Sedimentation Model of Piggyback Basins: Cenozoic Examples of San Juan Precordillera, Argentina

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Sedimentation model of piggyback basins: Cenozoic examples of San Juan Precordillera, Argentina

J. SURIANO1*, C. O. LIMARINO1, A. M. TEDESCO1,2 & M. S. ALONSO1 1IGeBA-Departamento de Ciencias Geolo´gicas, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires-CONICET, Intendente Guïraldes 2160 – Ciudad Universitaria-Pab.II-CABA, C1428EGA, Buenos-Aires, Argentina 2Present Address: SEGEMAR (Servicio Geolo´gico Minero Argentino). Av. General Paz 5445 Edificio 14 y Edificio 25 San Martıń (B1650 WAB), Buenos-Aires, Argentina *Corresponding author (e-mail: [email protected])

Abstract: Piggyback basins are one of the most important sediment storage systems for foredeep basins within foreland basin systems, so understanding the dynamics of sediment accumulation and allocyclic changes is essential. Three alluvial systems are proposed here to depict sediment movement along the piggyback basin: piedmont, axial and transference systems. We propose differen- tiation between open continental piggyback basins that include a transference system that is able to deliver sediment to the foredeep and closed piggyback basins that are isolated. Two idealized models of sedimentation in piggyback basins are proposed. For open piggyback basins we identify four stages: (a) the incision stage; (b) the confined low accommodation system tract; (c) the high accommodation system tract; and (d) the unconfined low accommodation system tract. Meanwhile two stages are proposed for closed ones: (a) the high accommodation system tract; and (b) the low accommodation system tract. To test these models, Quaternary deposits and a Miocene unit are analysed. The first one is controlled by climatic changes, and the second is related to tectonic activity in the Precordillera.

Most of the research in foreland basin systems foreland basin record that is eroded as the orogenic (DeCelles & Giles 1996) has been focused on the front advances can be preserved in the piggy- evolution of the foredeep region and its relation back basins. to the orogenic wedge and the forebulge areas In this contribution the piggyback basins located (Jordan 1981, 1995; Beaumont et al. 1988; Flem- along the Precordillera in the Argentinian Andes ings & Jordan 1989; Mitrovica et al. 1989; Holt & (San Juan Province, 30–318S, Fig. 1) are analysed. Stern 1994; Johnson & Beaumont 1995; DeCelles This study intends to characterize the sedimenta- & Giles 1996; Limarino et al. 2001; DeCelles & tion patterns and dynamics of piggyback basins as Horton 2003). These models are useful in under- well as to propose a new classification and to estab- standing the sedimentary patterns in the foredeep lish a sequence stratigraphic model. In order to as well as in establishing the close relationship accomplish these goals, the work is divided in two between tectonism and sedimentary filling. sections. First, a stratigraphic model based on the Even though they comprise a major storage sys- changes in the accommodation space is built, taking tem of sediments that can feed the foredeep, much into account the analysis of piggyback basins, their less attention has been paid to piggyback basins, definition, main sedimentological features, sedi- developed between thrust sheets, particularly the mentary environments, stacking patterns and rela- continental ones. Therefore, understanding the sedi- tionship with allocyclic controls. In the second mentary dynamics of piggyback areas is impor- part, the proposed model is tested, analysing two tant because: (a) piggyback basins are a significant stratigraphic successions (Quaternary deposits and reservoir of sediments exported periodically to Miocene Cuesta del Viento Formation) of the the foreland (DeCelles & Giles 1996; Horton & Jaćhal River area, controlled by climatic and tec- DeCelles 2001; Suriano & Limarino 2006); (b) the tonic changes. volume of exported sediments from piggyback basins may even exceed the volume supplied by the orogenic front to the foredeep; (c) the strati- Piggyback basin concept graphic record gives direct information about the uplifting of the different thrusts sheets and the The piggyback basins were defined by Ori & Friend advance of the clastic wedge; and (d) part of the (1984) as ‘basins that are formed and filled up while

From:Sepu´ lveda, S. A., Giambiagi, L. B., Moreiras, S. M., Pinto, L., Tunik, M., Hoke,G.D.&Farı´as, M. (eds) 2015. Geodynamic Processes in the Andes of Central Chile and Argentina. Geological Society, London, Special Publications, 399, 221–244. First published online February 28, 2014, http://dx.doi.org/10.1144/SP399.17 # 2015 The Geological Society of London. For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

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Fig. 1. Location maps. (a) Morphotectonic units related to the Andean orogen at 308S; numbers indicate the three major sectors of the Precordillera (1, western; 2, central and 3, eastern), the white frame shows the location of (b). (b) Geological map, where two main domains can be recognized: mainly granitic and volcanic (Cordillera) in the west and a metasedimentary one in the east (Precordillera); the frame shows the location of Figure 7. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

SEDIMENTATION MODEL OF PIGGYBACK BASINS 223 being carried on top of thrust sheets’. This term sorted breccias and conglomerates directly from is similar to ‘satellite basins’ proposed by Ricci the mountain front to the floor of the basin. This Lucchi (1986). Thrust-top basins or parched basins environment includes taluses, different kinds of (Turner 1990; Butler & Grasso 1993; Butler et al. colluvial fans (Bilkra & Nemec 1998), alluvial fans 1995; Bonini et al. 1999; Doglioni et al. 1999; and alluvial slopes. In the case studied here, four Hesse et al. 2010) have a related meaning, although piedmont associations related to accommodation they indicate a more specific arrangement associ- space were recognized (Fig. 3; Suriano & Limarino ated with basins that are formed and filled up 2009). As the piedmont area has permanent avail- while a portion of the foreland basin is dismantled. ability of material from the mountain front, the According to the above, piggyback and satellite movement of sediment is regulated by axial sys- basins are synonymous, and they are related to tems and, if present, by the transference system. thrust-top and parched basins. Years later, piggy- Sediment transport along the elongate axis of back basins were included by DeCelles & Giles the piggyback basins is represented by longitudinal, (1996) in their wedge-top depozone within the fore- frequently braided channels (the collector river– land system. Gugliotta (2012) divides the wedge- conoid systems of Suriano & Limarino 2009). As top depozone in inner and outer sequences. In this shown by Suriano & Limarino (2009), these sys- paper, we follow this terminology, using the term tems are defined as conoids and the associated col- inner-wedge-top depozone for the piggyback area, lector river as axial distributary systems. which designates basins separated from the foreland Finally, the transference systems (Fig. 2) con- by thrust sheets or anticlines, while the outer- nect piggyback basins among them and to the fore- wedge-top depozone is where blind thrust structures land basin. These transference systems can be have no superficial expression. This last zone transi- represented by different kinds of rivers or even by tionally passes into the foredeep. open lacustrine arrangements. Regarding this occurrence, we propose that continental piggyback basins (Type 2 of Wagerich Sedimentary dynamics of piggyback basins 2001) can be classified into two main types, open and closed (Fig. 4). The open piggyback basins To understand the auto and allocyclic factors that are those including a transference system that con- could affect sedimentation in piggyback basins, it nects them and is able to export sediment to the fore- is essential to inspect the sediment movement land. Closed piggyback basins do not have a pattern all along the basin. Based on the studied transference system, which makes them endorreic. examples, the pattern of sediment circulation in con- A piggyback basin can shift from open to closed tinental piggyback basins is here related to three and vice versa owing to allocyclic factors, not alluvial systems (Fig. 2). The first one corresponds only tectonics, directly related to the evolution to the piedmont systems, which convey poorly of the fold and thrust belt, but also climatic

