Cenozoic Foreland Basin System in the Central Andes of Northwestern Argentina: Implications for Andean Geodynamics and Modes of Deformation P

TECTONICS, VOL. 30, TC6013, doi:10.1029/2011TC002948, 2011

Cenozoic foreland basin system in the central Andes of northwestern Argentina: Implications for Andean geodynamics and modes of deformation P. G. DeCelles,1 B. Carrapa,1 B. K. Horton,2 and G. E. Gehrels1 Received 17 May 2011; revised 10 October 2011; accepted 12 October 2011; published 21 December 2011.

[1] Cenozoic strata in the central Andes of northwestern Argentina record the development and migration of a regional foreland basin system analogous to the modern Chaco‐Paraná alluvial plain. Paleocene‐lower Eocene fluvial and lacustrine deposits are overlain by middle‐upper Eocene hypermature paleosols or an erosional disconformity representing 10–15 Myr. This ‘supersol/disconformity’ zone is traceable over a 200,000 km2 area in the Andean thrust belt, and is overlain by 2–6 km of upward coarsening, eastward thinning, upper Eocene through lower Miocene fluvial and eolian deposits. Middle Miocene‐Pliocene fluvial, lacustrine, and alluvial fan deposits occupy local depocenters with contractional growth structures. Paleocurrent and petrographic data demonstrate westerly provenance of quartzolithic and feldspatholithic sediments. Detrital zircon ages from Cenozoic sandstones cluster at 470–491, 522–544, 555–994, and 1024–1096 Ma. Proterozoic‐Mesozoic clastic and igneous rocks in the Puna and Cordillera Oriental yield similar age clusters, and served as sources of the zircons in the Cenozoic deposits. Arc‐derived zircons become prominent in Oligo‐Miocene deposits and provide new chronostratigraphic constraints. Sediment accumulation rate increased from ∼20 m/Myr during Paleocene‐Eocene time to 200–600 m/Myr during the middle to late Miocene. The new data suggest that a flexural foreland basin formed during Paleocene time and migrated at least 600 km eastward at an unsteady pace dictated by periods of abrupt eastward propagation of the orogenic strain front. Despite differences in deformation style between Bolivia and northwestern Argentina, lithosphere in these two regions flexed similarly in response to eastward encroachment of a comparable orogenic load beginning during late Paleocene time. Citation: DeCelles, P. G., B. Carrapa, B. K. Horton, and G. E. Gehrels (2011), Cenozoic foreland basin system in the central Andes of northwestern Argentina: Implications for Andean geodynamics and modes of deformation, Tectonics, 30, TC6013, doi:10.1029/2011TC002948.

1. Introduction tectonic shortening in the upper crust is on the order of several hundred km [Kley, 1999; McQuarrie, 2002a]; deformation is [2] The most impressive topographic feature of the dominated by thin‐skinned thrusting above regional detach- Andean orogenic belt is the Central Andean Plateau, which ments that dip gently westward [Roeder, 1988; Sheffels, encompasses an area of ∼500,000 km2 between 15°S and 1990; Dunn et al., 1995; Baby et al., 1997; McQuarrie, 27°S latitudes where the average surface elevation exceeds 2002a; Echavarria et al., 2003; Uba et al., 2009]; deforma- 3km[Isacks, 1988; Allmendinger et al., 1997; Strecker et al., tion propagated eastward through time [McQuarrie, 2002a; 2007]. It is now widely documented that the plateau is a result Horton, 2005; Gillis et al., 2006; Ege et al., 2007; McQuarrie of crustal shortening, but the mode and history of shortening et al., 2008; Barnes et al., 2008]; and the crust is relatively remain topics of active research. Allmendinger et al. [1983, thick (ca. 65–70 km) [Beck and Zandt, 2002; Heit et al., 1997] and Kley and Monaldi [1998] pointed out that a 2008]. South of this latitude, documented shortening is number of major changes take place in the Central Andean – only about 100 km and was accommodated by steeply dip- Plateau at about 23 24°S. North of this latitude, horizontal ping, bivergent thrust faults that cut deeply into the crust (>25 km) [Cristallini et al., 1997; Kley and Monaldi, 2002; 1Department of Geosciences, University of Arizona, Tucson, Arizona, Mortimer et al., 2007]; deformation is considered to have USA. persisted throughout the orogenic belt during Miocene‐ 2Institute for Geophysics and Department of Geological Sciences, Pleistocene time [Allmendinger and Gubbels, 1996]; and Jackson School of Geosciences, University of Texas at Austin, Austin, the crust is much thinner (45–55 km) and more variable Texas, USA. [Yuan et al., 2002; Heit et al., 2008]. ‐ ‐ Copyright 2011 by the American Geophysical Union. [3] Significant along strike differences in the pre existing 0278‐7407/11/2011TC002948 geological structure and lithologic composition of Andean

TC6013 1of30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

developed regional foreland basin system in Bolivia and northernmost Argentina, where the presence of a major thin‐ skinned thrust belt—attesting to orogen‐scale simple shear— is well documented [e.g., Dunn et al., 1995; McQuarrie, 2002a; Echavarria et al., 2003]. On the other hand, if pure shear deformation has been dominant south of 23°S, a flexural signal in Cenozoic strata should be absent or significantly diminished, insofar as pure shear lithospheric shortening does not require regional (flexural) compensation [Allmendinger and Gubbels,1996]. [5] Previous work in the Bolivian Cenozoic record demonstrates that a regional scale foreland basin system developed during Paleocene time and migrated 800–1,000 km eastward to its present location in the Chaco plain [Horton and DeCelles, 1997; Sempere et al., 1997; Horton et al., 2001; DeCelles and Horton, 2003; Uba et al., 2006, 2009]. On the other hand, no consensus has been reached concerning the development and evolution of a foreland basin system south of 23°S in northwestern Argentina. Whereas some Figure 1. Cartoons illustrating differences between pure studies conclude that a foreland basin was present in north- and simple shear modes of orogenic strain and lithospheric western Argentina from Eocene time onward [Jordan and thickening, after Allmendinger [1986] and Allmendinger Alonso, 1987; Starck and Vergani, 1996; Kraemer et al., and Gubbels [1996]. Of particular importance is the lateral 1999; Coutand et al., 2001; Carrapa et al., 2005; Hongn offset of flexural isostatic compensation required in the et al., 2007; Carrapa and DeCelles, 2008], others suggest simple shear case, in contrast to the vertically juxtaposed that Paleocene‐Eocene strata in northwestern Argentina compensation required by pure shear. were accommodated by thermal subsidence following Cre- taceous rifting, with foreland basin development delayed until upper crust may be responsible for some of the major dif- late Oligocene‐early Miocene time [Jordan and Alonso, ferences noted above [Allmendinger et al., 1983, 1997; 1987; Salfity and Marquillas, 1994; Cominguez and Ramos, Allmendinger and Gubbels, 1996; McQuarrie, 2002b]. For 1995; Marquillas et al., 2005; del Papa, 2006]. The late example, changes in structural style and shortening coincide Miocene‐Quaternary history of basin evolution in north- with a southward decrease in the thickness of Paleozoic western Argentina is also a subject of debate, with some cover strata and the presence of a Cretaceous rift system authors arguing for continued eastward propagation of south of 23°S [Kley and Monaldi, 2002]. Still farther deformation and migration of the foreland basin [Carrapa south (27°S), Andean crustal shortening is dominated by et al., 2011a, 2011b] while others advocate a change to massive crystalline basement block uplifts of the Sierras localized basins associated with thick‐skinned deformation Pampeanas, where the Paleozoic cover section is largely and regionally non‐systematic strain propagation [Hain et al., absent. Allmendinger [1986] and Allmendinger and Gubbels 2011; Strecker et al., 2011]. These debates are critical for [1996] suggested that these differences in orogenic structure accurately assessing the mechanisms and magnitude of and history are manifestations of two distinct modes of shortening in the central Andes and for constraining models lithospheric shortening: simple shear in the north, and pure that link westward underthrusting of South American cra- shear in the south (Figure 1). Isacks [1988] proposed that tonic basement to arc magmatism and upper mantle pro- the central Andes experienced a temporal transition from cesses [Kay et al., 1994; Beck and Zandt, 2002; McQuarrie dominantly pure shear to simple shear during the Miocene. et al., 2005; Sobolev et al., 2006; Haschke et al., 2006; Kay The idea of pure shear mountain building has had consid- and Coira, 2009; DeCelles et al., 2009]. erable influence on subsequent tectonics research in the [6] In this paper we present new evidence from north- central Andes [see, e.g., Sobolev and Babeyko, 2005; Hindle western Argentina to support the view that orogenic short- et al., 2005; Sobolev et al., 2006] and similar models have ening and foreland basin development began no later than late been applied to other major orogenic systems in order to Paleocene time throughout the central Andes from northern explain first‐order features in the distribution of deformed Bolivia to at least as far south as 26°S. This interpretation is lithosphere [England and Houseman, 1985; Houseman and based on sedimentological observations from >14,000 m of England, 1993; Molnar et al., 1993; Ellis et al., 1995; detailed measured stratigraphic sections, 56 modal petro- Molnar and Houseman, 2004]. graphic analyses, >2,500 U‐Pb ages of detrital and igneous [4] Simple and pure shear modes of deformation should zircons, and apatite fission track dating of cobbles in synoro- be accompanied by drastically different responses in later- genic conglomerates. Our results indicate that the central ally adjacent lithosphere [Allmendinger and Gubbels, 1996]. Andean foreland basin system in northwestern Argentina Pure shear lithospheric shortening and thickening should be has migrated at least 600 km laterally at an unsteady pace compensated locally, whereas simple shear shortening and varying from ∼5 mm/yr to more than 40 mm/yr to its present thickening should produce a flexural response in the fore- location east of the orogenic belt, and that this migration land lithosphere (Figure 1). It follows that the Cenozoic was superimposed upon paleotopographically and geologi- stratigraphy of the central Andes should contain a well‐ cally complex lithosphere with pre‐existing Cretaceous rift‐

2of30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013 related structures that locally influenced sediment accom- South of latitude 23°S, the frontal thrust belt is repre- modation and composition. sented by the Santa Bárbara system, which is characterized by large uplifted blocks of Paleozoic‐Cenozoic sedimentary 2. Geological Setting rocks that are bounded by relatively steep, generally west‐ ∼ verging reverse faults [Cristallini et al., 1997; Kley and [7] Spanning the entire 7000 km long western margin of Monaldi, 2002]. Cutting across the Santa Bárbara system, the South American plate, the Andean orogenic belt is ’ ‐ parts of the Cordillera Oriental, local areas in the eastern Earth s best example of an active Cordilleran style orogenic Puna, and also present in the subsurface beneath the modern system [Coney and Evenchick, 1994; Ramos, 2009]. The foreland basin is the Salta rift, a complex branching array of central Andes in Bolivia and northern Chile and Argentina extensional basins that formed during Aptian‐Campanian are where the orogen is highest and widest and where time [Salfity and Marquillas, 1994]. Reactivation of normal shortening is greatest [James, 1971; Isacks, 1988; Kley and faults associated with the Salta rift partly controlled devel- Monaldi,1998;Beck and Zandt, 2002; McQuarrie et al., opment of the Santa Bárbara ranges and structures within 2005; Oncken et al., 2006]. Flanking the modern Andes ‐ the Cordillera Oriental [Grier et al., 1991; Cladouhos et al., on the east is a continental scale retroarc foreland basin 1994; Cristallini et al., 1997; Kley and Monaldi, 2002; system [Chase et al., 2009] that provides a rich archive of Monaldi et al., 2008]. Many previous workers have inter- surficial and geodynamic processes that have shaped the preted the lower Cenozoic deposits documented in this paper Andes. as the results of late‐stage thermal subsidence in the Salta [8] Eastward from the modern forearc region, the central rift system [e.g., Salfity and Marquillas, 1994; del Papa and Andes are divisible into four longitudinal tectonomorphic ‐ Salfity, 1999], and petroleum company reflection seismic zones, including the Cordillera Occidental, Altiplano Puna data from the Lomas de Olmedo arm of the rift indicate that plateau, Cordillera Oriental, and the frontal Subandean and the Santa Bárbara Subgroup was influenced by late‐stage Santa Bárbara ranges (Figure 2) [Allmendinger et al., 1997; thermal subsidence [Cominguez and Ramos, 1995]. East Strecker et al., 2007]. The Cordillera Occidental is the locus of the Andean topographic front lies the vast low‐elevation of most active arc magmatism in this sector of the Andes Chaco plain, which is the locus of upper Neogene to modern since early Miocene time [Kay and Coira, 2009]. A com- foreland basin sediment accumulation [Horton and DeCelles, plex of large, internally drained, late Cenozoic basins, local 1997; Aalto et al., 2003; Chase et al., 2009]. volcanic centers, and deformed bedrock outcrops occupies the Altiplano portion of the high plateau. Regional elevation in the Altiplano is ∼3800 m [Isacks, 1988; Masek et al., 3. Cenozoic Stratigraphy of Northwestern 1994]. The Puna part of the high plateau is approximately Argentina 400 m higher and more rugged than the Altiplano, and [10] Cretaceous through Cenozoic, predominantly clastic contains numerous smaller internally drained late Cenozoic strata are widely distributed from the eastern Puna to the basins separated by rugged mountain ranges composed of frontal Santa Bárbara ranges (Figures 2 and 3). These units Precambrian and Paleozoic sedimentary, igneous, and low‐ are assigned to the Salta and Payogastilla (or Orán) Groups. grade metamorphic rocks. Neogene volcanic rocks, strato- The Salta Group is divided into three formal Subgroups: the volcanoes, and calderas of the magmatic arc extend east- Pirgua, Balbuena, and Santa Bárbara. Overlying the Salta ward into the eastern part of the Puna (Figure 2). The Group is the Orán Group, which is composed of the Métan Cordillera Oriental in northern Argentina is dominated by and Jujuy Subgroups (Figure 3) [Moreno, 1970; Reyes and upper Proterozoic‐Carboniferous sedimentary rocks, and Salfity, 1973]. The Neocomian‐lower Maastrichtian Pirgua widespread exposures of Ordovician (ca. 470 Ma) and Subgroup consists of conglomerate, sandstone, siltstone and Cambrian (ca. 517 Ma) granitoid rocks (Figure 2). Within alkaline volcanic/hypabyssal rocks that recorded the opening the study area, the Cordillera Oriental is composed of Pro- of the Salta rift [Galliski and Viramonte,1988;Grier et al., terozoic and Cambrian‐Carboniferous strata north of the 1991; Salfity and Marquillas, 1994]. Thickness of the Pirgua northwest‐southeast–striking El Toro lineament, whereas Subgroup ranges up to ∼6,000 m, and is controlled by the only the Proterozoic metasedimentary and early Paleozoic boundary faults of the Salta rift [Salfity and Marquillas, 1994; igneous rocks are present to the south (Figure 2). Marquillas et al., 2005]. The rift consists of three elongated [9] Major faults in the Cordillera Oriental are generally sub‐basins arrayed about a central, structurally higher region interpreted to have relatively steep trajectories in the upper- referred to as the Salta‐Jujuy high. The Maastrichtian‐lower most crust, verging toward both the east and west and Paleocene Balbuena Subgroup comprises sandstone, shale, merging downward into a regional detachment [Cladouhos and limestone of the Lecho, Yacoraite, and Olmedo/Tunal et al., 1994; Yuan et al., 2000; Kley and Monaldi, 2002]. Formations. These strata are more widespread than the Pirgua Data bearing on the structure of the middle and lower crust Subgroup, and consist of eolian, lacustrine, and fluvial deposits. are generally lacking, however, such that the presence of Numerous workers have argued that the Balbuena Subgroup regional detachments is speculative. The Subandean ranges was deposited during an early phase of post‐rift thermal in Argentina are the southward continuation of the thin‐ subsidence [e.g., Grier et al.,1991;Salfity and Marquillas, skinned Subandean fold‐thrust belt that dominates the frontal 1994; Marquillas et al., 2005]. part of the Bolivian Andes. These ranges are composed of [11] Above the Balbuena Subgroup lies the upper Paleo- Paleozoic through Cenozoic sedimentary rocks that are cene‐Eocene Santa Bárbara Subgroup, which consists of the detached from structural ‘basement’ along a regional décol- Mealla, Maiz Gordo, and Lumbrera Formations. These units lement below a thick Silurian shale unit [Allmendinger et al., are distributed throughout the eastern Puna, Cordillera Ori- 1983; Starck and Schulz, 1996; Echavarria et al., 2003]. ental, and Subandean zone (including the Santa Bárbara

3of30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 2. Geological map of the study area in northwest Argentina and northern Chile, after Reutter et al. [1994]. Inset map (lower right) shows location of study area in the context of morphotectonic zones of the central Andes. Gray areas show the Santa Bárbara ranges (SBS). ranges). Deposition of the Santa Bárbara Subgroup took the Lumbrera Formation is divisible into a lower member place in fluvial and shallow lacustrine environments, and that forms the upper part of the Santa Bárbara Subgroup, paleosols are abundant, particularly in the Maiz Gordo and and an upper member that represents the fine‐grained distal Lumbrera Formations. Starck and Vergani [1996] noted that equivalent of the Quebrada de los Colorados Formation in

