Evolution of the late Cenozoic Chaco foreland basin, Southern Bolivia

Abstract

Eastward Andean orogenic growth since the late Oligocene led to variable crustal loading, £exural subsidence and foreland basin sedimentation in the Chaco basin.To understand the interaction between Andean tectonics and contemporaneous foreland development, we analyse stratigraphic, sedimentologic and seismic data from the Subandean Belt and the Chaco Basin.The structural features provide a mechanism for transferring zones of deposition, subsidence and uplift.These can be reconstructed based on regional distribution of clastic sequences. Isopach maps, combined with sedimentary architecture analysis, establish systematic thickness variations, facies changes and depositional styles.The foreland basin consists of ¢ve stratigraphic successions controlled by Andean orogenic episodes and climate: (1) the foreland basin sequence commences between $27 and 14 Ma with the regionally unconformable, thin, easterly sourced £uvial Petaca strata. It represents a signi¢cant time interval of low sediment accumulation in a forebulge-backbulge depocentre. (2) The overlying $14^7 Ma-old Yecua Formation, deposited in marine, £uvial and lacustrine settings, represents increased subsidence rates from thrust-belt loading outpacing sedimentation rates. It marks the onset of active deformation and the under¢lled stage of the foreland basin in a distal foredeep. (3) The overlying $7^6 Ma-old, westerly sourced Tariquia Formation indicates a relatively high accommodation and sediment supply concomitant with the onset of deposition of Andeanderived sediment in the medial-foredeep depocentre on a distal £uvial megafan. Progradation of syntectonic, wedge-shaped, westerly sourced, thickening-and coarsening-upward clastics of the (4) $6^2.1 Ma-old Guandacay and (5) $2.1 Ma-to -Recent Emborozu¤ Formations represent the propagation of the deformation front in the present Subandean Zone, thereby indicating selective trapping of coarse sediments in the proximal foredeep and wedge-top depocentres, respectively.Overall, the late Cenozoic stratigraphic intervals record the easterly propagation of the deformation front and foreland depocentre in response to loading and £exure by the growing Intra-and Subandean fold-and-thrust belt.

Distributions and phylogeographic data of rheophilic freshwater fishes provide evidences on the geographic extension of a central-brazilian amazonian palaeoplateau in the area of the present day Pantanal Wetland

“…Foreland basin systems develop as a result of flexural warping of the lithosphere in response to supralithospheric and sublithospheric orogenic wedging (DeCelles & Giles, 1996). Lithospheric flexure under static loads generates downbending exure proximal to the orogen, which migrates away from the orogen as the load increases (Uba et al, 2006). The Andean foreland basins can be described as sets of "expanding lowlands" into which adjacent uplands become incorporated as the tectonic load advances eastward (Lima & Ribeiro, 2011).…”

Structural, Geomorphic, and Depositional Characteristics of Contiguous and Broken Foreland Basins: Examples from the Eastern Flanks of the Central Andes in Bolivia and NW Argentina

“…As the fold-and-thrust belt advances into the foreland, these different tectonic and associated depositional domains also migrate systematically basinward, often leading to vertical stacking of sediments created within these domains (e.g., DeCelles and Horton, 2003). The fold-and-thrust belt geometry approximates that of a self-similarly growing tectonic wedge that progressively entrains foreland-basin sediments by frontal accretion and motion along a detachment horizon, such as currently observed in the Subandean belt of Bolivia in the central Andes (e.g., Sempere et al, 1990;Kennan et al, 1995;Baby et al, 1997;Horton and DeCelles, 1997;McQuarrie, 2002;Uba et al, 2006). This standard model successfully explains the primary features of both ancient and modern peripheral (sensu Dickinson, 1974) and retroarc foreland basins (e.g., Jordan, 1981Jordan, , 1995DeCelles and Giles, 1996).…”

Cenozoic Evolution of Hinterland Basins in the Andes and Tibet

“…The Andes ( Fig. 21.1) are the type example of an ocean-continent convergent plate boundary, providing insights into subduction zones, magmatic arcs, retroarc thrust belts, and retroarc foreland basins (Jordan et al, 1983;Isacks, 1988;Horton and DeCelles, 1997;James and Sacks, 1999;Kley et al, 1999;Beck and Zandt, 2002;Kay et al, 2005;McQuarrie et al, 2005;Uba et al, 2006). The Himalayan-Tibetan orogen ( Fig.…”