Fig. 2. Schematic distribution of the sedimentary circulation in piggyback basins. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

224 J. SURIANO ET AL.

Fig. 3. Arid piedmont associations for the Precordillera (modified from Suriano & Limarino 2009). Highest energy corresponds to association 1, composed of taluses and colluvial fans with steeper slopes; if there is enough lateral space this association could evolve into association 2. Association 3 is related to gentle slope mountain fronts as much as association 4, which develops in wider valleys and evolved drainages. modifications that affect the erosion capability of basin and transference system. Highly efficient the transference system. transference systems are those able to export all Open piggyback basins can change from highly the sediment delivered by piggyback basins to efficient to inefficient (or vice versa) according to the foredeep (Fig. 4). In contrast, a transference the efficacy of the major sediment exporter system system is inefficient if it is not able to transport formed by the fluvial systems inside the piggyback the material from the piggyback to the foredeep

Fig. 4. Piggyback basin classiﬁcation proposed in this work. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

SEDIMENTATION MODEL OF PIGGYBACK BASINS 225

(Fig. 4), which leads to the storage of sediment activity of the downstream thrust (Fig. 5c). Efficacy inside the piggyback basin. of this last factor is limited as major movements Before building a sedimentary model for piggy- produce narrowing and shallowing of the basins, back basins it is important to examine the factors which decreases the accommodation space (Fig. that control their patterns of sedimentation. They 5d; Talling et al. 1995). Lower local A/S ratio can be local if they affect each basin individually could also be generated by a downstream river or regional if they have influence over the entire capture (Fig. 5e). orogenic wedge. Another equally significant aspect There are also regional factors affecting the to take into account is if those factors affect the A/S relationship. Increase of the A/S ratio owing accommodation space (A) and/or the sediment to subsidence is related to the structural arrange- supply (S). These factors and their effects are ment and dynamics of the orogenic wedge, with shown in Figure 5. regard to tectonic loading and to slab pull (Fig. A local factor that increases the relationship 5f). Decrease in the accommodation space is A/S is the upstream thrust movement (Fig. 5a). instead associated with periods of tectonic quietness This factor produces an increase in the accommo- and isostatic rebound (Fig. 5h). Fluvial equilibrium dation space in the footwall as well a higher sedi- profiles, independently of their driving force, ment supply from the hanging wall. Another way could rise (Fig. 5g) or fall (Fig. 5i), causing an of increasing accommodation space is a local base increase or decrease in the accommodation space. level rise (Fig. 5b, c). This could be generated by Finally, dramatic changes in the amount of sedi- a sediment dam within the basin (Fig. 5b) or by ment production, owing to climatic factors or the

Fig. 5. Allocyclic controls on piggyback sedimentation. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

226 J. SURIANO ET AL. occurrence of explosive volcanism, should be taken sequences while hinterland-directed depocentre into account. migration seems to be related to out-of-phase thrust- The piggyback sedimentary models presented ing (Zoetemeijer et al. 1993). In the same way here are based on the principles of sequence strati- Bonini et al. (1999) showed that the depocentre graphy in continental environments (e.g. Shanley migration is controlled by the thrust having the & McCabe 1994; Quirk 1996; Dahle et al. 1997; highest displacement rate. Dalrymple et al. 1998; Blum & To¨rnqvist 2000; Sequence deposition is essentially ruled by the Miall 2002). According to Dahle et al. (1997), two above factors, which affect the A/S relationship. major stages can be recognized in continental On this basis we propose a sequence stratigraphy basins disconnected of the sea-level: (a) the high model for open piggyback basins involving: (a) accommodation system tract; and (b) the low the incision stage; (b) the confined low accommo- accommodation system tract. This proposal detaches dation system tract; (c) the high accommodation system tracts from sea-level and relates them system tract; and (d) the unconfined low accommo- to changes in accommodation space (Catuneanu dation system tract or overfill stage (Fig. 6). 2006). Following Shanley & McCabe (1994) and The first stage or incision stage begins with an Dalrymple et al. (1998), discontinuities generated important drop in the equilibrium profile (a in by fluvial incision are used here as sequence Fig. 6) that produces incision in the transference boundaries. Two kinds of erosive bounding sur- system and generates the entrenchment of the pied- faces were recognized according to their degree mont system and the development of an incision of confinement (confined or unconfined). Finally surface across the basin (incision stage, a in Fig. 6). the existence of sedimentological evidence of the As Shanley & McCabe (1994) pointed out, even in presence of a fluvial transference system can be high-incision events some remnant deposits can used to differentiate open from closed piggyback be found in the sides of the valley owing to basins, a concept that is also incorporated in the short moments of stabilization during this mainly proposed model. erosive phase. The confined low accommodation system tract can be separated into two substages. The first one Model for piggyback basins takes place following the incision stage when there is a time of relative instability during which the Using the elements mentioned above we construc- river profile is close to equilibrium, generating the ted a sedimentary model for continental piggyback infilling of incised transference system deposits basins that is based on the temporal variations of (b in Fig. 6). In this stage deposition of a coarsening- accommodation space and sediment supply. These up incised channel complex can be observed (Catu- changes are based in four supporting elements: neanu 2006). The amount of sediment involved (a) basin subsidence; (b) tectonic activity in the during this stage relates to the time span of this fold and thrust belt; and (c) changes in sediment unstable situation and therefore it is not always amount by climatic changes and/or major explosive recognized. The next stage occurs when the river volcanism. profile reaches or is slightly above the equilibrium Subsidence in piggyback basins has been profile. At that point slow aggradation takes place considered short-lived and of much smaller magni- in the previously eroded piggyback area (c in tude than that at the associated foredeep (Xie & Fig. 6). This stage is denoted by the presence of Heller 2009). In fact, subsidence owing to tectonic amalgamated high-energy braided channels, gen- loading, a major mechanism in foreland basins erated by the transference system and also by (Jordan 1981; Naylor & Sinclair 2008), has lower limited aggradation in the piggyback area. values in piggyback areas (Zoetemeijer et al. 1993; If the rise of the equilibrium profile continues, Xie & Heller 2009). The key factor in the creation the transference system produces high aggrada- of local accommodation space in most piggy- tion in its alluvial plain, promoting high equilib- back basins is the tectonic activity in the upstream rium profiles in the axial and piedmont systems thrust sheet (tectonically induced accommodation, and the consequent filling of the piggyback basins Fig. 5a), which in turn produces migration of the (high accommodation system tract, d in Fig. 6). As depocentre (Bonini et al. 1999; Zoetemeijer et al. the sediment supply from the mountain front is 1993). In this sense, migration of the depocentres more or less continuous, if no new accommodation in piggyback basins has been associated with space is created, the basin tends to fill up, reaching passive rotation of the internal thrusts owing to the the unconfined low accommodation system tract successive external thrust activation (Bonini et al. (or overfill stage, e in Fig. 6). 1999; Roure 2008) or active thrusting. In this For closed piggyback basins, only two stages last case, migration of the depocentre towards the are proposed. Initially, when the basin is created, foredeep has been interpreted as in-phase thrusting the A/S ratio is high, so there is also high Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