4of30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

1992], and consists of alluvial fan and fluvial deposits associated with local structural growth [Carrapa and DeCelles, 2008]. The Geste Formation rests upon Ordovi- cian rocks and is not part of the regional Paleogene stratigraphic system of the Eastern Cordillera and Santa Bárbara Ranges (Santa Bárbara Subgroup). [12] The Métan Subgroup comprises several formations that have local names. For simplicity, we use the nomen- clature from the Calchaqui Valley and Lerma Valley areas (Figure 3) for the western and eastern parts of the stratigraphic profile, respectively. In the Calchaqui Valley region, the lower unit of the Métan Subgroup is referred to as the Quebrada de los Colorados Formation, and the upper unit is named the Angastaco Formation (Figure 3) [Starck and Vergani, 1996]. In the northern part of the study area the Quebrada de los Colorados Formation is referred to as the Casa Grande Formation. Together these units form a several thousand‐meter‐thick upward coarsening succession, from mainly siltstone and sandstone in the lower part to cobble‐ boulder conglomerate in the upper part. In the Lerma Valley region, the Métan Subgroup is divided into the Rio Seco, Anta, and Jesús María Formations, which total ∼1,000 m in thickness and are collectively much finer‐grained than the Angastaco Formation. These three units are traceable into the frontal Subandean ranges [Gebhard et al., 1974; Hernández et al., 1996; Reynolds et al., 2000]. [13] The youngest units in the Cenozoic stratigraphic succession consist of the Palo Pintado, San Felipe, Guanaco, and Piquete Formations, which are generally younger than ∼9 Ma and contain abundant evidence for local tectonic activity in the form of angular and progressive unconformities [Starck and Anzótegui, 2001; Carrera and Muñoz, 2008; Carrapa et al., 2011a] and local provenance indicators [Hernández et al., 1999; Bywater‐Reyes et al.,2010;Carrapa et al., 2011a]. These units have been studied extensively by other groups [e.g., Gebhard et al.,1974;Hernández et al., 1996, 1999; Hernández and Echavarria, 2009; Reynolds et al., 2000; Starck and Anzótegui, 2001; Echavarria et al., 2003; Carrapa et al., 2011a; Hain et al., 2011] and must be taken into account in any regional analysis of the Cenozoic foreland basin system. [14] Starck and Vergani [1996] divided the Metán and Jujuy Subgroups into four unconformity‐bounded ‘megasequences’ that formed in response to progressive eastward migration of the foreland basin depositional framework (Figure 3). Megasequence I is represented by the Quebrada de los Colorados Formation and the eastward equivalent upper member of the Lumbrera Formation. Megasequence II consists of the Angastaco, Rio Seco, Anta, and Jesús María Formations, which form the bulk of the eastward tapering wedge of Cenozoic syntectonic strata exposed in the Cor- dillera Oriental and Subandean ranges. Megasequence III comprises the Palo Pintado, San Felipe, and Guanaco Forma- Figure 3. Stratigraphic chart for the eastern Puna, Cordil- tions, and Megasequence IV consists of the Piquete Formation. lera Oriental, and Subandean zones of northwestern Argen- tina, based on Starck and Vergani [1996], Reynolds et al. 4. Sedimentology [2000], and Marquillas et al. [2005]. Megasequences after Starck and Vergani [1996]. [15] This work focuses on the Santa Bárbara and Métan Subgroups, which together form a dramatically eastward the overlying Métan Subgroup. The middle to upper Eocene tapering prism of clastic syntectonic strata. Our sedimento- Geste Formation crops out in local areas of the Puna and logical data include 16 detailed measured stratigraphic Eastern Cordillera [Jordan and Alonso, 1987; Alonso, sections totaling >14 km in thickness and >1000 paleocur-

5of30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Table 1. Lithofacies (and Their Codes) Used in Logs of Measured Sections, and Interpretations in This Study, Modified After Miall [1978] and DeCelles et al. [1991] Lithofacies Code Description Process Interpretation Fsl Laminated black or gray siltstone Suspension‐settling in ponds and lakes Fcl Laminated gray claystone Suspension‐settling in ponds and lakes Fsm Massive, bioturbated, mottled (gleyed) siltstone; red, purple, Paleosols, usually calcic, histic, or vertic gray; carbonate or iron‐hydroxide nodules common Sm Massive medium‐ to fine‐grained sandstone; bioturbated Bioturbated sand, penecontemporaneous deformation Sr Fine‐ to medium‐grained sandstone with small, asymmetric, 2D Migration of small ripples under weak (∼20–40 cm/s), and 3D current ripples unidirectional flows in shallow channels St Medium‐ to very coarse‐grained sandstone with trough Migration of large 3D ripples (dunes) under moderately powerful cross‐stratification (40–100 cm/s), unidirectional flows in large channels Sp Medium‐ to very coarse‐grained sandstone with planar Migration of large 2D ripples under moderately powerful cross‐stratification (∼40–60 cm/s), unidirectional channelized flows; migration of sandy transverse bars Sh Fine‐ to medium‐grained sandstone with plane‐parallel lamination Upper plane bed conditions under unidirectional flows, either strong (>100 cm/s) or very shallow Gcm Pebble to boulder conglomerate, poorly sorted, clast‐supported, Deposition from sheetfloods and clast‐rich debris flows unstratified, poorly organized Gcmi Pebble to cobble conglomerate, moderately sorted, clast‐supported, Deposition by traction currents in unsteady fluvial flows unstratified, imbricated (long‐axis transverse to paleoflow) Gch Pebble to cobble conglomerate, well sorted, clast‐supported, Deposition from shallow traction currents in longitudinal horizontally stratified bars and gravel sheets Gchi Pebble to cobble conglomerate, well sorted, clast‐supported, Deposition from shallow traction currents in longitudinal horizontally stratified, imbricated bars and gravel sheets (long‐axis transverse to paleoflow) Gct Pebble conglomerate, well sorted, clast‐supported, Deposition by large gravelly ripples under traction flows trough cross‐stratified in relatively deep, stable fluvial channels Gmm Massive, matrix‐supported pebble to boulder conglomerate, Deposition by cohesive mud‐matrix debris flows poorly sorted, disorganized, unstratified M Micritic massive gray and yellow marl Lacustrine carbonate mud rent measurements. The measured sections are representa- current data from trough cross‐stratification (method I of tive of the numerous other sections that we observed in the DeCelles et al. [1983]) indicate paleoflow direction gener- field over six field seasons, and are augmented by sections ally toward the east‐northeast (Figures 5 and 6). studied in Bolivia [Horton et al., 2001; DeCelles and [18] The Maiz Gordo Formation is composed of pink and Horton, 2003; Horton, 2005] and sections documented by purple siltstone and coarse‐grained to conglomeratic sand- other groups in Argentina (most notably Starck and Vergani stone. The abundance of sandstone beds varies dramatically; [1996], Hernández et al. [1999], Reynolds et al. [2000, some sections of the Maiz Gordo are composed almost 2001], Echavarria et al. [2003], del Papa et al. [2010], and exclusively of sandstone, whereas others are rich in silt- Carrapa et al. [2011a, 2011b]). In the following brief sed- stone. Lithofacies and primary sedimentary structures in the imentological descriptions, standard codes are used to Maiz Gordo are almost completely overprinted by post‐ denote lithofacies as summarized in Table 1. depositional, pedogenic processes. Pedogenic nodules of carbonate and iron‐manganese oxide are abundant. Large 4.1. Mealla and Maiz Gordo Formations vertical burrows similar to Krausichnus trompitus [Hasiotis [16] Sandy lithofacies of the Mealla and/or Maiz Gordo and Bown, 1992; DeCelles and Horton, 2003] are abundant Formations overlie the upper Cretaceous Yacoraite Forma- at many localities (Figure 4b). tion (and locally the Pirgua Subgroup). At many of the localities studied these two units are difficult to consistently 4.2. Lumbrera Formation separate using lithological criteria, so we find it useful to [19] The Lumbrera Formation is composed of distinctive, consider them together. The composite thickness of the bright brick‐red siltstone with variable amounts of thin‐ Mealla and Maiz Gordo Formations ranges between ∼10 m bedded sandstone and, in some sections, thin layers of gray/ and 121 m. white marl (Figure 4c) and stromatolitic limestone. One or [17] The Mealla Formation consists of medium‐ to two zones of laminated gray and green siltstone, typically 5– coarse‐grained, pink and tan sandstone interbedded with red 10 m thick, are present in the lower part of the Lumbrera siltstone. Sandstone lithofacies are dominated by Sh, Sr, and Formation in some areas (e.g., section AL); these are St (Table 1) in beds generally less than 50 cm thick. In the referred to informally as the “Faja Verde” beds, and are Cachi and Susques regions, the Mealla Formation contains generally interpreted as perennial lacustrine deposits [del pebbly conglomerate and sandstone beds rich in milky‐ Papa et al., 2002]. Starck and Vergani [1996] divided the quartz clasts. Mealla Formation siltstones are massive (Fsm) Lumbrera into informal lower and upper members separated and contain abundant carbonate nodules (Figure 4a). These by a disconformity, and correlated the upper member with nodules are micritic, with features characteristic of pedo- the more proximal Quebrada de los Colorados Formation. genic glaebules, including sparry craze veins, mottling, and The lower member ranges between 70 m and 485 m thick, is compound nodular textures. The nodules are commonly coarser‐grained than the upper member, contains perennial present in the lower parts of massive siltstone units. Paleo- lacustrine deposits of the Faja Verde and, in some sections,

6of30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013 numerous paleosol layers. The upper member is generally del Papa, 2006]. Paleosols in the Lumbrera Formation are >100 m thick, and merges gradationally upward with dominated by nodular Calcisols [Mack et al., 1993], but coarser‐grained lithofacies more typical of the Quebrada Vertisols, Gleysols, and nodular Histosols are also present de los Colorados Formation. The upper member also con- (see section 4.3). tains ephemeral lacustrine deposits [del Papa et al., 2002; 4.3. Zone of Intense Pedogenesis [20] A distinctive zone of extremely mature, multistory paleosols is present at various stratigraphic levels in the Maiz Gordo and Lumbrera Formations. The interval, which we refer to informally as the “supersol zone,” is one of the most striking features in the Cenozoic stratigraphy of northwestern Argentina (Figure 7a). The supersol zone is typically 50–100 m thick, and grades upward and downward into fluvial and lacustrine lithofacies that either lack paleosols or contain only less mature paleosols intercalated with fluvial channel deposits. Paleosol types in the supersol zone include Calcisols, Gleysols, Histosols, and Vertisols; Cal- cisols and Histosols are the most abundant (Figures 4a and 7b–7d). The zone of Histosols is present in nearly every section in which we documented the supersol zone. It is characterized by generally gray or purple colors with numerous vertically elongated nodules of rusty‐colored iron‐ manganese oxide (Figure 7c). Mottling (gleying) is ubiqui- tous. Paleosols in the supersol zone are stacked on top of each other in an unbroken succession, regardless of original grain‐size; original sedimentary structures are completely obliterated throughout the supersol zone. [21] In some places in the eastern Cordillera Oriental, the supersol zone is absent and the contact between Eocene Lumbrera Formation and lower Miocene strata is an erosional disconformity. In the Subandean zone and Santa Bárbara ranges the supersol is either not present or is formed on top of pre‐Cenozoic rocks (e.g., section CV) [Echavarria et al., 2003; Hernández and Echavarria, 2009]. [22] The stratigraphic level of the supersol/disconformity generally climbs eastward. In the southern transect, its level ascends from just a few meters above the Pirgua Subgroup in the Pucara section (section PU), to the Maiz Gordo and lower Lumbrera Formations in the Monte Nieva, Tin Tin, and Obelisco sections (MN, 2TT, OB), to the upper Lumbrera Formation in the Alemanía (AL) section (Figure 5). The supersol is not as obviously developed at locations east of Alemanía; however, in the Pampa Grande (PG) section, numerous moderately developed paleosol horizons in the upper Lumbrera Formation could represent the supersol. Although del Papa et al. [2010] did not observe the supersol zone in their Simbolar section, the stratigraphy they depict is similar to, but thicker than, what we documented at Alemanía and Pampa Grande (Figure 5). These authors also reported aU‐Pb zircon age of ∼40 Ma from multigrain fractions

Figure 4. (a) Nodular Calcisol in the Mealla Formation. (b) Krausichnus trompitus trace fossils, attributed to colo- nial insects such as termites [see DeCelles and Horton, 2003]. Definitive aspects of the trace include the central vertical shaft, from which branching galleries spread out- ward. (c) Laminated marly siltstone in the Lumbrera For- mation in the Tres Cruces section (TC). (d) Interbedded fluvial channel deposits (pale pink) and massive loessite (darker red) in the Monte Nieva (MN) section. Thickness of section shown is ∼60 m.

7of30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 5. Measured stratigraphic sections of the Paleocene‐Miocene strata in the southern part of the study area.

8of30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 6. Measured stratigraphic sections of the Paleocene‐Miocene strata in the northern part of the study area. Section CZ is from D. Gingrich (unpublished data, 2010). separated from a tuffaceous layer in the upper Lumbrera younger than the ca. 40 Ma tuff or it resides directly below Formation. Comparing the Simbolar section of del Papa et the tuff in the upper Lumbrera Formation. If the supersol is al. [2010] with our nearby sections from Pampa Grande absent at Simbolar, then the contact between the basal (PG) and Alemanía (AL) (Figure 5) suggests that if the Neogene and the Lumbrera Formation is a major discon- supersol zone is present in the Simbolar area, it is either formity, separating rocks that are as old as ∼20 Ma above

9of30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013 from rocks that are approximately 40 Ma below. Farther east [23] In the northern transect (Figure 6), the supersol zone at the Rio González section [Reynolds et al., 2000] the steps up section eastward from the Maiz Gordo Formation in Neogene rests disconformably upon the Lumbrera Formation the Susques section (SQ) to the upper Lumbrera Formation and no supersol has been documented [Hernández et al., in the Tres Cruces section (TC). In the Cianzo syncline 1999]. section (CZ), the supersol zone is located in the Maiz Gordo and upper part of the lower Lumbrera Formation. As in the southern transect, the supersol zone is either not as thickly developed or is accompanied by a major erosional disconformity in sections in the Subandean zone (section CV, Figure 6). In the Subandean zone of northernmost Argen- tina, Reynolds et al. [2001] interpreted the Tranquitas For- mation as a zone of possible Paleogene or earliest Neogene stratigraphic condensation, which is capped by a significant disconformity. [24] Overall, progressively younger strata from west to east overlie the supersol/disconformity [Starck and Vergani, 1996; Hernández et al., 1999]. In the west the ca. 40 Ma Quebrada de los Colorados Formation sits above the supersol, whereas in the east the ca. 20 Ma Rio Seco Formation rests on top of the supersol or the disconformity. In addition, the time‐ span of the disconformity increases eastward [Hernández et al., 1999]. Together, the supersol and disconformity may be taken to represent different manifestations of similar conditions of extremely slow or zero net sediment accumulation. [25] A remarkably similar zone of intense pedogenesis was documented by Horton et al. [2001] and DeCelles and Horton [2003] in Eocene strata of the Bolivian Cordillera Oriental. Uba et al. [2006] extended the Bolivian supersol zone into the upper Oligocene‐lower Miocene section of the western Subandean zone in Bolivia. 4.4. Quebrada de los Colorados Formation (Casa Grande Formation) [26] The Quebrada de los Colorados Formation (Casa Grande Formation in the northern part of the study area) consists of an upward coarsening succession of sandstone and conglomeratic sandstone, with interbedded brick‐red silstone beds (Figure 4d). This unit is roughly correlative with the upper member of the Lumbrera Formation [Starck and Vergani, 1996], and where the two are present and distinguishable, the Quebrada de los Colorados Formation is much coarser‐grained than the Lumbrera Formation. Coarse‐ grained units are broadly lenticular with erosional basal surfaces and crude upward fining grain‐size trends in ∼2– 5m‐thick compound depositional units. Trough cross‐ stratification (St) is most common in the lower parts of these upward fining sequences, giving way to ripples (Sr) and plane beds (Sh) in the upper parts. Imbricated (Gcmi), horizontally stratified (Gch) and trough cross‐stratified (Gct) conglomerates are common in the lower parts of these units as well. In the Monte Nieva section, lenticular sandstone and

Figure 7. (a) Lower part of measured section 2TT, showing Mealla and Maiz Gordo Formations in the foreground and middle distance. Dark gray band is the Histosol interval within the supersol zone. (b) Thin bed of fluvial sandstone riddled with Krausichnus trompitus burrows, resting upon a gleyed nodular Calcisol with large root traces; section CZ. Hammer for scale. (c) Iron‐oxide nodules in blue‐gray Histosol in the Susques section (SQ). (d) Vertisol in Lum- brera Formation at the Alemanía section (AL).

