N. Jb. Geol. Paläont. Abh. Article Stuttgart, July 2012

Basin evolution of the margin of Gondwana at the Neoproterozoic/ Cambrian transition: the Puncoviscana Formation of Northwest Argentina

Alejandro J. Toselli, Guillermo F. Aceñolaza, Hubert Miller, Christopher Adams, Florencio G. Aceñolaza, and Juana N. Rossi With 4 figures

Toselli, A.J., Aceñolaza, G.F., Miller, H., Adams, C., Aceñolaza, F.G. & Rossi, J.N. (2012): Basin evolution of the margin of Gondwana at the Neoproterozoic/Cambrian transition: the Puncoviscana Formation of Northwest Argentina. – N. Jb. Geol. Paläont. Abh., 265: 000-000; Stuttgart.

Abstract: The Puncoviscana Formation is an important stratigraphic sequence of sandstones and shales, with intercalated conglomerates, limestones and volcanic rocks. It was deposited at the Neo- proterozoic-Cambrian boundary in a shallow basin on the western margin of Gondwana. Trace fos- sils of the Puncoviscana Formation s.l. are represented by the Oldhamia and Nereites ichnoassocia- tions and the geographical distribution of assemblages are alignedproofs as parallel belts, with a shallower eastern Nereites association and a deeper western Oldhamia association. They represent different temporal levels on the evolution of the basin. Detrital zircon spectra display a wide range of ages, which indicate their provenance from Neoproterozoic to Cambrian source areas as well as Meso- to Paleoproterozoic basement units, exhibiting typical Gondwanan ages. Thick limestone banks are interbedded in the Puncoviscana Formation s.l. that included the siliciclastic sequences, with very low- to medium-metamorphic grade. δ13C values for the limestones vary from -1.57 to +3.40/00 VPDB, while in the Sierras Pampeanas, δ13C values vary from +2.6 to +80/00 VPDB. Also, reported 87Sr/86Sr values allow a clear differentiation of two rock sets. The limestones interbedded with the Puncoviscana Formation yielded values typical for the Neoproterozoic-Cambrian transition, between 0.70868 and 0.70896; while the limestones of the Sierras Pampeanas display values between 0.70748 and 0.70756, common in the middle to late Ediacaran. Deformation and uplift of the Puncoviscana Formation is clearly represented in northern Argentina by the Tilcarian unconformity, which is over- lain by the Mesón Group.

Key words: Puncoviscana Formation, Nereites and Oldhamia associations, δ13C values, Neoproter- ozoic-Cambrian transition.uncorrected

1. Introduction Pampeanas of northwest Argentina, continuing into Bolivian territory, where it is known as San Cristobal Formation (Turner 1960; Turner & Mon, 1979; The Puncoviscana Formation of NW Argentina Suárez Soruco 1992; Aceñolaza et al. 1999; Ramos represents the basement unit in the South American 1999; Aceñolaza & Toselli 2009). Early Paleozoic Central Andean Basin. It crops out These Ediacaran-Lower Cambrian rocks are mostly in the Cordillera Oriental, Puna and Sierras represented by a thick and heterogeneous succession

©2012 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/0077-7749/2012/0246 0077-7749/2012/0246 $ x.00 2 A.J. Toselli et al.

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uncorrected

Fig. 1. Basin evolution of the margin of Gondwana 3

of deformed and slightly metamorphosed sedimentary is essentially based on trace fossil data (e.g. Durand & rocks, with shales, greywackes, sandstones, carbonates, Aceñolaza 1990; Aceñolaza & Aceñolaza 2005) that volcanic rocks and conglomerates. Scarce fossiliferous point to an Ediacaran-Early Cambrian age. levels occur associated to shale intercalations. The Southwards, the San Luis Formation (Prozzi & whole sequence is intruded by granitic plutons in Ramos 1988; Prozzi 1990) is exposed in two belts of several sectors (Aceñolaza & Toselli 2009). the homonymous range. It consists of alternating phyl- To understand the structural outline of the basin lites and meta-quartzites with minor meta-conglom- where the Puncoviscana Formation was deposited, erates and meta-rhyolitic rocks (Sato et al. 2002, and the pre-Ediacaran evolution of the Gondwana border references therein). The succession is characterized needs to be considered. Several hypotheses have been as a turbiditic sequence and compared with the Edia- proposed on this matter. We consider this basin as de- caran-Lower Cambrian Puncoviscana Formation. This veloped from a NNE-SSW- trending aulacogen (Ace- regional correlation is supported by the U-Pb crystalli- ñolaza & Durand 1986) that evolved from the “Bo- zation age of 529 +/- 12 Ma obtained from meta-mag- livian Triple Joint”, which occurs in the eastern plain matic layers (Söllner et al. 2000). regions of the country (Suárez Soruco 1989, 2000). Available Nd-isotope data for the low-grade The Puncoviscana Basin (Pampean Orogen) ex- metasedimentary rocks (Bock et al. 2000) and medium- tends from Bolivia to Central Argentina, limited to to high-grade metamorphic rocks (schists, gneisses the west by the Arequipa-Antofalla terrane and to the and calc-silicates; see Pankhurst et al. 1998, Rapela east by the Guaporé and Río de la Plata cratons. In et al. 1998, and Lucassen et al. 2000), represent only the northern part of the basin very low- to low-grade restricted areas. Reported model ages vary between metasedimentary rocks dominate, while the south- 1.5 and 1.8 Ga for the low-grade metasediments, and ern area is dominated by gneisses, migmatites and 1.5-2.1 Ga for the higher-grade metamorphic rocks. medium-grade metamorphic rocks (Aceñolaza et al. Geochronological data of the eastern Sierras Pam- 2002) (Fig. 1). The contacts between isolated very-low peanas, in theproofs Santiago del Estero and northern Córdo- to low-grade metasedimentary rocks with the adjacent ba provinces, show that this area is mainly composed gneisses and migmatites are mostly not exposed (Cami- by a series of granitoids of Late Proterozoic-Early nos 1979). Some authors (Willner 1990; Willner & Cambrian with ages between 500-567 Ma (Koukhar- Miller 1986) argue that the more intensely deformed sky et al. 2003; Castellote 1989). These intruded and metamorphosed rocks represent deeper crustal into a metamorphic basement constituted by schists, equivalents of the supra-crustal succession, whereas gneisses, amphibolites and migmatites with K/Ar ages Mon & Hongn (1991) interpret the variety of metamor- between 407 +/- 10 and 665 +/- 20 Ma (Castellote phic rocks related to different tectono-metamorphic 1989). These metamorphic rocks and granitoids are in- events. However, both successions are affected by the truded by volcanic rocks known as Los Burros Dacite Tilcaric orogeny and the Middle Cambrian to Early (513 Ma, Leal et al. 2003), dykes of the Oncán Rhyo- Ordovician plutonic activity (Rapela et al. 1998). The lite (Rb-Sr isochron of 494 Ma, Rapela et al. 1991), sedimentary aspects of low-grade metasedimentary and basaltic and andesitic to dacitic rocks that com- rocks of the Puncoviscana Formation were described prise the Balbuena Formation with an K-Ar age of 514 by Omarini (1983), Ježek (1990)uncorrected and Durand (1990). +/- 15 Ma (Koukharsky et al. 2003). The depositional age of the thick clastic sequence