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Fig. 6. Proposed model for piggyback basin evolution. (a) Schematic sedimentary section. (b) Transference system proﬁle and its equilibrium proﬁle through time. Numbers relate to time. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

228 J. SURIANO ET AL. accommodation space. This stage is dominated by basins was analysed in detail. Taking into account fine-grained playa lake deposits (f in Fig. 6) with the presence of incision surfaces, resulting in deca- an external ring of coarse piedmont facies. Again, metric- to metric-scale relief, the sedimentary infill if there is no newly created accommodation space, of the four Jaćhal River piggyback basins (La the basin tends to fill up, and the overfill stage is Tranca, Caracol, Zanja Honda and Pachimoco) developed. This stage is represented by the was divided into four depositional sequences (Fig. progradation of low-energy piedmont associations 8). The Pleistocene–Holocene sequences studied (2 in Fig. 3) like alluvial slopes and fluid flow- here do not show evidence of significant tectonic dominated colluvial fans and a marked decrease in disturbance. This suggests that tectonic uplift of the area previously occupied by playa lake depos- thrust sheets was not a main mechanism to pro- its. The late stage of this system tract is character- duce changes in the accommodation space during ized by a decrease in sediment supply associated Pleistocene–Holocene times. Moreover, the lack with an extensive aeolian reworking and develop- of evidence of volcanic activity (Kay et al. 1988) ment of a desert pavement. sets climate change as a major allocyclic control for sedimentation in these basins. In addition, the sequence’s age fits with regional climate changes Stratigraphic context (Iriondo 1999).

Between 308 and 318S, the Andean orogen is Depositional sequences made up of five morphotectonic units (Fig. 1a): (a) western and higher Cordillera de los Andes; (b) Sequence I: pediment. The base of this unit is the wide intermontane Rodeo–Iglesia Basin; (c) formed by a low-relief erosive pedimentation sur- the fold and fault thrust belt of Precordillera; (d) face on Miocene and Palaeozoic deformed rocks. the Bermejo Basin; and (e) the Pampean Ranges. Over this unconformity a relatively thin layer (up In this area the Cordillera Frontal (part of (a)) is to 10 m thick) of Quaternary deposits is found composed of a Carboniferous metasedimentary (Fig. 8). These deposits are dominated by mono- rocks (Cerro de Agua Negra Formation), Triassic mictic breccias of piedemont accumulations with batholiths (Llambıás & Sato 1990) and Triassic minor participation of lenses of polimictic con- to Miocene volcanic rocks (Ramos 1999). To the glomerates. east, the wide Rodeo-Iglesia Basin is developed, The monomictic breccias are fine-grained and where Cenozoic volcaniclastic rocks are exposed. occur mainly as clast-supported tabular, massive The Precordillera belt is divided into three struc- or horizontally stratified beds. Lenticular bodies of tural provinces (Fig. 1a): western, central and massive mud-supported breccias interbedded with eastern (Ortiz & Zambrano 1981). The studied clast-supported breccias are scarce. The latter area is located within the western Precordillera show planar cross-bedding or clast imbrications, (Fig. 1b), which has been built since the Early and it is worth mentioning that their scarcity does Miocene (Jordan et al. 1993, 2001; Cardozo & not allow a statistical measurement of palaeocur- Jordan 2001; Alonso et al. 2011) by eastward rents. Clasts are pebbles, mainly slates (more than migration of the orogenic front. The thin-skinned 95%) and basic volcanic rocks derived from the fold and thrust belt of the western Precordillera Yerba Loca Formation, which indicates local prove- expose Early Palaeozoic rock sheets that contain nance as it is the sole unit outcropping in the Pre- the Miocene to Holocene piggyback sedimentation. cordillera in the area. Deposits are interpreted as In particular, we studied the Quaternary piggyback having formed in alluvial slopes (Smith 2000) basins along the Jaćhal River (Figs 1b & 7) and with minor participation of colluvial fans (Bilkra the Cuesta del Viento Formation, a Miocene unit & Nemec 1998), so they can be interpreted as a deposited within the same stratigraphic context low-energy piedmont association (2 in Fig. 3). (Fig. 7). The western Precordillera is characterized The infrequent polimictic conglomerates are by its west vergence of thick-skinned structures coarse, well-rounded and clast-supported. They (Zapata & Allmendinger 1996). Finally, Bermejo show imbrication, horizontal and planar cross- Basin separates the Precordillera from the basement bedding. They appear as lenticular to lentiform uplifted blocks of Pampean Ranges. beds and are interpreted as gravel bars in a multi- channelized fluvial system. Cobbles are dominated by granites and acid volcanics fragments. These Dynamics of the Quaternary piggyback lithologies are widely present at the Colanguïl Cor- basins of Jaćhal River area dillera located to the west (Fig. 1b), indicating an external provenance. An ancient transference sys- In order to apply the models described to the Jaćhal tem (ancient Jaćhal River) draining the Precordil- River area, the Quaternary filling of the piggyback lera from west (Cordillera de los Andes) to east Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

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Fig. 7. Detailed geological map of La Tranca Valley. See Figure 1b for general location.