10 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

data from trough cross‐stratification and imbricated clasts indicate eastward and northeastward paleoflow (Figures 5 and 6). [27] We interpret the Quebrada de los Colorados Forma- tion as the deposits of a sandy to gravelly braided fluvial system. The upward coarsening and thickening intervals of stacked channel deposits that are common in this unit could represent distributary fluvial behavior [Hartley et al., 2010], such as seen on fluvial megafans in the modern Andean foreland basin [Horton and DeCelles, 2001]. 4.5. Angastaco Formation [28] The transition from the Quebrada de los Colorados Formation to the overlying Angastaco Formation is gra- dational [see also Carrapa et al., 2011a]. The contact is generally placed at the base of a prominent interval of well‐sorted medium‐grained sandstone containing large‐ scale cross‐stratification typical of eolian dune slipface deposits (Figure 8a) [Starck and Vergani, 1996; Carrapa et al., 2011a]. In the Monte Nieva section the eolian interval is approximately 800 m thick, and contains distinctive, orange‐colored, homogeneously structureless fine‐ to medium‐grained sandstone units that we interpret to be coarse‐grained loessite [e.g., Soreghan et al., 2008]. Indi- vidual units of the coarse‐grained loessite are up to ∼15 m thick, and are commonly interbedded with units of coarse‐ grained to pebbly trough cross‐stratified sandstone (Figure 4d). The loessite facies are gradually replaced up‐section by cross‐stratified dune facies (Figure 8a) that indicate eastward paleowind directions (Figure 5, section MN), suggesting that the core of the erg migrated eastward over the top of a fringing loess belt [e.g., Crouvi et al., 2010]. The eolian interval is much thinner (less than 100 m) in the Angastaco area. [29] The upper 2,000 m of the Angastaco Formation are dominated by pebble to cobble conglomerate and very coarse‐grained to pebbly sandstone beds (Figure 8b). Bed- ding is highly lenticular, with erosional basal contacts and crude upward fining sequences. The predominant lithofacies are well‐organized conglomerate (Gcm, Gct, Gcmi), and horizontally stratified (Sh) and trough cross‐stratified (St) sandstone (Table 1). The assemblage of lithofacies in the upper Angastaco Formation is typical of coarse‐grained low‐ sinuosity (braided) fluvial systems. Although we did not observe any clear‐cut evidence of sediment‐gravity flow deposits, it is plausible that the coarser‐grained portions of the Figure 8. (a) Eolian large‐scale cross‐stratification pro- Angastaco Formation were deposited in medial to distal alluvial fan environments [Carrapa et al., 2011a]. Imbricated duced by dune slipface deposition in the Angastaco Forma- ‐ tion in section MN. Height of cliff is ∼25 m. (b) Well‐ conglomerates (Gcmi and Gchi; clast long axes perpendicular to paleoflow direction) indicate generally eastward paleoflow organized lithofacies Sh and Gch in lower Angastaco For- – mation at section MN. (c) Agujas Conglomerate in section in the azimuthal range 000° 140° (Figures 5 and 6). QT, showing changes in dip of bedding from overturned [30] The Angastaco Formation tapers rapidly eastward dipping west (left) to upright dipping east (right). Person from its type area in the Calchaqui valley to the Lerma and for scale highlighted in ellipse at bottom center. Los Conchas valleys (compare sections MN and AL, Figure 5), where roughly equivalent strata are represented by the Rio Seco, Anta, and Jesús María Formations. The Rio Seco For- conglomerate bodies are stacked in 8–15 m thick packages mation consists of a few tens of meters of medium‐grained, that coarsen and thicken upward, and are capped by sharp, cross‐stratified sandstone, resting unconformably upon the flat surfaces marking an abrupt transition to siltstone. The Lumbrera Formation. The Rio Seco Formation has also been fine‐grained intervals between coarse‐grained units are interpreted as eolian and fluvial deposits [Starck and Vergani, typically massive siltstone and silty sandstone, usually red, 1996]. In the Alemanía section (AL, Figure 5) the Rio Seco with little internal sedimentary structure (Fsm). Paleocurrent consists of sandy trough cross‐stratified fluvial facies. The

11 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Anta Formation is ∼265–720 m thick in the Alemanía area 2003], radio‐isotopic ages from tuffaceous layers [Reynolds and the Santa Bárbara ranges [Reynolds et al., 2000], and et al., 2000], and recently acquired U‐Pb ages from tuffa- consists of red fine‐grained sandstone and mudrocks, with ceous rocks and detrital samples [DeCelles et al., 2007; occasional thin carbonate layers that have been interpreted Carrapa et al., 2008, 2011a, 2011b; Bywater‐Reyes et al., as marginal marine deposits [Galli et al., 1996]. The Jesús 2010; Hain et al., 2011] (see also new ages reported in María Formation consists of ∼1000–1200 m of fluvial this study; Figures 9 and 10). The ages of the Mealla and sandstone and mudstone. Additional information about the Maiz Gordo Formations are based on paleontology and are Rio Seco, Anta, and Jesús María Formations may be found well established as early–mid‐Paleocene and late Paleocene‐ in the works by Gebhard et al. [1974], Galli et al. [1996], early Eocene, respectively [see del Papa and Salfity, 1999, and Reynolds et al. [2000]. and references therein]. The Lumbrera Formation is also dated mainly by paleontology as middle to late Eocene 4.6. Agujas Conglomerate, Quebrada del Toro Section [del Papa and Salfity, 1999; Hongn et al., 2007]. Our [31] We measured and sampled an approximately 1200 m observations suggest that most of the Eocene is represented thick section of the Agujas Conglomerate [Marrett and by the supersol. In the Tres Cruces section (section TC, Strecker, 2000] (section QT), which crops out along Queb- Figure 6), a paleosol carbonate nodule from the 330 m level rada Cerro Bayo, a tributary arroyo to the Quebrada del Toro yielded a U‐Pb mean age of 47 ± 7 Ma (MSWD = 7.5, 95% (Figure 5). This unit is age‐equivalent to the upper part of the confidence; M. N. Ducea, unpublished data, 2011). This Angastaco Formation and the lowermost part of the Palo sample was collected from just a few meters below the top of Pintado Formation (Figure 3). The predominant lithofacies the supersol zone, and is interpreted as the approximate age include pebble to cobble conglomerate (Gcm) and massive, of formation of the paleosol carbonate. A ca. 40 Ma U‐Pb red, coarse‐grained sandstone (Sm) (Table 1). Several thin age from zircon in a tuffaceous layer was reported by beds of light‐colored tuffaceous sandstone and tuff were del Papa et al. [2010] in the upper Lumbrera Formation at observed and sampled for geochronological analysis. The Simbolar, and we obtained an age of ∼40.6 ± 0.3 Ma from a section is folded into a north‐trending syncline, and our single detrital zircon in a sample from the Quebrada de los measured section is located in the western limb of the syn- Colorados Formation (approximately equivalent to the upper cline. The western boundary of the section is marked by the member of the Lumbrera Formation) at the 755 m level of Solá reverse fault, which juxtaposes phyllite and quartzite of section MN, 230 m above the top of the supersol zone the Proterozoic‐lower Cambrian Puncoviscana Formation (Figures 5 and 9). An additional sample from the lower with the Agujas Conglomerate [Marrett and Strecker, 2000]. part of the Quebrada de los Colorados Formation in the Bedding in the western limb of the syncline is overturned and Angastaco area yielded a cluster of detrital zircon U‐Pb ages dipping westward, but becomes upright and decreases in with mean age of ∼37.6 ± 2.0 Ma [Carrapa et al., 2011a]. magnitude from ∼70°E to 25°E upward through the measured These ages are consistent with middle Eocene paleontolog- section (Figure 8c). Faulting obscures the nature of the basal ical ages from the lower part of the Quebrada de los Color- contact of the Agujas Conglomerate, but its stratigraphic ados Formation in the la Poma area [Hongn et al., 2007]. context can be determined by tracing the interval along strike Another sample from a cobble in the Quebrada de los Col- toward the south, where it rests directly above strata that orados Formation in section MN (1333 m level) produced an correlate with the Quebrada de los Colorados Formation in apatite fission track pooled age of 28.7 ± 1.9 Ma (Table 2). the Tin Tin and Monte Nieva areas. We therefore infer that Because other cobbles sampled farther upsection yielded this interval is roughly equivalent to the upper part of the similar (within errors) apatite fission track pooled ages, we Angastaco Formation; this interpretation is borne out by U‐Pb interpret this age as a true indication of the age of exhuma- zircon ages from tuffaceous layers (see section 5). tion in the source terrane and not a result of partial annealing [32] We tentatively suggest that the progressive up‐section during burial. Therefore the depositional age of this sample decrease in dip magnitude reflects syndepositional structural must be younger than ∼28.7 Ma. growth in response to slip on the Solá fault. This interpre- [34] Samples of sandstone from the Geste Formation in tation is consistent with findings of Mazzuoli et al. [2008], the eastern Puna (section SP, Figure 5) yielded minimum who reported growth structures in the Agujas Conglomerate U‐Pb zircon age clusters between ∼38 Ma and 34 Ma 10–15 km north of our measured section. The coarse grain‐ [DeCelles et al., 2007], and fission track and U‐Pb double size and association of lithofacies in the Agujas Conglom- dates from detrital apatites in the Geste Formation support a erate suggest deposition in an alluvial fan system, and the late Eocene depositional age [Carrapa et al., 2008] that presence of a progressive unconformity and clast‐compositions is consistent with vertebrate paleontology from the same dominated by the Puncoviscana Formation indicate close section [Pascual, 1983; Alonso, 1992]. proximity to the topographically rising source area in the [35] Sandstone samples from several sections produced hanging wall of the Solá fault. early Miocene minimum detrital zircon U‐Pb age clusters, providing useful constraints on depositional ages of the 5. Chronostratigraphy Angastaco Formation and its lateral equivalents (Figure 9). Additional detrital zircon ages reported by [Carrapa et al., [33] The ages of Cenozoic stratigraphic units in north- 2011a] provide constraints on ages of upper Miocene units western Argentina are known from a locally rich fossil in the region. Detrital zircons separated from sandstones in assemblage (including both vertebrate fossils and palynol- the Angastaco and Rio Seco Formations yielded numerous ogy) [Quattrocchio et al., 1997; del Papa and Salfity, 1999; Miocene U‐Pb ages, supporting a depositional age range Hongn et al., 2007; del Papa et al., 2010], paleomagnetic of ∼19–9 Ma for the Angastaco [Carrapa et al., 2011a], and stratigraphy [Reynolds et al., 2000, 2001; Echavarria et al., a <19 Ma age for the Rio Seco Formation. The detrital

12 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 9. U‐Pb detrital zircon age probability plots and mean youngest‐age plots for samples from the Cenozoic deposits. Mean age plots incorporate both random and systematic errors. Ages shown on mean age plots are not included in the probability plots. See Table S2 for data.

13 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

and by magnetostratigraphy [Kraemer et al., 1999; Reynolds et al., 2000, 2001; Coutand et al., 2001; Hain et al., 2011; Carrapa et al., 2011a, 2011b]. Three tuffaceous beds were sampled in the Agujas Conglomerate (section QT, Figure 5), and yielded mean U‐Pb zircon ages of 10.49 ± 0.56 Ma, 9.1 ± 1.6 Ma, and 8.85 ± 0.35 Ma (Figure 10). Evidence for structural growth in this section (see section 4.6) provides a basis for locating the orogenic strain front directly west during late Miocene time.

6. Provenance Data: Sedimentary Petrology and Apatite Fission Track Data

[37] Fifty‐six standard petrographic thin sections from the Monte Nieva and Tres Cruces sections were stained for Ca‐ and K‐feldspars and point‐counted (450 counts per slide) according to the Gazzi‐Dickinson method [Ingersoll et al., 1984] in order to assess bedrock provenance of the Ceno- zoic deposits of the study area. Petrographic parameters are listed in Table 3, and recalculated modal data are listed in Table 4. Standard ternary diagrams are shown in Figure 11. [38] These sandstones are quartzolithic and feldspatholithic arenites, containing abundant monocrystalline quartz (Qm) grains, with lesser amounts of polycrystalline quartz (Qp), tectonized polycrystalline quartz (Qpt), and quartzose sedimentary lithic fragments (Qss). Plagioclase is slightly more abundant than K‐feldspar. K‐feldspar types include orthoclase (dominant), microcline, and perthite. Sedimentary and low‐grade metasedimentary lithic fragments comprise limestone, shale, chert, quartzose sandstone (Qss), siltstone, phyllite, and fine‐grained quartz‐mica schist. Volcanic grains include lathwork (Lvl), microlitic (Lvm), vitric (Lvv), felsic (Lvf), and rare mafic (Lvma) varieties. Trace amounts of micas, tourmaline, cordierite, epidote and zoisite, zircon, magnetite, and Fe‐oxide alterite fragments are present. [39] Modal sandstone compositions are regionally consistent, with monomineralic fractions dominated by quartz, and lithic compositions dominated by low‐grade metasedimentary grains (Figure 11). Average values of key ternary modes are given in Table 4. These data are consistent with deposition in a basin dominated by upper crustal source terranes, and indicate hybrid Recycled Orogenic and Con- tinental Block provenance (Figure 11) [Dickinson, 1983], with some influence from magmatic arc sources. In both sections the ratio Lt/QmFLt increases upward, and Qm/ QmFLt decreases upward. Increased influence of magmatic arc provenance is evident in both sections as the proportion of volcanic lithic grains increases upward. Increased arc influence is also indicated by influx of detrital zircons with ‐ ages that are roughly equivalent to depositional age (see Figure 10. Mean U Pb ages for three tuffs collected in sec- section 7). The major sandstone compositional difference tion QT. Mean ages include random and systematic errors; “ ” between northern (Tres Cruces) and southern (Monte Nieva) n represents number of grains used in each calculation. localities is in the amount of feldspar present. Sandstones in the Monte Nieva locality contain approximately twice as zircon ages demonstrate that eolian lithofacies recognized much feldspar as those from Tres Cruces (Table 4). The widely from the Puna to the Cordillera Oriental [Starck and increase in feldspar toward the south includes both plagio- ‐ Vergani, 1996] were deposited between ∼22 and 18 Ma clase and K feldspar. [Carrapa et al., 2011a; this study]. [40] Conglomerate clast counts (at least 100 per station, [36] Upper Miocene strata in the Puna, Cordillera Oriental, counted on a regular grid spacing) in the Quebrada de los and Santa Bárbara ranges are relatively well‐dated by U‐Pb Colorados and Angastaco Formations and the Agujas Con- ‐ zircon and fission track methods on volcanogenic deposits, glomerate are dominated by sedimentary metasedimentary

14 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Table 2. Apatite Fission Track Dataa Cobble Irridiation Number N Rho‐S(e5) NS Rho‐I(e5) NI U (ppm) P(c)2 Rho‐D(e6) ND Age (Ma) Error MN2936 UW09‐03‐42 12 2.785 166 19.509 1163 25.25 24.95 1.0081 4018 26.5 2.3 MN3(1835 m) UW10‐05‐14 18 4.415 203 32.711 1504 33.89 25.11 1.2024 3146 29.7 2.7 MN1333 UW09‐03‐35 25 4.255 361 29.211 2478 35.45 24.22 1.0681 4018 28.7 1.9 aAge is pooled when c2 > 5% and central when c2 < 5%. Error is one s, calculated using the zeta calibration method [Hurford and Green, 1983] and the following Zeta. For MN2936 and MN1333, 369.69 ± 6.82; samples analyzed using a Leica DMRM microscope (UW) at 1250 magnification. For MN3, 366.44 ± 17.31; sample analyzed using Olympus microscope (UA) at 1600 magnification. Analyses conducted using a drawing tube located above a digitizing tablet and kinetic computer‐controlled stage driven by the FTStage program [Dumitru, 1993]. Samples were irradiated at Oregon State Uni- versity. Samples were etched in 5.5 molar nitric acid at 21°C for 20 seconds. Following irradiation, the mica external detectors were etched with 21°C in 40% hydrofluoric acid for 45 minutes. N is the number of individual crystals dated. Rho‐S and Rho‐I are the spontaneous and induced track density measured, respectively (tracks/cm2). NS and NI are the number of spontaneous and induced tracks counted, respectively. The chi‐square probability is c2 (%) [Galbraith and Green, 1990; Green, 1981]. Values greater than 5% are considered to pass this test and represent a single population of ages. Rho‐Dis the induced track density in external detector adjacent to CN5 dosimetry glass (tracks/cm2). ND is the number of tracks counted in determining Rho‐D. Dpar is fission track etch pit measurements; SD is the related standard deviation. and volcanic clast types, mainly quartzite and andesite‐ more precise for older ages, we rely on 206Pb/238U ages up dacite. In the Mealla and Maiz Gordo Formations milky to 1000 Ma and 206Pb/207Pb ages if the 206Pb/238U ages are quartz pebbles are common. Granitoid and granitic gneiss >1000 Ma [Gehrels et al., 2008]. These analyses are plotted clasts are also present in some sections in the Quebrada de on relative age‐probability diagrams (Figures 9 and 12), los Colorados and Angastaco Formations (e.g., section MN). which represent a sum of the probability distributions of all [41] Apatite fission track data were collected from three analyses from a sample, normalized such that the areas granitic clasts from the MN section. Sample preparation beneath the probability curves are equal for all samples. Age followed standard procedures and analyses were performed peaks on these diagrams are considered robust if defined by using the zeta age calibration method [Hurford and Green, several analyses. 1983]. More information can be found in Table 2. The three conglomerate clasts produced pooled ages of 28.7 ± ‐ 1.9 Ma, 29.7 ± 2.7 Ma, and 26.5 ± 2.3 Ma (Table 2). Clast Table 3. Modal Petrographic Point Counting Parameters sample MN1333, with a pooled AFT age of 28.7 ± 1.9 Ma, Symbol Description also produced a U‐Pb zircon mean age of 486.7 ± 6.1 Ma 1 Qm monocrystalline quartz (MSWD = 1.2) (Table S1 in the auxiliary material). This Qp polycrystalline quartz age suggests that the clast (and the many others like it in the Qpt foliated polycrystalline quartz MN section) was derived from local Ordovician granitoid Qms monocrystalline quartz in sandstone rocks such as those exposed in the nearby Nevado de Cachi. or quartzite lithic grain C chert A sample from 6150 m elevation in the Nevado de Cachi S siltstone produced an AFT pooled age of 28.2 ± 3.6 Ma (B. Carrapa, Qt total quartzose grains unpublished data, 2011), consistent with rapid exhumation (Qm + Qp + Qpt + Qms + C + S) at that time near the orogenic front. K potassium feldspar (including perthite, myrmekite, microcline) P plagioclase feldspar 7. Detrital Zircon Geochronology (including Na and Ca varieties) ‐ ‐ ‐ F total feldspar grains (K + P) [42] Twenty two samples of medium to coarse grained Lvma mafic volcanic grains sandstone were processed by standard methods for dense (epidote ± pyx ± plag) minerals, and detrital zircon grains were separated from these Lvf felsic volcanic grains concentrates. Zircons were mounted in epoxy, polished and (sericite + qtz ± feldspar) ‐ Lvv vitric volcanic grains analyzed for U Pb ages by laser ablation multicollector Lvx microlitic volcanic grains inductively coupled plasma mass spectrometry (LA‐MC‐ Lvl lathwork volcanic grains ICPMS) at the University of Arizona LaserChron Center. Lv total volcanic lithic grains Details of the method are described by Gehrels et al. [2008]. (Lvm + Lvf + Lvv + Lvx + Lvl) A total of 1,925 grains from the Cenozoic samples produced Lsh Mudstone Lph Phyllite data of sufficient precision for geochronological interpreta- Lsm schist (mica schist) tion. We also obtained 524 U‐Pb zircon ages from six sam- Lc carbonate lithic grains ples of key Paleozoic and Mesozoic rock units in the Puna Lm total metamorphic lithic grains and Cordillera Oriental, in order to provide a basis for (Lph + Lsm + Qpt) Ls total sedimentary lithic grains interpreting the provenance of the zircons in the Cenozoic (Lsh + Lc + C + S + Qms) samples. Analyses that yielded isotopic data of acceptable Lt total lithic grains discordance, in‐run fractionation, and precision are shown (Ls + Lv + Lm + Qp) in Tables S1 and S2. Because 206Pb/238U ages are generally L total nonquartzose lithic grains more precise for younger ages whereas 206Pb/207Pb ages are (Lv + Ls + Lph + Lsm + Lc) Accessory minerals Epidote/Zoisite, Chlorite, Muscovite, Biotite, Zircon, Sphene, Clinopyroxene, Orthopyroxene, 1Auxiliary materials are available in the HTML. doi:10.1029/ Monazite, Magnetite 2011TC002948.

