Petrology and provenance of the Toro Negro Formation (Neogene) of the Vinchina broken-foreland basin (Central Andes of Argentina)

Journal of South American Earth Sciences 49 (2014) 15e38

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Petrology and provenance of the Toro Negro Formation (Neogene) of the Vinchina broken-foreland basin (Central Andes of Argentina) P.L. Ciccioli*, S.A. Marenssi, C.O. Limarino Departamento de Ciencias Geológicas, IGeBA, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, CONICET, Ciudad Universitaria, Pabellón 2, 1
piso, C1428EHA Buenos Aires, Argentina

a r t i c l e i n f o

a b s t r a c t

Article history: Received 8 December 2012 Accepted 5 October 2013

Detrital modes of sandstones and conglomerates of the Toro Negro Formation (Late Miocene-early Pliocene) were used to analyze the evolution of the broken-foreland stage of the Vinchina Basin (28
300 e29
000 S and 68
300 e68
200 W) of NW Argentina. This basin located in the Western Sierras Pampeanas is bounded to the west by the Precordillera and to the east by the Famatina System. Three sandstone petrofacies: plutonic-metamorphic, volcanic and mixed petrofacies and three conglomerate lithic associations: basement, sedimentary and volcanic lithic associations were recognized, allowing to establish three source areas: Western Sierras Pampeanas (Toro Negro and Umango Ranges), Cordillera Frontal and Precordillera. During the Late Miocene, the Toro Negro Range (to the north) together with the Cordillera Frontal and Precordillera (to the west) were the main sources for depositional sequences I and II (lower member of the Toro Negro Formation). On the contrary, during the latest Miocene-early Pliocene, Depositional Sequence III (upper member) exhibited a progressive increase in the supply from the eastern Precordillera (to the west) with additional material from the Umango Range to the south. Besides, evidence of synchronic volcanism is recorded in the upper part of Depositional Sequence II and the lower part of Depositional Sequence III. The coexistence of the three source areas and the changing distribution patterns due to reaccommodation of sediment dispersal routes demonstrate that the evolution of this type of basin is much more complex than previously envisaged. Therefore, an integrated analysis using different tools (sedimentary facies, paleocurrent measurements, sandstone petrography and conglomerate composition) is needed for a clearer understanding of broken-foreland basins. Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Sedimentary petrology Petrofacies Broken-foreland Neogene Andes

1. Introduction The modal composition of sandstones is a useful tool not only for establishing source areas but also to look into the relation between shifts in compositional framework and paleogeographic modifications in sedimentary basins (Ingersoll, 1983; Net and Limarino, 2006; Garzanti et al., 2007; Caracciolo et al., 2011; Spalletti et al., 2012). Sandstone composition does not depend exclusively on the source rocks, since it may also be affected by the physiography and chemical weathering in the source area, the reworking and abrasion of the sediments during transportation and

* Corresponding author. Tel.: þ54 11 4576 3300/09x317; fax: þ54 11 4576 3329. E-mail addresses: [email protected], [email protected] (P. L. Ciccioli), [email protected] (S.A. Marenssi), [email protected] (C. O. Limarino). 0895-9811/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsames.2013.10.003

sedimentation, and diagenetic effects (e.g. Dickinson and Suczek, 1979; Espejo and López-Gamundi, 1994; Scasso and Limarino, 1997; Amorosi and Zuffa, 2011). Notwithstanding, the study of sandstone composition and conglomerate clasts may help to determine the tectonic evolution of the basin and allows to be established the historical uplift of the different mountain ranges (source areas). The Toro Negro Formation (Turner, 1964; Late Miocene-early Pliocene) corresponds to the upper infill of the Vinchina Basin, an Andean composite foreland basin, in northwestern Argentina (Fig. 1). This unit records sedimentation during the transition from the transpressional foreland stage into the broken-foreland stage of Ciccioli et al. (2011). The Toro Negro Formation was divided into two members (Ramos, 1970). The lower member is composed of sandstones, mudstones, intraformational breccias and conglomerates with some tuff layers and overlies a high-relief unconformity carved in the underlying Vinchina Formation (Turner, 1964; Miocene). Two depositional sequences were recognized in the

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Fig. 1. Geological map of Vinchina Basin and surroundings showing the location of the three studied sections and the main morphostructural units. Modified from Ciccioli and Marenssi (2012).

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lower member (Ciccioli et al., 2010a; Fig. 2). The upper member comprises conglomerates, coarse-grained sandstones, a minor amount of mudstones and some tuff in depositional sequence III (Ciccioli et al., 2010a; Fig. 2). This member is separated from the lower member by a low-relief unconformity (Ciccioli, 2008; Limarino et al., 2010). Modal analyses in the Vinchina Basin have rarely been undertaken, with the exception of the paper by Tripaldi et al. (2001) focused on the provenance of the Vinchina Formation. Detrital modes of the overlying Toro Negro Formation have not been studied yet, although, as will be shown later in this paper, this information is critical for reconstructing the evolution of the basin. Paleogeographic reconstructions, mainly based in paleoenvironmental interpretations and paleocurrent data, suggest multiple source areas for the Toro Negro Formation, including the volcanic arc located in the Cordillera Frontal, the fold and thrust belt placed in Precordillera and uplifted basement blocks belonging to the Western Sierras Pampeanas (Ciccioli and Marenssi, 2012). However, provenance studies have not been carried out at present in the Toro Negro Formation and therefore source areas and paleogeographic models for the foreland during the Late Miocene-early Pliocene are somewhat speculative. Therefore, changes in detrital modes should be expected whenever tectonic activity affected some of these positive areas. At a more detailed scale, the relationship between internal stratigraphic discontinuities and shifts in modal composition are considered here in order to interpret their origin (e.g. Amorosi, 1995; Arribas et al., 2003; Amorosi and Zuffa, 2011). According to the above mentioned, provenance studies in the Toro Negro Formation are necessary not only to understand the paleogeography of the basin but also to examine the relative importance of the different source areas. Moreover, provenance analysis of the Toro Negro Formation allow considering some important questions about the importance of detrital modes in the reconstruction of foreland basins exhibiting complex basements. The provenance of the Toro Negro Formation is studied using both the composition of sandstone and conglomerate framework

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clasts. The evolution of the detrital modes (petrofacies) is used to interpret recurrent changes in source areas and to assess the relative chronology of the uplift of the main morphostructural units during the Late Miocene and early Pliocene. 2. Geological setting and stratigraphy The study area is located in the flat slab segment of the Central Andes of Argentina (27
e33
S) encompassing from west to east the Main Cordillera, the Cordillera Frontal, the Precordillera (a thin-skinned thrust belt), the Sierras Pampeanas (thick-skinned systems of thrusts) and the Famatina System (Ramos et al., 2002). This segment is characterized by low-angle subduction of the Nazca Plate (Ramos et al., 2002) that converges at an oblique angle with respect to the South American Plate, producing a very complex deformation pattern including some degree of strike-slip movement (Rossello et al., 1996; Introcaso and Ruiz, 2001). In this area several foreland basins were formed during the Cenozoic including the Vinchina Basin located near of the boundary between the Western Sierras Pampeanas and Precordillera (28
and 29
S). This basin was bounded to the east by an emerging upland area that forms the present-day Famatina System and to the north and south by basement blocks (Toro Negro and UmangoeEspinal Ranges, respectively, Fig. 1). The Vinchina Basin is a complex foreland basin that evolved from a retroarc stage in the Paleogene to a brokenforeland stage related to transpression in the Neogene (Ciccioli et al., 2011). In this basin several thousand meters of sediment accumulated in non-marine environments from the Paleogene to the Recent. The stratigraphic scheme of the Vinchina Basin (Fig. 1) includes five formations: the Puesto La Flecha (Eocene), Vallecito (Oligocene-early Miocene?), Vinchina (Miocene), Toro Negro (Late Miocene-early Pliocene) and El Corral Formations (Pliocene) (Ciccioli, 2008; Ciccioli et al., 2010b). The 2500 m-thick Toro Negro Formation is made up of yellowish to greenish sandstones, mudstones, conglomerates, and muddy

Fig. 2. Schematic diagrams showing the depositional sequences recognized in the Toro Negro Formation. Modified from Ciccioli et al. (2010a).

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intraformational breccias with several tuff layers. The boundary between the Toro Negro and the underlying Vinchina Formations was described as unconformable (Turner, 1964; Ramos, 1970; Limarino et al., 2001; Ciccioli et al., 2004). Ciccioli (2008) documented a high-relief unconformity surface separating the Vinchina and Toro Negro Formations which forms the floor of a large paleovalley in the northern part of the basin (Los Pozuelos-Aguada Creek). More recently, this unconformity was analyzed by Limarino et al. (2010) who established that to the north up to 25% of the underlying Vinchina Formation was eroded, while to the south this surface flattens out becoming a paraconformity. The Toro Negro Formation is divided into two members (Ramos, 1970) separated by a low-relief erosional surface (Ciccioli, 2008). The lower member is composed mainly of sandstones, mudstones, muddy intraformational breccias and extraformational conglomerates with some tuff layers. These rocks were deposited in various kinds of anastomosing fluvial systems, braided rivers, siliciclastic and saline shallow lakes (playa lakes), as well as eolian and fluviale eolian interaction systems (Ciccioli, 2008; Ciccioli and Marenssi, 2012). For the most part, sedimentation took place under semiarid to arid climatic conditions indicated by abundant desiccation cracks and intercalations of eolian and eolianefluvial interaction deposits. The upper member of the Toro Negro Formation is mainly composed of cobble conglomerate and coarse-grained sandstone deposited in braided rivers and streamflow-dominated piedmonts with some thin intercalations of fine-grained sediments corresponding to a tuffaceous braidplain (Ciccioli, 2008; Ciccioli and Marenssi, 2012). Lastly, the basin fill culminates with breccias, conglomerates and coarse sandstones deposited in alluvial fans and piedmont systems during the eastward migration of the orogenic front (El Corral Formation, Pliocene). The age of the Toro Negro Formation was constrained by two radiometric ages obtained by Ciccioli et al. (2005) from tuff beds collected few meters below the boundary between the lower and upper members of the unit. These data provided a Late Miocene age (8.6 and 6.8 Ma) but the top of the unit may probably reach the Pliocene (Fig. 2). Besides, new U/Pb ages in detrital zircons were obtained in the underlying Vinchina Formation by Dávila et al. (2008) and Ciccioli et al. (2012b) establishing a Miocene age for this unit. Thus, depositional sequences I and II (lower member of the Toro Negro Formation) can be referred to the Late Miocene while depositional sequence III (upper member) may be latest Miocene-early Pliocene (Fig. 2).

3. Depositional sequences and potential source areas of the Toro Negro Formation Three depositional sequences (DS) were defined by Ciccioli et al. (2010a) for the Toro Negro Formation using accommodation space and the degree of incision of the fluvial systems (Fig. 2). Depositional sequence I (lower half of the lower member, Late Miocene) represents the filling of a paleovalley carved into the Vinchina Formation and comprises conglomerates and cross-bedded coarsegrained sandstones deposited in braided to anastomosing fluvial systems (Ciccioli et al., 2010a). The regional extension of DSI rocks is limited because sedimentation was mainly confined inside the paleovalley formed in the north of the basin (Fig. 2) although a thin unconfined section was developed along the basin after the valley was filled. In contrast, depositional sequence II (upper half of the lower member, Late Miocene) and depositional sequence III (upper member, latest Miocene-early Pliocene, Fig. 2) rocks are recorded throughout the basin and correspond to sedimentation in unconfined fluvial systems (Ciccioli et al., 2010a; Fig. 2).