Fig. 1. Simplified geological map of Northwestern Argentina, showing the distribution of Ediacaran – Paleozoic sedimentary, metamorphic and magmatic rocks of the Puncoviscana Formation and equivalents, including Ordovician outcrops. Locations are: SA: Sierra de Ancasti; SF: Sierra de Fiambalá; SFa: Sierra de Famatina; SC: Sierras de Córdoba; SNC: Sierra Norte de Córdoba; SL: Sierras de San Luis, and SO: Sierra de la Ovejería. QH: Quebrada de Humahuaca, and QT: Quebrada del Toro. Granites are: A: Ambargasta; C: Cañaní; T: Tipayoc, and SR: Santa Rosa). Localities with magmatic and metamorphic ages, C and Sr isotopes and detrital zircons are shown and discussed in the text. 4 A.J. Toselli et al.

Fig. 2. Correlation chart of the Puncoviscana Formation and equivalents including granites, volcanic rocks, limestones, metamorphic ages and trace fossils (modified after Aceñolaza & Toselli 2009).proofs

2. Geological setting graded-bed successions (Fig. 3) are widespread; limestones and intercalated volcanic rocks are rare. Ediacaran-Lower Cambrian rocks that constitute the The sediments of the Puncoviscana Formation Puncoviscana Formation (Turner 1960) are repre- and their higher metamorphic equivalents have been sented in northwest Argentina by a thick and hetero- identified as greywackes and lithic arenites byJ ežek et geneous succession of deformed and slightly meta- al. (1985), Ježek & Miller (1986). Geochemically the morphosed sedimentary rocks. These are shales, grey- source area corresponds to an uplifted orogen within a wackes, sandstones, carbonates, volcanic rocks and stable continental margin (Ježek et al. 1985; Do Campo conglomerates, with sparse fossiliferous levels. Con- & Ribeiro Guevara 2005). tinuous stratigraphic sections are rare, which makes Within the clastic sediments Ježek et al. (1985) formal subdivision impossible. However, maximum uncorrecteddistinguished 5 facies types: proximal, intermediate, ages of detrital zircons from the turbiditic facies of the distal, pelagic and channel facies. The proximal Puncoviscana Formation and equivalent units suggest facies is characterized by massive graywackes, lithic a certain decrease of ages of this facies from east to greywackes and subgreywackes of a psammite/pelite west. In addition, whereas limestones are bound to the ratio > 5. Load casts, and flute marks are typical lower parts of the Puncoviscana Formation s.l., vol- surface structures. The intermediate facies consists of canic rocks mostly occur in younger sections (Fig. 2) greywackes, siltstones and pelites, of a psammite/pelite Large tracts of higher-grade metamorphic equivalents ratio of 1 to 5. Flute and ripple marks are frequent. occur to the south, in Catamarca and Tucumán prov- There are typical turbidites with Bouma sequences inces (Aceñolaza & Miller 1982). starting with a scoured bed overlied by a massive A Sedimentological features indicate a range of bed, represented by the coarsest material settled out environments, ranging from above wave-base, shallow- of suspension as the turbidite current slowed. Above, water mainly in the east, to mid-fan turbidites mainly the plane laminated sandstones (unit B) represents in the west. Greywacke (dominant)–siltstone-mudstone Basin evolution of the margin of Gondwana 5

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Fig. 3. Facies and structures of the Puncoviscana Formation in NW Argentina; A – Heterolithic section with ripple-bedded top at Cachiñal locality, Salta; B – Limestone facies at Ancaján, Catamarca; C – Tight folds at El Alisal, Salta; D – General view of the Tilcara unconformity showing the Mesón Group overlying the Puncoviscana Formation at the homonymous locality in Jujuy; E – Conlomerates at Papachacra with slates, limestone and volcanic clasts, Catamarca; F – Limestones interbedded with shales at Papachacra Range, Catamarca; G – Folded slates cropping out at Quebrada Don Braulio, Salta; H – Sandstone and slate beds in the western facies of Puncoviscana close to El Mojón locality, Salta; I – Ripple-bearing sandstones cropping out at Purmamarca, Jujuy.

