Abstract
Abstract The Pantanal wetland is an active sedimentary basin representing a relevant depositional setting for alluvial sedimentation studies. However, sedimentation homogeneity and the lack of outcrops makes sedimentary analysis more difficult. The Lower Nhecolândia is located at the Southern edge of the Taquari river megafan, whose genetic origin has been disputed as fluvial or eolian deposition. GPR analysis was used to characterize the subsurface stratigraphy and understand the region’s geomorphic evolution. The 100 MHz GPR provided continuous good quality sections up to a depth of 8 m. Two continuous reflections are disconformities that bound three depositional sequences characterized by distinct radar facies. The lower facies presents an upper erosional truncation followed by reflections presenting ∼1.5 m deep channelized forms and concave-up low amplitude reflections. The intermediate facies (∼4 m thick) presents a base with erosional truncation followed by concave-upward forms, ∼10 m wide, 1–3 m deep, separated by 1–2 m, and offlapping geometry. The upper facies has a flat base and thickness of 2–4 m, with parallel reflections; it shows a strong correlation between the radar facies and the forms preserved in the landscape, suggesting that channelized fluvial streams did not form them. The results obtained indicate that GPR use in the Pantanal is an important method to elucidate its geologic evolution.
Highlights
The Pantanal region, located in West Central Brazil, is one of the most important wetlands in the world (Por 1995, Junk et al 2006), with large pristine alluvial plains (Assine 2015)
To evaluate the applicability of ground penetrating radar (GPR) in characterizing the subsurface stratigraphy and in understanding the geomorphic evolution of the Pantanal wetland (Fig. 1), we have investigated the enigmatic landscape of the Lower Nhecolândia, in the Southern fringe of the Taquari fluvial megafan (Assine et al 2015b, Assine et al 2015c)
The GPR technique applied to the sedimentation study in the Taquari megafan provided continuous sections
Summary
The Pantanal region, located in West Central Brazil, is one of the most important wetlands in the world (Por 1995, Junk et al 2006), with large pristine alluvial plains (Assine 2015). It is an important depositional site where modern alluvial sedimentation can be studied (Assine and Soares 2004, Assine 2005, Assine et al 2015b). Facies analysis is extremely difficult due to the absence of natural outcrops and the homogeneity of sediments, which consists mainly of medium to fine-grained sand. Subsurface investigations using GPR in modern deposition sites in the Pantanal were solely conducted in the modern Taquari river channel (Souza et al 2002, Porsani et al 2005)
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