(present day foredeep) can be interpreted from the Deposits are few and scattered, with relatively clast composition of this conglomerate unit. small thicknesses (up to 25 m). This unit is dominated by polimitic conglomerates with scarce inter- Sequence II: Quaternary incised valley. The lower calations of gravelly sandstones. boundary of Sequence II is a high relief surface The polimictic conglomerates are coarse to carved on Quaternary deposits of Sequence I, very coarse and clast-supported, with erosive base, Miocene or Palaeozoic rocks (Figs 8 & 9a). and occur as massive or planar cross-bedded beds. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

230 J. SURIANO ET AL.

Fig. 8. Schematic distribution of the Quaternary sequences and ages in the Ja´chal Valley.

The clasts (sized up to boulders) are rounded to sandstones; (b) monomictic roughly stratified brec- well-rounded, compositions are granite and acid- cias; and (c) polimictic conglomerates. volcanic (reflecting external provenance), with lit- The fine-grained association is dominant and is tle participation of greenish grey and yellow sand- formed mainly by muddy and sandy lithofacies (1 stones, quartz and greenish slates. The gravelly in Fig. 11a, c) with scarce breccias. Tabular beds sandstones have planar or trough cross-bedding. of whitish grey mudstones with horizontal lami- The described facies are interpreted as ancient nation or massive are abundant. Mudstones com- Jaćhal River deposits, as they are similar to the monly show root marks and mudcracks and there present Jaćhal River, sharing the provenance, lithol- are also some levels with shells of freshwater ogy and sedimentary structures. Occasionally, brec- gastropods (Colombo et al. 2005) and others with cias associated with taluses, coluvial fans and plant remains. Brown shales with high contents of collector rivers (piedmont and axial systems) are organic matter are present, though scarce. Gypsum interbedded within the fluvial conglomerate. levels are present towards the top. Light brown We correlate this sequence with an important sandstones are massive or with ripple lamination, erosive event responsible for the generation of and some planar cross-bedded structures are also the lowest Quaternary valley floor, which can be found. traced up to Llano del Me´dano, an upstream site Fine-grained lithofacies are interpreted as pro- (Fig. 1b), where the incision is evidenced by sev- duced by both decantation and underflows, which eral hundred metres of relief between the oldest according to May et al. (1999) can take place in Quaternary deposits and the valley floor (Suriano shallow lacustrine environments. The ephemeral & Limarino 2006). The eroded material was prob- nature of the lake system is inferred by the root ably exported from the piggyback area and formed marks, mudcracks and evaporite deposits at the two megafans (Damanti 1993; Horton & DeCelles top of the association (May et al. 1999; Colombo 2001) that can currently be seen at the mouth et al. 2009). Massive sandstones represent rapid of Huaco and Jaćhal Rivers in the Bermejo Valley deposition from sheet floods. Horizontally lami- (Fig. 10). nated sandy lithofacies record the migration of sub- aqueous micro- and mesoforms and represent the Sequence III: sedimentary dams. The lower bound- coastal zone of the lake when dominant. ary of this sequence largely fits the incision marking The palynological assemblage of these lacus- the base of Sequence II (Fig. 8). Above this surface, trine deposits has been studied by Colombo et al. there is one of the thickest and best preserved (2009), who proposed periods of heavy rain, alter- Quaternary units in the area, characterized by the nating with episodes of extreme aridity in a warm presence of conspicuous intermontane shallow climate for the base of the section, turning arid lacustrine sediments (Colombo et al. 2000, 2005, towards the top. Colombo et al. (2005) dated 2009; Suriano & Limarino 2005, 2008, 2009). gastropods shells and organic matter by 14C tech- Deposits of these natural dams can be found in nique obtaining ages from 8930 + 50 (near the Rodeo, La Tranca, Caracol and Zanja Honda base of the lacustrine deposits) to 6497 + 45 basins, all of them with similar characteristics. years BP (in the upper part). These ages indicate Three main facies associations could be recognized that the lacustrine system persisted for at least in the lacustrine system: (a) siltstones and fine 2700 years. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

SEDIMENTATION MODEL OF PIGGYBACK BASINS 231

Fig. 9. (a) Quaternary valley carved on Miocene aeolian units. (b) Deposits of Sequence IVa in the Pachimoco area; the white arrow shows the abundant bioturbation in the ﬂoodplain deposits; the red line shows the scale. (c) Massive matrix-supported chaotic breccias (Bmm) of facies association 1, Cuesta del Viento Formation. (d) Mudstones with polimictic conglomerates in coarsening-up arrangements of facies association 4, Cuesta del Viento Formation; the red bar is 1.5 m long. (e) Mudstones with monomictic breccias in coarsening-up arrangements belonging to facies association 5, Cuesta del Viento Formation. (f ) Close view of the coarsening-up cycles of facies association 5; the red bar is 1.5 m long.

This fine-grained association alternates with Breccias are clearly dominant downstream (2 in breccia levels. Roughly stratified matrix- and clast- Fig. 11c), and are interpreted as conoids (axial dis- supported monomictic breccias appear as tabular tributaries systems). As they always occur down- massive beds. Some of them also show imbricated stream from the lacustrine deposits, these breccias clasts, normal gradation or planar cross-bedded stra- are interpreted as resulting from the dam closure tification. Massive and laminated mudstones occur (Fig. 11d, Colombo et al. 2000, 2009 Suriano & to the top of some bodies. Limarino 2005). Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

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Fig. 10. Satellite image of Huaco and Ja´chal megafans.