DSII rests on a low-angle erosive surface and shows notable northesouth facies changes. Fluvial conglomerates and coarsegrained sandstones dominate in the north (Los Pozuelos section, Fig. 2) while fine-grained successions deposited in a playa lake are common in the south (Del Yeso section, Fig. 2). Intermediate lithologies appear in the central part of the basin (La Troya section, Fig. 2) where conglomerates and sandstones are intercalated with thick units of fine-grained fluvial deposits. DSIII is composed of thick successions of coarse-grained conglomerates disposed over a low-relief incision surface. Clastsupported conglomerates and coarse-grained sandstones, deposited in piedmont and proximal braided plains, are dominant and alternate with relatively thin intervals dominated by mudstones, fine-grained tuffs and tuffaceous deposits (Ciccioli, 2008; Ciccioli and Marenssi, 2012). Regional information, facies distribution and paleocurrent data suggest that at least three main morphostructural elements constituted potential source areas for the sediments of the Toro Negro Formation: 1) basement blocks of Western Sierras Pampeanas (the Toro Negro Range, to the north and the UmangoeEspinal Ranges in the south); 2) the Cordillera Frontal, located in a distal position to the west and 3) the Precordillera fold and thrust belt, located to the west, here composed of the Del Peñón, Santo Domingo, Punta del Agua and Punta Negra ranges from west to east. A schematic diagram showing the location of the potential source areas is shown in Fig. 3. Note that the Famatina System is not considered as a source area because in addition to the regional slope to the east, our paleocurrent measurements do not indicate paleoflows from the east (Ciccioli, 2008; Ciccioli and Marenssi, 2012). The Toro Negro and UmangoeEspinal Ranges (Western Sierras Pampeanas) are formed by high- to medium-grade metamorphic rocks, mainly, schists, amphibolites, gneisses, migmatites and quartzites with scarce marbles (Turner, 1964; Caminos, 1972). These sources most probably supplied a large amount of monocrystalline quartz as well as much of the polycrystalline quartz derived from medium- and high-grade metamorphic rocks and mylonites. Likewise, much of the K-feldspar (both orthoclase and microcline), with abundant acicular inclusions and/or forming perthites or simplectites, come from this source area, as do almost all of the medium- and high-grade metamorphic lithic fragments. It is interesting to note that the supply of volcanic clasts from the Western Sierras Pampeanas is extremely scarce, with the exception of some Paleozoic volcanics or Precambrian metamorphosed volcanic rock fragments. Thus, the higher proportion of total lithics in comparison with volcanic fragments is obvious. The Cordillera Frontal, essentially composed of volcanic rocks, shed large amounts of acid to intermediate volcanic rock fragments, corresponding to the magmatic rocks of the PermianeTriassic Choiyoi Group (paleo-volcanic source) and the Neogene volcanic arc (neo-volcanic source). Moreover, this source area could have also supplied a higher percentage of plagioclase in relation to Kfeldspar. The Precordillera is a very complex source due to the association of different rock types. On the one hand, the Del Peñón Granite was a potential source of quartz and K-feldspar clasts. The K-feldspars with perthites could derive from this source or from the crystalline basement of the Toro Negro and UmangoeEspinal Ranges. On the other hand, the Precordillera shed clasts of Paleozoic and Mesozoic sedimentary and low-grade metamorphic rocks, mainly slates, as well as an undoubted supply of Carboniferous volcanic rocks (paleo-volcanic clasts). Thus, the Precordillera supply is complex and its sediments were highly variable depending on the age of the thrust wedges. Based on the bed-rock geology summarized in the previous paragraphs, a logical modal composition was derived from each of

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19

Fig. 3. A. Potential provenance sources to the Toro Negro Formation; and B. Main features of these potential sources. KeF: K-feldspars, P: plagioclase, Q: quartz, Lt: lithics and Lv: volcanic fragments.

the source areas mentioned above and its interpretation from a tectonic point of view is summarized in Fig. 3B. 4. Methodology To characterize the petrography of the Toro Negro Formation we studied 95 unaltered medium- to coarse-grained sandstone samples and 36 conglomerate beds collected from the three stratigraphic sections named from north to south: Pozuelos-Aguada Creek, La Troya creek and Yeso Creek (Fig. 1). Detailed sedimentological descriptions and paleoenvironmental interpretations of these sections were published by Ciccioli (2008) and Ciccioli and Marenssi (2012). Sandstone thin sections were subjected to standard petrographic analysis. In each sandstone sample, 300e500 grains were counted by the GazzieDickinson method for minimizing the effect of the grain size on the modes (Gazzi, 1966; Dickinson, 1970). Roundness and sorting were estimated by visual comparison in thin sections after Powers’s (1953) and Beard and Weyl’s (1970) tables, respectively. Sandstone framework elements of the Toro Negro Formation are shown in Table 1. Quartz (Q) grains were separated into monocrystalline (Qm) and polycrystalline (Qp) types (Fig. 4AeD). Qm was divided into monocrystalline quartz with mineral acicular inclusions (Qmi) whereas Qp types were divided into mylonitic quartz (Qpm) and chert (Ch). Among the feldspars (F), K-feldspar (O), microcline (M) and plagioclase (P) were recognized (Fig. 4Ee H). Particularly, feldspars with perthites (Op, Mp), with mineral intergrowths (Oi, Pi, Mi) and zoned plagioclase (Pz, Fig. 4E) were counted separately. Rock fragments (L) include volcanic (Lv), metamorphic (Lm) and sedimentary (Ls) lithics (Fig. 5). In turn, volcanic grains were subdivided according to their textures reflecting different magma compositions (e.g. Dickinson, 1970; Critelli and Ingersoll, 1995; Critelli et al., 2002). Thus, we recognized volcanic lithics (Fig. 5AeD) with felsitic (Lvf), microlitic (Lvm), lathwork (Lvl) and vitric (Lvv) textures as well as metamorphosed volcanic lithic (Lvme) and fresh glass shards and pumices (Lvp). In addition, volcanic grains were differentiated into paleo-volcanic (Paleo-V) and neo-volcanic (Neo-V) grains following Critelli and Ingersoll (1995). The paleo-volcanic grain category includes altered and rounded volcanic fragments of acid,

intermediate to basic composition (Lvf, Lvm, Lvl) and metamorphosed volcanic lithics (Lvbm). The neo-volcanic grains comprise angular and fresh glass shards and pumices (Lvp) and they are considered to derive from active volcanism during sedimentation (synsedimentary or coeval to the sedimentation). Metamorphic fragments (Lm; Fig. 5EeG) are separated into low grade (Lmb) including phyllite and slates, micacites (Lmm), highgrade (Lma) (schists and amphibolites) and marbles (Lmc). Sedimentary rock fragments (Ls) were categorized as siliciclastic (Lss, Fig. 5H) and carbonate lithic fragments (Lsc). Accessory minerals include micas (biotite and muscovite), amphiboles, pyroxenes, zircons and opaques. The composition of framework grains is the basis for sandstone classification and to infer source rocks. Sandstones are classified according to the Q:F:L (quartz, feldspars and rock fragments) ratio following Folk et al. (1970). The relation among quartz, feldspars and rock fragments, the presence of different kinds of feldspars, the relative amounts of volcanic, sedimentary and metamorphic rock fragments and the discrimination between different types of volcanic lithics, among other features, are the basis for inferring the sediment source (Dickinson and Suczek, 1979; Dickinson, 1985; Ingersoll, 1990; Le Pera and Critelli, 1997; Critelli et al., 1997, 2002; Caracciolo et al., 2011). Provenance studies are enhanced by using a combination of several ternary diagrams rather than relying on a single diagram because combinations of specific end members discriminate between different grain properties (Hulka and Heubeck, 2010). Petrofacies or stratigraphic intervals characterized by a particular modal composition (Dickinson and Rich, 1972; Scasso and Limarino, 1997) were then defined interpreting them to reflect a specific area of origin or a mixture of areas. Diagrams proposed by Dickinson et al. (1983) and Dickinson and Suczek (1979) as well as modal regeneration diagrams (see Scasso and Limarino, 1997; Critelli and Ingersoll, 1995) specially designed for this case, were used in order to characterize the provenance areas. These ternary diagrams were constructed using groups of specific modal components that in this paper are considered as good (secure, effective) indicators of provenance sources. At each conglomerate bed the composition of more than 350 clasts ranging between pebbles (up to 5 cm) and cobbles (up to

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5. Petrology of the Toro Negro Formation

Table 1 Lithotypes of sandstones. Codes

Lithoclasts

Qm Qm(Lp) Qm(Lm) Qm (Ls) Qm(Lv) Qm(Lvme) Qm(Lmm) Qm(Lsm) Qmi Qp Qpmb Qp (Lp) Qpm Ch O O(Lp) O(Lm) O(Ls) O(Lv) O(Lvm) O(Lsm) Op Oi M M(Lp) M(Lm) Mp Mi P Pz P(Lp) P(Lm) P(Ls) P(Lv) P(Lvm) Pp Pi Lv Lvf Lvm Lvl Lvv Lvp Lvme Ls Lsp Lsc Lm Lmb Lmm Lma Lmc

Monocrystalline quartz In plutonic lithics In metamorphic lithics In sedimentary lithics In volcanic lithics In metamorphosed volcanic lithics In mylonitic metamorphic lithics In metamorphosed sedimentary lithics With interqrowths Polycrystalline Quartz (include<3 individuals) Qp of low grade (>3 individuals) Qp in plutonic lithics Qp milonithic Chert Orthoclase In plutonic lithics In metamorphic lithics In sedimentary lithics In volcanic lithics In metamorphosed volcanic lithics In metamorphosed sedimentary lithics With perthites With intergrowths Microcline In plutonic lithics In metamorphic lithics With perthites With intergrowths Plagioclase Zoned In plutonic lithics In metamorphic lithics In sedimentary lithics In volcanic lithics In metamorphosed volcanic lithics With perthites With intergrowths Fragment of volcanic rock Felsitic texture Microlitic texture Lathwork texture Vitric texture Glass shards and pumicites Metamorphosed Fragment of sedimentary rock Mudstone Limestone Fragment of metamorphic rock Low grade (slates-phyllites) Micacites Schists e amphibolites Marble

25 cm) was determined weighting the mode according to the size of the clasts (Cavazza, 1989; Howard, 1993). The classification proposed by Limarino et al. (1996; in Scasso and Limarino, 1997) was used to characterize the conglomerates. Conglomerate lithotypes of the Toro Negro Formation are shown in Table 2. They were grouped into seven classes (Fig. 6): volcanic (V), sedimentary (S1, corresponding to red and brown sandstones and mudstones, and S2, including green and yellow sandstones and conglomerates), low-grade metamorphic (Lmb), pink pegmatitic granites and white granites (G), quartz and quartzites (Q) and finally high-grade metamorphic (Lma) that includes mainly clasts of gneisses and amphibolites. To infer source areas, lithic associations were defined by grouping specific components of the conglomerate clasts mentioned before. Ternary and binary diagrams were constructed using groups of specific clasts considered as indicators of provenance sources.

5.1. Sandstone composition The Toro Negro Formation sandstones correspond mainly to litharenites (47%) feldspathic litharenites (45%) and lithic feldsarenites (8%) according to Folk et al. (1970, Fig. 7; Table 3). There are minor variations in the percentages of types of sandstone present in each depositional sequence. DSI is mainly composed of feldspathic litharenites (84%) with some lithic feldsarenites (9%) and litharenites (7%). DSII is dominated by feldspathic litharenites (69%) with some litharenites (23%) and scarce lithic feldsarenites (8%). Finally, DSIII comprises feldspathic litharenites (55%) and litharenites (45%). Particularly, some litharenites are enriched by volcanic and neo-volcanic lithics. Most sandstones are framework-supported, matrix-poor (less than 6%) and composed of different types of cements including calcite, zeolites, clays (chlorite and illite), iron (hematite) and manganese oxides and sulfates (gypsum). Silica, as secondary overgrowth, megaquartz or microcrystalline, is scarce and authigenic feldspar is very scarce, being recognized only in the DSIII. Although the percentage of these cements is highly variable it is likely that calcite and zeolite are the most represented. Zeolitic cement may become exclusive in samples with a high percentage of neo-volcanic lithics while sulfate cement (gypsum) is dominant in the sandstones of the southern section (Del Yeso Creek) of the study area. 5.2. Conglomerate composition Table 4 summarizes the compositional data of the conglomerates. Conglomerates were classified mainly as polymictic clastsupported orthoconglomerates (68%) and polymictic matrixsupported orthoconglomerates (29%) according to Limarino et al. (1996; in Scasso and Limarino, 1997) (Fig. 8). Conglomerates are compositionally immature. The matrix is medium- to coarsegrained sandstone and the clasts are subrounded to subangular with equant to prolate shapes. In the southern section (Del Yeso Creek) clasts are dominated by subangular, low-grade metamorphic rocks with tabular shapes. Finally, the matrix-supported paraconglomerates are scarce (3%) and they are generally composed of subangular clasts. 6. Provenance of the Toro Negro Formation Sandstone modal composition (Table 5) was plotted on the QFL and QmFLt ternary diagrams of Dickinson et al. (1983) and on the QmPF complementary diagram of Dickinson and Suczek (1979) (Fig. 9). The QmPF diagram was used in order to differentiate the supply of the crystalline basement from the volcanic arc. In the Dickinson et al. (1983) provenance diagram the majority of the detrital modes of DSI is located in the dissected and transitional volcanic arc fields. Samples of DSII plotted in the same sectors, but the amount of samples in the transitional arc field diminishes and very few samples fall in the recycled orogen field (Fig. 9). Finally, the dispersion of the detrital modes is greater, ranging from the dissected to undissected arc with a few samples plotting in the recycled orogen in the DSIII (Fig. 9). In the QmPF complementary diagrams most of the samples of DSI and DSII fall in the central part indicating a similar content of Kfeldspar and plagioclase, although a few samples is enriched in each one (Fig. 9). Samples of the DSIII are divided into two differentiated groups. One of them is enriched in K-feldspars and quartz indicating a recycled orogen source (or provenance from crystalline rocks), while the other group contains more plagioclase and a

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Fig. 4. Thin-section photomicrographs of modal component from sandstones of the Toro Negro Formation. A. Embayed grain of monocrystalline quartz (Qm); B. Quartz with simplectites associated to plagioclase with intergrowths (Pi); C. Polycrystalline quartz (Qp); D. Mylonitic polycrystalline quartz (Qpm); E. Zoned plagioclase (Pz); F and G. K-feldspars microcline (M), orthoclase (O), with intergrowths (Mi, Oi) and monocrystalline quartz (Qm); and H. Orthoclase with perthites (Op).