15 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Table 4. Recalculated Modal Petrographic Data From Sections MN and 1TC Sample Qm% F% Lt% Qt% F% L% Qm% P% K% Lmet% LV% Lsed% MN1 59.8 19.1 21.1 74.4 18.1 7.5 75.8 17.9 6.3 48.4 4.8 46.8 MN13 56.8 24.6 18.6 68.3 23.9 7.8 69.8 9.3 20.9 33.3 2.1 64.6 MN29 57.6 27.5 15.0 67.4 25.9 6.7 67.7 29.7 2.6 67.4 2.3 30.2 MN93 64.7 22.3 12.9 72.3 21.8 5.9 74.4 11.5 14.1 36.7 0.0 63.3 MN176 53.3 31.1 15.6 64.6 29.9 5.5 63.2 31.8 5.0 52.6 0.0 47.4 MN318 75.7 9.1 15.1 86.1 8.8 5.2 89.2 6.3 4.5 40.5 9.5 50.0 MN491 54.4 29.5 16.1 65.6 28.5 5.9 64.9 22.4 12.7 38.5 7.7 53.8 MN595 56.3 19.4 24.3 73.1 18.4 8.5 74.4 6.8 18.8 37.6 7.1 55.3 MN610 62.9 23.0 14.2 70.8 22.6 6.6 73.2 17.8 8.9 32.5 15.0 52.5 MN659 55.9 26.2 17.9 64.6 25.8 9.6 68.0 16.8 15.2 37.3 19.6 43.1 MN723 59.1 34.2 6.7 62.9 34.0 3.1 63.4 23.6 13.0 26.3 36.8 36.8 MN758 74.8 15.9 9.3 80.5 15.7 3.8 82.5 14.7 2.9 66.7 22.2 11.1 MN765 49.8 34.0 16.2 58.0 33.0 9.1 59.4 40.3 0.3 46.0 26.0 28.0 MN801 41.3 34.5 24.2 54.5 33.5 12.0 54.5 24.1 21.4 50.0 22.9 27.1 MN893 59.9 23.0 17.2 67.0 22.2 10.8 72.3 24.9 2.8 64.7 23.5 11.8 MN1026 44.2 27.0 28.8 56.4 25.8 17.8 62.1 32.2 5.7 64.6 5.1 30.3 MN1123 47.0 28.0 25.0 56.5 26.9 16.6 62.7 17.1 20.2 54.8 15.5 29.8 MN1262 75.5 20.7 3.8 78.3 20.6 1.1 78.5 9.3 12.3 28.6 14.3 57.1 MN1371 57.8 29.5 12.7 63.9 28.5 7.6 66.2 20.2 13.6 52.3 11.4 36.4 MN1405 51.9 30.8 17.2 58.9 29.8 11.4 62.7 33.7 3.6 74.1 6.9 19.0 MN1663 66.4 24.8 8.8 70.8 24.6 4.6 72.8 16.9 10.4 56.5 0.0 43.5 MN1665 44.8 44.8 10.3 48.2 44.1 7.7 50.0 31.8 18.2 32.4 54.1 13.5 MN1772 71.6 18.5 9.9 76.4 18.3 5.3 79.5 20.5 0.0 54.2 33.3 12.5 MN1986 46.5 31.4 22.0 56.0 30.3 13.7 59.7 31.7 8.6 55.7 28.6 15.7 MN2094 46.1 25.3 28.6 60.1 24.1 15.8 64.6 16.9 18.5 66.7 11.9 21.4 MN2179 44.3 30.1 25.6 57.1 28.8 14.2 59.5 10.6 29.9 71.1 9.2 19.7 MN2226 50.0 29.6 20.4 60.7 28.5 10.8 62.8 13.0 24.2 60.3 24.1 15.5 MN2290 55.6 26.5 17.9 63.9 25.4 10.8 67.8 18.3 13.9 63.0 13.0 24.1 MN2552 42.6 24.0 33.4 55.4 23.0 21.7 64.0 15.2 20.9 57.3 18.2 24.5 MN2702 43.2 27.5 29.3 51.3 26.6 22.1 61.1 16.8 22.2 65.1 18.3 16.5 MN2886 48.2 26.9 24.9 57.8 26.2 16.0 64.2 10.2 25.6 76.6 15.6 7.8 MN3492 46.1 29.0 24.9 53.9 28.3 17.8 61.4 13.5 25.1 72.1 9.3 18.6 MN3559 41.1 26.6 32.4 50.6 25.8 23.6 60.7 25.1 14.2 61.2 17.4 21.5 MN3908 42.9 27.4 29.7 56.7 26.1 17.1 61.0 26.5 12.5 64.9 13.8 21.3 MN4198 48.0 29.5 22.5 57.7 29.0 13.4 61.9 16.4 21.7 52.9 25.0 22.1 MN4340 39.4 25.9 34.6 47.1 25.6 27.4 60.4 23.5 16.1 66.7 24.6 8.7 Averages 53.8 26.6 19.6 63.0 25.8 11.2 66.6 19.9 13.5 53.6 15.8 30.6

1TC104 64.6 7.1 28.3 64.6 7.1 28.3 90.1 9.9 0.0 0.0 0.0 100.0 1TC194 74.8 16.9 8.2 81.1 16.9 2.0 81.6 8.0 10.4 22.2 44.4 33.3 1TC378 87.5 7.1 5.3 90.7 7.1 2.2 92.5 6.4 1.2 12.5 37.5 50.0 1TC380 89.7 7.4 2.9 90.8 7.4 1.8 92.4 5.5 2.1 10.0 70.0 20.0 1TC416 93.3 5.4 1.3 93.9 5.4 0.7 94.5 2.7 2.7 0.0 50.0 50.0 1TC456 70.7 11.1 18.2 77.1 10.8 12.1 86.4 12.2 1.4 29.7 29.7 40.6 1TC462 79.5 8.0 12.5 87.2 7.8 5.0 90.8 4.8 4.3 65.4 19.2 15.4 1TC468 81.7 8.5 9.8 87.6 8.2 4.1 90.6 6.4 3.0 65.2 17.4 17.4 1TC502 72.0 13.2 14.8 78.2 13.1 8.7 84.5 15.0 0.5 26.0 12.0 62.0 1TC530 75.9 15.3 8.8 79.9 15.2 4.9 83.2 15.8 1.0 75.0 4.2 20.8 1TC568 70.3 15.4 14.3 75.9 15.1 9.0 82.0 16.7 1.3 56.8 22.7 20.5 1TC651 62.8 16.7 20.5 67.9 16.2 15.9 79.0 18.4 2.6 44.2 5.8 50.0 1TC675 56.0 18.9 25.2 63.2 18.6 18.2 74.8 17.7 7.5 36.5 27.1 36.5 1TC695 59.4 7.1 33.5 66.1 7.0 26.9 89.3 9.7 1.0 13.4 17.9 68.7 1YC725 54.4 15.8 29.8 62.8 15.5 21.7 77.5 15.5 7.0 27.0 38.5 34.4 1TC852 46.4 17.3 36.3 54.6 16.8 28.6 72.9 24.3 2.8 38.7 44.4 16.9 1TC948 52.6 18.5 29.0 59.5 18.1 22.4 74.0 11.6 14.4 41.1 25.9 33.0 1TC1069 46.5 22.3 31.2 52.7 22.1 25.2 67.5 31.8 0.7 28.7 55.7 15.6 1TC1260 49.4 14.6 36.0 57.9 14.1 28.0 77.2 15.4 7.4 63.1 15.6 21.3 1TC1295 48.4 13.7 37.8 57.3 13.2 29.5 77.9 18.5 3.6 50.3 28.2 21.5 Averages 66.8 13.0 20.2 72.4 12.8 14.8 82.9 13.3 3.7 35.3 28.3 36.4

[43] Almost all of the Cenozoic samples exhibit three age Scattered mid‐Cretaceous, Triassic, Carboniferous, Paleo- clusters at ∼500 Ma, 555–994 Ma, and ∼1050 Ma (Figure 9). proterozoic, and Archean ages are also present. In detail, the ca. 500 Ma peak is divided into two sub- [44] Six samples yielded small populations of Oligocene populations with ages of 470–491 Ma (latest Cambrian‐Early and Miocene zircons, and at least five of these are of Ordovician) and 522–544 Ma (latest Proterozoic‐Early probable depositional age (see section 5). A seventh sample, Cambrian). The ∼1050 Ma population ranges between MNDZ3‐755, yielded a single Cenozoic grain with an age 1024 Ma and 1096 Ma, with a few outliers in the 1124– of 40.6 ± 0.3 Ma, which is also probably close to the 1149 Ma range. The late Proterozoic (555–994 Ma) popu- depositional age of the sample. lation has a concentration of ages in the 620–675 Ma range.

16 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 11. (top) Standard ternary diagrams illustrating modal framework grain compositions of sandstones from the Tres Cruces and Monte Nieva sections. Standard provenance fields of Dickinson [1983] labeled as follows: CB, Continental Block, RO, Recycled Orogen, MA, Magmatic Arc. (bottom) Vertical trends in total lithic grains (Lt) normalized to monocrystalline quartz (Qm) and feldspar (F). See Table 3 for definitions of parameters and Table 4 for recalculated data.

[45] From a regional standpoint, detrital zircons from the area (1TC, SQ, and CV) are more complex, with many grains sections in the southern part of the study area (sections MN, in the Cretaceous‐Devonian and middle to late Proterozoic 1TT, 2TT, AL, and OB) are dominated by the ca. 500 Ma ranges. and ca. 1050 Ma age clusters, with lesser amounts of late [46] First‐cycle sources of detrital zircons with early Proterozoic ages. One exception is the Rio Seco Formation Paleozoic ages are abundant in felsic rocks of the Famatina sample AL177, which closely resembles samples from far- magmatic belt (sample CPLoire, Figure 12) and the Santa ther north. Age spectra from sections in the northern study Rosa de Tastil granite [Pankhurst et al., 1998; Kirschbaum

17 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

from granitoid plutons and Proterozoic‐lower Cambrian (Puncoviscana) strata of the Puna and Cordillera Oriental.

8. Sediment Accumulation History

[47] The Monte Nieva section is the most complete and densely dated of those that we measured, rendering it useful for assessing the long‐term sediment accumulation history of the Cenozoic foreland basin system (Figure 14). More- over, this section is representative of the regional stratigraphy throughout the study area. Chronostratigraphic control is provided by the youngest U‐Pb ages from detrital zircons [e.g., DeCelles et al., 2007], and apatite fission track pooled ages from granite clasts. We assume that (1) the depositional age of a detrital zircon sample cannot be older than its youngest grain, and (2) the AFT ages were not partially or entirely reset during burial and subsequent exhumation. The first assumption is legitimate because U‐Pb systematics of zircons are not reset at the burial temperatures experienced by these rocks. The second assumption is based on the fact that AFT ages of the analyzed clasts do not decrease down‐ section, as would be expected for progressively annealed samples with increasing depth. Moreover, these ages are within error of each other and similar to AFT ages obtained from bedrocks in nearby mountain ranges [Deeken et al., 2006]. Of the three AFT ages depicted on the diagram (Figure 14) only the age from sample MN1333 is likely to be a constraint on depositional age. The other two AFT ages are older than minimum ages from detrital zircons in their respective parts of the section, and they are older than the minimum AFT age from sample MN1333 despite coming from many hundreds of meters up‐section. All of the ages depicted in Figure 14 are from the Monte Nieva section except that from sample TC330 (Ducea, unpublished data, Figure 12. U‐Pb detrital zircon age probability plots for ‐ 2011), which was collected from a few meters below the top samples from the upper Proterozoic Cambrian Puncovis- of the supersol zone in the Tres Cruces section (Figure 6). cana Formation, Cambrian Meson Group, Ordovician Com- Although the Tres Cruces section is far to the north of the plejo Eruptiva Oire, Ordovician Copalaya Formation at the Monte Nieva section, the two sections are approximately base of section SP, Ordovician Santa Victoria Group, and along‐strike of each other, and it is plausible that the Tres the Cretaceous Lecho Formation. See Table S1 for data. Cruces sample provides a useful estimate of the age of the upper part of the supersol at Monte Nieva. et al., 2006; Hongn and Riller, 2007; Ramos, 2009; Hongn [48] Geochronological control on the earliest portion of the et al., 2010; Lucassen et al., 2011] of the Cordillera accumulation history (Mealla and Maiz Gordo Formations) Oriental. Detrital zircons with ages in all three of the major is lacking because samples did not yield Cenozoic zircon populations recovered from the Cenozoic samples (∼500 Ma, populations or apatite grains of sufficient quality for fission – ∼ track analysis. However, robust paleontological ages from 555 994 Ma, 1050 Ma) are present in Cambrian, ‐ Ordovician, and Cretaceous samples from the eastern Puna these units establish their late Paleocene middle Eocene ages and Cordillera Oriental (Figure 12). The ∼1050 Ma grains [Quattrocchio and Volkheimer, 1990; Quattrocchio et al., 2000; del Papa et al., 2002; Marquillas et al., 2005]. The were ultimately derived from orogenic rocks of the Sunsas ‐ belt which formed a prominent fringing terrane along the Rio González section of Reynolds et al. [2000] is also well western margin of most of South America [e.g., Ramos, dated by paleomagnetic stratigraphy and isotopic ages on 2008, 2009, and references therein]. The relative abun- tuffs, and provides an opportunity to compare sediment dance of middle Paleozoic and Cretaceous grains in the accumulation histories in the frontal and interior parts of the northern samples (e.g., samples CV1, CV2, and all of the orogenic belt during the late Miocene (Figure 14). 1TC samples) is consistent with derivation from Paleozoic‐ [49] At Monte Nieva, the accumulation curve is upward Mesozoic strata and Cretaceous igneous rocks [Coira, 1979; convex and exhibits an overall acceleration of accumulation from a rate of ∼25 m/Myr from 60 to 47 Ma, to ∼200 m/Myr Gemmell et al., 1992] that are generally absent south of the – El Toro lineament (Figures 2 and 13c). In contrast, samples over the period 17 7 Ma (Figure 14). At the Rio González from the southern sections (OB50, AL32, AL177, and all section, sediment accumulation rates range from 300 to 600 m/Myr, and the trend decreases slightly through time of the MN and 2TT samples) contain very few grains ∼ ∼ younger than 470 Ma (Figure 9), consistent with derivation from 15 Ma to 9Ma[Reynolds et al., 2000] (Figure 14). In the la Porcelana section of the northernmost Argentine

18 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 13. (a–d) Block diagrams illustrating the temporal and spatial evolution of the Cenozoic foreland basin system in northwestern Argentina based on results of this study. Outlines of the Salta rift paleogeography shown in Figure 13a are from Salfity and Marquillas [1994]. See text for discussion.