highflow-regime plane beds.uncorrected These are followed by from flute marks, pebble imbrication in conglomerates ripples and wavy lamination (unit C), indicative of and from the vergence of slump folds (Ježek et al. lower flow regime. Rarely the unit D is identified 1985). Most data show flow directions from 45° to in the unit by laminated silt. The distal facies type 150° that is from the East (Ježek et al. 1985). Fining- is characterized by bed thicknesses < 10 cm which upward successions indicate transgressive trends are plane-parallel bedded, grain size is clay to silt, during a uniform continuous subsidence period siltstones and interbedded pelites. The psammite/pelite causing basinward migration of the fan system. Thus, ratio is <1. The pelitic facies is characterized by red, deposition was continuously bound to the upper structureless pelites possibly representing background parts of a slope with relatively regular shallow water sedimentation. The channel facies, composed of conditions. conglomerates, deserves a particular description (see The geochemical and petrological features of below). the sediments suggest a recycled-orogen provenance Paleocurrent directions were obtained from (Ježek et al. 1985; Ježek & Miller 1976; Ježek 1990; diverse structures: mostly from ripple marks, but also Pankhurst & Rapela 1998; Do Campo & Guevara 6 A.J. Toselli et al.

2005; Zimmermann 2005). Omarini (1983) and Omarini In the Northwestern Sierras Pampeanas Durand et al. (1999b) considered the Puncoviscana Formation (1990) described at Sierra de la Ovejería a polymictic to be mostly Late Proterozoic in age, with only a minor conglomerate, with well rounded clasts of quartzites, Early Cambrian part but, on faunal evidence, Durand greywackes, sandstones, quartzites, limestones, & Aceñolaza (1990) and Aceñolaza & Aceñolaza rhyolites and ignimbrites. According to Durand (1990) (2005) assigned it mostly to the Early Cambrian, the conglomerates are intercalated in the turbidite and only minor parts to the Neoproterozoic. This sequences of the Suncho Formation (equivalent to the latter assignment is supported by Early Cambrian Puncoviscana Formation), which can be interpreted U-Pb ages of euhedral (volcanic) detrital zircons in as submarine fans, in which gravitational flows of greywackes near Cachi (Lork et al. 1990). This initial sliding, slumping and debris flows (Ježek 1990). geochronological work was considerably extended The provenance of clastic material is probably from with new U-Pb (single crystal) detrital zircon and consolidated sedimentary regions and low-grade Rb-Sr metamorphic age studies (Adams et al. 2005, metamorphic rocks, and also from outcrops of acid 2008, 2009, 2010) of the Puncoviscana Formation, and volcanics and limestones (Spalletti & Durand 1987; similar work on possibly correlative rocks in central Durand 1988). and western Argentina (Schwartz & Gromet 2004; The San Luis Formation (Prozzi & Ramos 1988) is Finney et al. 2005; Escayola et al. 2007; Rapela et al. exposed in two belts of the central and western parts of 2007; Gómez Peral et al. 2007). the Sierra de San Luis. It consists of alternating phyllites In northwest Argentina, the Puncoviscana Formation and meta-quartzites with minor meta-conglomerates was strongly folded and weakly metamorphosed, and acid meta-magmatic rocks. The succession was and then intruded by granitoids during the Tilcarian characterized as a turbiditic sequence, and compared Orogeny in mid-Cambrian times. This orogenic event with the Puncoviscana Formation by Prozzi (1990) is also known from metamorphic rocks of provinces and v. Gosen & Prozzi (1998). The metamorphic grade to the south, Catamarca and La Rioja, and in central is lower- to proofsmiddle-greenschist facies. Argentina from the Sierras de Córdoba and San Luis. These metamorphic rocks have been compared with 3. Chemostratigraphy of carbonates the Puncoviscana Formation by Aceñolaza & Miller (1982); Prozzi (1990); von Gosen & Prozzi (1998); Thick limestone banks are interbedded in the Punco- Söllner et al. (2000) and Pankhurst & Rapela (1998), viscana Formation s.l. in the Salta, Jujuy, Tucumán, and more recently confirmed byS teenken et al. (2008), Catamarca, Santiago del Estero and Córdoba provinc- in contrast to Steenken et al. (2004). es. They are interbedded in the siliciclastic sequenc- Conglomerate deposits are interbedded with es, ranging from very low- to medium- metamorphic psammites and shales of the Puncoviscana Formation grade (Fig. 1). and metamorphosed equivalents; this facies constitutes In the Salta province, limestones crop out in the about 1% (Ježek 1990). They are subdivided in: pebbly Castillejo Range and are known as Las Tienditas For- sandstones (Seclantás), pebbly mudstones (Escalchi, mation. This formation, 160 to 240m thick, is com- Tin-Tin, Corralito and Las Tienditas), unorganized posed of fine-grained, dark limestones, alternating conglomerates (Seclantás) anduncorrected massive conglomerates with marls and brecciated limestones (Ortiz 1962; (Las Tienditas and Corralito). These outcrops are Salfity et al. 1975; Baldis & Omarini 1984). located in Cordillera Oriental and Northwestern In Jujuy, limestones are known at the localities Sierras Pampeanas. of Quebrada de Humahuaca at León and Volcán. In the Cordillera Oriental the conglomerates of These are represented by highly deformed, dark, fine- Corralito, Las Tienditas, Tin-Tin and Seclantás are grained micritic limestones that, in some sectors, are significant, which were studied among others by: found interbedded with shales and sandstones (Loss Durand (1988, 1990); Spalletti & Durand (1987); & Giordana 1952). Scanavino & Guichón (1971) mea- Omarini & Baldis (1984) and Ježek (1986, 1990). They sured for the sequence a maximum thickness of 800 are generally classified as polymictic conglomerates, meters, decreasing laterally. consisting of rounded granules to blocks, embedded δ13C values for the Las Tienditas Formation vary in a psammitic matrix (5%). Clasts in the Seclantás from -1.57 to +3.4 ‰ VPDB, with the highest positive conglomerate consist of greywackes, quartzites, purple values close to the base of the sequence and decreasing mudstones and rhyolites. upsection, displaying a negative excursion at 15 me- Basin evolution of the margin of Gondwana 7 ters below the top of the sequence. This excursion has yet in the associated limestone nor in the conglomer- been formerly interpreted as the possible Precambri- ates (Aceñolaza & Aceñolaza 2007). an-Cambrian boundary (Sial et al. 2001). The Volcán- The existence of exclusively Ediacaran fossils is León limestones display δ13C values from +6.11 to not clear due to the lack of a precise link between the +4.58‰ VPDB (Toselli et al. 2008). chronological data and the fossiliferous strata. The Sierra de Ancasti (Sierras Pampeanas of Cat- An updated review of the trace fossils in the amarca) is represented by the Ancasti and Sierra Brava Puncoviscana Formation provides the following formations and the El Portezuelo Complex (Aceñola- list: Archaeonassa fossulata, Asaphoidichnus isp., za & Toselli 1977). Among them, the Sierra Brava Cochlichnus anguineus, Didymaulichnus lyelli, Di- Formation displays the carbonatic La Calera Member, morphichnus obliquus, Diplichnites isp., Glockerich- integrated by a heterolithic sequence of fine- to me- nus isp., Helminthoraphe isp., Helminthopsis abeli, dium-grained limestones, interbedded with quartzites Helminthopsis tenuis, Helminthoidichnites tenuis, and schists. Granoblastic texture is common, with the Monomorphichnus lineatus, Monomorphichnus isp., presence of quartz and opaque minerals (magnetite cf. Multipodichnus, Nereites saltensis, Neonereites and graphite). Muscovite and dispersed calcite can be uniserialis, N. biserialis, Oldhamia alata, O. antiqua, observed as well (Toselli et al. 2008). O. curvata, O. flabellata, O. geniculata, O. radiata, cf. In the La Calera Member, d13C values start up with Thalassinoides isp., Palaeophycus tubularis, Palaeo- +2.6‰ VPDB reaching a plateau around +8‰ upsec- phycus isp., Protichnites isp., Protovirgularia isp., tion. It is interesting to highlight that the homogeneity Tasmanadia cachii, Treptichnus isp., Treptichnus cf. of d13C close to +8‰ is recognized worldwide to the aequalternus, and T. pollardi (Aceñolaza et al. 2009). lapse of 600 to 730 Ma (Jacobsen & Kaufman, 1999; The trace fossils of the Puncoviscana Formation Melezhik et al. 2001). Recent papers display addition- s.l. are represented by the Oldhamia and Nereites al data on d13C values occurring ca. 850 and 750, and ichnoassociations, named after the homonymus trace again around 670-650 Ma (e.g. Halverson et al. 2010). fossils (Aceñolproofsaza & Durand 1986; Aceñolaza & 87Sr/86Sr values allow to clearly differentiate two sets Aceñolaza 2005). The spatial distribution of assem- of rocks: blages display a remarkable alignment as parallel belts, (a) Limestones interbedded to the Puncoviscana with a shallower eastwards Nereites association, and a Formation (Las Tienditas and Volcán formations) deeper westwards Oldhamia associacion, that do not yielded values typical for the Neoproterozoic-Cambri- represent archetypal ichnofacies. These are related to an transition, between 0.70868 and 0.70896 (Toselli the morphology of the basin, the chronological record et al. 2010). of the ichnofaunas, and may also represent different (b) Limestones of the Sierras Pampeanas of Cat- temporal levels on the evolution of the Puncoviscana amarca (La Calera and Ancaján) display values of sea. 0.70748 and 0.70756 (Toselli et al. 2010), common Within the Oldhamia association most trace fossils in the middle to late Ediacaran (e.g. Gaucher et al. are small-sized, parallel to bedding planes, and bio- 2009a). The latter Sr-isotope values fit δ13C data be- turbation is essentially restricted to the first millime- tween -1.0 and +1.0‰VPDB, typical for the early Cam- ters of strata. Deeper burrowers are recognized in the brian period, while δ13C uncorrected values around +5‰VPDB base of sandstone layers of the sequences. This spatial are common in the Ediacaran period. These current restriction of bioturbation with the frequent presence data suggest older ages for the analyzed limestones of of wrinkle marks denotes a mostly – but not only – the Sierras Pampeanas (Catamarca) and, younger ages microbial mat related lifestyles of the fauna as it hap- for the carbonates in the Cordillera Oriental (Salta and pens in other Neoproterozoic/Early Cambrian basins Jujuy). (McCall 2006). Within the Nereites association, a more diverse trace fossil set is recognized, with large 4. Paleontologic associations and mid size grazing and crawling traces developed in sand-mud interfaces. Arthropod traces are common in As mentioned earlier, the Puncoviscana Formation this association. (s.l.) records a variety of trace fossils, few body fossils Although most trace fossils were found in the Salta and some problematical bio-sedimentary structures, Province (NW Argentina), other material from Jujuy, being all of them restricted to the slates and sandstone Catamarca, Tucumán and La Rioja is important to facies of the unit (Fig. 4). No fossils have been found complete the picture of the Puncoviscana Basin, and 8 A.J. Toselli et al.