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Fig. 5. Thin-section photomicrographs of modal component from sandstones of the Toro Negro Formation. AeD. Volcanic modal components: Pumicite (Lvp), lithic with felsic texture (Lvf), vitric texture (Lvv), lathwork texture (Lvl) and metamorphosed volcanic lithic (Lvme); E and F. High-grade (Lma) and low-grade (Lmb) metamorphic lithics, limestone lithic fragment (Lsc), monocrystalline quartz (Qm) and plagioclase (P); G. High-grade metamorphic lithic (Lma), polycrystalline quartz (Qp) and plagioclase (P); and H. Mudstone lithic fragment (Lss), monocrystalline quartz (Qm) and orthoclase (O).

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38 Table 2 Lithotypes of conglomerates. Code

Lithotypes

V S1 S2 G Q Lmb

Green, purplish and red volcanic rocks. Red, brown and grey sandstones. Green and yellow sandstones and green conglomerates. Granites as feldspar clasts. Quartz and quartzite clasts. Green and grey slates, phyllites and other low-grade metamorphic rocks. Gneisses, amphibolites and schists.

Lma

minor proportion of quartz probably associated with an undissected arc source (Fig. 9). Taking into account the presence of significant proportions of Kfeldspars (microcline and orthoclase) with perthites and intergrowths and various types of metamorphic rock fragments, the

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modal composition of sandstones of the Toro Negro Formation suggests a mix of multiple source areas rather than a volcanic arc provenance (Fig. 9). Therefore, in this case the use of basic modal components cannot separate different source areas. Thus, it is necessary to use regeneration diagrams and petrofacies for a more detailed description of the provenance areas and their evolution through time. Regenerated point-counts were obtained referring non-monomineral components to the lithic fragments from which they were counted using the GazzieDickinson methodology (Table 5). All data are available in the supplementary table (Appendix 1). 6.1. Petrofacies and provenance from sandstones The term petrofacies was created to refer to sandstones of similar composition, usually defined by parameters such as QFL percentages and/or the ratio of different grain types (Dickinson and

Fig. 6. Lithotypes of conglomerates. A. High-grade metamorphic rocks (Lma); B. Pegmatitic granites (G); C and D. Volcanic rocks (V), red (S1) and green (S2) sandstones; E. green conglomerate (S2); and F. white granite (G). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

Fig. 7. Q:F:L (quartz, feldspars and rock fragments) ratio according Folk et al. (1970) sandstone classification.

Rich, 1972; Net and Limarino, 2006). Thus, petrofacies outline stratigraphic entities that can be referred to as petrologic intervals (Dickinson and Rich, 1972). To define the petrofacies of the Toro Negro Formation we used regeneration modal diagrams whose components characterize the main source areas outlined above (e.g. Critelli and Le Pera, 1994; Critelli and Ingersoll, 1995; Net and Limarino, 2006). The nature of the regenerated components is shown in Table 6. As can be seen, Lv is defined as a product regenerated from volcanic sources including volcanic groundmasses in addition to fragments of quartz, plagioclase and feldspar identified in volcanic lithics. The Lp þ Lma component groups clasts derived from crystalline rocks including aplites, migmatites, different types of schists, amphibolites, fine-grained gneisses and monomineral components of them. The Ls þ Lmb component includes rock fragments of fine-grained sandstones, mudstones and low-grade metamorphic rocks (slates and phyllites). The analysis of the stratigraphic distribution of the sandstone detrital modes within the Toro Negro Formation allows differentiating three petrofacies (Fig. 10): plutonic-metamorphic petrofacies (PMP), volcanic petrofacies (VP) and mixed petrofacies (MP). The PMP shows a P/FK < 1 ratio, with abundant orthoclase and microcline with perthites and a prevalence of high-grade metamorphic lithics (Lm/Lv > 1). Moreover, PMP petrofacies shows more than 60% of clasts derived from crystalline rocks (Lp þ Lma). The VP is composed by more than 60% of volcanic components and a high amount of plagioclase (P/FK > 1). Finally, the mixed petrofacies (MP) shows a relative decrease in volcanic groundmasses when it is compared to the VP as well as a variable P/FK ratio and depletion in quartz and Lp þ Lma components in relation to the PMP (Table 6). 6.1.1. Depositional sequence I The lowest part of the Toro Negro Formation comprising valleyconfined deposits of the DSI is only represented in the northern section (Los Pozuelos-Aguada Creek) of the basin. The variation of the regenerated modal components for this interval according to facies associations recognized by Ciccioli and Marenssi (2012) is shown in Fig. 11. This stratigraphic interval presents a recurrent repetition of the mixed (MP) and volcanic petrofacies (VP) (Fig. 11). In the central section (La Troya Creek), the lowermost unconfined deposits of the DSI are dominated by the plutonic-metamorphic petrofacies (PMP) grading into a mixed petrofacies (MP) toward the top of the section (Fig. 11). However, in the southern section (Del Yeso Creek, Fig. 11) this sequence presents a mixed supply (MP). Thus, the cyclic repetition of the MP/VP petrofacies exposed in the basal interval of the DSI (confined deposits) in the northern section could indicate a mixed supply from basement crystalline

rocks (Western Sierras Pampeanas) with volcanic and some sedimentary rocks (Cordillera Frontal and Precordillera). The provenance from the volcanic arc is in agreement with the westeeast paleocurrents recorded by Ciccioli (2008) and Limarino et al. (2010) for the confined part of the lower member of the Toro Negro Formation. This paleodrainage direction was the responsible of the westeeast oriented paleovalley carved into the Vinchina Formation (Limarino et al., 2010). The upper stratigraphic levels of this sequence (unconfined deposits) initiate with a wedge of plutonic-metamorphic petrofacies (PMP) passing upwards and to the south to a mixed petrofacies (MP), indicating pulses of sediments from the crystalline basement (Western Sierras Pampeanas). This interpretation is supported by the abundant presence of schist and gneiss fragments as well as different types of simplectites characteristic of such basement ranges. 6.1.2. Depositional sequence II In the central section and its surroundings, the DSII is dominated by the plutonic-metamorphic petrofacies (PMP) with abundant schist, gneiss and metamorphosed volcanic fragments as well as different types of simplectites (Fig. 11). Toward the top of this sequence a change to a mixed petrofacies (MP) due to the increasing participation of volcanic components is recognized (Fig. 11). In the southern section (Del Yeso Creek, Fig. 11), this sequence presents a mixed composition (MP) enriched in volcanics and with an increase in sedimentary and low-grade metamorphic components in relation to the central and northern sections. As can be seen in Fig. 11, there are subtle variations in the composition but within the same petrofacies (MP). Thus, the lower part of the DSII shows a clear dominance of plutonic-metamorphic petrofacies (PMP) in the central and north area, indicating a supply from crystalline basement (Western Sierras Pampeanas). The shift into the mixed petrofacies (MP), enriched in volcanics, toward the top of this sequence could indicate an increase in supply from Paleozoic and Mesozoic volcanic rocks of the Precordillera together with a more distal supply from Tertiary volcanic rocks of the Cordillera Frontal and probably mixing with some neo-volcanic components. 6.1.3. Depositional sequence III The DSIII exhibits different compositions both from base to top and along the strike. In the La Troya section the mixed petrofacies (MP) recognized in the basal part passes up sharply to a volcanic petrofacies (VP) in the middle of the sequence (Fig. 11). At the top of the sequence the VP petrofacies is replaced by the the plutonic-

Table 3 Main features of the Toro Negro Formation sandstones. Sample

Depositional Sequence I

FA

Mode

Sort.

Round Text

cs cs cs cs cs cs cs cs cs cs cs cs cs cs cs cs cs cs cs cs

(f)

(m) (f) (f) (m)

(f) (f)

Clast

T

S %

M M M M M S S M M M M M M M M M M M M M

R

CC

S E E

S S S E

M M M E S E S S E S S

M E

cs cs (f) cs (f) cs (f) cs (f) cs cs cs (f) cs cs cs cs f (cs) cs cs cs cs (f) cs (f) cs

M M M M M M M S M M M M M M M M M M M

cs cs

M S M M

cs (m) cs cs cs cs cs

M S M M M S

L

Zeol

Clay Si

Mqz CO3

11.4 17.4 8.8 14.8 14.8 8.3 12.3 20.2 10.5 19.0 7.8 9.8 17.7 13.4 12.0 14.3 18.8 10.2 14.9 9.0

1.1 1.8 1.1 1.0 0.7 1.0 1.1 0.6 1.1 1.0 1.0 0.5 1.0 1.1 1.0 1.0 1.0 0.6 1.0 1.0

24.8 29.1 28.1 19.4 9.5 22.0 23.5 36.1 15.1 28.8 20.4 21.6 28.8 12.2 31.6 22.2 26.3 22.1 18.1 16.7

30.1 34.2 26.8 29.9 9.5 28.8 32.9 35.2 22.0 40.0 28.5 28.4 39.0 25.9 30.8 33.3 30.1 35.9 22.0 21.5

45.1 36.8 45.1 50.7 81.1 49.2 43.6 28.7 62.9 31.2 51.1 50.0 32.2 61.9 37.6 44.4 43.6 42.0 59.8 61.8

Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Lithic Feldsarenite Feld. Lithoarenite Lithic Feldsarenite Feld. Lithoarenite Feld. Lithoarenite Lithic Feldsarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite

23.8 62.5 62.5 87.5 95.2 50.0 80.0 34.7 69.6 59.1 0.0 10.5 2.6 68.0 4.8 69.0 69.4 0.0 15.4 47.1

9.5 6.3 12.5 6.3 4.8 0.0 16.0 16.3 8.7 13.6 0.0 36.8 33.3 20.0 0.0 6.9 0.0 18.8 11.5 11.8

4.8 0.0 0.0 0.0 0.0 0.0 0.0 4.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

S S

78.0 86.3 86.2 77.9 89.7 83.2 73.1 76.8 87.2 72.6 95.5 77.1 75.6 95.5 76.8 80.9 85.7 72.3 87.9 79.5 91.5

0.0 0.9 2.1 3.6 0.7 0.6 5.0 0.0 1.9 4.8 0.6 1.5 4.3 0.0 2.8 1.4 4.3 1.2 0.6 0.0 0.0

16.8 12.5 10.1 17.5 8.5 15.3 20.7 21.4 8.3 19.6 3.4 16.2 17.2 4.0 12.2 16.1 9.0 19.1 8.7 19.0 8.0

5.2 0.3 1.6 1.1 1.1 0.9 1.2 1.7 2.6 3.0 0.5 5.2 2.9 0.5 8.3 1.7 0.9 7.4 2.8 1.5 0.5

13.3 20.4 21.7 25.8 13.1 20.8 33.3 18.2 27.4 30.8 22.9 21.8 22.9 15.8 19.3 20.5 17.3 20.3 29.1 19.3 28.1

20.8 21.1 26.3 38.5 32.4 38.0 29.6 22.9 30.1 33.6 28.1 30.1 37.9 23.8 26.8 28.1 30.5 24.6 14.3 21.4 25.9

65.9 58.6 52.0 35.7 54.5 41.2 37.0 58.9 42.5 35.5 49.0 48.1 39.2 60.4 53.9 51.3 52.3 55.1 56.6 59.3 45.9

Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Lithic Feldsarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Lithoarenite Feld. Lithoarenite Feld. Lithoarenite

64.5 76.7 26.3 57.8 34.8 9.6 3.0 52.7 23.1 23.1 54.5 33.3 67.8 23.3 28.6 19.4 41.4 43.2 10.7 66.7 64.7

21.0 11.6 10.5 23.4 0.0 11.5 20.9 27.0 30.8 30.8 24.2 33.3 15.3 30.0 28.6 14.5 37.9 24.7 32.1 28.2 29.4

0.0 0.0 0.0 1.6 0.0 0.0 0.0 2.7 0.0 0.0 0.0 0.0 5.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

11.3 2.3 0.0 3.1 8.7 0.0 0.0 8.1 30.8 30.8 6.1 0.0 10.2 0.0 0.0 6.5 0.0 16.0 32.1 0.0 0.0

S S

77.6 0.0 85.1 0.5

21.4 18.4

1.1 1.0

26.6 29.2

31.2 34.3

42.2 36.5

Feld. Lithoarenite Feld. Lithoarenite

23.5 20.4

4.4 2.0

0.0 0.0

1.5 2.0

75.2 81.5 88.6 85.7 78.7 86.8

13.3 13.5 8.4 12.2 15.8 9.2

7.6 3.6 0.3 1.0 3.9 2.6

24.8 22.7 33.0 24.4 28.5 22.6

27.7 25.5 30.4 25.8 29.4 19.5

47.5 51.8 36.6 49.8 42.1 57.8

Feld. Feld. Feld. Feld. Feld. Feld.

