Stratigraphic analysis and geomorphological reconstruction of Grumari coastal plain, Rio de Janeiro, Brazil

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Highlights

  • Geophysical investigation of Grumari's coastal plain stratigraphic and geomorphological evolution.

  • Recognition of three stratigraphic units, separated by two regional surfaces.

  • Identification of high-frequency surfaces in the retrogradational package.

  • Registering events from different hierarchies during the Holocene transgression.

  • Geomorphological reconstruction and characterization of the most recent landscape as a strandplain

Abstract

Between Marambaia spit and Jacarepagua barrier island system, two major coastal plains in Rio de Janeiro State, Grumari's type of evolution remains unknown, since it was anthropologically modified from the 1960s, where all superficial sedimentary deposits were devastated, intensively changing its natural landscape, and hiding how it has been formed through the Holocene. Aiming to fill these blanks in Grumari's geological history and complementing Rio de Janeiro's coastal studies, the Ground Penetrating Radar method (GPR) was applied to enable the 2D subsurface imaging. The reflection patterns recognition and their correlation with geological features allow a radarfacies interpretation, in a radar stratigraphy context. For coastal plain studies, geological interpretation takes into consideration the sedimentary processes involved in their formation, driven by the balance between sedimentary supply and sea level variations. In the adjacent areas' researches, geological and geophysical data show, from bottom to top, continental deposits formed during the last regional marine regression, in the Late Pleistocene, covered by sand deposits and marine fossils deposited during the last marine trangression, already in the Holocene, followed by sand barriers and lagoons formed and exposed during the last sea falling until the present shoreline. For Grumari coastal plain, this work presents geophysical data interpretation of five GPR sections, collected in about 15 m thick sedimentary deposit, with a sequence of three main units, separated by regional stratigraphic surfaces: a transgressive unit followed by a regressive one, being this one covered by the most recent deposits composing a third unit. The Unit 1 is related to the Holocene sea level rise, from about 7,000 yr BP, and is characterized by truncation relationships between seawards downlapping reflectors and flat-parallel ones, showing a constant change in deposition direction, as the accommodation space was still small at the beginning of this process. At the Unit 1 top, as the accommodation space rate increased, the deposition became more regular, seen by a flat-parallel reflection pattern. While mean sea level reached its maximum range, from about 5,500 yr BP, its rising rate decreased, while the sedimentary supply rate raised due to the continental shelf and the mountain system erosion. This variation in radarfacies sequence is registered by a regional surface, marking the regressive Unit 2 beginning. The change in the rates led to the continental progradation through sand ridges formation, represented by seawards sigmoidal radarfacies. The mean sea level continued to drop gradually to the current level, exposing the sand ridges to erosion, and newer aeolian, fluvial, lagoonal and storm deposits could be formed above them, composing the Unit 3, limited at the bottom by a second regional high amplitude surface. Storm deposits from 4,450 ± 180 yr BP and 3,780 ± 200 yr BP, as washover fans, have been already identified in Jacaperagua plain, therefore, there were episodical events in the region, in the last 4,450 years, seen also in Grumari's data. This primary radar stratigraphic analysis and geomorphological reconstruction of Grumari most recent deposits show that the most recent evolution occurred through the prograding sand ridges formation, mostly attached to each other, with some inter-ridge areas development, and then is likely to be considered as a strandplain.

Introduction

The Southeastern Brazilian coastal area has been constructed by the formation of a barrier island or by a regressive beach ridge system, during Pleistocene and Holocene, being driven by the balance between paleoclimatic controlled sea-level changes and sedimentary supply (Villwock et al., 2005). In the Rio de Janeiro metropolitan region, two major coastal areas have been studied since 1940's: the Marambaia spit, separated from the mainland by the Sepetiba bay (Lamego, 1945; Ponçano et al., 1979; Dadalto, 2017; Alves Martins et al., 2020), and the Jacarepagua plain, a two-barriers island system (Roncarati and Neves, 1976; Maia et al., 1984). Between them, a secondary coastal plain has not been well defined yet, presenting features different from the surrounded areas.

Grumari plain (Fig. 1a) was anthropologically modified from the 1960s, where all superficial sedimentary deposits were devastated, and the area was flattened for residential construction. As it became part of Pedra Branca National Park, the urbanization was interrupted and the area went through a reforestation process (Guerra, 2005). Nowadays, although the area seems preserved from urbanization, its original landscape and its type of evolution is not clear: whether it is an old barrier island system or a strandplain. Pereira et al. (2012) point to the hypothesis that the area is an old barrier island system, such as the adjacent areas, however, still remains the possibility to be a strandplain up to be investigated. As there are currently no outcrops or superficial sedimentary body remnants and exposed, geophysics comes as a method to understand the area's recent development.

In coastal evolution studies, the Ground Penetrating Radar (GPR) method is commonly applied, allowing the correlation between geophysical and geological features, through inferences of paleoenvironment and sedimentary processes, enabling a geological reconstruction (Beres and Haeni, 1991; Jol and Smith, 1991; Martins et al., 2020). The interpretation of the sedimentary and geomorphological processes of the coastal plain internal architecture and its related deposits is essential to understand their evolution in geological time. Several authors have used the radar stratigraphy and radarfacies interpretation methods with this purpose (Neal and Roberts, 2000; Gandolfo et al., 2001; Neal and Roberts, 2001; Bristow and Pucillo, 2006; da Rocha et al., 2013; Barboza et al., 2014; Fernandez and Rocha, 2015; Rosa et al., 2017; Dillenburg et al., 2017; Angulo et al., 2018; Barboza et al., 2018; Montes et al., 2018; Berton et al., 2019; Oliveira et al., 2019).