proofs

Fig. 4. Selected fossils of the Puncoviscana Formation and equivalent units of NW Argentina. A – Oldhamia curvata; B – Monomorphichnus lineatus; C – Treptichnus cf. aequalaternus); D – Selkirkia sp.; E – Nereites saltensis (non Psammichnites saltensis); F –uncorrected 1: Neonereites biserialis; 2: N. uniserialis; G – Nemiana sp.; Scale = 1 cm

their significance for the Ediacaran-Early Cambrian Puncoviscana Formation, such as Selkirkia sp. and strata in the SW margin of Gondwana. Ivesheadia sp. that are mentioned for the sandstone The co-existence of different tiering structures and levels cropping out at Choromoro locality, in the the non-exclusively biomat-related feeding strategies Tucumán province. Additional material has been re- require a more complex ecological structure for the cently discovered and assigned to Sewkia, Aspidella Puncoviscana Formation than previously suggested and Nemiana from the Cordillera Oriental of Salta and (Aceñolaza & Aceñolaza 2001; Buatois & Mángano Jujuy (Aceñolaza & Aceñolaza 2008), all data sup- 2003; Aceñolaza 2005). porting the existence of Ediacaran levels in the basin. A few body fossils have been described from the Westwards of Salta, possible Ediacaran strata have Basin evolution of the margin of Gondwana 9