22.7 0.0 7.1 14.3 44.1 50.0

50.0 8.2 60.7 51.4 39.0 21.9

0.0 0.0 0.0 0.0 0.0 0.0

22.7 2.0 21.4 20.0 10.2 6.3

S S E

E

E E

ME

E S E E E E

E E E S S

F

1.6 1.2 1.1 0.6 0.0 0.7 1.1 1.1 4.1 0.0 4.4 1.5 1.7 1.7 0.6 0.6 0.5 0.0 1.2 1.8

E E E

E VE M S E E E

Q

Cements

85.9 79.6 89.0 83.7 84.5 90.0 85.6 78.1 84.3 80.0 86.8 88.1 79.6 83.9 86.3 84.1 79.7 89.2 82.9 88.2

E VE

cs

Mat (%) Cem (%) Por (%) Folk et al. (1970) 2classification

E

E E VE E E E M S

3.9 1.4 2.7 1.0 1.5 1.4

Lithoarenite Lithoarenite Lithoarenite Lithoarenite Lithoarenite Lithoarenite

0.0 61.9 3.1 18.8 6.3 12.5 0.0 0.0 0.0 0.0 0.0 25.0 0.0 0.0 0.0 36.7 0.0 4.3 0.0 13.6 0.0 100 0.0 31.6 0.0 7.7 0.0 0.0 0.0 95.2 3.4 10.3 0.0 22.2 0.0 81.3 0.0 3.8 0.0 35.3 3.2 4.7 63.2 7.8 56.5 67.3 65.7 2.7 0.0 0.0 9.1 33.3 0.0 31.7 21.4 53.2 6.9 9.9 10.7 2.6 5.9

OFe

Gy

C2F

0.0 9.4 6.3 6.3 0.0 25.0 4.0 8.2 17.4 13.6 0.0 21.1 56.4 12.0 0.0 10.3 8.3 0.0 69.2 5.9

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 4.7 0.0 6.3 0.0 11.5 10.4 6.8 15.4 15.4 6.1 0.0 1.7 15.0 21.4 6.5 13.8 6.2 14.3 2.6 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

North section (Los Pozuelos-Aguada creek) TN1/06 FAI Sm-g bs-mbs sr TN-47/04 FAI Sm mbs sr-sa TN-48/04 FAI Sm-mg mbs sr TN15/06 FAI Sg (G) mbs sr TN19/06 FAI Sm (P) bs sa TN23/06 FAI Sm bs sa-sr TN3/06 FAIII Sm-g mbs sa-sr TN4/06 FAIII Sm mbs sr-sa TN6/06 FAIII Sg-Mg mbs-ps sr TN7/06 FAIII Sf-m bs sr TN10/06 FAIII Sm ps sr TN14/06 FAIII Sm-g mbs sr TN5/06 FAIII Sf-m Mbs sr TN9/06 FAIII Sm-g mbs sa TN20/06 FAIII Sm-g mbs sa-sr TN21/06 FAIII Sm-g bs-mbs sa-sr TN22/06 FAIII Sm-g mbs sr-sa TN11/06 FAIV Sg-Mg ps sr-sa TN13/06 FAIV Sg-Mg mbs sr TN16/06 FAIV Smg-P ps sa-sr Depositional Central section (La Troya creek) Sequence II TN9 FAII Sg mbs-ps r TN10 FAII Sm-g bs-mbs TN11 FAII Sg (G) mbs sa-sr TN13 FAII Sf bs sa-sr TN14 FAII Sm bs-mbs sr-sa TN15 FAII Sm bs sr-sa TN16 FAII Smf-f mbs-ps sr-sa TN 17 FAII Sm mbs sr-sa TN-30/04 FAII Sg-S mbs sr TN1/05 FAII Sm (P) mbs sa-sr TN2/05 FAII Sm (P) mbs sr TN19 FAV Sg bs-mbs sr-sa TN20 FAV Sf-m mbs sr-sa TN21 FAV Sm bs sr-sa TN22 FAV Sf-m bs sa-sr TN24 FAV Sm mbs sr-sa TN25 FAV Sf-m mbs-ps sr-sa TN26 FAV Sm mbs-bs sr-sa TN27 FAV Sm bs-mbs sr-sa TN5/05 FAV Sm bs-mbs r-sr TN6/05 FAV Sm Mbs sa-sr South section (del Yeso creek) TN1/07 FAVIII Sm Mbs sa-sr TN2/07 FAVIII Sm bs sr-sa Central section (La Troya creek) TN29 FAVI Sg mbs-bs sa-sr TN31 FAVI Sg (G) ms-bs r-sr TN33 FAVI Sm bs-mbs sa-sr TN34 FAVI Sm-(g) bs sa-sr TN37 FAVI Sm mbs sa-sr TN38 FAVI Sg bs (mbs) sa-sr

Contacts

22.1 10.3 38.2 0.0 26.5 8.2 40.8 0.0 0.0 87.8 7.1 11.4 1.7 21.9

4.5 2.0 3.6 2.9 5.1 0.0

0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 25

(continued on next page)

Sample

26

Table 3 (continued ) FA

Mode

Sort.

Round Text

Clast S %

T

R

CC

M M M M M M M M M M M M M M M

S S E S E

S E

S

S

M M M M M M

E E E E S E

E

M M M M M M M M M M M M M M M M M E M M

E S E S

E

VE

VE

E

E E E

E E

E E E

S

E E

E E

E VE VE VE VE E E

M E M S M

E E

Mat (%) Cem (%) Por (%) Folk et al. (1970) 2classification

Cements

Q

F

L

90.6 84.3 74.8 86.5 93.9 80.9 90.3 76.1 83.7 85.2 78.3 76.6 90.4 84.6 93.3

2.0 2.0 5.6 4.0 1.0 1.5 1.1 2.8 0.6 0.0 1.5 2.7 1.4 0.4 0.0

7.5 12.5 17.9 8.9 4.5 15.9 7.1 16.2 15.3 13.4 12.6 17.3 7.2 14.3 6.2

0.0 1.2 1.7 0.6 0.6 1.7 1.5 5.0 0.3 1.4 2.6 3.3 0.9 0.8 0.5

27.5 28.0 32.4 28.7 23.1 25.1 16.8 23.1 31.2 24.1 32.5 17.7 16.5 11.5 17.2

21.6 22.0 29.8 31.3 23.5 24.3 16.3 24.4 24.2 19.3 25.4 20.0 15.8 18.5 20.2

51.0 50.0 37.8 40.0 53.4 50.6 66.8 52.6 44.6 56.6 42.1 62.3 67.6 70.0 62.6

Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Feld. Lithoarenite Lithoarenite Lithoarenite Lithoarenite Lithoarenite

Zeol

Clay Si

78.3 46.0 21.8 13.8 28.6 24.1 26.3 1.6 18.8 79.3 6.0 6.0 28.0 16.7 100.0

17.4 4.3 0.0 26.0 0.0 2.0 23.1 0.0 3.8 37.9 0.0 13.8 28.6 0.0 0.0 8.6 1.7 1.7 10.5 10.5 21.1 6.5 4.8 6.5 39.6 2.1 4.2 20.7 0.0 0.0 22.4 0.0 4.5 22.4 0.0 4.5 32.0 0.0 0.0 9.5 0.0 0.0 0.0 0.0 0.0

76.8 83.2 87.5 73.6 81.6 69.9

1.1 0.0 0.0 0.0 1.2 4.1

20.4 16.8 10.0 20.7 14.1 20.5

1.7 0.0 2.5 1.7 3.1 5.5

33.7 32.5

31.7 36.8

34.6 30.7

25.4 24.8 37.9

27.1 15.2 36.4

47.5 60.0 25.8

Feld. Lithoarenite Lithic Feldsarenite Ooesparitea Feld. Lithoarenite Lithoarenite Lithic Feldsarenite

78.5 76.3 75.1 91.7 79.8 77.8 81.7 97.1 81.4 88.3 75.8 73.7 78.3 91.2 93.3 93.1 84.5 85.1 75.0 86.2 80.3 84.3 76.7 93.3

0.9 3.7 3.2 0.0 0.0 1.1 1.3 0.0 1.0 0.0 0.0 4.7 1.2 3.7 3.1 3.1 0.0 0.6 2.3 0.3 0.6 0.5 1.2 1.7

18.3 16.3 20.1 7.3 16.0 18.8 15.4 2.9 13.6 11.8 19.6 19.0 18.9 0.0 1.8 1.9 13.8 12.1 15.7 13.8 16.7 13.1 19.2 3.9

2.3 3.7 1.6 1.0 4.2 2.2 1.7 0.0 2.0 2.0 4.6 2.6 1.6 5.1 1.8 1.9 1.7 2.3 5.0 1.6 2.4 2.1 2.9 1.1

27.0 28.8 21.1 15.8 25.1 16.5 23.2 18.9 25.7 28.9 17.6 26.2 10.4 18.2 9.3 11.7 24.4 7.7 9.4 26.9 23.2 15.6 26.7 15.5

28.9 25.3 21.6 32.2 21.4 24.0 19.8 15.3 33.8 29.5 16.6 20.0 25.2 18.2 14.8 13.6 16.3 19.7 3.6 22.2 28.8 25.3 12.9 9.7

44.1 45.9 57.3 52.0 53.5 59.6 57.1 65.8 40.5 41.6 65.8 53.8 64.4 63.6 75.9 74.8 59.3 72.5 87.0 50.9 48.1 59.1 60.3 74.8

Feld. Lithoarenite 20.0 Feld. Lithoarenite 4.5 Feld. Lithoarenite 55.7 Feld. Lithoarenite 84.6 Feld. Lithoarenite 10.9 Feld. Lithoarenite 13.4 Feld. Lithoarenite 0.0 Lithoarenite 16.7 Feld. Lithoarenite 16.1 Feld. Lithoarenite 4.2 Lithoarenite 17.8 Feld. Lithoarenite 51.8 Feld. Lithoarenite 23.2 Neovol. Lithoarenite Neovol. Lithoarenite 100 Neovol. Lithoarenite 100 Neovol. Lithoarenite 87.5 Volc. Lithoarenite 0.0 Lithoarenite 0.0 Feld. Lithoarenite 0.0 Feld. Lithoarenite 5.8 Feld. Lithoarenite 0.0 Lithoarenite 27.8 Lithoarenite 28.6

5.3 5.3 4.0 8.0 0.0 0.0 18.2 0.0 4.3 0.0 30.4 15.2

0.0 0.0 0.0 0.0 0.0 0.0

Mqz CO3

0.0 0.0 0.0 2.3 0.0 4.3

4.0 9.1 18.0 15.4 7.3 16.4 13.5 33.3 6.5 0.0 5.5 26.8 1.8

6.0 6.0 4.5 2.3 1.6 4.9 0.0 0.0 3.6 1.8 0.0 0.0 8.1 10.8 0.0 16.7 0.0 9.7 0.0 4.2 1.4 4.1 1.8 0.0 3.6 1.8

0.0 0.0 12.5 0.0 6.5 9.3 10.1 13.8 5.6 14.3

0.0 0.0 0.0 0.0 0.0 0.0 1.4 0.0 0.0 0.0

0.0 16.0 46.2 13.8 21.4 56.9 15.8 79.0 25.0 0.0 55.2 55.2 0.0 64.3 0.0

OFe 0.0 10.0 5.1 20.7 21.4 6.9 15.8 1.6 10.4 0.0 11.9 11.9 40.0 9.5 0.0

Gy 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

C2F 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

17.5 8.8 63.2 0.0 4.0 0.0 84.0 0.0 95.0 5.0 0.0 0.0 15.9 11.4 52.3 0.0 95.7 0.0 0.0 0.0 32.6 17.4 0.0 0.0 60.0 79.5 18.0 0.0 72.7 65.7 56.8 33.3 48.4 79.2 65.8 7.1 64.3

2.0 0.0 1.6 0.0 3.6 4.5 10.8 0.0 19.4 12.5 4.1 12.5 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

2.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.4 0.0 5.4

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 100 0.0 0.0 93.5 0.0 0.0 90.7 0.0 4.3 71.0 7.2 6.9 72.4 6.9 0.0 66.7 0.0 0.0 42.9 14.3

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

References: S: sandstone; P: pebble; G: granule; f: fine, m: median, g: coarse and Mg: very coarse; cs: clast-supported, ms: matrix-supported and f: flotant; bs: good, Mbs: very good, mbs: moderately and ps: poorly sorted; r: rounded, sr: subrounded, sa: subangular and a: angular; T: tangential, R: straight, CC: concaveeconvex and S: suturate; M: main, S: secondary, E: scarce and VE: very scarce; Zeol: zeolite; Si: secondary growth of silice; Mqz: megaquartz; CO3: carbonate; Gy: gypsum; OFe: iron oxide; C2F: secondary growth of feldspar. a Folk (1962) classif.

