Neogene to Quaternary broken foreland formation and sedimentation dynamics in the Andes of NW Argentina (25°S)

Abstract

[1] The northwest Argentine Andes constitute a premier natural laboratory to assess the complex interactions between isolated uplifts, orographic precipitation gradients, and related erosion and sedimentation patterns. Here we present new stratigraphic observations and age information from intermontane basin sediments to elucidate the Neogene to Quaternary shortening history and associated sediment dynamics of the broken Salta foreland. This part of the Andean orogen, which comprises an array of basement-cored range uplifts, is located at ∼25°S and lies to the east of the arid intraorogenic Altiplano/Puna plateau. In the Salta foreland, spatially and temporally disparate range uplift along steeply dipping inherited faults has resulted in foreland compartmentalization with steep basin-tobasin precipitation gradients. Sediment architecture and facies associations record a three-phase (∼10, ∼5, and <2 Ma), east directed, yet unsystematic evolution of shortening, foreland fragmentation, and ensuing changes in precipitation and sediment transport. The provenance signatures of these deposits reflect the trapping of sediments in the intermontane basins of the Andean hinterland, as well as the evolution of a severed fluvial network. Present-day moisture supply to the hinterland is determined by range relief and basin elevation. The conspiring effects of range uplift and low rainfall help the entrapment and long-term storage of sediments, ultimately raising basin elevation in the hinterland, which may amplify aridification in the orogen interior. Citation: Hain, M. P.,

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

“…Instead, inverted normal faults and transfer structures related to the Cretaceous Salta Rift have often accommodated shortening during the Cenozoic Andean orogeny (Grier et al, 1991;Kley and Monaldi, 2002;Carrera et al, 2006;Hongn et al, 2007;Hain et al, 2011). In addition, the metamorphic fabrics generated during the early Paleozoic (Ordovician) Ocloyic orogeny follow the western margin of the broken foreland uplifts in the transition to the Puna Plateau and are inferred to have affected the spatial characteristics of contractile reactivation during Andean shortening (e.g., Mon and Hongn, 1991).…”

“…For such a weak crust, the principal pattern of accommodation space mimics that of the deformation. In the northwestern Argentine Andes, flexural accommodation may thus be spatially limited and discontinuous, and the location of basins may ultimately be controlled by the distribution of reactivated zones of crustal weakness Kley et al, 2005;Hongn et al, 2007;Hain et al, 2011). In addition, due to the link between crustal heterogeneities and their compressional reactivation, the evolution of the broken foreland is unsystematic, diachronous, and may additionally depend on the local lithostatic stresses exerted by the neighboring range uplifts.…”

Cenozoic Evolution of Hinterland Basins in the Andes and Tibet

“…This led to topographic isolation and initiation of internal drainage that persists today as sedimentation continues in various isolated basins, commonly in evaporative saline lakes or salars (Alonso et al, 1991;Vandervoort et al, 1995). Neogene growth of orographic barriers during upper crustal shortening helped generate a unique geomorphic history of intermontane processes involving periodic topographic ponding and excavation (Sobel et al, 2003;Hilley and Strecker, 2005;Coutand et al, 2006;Strecker et al, 2007, this volume;Hain et al, 2011).…”

Basin fragmentation controlled by tectonic inversion and basement uplift in Sierras Pampeanas and Santa Bárbara System, northwest Argentina

“…Since then, deformation has propagated towards the east but with jumps back to the west intercalated in an out-of-sequence deformation (Carrera et al 2006;Carrera & Muñoz 2008;Hain et al 2011).…”