While downstream the muddy lacustrine associ- related to a high equilibrium profile in the transfer- ation pinches out into conoid facies, upstream ence system owing to the damming that also caused intercalations of polimictic conglomerates become a local level rise in the whole piggyback basin, so frequent (at left in Fig. 11c), forming the last that aggradation was favoured. This led to the depo- facies association. The beds of polimictic conglom- sition of thick units in conoids and collector rivers erate form biconvex beds from 2 to 7 m in thick- (axial systems) as well as in the piedmont areas. ness. They show horizontal, planar cross-bedded or massive structures. Between the conglomeratic Sequence IV Jaćhal River. This stage is developed beds, sandy facies are common, forming beds up over an important incision surface that corresponds to 1 m with a coarsening upward arrangement (3 to the present Jaćhal River Valley (Fig. 8) and in Fig. 11b). includes two subsequences. The first subsequence The interpretation of these deposits and their (IVa) involves the highest terraced levels dated by lateral variations is shown in Figure 12. Fine- Colombo et al. (2005) in La Tranca area between grained sediments are found at the centre zone of 978 + 20 and 525 + 32 years BP. This unit is the lake (Fig. 11a). In the upstream area, the trans- composed of two types of deposits, the first charac- ference system (ancient-Jaćhal River) flowing into terized by clast-supported conglomerates and sand- the lake generated a microdeltaic arrangement stones with lenticular to lentiform geometry, which (Fig. 11b). Figure 11c shows the natural dam depos- represents channel facies, and the second corre- its represented by the light grey fine lacustrine sedi- sponding to tabular mudstones floodplain beds. ments that laterally pinch out to the downstream The conglomerates of the channel facies have conoid breccias (dark grey) responsible for the clasts of granite and acid volcanic rocks, indicating dam closure. The above-described arrangement is a foreign provenance similar to those of the Stage II, Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

SEDIMENTATION MODEL OF PIGGYBACK BASINS 233

Fig. 11. Scheme and pictures from the Quaternary lacustrine arrangement. (a) Dam–lacustrine fine-grained association. (b) Coarsening-up cycles from a micodeltaic system. (c) Closure of a dam represented by conoid facies, lateraly related to fine dam–lacustrine facies. (d) Scheme of the dam facies; numbers in the scheme correspond to those shown in the photos. but clasts have a smaller mean diameter (minor to the geometry of the beds, they are interpreted as 30 cm). There are two types of channel arrange- migrating in a conglomeratic channel of low to ments according to their hierarchy; the first one is medium sinuosity. dominated by polimictic clast-supported conglom- The second type of channel facies (Fig. 9b) erates. Some of the beds begin with massive comprises gravelly sandstone or sandstone lenti- or imbricate conglomerates, but overlying clast- form to lenticular beds. Massive or horizontally supported conglomerates are a conspicuous litho- laminated fine-grained conglomerates or gravelly facies, with planar cross-bedding and horizontal sandstones are found at the base. Above them, sand- stratification. On top of beds, gravelly sandstones stones with planar and trough cross-bedded strat- and sandstones with planar cross-bedded and hori- ification occur. This association is interpreted as zontal lamination are found. This arrangement cor- having been deposited by sinuous channels in responds to migrating transversal and longitudinal which longitudinal gravel bars and 2D and 3D gravelly bars (Hein & Walker 1977). Considering sand dunes migrated. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

234 J. SURIANO ET AL.

Fig. 12. Schematic section of the Quaternary sequences, with system tract interpretation and geological events that caused them (right column).

Floodplain beds are the dominant facies of the massive structures. They are greenish or light Subsequence IVa. They are formed by mudstones brown and have intense root bioturbation. Sporadic and subordinated sandstones. Mudstones show beds of planar cross-bedded, horizontally laminated horizontal lamination, ripple cross lamination or or massive sandstones are intercalated within Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

SEDIMENTATION MODEL OF PIGGYBACK BASINS 235 mudstones. The fine-grained lithofacies were addition to the incision surface between them, formed by decantation or low-energy fluid flows in the difference among Subsequences IVa and b is the waning of floods. These floodplains (Fig. 9b) the minor participation of fine-grained floodplain show different degrees of maturity (according to deposits in Subsequence IVb that could be des- Reinfelds & Nanson 1993), which range from inci- cribed as a bed load-dominated system intermediate pient to well evolved, this last one with important between braided and wandering (Miall 1996). development of palaeosols. During the flood events, the sandstones reach these areas with the migration of megaripples, plane bed or sudden Accommodation stages in the Quaternary deposition by competence loss. Precordillera’s piggyback basins In summary, this association is characterized by different hierarchy channels with low to inter- In this section, we present the evolution of the mediate sinuosity and extensive development of Quaternary sequences in the context of temporal confined floodplains (Nadon 1994) or cohesive changes in relative accommodation space and low-energy floodplains (Nanson & Croke 1992). sediment supply. The scenario before the deposition Therefore we interpret the subsequence IVa as an of Sequence I is a regional-scale erosive surface anastomosed fluvial system (Smith & Smith 1980; (pediment) carved into Palaeozoic to Miocene Nadon 1994), which represents the Early Holocene rocks (Figs 9a, 12 & 13). This low-relief surface dynamics of the Jaćhal River. indicates a long erosive period. Its origin cannot Subsequence IVa is best developed in Pachi- be stated unequivocally but may be associated moco area (Fig. 2), where a wider piggyback with a period of relative tectonic quiescence of the basin allowed for the deposition of large amounts fold and fault thrust belt. Tectonic quiescence of fine-grained deposits (Pachimoco Formation could have been related to an isostatic rebound after Furque 1979) of ancient Jaćhal River. Subse- phase owing to erosion, during which a slow but quence IVb includes the recent and present deposits continuous fall in the equilibrium profile (Fig. 13) of the Jaćhal River, younger than 525 + 32 years led to an important erosive event throughout the BP. Its lower limit is marked by a low relief entire orogenic wedge, generating a pedimentation surface (up to 5 m high) carved into the Subse- surface all over the piggyback area. That situation quence IVa deposits (Fig. 8). Above this surface, was followed by a small rise in the equilibrium the youngest terraces and active channels with profile that produced a relatively thin layer of brec- scarce floodplains of the Jaćhal River are found. In cias and conglomerates of Sequence I deposited in

Fig. 13. Changes in the accommodation space through time, and their relationship with different system tracts (at right) and with the Quaternary sequences. The black arrows show an increase in accommodation space and the white ones a decrease. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