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

TN39 FAVI Sg mbs sr-sa cs TN40 FAVII Sf bs-mbs sr-sa cs (f) TN41 FAVII Sf bs-mbs sr-sa cs (m) TN42 FAVII Sf (m) bs-mbs sa-sr cs (m) TN44 FAVIII Sm bs-mbs sr-sa cs TN45 FAVIII Sg mbs sr-sa cs (f) TN46 FAVIII Sm bs-mbs sa-sr cs TN47 FAVII Sg mbs-bs sr-sa cs TN48 FAVII Sm bs-mbs sr-sa cs TN49 FAVII Sm mbs sa cs (f) TN51 FAVII Sf mbs sr-sa cs (f) TN52 FAVI Sm mbs sr cs TN53b FAVI Sm mbs sa-sr cs TN54 FAVI Sm-g mbs sr-sa cs (f) TN57 FAVI Sm bs sr-sa cs South section (del Yeso creek) TN3/07 FAVIII Sf bs sa-sr cs (m-f) TN4/07 FAVIII Sf-m bs-mbs sa-sr cs TN6/07 FAVIII Sm-Mg mbs sa-sr cs (f) TN7/07 FAVIII Sf bs-mbs sa-sr cs (f) TN8/07 FAVIII Sm (P) mbs sr cs TN9/07 FAVIII Sf mbs r cs (f) Depositional Central (La Troya creek) and South (del Yeso creek) sections Sequence II TN63 FAIX Sg bs sr-r cs (f) TN2/04 FAIX Sm-g mbs-bs sa-sr cs TN5/04 FAIX Sm mbs sa cs (m) TN6/04 FAIX Sg mbs sr cs (m) TN-64 FAIX Sm bs sa-sr cs TN-65 FAIX Smg-G bs-mbs sa-sr cs (f) TN-66 FAX Sm(P)-Sf ps-mbs sr-sa cs (f) TN68 FAX Sg-G ps sa-sr cs TN12/04 FAX Sm(g) bs-mbs sr-sa cs TN14/04 FAX Sg mbs sa cs TN16/04 FAX Sm mbs-bs sr cs (f) TN9/04 FAX Sm (g) mbs sa cs TN10A/04 FAX Sm-g mbs sa-sr cs (f) TN19/04 FAX Sm-g mbs sa-sr cs TN20/04 FAX Sm mbs sa cs TN21/04 FAX Sm-f mbs sa-a cs TN7/05 FAX Sm (P) bs-mbs sr-sa cs (f) TN26/06 FAX Sm (P) bs sr-r f (cs) TN71 FAXI Smg-P ps sa-sr cs (f) TN72 FAXI Sg bs-mbs sa-sr cs (f) TN73 FAXI Sm bs-mbs sa-sr f TN29/04 FAXI Sg-P mbs sr-sa cs (f) TN11/07 FAXI Sm (P) Mbs sa-sr cs TN12/07 FAXI Sm (P) ps sr cs (m)

Contacts

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

27

Table 4 Point-count data of the Toro Negro Formation conglomerates. Counts

Texture

Northern Section e Los Pozuelos-Aguada creek Lower Depositional Sequence I C1 Clast-orthoconglomerate Member C2 Clast-orthoconglomerate C3 Clast-orthoconglomerate C4 Clast-orthoconglomerate C5 Clast-orthoconglomerate C6 Clast-orthoconglomerate Depositional Sequence II Central Section e La Troya creek C7 Matrix-paraconglomerado C8 Matrix-orthoconglomerate C9 Matrix-orthoconglomerate C10 Matrix-orthoconglomerate C11 Matrix-orthoconglomerate C12 Clast-orthoconglomerate C13 Clast-orthoconglomerate C14 Clast-orthoconglomerate C15 Matrix-orthoconglomerate Upper Depositional Sequence III C16 Matrix-orthoconglomerate Member C17 Clast-orthoconglomerate C18 Clast-orthoconglomerate C19 Clast-orthoconglomerate C20 Clast-orthoconglomerate C21 Clast-orthoconglomerate C22 Clast-orthoconglomerate C23 Clast-orthoconglomerate C24 Clast-orthoconglomerate C25 Clast-orthoconglomerate C26 Matrix-orthoconglomerate C27 Clast-orthoconglomerate C28 Clast-orthoconglomerate C29 Clast-orthoconglomerate South Section e del Yeso creek C30 Matrix-orthoconglomerate C31 Matrix-orthoconglomerate C32 Matrix-orthoconglomerate C33 Clast-orthoconglomerate C34 Clast-orthoconglomerate C35 Clast-orthoconglomerate C36 Clast-orthoconglomerate

metamorphic petrofacies (PMP) due to an increase in high-grade metamorphic lithics coupled with sedimentary and low-grade metamorphic lithics (Fig. 11). At the same time, a PMP petrofacies enriched in Ls þ Lmb components dominates in the southern section (Fig. 11). So, this depositional sequence shows a lateral shift from PMP (locally persistent in the south close to the UmangoeEspinal Ranges) to MP (in the central area) petrofacies and later an incursion of the volcanic petrofacies (VP), indicating an important event of coeval volcanism for this interval due to the large amount of intrabasinal fresh and glassy volcanic components. Finally, to the top of this unit, a predominance of the PMP petrofacies but this time with a light increase in the Ls þ Lmb components is recognized. This composition most probably indicates that the Precordillera was the main source during this interval. 6.2. Conglomerate lithic associations and provenance The conglomerate data were plotted on a Lv:(Ls þ Lmb):(Lp þ Lma) ternary diagram defined here with the intent of establishing a relationship between the composition of conglomerates and sandstones. According to the different potential sources (Fig. 12), the Lv apex groups all volcanic lithics, indicating supply from old (paleo) or (neo)-volcanic arcs synchronic with sedimentation. The lower left apex (Ls þ Lmb) includes all sedimentary and metasedimentary (slates, phyllites) lithics that are, on a theoretical affinity, a contribution of recycled orogens. Finally, the

Size

G

Q

V

S1

S2

Lma

Lmb

26.0 30.0 10.8 4.0 23.0 13.0

1.0 2.0 6.2 7.0 2.0 5.0

19.7 20.0 60.0 2.0 35.0 40.0

33.3 8.0 3.0 50.0 20.0 15.0

2.1 15.0 3.1 4.0 2.0 2.0

17.7 10.0 10.8 30.0 18.0 25.0

0 15 6.2 3.0 0 0

5 cm (10e15 cm) 5 cm (15e20 cm) 7 cm (20 cm) 7 cm (>20 cm) 10 cm(>20 cm) 20 cm (35 cm) 4 cm (>8 cm) 5 cm (>10 cm) 3 cm (>5 cm) 5 cm (>15 cm) 7 cm (30 cm) 5 cm (15 cm) 10 cm (>15 cm) 10 cm (>15 cm) 10 cm (20 cm) 7 cm (20 cm) 4 cm (15 cm) 5 cm (15 cm) 4 cm (>10 cm) 5 cm (20 cm) 6 cm (30 cm) 6 cm (30 cm) 5 cm (12 cm)

25.0 10.7 14.0 11.7 13.2 15.3 14.5 15.5 24.5 26.8 23.4 35.7 41.8 34.8 12.7 18.2 14.5 11.3 20.0 20.6 10.9 11.4 11.2

2.5 1.8 1.8 1.7 1.3 1.7 1.6 1.4 0.0 1.4 1.3 3.6 1.5 1.5 1.3 1.5 4.8 3.2 1.7 1.6 2.7 3.8 2.2

30 33.9 22.8 23.3 22.3 30.5 29.0 33.8 37.7 33.8 36.3 25.0 23.8 22.7 36.7 33.3 42.1 31.1 33.3 25.3 28.4 29.7 32.5

7.5 19.6 24.5 25.0 18.4 10.1 19.3 28.1 24.5 29.5 22.0 17.8 10.4 21.2 11.3 22.7 7.2 12.9 0.0 15.8 19.6 16.7 10.1

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 25.0 15.9 0.0 0.0 0.0

35.0 33.9 36.8 38.3 44.7 42.4 35.5 21.1 13.2 8.5 16.9 17.9 22.4 19.7 38.0 24.2 14.5 19.9 20.0 20.6 19.1 10.3 33.7

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 16.8 21.5 0.0 0.0 19.1 28.1 10.1

4 4 5 5 5 30 7

26.4 24.0 28.2 4.9 22.4 63.3 25.0

1.1 1.3 1.3 1.6 1.7 3.3 1.6

27.5 36.0 30.8 3.3 32.8 3.3 29.7

3.3 4.0 0.0 0.0 1.7 0.0 3.1

18.7 13.3 17.9 8.2 13.8 23.3 25.0

8.8 9.3 15.4 82.0 22.4 3.3 15.6

14.3 12.0 6.4 0.0 5.2 3.3 0.0

7 8 7 7 7 7

cm cm cm cm cm cm

cm cm cm cm cm cm cm

(15 (20 (15 (30 (15 (15

cm) cm) cm) cm) cm) cm)

(>7 cm) (>7 cm) (>7 cm) (>10 cm) (>15 cm) (50 cm) (15 cm)

upper right apex (Lp þ Lma) comprises all the components derived from crystalline rocks (granites, migmatites, K-feldspars, low-grade and high-grade metamorphic rocks and quartz). This diagram (Fig. 12) defines three main fields: 1) volcanic lithic association (VLA), 2) sedimentary lithic association (SLA) and basement lithic association (BLA). Other ternary diagrams were designed to discriminate the supply from high-grade metamorphic basement and other crystalline rocks such as granites (Fig. 13). This distinction is important due to the presence of two types of granite sources: the Western Sierras Pampeanas and the western granites (e.g. Come Caballos, Las Tunas in the Cordillera Frontal and Del Peñón Granite in the Cordillera Frontal/Precordillera; Caminos, 1972). Thus, we developed Lma:Ls þ Lmb:Lp and Lma:Lmb þ Ls:Lp þ Lv diagrams (Fig. 13). In the last case, the volcanic component (Lv) was added to the plutonic one (Lp) since they represent the western source (Cordillera Frontal and Precordillera). Finally, binary diagrams plotting separately individual components were made to better visualize changes in the composition of conglomerates (Fig. 14). 6.2.1. Depositional sequence I Conglomerates of the DSI are only present in the northern section (Los Pozuelos-Aguada Creek) because fine-grained sedimentation took place in the central and southern part of the basin (Ciccioli and Marenssi, 2012). Although most of conglomerates fall in the BLA field (Fig. 12), they are enriched in both volcanic and

28

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

Fig. 8. Conglomerates classification of the Toro Negro Formation following the proposal of Limarino et al. (1996, in Scasso and Limarino, 1997). References: C, quartz þ chert; G, granites þ gneiss þ feldspars, and L, lithic fragments remaining.

sedimentary components. In addition, two samples show a different composition being clearly enriched in volcanic (VLA) and sedimentary lithics (SLA), respectively (Fig. 12). Therefore the conglomerates of DSI mainly reflect provenance from mixed sources. In the Lma:Ls þ Lmb:Lp diagram that separates the basement components, we can see a mixed composition for conglomerates of the DSI in the northern section (Fig. 13A), whereas the Lma:Lmb þ Ls:Lp þ Lv diagram shows a clear tendency of clustering in the Lp þ Lv field indicating a western source (Fig. 13B). As can be seen in the binary diagram (Fig. 14), in the DSI (northern section) there is a random mix of all components with peaks of V and S1 þ Lma. Thus, a western source area (Cordillera Frontal and Precordillera) with a minor supply from the north (Western Sierras Pampeanas) is interpreted for this sequence. 6.2.2. Depositional sequence II In the central section (La Troya Creek), most conglomerates of the DSII plot in the BLA field (Fig. 12) showing a predomination of high-grade metamorphic components (Lma). This can also be seen in the complementary diagrams where these samples clearly group in the Lma field (Fig. 13A). The shift toward the Lp þ Lv apex in Fig. 13B indicates the presence of a clear volcanic component toward the top of this unit. In the binary diagram (Fig.14), the Lma component predominates (crystalline basement source) with secondary amount of V and S1 and a lack of Lmb component. Toward the top of this sequence, the V and S1 components increase their participation. This composition evidences a mix from two main supply areas for the DSII: a western source (S1 þ V þ G) and a northern or southern source (Lma) the latter corresponding to the Western Sierras Pampeanas. Taking into account paleocurrent data, the distribution of sedimentary environments and the grain-size trend (Ciccioli, 2008; Ciccioli and

Marenssi, 2012) a southern source from the Umango Range is ruled out and a northern provenance is favored for this interval. 6.2.3. Depositional sequence III Conglomerates of the DSIII (upper member) show a similar composition from north to south in the basin, most of them plotting in the BLA field with only three samples within the VLA field (Fig. 12) showing a slight predominance of high-grade metamorphic (Lma) and plutonic (Lp) components. Two samples from the southern section plot separately due to their marked enrichment in plutonic and high-grade metamorphic (Lp þ Lma) components (Fig. 12). This is also observed in the complementary diagrams (Fig. 13) where one sample is enriched in Lma (Fig. 13A) and another in Lp (Fig. 13A). Notwithstanding this, most of the samples fall in the central part between the Ls þ Lmb and Lp fields (Fig. 13A) and in the Lp þ Lv field (Fig. 13B) indicating a clear sedimentary, volcanic and granitic supply. In the binary diagram (Fig. 14), the DSIII shows a mixed composition with pulses of V, G and Lma components indicating supply from a western source (Cordillera Frontal and Precordillera) and a northern or southern source (Western Sierras Pampeanas). However, toward the upper part of the sequence, the S2 þ Lmb components become important indicating the beginning of the supply from eastern Precordillera. In the southern section pulses of the Lma and G components are registered with a higher development than in the central section indicating a southern supply (Fig. 14). This is interpreted as the supply from the Umango Range to the south of the basin. 7. Evolutionary model The analysis of the changes in sandstone petrofacies and conglomerate lithic associations, identified in the three sections of