been recognised with the presence of algal impres- (Adams et al. 2008; Drobe et al. 2009). A Mesopro- sions (fucoid type material). terozoic orogen would probably undergo prolonged The sedimentary characteristics of the unit and the and substantial erosion in the Neoproterozoic-Early presence of this particular suite of trace fossils, body Cambrian interval, and thus one could also expect the fossils, algal and microbial-mediated structures empa- amount of Mesoproterozoic zircons to decrease during thises a sedimentation on a wave and tide affected sea the period of deposition of the Puncoviscana Forma- platform within the euphotic zone. tion, which lasted perhaps more than 50 million years. The late Neoproterozoic group of zircons is probably 5. Detrital zircons, origin and maximum related to the rising Brasiliano Orogen of south-east- depositional ages ern and central south Brazil (Adams et al. 2008, 2010) and possibly also to a magmatic belt of the Eastern The heavy mineral analyses including zircon grains Sierras Pampeanas (Llambías et al. 2003). have been used as a method for correlation of depo- sitional settings of sediments and their provenance ar- 6. Igneous rocks, petrology and eas. Furthermore, detrital zircon ages provide a maxi- geochemistry mum age estimate for deposition of sedimentary and metasedimentary rocks. Volcanic and plutonic rocks are present in the Pun- The detrital zircon ages show that Puncoviscana coviscana Formation. They can possibly be divided Formation age patterns contain three broad groups: in two phases: A) pre-Tilcarian (pre-mid Cambrian) Paleoproterozoic-Mesoproterozoic (2400-1400 Ma), events and, B) Tilcarian (Middle Cambrian) events. late Mesoproterozoic-early Neoproterozoic (1150-850 A) The existence of volcanogenic levels interbedded in Ma) and late Neoproterozoic-Early Cambrian (650- the Puncoviscana Formation was recognized at several 515 Ma) (Adams et al. 2008, 2010). The 2400-1400 localities of the Cordillera Oriental, Puna and Eastern Ma ages are scarce and statistically not significant. Sierras Pampeanas; they correspond to the pre-Tilcar- The 1150-850 Ma age components are dominant in ian event. Inproofs most cases, the volcanic rocks are inter- greywackes with oldest late Neoproterozoic compo- bedded bodies usually less than 3 m in thickness. They nents >600 Ma. The former diminish considerably are grey or greenish grey with porphyritic texture. The when late-Neoproterozoic components become domi- outcrops in the Eastern Cordillera and Puna are most- nant and younger, reaching 515 Ma. A northernmost ly tholeiitic and alkaline basalts (Coira et al. 1990). greywacke sample from Purmamarca (Jujuy) is dis- The petrographic and geochemical characteristics of tinctive: whilst its zircon age pattern partly resembles the volcanic rocks have been published by Chayle & other Puncoviscana Formation samples, it contains no Coira (1987); Coira et al. (1990) and Omarini et al. Cambrian-late Neoproterozoic ages, the youngest ages (1999a). being early-Neoproterozoic. The magmatism might be interpreted as a conse- The youngest age components, c. 515 Ma, in a quence of several tectonic events and is recorded in greywacke from Rancagua (Cachi, Salta province), three different groups of volcanic rocks. They vary dominate an almost unimodal pattern suggestive of from intraplate alkaline basalts and transitional tholei- contemporary volcanic sourcesuncorrected at a late Early Cam- itic basalts (between continental and oceanic to island brian depocentre, similar to those obtained by Lork et arc basalts emplaced next to the continent). This in- al. (1990) of 527 Ma. dicates a tectonic evolution from an intraplate setting An almost constant feature of the U-Pb detrital (alkaline basalts) becoming extensional (continental zircon age patterns is the persistence of zircons de- and oceanic tholeiitic basalts) and finally turning into rived from a Late Mesoproterozoic source; in general, a compressional subduction phase typical of oceanic in the range 1000-1090 Ma (Adams et al. 2005, 2008, islands arc (oceanic basalts). 2010; Drobe et al. 2009). These zircon sources must Geochronological data in the Santiago del Estero originate in extensive and voluminous complexes of and north of Córdoba provinces, show that the regional plutonic and metamorphic rocks, rather than more geology of this area is mainly composed of a series of limited and superficial volcanic successions. Clearly Late Proterozoic-Early Cambrian granitoids with ages a Precambrian craton offers the best environment, and between 500-567 Ma (Koukharsky et al. 1999; Cas- provides the possibility of an additional and variable tellote 1982) which intruded in a metamorphic base- supply of older Paleoproterozoic and Archean zircons ment made up of schists, gneisses, amphibolites and 10 A.J. Toselli et al. migmatites. Dacitic to rhyolitic domes and dikes were the Sierra Norte de Córdoba are intruded by granodio- intruded during the last stages of the batholiths, and ritic and monzogranitc plutons of Cambrian age. rhyolitic ignimbrites sheets, with a conventional U-Pb According to Leal et al. (2003), the magmatic arc zircon age of 584+22/-14 Ma, are intercalated with the might have developed during the Late Precambrian to metaconglomerates of the La Lidia Formation (Llam- Early Cambrian as the result of eastward subduction. bias et al. 2003). This collision may have controlled extensive deforma- B) The Tilcarian plutonic event of the Pampean tion and metamorphism at 530 Ma (Kraemer et al. Cycle is classically restricted to the Jujuy and Salta 1995; Sims et al. 1998; Miró 1998; Miró et al. 2004). provinces, although rocks belonging to this cycle have The meta-sedimentary sequence of the San Luis also been recognized further south in the Ancasti (Cat- Formation (Prozzi & Ramos 1988) is correlated with amarca province), Ambargasta and Córdoba ranges. the Puncoviscana Formation (Prozzi 1990; v. Gosen The granites described from the northern sector of Ar- & Prozzi 1998). This correlation is supported by litho- gentina are represented by the Cañaní, Tipayoc, Santa logical similarity and the U-Pb crystallization age of Rosa de Tastil and Mojotoro plutons, all of which are 529 +/- 12 Ma obtained from two meta-magmatic lay- post-tectonic, and related to the diastrophic Tilcarian ers (Söllner et al. 2000). orogenic phase, with ages between 536 and 514 Ma The Neoproterozoic silicic ignimbrites, together (Omarini et al. 1987a, b, 1999b; Bachmann et al. 1987; with the Cambrian calc-alkaline batholiths and related Matteini et al. 