Abstract
The Pantanal region can be characterized as a quaternary floodplain with predominant sedimentation in the form of alluvial fans. In the geomorphologic and sedimentary evolution, the avulsion process is inherent to this depositional system and its dynamics, together with surface water floods, influence soil sedimentation on this plain. The knowledge and differentiation of these two events can contribute to a better understanding of the variability of soil properties and distribution under the influence of these sedimentation processes. Therefore, this study investigated the genesis of soils in the Northern Pantanal with textural contrasts in deeper horizons and their relationship with the depositional system dynamics. We analyzed four soil profiles in the region of Barão de Melgaço, Mato Grosso State, Brazil (RPPN SESC Pantanal). Two profiles were sampled near the Rio Cuiabá (AP1 and AP4) and two near the Rio São Lourenço (AP10 and AP11). In AP11, the horizons contrast in particle size between the profile basis and the surface. In AP1, AP4 and AP10, the horizons overlaying the sand layer have similar particle size properties, mainly in terms of sand distribution. In the first case, floods (surface water) seem to have originated the horizons and layers with contrasting texture. In the second case, avulsion is the most pronounced process. Therefore, the two modes can form soils with contrasting texture that are discriminable by soil morphology, based on the distinct features associated to the specific sedimentation processes.
Highlights
IntroductionThe Pantanal is a huge sedimentary basin that comprises several depositional systems (lacustrines, alluvial fans and floodplains), which define the region as a depositional systems tract (Assine, 2003; Assine & Silva, 2009)
The Pantanal is a huge sedimentary basin that comprises several depositional systems, which define the region as a depositional systems tract (Assine, 2003; Assine & Silva, 2009)
One of the most common depositional systems in this humid tropical region seems to be that of alluvial fans (Assine & Silva, 2009), in which sedimentation is mainly controlled by overbank flows on the floodplain (Bridge, 2006)
Summary
The Pantanal is a huge sedimentary basin that comprises several depositional systems (lacustrines, alluvial fans and floodplains), which define the region as a depositional systems tract (Assine, 2003; Assine & Silva, 2009). Aside from the overbank flows, which are common in this region, the peculiar dynamics of alluvial fans are characterized by the frequent construction and abandonment of a main river channel (Nichols & Fisher, 2007). This abandonment may occur due to a process known as avulsion, defined as a shift in the main channel bed of the river to a new course, causing the water course to flow through the former floodplain (Figure 1)
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