236 J. SURIANO ET AL. an unconfined low accommodation system tract result of this, huge volumes of sediments eroded, (overfill stage; Fig. 12). promoting the deposition of large megafans (DeCel- Then, long-term degradation in the piggyback les & Cavazza 1999; Horton & DeCelles 2001) in area, which generated the present valley of the the foredeep. According to Damanti (1993), the Jaćhal River, took place. This phase had probably megafans of Huaco and Jaćhal reach areas of 700 begun in late Pleistocene and involved an intensive and 1400 km2 with catchment areas of 7100 and erosion period, with a low degree of discontinuous 27 700 km2, respectively. Owing to the huge stages of deposition in isolated patches which amount of sediment delivered to the foredeep, were gathered within Sequence II (incision stage; Bermejo River had to divert its course next to the Figs 12–14a). Pampean range. The origin of Sequence II is related to deglacia- Sequence III deposits represent the end of tion times that took place after the late glacial the deglaciation phase little before 8930 + 50 to maximum (isotopic stage 2; Iriondo & Kro¨ling beyond 6.497 + 45 years BP (Colombo et al. 1996; Iriondo 1999), when the Cordillera de los 2005), when a dramatic fall in the flow rates of Andes was glaciated (above 3500 m). During the the transference rivers occurred. This situation deglaciation (between 15 500 and 16 500 years favoured high rates of aggradation (up to 150 m BP; Iriondo & Kro¨ling 1996) melted ice generated thickness) and the occurrence of the high accommo- high discharge in rivers that drained the Andes, dation system tract (Figs 12 & 13) in the piggyback including the transference systems across the Pre- basins. Note that these ages, according to our cordillera (i.e. Huaco and Jaćhal Rivers), all of interpretation, are related to climatic amelioration them with catchment areas including large portions proposed by Iriondo & Kro¨ling (1996). During this of glaciated regions. The climate amelioration period, the loss of efficiency of the transference caused a higher flow of the transference fluvial system together with an increase in sediment systems that increased its efficiency and produced supply from piggyback basins could have produced the fall of the equilibrium profile (Fig. 13). As a the advance of these axial systems (conoid-collector

Fig. 14. Block diagrams of the Jaćhal River-related basins. C2 ¼ sediment transport efficiency of the longitudinal fluvial system; C3 ¼ sediment transport efficiency of the transference system. (a) Sequence II deposition arrangement scheme (mainly erosive phase, few related isolated deposits). (b) Sequence III deposition scheme. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

SEDIMENTATION MODEL OF PIGGYBACK BASINS 237 rivers) over the transference system valley. In by Suriano et al. (2011), located within the same addition, it would have led to the formation of the geographic context as the previous Quaternary numerous sedimentary dams (La Tranca, Caracol basins. These are the oldest synorogenic strata in and Zanja Honda), recorded at the margins of the the area and record the transition from outer- present Jaćhal River Valley (Figs 11c & 14b). The wedge-top to inner-wedge-top (piggyback basin) increase of sediment supply can be related to the sedimentation. The upper section was dated as humid period associated with the deglaciation Lower Miocene (19.5 + 1.1 and 19.1 + 1.3 Ma) proposed by Garcıá et al. (1999) for the southern by Jordan et al. (1993). Precordillera. It is also consistent with the pollen record of the base of the lacustrine sediments in Sedimentary environments the area studied by Colombo et al. (2009). Although thick monomictic breccias, from piedmont and This unit was studied in detail by Suriano et al. axial systems, were deposited in the piggyback (2011), who have defined six facies association area, it is important to point out that, despite the that are summarized here. local high sediment supply and the low efficiency of the transference system, the overfill stage was Facies association 1 (chaotic breccias). This facies never reached. This was probably due to the large association comprises monomitic breccias, with accommodation space created during the previous metamorphic clasts from the Yerba Loca Forma- stage (deglaciation; Figs 12 & 13). tion. They are dominated by coarse-grained chaotic A new incision surface, which contains terraces matrix-supported massive breccias (Fig. 9c) in beds and the present day alluvial belt of the Jaćhal up to 60 cm thick. Massive and imbricated clast- River, was carved into the lacustrine deposits of supported breccias in lenticular amalgamated beds the Sequence III, which form the lower boundary also appear. This is interpreted as a high energy of Sequence VIa. The origin of the change in the piedmont arrangement composed of hyperconcen- accommodation space between sequences III and trated flow-dominated colluvial fans, with some par- IVa is not clear, but it may have resulted from ticipation of taluses (1 in Fig. 3). the adjustment of the transference system to its regional base-level fall (the Bermejo River). This Facies association 2 (breccias). This facies was associated with the end of lacustrine system association is composed of breccias with the same sedimentation (the local-base level of the piggy- provenance as facies association 1, sandstones and back basins in Sequence III), which could be mudstones (Fig. 15). It is dominated by clast- related to the breaking of dams by connection with supported massive and imbricated breccias. Matrix- the foredeep (regional-base level) and/or the read- supported breccias appear as tabular bodies with justment to the new base level (probably falling by massive or strong parallel fabric deposited by hyper- a continued subsidence in the foredeep). For this concentrated flows (Bilkra & Nemec 1998). Sand- reason the Jaćhal River produced an incision in its stones and gravelly sandstones locally appear with valley in order to catch up with its new base level massive, planar cross-bedded or horizontal lami- (degradation stage in the base of Sequence IV; nation. These lithofacies are more common to the Figs 8, 12 & 13). This period of degradation, with top of the section (Fig. 15). Massive and laminated very limited or no aggradation, also reached the mudstones also appear as milimetric mud drapes piggyback area. From 978 + 20 to 525 + 32 years or as continuous centimetre-thick levels. BP (Colombo et al. 2005) the Jaćhal River had a This facies association is interpreted as braided short aggradation period recorded by Sequence river deposits, in particular a transitional system IVa, corresponding to a high accommodation sys- between gravel-bed braided with sediment-gravity- tem tract (Fig. 12). A minor incision surface (Figs flow and shallow gravel-bed braided types of 8 & 12) separates Sequence IVa from the present- Miall (1996). The full interpretation of this facies day fluvial deposits of the Jaćhal River, only inter- association depends upon its geomorphic context rupted by short episodes of aggradation limited to (Suriano et al. 2011). At both the bottom and the the transference system that form Sequence IVb. top of the section (Fig. 15) it appears as braided channels developed in piedmonts, colluvial fans and alluvial slopes, associated with proximal Ancient record of piggyback basin facies. In contrast, in the middle part of the unit an sedimentation in La Tranca alternation of transference and dam facies occurs, allowing their interpretation as collector river The proposed model for piggyback sedimentation deposits (axial systems). These interpretations are can also be applied to ancient settings. As an supported by the scarce clast imbrications observed example, we analysed the Cuesta del Viento For- (Fig. 15), which are not abundant enough to make a mation, a Miocene unit, described and proposed statistical analysis. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

238 J. SURIANO ET AL.

Fig. 15. Sedimentary section of Cuesta del Viento Formation and summary of its facies associations, characteristics and interpretation. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

