Introduction

Sedimentary basin evolution provides crucial information to decipher past geodynamic constraints. The Ediacaran—Early Paleozoic proto-Pacific margin of Gondwana (sensu Pankhurst and Rapela 1998) has a complex geodynamic history affected by various compressive, extensive and transpressive phases (e.g., Bahlburg and Moya 1994; Mon and Salfity 1995; Bahlburg and Hervé 1997; Dalziel 1997; Bock et al. 2000; Zimmermann and Bahlburg 2003; Bahlburg et al. 2009; Casquet et al. 2012; Zimmermann et al. 2014; Ramos 2018). The upper Cambrian (Furongian—Stage 10) to Lower Ordovician (Tremadocian—Tr1) strata of the Cordillera Oriental were deposited along the previously mentioned margin under shallow-marine to locally fluvial conditions. Nowadays, theses strata crop out extensively in northwest Argentina (Provinces of Salta and Jujuy; Figs. 1 and 2). These stratigraphic units were subject to intense paleontological (e.g., Harrington and Leanza 1957; Tortello et al. 1999; Benedetto and Carrasco 2002; Tortello and Esteban 2003; Vaccari et al. 2004; 2010; Balseiro et al. 2011; Balseiro and Waisfeld 2013; Albanesi et al. 2015; Muñoz and Benedetto 2016; Waisfeld and Balseiro 2016; Aris et al. 2017; Meroi Arcerito et al. 2018; Muñoz et al. 2018; Salas et al. 2018; Serra et al. 2019), paleoenvironmental (e.g., Moya 1988; 1998; Astini 2003; Buatois and Mángano 2003; Tortello and Esteban 2003; Buatois et al. 2006; Duperron and Scasso 2020), and sequence stratigraphic studies (Astini 2003; Buatois and Mángano 2003; Buatois et al. 2006) during the last decades. In addition, some studies focused on regional tectonostratigraphic reconstructions (e.g., Gohrbandt 1992; Bahlburg and Moya 1994; Bahlburg and Furlong 1996; Bahlburg and Hervé 1997; Ramos 2018). However, there is a marked paucity of studies that attempted detailed facies characterization within the context of basin evolution (Astini 2003, 2008; Egenhoff 2007).

Fig. 1
figure 1

Map of the studied area in the northwest of Argentina (Province of Jujuy). Satellite picture from Google Earth ©. P, Purmamarca; T, Tilcara; H, Humahuaca; EA, El Aguilar; EM, El Moreno

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Fig. 2
figure 2

Simplified geological map showing the main lower Paleozoic units cropping out in the northwest of Argentina. The name of the localities mentioned in that study are also shown. Modified after Astini (2003). SC, Sierra de Cajas; AM, Angosto del Moreno; QT, Quebrada de Trancas; QM, Quebrada de Moya

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During the late Cambrian, an extensional phase started in the basin, leading to northward widening, as well as deposition of a thicker and more extensive succession in the northern part of the basin in Bolivia (Gohrbandt 1992; Egenhoff 2007). Around the Cambrian-Ordovician transition, the onset of a subduction zone on the western border of the basin led to the development of the Puna-Famatinian arc in the Puna and Famatina areas (Figs. 1 and 2; Clemens 1993; Mannheim 1993; Mángano and Buatois 1996, 1997; Zimmermann and Bahlburg 2003; Kleine et al. 2004; Zimmermann et al. 2010; Niemeyer et al. 2018). The Furongian—lower Tremadocian Santa Rosita Formation and coeval Guayoc Chico Group were previously considered as sedimentary successions affected by relative sea-level fluctuations (Moya 1988; Astini 2003; Buatois and Mángano 2003; Buatois et al. 2006). However, Bahlburg and Hervé (1997) expected significant tectonic disturbance related to the active geodynamic context in the Puna and Famatina areas. Shortening has been estimated around 45–70 km for this area (Kley et al. 1999), although deformation associated with the development of a continental arc could occur hundreds of kilometers within the retro-arc basin (e.g., Jordan 1995).

