteristics (dipping seaward reflectors). These different behaviors are associated with the slight changes on the coastal orientation and on the slopes of the shoreface and upper continental shelf. These two factors influence in how waves approach the coast, generating an imbalance in the sediment budget, which is shown in the characteristics of the distinct sectors studied.

Geological and Stratigraphic Characteristics of a Holocene Regressive Barrier in Southern Brazil: GIS and GPR Applied for Evolution Analysis

ABSTRACT Leal, R.A.; Barboza, E.G., Bitencourt, V. Jr. Biancini da Silva, A. and Manzolli, R.P., 2016. Geological and Stratigraphic Characteristics of a Holocene Regressive Barrier in Southern Brazil: GIS and GPR Applied for Evolution Analysis. 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. 750–754. Coconut Creek (Florida), ISSN 0749-0208. The observation of geological and geomorphological factors in coastal barriers to allows interpret the processes involved and the temporal trends over time. During the Holocene, the Balneário Torneiro barrier, located in the southern coast of Santa Catarina, prograded approximately 1.3 km, preserving the records of Urussanga rivers system dynamics in surface and subsurface paleochannels. The presence of such features close to the boundary with the Pleistocene deposits up to the present coastline indicates that the evolutionary behavior of the barrier is progradational. The identification of superficial morphological features interpreted on the barrier such as transgressive dune sheets and beach ridges corroborates this interpretation. In subsurface, three main radar facies (RF-1, RF-2, RF-3), a surface radar (erosive surface) and a subsurface feature (SF) were identified in the Ground Penetrating Radar (GPR) profiles. Continuous to discontinuous reflectors, sub parallel with high amplitude, were interpreted as corresponding to the beach/shallow marine environment (RF-1) formed by the barrier progradation. An erosive surface in concave form truncating these reflectors, with onlap and downlap reflectors in the concave face, and truncation in the convex base, was interpreted as the base of a paleochannel. The others radar facies (RF-2 and RF-3) are related to the filling of the channel. The integrated interpretation of GIS and GPR data have allowed to interpret evolutionary characteristics at different time scales of the studied barrier sector.

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.