Dynamics of deformation and sedimentation in the northern Sierras Pampeanas: An integrated study of the Neogene Fiambala basin, NW Argentina

Abstract

The thick-skinned Sierras Pampeanas morphotectonic domain of western and northwestern Argentina (27°S-33°S) is characterized by reverse-fault-bounded basement blocks that delimit internally deformed, Neogene sedimentary basins. Forelandbasin evolution in this part of the Andes is still not very well understood. For example, challenging questions exist as to how thickskinned deformation develops, if there are distinct spatiotemporal trends in deformation and exhumation, how such deformation styles infl uence sedimentation patterns, and whether or not broken foreland basins are related to regional plate-tectonic processes, such as fl at-slab subduction.The Fiambalá basin of the northwestern Sierras Pampeanas is the largest of several intermontane basins in the transition to the southern margin of the Puna Plateau. This basin preserves a thick continental Neo-gene sequence that provides information on the dynamics of thick-skinned deformation and resulting sedimentation. The Fiambalá basin contains ~4 km of fl uvial-alluvial sedimentary rocks that comprise the Tamberia, Guanchin, and Punaschotter Formations. U-Pb geochronology of ashes intercalated within the Fiambalá stratigraphic sequence demonstrates that these sedimentary rocks are late Miocene to Pliocene (8.2 ± 0.3 Ma to 3.05 ± 0.4 Ma) in age. Sedimentology and provenance data indicate that the source of the Tamberia Formation was located to the west of the modern western basin-bounding range. The Guanchin and Punaschotter Formations record input from local sources, including the modern basin-bounding range to the west and the southern Puna Plateau to the north, suggesting reorganization of the catchment area at ca. 5.5 Ma.The coarsening-upward trends recorded by the fl uvial Tamberia and Guanchin Formations indicate enhanced tectonics and relief during sedimentation. The Punaschotter conglomerates record alluvial-fan sedimentation and local sources. Fault kinematic data document a contractional regime, characterized by E-W and NE-SW shortening, active throughout the middle-late Miocene and Pliocene. Furthermore, a comparison between the Fiambalá basin and similar sedimentary basins in the Sierras Pampeanas (e.g., Bermejo foreland basin) and the Eastern Cordillera leads us to propose that the study area originally constituted an integral part of a continuous and more extensive foreland-basin system (thin-skinned) for much of its early history. Our data suggest coeval intrabasin deformation along strike from the Bermejo region northward to the Eastern Cordillera. The coeval change at ca. 6 Ma from a regional to more compartmentalized (thick-skinned) tectono-sedimentary environment in the regions adjacent to the Eastern Cordillera, the southern Puna margin, and other sectors within the Sierras Pampeanas domain may thus refl ect a regional tectonic process related to fl at subduction. Our data, combined with existing sedimentological and petrological evidence, imply that the passage from steep to fl at subduction occurred synchronously from ~30°S to ~26°S.

Magnetostratigraphy and paleomagnetism of early and middle Miocene synorogenic strata: basement partitioning and minor block rotation in Argentine broken foreland

“…Jordan et al (2001) and Ramos et al (2002) constrained the ''broken foreland stage'', involving the study region, between 6.5 Ma and present. A similar model was recently proposed by Carrapa et al (2008), who suggested that the transition from thin-skinned to basement thrusting occurred contemporaneously along the Andean foreland (from the Eastern Cordillera in the north to the Bermejo Basin in the south) at ca. 6 Ma.…”

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

“…The study area is situated at ∼25°S, between the arid, internally drained orogenic Puna Plateau in the west and the undeformed Chaco Plain foreland basin in the east. Specifically, this region comprises the southern sectors of the Eastern Cordillera (EC), the Santa Barbara System (SBS), and the Sierras Pampeanas morphotectonic provinces (Figures 1 and 2b); here, we refer to the study area as a whole as the “Salta foreland.” At this latitude the Andean orogen was, until the middle Miocene, bordered by a contiguous foreland basin [e.g., Coutand et al , 2001; Hernández et al , 2005; Carrapa et al , 2008; Bosio et al , 2009]. Since that time, contractile inversion of the Cretaceous Salta Rift [e.g., Baldis et al , 1976; Rolleri , 1976; Bianucci and Homovec , 1982; Salfity , 1982; Allmendinger et al , 1983; Marquillas and Salfity , 1988; Mon and Salfity , 1995; Grier et al , 1991; Viramonte et al , 1999; Kley and Monaldi , 2002; Kley et al , 2005; Carrera et al , 2006; Carrera and Muñoz , 2008] has led to a patchwork of basement‐cored ranges and intervening intermontane basins that have experienced episodes of internal, or reduced external, drainage conditions [e.g., Malamud et al , 1996; Bookhagen et al , 2001; Salfity et al , 2004], but have been recaptured by rivers that are adjusted to the undeformed foreland (Figure 2a).…”

“… Reynolds et al , 2000]. The deformation history is only adequately resolved in the arid, well exposed western sector of the foreland, along the eastern flanks of the Puna Plateau [ Salfity et al , 2004; Deeken et al , 2006; Coutand et al , 2006; Hongn et al , 2007; Mortimer et al , 2007; Carrapa et al , 2008; Carrera and Muñoz , 2008; Bosio et al , 2009; Bywater‐Reyes et al , 2010].…”

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

“…The discontinuous nature of deformation within northwestern Argentina has produced spatially disparate and diachronous storage of sediments upstream of the uplifting ranges (Bossi and Palma, 1982;Strecker et al, 1989Strecker et al, , 2009Carrapa et al, 2009). Within basins flanking the margins of the Puna Plateau, conglomerates sourced from the Puna margin and ranges surrounding these basins are sometimes intercalated with lacustrine sediments as well as tephras that constrain the timing of deposition of these sediments.…”