The lower part of the Santa Rosita Formation and the coeval Guayoc Chico Group represent the focus of this study. The stratigraphic sections used herein were chosen because of (1) their exceptional vertical and lateral continuity; and (2) the highly fossiliferous content, which allowed accurate stratal correlation. This study provides new data aiming to propose an integrative and detailed reconstruction of the initiation and evolution of the Furongian—early Tremadocian at the Cordillera Oriental (Province of Jujuy; Argentina). This work combines facies analysis, biostratigraphy, and sequence stratigraphy to provide a conceptual framework of the evolution of an active margin. This contribution shows (1) previously unrecognized tectonic uplifts that occurred during the Cambrian-Ordovician transition, related to the emplacement of the volcanic arc to the west; and (2) the evolution of the basin from an extensional to a retro-arc style. Therefore, these data are not only important for the reconstruction of the studied basin but also provide new evidence helping to refine the geodynamic evolution of the western margin of Gondwana, while suggesting future research areas.

Stratigraphic nomenclature update

Cambrian (Stage 10)—Ordovician (Tr1) sedimentary successions exhibit a complex nomenclature made of formal and informal formation names that have been employed among different localities across the basin (Astini 2003 and references therein). Buatois et al. (2006) refined the stratigraphic framework of the Santa Rosita Formation for the Quebrada de Humahuaca area (east of Cordillera Oriental; Fig. 2) based on an integrated sedimentologic, sequence-stratigraphic and biostratigraphic study. In contrast, for the western border of the Cordillera Oriental and Salinas Grandes area (i.e., Sierra de Cajas and Angosto del Moreno; Figs. 2 and 3), formational names largely derive from uncertain correlations. Ramos (1973) proposed the Guayoc Chico Group to include the Lampazar, Cardonal, and Saladillo formations in this area (Fig. 3). These names were previously used by Harrington (1957), partially based on Keidel (in Harrington 1937), for the successions exposed in the Incamayo region (south of Angosto del Moreno; Fig. 2). However, subsequent authors (e.g., Malanca and Brandán 2000; Moya and Monteros 2000) did not use the names Santa Rosita Formation nor Guayoc Chico Group but referred these successions to Lampazar, Cardonal, and Saladillo formations (Fig. 3). Astini (2003, 2005) indicated that these formations should not be extended from Incamayo to Salinas Grandes due to substantial stratigraphic differences between these regions. Astini (2003, 2008), therefore, restricted the use of the Guayoc Chico Group for the Angosto del Moreno area, excluded from this group the Lampazar Formation, and proposed five informal members for the interval that Ramos (1973) and subsequent authors referred to as the Cardonal and Saladillo formations. Following the idea of not using previously defined formational names for the Angosto del Moreno area, Buatois et al. (2003) and Moya et al. (2003) proposed an informal stratigraphic framework that included four units (I, II, II, IV; Fig. 3).

Fig. 3
figure 3

Stratigraphic nomenclature update for the localities of Sierra de Cajas and Angosto del Moreno. The previously used nomenclature (see main text for details) is now updated providing easiest correlation between the western and the eastern part of Cordillera Oriental (Fig. 4). The Guayoc Chico Group is bracketed between the Mesón Group and the Tumbaya Unconformity, encompassing Pardioc, Lampazar, Angosto del Moreno and Pupusa formations. T.U., Tumbaya Uncomformity. Refer to Fig. 4, for the lithological pattern

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Based on a biostratigraphically well-constrained, sedimentologic and stratigraphic study, it is here suggested to retain the Guayoc Chico Group for the succession bracketed between the Mesón Group and the Tumbaya Unconformity (Moya 1997) that separates this stratigraphic interval from the Acoite Formation (Fig. 3). Thus, the Guayoc Chico Group encompasses the Padrioc, Lampazar, Angosto del Moreno, and Pupusa formations (Fig. 3). The last two names are proposed herein to replace the informal members/units of previous authors and are formally defined in Appendix 1. The Lampazar and Angosto del Moreno formations correspond to the Furongian Neoparabolina frequens argentina biozone, whereas the Pupusa Formation encompasses the early Tremadocian Jujuyaspis keideli and Kainella andina biozones of the scheme proposed by Vaccari et al. (2010) (Fig. 4). The same stratigraphic pattern is recognized for the Furongian to lower Tremadocian deposits of Sierra de Cajas (Fig. 3).