19 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 14. Thickness versus time plot for the Monte Nieva section (solid line), Rio González section [after Reynolds et al., 2000], and la Porcelana section [after Reynolds et al., 2001]. Arrows pointing toward the right signify that ages are maximum depositional ages; the actual depositional age could be younger.

Subandes, Reynolds et al. [2001] documented accumulation [51] We propose that the Cenozoic strata of northwestern rates of ∼580 m/Myr from ∼8Mato∼2 Ma. The three Argentina were deposited in a regional foreland basin sediment accumulation curves depicted in Figure 14 show a system that formed and migrated eastward under the influ- systematic eastward migration of the onset of accelerated ence of crustal shortening that originated in Chile and accumulation: in the Monte Nieva section rapid accumula- expanded eastward throughout the last ∼60 Myr. The mod- tion commenced between ∼47 and 40 Ma; at Rio González, ern foreland basin system east of the central Andes provides rapid accumulation began ∼15 Ma; and at la Porcelana an analog for the ancient system preserved in outcrops in the accumulation accelerated at ∼8 Ma. Several other strati- modern orogenic belt. Chase et al. [2009] used geoid and graphic sections in the Subandes of northernmost Argentina flexural modeling to analyze gravity and topographic data exhibit rapid accumulation rates commencing at ∼8.5–9Ma for the modern foreland region, and showed that the modern [Echavarria et al., 2003]. basin contains a 300 km wide foredeep, a mostly buried 450 km wide forebulge, and a several hundred km wide 9. Regional Synthesis diffuse back‐bulge depozone. Recent studies show that the foredeep is dominated by fluvial megafans [Horton and [50] Key features of the Cenozoic stratigraphic record in DeCelles, 1997, 2001] (or distributary fluvial systems northwestern Argentina that must be explained by any [Hartley et al., 2010]); the forebulge is marked by shallow holistic basin model include the regionally thin but wide- incision and a transition from well‐drained to poorly drained spread Paleogene clastic lithofacies of the Santa Bárbara floodplain environments [McGlue and Cohen, 2006]; and Subgroup; the supersol zone and its eastward continuation the back‐bulge region is characterized by fluvial, lacustrine, as a major disconformity; the overlying eastward tapering, ‐ and wetland environments that are strongly controlled by the eastward onlapping wedge of upward coarsening Neogene seasonal hydrological cycle associated with the South fluvial and alluvial fan deposits, which are locally incor- American monsoon [Iriondo, 2004; Assine and Soares, porated into syncontractional growth structures in the upper 2004; McGlue and Cohen, 2006]. The modern back‐bulge Miocene part of the section; the consistent westerly prove- and forebulge regions contain most of the morphological nance of all of these deposits; and increasing sediment ‐ features that are represented in the Mealla, Maiz Gordo, and accumulation rates in Paleocene Pliocene strata, with pro- lower Lumbrera Formations, including lacustrine (perennial gressive eastward migration of the temporal onset of rapid and ephemeral), wetland, and high‐sinuosity fluvial litho- accumulation. facies, as well as intensely developed paleosols.

20 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 15. Regional time‐stratigraphic chart (or Wheeler diagram) for northwestern Argentina based on measured sections reported in this paper, plus the Angastaco (ANG) section from Carrapa et al. [2011a] and the Rio González section (GZ) of Reynolds et al. [2000].

[52] Notwithstanding local control by paleotopographic region, and forebulge migration. We reject isostatic rebound elements (Figure 13b), Paleocene‐lower Miocene strata of as a cause of the supersol zone because the contemporaneous the Santa Bárbara and Métan Subgroups form an integrated, thrust belt was located several hundred kilometers toward overall upward coarsening foreland basin succession that is the west, beyond any reasonable wavelength of flexural readily interpreted in terms of foreland basin depozones isostatic rebound. Moreover, Paleocene‐Eocene foredeep [DeCelles and Giles, 1996]. An important feature of the deposits, temporally equivalent to the supersol zone, are succession is the supersol in the Maiz Gordo and Lumbrera well documented in northern Chile [Mpodozis et al., 2005; Formations (Figure 7). This supersol zone represents at least Arriagada et al., 2006] and demonstrate that the proximal 10–15 Myr of geological time during which the average part of the Paleogene foreland was actively subsiding in sediment accumulation rate was near zero (Figure 14), and is response to nearby crustal thickening during the develop- therefore a zone of intense stratigraphic condensation. ment of the supersol zone. Dynamic uplift of the foreland Eastward in the Subandean zone, the supersol zone is either region owing to processes driven by circulation in the absent or rests upon a regional erosional unconformity that mantle wedge beneath the western South American conti- truncates strata from Permian to Cretaceous age. Combined nental plate [e.g., Mitrovica et al., 1989; Gurnis, 1992] is a with the Bolivian supersol zone, its original palinspastic plausible mechanism for development of the supersol zone; extent exceeded 200,000 km2. The great aerial extent of the it remains difficult, however, to reconcile dynamic uplift in supersol zone requires an extrinsic control on its origin the distal foreland with relatively rapid subsidence in the (such as climate or geodynamics) rather than local processes proximal region and eastward younging in the age of the that were intrinsic to the depositional system (e.g., normal supersol/disconformity. It is conceivable, however, that fluvial overbank processes). The prolonged duration (ca. dynamic subsidence at a wavelength on the order of 103 km 10–15 Myr) and extreme variability in paleosol types in the from the trench helped to create the minor accommodation supersol zone argue against a climatic control. Indeed, the above the forebulge required to preserve the supersol zone paleosol types in the supersol zone require a complete range [e.g., Catuneanu, 2004; Allen and Allen, 2005]. of hydrological and climatological conditions, from water‐ [54] We interpret the supersol/disconformity zone as the logged to arid (Figure 7). More importantly, paleoclimatic result of migration of the flexural forebulge through this processes cannot explain the migration of the supersol zone/ region (Figures 13 and 16) [DeCelles and Horton, 2003]. basal Neogene disconformity up‐section toward the east The up‐section migration and increased lacuna of the (Figure 15). supersol/disconformity toward the east (Figure 15) [Starck [53] Possible geodynamic mechanisms to explain the and Vergani, 1996; Hernández et al., 1999] are predicted supersol/disconformity zone include regional isostatic by geodynamic models of forebulge unconformity behavior rebound of the foreland basin during a period of tectonic [Sinclair et al., 1991; Coakley and Watts, 1991; Crampton inactivity, mantle‐driven (dynamic) uplift of the foreland and Allen, 1995; Schlunegger et al., 1997; Burkhard and

21 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 16

22 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Sommaruga, 1998]. Analogous supersols mark forebulge‐ rate. The combined Bolivian‐northern Argentine foreland related disconformities and condensation zones in the basin system was of regional scale, measuring at least 1000 Himalayan, North American Cordilleran, North Alpine, and km in a north‐south direction, and ∼300 km in an east‐west many other major foreland basins (see review by DeCelles direction. Palinspastic restoration of shortening [Kley and [2011]). The Mealla and Maiz Gordo Formations locally Monaldi, 1998; McQuarrie, 2002a] in the Andean thrust contain pebbly conglomeratic sandstones that could have belt would significantly increase the width of this paleo‐ been partly derived from local granitic rocks associated with foreland basin. paleotopographic features associated with the margins of the [56] The documented sediment accumulation rates Salta rift (Figure 13b). As the flexural forebulge swept (Figure 14) are also typical of foreland basins worldwide through the region now occupied by the Cordillera Oriental, [Xie and Heller, 2009; DeCelles, 2011]. The increasing rate remnant paleotopographic features along the old rift shoulders of accumulation from Eocene time onward is interpreted to were likely rejuvenated [e.g., Blisniuk et al., 1998]. How- represent increasing subsidence rate, which results from the ever, the thinness of the Mealla and Maiz Gordo Formations, migration of the exponential flexural subsidence profile past together with the localized distribution of the coarse‐grained a given location in the foreland. Early accumulation is slow material, suggests that these rejuvenated topographic ele- because the flexural forebulge reduces or eliminates sediments were not large enough to generate a large amount of ment accommodation. In this case, the part of the section clastic sediment. Instead paleocurrent data from these units marked by forebulge accumulation is strongly overprinted indicate east‐northeastward sediment transport from source by pedogenic processes. Farther east, the passage of the terranes located to the west (Figures 5 and 6). We interpret forebulge is marked in the Rio González section by an the strata located beneath the supersol zone, including the erosional disconformity at the base of the foredeep deposits Mealla and part of the Maiz Gordo Formation, as back‐bulge [Reynolds et al., 2000]. The erosional disconformity at the deposits that accumulated in the region east of the flexural base of the foredeep strata is present at all of the sections forebulge, probably several hundred km to the east of the documented in the Santa Bárbara Ranges and in the east- Paleocene‐early Eocene thrust belt. ernmost Cordillera Oriental (e.g., Alemanía and Campa- [55] Above the supersol/disconformity, the Quebrada de mento Vespucio sections [see also Starck and Vergani, 1996; los Colorados Formation, uppermost part of the Lumbrera Hernández et al., 1999; Reynolds et al., 2000, 2001]). The Formation, and the overlying lower Angastaco, Rio Seco, eastward migration of the onset of rapid subsidence as Anta, and Jésus María Formations represent a classic, illustrated in Figure 14 is consistent with progressive eastward tapering foredeep wedge [Starck and Vergani, migration of the flexural subsidence wave. 1996; Hernández et al., 1999; Reynolds et al., 2000] [57] Isolated outcrops of Eocene strata (including the (Figures 15). Evidence for local tectonic shortening in the Geste Formation) that contain evidence for local syndepo- Cordillera Oriental becomes abundant in the upper part of sitional tectonic shortening are present in the eastern Puna the Angastaco Formation and the Agujas Conglomerate in and western Cordillera Oriental (Figure 15) [Carrapa et al., the form of angular and progressive unconformities 2005; Carrapa and DeCelles, 2008]. These strata are gen- [Carrera and Muñoz, 2008; Carrapa et al., 2011a, 2011b; erally correlative with the Quebrada de los Colorados For- this study]. The previously unbroken regional foreland basin mation, but they are not spatially contiguous with the was disrupted and actively exhumed between ∼14 Ma and continuous Paleocene‐Pliocene succession of the regional 3 Ma as indicated by apatite (U‐Th)/He ages of Cretaceous foreland basin system. The Geste Formation rests depos- and Cenozoic sedimentary rocks in the Angastaco area. itionally upon Paleozoic basement rocks, was locally These data are interpreted as the result of eastward migration derived from orogenic highlands, and yields detrital ther- of the strain front through this part of the Cordillera Oriental mochronological evidence of rapid exhumation, probably [Carrapa et al., 2011a, 2011b], and are consistent with related to local shortening [Carrapa et al., 2008]. We ten- previously reported evidence for the onset of syndepositional tatively interpret the Geste Formation as a remnant of the deformation in the Subandean zone during the latest Miocene wedge‐top portion of the early foreland basin system. It is and Pliocene [Reynolds et al., 2000; Echavarria et al., 2003; also plausible that Geste Formation depocenters were never Uba et al., 2009; Hain et al., 2011]. We therefore interpret integrated into the regional foreland basin system, and the Cenozoic succession in terms of foreland basin depo- instead represent local intermontane basins [e.g., Horton, zones that migrated eastward in response to the progres- 2005]. Hongn et al. [2007] and Bosio et al. [2009] also sive growth of the Andean orogenic wedge (Figures 15 reported evidence for late Eocene structural growth in the and 16). Although evidence for out‐of‐sequence deforma- Eastern Cordillera. tion and local rapid exhumation during late Oligocene‐early Miocene time is documented in the Puna and Cordillera 10. Discussion Oriental [Marrett et al., 1994; Coutand et al., 2001; Carrapa et al., 2005, 2011a; Deeken et al., 2006], the [58] Three questions may be addressed using the results overall pattern is an eastward migration of the orogenic presented herein: (1) What information does the foreland strain front and foreland flexural wave, albeit at an unsteady basin succession provide about the distance and tempo of flexural wave migration—what was the rate of migration of

Figure 16. (a–e) Schematic paleogeographic maps for the study area showing the evolution of the orogenic belt and adjacent foreland basin system from latest Cretaceous to present. Paleogeography depicted in Figure 16a is based on Salfity and Marquillas [1994] and Mpodozis et al. [2005]. Barbed lines represent approximate locations of the deformation front at times (in Ma) corresponding to associated numbers.

23 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Figure 17. Diagram illustrating the migration of the foreland basin flexural wave through the region now occupied by the Andean orogenic belt in northwestern Argentina, in a fixed flexural wave frame of reference. Four flexural profiles based on flexural rigidities listed at the top are shown to illustrate the plausible distribution of foreland depozones. The flexural profiles were generated by flexing an unbroken plate under a rectangular load with a half‐width of 300 km and a topographic elevation of 2.5 km. These profiles are anchored to the modern front of the Andes, and held fixed while the thrust belt is palin- spastically restored at 10 Myr intervals back to 60 Ma. Each thrust belt panel is labeled with the progressively restored locations and sizes of the Cordillera de Domeyko (CD), Cordillera Occidental (COC), Puna and Cordillera Oriental (COR), and the Santa Bárbara ranges (SB), based on total shortening estimates from Kley and Monaldi [1998] and kinematic timing as discussed in this paper and by Carrapa et al. [2011a, 2011b]. Shaded zone represents average location of the forebulge zone for the two inter- mediate flexural rigidities, which are based on Tassara et al. [2007] and Chase et al. [2009]. Curves for flexural rigidity of 1023 Nm and 1024 Nm are also shown. Placement of each thrust belt panel is dictated by our interpretation of foreland basin depozones. On the right is a Wheeler diagram showing stratigraphic information used to reconstruct the foreland depozones. For example, between 60 and 50 Ma, the Puna and Cordillera Oriental were occupied by the flexural forebulge (based on the presence of the supersol zone), and by ∼40 Ma these regions were within the foredeep depozone. Velocities of migration of the system at different times are labeled along double‐arrowed lines. the foreland basin through time? (2) To what extent did the of the supersol zone, the eastern Puna and Cordillera Oriental vestigial Salta rift interact with the distal flexural signal of were located within the region occupied by the forebulge the Andean orogenic wedge? and (3) What are the impli- during late Paleocene through middle Eocene time. The cations of this work for pure‐shear versus simple‐shear palinspastic thrust belt panel is therefore adjusted horizon- deformation in the central Andes? tally to a location consistent with these regions straddling the [59] 1. Figure 17 illustrates a spatial‐temporal recon- forebulge (in a fixed flexural wave frame of reference). Thus, struction of the foreland basin flexural wave, calibrated to through time, we can estimate the distance and rate of flex- available shortening estimates in the Andean thrust belt and ural wave migration [e.g., DeCelles and Horton, 2003]. the stratigraphic record documented in this paper. Shorten- [60] Important caveats in such an analysis include the ing estimates are from Kley and Monaldi [1998, and refer- possibility that flexural rigidity and orogenic loading ences therein], and the horizontal locations through time of changed through time, and that the amounts of shortening palinspastic panels are fixed according to the interpreted used in the reconstruction are extremely inaccurate. Changes foreland depozone in a given region, plotted against mod- in flexural rigidity are inscrutable from the viewpoint of the eled flexural subsidence profiles based on flexural rigidities stratigraphic record, but we might safely assume that rigidity for central South American foreland lithosphere [Tassara would have increased through time as older, stronger South et al., 2007; Chase et al., 2009]. Sequential palinspastic American lithosphere became involved in the flexural pro- restoration of the thrust belt panel is based on available file. The effect of this would be that through time the kinematic timing constraints [Kraemer et al., 1999; Reynolds wavelengths of foreland depozones would have increased. et al., 2000; Echavarria et al., 2003; Coutand et al., 2006; The values of flexural rigidity used in Figure 17 are based Carrapa et al., 2005, 2008, 2011a, 2011b; Mazzuoli et al., on present estimates for the central Andean foreland 2008; this study]. For example, based on our interpretation [Tassara et al., 2007; Chase et al., 2009], and are probably