Table 5 Recalculated modal point-count data of the Toro Negro Formation sandstones (See Appendix 1 for more detail data). Sample

FA

Dickinson et al. (1983) Qt

Depositional Sequence I

North section (Los Pozuelos-Aguada creek) TN1/06 FAI 30.5 30.5 TN47/04 FAI 32.5 35.9 TN48/04 FAI 36.6 30.7 TN15/06 FAI 24.1 32.1 TN19/06 FAI 12.3 43.0 TN23/06 FAI 34.7 31.4 TN3/06 FAIII 29.5 34.9 TN4/06 FAIII 36.0 36.9 TN6/06 FAIII 26.9 26.3 TN7/06 FAIII 30.2 40.5 TN10/06 FAIII 27.0 29.9 TN14/06 FAIII 29.3 31.1 TN5/06 FAIII 30.3 39.5 TN9/06 FAIII 15.8 26.6 TN20/06 FAIII 38.3 32.3 TN21/06 FAIII 25.9 34.1 TN22/06 FAIII 26.3 30.1 TN11/06 FAIV 31.3 38.9 TN13/06 FAIV 25.2 26.8 TN16/06 FAIV 22.9 25.7 Central section (La Troya creek) TN9 FAII 48.2 33.7 TN10 FAII 37.6 25.2 TN11 FAII 29.2 29.2 TN13 FAII 30.9 41.5 TN14 FAII 24.4 34.3 TN15 FAII 31.6 40.6 TN16 FAII 40.2 36.5 TN17 FAII 34.3 35.6 TN30/04 FAII 31.9 42.2 TN1/05 FAII 35.5 34.6 TN2/05 FAII 28.8 30.8 TN19 FAV 44.2 40.1 TN20 FAV 28.1 39.5 TN21 FAV 25.1 34.0 TN22 FAV 34.2 46.5 TN24 FAV 28.8 30.7 TN25 FAV 22.6 37.0 TN26 FAV 35.7 32.4 TN27 FAV 41.7 24.0 TN5/05 FAV 24.5 23.8 TN6/05 FAV 23.8 40.5 South section (Del Yeso creek) TN1/07 FAVIII 30.6 32.4 TN2/07 FAVIII 34.3 34.3 Central section (La Troya creek) TN29 AFVI 42.9 39.1 TN31 AFVI 42.8 32.7 TN33 AFVI 44.3 35.9

Dickinson and Suczek (1979)

Index

Types of Lv

Regenerated lithics

Regenerated

Lv/Lm

Neo

Paleo

Met

RLv

RLm

RLs

RLv/Lm

Ls þ Lmb

Lv

Lp þ Lma

0.6 2.0 0.8 1.4 15.3 0.9 1.1 3.6 0.6 1.0 0.5 1.2 1.4 1.6 1.4 1.3 1.0 1.0 0.7 1.5

2.4 0.7 2.1 6.1 2.2 0.0 1.8 0.4 3.1 2.3 2.0 1.8 0.0 4.8 0.2 0.1 0.2 2.1 3.4 1.3

2.8 23.1 12.9 11.6 6.9 0.0 10.7 0.0 4.0 13.0 13.9 5.7 48.6 0.0 0.0 0.0 0.0 43.5 5.4 7.7

88.9 53.8 67.7 72.1 89.7 100 71.4 100 62.0 87.0 77.8 88.6 51.4 89.7 100 75.0 100 56.5 73.0 73.1

8.3 23.1 19.4 16.3 3.4 0.0 17.9 0.0 34.0 0.0 8.3 5.7 0.0 10.3 0.0 25.0 0.0 0.0 21.6 19.2

53.7 30.2 50.0 64.2 51.7 1.8 43.8 25.8 54.6 59.0 53.7 45.5 92.1 69.9 6.3 6.8 12.1 45.1 50.0 30.7

28.4 55.8 37.1 19.4 32.8 87.3 35.9 67.7 29.9 30.8 34.3 39.0 5.3 18.1 45.8 61.0 50.0 43.1 27.0 31.8

17.9 14.0 12.9 16.4 15.5 10.9 20.3 6.5 15.5 10.3 11.9 15.6 2.6 12.0 47.9 32.2 37.9 11.8 23.0 37.5

1.9 0.5 1.3 3.3 1.6 0.0 1.2 0.4 1.8 1.9 1.6 1.2 17.5 3.9 0.1 0.1 0.2 1.0 1.9 1.0

21.0 26.3 12.2 19.0 16.5 7.2 26.6 22.7 21.5 9.1 22.3 22.3 1.9 13.1 32.1 27.4 24.5 15.4 24.7 38.0

34.0 17.5 25.5 46.4 67.0 1.2 24.5 25.0 30.6 36.4 35.1 35.1 67.9 52.5 3.6 3.2 7.1 25.3 31.2 20.4

45.0 56.1 62.2 34.5 16.5 91.6 48.9 52.3 47.9 54.5 42.6 42.6 30.2 34.3 64.3 69.5 68.4 59.3 44.1 41.7

36.6 36.6 27.6 24.7 24.6 17.2 23.3 28.0 23.4 23.5 25.4 23.1 33.7 22.3 20.2 26.3 23.1 17.8 22.1 30.0 20.3

1.0 0.9 0.8 0.5 0.4 0.6 0.3 1.0 1.3 0.7 1.0 0.8 0.4 0.7 0.4 0.5 0.7 2.8 1.8 3.3 4.7

0.5 3.2 0.8 0.6 0.5 0.4 0.7 2.7 1.0 0.6 1.1 0.7 0.5 0.9 1.9 0.2 0.7 1.9 1.9 1.8 1.1

0.0 73.0 14.3 0.0 3.8 0.0 0.0 32.7 25.0 0.0 7.4 0.0 0.0 1.9 20.7 0.0 8.1 16.3 0.0 22.2 50.0

38.5 23.0 64.3 76.0 50.0 44.4 100 55.8 58.3 50.0 81.5 66.7 72.7 53.7 72.4 35.3 86.5 69.8 73.7 66.7 50.0

61.5 4.1 21.4 24.0 46.2 55.6 0.0 11.5 16.7 50.0 11.1 33.3 27.3 44.4 6.9 64.7 5.4 14.0 26.3 11.1 0.0

11.7 49.3 36.4 31.6 25.0 18.9 24.3 49.6 33.3 26.3 36.5 16.2 25.6 41.8 40.7 13.1 42.1 52.6 54.4 54.9 48.4

83.4 45.4 59.7 64.6 64.4 74.7 71.4 49.6 50.0 63.2 43.2 78.8 65.1 50.8 53.1 76.9 50.8 46.5 45.6 37.8 48.4

4.8 5.3 3.9 3.8 10.6 6.3 4.3 0.8 16.7 10.5 20.3 5.1 9.3 7.4 6.2 10.0 7.1 0.9 0.0 7.3 3.2

0.1 1.1 0.6 0.5 0.4 0.3 0.3 1.0 0.7 0.4 0.8 0.2 0.4 0.8 0.8 0.2 0.8 1.1 1.2 1.5 1.0

9.2 9.0 18.9 25.0 12.8 23.0 31.1 3.5 16.7 22.4 25.0 10.1 29.4 22.2 17.7 44.4 27.7 8.3 13.0 12.8 17.8

3.6 39.2 22.6 15.0 9.9 5.1 16.5 32.6 19.7 10.2 27.0 8.3 12.5 17.4 29.9 3.9 32.1 43.2 38.5 45.7 62.4

87.2 51.9 58.5 60.0 77.3 71.9 52.4 64.0 63.6 67.3 48.0 81.7 58.1 60.4 52.4 51.7 40.3 48.5 48.4 41.5 19.8

5.7 17.1

18.1 25.6

1.3 1.1

1.3 1.0

35.0 5.3

65.0 94.7

0.0 0.0

44.4 38.8

44.4 53.1

11.1 8.2

1.0 0.7

17.2 20.3

37.9 29.7

44.8 50.0

30.4 13.7 17.6

20.7 35.5 31.9

0.6 1.3 0.9

1.4 3.7 3.1

33.3 23.1 0.0

54.2 13.5 55.0

12.5 63.5 45.0

37.2 42.6 47.2

57.4 52.7 49.4

5.3 4.7 3.4

0.6 0.8 1.0

8.9 8.5 10.8

18.4 12.4 18.5

72 79 70

L

Qm

F

L

Lv

Ls

Qp

KeF

P

Qmt

Plg/KeF

39.0 31.6 32.7 43.8 44.7 33.9 35.6 27.0 46.9 29.4 43.1 39.6 30.3 57.6 29.3 40.0 43.6 29.8 48.0 51.4

28.4 30.8 34.6 20.3 8.7 23.7 25.2 34.8 19.4 28.6 23.4 23.0 28.3 14.4 34.6 23.0 26.3 25.2 17.7 19.9

30.3 35.9 30.7 31.9 42.6 31.4 34.4 36.6 25.5 40.5 29.9 30.9 39.2 26.6 32.3 34.1 30.1 38.9 26.2 25.3

41.3 33.3 34.6 47.8 48.7 44.9 40.4 28.6 55.2 31.0 46.7 46.1 32.5 59.0 33.1 43.0 43.6 35.9 56.2 54.8

57.1 33.3 58.5 66.2 52.7 1.9 47.5 25.8 58.1 59.0 56.3 46.7 92.1 70.7 6.8 6.9 12.1 48.9 55.2 33.3

14.3 12.8 7.5 15.4 16.4 11.3 15.3 6.5 10.5 10.3 7.8 14.7 2.6 12.2 47.7 32.8 37.9 10.6 19.4 35.9

4.8 5.1 5.7 7.7 7.3 24.5 10.2 3.2 12.8 5.1 7.8 13.3 5.3 2.4 11.4 6.9 0.0 17.0 9.0 5.1

18.2 10.9 16.0 12.2 2.5 14.4 15.5 7.0 15.7 18.0 19.3 13.5 15.4 9.6 12.9 13.5 13.8 18.6 14.7 10.0

11.3 21.9 13.0 17.7 38.3 13.6 16.8 25.0 9.6 18.7 9.0 16.4 20.8 15.8 18.0 17.6 13.8 17.9 10.3 14.7

27.7 28.1 32.7 19.0 8.3 21.2 23.6 30.5 19.3 25.9 22.1 22.2 26.2 13.7 33.1 20.9 24.1 23.6 16.9 19.3

18.0 37.2 41.6 27.6 41.3 27.7 23.3 30.1 25.9 29.9 40.4 15.7 32.5 40.9 19.3 40.5 40.3 31.9 34.3 51.7 35.7

38.4 29.0 26.0 28.5 19.7 25.5 34.4 25.9 27.6 28.7 24.8 36.4 25.9 22.4 28.9 25.4 20.0 23.7 33.5 21.7 22.5

33.7 25.1 29.2 41.5 34.3 40.2 35.9 35.6 42.2 34.3 30.6 40.1 39.5 34.0 46.5 30.7 36.7 32.2 24.0 23.8 40.2

27.8 45.9 44.8 30.1 46.0 34.4 29.7 38.5 30.2 37.0 44.6 23.6 34.6 43.6 24.6 43.9 43.3 44.1 42.5 54.5 37.3

18.6 57.4 40.6 33.8 26.5 20.9 31.5 56.5 34.3 29.4 39.1 26.3 27.8 40.9 51.8 14.7 35.6 46.7 52.8 57.7 48.4

8.6 6.2 4.3 4.1 11.2 7.0 5.6 1.1 17.1 11.8 17.4 0.0 10.1 9.1 0.0 8.6 8.7 1.1 0.0 5.1 3.2

34.3 18.6 7.2 8.1 10.2 17.4 18.5 21.7 14.3 5.9 8.7 33.3 6.3 6.1 21.4 7.8 5.8 27.2 19.4 5.1 3.2

15.7 15.7 12.5 15.4 23.9 21.7 23.3 22.5 16.2 15.4 18.0 14.2 21.1 24.6 18.5 29.9 18.6 19.6 8.0 7.8 5.2

16.4 16.4 11.4 12.3 11.9 8.2 13.4 6.8 15.8 20.6 12.3 14.2 16.1 9.5 12.2 12.4 9.3 13.0 22.1 13.8 17.0

36.9 31.4

27.0 29.9

32.4 34.3

40.5 35.8

44.4 38.8

11.1 8.2

8.9 12.2

12.8 13.7

18.1 24.5 19.8

36.8 33.8 37.4

38.9 32.7 35.9

24.3 33.5 26.7

42.1 55.9 54.8

3.5 2.2 1.4

24.6 26.9 26.0

6.5 23.8 13.2

29

(continued on next page)

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

Depositional Sequence II

F

Sample

30

Table 5 (continued ) FA

Dickinson et al. (1983) Qt

a b

Eolian sandstone samples. Count corresponds to terrigenous components.

