Regional variations in sediment thickness, internal structures, average elevation, and Bouguer gravity define a four-component foreland basin system adjacent to the Central Andes. In the most proximal part of the foreland basin system, the eastern Subandean zone and westernmost Chaco Plain, 1–3 km of Cenozoic deposits overlies active folds and thrusts of the frontal Andean orogenic wedge. These wedge-top deposits pass cratonward into a foredeep depozone containing a 3–4-km-thick sedimentary prism that tapers toward (and locally pinches out against) a broad-wavelength forebulge in the central-eastern Chaco Plain. The forebulge is underlain by Precambrian–Mesozoic rocks and is largely covered by a thin veneer of Quaternary alluvium. East of the forebulge, a thin (0.5 km) saucer-shaped accumulation of sediment beneath the Pantanal Wetland represents a back-bulge depozone. Ancient counterparts of these four depozones can be identified in the Central Andes, suggesting that modern basin architecture is the result of continuous, eastward migration of the coupled orogenic wedge and foreland basin system since the Late Cretaceous–Paleocene.

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