2008; Hongn et al. 2010; Hauser 2011). volcanic rocks indicate the existence of a magmatic The petrographic characteristics show that the plutons arc associated with the active margin of the Gondwana are mainly tonalites, hornblende granodiorites, trond- continent. This arc was active since Neoproterozoic hjemites and biotite granites, and together with the times, with a duration of more than 60 Ma. A correla- geochemical data that defines them as calc-alkaline tion of the late Neoproterozoic metasedimentary and and meta- to peraluminous. The initial 87Sr/86Sr ra- volcanic rocks of the Sierra Norte de Córdoba with the tio of 0.7050 allowed Omarini et al. (1996, 1999) to Puncoviscanaproofs Formation of Northwestern Argentina propose an origin by partial fusion of the continental was suggested by Llambias et al. (2003). crust beneath a continental arc or related to continental collision. Hauser (2011) also suggested a subduction- 7. Metamorphic ages related origin. Basic and ultrabasic rocks associated to the Pun- Rb-Sr whole rock isochron ages were obtained by Ad- covicana Formation have been described from differ- ams et al. (2008b) from slates in the Puncoviscana For- ent localities in the northwestern Sierras Pampeanas. mation at Rio Choromoro (541 +/- 23 Ma), Quebrada In the Sierra de Ancasti, Bassi (1952) and Schalamuk del Toro (540 +/- 33 Ma), and Quebrada Don Bartolo et al. (1983) described the Albigasta and Icaño basic- (504 +/- 15 Ma). The ages from the Quebrada del Toro ultrabasic rocks with K-Ar ages between 512 and 468 and Rio Choromoro samples place the metamorphism Ma, which intrude in the Ancasti Formation. Their in the Early Cambrian or latest Neoproterozoic, and mineralogy consists of hornblende, plagioclase, bio- are consistent with the maximum possible depositional tite, titanite, epidote and sulphides. In the Sierra de age that is constrained by the youngest detrital zircon Fiambalá, Grisson et al. uncorrected (1998) recognized a two peaks at 636 +/- 7 Ma and 551 +/- 5 Ma, respectively, phase metamorphic event, one related to greenschist- from greywackes at the same localities. The anoma- amphibolite facies with ages between 550 and 540 lously young Rb-Sr age of 504 +/- 5 Ma from Que- Ma, and other associated to a 510-515 Ma old gabbro- brada Don Bartolo is likely due to the sample being norite. located within the thermal aureole of younger granites At the Santiago del Estero and north of Córdoba exposed nearby at La Punilla. provinces, late Proterozoic-early Cambrian granitoids are intruded by sub-volcanic rocks known as Los Bur- 8. Tilcarian Orogeny ros Dacite (513 Ma, Leal et al. 2003), the rhyolitic dykes known as the Oncán Rhyolite (Rb-Sr isochron The deformation process as well as the metamorphism of 494 Ma, Rapela et al. 1991), and basaltic, andesitic and associated plutonism which affected the Punco- to dacitic rocks that give rise to the Balbuena Forma- viscana basin begun in the Early Cambrian and fin- tion with a K-Ar age of 514 +/- 15 Ma (Koukharsky et ished in the early Middle Cambrian. These processes al. 2003). Small outcrops of metasedimentary rocks in were active through the closure of the basin, probably Basin evolution of the margin of Gondwana 1 1 related to the Arequipa-Antofalla Terrane colliding ranes named as Cuyania-Antofalla-Belén-Arequipa with the western Gondwanan margin, and the activ- (CABA). Within collisional schemes Keppie & Bahl- ity of the Paleo-Pacific Plate, resulting in folding with burg (1999), Loewy (2003), Pankhurst et al. (2006), open to closed structures and an axial plane cleavage, Drobe et al. (2009), Siegesmund et al. (2009), and Ra- mostly recognized in the pelitic facies. This folding pela et al. (2010) consider a geodynamic interpreta- was characterized by Willner & Miller (1986), and tion with the interaction of the Kalahari Craton and the Willner (1990) as F1 and F2. Axial planes of these terrane represented by the Puncoviscana Formation. A folds arranges are roughly NS and show a variable ver- major problem in these hypotheses is the lack of the gence to the E or W in depending on the studied loca- characteristic high pressure metamorphic units associ- tion. There are areas where chevron folds and flank ated to these schemes. slides are quite frequent. Finally, contributions by Ramos (2010a, b, with Nevertheless, the metamorphic events north of references) include a complex terrane transfer between Tucumán were of low grade with syn-kinematic and Laurentia and Gondwana, considering displacements, thermal characteristics that are particularly distin- detachments and amalgamations that include a hypo- guished near the granitic plutons. Metamorphism usu- thetic craton named “Pampia Terrane”. The latter is ally generates a weak recrystallization of the matrix proposed to collide with the western margin of Gond- and an oriented biotite growth. In some areas meta- wana on a problematic model that considers its accre- morphism reaches the chlorite zone and even higher, tion to the Amazonia Craton, remaining attached to it as in the Sierras Pampeanas south of Tucumán. In after the Rodinia amalgamation. these localities it is not easy to determine whether the Considering both models there must be mentioned metamorphic events correspond to the Tilcarian Orog- that there is no typical collisional effect verified for eny or to later Ordovician events (Famatinian Cycle, the region. sensu Aceñolaza & Toselli 1976). It is important to point out that from Tucumán to 10. Conclusionsproofs the north, the Tilcarian Orogeny terminates at the base of the mid to late Cambrian Mesón Group which un- Neoproterozoic to Cambrian sedimentation, metamor- conformably overlies the Puncoviscana Formation s.l. phism, plutonism, and orogenesis constitute the “Pam- pean Cycle” that is recorded in the Pampean Orogen. 