SEDIMENTATION MODEL OF PIGGYBACK BASINS 239

Facies association 3 (polimictic conglomerates). lacustrine system deposits, dominated by decanta- This unit comprises lenses of coarse- to fine-grained tion processes and the prograding lobes of sandstone clast-supported conglomerates and sandstones. The sheetfloods or thin monomictic gravel bars with conglomerates bearing granites, mudstones, slates, local provenance (microdeltaic facies with local acid and ultrabasic volcanic clasts record a mix- provenance). ture of local and foreign provenance (Suriano et al. 2011). The conglomeratic lenses occur as mas- Facies association 6 (stratified breccias). This is sive beds or with imbricated or horizontally strati- made up of tabular beds of 10–20 cm of thickness fied structures, thus indicating the deposition of composed of fine to medium clast-supported brec- transversal gravel bars (Hein & Walker 1977). cias, imbricated or massive. Locally, some lenses Subordinately massive or horizontally laminated of planar cross-bedded stratification are found. sandstones appear as bar tops. Tabular beds of sand- Some palaeocurrent measurements indicate east to stones and mudstones, massive or laminated, depos- west direction of flow. This unit is interpreted as ited in a floodplain environment are also present. shallow channels with broad interchannel areas This facies association is interpreted as a low- dominated by gravel sheetfloods, corresponding to sinuosity river with channels of multiple hierar- alluvial slopes (Smith 2000) developed in a low- chies, similar to the deep gravel-bed braided river energy piedmont environment (2 in Fig. 5). of Miall (1996) or the Donjek type of Williams & Rust (1969). Owing to its lithology and environ- Basin evolution mental interpretation, this association is envisaged as a transference system, which represents the The Cuesta del Viento Formation records the ear- ancient Jaćhal River. liest stages of the Bermejo Foreland Basin (Jordan et al. 1993, 2001; Alonso et al. 2011; Suriano Facies association 4 (mudstones with polimictic et al. 2011), related to the uplift of the Sierra de conglomerates). Two fine-grained facies associ- La Tranca. The base of the unit (Figs 15 & 16, ations were recognized in this formation. The facies association 1 and 2) corresponds to wedge- facies association 4; Fig. 9d) is formed from top deposition in the inner wedge-top depocentre, coarsening-up cycles up to 20 m thick. The cycles represented by the development of high-energy are dominated by massive or slightly laminated and local provenance piedmont (Figs 16 & 17a). light brown mudstones, intercalated with fine- Overlying this basal unit, lower-energy piedmont grained sandstones. Deposition took place owing to facies were deposited, represented by braided chan- alternating processes of sheetfloods (Davis 1938) nels of colluvial fans. Finally, the last facies associ- and decantation. These facies are overlaid by sand- ations deposited in this basin correspond to the stones with ripple cross-lamination and planar ancient Jaćhal River, interbedded with colluvial cross-bedded, which are covered in turn by lenses fans (Fig. 16, facies associations 3 and 2). of polimictic conglomerates. Conglomerate com- As the Andean deformation advanced to the position is similar to that described in the facies east, the uplift of the Caracol Range started. This association 2, highlighting a mixing of local and phase represents the onset of the La Tranca area as external provenance. Conglomerate beds have an a piggyback basin configuration, and the deposition erosive base and appear as massive or planar cross of lacustrine and microdeltaic facies recording this stratification, deposited by channelized fluid flows. change (Fig. 16, facies association 4). The dam In summary, facies association 4 is interpreted as was, in this case, related to an increase in the local the occurrence of clastic ephemeral lake (natural accommodation space owing to the Caracol range damming) associated with microdeltaic bars facies uplift (Fig. 17b). Afterwards, the base level was related to ancient Jaćhal River. The fine-grained readjusted to the foreland, probably because the tabular facies are related to lacustrine deposits and damming was broken, an incision surface was the sandstones and conglomerates in coarsening carved (incision stage, Fig. 16) and axial systems arrangements are interpreted as microdeltaic bars prograded in response to a low equilibrium profile facies in the ancient Jaćhal channel mouths. on the transference system (confined low accommodation system tract; Fig. 17c). Finally, the major Facies association 5 (mudstones with monomictic uplift of the Caracol range took place. La Tranca breccias). This facies association (Fig. 9e, f ) is area was isolated, forming a closed piggyback formed from thick tabular beds of light greenish basin (Figs 16 & 17d), recording a high accommo- mudstones, dominantly laminated. Coarsening-up dation system tract, registered by muddy lacustrine arrangements of laminated sands and massive and deposits and a high-energy piedmont associa- trough cross-bedded breccias, with local prove- tion (Fig. 16). In the latter phase, low-energy pied- nance, appear in a minor proportion. This associ- mont systems (facies association 3) prograded ation is interpreted as closed ephemeral clastic onto playa lake facies, producing the filling of Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

240 J. SURIANO ET AL.

Fig. 16. Schematic section of the Cuesta del Viento Formation, with system tract interpretation and geological events that caused them (right column). Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

SEDIMENTATION MODEL OF PIGGYBACK BASINS 241

Fig. 17. Block diagrams showing the evolution of Cuesta del Viento Formation and its relationship with the facies association (thick arrows represent active thrusting). the basin (unconfined low accommodation system piggyback areas can be open when a new transfer- tract, Fig. 16). ence fluvial system develops in the thrust and fold belt. The stratigraphic record of open piggyback Conclusions basins has been divided in this paper into four major theoretical stages: (a) the incision stage; The movement of sediments within continental (b) a confined low accommodation system tract; piggyback basins can be sketched as driven by (c) a high accommodation system tract; and (d) an three different types of alluvial–fluvial systems: unconfined low accommodation system tract or (a) piedmont accumulations (talus, different types overfill stage. The incision stage is reached when of colluvial fans and, in wide enough basins, alluvial long-lived periods of erosion within the piggyback fans) forming alluvial aprons during mountain allow/produce a massive transference of sediments denudation; (b) axial fluvial systems which collect to the foreland. Degradation stages are recorded sediments derived from the piedmont area and by incision surfaces. These surfaces can be related transport them to transversal rivers; and (c) transfer- not only to changes in subsidence or tectonism in ence systems formed by large rivers draining the the foreland or in the fold and thrust belt, but also fold and thrust belt and transferring sediments to climatic fluctuations significant enough to pro- from the piggyback basins to the foredeep region. duce an increase in the sediment transport capacity Despite the fact that this model is a simplifica- of the third-order fluvial systems. The high accom- tion of the alluvial–fluvial systems in the Precor- modation system tract is characterized by strong dillera, it is useful to explain the transference of aggradation in the piggyback basins mainly related sediments not only within the piggyback basins to either low rates of subsidence in the foredeep or but also from the piggyback area to the foreland. inefficiency of the transference fluvial systems. In addition, the existence of transference fluvial Low-accommodation stages reflect limited capacity systems (in our case the Jaćhal River) enables the of the piggyback to store sediments. The confined recognition of two different types of piggyback: stage occurs in subsequent periods of erosion and open and closed piggyback basins (when the lack transference of sediments towards the foreland, of transference fluvial systems prevents the trans- recorded as the first fill over the incision surface. port of sediments from the piggyback to the fore- Finally, the unconfined stage is associated with land, turning the piggyback into an endorheic basin overfill. isolated basin). The evidence obtained from Ceno- The deposits of close piggyback basins have zoic deposits as analysed in this paper clearly been divided in two end members stages: (a) high shows that open piggyback basins can undergo tem- accommodation system tracks; and (b) low accom- porary closures and, in the same way, closed modation system tracts. In order to examine the Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