24 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013 maxima. The issue of tectonic shortening is especially subsurface beneath the modern foredeep depozone problematic, inasmuch as the total shortening documented in [Cominguez and Ramos, 1995]. In our view, the late this region (no more than ca. 110 km [Allmendinger, 1986; Miocene‐Quaternary deformation in the easternmost Cor- Grier et al., 1991; Cladouhos et al., 1994; Monaldi and dillera Oriental and frontal Santa Bárbara ranges highlighted Kley, 1997; Kley and Monaldi, 1998]) is far below that by Strecker et al. [2007] and Hain et al. [2011] is reconcil- required to explain the great thickness of the crust [Kley and able with an eastward propagating orogenic wedge, whether Monaldi, 1998]. However, increased shortening would only or not the deformation has taken place along relatively increase the distance of flexural wave migration interpreted shallow (<10 km) low‐angle thrust décollements. In this in this manner, so that our reconstruction is somewhat context, the upper Miocene‐Quaternary deposits represent conservative. wedge‐top accumulations that were depositionally integrated [61] The reconstruction (Figure 17) suggests that the into the regional foreland basin system, as in the case of the flexural wave in northwestern Argentina migrated unstead- Quaternary to modern record of the frontal Andes. This view ily eastward over a total distance of approximately 600 km, is consistent with the regional kinematic history of the central with two episodes of rapid migration (ca. 23–48 mm/yr) Andes and reflection seismic data and balanced regional separated by periods of relatively slow migration (ca. 4– cross‐sections that show faults of the Santa Bárbara system 5 mm/yr). The periods of rapid flexural wave migration merging with a regional detachment at 15–20 km depth occurred at ∼50–40 Ma and ∼5–0 Ma, and are consistent with [Grier et al., 1991; Cristallini et al., 1997; Mortimer et al., major eastward jumps in the position of the contractional 2007]. strain front as indicated by thermochronologically deter- [63] 2. As discussed in the Introduction, previous workers mined exhumation events [Deeken et al., 2006; Coutand have interpreted the Santa Bárbara Subgroup as the result of et al., 2006; Carrapa et al., 2008, 2011b], growth structures post‐Salta rift thermal subsidence [e.g., Marquillas et al., and angular unconformities in reliably dated stratigraphic 2005, and references therein]. This interpretation is prob- units [Hongn et al., 2007; Mazzuolietal., 2008; Carrapa lematic for several reasons. First, the Santa Bárbara and DeCelles, 2008; Carrera and Muñoz, 2008; Carrapa Subgroup and its stratigraphic equivalents in Bolivia blanket et al., 2011a; Hain et al., 2011; this study], and patterns of the entire Cordillera Oriental, Subandes, Santa Barbara provenance and paleotopographic reconstructions [Carrapa system, and the eastern Puna and Altiplano [Sempere et al., et al., 2011a; Hain et al., 2011; this study]. The first of 1997; DeCelles and Horton, 2003], far exceeding what these kinematic jumps took place as deformation propagated would be expected for post‐rift deposits related exclusively from the Cordillera de Domeyko in northern Chile during to the Salta rift. Control by the Salta rift on the spatial late Paleocene‐early Eocene time into the western part of the distribution of the Santa Bárbara Subgroup is not evident, Cordillera Oriental by about 40 Ma [Maksaev and Zentilli, with the exception of the Lomas de Olmedo arm of the 1999; Deeken et al.,2006;DeCelles et al., 2007; Carrapa rift, where subsurface data show axial thickening of Santa and DeCelles, 2008]. The second major jump is expressed Bárbara strata [Cominguez and Ramos, 1995] (see also as rapid eastward propagation of strain from the eastern unpublished petroleum company seismic data). Second, it is Cordillera Oriental into the frontal ranges no earlier than not clear how the Santa Bárbara Subgroup relates to the ∼5Ma[Reynolds et al., 2000; Echavarria et al., 2003; underlying Balbuena Subgroup in terms of standard models Carrera and Muñoz, 2008; Carrapa et al., 2011a; Hain et al., for rift‐basin subsidence [e.g., McKenzie, 1978; Bond and 2011]. Major deformation in the Santa Bárbara Ranges Kominz, 1984]. Salfity and Marquillas [1994] proposed commenced after 2 Ma [Reynolds et al., 2000; Hain et al., that these two packages of rocks represent discrete pulses of 2011]. It is important to note that no evidence exists in ‘post‐rift’ thermal subsidence. Whereas we concur with the either stratigraphic or structural records for complete cessa- post‐rift thermal subsidence interpretation for the fine‐ tion of shortening or long‐term stasis of the strain front in the grained carbonate‐rich Balbuena Subgroup—indeed the time interval between these periods of rapid eastward strain Balbuena Subgroup lies in a depositional continuum on top propagation. Instead, deformation occurred more or less of the synrift Pirgua Subgroup and exhibits many of the continuously in the Andean orogenic wedge from Eocene classic features of post‐rift sedimentation—models for rift‐ time onward [Coutand et al., 2006; Deeken et al., 2006; basin subsidence provide no explanation for a second, post‐ Carrera et al., 2006; Carrapa et al., 2009, 2011a, 2011b]. rifting pulse of thermally driven subsidence that would be [62] Several workers [Strecker et al., 2007; Hain et al., necessary to accommodate the Santa Bárbara Subgroup and 2011] have argued that a fundamental change has occurred its equivalents in Bolivia. Third, the post‐rift interpretation in the eastern retroarc region of northwestern Argentina since provides no explanation for the abrupt coarsening in the late Miocene time, during the transition from an unbroken Mealla and Maiz Gordo Formations; in many sections these foreland to a topographically complex frontal thrust belt units are dominated by sandstone and are locally conglom- dominated by the structural inversion of fault systems that eratic. Standard models for rift‐ to post‐rift sediment accu- originated during Cretaceous extension (the Salta rift). In this mulation predict continued fining and decreased sediment view, upper Miocene‐Quaternary synorogenic deposits in accumulation rates with time. We suggest that paleotopo- the eastern Cordillera Oriental and Santa Bárbara system graphic elements associated with the Salta rift were locally were strongly influenced by local structural uplift and prominent during Paleocene‐early Eocene time in north- formed in an intramontane tectonic setting isolated from the western Argentina, such as in the Angastaco and sur- regional foreland basin system. However, we note that the rounding regions [Sobel and Strecker, 2003; Mortimer et al., modern Andean foreland basin system at these latitudes is 2007; Carrera and Muñoz, 2008; Carrapa et al., 2011a] typical of regional‐scale unbroken forelands, despite the (Figure 13), but that the overall distribution of the Santa presence of the Lomas de Olmedo arm of the Salta rift in the Bárbara Subgroup was dictated by the existence of the

25 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013 nascent Andean orogenic wedge, which was located several perhaps local late‐stage thermal subsidence in easternmost hundred km to the west in northern Chile during Paleocene‐ regions of Cretaceous rifting. However, post‐rift thermal early Eocene time [Maksaev and Zentilli, 1999; Arriagada subsidence alone cannot account for the dominantly et al., 2006]. Fourth, paleocurrent data from fluvial sand- westerly provenance and widespread distribution of the stones in these units indicate consistent paleoflow from the Paleocene‐Eocene deposits from northwestern Argentina west (in Bolivia) and southwest (Argentina), and sedimen- into central Bolivia. Nor is post‐rift thermal subsidence tary petrological data and detrital zircon ages indicate a consistent with the presence of a regional (>200,000 km2) cosmopolitan provenance in Proterozoic and Paleozoic accumulation of extremely mature paleosols in the Eocene sedimentary and igneous rocks distributed over a wide record, which we interpret to be the result of stratigraphic region in the Puna, Altiplano, and the orogenic hinterland. condensation during passage of the flexural forebulge Were the Mealla and Maiz Gordo related exclusively to post‐ through the region. rift thermal subsidence, we would expect to see stronger [66] 2. The Cenozoic foreland basin record of northern local provenance and paleoflow control by remnant rift‐ Argentina is remarkably similar to that in Bolivia. Palin- related topographic highlands. Fifth, the post‐rift thermal spastic restoration of minimum shortening estimates and subsidence interpretation does not provide an explanation for paleogeographic restoration of the foreland basin system the supersol/disconformity and its progressive eastward using modeled flexural profiles demonstrates that the system migration. Indeed, the supersol has not been recognized in migrated at least 600 km eastward. This migration took place literature that attributes the Santa Bárbara Subgroup to post‐ in two large jumps at rates of ∼20–50 mm/yr (50–40 Ma, and rift thermal subsidence, suggesting that its existence has not 5–0 Ma), separated by periods during which migration was heretofore been taken into account. Some authors have much slower, only ∼5 mm/yr. highlighted minor (ca. 10 m) fault offsets in the Santa [67] 3. The presence of a regional foreland basin system in Bárbara Subgroup in reflection seismic profiles as evidence northwestern Argentina and Bolivia throughout the Ceno- that the interval accumulated while extension continued zoic effectively nullifies the notion that these two regions [Cominguez and Ramos, 1995; Monaldi et al., 2008]. behaved significantly different in terms of simple versus However, these minor offsets could be explained as well by pure shear; in particular, there is no support in the foreland flexural extension during passage through the region of the basin history for dominantly pure shear thickening in the flexural forebulge [e.g., Bradley and Kidd, 1991; Blisniuk Puna and Cordillera Oriental of northwestern Argentina et al., 1998; Londoño and Lorenzo, 2004]. north of 26°S. Nor is there a rationale for viewing the late [64] 3. Finally, we note that the persistence of a regional, Miocene‐Pliocene kinematic history of the northwestern eastward migrating foreland basin system in northwestern Argentina portion of the orogenic belt and foreland basin Argentina since Paleocene time is not consistent with a system as fundamentally different from its northerly coun- dominantly pure shear mode of crustal thickening in this terpart in Bolivia, aside from the style of deformation. part of the Andes [Allmendinger, 1986; Allmendinger and Instead, the Paleocene through Pliocene stratigraphic record Gubbels, 1996]. Instead, it appears that shortening and of northwestern Argentina and Bolivia documents the crustal thickening in this part of the orogenic belt produced a development and expansion of the Andean orogenic belt and load that was supported by the flexural strength of adjacent its associated foreland basin flexural wave. foreland lithosphere from Paleocene time to the present. South of latitude 27°S, however, a Paleogene foreland basin has not been documented [Carrapa et al., 2008], large [68] Acknowledgments. We are grateful to D. Starck, R. M. Hernandez, J. H. Reynolds, L. Schoenbohm, and R. N. Alonso for numerous insightful basement blocks are involved in the orogenic belt (the discussions and assistance in locating stratigraphic sections in the field. northern Sierras Pampeanas) [Jordan et al., 1983; Jordan T. P. Ojha helped with graphics, and D. Gingrich kindly provided details and Allmendinger, 1986], and the timing of deformation for the measured section at Cianzo. J. McNabb assisted with sample preparation for U‐Pb zircon analyses. The U.S. National Science Foundation– may be more regionally diffuse [Mortimer et al., 2007; Tectonics and ExxonMobil provided funding. This paper represents part Dávila and Astini, 2007; Carrapa et al., 2006, 2008]. This of an ongoing collaboration with ExxonMobil scientists on convergent oro- leaves open the possibility that pure shear shortening may be genic systems. Careful reviews by F. Schlunegger, an anonymous reviewer, operating farther south. In addition, our argument against and Associate Editor Andrew Carter helped us to substantially improve the manuscript. dominantly pure shear thickening does not preclude the possibility that the orogenic belt thickened by pure shear in its hinterland while the frontal part of the orogenic belt References operated in a simple shear mode. Aalto, R., L. Maurice‐Bourgoin, T. Dunne, D. R. Montgomery, C. A. Nittrouer, and J. L. Guyot (2003), Episodic sediment accumulation 11. Conclusions on Amazonian flood plains influenced by El Nino/Southern Oscillation, Nature, 425, 493–497, doi:10.1038/nature02002. [65] 1. The Paleogene‐Neogene stratigraphy of north- Allen, P. A., and J. R. Allen (2005), Basin Analysis, 2nd ed., 549 pp., western Argentina records the early to mature central Blackwell, Malden, Mass. Allmendinger, R. W. (1986), Tectonic development, southeastern border of Andean foreland basin system. Previously interpreted the Puna Plateau, northwestern Argentine Andes, Geol. Soc. Am. Bull., Paleocene‐Eocene post‐rift sag deposits are reinterpreted to 97, 1070–1082, doi:10.1130/0016-7606(1986)97<1070:TDSBOT>2.0. contain evidence of nascent Andean thrust belt develop- CO;2. Allmendinger, R. W., and T. Gubbels (1996), Pure and simple shear plateau ment, far to the west in northern Chile. Accommodation for uplift, Altiplano ‐ Puna, Argentina and Bolivia, Tectonophysics, 259, these deposits was likely a result of combined distal back‐ 1–13, doi:10.1016/0040-1951(96)00024-8. bulge subsidence, some component of dynamic subsidence Allmendinger, R. W., V. A. Ramos, T. E. Jordan, M. Palma, and B. L. Isacks (1983), Paleogeography and Andean structural geometry, northwest associated with the subducting oceanic Nazca plate, and Argentina, Tectonics, 2,1–16, doi:10.1029/TC002i001p00001.

26 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Allmendinger, R., T. Jordan, S. Kay, and B. Isacks (1997), The evolution Carrera, N., J. A. Muñoz, F. Sàbat, R. Mon, and E. Roca (2006), The role of the Altiplano‐Puna Plateau of the Central Andes, Annu. Rev. Earth of inversion tectonics in the structure of the Cordillera Oriental (NW Planet. Sci., 25, 139–174, doi:10.1146/annurev.earth.25.1.139. Argentinean Andes), J. Struct. Geol., 28,1921–1932, doi:10.1016/j. Alonso, R. N. (1992), Estratigrafía del Cenozoico de la cuenca Pastos jsg.2006.07.006. Grandes (Puna Salteña) con énfasis en la Formación Sijes y sus boratos, Catuneanu, O. (2004), Retroarc foreland systems—Evolution through time, Asoc. Geol. Argent. Rev., 47, 189–199. J. Afr. Earth Sci., 38(3), 225–242, doi:10.1016/j.jafrearsci.2004.01.004. Arriagada, C., P. R. Cobbold, and P. Roperch (2006), Salar de Atacama Chase, C. G., A. J. Sussman, and D. D. Coblentz (2009), Curved Andes: basin: A record of compressional tectonics in the central Andes since Geoid, forebulge, and flexure, Lithosphere, 1(6), 358–363, the mid‐Cretaceous, Tectonics, 25, TC1008, doi:10.1029/ doi:10.1130/L67.1. 2004TC001770. Cladouhos, T. T., R. W. Allmendinger, B. Coira, and E. Farrar (1994), Late Assine, M. L., and P. C. Soares (2004), Quaternary of the Pantanal, west‐ Cenozoic deformation in the central Andes; fault kinematics from the central Brazil, Quat. Int., 114,23–34, doi:10.1016/S1040-6182(03) northern Puna, northwestern Argentina and southwestern Bolivia, 00039-9. J. South Am. Earth Sci., 7, 209–228, doi:10.1016/0895-9811(94)90008-6. Baby, P., P. Rochat, G. Mascle, and G. Hérail (1997), Neogene shortening Coakley, B. J., and A. B. Watts (1991), Tectonic controls on the develop- contribution to crustal thickening in the back arc of the Central Andes, ment of unconformities, North Slope Alaska, Tectonics, 10, 101–130, Geology, 25, 883–886, doi:10.1130/0091-7613(1997)025<0883: doi:10.1029/90TC01982. NSCTCT>2.3.CO;2. Coira, B. L. (1979), Descripción geológica de la Hoja 3c Abra Pampa, Barnes, J. B., T. A. Ehlers, N. McQuarrie, P. B. O’Sullivan, and S. Tawackoli provincia de Jujuy, Bol. Argent. Serv. Geol. Nac., 170,1–85. (2008), Thermochronometer record of central Andean Plateau growth, Cominguez, A. H., and V. A. Ramos (1995), Geometry and seismic Bolivia (19.5°S), Tectonics, 27, TC3003, doi:10.1029/2007TC002174. expression of the Cretaceous Salta rift of northwestern Argentina, in Beck, S., and G. Zandt (2002), The nature of orogenic crust in the Central Petroleum Basins of South America, edited by A. J. Tankard, R. Suarez, Andes, J. Geophys. Res., 107(B10), 2230, doi:10.1029/2000JB000124. and H. J. Welsink, AAPG Mem., 62, 325–339. Blisniuk, P. M., L. J. Sonder, and R. J. Lillie (1998), Foreland normal Coney, P. J., and C. A. Evenchick (1994), Consolidation of the American fault control on NW Himalayan thrust front development, Tectonics, Cordilleras, J. South Am. Earth Sci., 7, 241–262, doi:10.1016/0895- 17, 766–779, doi:10.1029/98TC01870. 9811(94)90011-6. Bond, G. C., and M. A. Kominz (1984), Construction of tectonic subsi- Coutand, I., P. R. Cobbold, M. de Urreiztieta, P. Gautier, A. Chauvin, dence curves for the early Paleozoic miogeocline, southern Canadian D. Gapais, E. A. Rossello, and O. Lòpez‐Gamundí (2001), Style and Rocky Mountains: Implications for subsidence mechanisms, age of history of Andean deformation, Puna plateau, Northwestern Argentina, breakup, and crustal thinning, Geol. Soc. Am. Bull., 95,155–173, Tectonics, 20, 210–234, doi:10.1029/2000TC900031. doi:10.1130/0016-7606(1984)95<155:COTSCF>2.0.CO;2. Coutand, I., B. Carrapa, A. Deeken, A. K. Schmitt, E. Sobel, and Bosio, P. P., J. Powell, C. del Papa, and F. Hongn (2009), Middle Eocene M. R. Strecker (2006), Orogenic plateau formation and lateral growth deformation– sedimentation in the Luracatao Valley: Tracking the begin- of compressional basins and ranges: Insights from sandstone petrography ning of the foreland basin of northwestern Argentina, J. South Am. Earth and detrital apatite fission‐track thermochronology in the Angastaco Sci., 28, 142–154, doi:10.1016/j.jsames.2009.06.002. Basin, NW Argentina, Basin Res., 18,1–26, doi:10.1111/j.1365-2117. Bradley, D. C., and W. S. F. Kidd (1991), Flexural extension of the upper 2006.00283.x. continental crust in collisional foredeeps, Geol. Soc. Am. Bull., 103, Crampton, S. L., and P. A. Allen (1995), Recognition of flexural forebulge 1416–1438, doi:10.1130/0016-7606(1991)103<1416:FEOTUC>2.3. unconformities in the geologic record, AAPG Bull., 79, 1495–1514. CO;2. Cristallini, E., A. H. Cominguez, and V. A. Ramos (1997), Deep structure Burkhard, M., and A. Sommaruga (1998), Evolution of the western Swiss of the Metán‐Guachipas region; tectonic inversion in northwestern Molasse basin: Structural relations with the Alps and the Jura belt, in Argentina, J.SouthAm.EarthSci., 10(5–6), 403–421, doi:10.1016/ Cenozoic Foreland Basins of Western Europe, edited by A. Mascle et S0895-9811(97)00026-6. al., Geol. Soc. Spec. Publ., 134, 279–298. Crouvi, O., R. Amit, Y. Enzel, and A. R. Gillespie (2010), Active sand seas Bywater‐Reyes, S., B. Carrapa, M. Clementz, and L. Schoenbohm (2010), and the formation of desert loess, Quat. Sci. Rev., 29, 2087–2098, The effect of late Cenozoic aridification on sedimentation in the Eastern doi:10.1016/j.quascirev.2010.04.026. Cordillera of NW Argentina (Angastaco basin), Geology, 38(3), 235–238, Dávila,F.M.,andR.A.Astini(2007),Cenozoicprovenancehistoryof doi:10.1130/G30532.1. synorogenic conglomerates in western Argentina (Famatina Belt): Impli- Carrapa, B., and P. G. DeCelles (2008), Eocene exhumation and basin cations for Central Andean foreland development, Geol. Soc. Am. Bull., development in the Puna of Northwestern Argentina, Tectonics, 27, 119, 609–622, doi:10.1130/B26007.1. TC1015, doi:10.1029/2007TC002127. DeCelles, P. G. (2011), Foreland basin systems revisited: Variations in Carrapa, B., D. Adelmann, G. E. Hilley, E. Mortimer, E. R. Sobel, and response to tectonic settings, in Tectonics of Sedimentary Basins: Recent M. R. Strecker (2005), Oligocene uplift and development of plateau Advances, edited by C. Busby and A. Azor, Blackwell, Cambridge, morphology in the southern central Andes, Tectonics, 24, TC4011, Mass., in press. doi:10.1029/2004TC001762. DeCelles, P. G., and K. N. Giles (1996), Foreland basin systems, Basin Carrapa, B., M. R. Strecker, and E. R. Sobel (2006), Cenozoic orogenic Res., 8, 105–123, doi:10.1046/j.1365-2117.1996.01491.x. growth in the central Andes: Evidence from sedimentary rock prove- DeCelles, P. G., and B. K. Horton (2003), Early to middle Tertiary foreland nance and apatite fission track thermochronology in the Fiambalá basin, basin development and the history of Andean crustal shortening in southernmost Puna plateau margin (NW Argentina), Earth Planet. Sci. Bolivia, Geol. Soc. Am. Bull., 115(1), 58–77, doi:10.1130/0016- Lett., 247,82–100, doi:10.1016/j.epsl.2006.04.010. 7606(2003)115<0058:ETMTFB>2.0.CO;2. Carrapa, B., B. Hauer, L. Schoenbohm, M. R. Strecker, A. K. Schmitt, DeCelles, P. G., R. P. Langford, and R. K. Schwartz (1983), Two new A. Villanueva, and A. S. Gomez (2008), Dynamics of deformation and methods of paleocurrent determination from trough cross‐stratification, sedimentation in the northern Sierras Pampeanas: An integrated study J. Sediment. Res., 53, 629–642. of the Neogene Fiambalá basin, NW Argentina, Geol. Soc. Am. Bull., DeCelles, P. G., M. B. Gray, R. B. Cole, N. Pequera, D. A. Pivnik, 120, 1518–1543, doi:10.1130/B26111.1. K. D. Ridgway, and P. Srivastava (1991), Controls on synorogenic Carrapa, B., P. G. DeCelles, P. Reiners, and G. E. Gehrels (2009), Apatite alluvial‐fan architecture, Beartooth Conglomerate, Wyoming and triple dating and white mica 40Ar/39Ar thermochronology of syn‐tectonic Montana, Sedimentology, 38, 567–590, doi:10.1111/j.1365-3091.1991. detritus in the Central Andes: A multi‐phase tectono‐thermal history, tb01009.x. Geology, 37, 407–410, doi:10.1130/G25698A.1. DeCelles, P. G., B. Carrapa, and G. E. Gehrels (2007), Detrital zircon U‐Pb Carrapa, B., S. Bywater‐Reyes, P. G. DeCelles, E. Mortimer, and ages provide provenance and chronostratigraphic information from G. E. Gehrels (2011a), Eocene‐Miocene synorogenic basin evolution in Eocene synorogenic deposits in northwestern Argentina, Geology, 35(4), the Eastern Cordillera of northwestern Argentina (25°–26°S): Regional 323–326, doi:10.1130/G23322A.1. implications for Andean orogenic wedge development, Basin Res., 23, DeCelles, P. G., M. N. Ducea, G. Zandt, and P. Kapp (2009), Cyclicity in 1–20. Cordilleran orogenic systems, Nat. Geosci., 2,251–257, doi:10.1038/ Carrapa, B., J. D. Trimble, and D. F. Stockli (2011b), Patterns and timing ngeo469. of exhumation and deformation in the Eastern Cordillera of NW Argentina Deeken, A., E. R. Sobel, I. Coutand, M. Haschke, U. Riller, and revealed by (U‐Th)/He thermochronology, Tectonics, 30, TC3003, M. R. Strecker (2006), Development of the southern Eastern Cordillera, doi:10.1029/2010TC002707. NW Argentina, constrained by apatite fission track thermochronology: Carrera, N., and J. A. Muñoz (2008), Thrusting evolution in the southern From early Cretaceous extension to middle Miocene shortening, Cordillera Oriental (northern Argentine Andes): Constraints from growth Tectonics, 25, TC6003, doi:10.1029/2005TC001894. strata, Tectonophysics, 459, 107–122, doi:10.1016/j.tecto.2007.11.068.

