Morphology of the Itapeva to Tramandai transgressive dunefield barrier system and mid‐ to late Holocene sea level change

Abstract

The surface morphology of the transgressive dunefield barrier extending from Itapeva to Tramandai along the northern littoral of Rio Grande do Sul, is examined and an attempt is presented to link morphological changes across the barrier to Holocene sea level changes. The 4·5 km wide Holocene barrier displays two typical morphologies: an inner part dominated by large-scale, continuous alongshore, overlapping dunefield phases comprising sand sheets, dunes, deflation plains and precipitation ridges; and an outer part dominated by discontinuous, medium-to small-scale, triangular to lobate transgressive dunefield phases, cut by both active and relict (palaeo-) creeks or washouts. Holocene sea level in the region rose to c. + + + + +1 to + + + + +3 m above present reaching a maximum around 5100 years BP and then progressively fell to the present level. We argue that the effect on barrier development was to suppress the development of a drainage system during the rising and maximum stages, and encourage the development of an organized drainage system in the form of regularly spaced washouts during the falling period, and that this change in sea level from rising to falling therefore produced the large-scale differences in barrier morphology. Regional SettingRio Grande do Sul has a low-relief coastal plain formed during the Quaternary by juxtaposition of sedimentary deposits of four barrier/lagoon systems designated I (oldest) to IV (youngest) by Villwock et al. (1986). The coastal Figure 1. Holocene barrier types along the southern Brazilian coast from Torres to Chui. The first map (I) displays the northernmost sector and II, III and IV the progressively more southern sectors. This re-interpretation of Dillenburg et al.'s (2000) figure indicates that the Holocene barrier system comprises relict (vegetated) transgressive dunefields, active transgressive dunefields, or a complex barrier type comprising both foredune ridges and transgressive dunefields.plain ranges from 20 to 80 km wide and is bordered landward by bedrock highlands. Climate is humid temperate with generally warm to hot temperatures in summer (mean 25°C), and cool temperatures in winter (mean 17°C). Rainfall ranges from 1000 to 1500 mm and is evenly distributed throughout the year.Rio Grande do Sul (RS) has a uniform and gently undulating barrier coast 625 km long, oriented NE-SW and subject to dominant swell waves generated in southern latitudes and wind-generated waves produced by strong spring-summer sea breezes from the northeast. The average significant wave height is 1·5 m measured in water depths of 15-20 m (Motta, 1969). During autumn and winter storms (April to July) wave height may frequently exceed 2·0 m Morphology of transgressive dunefield 409 Figure 2. Sea level envelope and palaeo-sea level reconstructions for the Brazilian coast north of 28° (solid line) and south of 28°( dashed line), based on vermetid samples and with outliers removed (data from Angulo et al., 2006).410 P. A. Hesp et al.Figure 3. Vertical aerial photograph of the Curumim b...

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 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).…”

“…In the GPR sections, progradational staking is composed by radarfacies related to aeolian, backshore, foreshore and shoreface deposits, forming a set of reflections dipping seaward Rosa 2012;). Barrier morphology is mostly represented by strandplains, with complex foredune ridges and dunefield combination (Dillenburg et al 2000Hesp et al 2005Hesp et al , 2007Martinho et al 2008Martinho et al , 2010. The third pattern is defined as aggradational, with parallel to subparallel horizontal reflections related to aeolian deposits, where the barrier morphology is mainly of dunefields (Rosa 2012;.…”

Geomorfologia e arquitetura deposicional de uma planície de cordões litorâneos na margem NE da Lagoa dos Quadros, RS, Brasil

“…A geologia local e os depósitos sedimentares adjacentes à área em apreço foram pesquisados e mapeados por Villwock (1984), Horn Filho (1988, Hesp et al (2005Hesp et al ( , 2007, Dillenburg et al (2006), . Além do mais, Cwik (1999) e Meyer et al (2005Meyer et al ( , 2006 realizaram importantes estudos em relação a aspectos físicos, sedimentológicos e evolutivos da Lagoa dos Quadros.…”

“…Na figura 14B, de 1964, nota-se um grande estoque de areia, na forma de dunas frontais paralelas. À época, ventos do quadrante SW-SSW e períodos de baixa umidade encontrados na área de estudo, principalmente entre 1940 a 1970 (Hesp et al 2007;Martinho et al, 2008), associados à disponibilidade de areia fina e a vege-tação no pós-praia da margem lacustre, sugerem períodos de intensa atividade e deposição eólica no pós-praia, permitindo uma acresção vertical nos cordões de praia e desenvolvendo cordões de dunas frontais. Embora ventos de NE sejam dominantes na maior parte do ano, a orientação da linha de costa da lagoa permite o desenvolvimento de dunas frontais a partir de ventos SW e SSW.…”

“…Segundo Bracco et al (2005) as fases de construção de campos de dunas transgressivos, nos estágios de agradação da barreira de Curumim (Hesp et al, 2005(Hesp et al, , 2007Martinho et al, 2008), ocorrida entre 7,1 e 5,5 ka, podem ter contribuído com o transporte de areias para o interior da lagoa, pelo assoreamento por depósitos eólicos transgressivos, e assim proporcionado sedimentos para a construção da planície de cordões.…”