242 J. SURIANO ET AL. utility of the proposed model, two case studies in the Paleozoic in the eastern interior of North America. Precordillera of San Juan province, Argentina were Tectonics, 7, 389–416. analysed: the Pleistocene–Holocene deposits of the Bilkra,L.H.&Nemec, W. 1998. Postglacial colluvium Jaćhal River piggyback basins and the Oligocene– in western Norway: depositional process, facies and Miocene Cuesta del Viento Formation. paleoclimatic record. Sedimentology, 45, 909–959. Blum,M.D.&To¨rnqvist, T. E. 2000. Fluvial responses The first example associated with relative rela- to climate and sea-level chamge: a review and look tively quiescent tectonic shows that changes in sub- forward. Sedimentology, 47, 2–48. sidence rates along the foreland under these Bonini, M., Moratti,G.&Sanib, F. 1999. Evolution and conditions can exert a strong control in the equili- depocentre migration in thrust-top basins: inferences brium profiles of the transference systems, thus pro- from the Messinian Velona Basin (Northern Apen- moting periods of aggradation and degradation of nines, Italy). Tectonophysics, 304, 95–108. the piggyback. A good example of this situation Butler,R.W.H.&Grasso, M. 1993. Tectonic controls appears in Sequence I, which illustrates how the iso- on base-level variations and depositional sequences static rebound in the thrust and fold belt controlled within thrust-top and foredeep basins: examples from the Neogene thrust belt of central Sicily. Basin the enhancement of aggradation phases. On the Research, 5, 137–151. other hand, changes in climatic conditions should Butler, R. W. H., Lickorish, W. H., Grasso, M., not be overlooked, In fact, the widespread develop- Pedley,H.M.&Ramberti, L. 1995. Tectonics and ment of intermontane lakes (Sequence III) and the sequence stratigraphy in Messinian basins, Sicily: con- large progradation of megafans (Sequence II) into straints on the initiation and termination of the Medi- the foreland are linked to postglacial conditions terranean ‘salinity crisis’. Geological Society of and result in good examples of how climate plays America, Bulletin, 107, 425–439. Cardozo Jordan an important role in the accumulation patterns in ,N.& , T. 2001. Causes of spatially both piggyback and foreland basins. variable tectonic subsidence in the Miocene Bermejo Foreland Basin, Argentina. Basin Research, 13, The second case study records the transition 335–357. between the outer-wedge-top depozone and piggy- Catuneanu, O. 2006. Principles of Sequence Stratigra- back basin as well as different types of piggyback phy. Elsevier, Amsterdam. basin (open to close). We conclude that the model Colombo, F., Busquets, P., Ramos, E., Verge´s,J.& proposed here is useful to analyse the sediments of Ragona, D. 2000. Quaternary alluvial terraces in an the Jaćhal River area deposited during limited or active tectonic region: the San Juan River Valley, absent tectonic activity with climatic controls, as Andean Ranges, San Juan Province, Argentina. well as the Cuesta del Viento Formation deposited Journal of South American Earth Sciences, 13, in an active fold and thrust belt. In both cases, the 611–626. Colombo, F., Limarino, C., Busquets, P., Sole´ de model provides a framework in which piggyback Porta, N., Heredia, N., Rodrı´guez Fernańdez,R. basin evolution can be described and related to the & Alvarez Marroń, J. 2005. Primeras edades absolu- factors that control the dynamics of sedimentation. tas de los depo´sitos lacustres holocenos del rıóJaćhal, Precordillera de San Juan. Revista de la Asociacioń Geolo´gica Argentina, 60, 605–608. This study was supported by grant BID 1728 OC/AR PICT Colombo, F. P., Busquets Buezo, P., Sole´ de Porta, 20752 of the Agencia de Promocioń Cientı´fica y Tecnolo´- N., Limarino, C. O., Heredia, N., Rodrı´guez Fer- gica (Argentina), UBACyT 20020110300025 and the nańdez,L.R.&A´ lvarez Marroń, J. 2009. Holo- Departamento de Ciencias Geolo´gicas of the Universidad cene intramontane lake development: a new model in de Buenos Aires. We would like to thank J. Mescua for the Jaćhal River Valley, Andean Precordillera, San critical comments that helped to improve our manuscript. Juan, Argentina. Journal of South American Earth The authors acknowledge the critical reading and the valu- Sciences, 28, 228–238. able proposals suggested by the reviewers (M. Tunik andan Dahle, K., Flesja, K., Talbot,M.R.&Dreyer, T. 1997. anonymousreviwer). Correlation of fluvial deposits by the use of Sm-Nd isotope analysis and mapping of sedimentary architecture in the Escanilla Formation (Ainsa Basin, Spain) References and the Statfjord Formation (Norwegian North Sea), Sixth International Conference on Fluvial Sedimentol- Alonso, S., Limarino, C. O., Litvak, V., Poma, S. M., ogy, Cape Town, South Africa, 46. Suriano,J.&Remesal, M. 2011. Paleogeographic, Dalrymple, M., Posser,J.&Williams, B. 1998. magmatic and paleoenviremontal scenarios at 308SL A dynamic systems approach to the regional controls during the andean orogeny: cross sections from the on deposition and architecture of alluvial sequiences, volcanic-arc to the orogenic front (San Juan Province, illustrated in the Stafjord Formation (United King- Argentina). In: Salfity,J.A.&Marquillas,R.A. dom, northern North Sea). In: Shanley,K.W.& (eds) Cenozoic Geology of the Central Andes of Argen- McCabe, P. J. (eds) Relative Role of Eustasy, Cli- tina. SCS, Salta, 23–45. mate and Tectonism in Continental Rocks. Society of Beaumont, C., Quinlan,G.M.&Hamilton, J. 1988. Economic Paleontologists and Mineralogists, Tulsa, Orogeny and stratigraphy: numerical models of the OK, Special Publications, 65–81. Downloaded from http://sp.lyellcollection.org/ at MINCYT-Universidad De Buenos Aires on May 8, 2017

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