9. Geodynamic model The sedimentation and associated phenomena were de- veloped on a peri-Gondwanan position. Zimmermann Various geodynamic interpretations have been put for- (2005), based on petrographic and geochemical data, ward for the Puncoviscana Basin. In different papers considered that the Puncoviscana Group represents a we have supported the idea of a typical aulacogenic foreland basin deposit, developed during the Neopro- basin developed at the western margin of Gondwana terozoic to Early Cambrian on the western part of the (Aceñolaza & Toselli 2009, with references). Mesoproterozoic belt or the Rio de la Plata Craton. The opening of the Puncoviscana Basin was due Even though the eastern facies of the Puncoviscana to the interaction of continental plates and the paleo- Formation accumulated in a shallow marine setting, Pacific ocean plate, generating a distensive process the generally accepted “deep-water” model for the that allowed the sinking ofuncorrected the area and favoured the western facies is challenged by the present authors. A development of an extensive epicontinental sea. These deeper area is accepted when compared to the east- characteristics are supported by the sedimentary re- ern facies, but an overall shallow marine environment, cord, with dominance of siliciclastic facies and minor deepening towards the west, is supported by sedimen- carbonatic bodies. Associated distensive volcanism, tary and ichnological data (Aceñolaza et al. 2009). faunal and trace fossil content and the overall environ- Whereas exclusively Ediacaran fossils have not mental interpretation, support a relatively shallow sea been recognized in the Puncoviscana Formation, with a moderate bottom relief allowing the formation metamorphic ages indicate that Ediacaran strata ex- of turbidite flows J( ežek 1990; Aceñolaza & Toselli ist in the basin. Trace fossil associations and new data 2009, with references). on body fossils shall provide additional elements to Other interpretations (Omarini & Sureda, 1993; improve the biochronological knowledge of the unit. Omarini et al. 1999) support a plate tectonic concept In addition, the co-existence of different tiering struc- that implies collisional models between different ter- tures and the non-exclusively biomat-related feeding 12 A.J. Toselli et al. strategies of trace fossil producer organisms require younger ages, for the carbonates in the Cordillera Ori- a more complex ecological structure for the unit than ental (Salta and Jujuy). previously suggested. Rb-Sr and K-Ar metamorphic ages of slates, in the The distribution of Detrital zircon age populations range 540-500 Ma (Adams et al. 1990, 2008; Cordani suggests a sediment provenance from a continental et al. 1990), are consistent with an Ediacaran- Early hinterland having a stabilized, extensive Late Meso- Cambrian depositional age. proterozoic – Early Neoproterozoic orogen, 1080-850 The magmatic rocks associated with the Punco- Ma, with minor Paleoproterozoic and Archean precur- viscana Formation can be adscribed to two events, sors (>1800 Ma), and more variable Late Neoprotero- pre-Tilcarian (pre-mid Cambrian), and Tilcarian (mid zoic (650-540 Ma) regions. Source of these sediments Cambrian). The first one is related to the evolution of may have been the Brazilian shield and Rio de la Plata the Puncoviscana Formation, with intraplate alkaline craton, Mesoproterozoic belts (Sunsás) and Late Neo- basalts and transitional evolution to tholeiitic basalts, proterozoic orogens (Brasiliano), which are consid- typical of extensional settings, and finally oceanic ered the main sediment source for the rivers flowing basalts that correspond to a subduction phase, pres- towards the passive margin of the palaeo-Pacific ocean ent in oceanic island arcs. In the Santiago del Estero (Adams et al. 2005, 2008; Gaucher et al. 2009a, b). and northern Córdoba provinces, granitoids intruded The youngest U-Pb detrital zircon ages in grey- into a high-grade metamorphic basement, and rhyo- wackes of the Puncoviscana Formation probably origi- litic domes with ignimbrites are interpreted as part of nated from contemporary volcanic sources, indicating a calc-alkaline magmatic arc (Llambias et al. 2003). a maximum depositional age of late Early Cambrian, Tilcarian granitic plutons occur in Jujuy and Sal- and this age range might extend down into the latest ta provinces, and likewise in the Sierras Pampeanas, Neoproterozoic. with ages between 536 and 514 Ma. Their geochemical The morphology of zircons supports a coeval vol- calc-alkaline affinity is probably related to a continen- canic provenance for these youngest beds, which oc- tal arc or continentalproofs collision environment (Omarini curred in the Early Cambrian near the depositional et al. 1996, 1999). In the Sierras Pampeanas basic-ul- areas of the Puncoviscana Formation. Contemporary trabasic rocks are associated with granites. volcanism developed in the Early Cambrian close to We envisage a geodynamic model that considers depositional sites in Cachi (Salta) and La Ovejería the Puncoviscana Basin as a large aulacogenic struc- (Catamarca) ranges. ture developed at the western margin of Gondwana. In addition, biostratigraphical and isotopic data are consistent, suggesting a depositional age for the Pun- Acknowledgements coviscana Formation, encompassing the Ediacaran- early Cambrian (Aceñolaza & Aceñolaza 2007; Ace- The authors are grateful to the CIUNT - 26G438 project ñolaza et al. 2009, and references therein). of Universidad Nacional de Tucumán, and the PIP 0595 The limestones are interbedded in the Puncovis- Project of CONICET, for financial support. Valuable recommendations for improving the manuscript by Dr. cana Formation and in the phyllites and schists of Claudio Gaucher and an anonymus reviewer are gratefully the northwestern Sierras Pampeanas. The 87Sr/86Sr acknowledged. values allow to clearly differentiateuncorrected two sets of rocks (Toselli et al. 2010): (a) Limestones interbedded to References the Puncoviscana Formation (Las Tienditas and Vol- cán formations) yielded values typical for the Neo- Aceñolaza, F.G. & Aceñolaza, G. (2005): La Formacion proterozoic-Cambrian transition, between 0.70868 Puncoviscana y unidades estratigráficas equivalentes en and 0.70896, and (b) Limestones of the Sierras Pam- el Neoproterozoico – Cámbrico Temprano del Noroeste Argentino. – Latin American Journal of Sedimentology peanas of Catamarca (La Calera and Ancaján) display and Basin Analysis, 12: 7-91. values of 0.70748 and 0.70756, common in middle to Aceñolaza, F.G. & Aceñolaza, G. (2008): El Ediacarano- late Ediacaran. The former Sr-isotope values fit δ13C Cámbrico temprano de la provincia de Jujuy: Caracteres data between -1.0 and +1.0‰VPDB, typical for the paleontológicos, Paleoecológicos y Paleogeográficos. early Cambrian period, while δ13C values around +5 – In: Coira, B. & Zappettini, E. (Eds.): Geología y Re- cursos Naturales de la provincial de Jujuy. Relatorio, 17º ‰VPDB are common in the Ediacaran period. These Congreso Geológico Argentino, 29-3;. Jujuy. current data suggest older ages for the analyzed lime- Aceñolaza, F.G., Buatois, L.A., Mángano, M.G., Este- stones of the Sierras Pampeanas (Catamarca) and, ban, S.B., Tortello, M.F. & Aceñolaza, G.F. (1999): Basin evolution of the margin of Gondwana 3 1