27 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013 del Papa, C. (2006), Estratigrafía y Paleoambientes de la Formación Haschke, M., A. Günther, D. Melnick, H. Echtler, K.‐J. Reutter, Lumbrera, Grupo Salta, Noroeste Argentino, Rev. Asoc. Geol. Argent., E. Scheuber, and O. Onken (2006), Central and southern Andean tectonic 61(3), 15–29. evolution inferred from arc magmatism, in The Andes: Active Subduction del Papa, C. E., and J. Salfity (1999), Non‐marine Paleogene sequences, Orogeny, edited by O. Oncken et al., pp. 337–353, Springer, Berlin. northwest Argentina, Acta Geol. Hisp., 34(2–3), 105–122. Hasiotis, S. T., and T. M. Bown (1992), Invertebrate trace fossils: The del Papa, C. E., V. García, and M. Quattrocchio (2002), Sedimentary facies backbone of continental ichnology, in Trace Fossils, Short Courses and palynofacies assemblages in an Eocene perennial lake, Lumbrera Paleontol., vol. 5, edited by C.G. Maples and R. R. West, pp. 64–104, Formation, northwest Argentina, J. South Am. Earth Sci., 15, 553–569, Paleontol. Soc., Knoxville, Tenn. doi:10.1016/S0895-9811(02)00081-0. Heit, B., I. Koulakov, G. Asch, X. Yuan, R. Kind, I. Alcozer, S. Tawackoli, del Papa, C., A. Kirschbaum, J. Powell, A. Brod, F. Hongn, and and H. Wilke (2008), More constraints to determine the seismic structure M. Pimentel (2010), Sedimentological, geochemical and paleontological beneath the Central Andes at 21°S using teleseismic tomography analysis, insights applied to continental omission surfaces: A new approach for J. South Am. Earth Sci., 25,22–36. reconstructing Eocene foreland basin in NW Argentina, J. South Am. Hernández, R. M., and L. Echavarria (2009), Faja plegada y corrida Earth Sci., 29, 327–345, doi:10.1016/j.jsames.2009.06.004. Subandina del noroeste Argentina: Estratigrafía, geometría y cronología Dickinson, W. R. (1983), Provenance of North American Phanerozoic de la deformación, Asoc. Geol. Argent. Rev., 65,68–80. sandstones in relation to tectonic setting, Geol. Soc. Am. Bull., 94, Hernández, R. M., J. Reynolds, and A. Di Salvo (1996), Análisis tectose- 222–257, doi:10.1130/0016-7606(1983)94<222:PONAPS>2.0.CO;2. dimentario y ubicación geocronológica del Grupo Orán en el río Iruya, Dumitru, T. A. (1993), A new computer automated microscope stage Bol. Inf. Petrol., 45,80–93. system for fission track analysis, Nucl. Tracks, 21, 575–580. Hernández, R. M., C. I. Galli, and J. Reynolds (1999), Estratigrafía del Dunn, J. F., K. G. Hartshorn, and P. W. Hartshorn (1995), Structural styles Terciario en el noroeste Argentino, in Geologia del Noroeste Argentino: and hydrocarbon potential of the Sub‐Andean thrust belt of southern Relatorio del XV Congreso Geológico Argentino, edited by G. González Bolivia, in Petroleum Basins of South America, edited by A. J. Tankard, Bonorino, R. Omarini, and J. Viramonte, pp. 316–328, Univ. Nac. de R. Suárez, and H. J. Welsink, AAPG Mem., 62, 523–543. Salta, Salta, Argentina. Echavarria, R., R. Hernández, R. W. Allmendinger, and J. H. Reynolds Hindle, D., J. Kley, O. Oncken, and S. V. Sobolev (2005), Crustal balance (2003), Subandean thrust and fold belt of northwest Argentina: Geometry and crustal flux from shortening estimates in the Central Andes, Earth and timing of the Andean evolution, AAPG Bull., 87(6), 965–985, Planet. Sci. Lett., 230, 113–124, doi:10.1016/j.epsl.2004.11.004. doi:10.1306/01200300196. Hongn, F. D., and U. Riller (2007), Tectonic evolution of the western Ege, H., E. R. Sobel, E. Scheuber, and V. Jacobshagen (2007), Exhumation margin of Gondwana inferred from syntectonic emplacement of history of the Central Andean plateau (southern Bolivia) constrained by Paleozoic granitoid plutons in northwest Argentina, J. Geol., 115(2), apatite fission track thermochronology, Tectonics, 26, TC1004, 163–180, doi:10.1086/510644. doi:10.1029/2005TC001869. Hongn, F. D., C. del Papa, J. Powell, I. Petrinovic, R. Mon, and V. Deraco Ellis, S. M., P. Fullsack, and C. Beaumont (1995), Oblique convergence of (2007), Middle Eocene deformation and sedimentation in the Puna‐ the crust driven by basal forcing: Implications for length‐scales of Eastern Cordillera transition (23°–26°S): Control by preexisting heteroge- deformation and strain partitioning in orogens, Geophys. J. Int., 120(1), neities on the pattern of initial Andean shortening, Geology, 35, 271–274, 24–44, doi:10.1111/j.1365-246X.1995.tb05909.x. doi:10.1130/G23189A.1. England, P., and G. Houseman (1985), Role of lithospheric strength hetero- Hongn, F. D., J. M. Tubía, A. Aranguren, N. Vegas, R. Mon, and geneities in the Tectonics of Tibet and neighbouring regions, Nature, G. R. Dunning (2010), Magmatism coeval with lower Paleozoic shelf 315, 297–301, doi:10.1038/315297a0. basins in NW‐Argentina (Tastil batholith): Constraints on current Galbraith, R. F., and P. F. Green (1990), Estimating the component ages in stratigraphic and tectonic interpretations, J. South Am. Earth Sci., a finite mixture, Nucl. Tracks, 17, 196–206. 29, 289–305, doi:10.1016/j.jsames.2009.07.008. Galli, C. I., R. M. Hernández, and J. H. Reynolds (1996), Análisis paleoam- Horton, B. K. (2005), Revised deformation history of the central Andes: biental y ubicación geocronológica del Subgrupo Metán (Grupo Orán, Inferences from Cenozoic foredeep and intermontane basins of the Eastern Neógeno) en el Río Piedras, departmento Metán: Salta, Argentina, Bol. Cordillera, Bolivia, Tectonics, 24, TC3011, doi:10.1029/2003TC001619. Inf. Petrol., 12,99–107. Horton, B. K., and P. G. DeCelles (1997), The modern foreland basin Galliski, M. A., and J. G. Viramonte (1988), The Cretaceous paleorift in system adjacent to the Central Andes, Geology, 25, 895–898, northwestern Argentina; a petrologic approach, J. South Am. Earth doi:10.1130/0091-7613(1997)025<0895:TMFBSA>2.3.CO;2. Sci., 1, 329–342, doi:10.1016/0895-9811(88)90021-1. Horton, B. K., and P. G. DeCelles (2001), Modern and ancient fluvial Gebhard, J. A., A. R. Guidice, and J. O. Gascon (1974), Geología de la megafans in the foreland basin system of the central Andes, southern comarca entre el Río Juramento y Arroyo las Tortugas, provincias de Bolivia: Implications for drainage network evolution in fold‐thrust belts, Salta y Jujuy, Asoc. Geol. Argent. Rev., 29, 359–375. Basin Res., 13,43–63, doi:10.1046/j.1365-2117.2001.00137.x. Gehrels, G. E., V. Valencia, and J. Ruiz (2008), Enhanced precision, Horton, B. K., B. A. Hampton, and G. Waanders (2001), Paleogene synoro- accuracy, efficiency, and spatial resolution of U‐Pb ages by laser genic sedimentation in the Altiplano plateau and implications for initial ablation–multicollector–inductively coupled plasma–mass spectrometry, mountain building in the central Andes, Geol. Soc. Am. Bull., 113, Geochem. Geophys. Geosyst., 9, Q03017, doi:10.1029/2007GC001805. 1387–1400, doi:10.1130/0016-7606(2001)113<1387:PSSITA>2.0.CO;2. Gemmell, J. B., H. Zantop, and L. D. Meinert (1992), Genesis of the Houseman, G., and P. England (1993), Crustal thickening versus lateral Aguilar zinc‐lead‐silver deposit, Argentina: Contact metasomatic vs. expulsion in the Indian‐Asian continental collision, J. Geophys. Res., sedimentary exhalative, Econ. Geol., 87, 2085–2112, doi:10.2113/ 98, 12,233–12,249, doi:10.1029/93JB00443. gsecongeo.87.8.2085. Hurford, A. J., and P. F. Green (1983), The zeta age calibration of fission‐ Gillis, R. J., B. K. Horton, and M. Grove (2006), Thermochronology, track dating, Chem. Geol., 41, 285–317, doi:10.1016/S0009-2541(83) geochronology, and upper crustal structure of the Cordillera Real: 80026-6. Implications for Cenozoic exhumation of the central Andean plateau, Ingersoll, R. V., T. F. Bullard, R. L. Ford, J. P. Grimm, J. D. Pickle, and Tectonics, 25, TC6007, doi:10.1029/2005TC001887. S. W. Sares (1984), The effect of grain size on detrital modes: A test of Green, P. F. (1981), A new look at statistics in fission‐track dating, Nucl. the Gazzi‐Dickinson point‐counting method, J. Sediment. Petrol., 54, Tracks, 5,77–86, doi:10.1016/0191-278X(81)90029-9. 103–116. Grier, M. E., J. A. Salfity, and R. W. Allmendinger (1991), Andean reac- Iriondo, M. (2004), Large wetlands of South America: A model for tivation of the Cretaceous Salta rift, northwestern Argentina, J. South Am. Quaternary humid environments, Quat. Int., 114,3–9, doi:10.1016/ Earth Sci., 4(4), 351–372, doi:10.1016/0895-9811(91)90007-8. S1040-6182(03)00037-5. Gurnis, M. (1992), Rapid continental subsidence following the initiation and Isacks, B. (1988), Uplift of the central Andean plateau and bending of the evolution of subduction, Science, 255,1556–1558, doi:10.1126/science. Bolivian orocline, J. Geophys. Res., 93, 3211–3231, doi:10.1029/ 255.5051.1556. JB093iB04p03211. Hain, M. P., M. R. Strecker, B. Bookhagen, R. N. Alonso, H. Pingel, and James, D. E. (1971), Plate‐tectonic model for the evolution of the A. K. Schmitt (2011), Neogene to Quaternary broken foreland formation central Andes, Geol. Soc. Am. Bull., 82, 3325–3346, doi:10.1130/0016- and sedimentation dynamics in the Andes of NW Argentina (25°S), 7606(1971)82[3325:PTMFTE]2.0.CO;2. Tectonics, 30, TC2006, doi:10.1029/2010TC002703. Jordan, T. E., and R. W. Allmendinger (1986), The Sierras Pampeanas of Hartley, A. J., G. S. Weissmann, G. J. Nichols, and G. L. Warwick (2010), Argentina: A modern analogue of Rocky Mountain foreland deformation, Large distributive fluvial systems: Characteristics, distribution and Am. J. Sci., 286, 737–764, doi:10.2475/ajs.286.10.737. controls on development, J. Sediment. Res., 80, 167–183, doi:10.2110/ Jordan, T. E., and R. N. Alonso (1987), Cenozoic Stratigraphy and Basin jsr.2010.016. Tectonics of the Andes Mountains, 20°–28° South Latitude, AAPG Bull., 71,49–64.

