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.

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

“…As already observed by Tomazelli and Villwock (1989), Dillenburg et al (2000Dillenburg et al ( , 2009, ), Rosa (2012, Dillenburg and Barboza (2014) and Barboza and Rosa (2014), the Pelotas Basin shoreline has sectors with different behaviors, with System IV presenting synchronous progradational, aggradational and retrogradational patterns along the coast.…”

“…As System IV has the most studied stratigraphic record of the coastal plain, and sea-level history during Holocene is quite well known we did not performed new measurements in this work. Barrier IV was studied in detail by Dillenburg et al (2000Dillenburg et al ( , 2009, Dillenburg and Barboza (2014) and Hesp et al (2005Hesp et al ( , 2007, which distinguished three main morphological barrier types: relict dunefields, active dunefields or a complex foredune ridges, and dunefields combination. The morphological types of Barrier IV are related to the stratigraphic stacking found in GPR data (Rosa 2012;Barboza & Rosa 2014).…”

“…GPR and seismic profiles (Fig. 13) show Geomorphology, remote sensing, outcrops, drilling, dating, GPR Barrier-lagoon Systems I or II through IV (part of high frequency sequences, each sequence cyclicity is 100 ka) Villwock, (1984), Villwock and Tomazelli (1995), Tomazelli and Villwock (2000), Lopes et al (2010Lopes et al ( , 2013Lopes et al ( , 2014, Rosa (2012) High II 20 ka Geomorphology, remote sensing, outcrops, drilling, dating, seismic, GPR System IV evolution (part of the younger high frequency sequence) Tomazelli & Villwock (1989), Dillenburg et al (2000Dillenburg et al ( , 2009, Tomazelli et al (2008), Barboza et al (2009, 2011), Rosa (2012, Dillenburg and Barboza (2014) High III 500, 300, 60 and 22 yr Geomorphology, remote sensing, including historical data, outcrops, drills, dating, beach profiles, monitoring of shoreline (DGPS), tide gauge, climatic, and meteorological data Phases of dunes (~500 yr), Lagoon level rise (Lagoa dos Patos -300 yr), increased vegetation in dune fields (60 yr), shoreline erosion (22 yr) Toldo Jr. et al (1999, 2004, Barboza et al (2006), Martinho et al (2008Martinho et al ( , 2009Martinho et al ( , 2010, Rosa (2012), Dillenburg et al 2017 (in press) the contact between the valley bottom and System III. 14 C age dating of shells obtained in SPT cores on the barrier indicates a Holocene age above this contact.…”

Descarga de água subterrânea para as lagoas costeiras do litoral norte do RS, Brasil

“…Possivelmente, este comportamento em nossa grade amostral possa ser explicado na encosta da serra, pela interação com a formação geológica, através de fraturas ou porções permeáveis sobre aquíferos confinados em terra (Corbett et al, 1999). Enquanto isso, a porção leste da área de estudo sofre efeito da barreira holocênica, parte progradante parte retrogradante Dillenburg & Barboza, 2014) que a comunica com o oceano, configurando uma membrana arenosa permeável, como o caso da Lagoa Mangueira (Andrade, 2010). Esta barreira apresenta diferentes estruturas deposicionais ao longo de sua formação, ora transgressivas, ora regressivas ou agradantes (Hesp et al, 2005;Barboza et al, 2011) que influenciam diretamente na descarga de água subterrânea em direção ao mar, criando nesta área uma zona de mistura (Attisano, 2008).…”

“…A planície costeira do Rio Grande do Sul foi formada, durante o Quaternário, através de sistemas de leques aluviais sendo seguidos por contínuos eventos de regressão e transgressão marinha, os quais deram origem aos sistemas Laguna/Barreira I, II, III e IV (Tomazelli, 1990;Villwock & Tomazelli, 1995;Tomazelli & Villwock, 2005;Tomazelli et al, 2011;Rosa, 2012;Dillenburg & Barboza, 2014). No Litoral Norte, esses processos deram início à formação das dezenas de lagoas cordiformes (Tomazelli & Villwock, 2005), como Itapeva, Quadros e Barros (Figura 1), que representam 38,5% da superfície local (Schwarzbold & Schafer, 1984), sendo a maioria dessas lagoas de pouca profundidade, mais rasas na margem oeste pelo avanço do sistema eólico (Tomazelli, 1993), interligadas entre si (Delaney, 1965) e que atuam como filtros daquilo que alcança o oceano, podendo apresentar taxa de sedimentação de alguns milímetros por ano (Ivanoff, 2013), e que estão situadas entre a encosta e a linha de praia.…”