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Willner, A. & Miller, H. (1986): Structural division Addresses of the authors: and evolution of the Lower Paleozoic basement in the Prof. Dr. Alejandro J. Toselli, Prof. Dr. Guillermo F. NW-Argentina Andes. – Zentralblatt für Geologie und Aceñolaza, Prof. Dr. Florencio G. Aceñolaza, Prof. Dr. Paläontologie, Teil. I, (9-10): 1245-1255. Juana N. Rossi, Instituto Superior de Correlación Geológica Zimmermann, U. (2005): Provenance studies of very low-to (INSUGEO), Miguel Lillo 205, CP. 4000 Tucumán, low-grade metasedimentary rocks of the Puncoviscana Argentina; Complex, northwest Argentina. – In: Vaughan, A., Leat, e-mail: [email protected] P. & Pankhurst, R. (Eds.): Geological Society of Lon- don, Special Publication, 246: 381-416. Prof. Dr. Hubert Miller, Department of Geo- and Environmental Sciences, Ludwig-Maximilians-Universität Manuscript received: April 30th, 2011. München, Germany; Revised version accepted by the Bonn editors: May 8th, e-mail: [email protected] 2012. Prof. Dr. Christopher Adams, GNS Science, Private Bag 1930, Dunedin, New Zealand; e-mail: [email protected]

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