28 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Jordan, T. E., B. L. Isacks, R. W. Allmendinger, J. A. Brewer, V. A. Ramos, McQuarrie, N., J. B. Barnes, and T. A. Ehlers (2008), Geometric, kinematic, and C. J. Ando (1983), Andean tectonics related to geometry of sub- and erosional history of the central Andean Plateau, Bolivia (15–17°S), ducted Nazca plate, Geol. Soc. Am. Bull., 94, 341–361, doi:10.1130/ Tectonics, 27, TC3007, doi:10.1029/2006TC002054. 0016-7606(1983)94<341:ATRTGO>2.0.CO;2. Miall, A. D. (1978), Fluvial sedimentology: An historical review, in Kay, S., and B. Coira (2009), Shallowing and steepening subduction zones, Fluvial Sedimentology, edited by A. D. Miall, Mem. Can. Soc. Pet. Geol., continental lithospheric loss, magmatism, and crustal flow under the 5,1–47. Central Andes, Mem. Geol. Soc. Am., 204, 229–259. Mitrovica, J. X., C. Beaumont, and G. T. Jarvis (1989), Tilting of continental Kay, S. M., B. Coira, and J. Viramonte (1994), Young mafic back‐arc interiors by the dynamical effects of subduction, Tectonics, 8, 1079–1094, volcanic rocks as indicators of continental lithospheric delamination doi:10.1029/TC008i005p01079. beneath the Argentine Puna plateau, Central Andes, J. Geophys. Res., Molnar, P., and G. A. Houseman (2004), The effects of buoyant crust on 99, 24,323–24,339, doi:10.1029/94JB00896. the gravitational instability of thickened mantle lithosphere at zones of Kirschbaum, A., F. Hongn, and N. Menegatti (2006), The Cobres Plutonic intracontinental convergence, Geophys. J. Int., 158,1134–1150, Complex, eastern Puna (NW Argentina): Petrological and structural con- doi:10.1111/j.1365-246X.2004.02312.x. straints for Lower Paleozoic magmatism, J. South Am. Earth Sci., 21(3), Molnar, P., P. England, and J. Martinod (1993), Mantle dynamics, the 252–266, doi:10.1016/j.jsames.2006.04.003. uplift of the Tibetan Plateau, and the Indian monsoon, Rev. Geophys., Kley, J. (1999), Geologic and geometric constraints on a kinematic model 31, 357–396, doi:10.1029/93RG02030. of the Bolivian orocline, J. South Am. Earth Sci., 12, 221–235, Monaldi, C. R., and J. Kley (1997), Balanced cross sections of the northern doi:10.1016/S0895-9811(99)00015-2. Santa Bárbara system and Sierra de Zapla, northwestern Argentina, paper Kley, J., and C. R. Monaldi (1998), Tectonic shortening and crustal thick- presented at VIII Congreso Geológico Chileno, Congr. Geol. Chil., ness in the Central Andes: How good is the correlation?, Geology, 26(8), Antofagasta, Chile. 723–726, doi:10.1130/0091-7613(1998)026<0723:TSACTI>2.3.CO;2. Monaldi, C. R., J. A. Salfity, and J. Kley (2008), Preserved extensional Kley, J., and C. R. Monaldi (2002), Tectonic inversion in the Santa Bárbara structures in an inverted Cretaceous rift basin, northwestern Argentina: system of the central Andean foreland thrust belt, northwestern Argen- Outcrop examples and implications for fault reactivation, Tectonics, tina, Tectonics, 21(6), 1061, doi:10.1029/2002TC902003. 27, TC1011, doi:10.1029/2006TC001993. Kraemer, B., D. Adelmann, M. Alten, W. Schnurr, K. Erpenstein, E. Kiefer, Moreno, J. A. (1970), Estratigrafía y paleogeografía del Cretácico superior en P. van den Bogaard, and K. Görler (1999), Incorporation of the la cuenca del noroeste argentino, con especial mención de los subgrupos Paleogene foreland into the Neogene Puna plateau: The Salar de Antofalla Balbuena y Santa Bárbara, Asoc. Geol. Argent. Rev., 24,9–44. area, NW Argentina, J. South Am. Earth Sci., 12, 157–182, doi:10.1016/ Mortimer, E., B. Carrapa, C. Isabelle, L. Schoenbohm, E. R. Sobel, S0895-9811(99)00012-7. J. S. Gomez, and M. R. Strecker (2007), Fragmentation of a foreland Londoño, J., and J. M. Lorenzo (2004), Geodynamics of continental plate basin in response to out‐of‐sequence basement uplifts and structural collision during late tertiary foreland basin evolution in the Timor Sea: reactivation: El Cajón–Campo del Arenal basin, NW Argentina, Geol. Constraints from foreland sequences, elastic flexure and normal faulting, Soc. Am. Bull., 119(5–6), 637–653, doi:10.1130/B25884.1. Tectonophysics, 392,37–54, doi:10.1016/j.tecto.2004.04.007. Mpodozis, C., C. Arriagada, M. Basso, P. Roperch, P. Cobbold, and Lucassen, F., R. Becchio, and G. Franz (2011), The Early Palaeozoic high‐ M. Reich (2005), Late Mesozoic to Paleogene stratigraphy of the Salar grade metamorphism at the active continental margin of West Gondwana de Atacama basin, Antofagasta, northern Chile: Implications for the tec- in the Andes (NW Argentina/N Chile), Int. J. Earth Sci., 100, 445–463, tonic evolution of the central Andes, Tectonophysics, 399,125–154, doi:10.1007/s00531-010-0585-3. doi:10.1016/j.tecto.2004.12.019. Mack, G. H., W. C. James, and H. C. Monger (1993), Classification of Oncken, O., D. Hindle, J. Kley, K. Elger, P. Victor, and K. Schemmann paleosols, Geol. Soc. Am. Bull., 105, 129–136, doi:10.1130/0016- (2006), Deformation of the central Andean upper plate system—Facts, 7606(1993)105<0129:COP>2.3.CO;2. fiction, and constraints for plateau models, in The Andes: Active Subduc- Maksaev, V., and M. Zentilli (1999), Fission track thermochronology of the tion Orogeny, edited by O. Oncken et al., pp. 3–27, Springer, Berlin. Domeyko Cordillera, northern Chile: Implications for Andean tectonics Pankhurst, R. J., C. W. Rapela, J. Saavedra, E. Baldo, J. Dahlquist, and porphyry copper metallogenesis, Explor. Min. Geol., 8,65–89. I. Pascua, and C. M. Fanning (1998), The Famatinian magmatic arc in the Marquillas,R.A.,C.delPapa,andI.F.Sabino(2005),Sedimentary southern Sierras Pampeanas, in The Proto‐Andean Margin of Gondwana, aspects and paleoenvironmental evolution of a rift basin: Salta Group edited by R. J. Pankhurst and C. W. Rapela, Geol. Soc. Spec. Pub., 142, (Cretaceous‐Paleogene), northwestern Argentina, Int. J. Earth Sci., 94, 343–367. 94–113, doi:10.1007/s00531-004-0443-2. Pascual, R. (1983), Novedosos marsupiales paleógenos de la Fm. Pozuelos Marrett, R., and M. R. Strecker (2000), Response of intracontinental defor- de la Puna: Salta, Ameghiniana, 20, 265–280. mation in the central Andes to late Cenozoic reorganization of South Quattrocchio, M., and W. Volkheimer (1990), Paleogene paleoen- American Plate motions, Tectonics, 19, 452–467, doi:10.1029/ vironmental trends as reflected by palynological assemblage types, Salta 1999TC001102. Basin, NW Argentina, Neues Jahrb. Geol. Palaeontol. Abh., 181(1–3), Marrett, R. A., R. W. Allmendinger, R. N. Alonso, and R. E. Drake (1994), 377–396. Late Cenozoic tectonic evolution of the Puna Plateau and adjacent Quattrocchio, M., W. Volkheimer, and C. del Papa (1997), Palynology and foreland, northwestern Argentine Andes, J. South Am. Earth Sci., 7(2), Paleoenvironment of the “Faja Gris”, Mealla Formation (Salta Group) at 179–207, doi:10.1016/0895-9811(94)90007-8. Garabatal Creek (NW Argentina), Palynology, 21, 231–247, Masek, J. G., B. L. Isacks, T. L. Gubbels, and E. J. Fielding (1994), Erosion doi:10.1080/01916122.1997.9989498. and tectonics at the margins of continental plateaus, J. Geophys. Res., 99, Quattrocchio, M., L. Ruiz, and W. Volkheimer (2000), Palynological zona- 13,941–13,956, doi:10.1029/94JB00461. tion of the Paleogene of the Colorado and Salta Group basin, Argentina, Mazzuoli, R., et al. (2008), Miocene magmatism and tectonics of the east- Rev. Esp. Micropaleontol., 32(1), 61–78. ernmost sector of the Calama–Olacapato–El Toro fault system in Central Ramos, V. A. (2008), The basement of the central Andes: The Arequipa Andes at ∼24°S: Insights into the evolution of the Eastern Cordillera, and related terranes, Annu. Rev. Earth Planet. Sci., 36, 289–324, Geol. Soc. Am. Bull., 120, 1493–1517, doi:10.1130/B26109.1. doi:10.1146/annurev.earth.36.031207.124304. McGlue, M. M., and A. S. Cohen (2006), The evolution of topographic Ramos, V. A. (2009), Anatomy and global context of the Andes: Main closure and foreland basin lakes: A modern time‐slice perspective from geologic features and the Andean orogenic cycle, Mem. Geol. Soc. the Andes, Geol. Soc. Am, Abstr. Programs, 38(7), 368. Am., 204,31–66. McKenzie, D. (1978), Some remarks on the development of sedimentary Reutter, K.‐J., R. Döbel, T. Bogdanic, and J. Kley (1994) Geological map basins, Earth Planet. Sci. Lett., 40,25–32, doi:10.1016/0012-821X(78) of the Central Andes between 20° and 26°S, in Tectonics of the Southern 90071-7. Central Andes,editedbyK.‐J. Reutter, E. Scheuber, and P. J. Wigger, McQuarrie, N. (2002a), The kinematic history of the central Andean fold‐ scale 1:1,000,000, Springer, Berlin. thrust belt, Bolivia: Implications for building a high plateau, Geol. Soc. Reyes, F. C., and J. A. Salfity (1973), Consideraciones sobre la estratigrafía Am. Bull., 114,950–963, doi:10.1130/0016-7606(2002)114<0950: del Cretácico (subgrupo Pirgua) del noroeste Argentino, Actas Congr. TKHOTC>2.0.CO;2. Geol. Argent., 5, 355–385. McQuarrie, N. (2002b), Initial plate geometry, shortening variations, and Reynolds, J., C. Galli, R. Hernández, B. Idleman, J. Kotila, R. Hilliard, and evolution of the Bolivian orocline, Geology, 30, 867–870, doi:10.1130/ C. Naeser (2000), Middle Miocene tectonic development of the Transition 0091-7613(2002)030<0867:IPGSVA>2.0.CO;2. Zone, Salta Province, northwest Argentina: Magnetic stratigraphy from McQuarrie, N., B. K. Horton, G. Zandt, S. Beck, and P. G. DeCelles the Metán Subgroup, Sierra de González, Geol. Soc. Am. Bull., 112(11), (2005), Lithospheric evolution of the Andean fold–thrust belt, Bolivia, 1736–1751, doi:10.1130/0016-7606(2000)112<1736:MMTDOT>2.0. and the origin of the central Andean plateau, Tectonophysics, 399, CO;2. 15–37, doi:10.1016/j.tecto.2004.12.013.

29 of 30 TC6013 DECELLES ET AL.: ANDEAN FORELAND BASIN TC6013

Reynolds, J. H., R. M. Hernández, C. I. Galli, and B. D. Idleman (2001), record in northwestern Argentina, J.SouthAm.EarthSci., 14, Magnetostratigraphy of the Quebrada La Porcelana section, Sierra de 763–774, doi:10.1016/S0895-9811(01)00066-9. Ramos, Salta Province, Argentina; age limits for the Neogene Orán Starck, D., and A. Schulz (1996), La configuración structural del limite Group and uplift of the southern Sierras Subandinas, J. South Am. Earth entre Cordillera Oriental y Sierras Subandinas en el extremo norte de Sci., 14, 681–692, doi:10.1016/S0895-9811(01)00069-4. la Republica Argentina, Bol. Inf. Petrol., 52,39–46. Roeder, D. (1988), Andean‐age structure of Eastern Cordillera (province of Starck, D., and G. Vergani (1996), Desarrollo tecto‐sedimentario del La Paz, Bolivia), Tectonics, 7,23–39, doi:10.1029/TC007i001p00023. Cenozoico en el sur de la Provincia de Salta—Argentina, Congr. Geol. Salfity, J. A., and R. Marquillas (1994), Tectonic and sedimentary evolu- Argent., 8, 433–452. tion of the Cretaceous–Eocene Salta Group, Argentina, in Cretaceous Strecker, M. R., R. N. Alonso, B. Bookhagen, B. Carrapa, G. E. Hilley, Tectonics of the Andes, Earth Evolution Sciences, edited by J. A. Salfity, E. R. Sobel, and M. H. Trauth (2007), Tectonics and climate of the pp. 266–315, Vieweg, Heidelberg. southern Central Andes, Annu. Rev. Earth Planet. Sci., 35,747–787, Schlunegger, F., T. E. Jordan, and E. M. Klaper (1997), Controls of doi:10.1146/annurev.earth.35.031306.140158. erosional denudation in the orogen on foreland basin evolution: The Strecker, M. R., G. E. Hilley, B. Bookhagen, and E. R. Sobel (2011), Oligocene central Swiss Molasse Basin as an example, Tectonics, 16, Structural, geomorphic and depositional characteristics of contiguous 823–840, doi:10.1029/97TC01657. and broken foreland basins: Examples from the eastern flanks of the Sempere, T., R. F. Butler, D. R. Richards, L. G. Marshall, W. Sharp, and central Andes in Bolivia and NW Argentina, in Tectonics of Sedimen- C. C. Swisher (1997), Stratigraphy and chronology of Late Cretaceous‐ tary Basins: Recent Advances, edited by C. Busby and A. Azor, Blackwell, early Paleogene strata in Bolivia and northwest Argentina, Geol. Soc. Cambridge, Mass., in press. Am. Bull., 109, 709–727, doi:10.1130/0016-7606(1997)109<0709: Tassara, A., C. Swain, R. Hackney, and J. Kirby (2007), Elastic thickness SACOUC>2.3.CO;2. structure of South America estimated using wavelets and satellite‐derived Sheffels, B. M. (1990), Lower bound on the amount of crustal shortening in gravity data, Earth Planet. Sci. Lett., 253,17–36, doi:10.1016/j. the central Bolivian Andes, Geology, 18,812–815, doi:10.1130/0091- epsl.2006.10.008. 7613(1990)018<0812:LBOTAO>2.3.CO;2. Uba, C. E., C. Heubeck, and C. Hulka (2006), Evolution of the late Sinclair, H. D., B. J. Coakley, P. A. Allen, and A. B. Watts (1991), Simu- Cenozoic Chaco foreland basin, southern Bolivia, Basin Res., 18, lation of foreland basin stratigraphy using a diffusion model of mountain 145–170, doi:10.1111/j.1365-2117.2006.00291.x. belt uplift and erosion: An example from the central Alps, Switzerland, Uba, C. E., J. Kley, M. R. Strecker, and A. K. Schmitt (2009), Unsteady Tectonics, 10, 599–620, doi:10.1029/90TC02507. evolution of the Bolivian Subandean thrust belt; the role of enhanced Sobel, E. R., and M. R. Strecker (2003), Uplift, exhumation and precipita- erosion and clastic wedge progradation, Earth Planet. Sci. Lett., 281, tion: Tectonic and climatic control of Late Cenozoic landscape evolution 134–146, doi:10.1016/j.epsl.2009.02.010. in the northern Sierras Pampeanas, Argentina, Basin Res., 15, 431–451, Xie, X., and P. L. Heller (2009), Plate tectonics and basin subsidence, Geol. doi:10.1046/j.1365-2117.2003.00214.x. Soc. Am. Bull., 121,55–64. Sobolev, S. V., and A. Y. Babeyko (2005), What drives orogeny in the Yuan, X., et al. (2000), Subduction and collision processes in the central Andes?, Geology, 33, 617–620, doi:10.1130/G21557.1. Andes constrained by converted seismic phases, Nature, 408, 958–961. Sobolev, S. V., A. Y. Babeyko, I. Koulakov, and O. Oncken (2006), Mech- Yuan, X., S. V. Sobolev, and R. Kind (2002), Moho topography in the anism of the Andean orogeny: Insight from the numerical modeling, in central Andes and its geodynamic implications, Earth Planet. Sci. Lett., The Andes: Active Subduction Orogeny,editedbyO.Onckenetal., 199, 389–402, doi:10.1016/S0012-821X(02)00589-7. pp. 513–535, Springer, Berlin. Soreghan, G. S., M. J. Soreghan, and M. A. Hamilton (2008), Origin and B. Carrapa, P. G. DeCelles, and G. E. Gehrels, Department of significance of loess in late Paleozoic western Pangaea: A record of trop- Geosciences, University of Arizona, 1040 E. 4th St., Tucson, AZ 85721, ical cold?, Palaeogeogr. Palaeoclimatol. Palaeoecol., 268, 234–259, USA. ([email protected]) doi:10.1016/j.palaeo.2008.03.050. B. K. Horton, Department of Geological Sciences, Jackson School of Starck, D., and L. M. Anzótegui (2001), The late Miocene climatic change — Geosciences, University of Texas at Austin, 1 University Station C1100, Persistence of a climatic signal through the orogenic stratigraphic Austin, TX 78712, USA.

30 of 30