Index

Types of Lv

Regenerated lithics

Regenerated

L

Qm

F

L

Lv

Ls

Qp

KeF

P

Qmt

Lv/Lm

Neo

Paleo

Met

RLv

RLm

RLs

Ls þ Lmb

Lv

Lp þ Lma

28.0 24.0 27.5 25.9 31.4 29.8 24.3 27.2 27.5 53.4 38.0 28.6 33.1 35.6 46.5 47.2 57.5 56.4

30.1 37.6 36.9 41.2 36.9 36.0 37.2 36.6 37.6 25.5 30.1 40.8 36.1 32.6 25.1 22.5 19.8 20.0

31.9 33.5 30.0 26.7 26.3 31.1 34.6 29.1 29.0 18.8 28.8 26.6 24.5 28.8 26.5 26.8 19.8 20.5

38.1 29.0 33.1 32.2 36.9 32.9 28.1 34.3 33.3 55.8 41.1 32.6 39.5 38.6 48.4 50.7 60.4 59.5

30.6 59.4 51.6 35.4 23.0 32.4 29.7 25.0 35.3 23.3 51.6 28.4 21.4 62.2 83.7 63.2 61.7 57.0

7.1 0.0 6.3 12.2 12.6 24.3 14.1 8.7 8.2 14.7 10.5 8.1 7.1 3.3 11.5 14.6 5.8 10.7

25.9 17.2 16.8 19.5 14.9 9.5 12.5 20.7 17.6 4.3 6.3 10.8 14.3 7.8 3.8 6.9 4.2 5.0

17.3 15.5 14.6 10.6 11.9 8.5 19.8 13.8 15.6 14.9 10.3 15.3 14.5 12.5 15.7 9.9 12.8 13.1

16.0 13.9 14.6 17.8 12.6 13.4 7.9 14.5 10.8 12.0 5.8 13.6 9.2 7.1 10.0 13.6 11.5 5.6

34.7 27.8 32.7 35.0 37.8 30.7 32.1 30.4 33.2 34.9 21.9 30.1 36.3 28.8 29.1 22.2 20.5 18.8

0.9 1.0 1.7 1.1 1.6 0.4 1.1 0.7 0.8 0.6 0.9 0.6 0.6 0.6 1.4 0.9 0.4 0.4

0.8 2.5 2.0 1.1 0.5 1.0 0.7 0.5 0.9 0.4 1.6 0.5 0.4 2.3 87.0 4.1 2.2 2.1

0.0 0.0 4.1 0.0 0.0 8.3 0.0 0.0 0.0 14.8 0.0 4.8 16.7 42.9 12.6 26.4 24.3 76.8

57.7 47.4 20.4 34.5 50.0 83.3 47.4 30.4 56.7 70.4 69.4 61.9 41.7 57.1 85.1 57.1 74.3 23.2

42.3 52.6 75.5 65.5 50.0 8.3 52.6 69.6 43.3 14.8 30.6 33.3 41.7 0.0 2.3 16.5 1.4 0.0

28.0 47.5 36.7 26.1 20.4 29.3 21.8 19.2 26.8 21.1 42.3 22.4 15.6 59.4 74.2 61.7 54.8 54.3

66.0 51.3 57.6 64.3 69.9 47.6 65.5 73.8 64.2 65.4 45.5 69.4 79.2 37.5 14.4 26.8 40.0 34.6

6.0 1.3 5.8 9.6 9.7 23.2 12.6 6.9 8.9 13.5 12.2 8.2 5.2 3.1 11.4 11.5 5.2 11.0

0.4 0.9 0.6 0.4 0.3 0.6 0.3 0.3 0.4 0.3 0.9 0.3 0.2 1.6 5.2 2.3 1.4 1.6

19.8 7.4 10.3 17.3 13.8 23.4 22.6 18.1 21.3 25.6 19.3 23.6 14.0 5.7 20.3 13.2 13.1 19.3

13.0 14.8 6.9 6.5 6.9 19.8 6.6 4.9 11.6 15.4 23.3 10.4 6.5 58.5 64.9 44.8 47.7 51.9

67 77 82 76 79 56 70 76 67 59 57 66 79 35 14 42 39 28

33.3 28.9 50.9 47.5 54.4 25.4

33.0 32.5 26.8 25.4 27.2 37.3

32.1 36.8 17.9 27.1 15.2 37.3

34.9 30.7 55.4 47.5 57.6 25.4

61.1 37.1 37.1 42.9 56.9 11.8

22.2 0.0 32.3 12.5 6.9 11.8

2.8 5.7 8.1 0.0 5.6 0.0

14.0 10.5 6.5 10.4 8.4 10.5

15.9 19.3 27.4 7.0 16.0 3.8

26.1 30.7 29.8 26.1 22.9 25.6

1.8 4.3 0.7 1.9 0.4 11.5

4.4 0.7 1.6 1.0 1.9 0.2

0.0 0.0 4.3 4.2 14.6 0.0

100 100 82.6 95.8 70.7 100

0.0 0.0 13.0 0.0 14.6 0.0

61.1 37.1 35.4 42.9 54.7 11.8

16.7 62.9 33.8 44.6 38.7 76.5

22.2 0.0 30.8 12.5 6.7 11.8

3.7 0.6 1.0 1.0 1.4 0.2

27.9 18.4 41.0 14.8 22.9 26.3

53.5 34.2 25.3 39.3 42.2 15.8

18 47 33 45 34 57

33.6 20.6 52.0 45.5 39.5 22.1 45.2 47.4 36.5 23.5 52.8 48.3 60.7 63.6 57.9 56.3 33.8 68.3 46.9 43.5 31.8

33.3 37.8 22.7 18.8 28.8 32.0 29.8 26.8 29.7 38.1 22.8 26.7 12.3 18.2 7.5 9.4 16.9 9.6 18.7 30.6 31.3

29.4 33.1 22.7 35.1 25.1 38.7 21.9 19.5 33.8 32.7 18.7 21.2 25.2 18.2 30.8 30.5 47.1 21.2 5.7 24.1 31.3

37.3 29.1 54.7 46.1 46.0 29.4 48.3 53.7 36.5 29.2 58.5 52.1 62.6 63.6 61.7 60.2 36.0 69.2 75.6 45.4 37.3

44.6 38.3 62.4 73.2 33.3 36.4 44.7 35.4 38.9 27.7 36.3 57.3 85.3 92.9 74.4 74.0 69.4 74.0 37.1 33.7 16.1

19.6 6.4 9.7 5.6 12.1 39.0 8.2 14.1 7.4 14.9 3.5 5.3 1.0 7.1 0.0 0.0 16.3 4.0 9.1 5.1 9.2

8.9 25.5 4.3 1.4 14.1 23.4 5.9 9.1 0.0 17.0 9.7 6.7 2.9 0.0 6.1 6.5 6.1 1.0 37.1 4.1 14.9

2.3 17.1 27.9 21.1 9.1 14.4 22.4 11.1 14.8 16.5 19.4 14.3 0.0 5.3 4.7 5.4 2.7 2.6 13.4 15.7 17.7

26.7 11.4 3.9 0.6 23.6 9.9 15.2 7.6 16.0 14.8 0.0 8.2 16.1 21.7 21.6 38.1 18.2 3.1 6.5 13.0 8.2

29.1 32.3 36.3 21.7 17.6 27.9 31.0 25.8 27.2 36.4 24.4 11.0 16.1 6.6 8.1 15.6 9.5 18.5 25.2 28.7 29.1

0.7 0.1 0.0 2.6 0.7 0.7 0.5 0.7 1.1 0.9 0.2 0.0 0.6

1.7 1.3 2.6 3.7 0.8 28.0 1.1 0.9 0.7 0.7 0.7 1.9 7.9 3.8 3.8 8.5 3.5 2.2 0.6 0.3

60.0 16.7 13.8 34.6 42.4 71.4 39.5 54.3 47.6 30.8 34.1 37.2 12.6 7.7 21.3 12.3 94.1 47.3 58.5 30.3 42.9

20.0 83.3 29.3 7.7 54.5 17.9 47.4 25.7 28.6 38.5 65.9 11.6 3.4 0.0 6.6 7.0 0.0 14.9 35.8 69.7 57.1

38.5 27.5 60.4 70.3 29.7 27.1 40.0 33.0 36.2 21.0 32.8 56.6 82.9 92.9 74.4 74.0 66.7 71.8 33.5 30.8 15.1

41.5 68.1 30.2 20.3 58.6 35.5 48.4 53.2 55.2 61.3 64.0 38.2 16.2 0.0 25.6 26.0 15.7 23.3 52.7 64.5 77.4

20.0 4.3 9.4 9.5 11.7 37.4 11.6 13.8 8.6 17.7 3.2 5.3 1.0 7.1 0.0 0.0 17.6 4.9 13.8 4.7 7.5

0.9 0.4 2.0 3.5 0.5 0.8 0.8 0.6 0.7 0.3 0.5 1.5 5.1

4.1 4.6 7.0 6.8 1.2 0.5 0.8

20.0 0.0 56.9 57.7 3.0 10.7 13.2 20.0 23.8 30.8 0.0 51.2 83.9 92.3 72.1 80.7 5.9 37.8 5.7 0.0 0.0

19.8 13.5 14.1 10.0 22.4 21.4 14.8 23.4 11.1 18.0 11.9 6.8 0.9 7.1 3.6 3.9 11.9 21.6 29.2 16.7 26.3

20.8 3.1 41.4 50.0 10.2 12.2 16.4 19.1 15.2 8.0 10.4 43.2 77.1 92.9 74.5 76.5 77.1 59.5 25.7 6.9 3.9

59.4 83.3 44.4 40.0 67.3 66.3 68.9 57.4 73.7 74.0 77.8 50.0 22.0 0.0 21.8 19.6 11.0 18.9 45.1 76.4 69.7

Plg/KeF

RLv/Lm

2.9 2.9 4.3 3.1 0.6 0.5 0.2

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

Depositional Sequence III

F

TN34 AFVI 40.0 32.0 TN37 AFVI 42.5 33.5 TN38 AFVI 42.5 30.0 TN39 AFVI 47.5 26.7 TN40 AFVII 42.4 26.3 TN41 AFVII 39.1 31.1 TN42 AFVII 40.9 34.8 TN44 AFVIII 43.7 29.1 TN45 AFVIII 43.5 29.0 TN46 AFVIII 27.9 18.8 TN47 AFVII 32.9 29.1 TN48 AFVII 44.6 26.8 TN49 AFVII 42.1 24.8 TN51 AFVII 35.6 28.8 TN52 AFVI 27.0 26.5 TN53B AFVI 26.1 26.8 TN54 AFVI 22.5 20.0 TN57a AFVI 23.0 20.6 South section (Del Yeso creek) TN3/07 AFVIII 34.3 32.4 TN4/07 AFVIII 34.2 36.8 b TN6/07 AFVIII 31.3 17.9 TN7/07 AFVIII 25.4 27.1 TN8/07 AFVIII 30.4 15.2 TN9/07 AFVIII 37.3 37.3 Central (La Troya creek) and South (del Yeso creek) Sections TN63 AFIX 36.8 29.6 TN02/04 AFIX 45.9 33.5 TN05/04 AFIX 25.1 22.8 TN06/04 AFIX 19.5 35.1 TN64 AFX 35.3 25.1 TN65 AFX 39.0 39.0 TN66 AFX 32.8 22.0 TN68 AFX 33.2 19.5 TN12/04 AFX 29.7 33.8 TN14/04 AFX 43.4 33.1 TN16/04 AFX 28.5 18.7 TN09/04 AFX 30.3 21.4 TN10A/04 AFX 14.1 25.2 TN19/04 AFX 18.2 18.2 TN20/04 AFX 11.3 30.8 TN21/04 AFX 13.3 30.5 TN7/05 AFX 19.1 47.1 TN26/06 AFX 10.3 21.4 TN71 AFXI 47.4 5.7 TN72 AFXI 32.4 24.1 TN73 AFXI 36.9 31.3

Dickinson and Suczek (1979)

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

31

Fig. 9. QmFLt and QFL diagrams of Dickinson et al. (1983) and QmPF diagram of Dickinson and Suczek (1979) for the Toro Negro Formation sandstones. Qm: monocrystalline quartz, F: feldespars, Lt: total lithics, Q: quartz (monocrystalline þ polycrystalline), F: lithics without polycrystalline quartz and P: plagioclase.

the Toro Negro Formation, leads us to suggest a regional shift of source areas over time. The proposed evolutionary model also takes into account and is in accordance with the distribution of facies associations and paleocurrent data presented by Ciccioli (2008) and Ciccioli and Marenssi (2012). The Vinchina Basin was a tectonically active setting, dominated by continental sedimentation under semiarid conditions, where interaction of tectonic uplift and subsidence dominated over eustasy and climate during the Neogene (Limarino et al., 2001; Tripaldi et al., 2001; Ciccioli and Marenssi, 2012). Major tectonic phases causing basin reorganization can be recorded in the composition of sediments of the stratigraphic units (e.g. Zuffa et al., 1995; Lawton et al., 2003). Following the conceptual framework of Amorosi and Zuffa (2011) on compositional changes versus

Table 6 Summary of the main characteristics of the potential source areas. Regenerated components

Source areas

Regenerated modal components

Lv

Volcanic Arc (Frontal Cordillera) Precordillera

Lv total þ Pz þ P(Lv) þ O(Lv) þ Qm(Lv)

Ls þ Lmb Lp þ Lma

Crystalline Basement (include plutonic rocks)

Ls total þ Lmb þ P [ (Qm þ O þ P) in Ls y Lsm] Lma þ Lmm þ Lmc þ Lvme þ Qpm þ P [ (Qm þ O þ P) in Lp, Lm, Lmm, Lvme] þ [M total  M(Ls)] þ Qmi þ Oi þ Pi þ Op þ Pp

32

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

Fig. 10. Regeneration diagrams for the Toro Negro Formation sandstones. The plotted data corresponds to the sample averages for each facies association and the polygons are the standard deviation on either side of mean. See references in Table 6.