As the radar reflection patterns allow the deposits characterization, as well as its related sedimentary processes, through the interpretation of GPR data, this current work aims to improve the understanding about the Grumari geological evolution during the Holocene, being a primary investigation to elucidate the plain stratigraphic and geomorphological evolution, guiding future sedimentological and geochronological studies. In order to interpret the possible latest coastal development of this area, were taken into account the mean sea level variations in Southeast Brazil (Martin et al., 1979; Angulo and Lessa, 1997; Angulo et al., 2006; Jesus et al., 2017) and in the adjacent areas (Maia et al., 1984; Dadalto, 2017). From correlations between them both, this research presents the interpretation of the stratigraphic evolution scenario added to a landscape reconstruction, contributing with other analogues investigations and complementing Rio de Janeiro's coastal plains researches.

Section snippets

Geological context

The study area is located in the Oriental Terrain of the Ribeira Belt, Santos Basin onshore northern portion, in the Cenozoic Rift System of Southeast Brazil context (Zalán and Oliveira, 2005). The geological evolution in the Southeastern Brazil is pronounced by the Paleocene tectonic reactivation responsible for the Serra do Mar and a series of continental rifts origin, carving a particular coastal geomorphology, characterized by narrow coastal plains settled between the mountains and the

Fieldwork

Two different types of GPR data acquisition were made, Fixed-offset and Common-midpoint (CMP), along Grumari plain, with a Differential Global Positioning System (DGPS), to guarantee geographic coordinates and altitude of the radargrams. The Fixed-offset section (2D) registers both vertical and lateral medium variations. The CMP (1D) measures the subsurface wave propagation velocity. Each Fixed-offset section has its corresponding CMP data, showing how velocity changes with depth in each point,

Results

In the GPR sections (Fig. 2, Fig. 3, Fig. 4) were recognized and interpreted seven radarfacies (Table 1), divided into three major units, according to their reflection pattern, and two main surfaces limiting these units.

Discussions

Mean sea level variations control the vertical translation of the shoreline equilibrium profile, while changes in sedimentary supply, on the other hand, influence the horizontal translation. Therefore, the main controlling factors for coastal plain development are the sedimentary supply and accommodation space creation rates.

The geological interpretation of Grumari's geophysical sections combined with recent mean sea level changes (Martin et al., 1979; Angulo and Lessa, 1997; Angulo et al., 2006

Conclusions

For Grumari stratigraphic evolution proposal, we suggest that at the sea level rise beginning in the region, from about 7,000 years BP, the sedimentary supply rate was higher than accommodation space creation rate, causing the shoreline tent to prograde, even though the sea level was rising. With the continual rise in sea level, the accommodation space creation rate is turning in equilibrium with the sedimentary supply, allowing a more aggradational/retrogradational deposition, in both vertical

Authorship statement

Conception and design of study: T. Mira and S.S. Martins; acquisition of data: T. Mira, S.S. Martins, S. Gouvêa and F. Dourado; analysis and/or interpretation of data: T. Mira; drafting the manuscript: T. Mira, S.S. Martins, S. Gouvêa and F. Dourado; revising the manuscript critically for important intellectual content: T. Mira; approval of the version of the manuscript to be published. The names of all authors must be listed: T. Mira, S.S. Martins, S. Gouvea and F. Dourado.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors acknowledge the Master Grant provided by CAPES, the Graduate Program in Geosciences (UERJ), Labsismo (UERJ), CEPEDES (UERJ), LEXMIN (UERJ) and LAMEMO (UFRJ) laboratories for equipment, software and work environment.

References (34)

  • E.G. Barboza et al.

    Stratigraphic analysis applied on the recognition of the interface between marine and fluvial depositional systems

    J. Coast Res.

    (2014)
  • E.G. Barboza et al.

    Diachronic condition between maximum transgressive and maximum eustatic sea-level in Holocene: subsidies for coastal management

    J. Coast Res.

    (2018)
  • M. Beres et al.

    Application of Ground Penetrating Radar methods in hydrogeologie studies

    Groundwater

    (1991)
  • C.S. Bristow et al.

    Quantifying rates of coastal progradation from sediment volume using GPR and OSL: the Holocene fill of Guichen Bay, southeast South Australia

    Sedimentology

    (2006)
  • T.P. Dadalto

    Arquitetura estratigráfica e evolução geológica da Restinga Da Marambaia (RJ). PhD Thesis

    (2017)
  • G.B. Fernandez et al.

    Barreiras Costeiras Holocênicas: geomorfologia e Arquitetura Deposicional no Litoral do Rio de Janeiro

    Revista Brasil. Geomorfol.

    (2015)
  • O.C.B. Gandolfo et al.

    Estratigrafia rasa da Ilha Comprida (SP): um exemplo de aplicação do GPR

    Rev. Bras. Geofís.

    (2001)
  • Cited by (0)

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