Fig. 11. Regeneration diagrams for the Toro Negro Formation sandstones in the different sections studied. The plotted data corresponds to the sample averages for each facies association and the polygons are the standard deviation on either side of mean. Arrows with numbers indicate the passage of different facies associations as it rises stratigraphically. See references in Table 6.

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

33

Fig. 12. Ternary diagrams of the conglomerates showing the lithic associations recognized in the Toro Negro Formation: basement (BLA), sedimentary (SLA) and volcanic (VLA). See references in Table 6.

stratigraphic units and their boundaries, we identified several types of compositional changes in the Toro Negro Formation. One of them is the vertical shift in composition within sequences interpreted to record changes in provenance areas due to tectonic activity, volcanism and paleogeographic reorganization through time. The second type of change, also within sequences, is linked to the

proximity-distality ratio to the coeval source areas. Surprisingly, petrofacies changes across depositional sequence boundaries are not clearly evident and they probably represented “congruence” boundaries (Lawton et al., 2003). In the beginning, sedimentation of the Toro Negro Formation was confined within the paleovalley in the northern section of the

Fig. 13. Ternary diagram proposed to discriminate crystalline basement granites of the Toro Negro Formation conglomerates. A. Lma:Ls þ Lmb:Lp diagram showing a dominance of the Lma component for the DSII in the La Troya creek in respect to the DSIII dominate by Lp (granites) and Ls þ Lmb (sedimentites); and B. Lma:Ls þ Lmb:Lp þ Lv diagram where Lp is added to the western volcanic component (Lv). There is grouping of the western components (Lp þ Lv) for the DSI in the Los Pozuelos-Aguada creek while in the DSII (La Troya creek) it is enriched in metamorphic component (Lma). The DSIII is dominated by plutonic-volcanic components (Lp þ Lv) with a subordinate proportion of sedimentary component (Ls þ Lmb).

34

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

Fig. 14. Binary diagrams plotting each lithotypes for the conglomerate of the Toro Negro Formation.

basin (SDI, Middle Miocene). At this stage there was an alternation of the VPeMP sandstone petrofacies coupled with the BLAeVLAe SLA lithic associations of conglomerates (Fig. 15). These detrital modes indicate a western source (Cordillera Frontal and Precordillera) with some contribution from the north (supply pulses from the Toro Negro Range). In the unconfined stage, the PMP petrofacies dominates both the northern and central parts of the basin changing to MP petrofacies in the south and toward the top (Fig. 15). Thus, the Toro Negro Range is considered as the main source for this interval with minor supply from the west (Fig. 16). This is also supported by the distribution of sedimentary environments and a grain-size decrease from north to south (Ciccioli and Marenssi, 2012; Ciccioli et al., 2012a) The DSII shows a similar petrofacies composition to the upper part of the DSI (PMP in both the northern and central sections and MP in the southern section; Fig. 15). However, the conglomerate clasts show a clear supply from a high-grade metamorphic basement (BLA lithic association with Lma predominance). Particularly, in the northern section, high-grade metamorphic clasts are dominant. The observed changes from north to south within the DSI and DSII cannot be interpreted as a source area shift but rather as changes in the drainage network due to basin readjustment in response to tectonic activity. Variable input from different, although coexistent watersheds are likely to have influenced the coeval onset of different petrofacies in different parts of the basin (Amorosi and Zuffa, 2011). In the Vinchina Basin, the increasing distance from the basement block source (Toro Negro Range) from north to south produces a mix of supply with sediments coming from the west (Frontal Cordillera and Precordillera). Toward the top of the DSII, the MP petrofacies and the BLA lithic associations, are both enriched in volcanic components. This change corresponds, on the one hand, to an increase of volcanic clasts suggesting that the western Cordillera Frontal and the Precordillera continued to be a source for this unit and, on the other hand, to the presence of large amounts of neo-volcanic grains derived from the erosion of intrabasinal tuffs and pyroclastic flow deposits as mentioned by Ciccioli (2008) and Ciccioli and Marenssi (2012). Radiometric datings from two of these tuffs shed a Late Miocene age for this interval (8.6 and 6.8 Ma, Ciccioli et al., 2005). The lower part of the DSIII shows BLAeVLA lithic associations with a MP petrofacies in the central section shifting to a PMP petrofacies in the southern section above the boundary surface (Fig. 15). This interesting change could indicate the emergence of a new basement source located to the south (Umango Range) during the latest Miocene-early Pliocene. This is supported by the larger amount of high-grade metamorphic lithics in the southern section and its decrease toward the central part of the basin (Figs. 14 and 15). A volcanic petrofacies (VP), enriched in fresh glass and pumice, appears in the middle of this sequence indicating western provenance probably related to the supply from the Tertiary volcanic arc (neo-volcanic components) coupled with volcanic clasts derived from Precordillera (paleo-volcanic components) (Fig. 15). Finally, the upper part of this sequence presents a dominance of PMP petrofacies and the BLA lithic associations showing an increase of low-grade metamorphic lithics and green sedimentary rocks (Figs. 14 and 15). This is interpreted to represent the supply of a new Precordillera thrust sheet during the latest Miocene-early Pliocene (Fig. 16). Meanwhile, in the southern section, the composition of the conglomerates shows a predominance of the basement lithic association (BLA) enriched in Lma þ Lp components which is lost toward the centralenorthern part of the basin, indicating episodic supply from south (Umango Range) favoring the dilution and mixing of this component from south to north.

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

35

Fig. 15. Schematic sections of the Toro Negro Formation showing the changes of composition (sandstone petrofacies and conglomerate lithic associations) in the three studied sections. Modified from Ciccioli and Marenssi (2012).

We conclude that during the sedimentation of the confined part of the DSI a mix sources were recognized: the Cordillera Frontal and the Precordillera to the west and the Toro Negro Range to the north. In the unconfined part of the DSI and DSII the Toro Negro Range (to the north) was the most important source area accompanied in a subordinate way by the Cordillera Frontal and the Precordillera (distal to the west) (Fig. 16). The first interpretation is also supported by the distribution of the sedimentary environments, the grain-size trend and the paleocurrents from north to south (Ciccioli, 2008; Ciccioli and Marenssi, 2012; Ciccioli et al., 2012a; Fig. 15). During the sedimentation of the DSIII (upper member, Fig. 16), the western sources predominated in the central part of the basin. However, the Umango Range started to act as a new sediment supply area in the southern part of the basin (Fig. 16) and toward the top of this sequence, there is a renew supply from the eastern Precordillera (proximal to the west).

8. Discussion and conclusions The source areas envisaged for the Vinchina Basin (Western Sierras Pampeanas, Cordillera Frontal and Precordillera), during the sedimentation of the Toro Negro Formation, are characterized by three ideal sandstone petrofacies: plutonic-metamorphic (PMP), volcanic (VP) and mixed (MP) petrofacies and three conglomerate lithic associations: basement (BLA), sedimentary (SLA) and volcanic (VLA). Provenance from basement blocks of the Western Sierras Pampeanas, located to the north and south of the basin (Toro Negro and Umango Ranges), are well represented by the PMP petrofacies and the BLA (Lma) lithic association; the Cordillera Frontal source to the west is characterized by the VP (including neo-volcanics) and MP (enriched in volcanic components) petrofacies and the VLA lithic association. Given its more complex geology the Precordillera provenance signal is not represented by any specific sandstone

36

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

Fig. 16. Evolution model of the source areas for the Toro Negro Formation. The biggest size of the arrows indicates the main source.

petrofacies. However, some samples falling into the MP petrofacies and the BLA (enriched into Lmb) as well as SLA conglomerate lithic associations are interpreted as supplied from the Precordillera. The evolutionary model proposed in this paper is in accordance with the distribution of sedimentary environments and paleocurrent data published by Ciccioli (2008) and Ciccioli and Marenssi (2012). In the basal (confined) section of DSI the contribution of all three main sources is recorded while in the unconfined part of DSI and most of DSII there is a clear input from the basement source located to the north (Toro Negro Range). From the upper part of DSII up to the middle part of DSIII there is an evident increase in sediments derived from a volcanic source located to the west (Cordillera Frontal and Precordillera). Finally, in the upper part of DSIII there is a progressive increase in the supply of clasts from the eastern Precordillera (to the west) with a contribution from the Umango Range to the south. The combined evidences indicate that the three main sources coexisted and therefore there are not sharp changes in modal composition between depositional sequences, but: 1) the Toro Negro Range to the north was a positive element since the beginning while the Umango Range to the south became a source just for DSIII; 2) the contribution of the Toro Negro basement is at a maximum in the lower part of DSII; 3) the contribution of volcanic and sedimentary fragments from the west was continuous although a neo-volcanic source peaked in the upper part of DSII and lower part of DSIII; and 4) an increase in supply from the eastern Precordillera is recorded in the upper part of DSIII being registered earlier in the southern section than in the central one. The major sandstone compositional data (QFL, QmFLt, QmPF) of the 2500 m-thick Toro Negro Formation reveal compositional patterns that are actually rather similar among the depositional sequences (DSIeDSIII). Therefore it is rather surprising to realize the data show less variation than many other basins in similar settings (at least for foreland, hinterland, piggyback, intermontane basins of the Andes, e.g. Nie et al., 2012). This circumstance could be explained by the fact that the three main sediment sources coexisted during all the time of deposition of the Toro Negro Formation (Late Miocene-early Pliocene). Notwithstanding the aforementioned, detailed modal studies in sandstones and conglomerates have revealed that compositional changes recorded in the Toro Negro Formation are much more abrupt along strike than across sequence boundaries indicating that the three main sources contributed differentially according to paleogeographic reorganizations either within the basin (e.g. incised versus un-incised stages) or along its margins (e.g. asynchronic uplift of different basement blocks). These events were previously detected and related to tectonism (including subsidence) by studying the sedimentary facies distribution and paleoenvironmental changes within the Toro Negro Formation (Ciccioli, 2008; Ciccioli and Marenssi, 2012; Ciccioli et al., 2012a). The slightly higher amount of Lma þ Lp in regenerated sandstone modes than in the clast composition of conglomerates in DSII along the La Troya section may be the result of a partial loss of volcanic groundmasses in the sand-size interval due to increased breaking and weathering associated to longer transportation distances. If this assumption is correct then the volcanic arc provenance may be underrepresented when its source area is located distally related to the basement one. The aforementioned situation can only be detected by comparing the sandstone detrital modes and the conglomerate clast composition. The petrographic evolution of a broken-foreland basin fill is much more complex than previously envisaged and then an integrated approach using various tools is necessary for its understanding (e.g. Hulka and Heubeck, 2010; Nie et al., 2012; Varela et al., 2013). In our case, the study of the detrital modes of sandstones and conglomerates of the Toro Negro Formation, in a

P.L. Ciccioli et al. / Journal of South American Earth Sciences 49 (2014) 15e38

complementary way with already published sedimentary facies, paleocurrent measurements, resulted a useful tool for the analysis of the evolution of the broken-foreland stage of the Vinchina Basin with multiple source areas. Acknowledgments The authors appreciate the many helpful comments and suggestions provided by B. Horton and an anonymous reviewer. This paper is the result of part of the Ph. D. Thesis of P.L Ciccioli. This study was funded by UBACyT GC01/W321, ANPCyT PICT-2079/2010 and CONICET PIP 0252 research grants. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jsames.2013.10.003. References Amorosi, A., 1995. Glaucony and sequence stratigraphy; a conceptual framework of distribution in siliciclastic sequences. J. Sediment. Res. 65, 419e425. Amorosi, A., Zuffa, G.G., 2011. Sand composition changes across key boundaries of siliciclastic and hybrid depositional sequences. Sediment. Geol. 236, 153e 163. Arribas, J., Alonso, A., Mas, R., Tortosa, A., Rodas, M., Barrenechea, J.F., AlonsoAzcárate, J., Artigas, R., 2003. Sandstone petrography of continental depositional sequences of an intraplate rift basin: Western Cameros Basin (North Spain). J. Sediment. Res. 73, 309e327. Beard, D.C., Weyl, P.K., 1970. Influence of texture on porosity and permeability of unconsolidated sand. Am. Assoc. Pet. Geol. Bull. 57 (2), 349e369. Caminos, R., 1972. Perfil geológico de la Cordillera entre los 28
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