Fig. 4
figure 4

Regional biostratigraphy and lithostratigraphy, correlated to the chart intervals used. Modified and updated form Balseiro and Waisfeld (2013). Note that the Humacha Member (the uppermost official member of the Santa Rosita Formation), which comes above the Rupasca Member is not shown since it is not part of this study

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Geologic and stratigraphic framework

The Cordillera Oriental represents one of the regions (with the Puna, the Sierras Subandinas, and the Sierra de Famatina; Figs. 1 and 2) exposing Cambrian-Ordovician strata in northwest Argentina. These strata were deposited along the proto-Pacific margin of Gondwana. Nowadays, the remains of this basin extend across northwest Argentina, north Chile, Bolivia and, Peru (Fig. 1; e.g., Astini 2003 and references therein). The oldest exposed rock in the Cordillera Oriental is the Ediacaran—Fortunian metasedimentary Puncoviscana Formation and equivalents (Figs. 2 and 4; e.g., Aceñolaza et al. 1988; Omarini et al. 1999; Augustsson et al. 2011; Escayola et al. 2011). This stratigraphic unit was subsequently exhumed during the early Cambrian Pampean Orogeny (e.g., Mon and Hongn 1996; Escayola et al. 2011; Casquet et al. 2018). Further, sandstone and mudstone of the lower to middle Cambrian Mesón Group unconformably overlie the Puncoviscana Formation and equivalents (Fig. 4; Sánchez and Salfity 1999; Mángano and Buatois 2004; Buatois and Mángano 2005; Augustsson et al. 2011). In the Cordillera Oriental, the upper Cambrian—Lower Ordovician Santa Victoria Group unconformably overlies the Mesón Group (Fig. 4; Moya 1988; Sánchez and Salfity 1999). On one hand, the contact between the Santa Victoria and the Mesón groups is considered as an unconformity related to extensive movements (Irúyica Event; Turner and Méndez 1975; Mon and Salfity 1995). Alternatively, this contact has been considered as an unconformity generated by a relative sea-level fall (e.g., Moya 1998; Buatois et al. 2000; Buatois and Mángano 2003; Mángano and Buatois 2004) or as a conformable depositional transition (e.g., Ruiz Huidobro 1975; Fernández et al. 1982). The Santa Rosita Formation and coeval strata may have been deposited after this opening phase, recording mostly long-term relative sea-level fluctuations (Moya 1988; Mon and Salfity 1995; Astini 2003; Buatois and Mángano 2003; Buatois et al. 2006).

The Santa Victoria Group encompasses the Santa Rosita Formation (upper Cambrian; Stage 10—Lower Ordovician; Tr1—Tr3) and the Acoite Formation (Lower Ordovician; Floian—Dapingian) (Turner 1960; Toro and Herrera Sánchez 2019). The Santa Rosita Formation is divided into six members, namely Tilcara, Casa Colorada, Pico de Halcón, Alfarcito, Ruspaca, and Humacha members, in stratigraphic order (Fig. 4). The Guayoc Chico Group is coeval with the lower part of the Santa Rosita Formation that is divided into four formations, namely Padrioc, Lampazar, Angosto del Moreno and Pupusa (Figs. 3 and 4). In all places, the Tilcara Member and the Padrioc Formation overlain the Mesón Group (e.g., Turner 1960; Moya 1988). In Sierra de Cajas and Angosto del Moreno, the sedimentary successions belong to the Guayoc Chico Group, whereas in Quebrada de Trancas and Quebrada de Moya, the stratigraphic successions are part of the Santa Rosita Formation (Figs. 3 and 4).

Methodology

Sedimentology and Stratigraphy

Sedimentologic field-based studies were undertaken in Cambrian-Ordovician sedimentary rocks of the Cordillera Oriental (Figs. 1 and 2) in northwest Argentina. The first step involved logging at a decimeter-scale of approximately 1700 m of cumulative thickness from four different sedimentary successions (namely Sierra de Cajas, Angosto del Moreno, Quebrada de Trancas, and Quebrada de Moya; see Figs. 1, 2 and 5). Lithology, grain size, sedimentary structures, beds thickness, bed contacts, and overall geometries were described, allowing the distinction of sedimentary facies that were grouped into four facies assemblages. Due to the extent of the studied area (~ 1500 km2) and the thickness of the deposits, the classic continental to shallow-marine subdivisions (e.g., Walker and James 1992; Clifton 2006; Plint 2010) have been simplified to allow for reconstruction of basin evolution. Accordingly, fluvial and tidal-influenced marginal-marine systems are here grouped as Estuary facies assemblages; foreshore, upper, middle and lower shoreface deposits composed the Foreshore-Shoreface facies assemblages (i.e., between mean sea-level and the fair-weather wave base; FWWB); distal and proximal delta-front facies constitute the Delta-front; and offshore transition, upper and lower offshore deposits are referred to as the Offshore facies assemblages (i.e., from the fair-weather wave base to the storm wave base). An integrative approach describing the basin evolution is then proposed for the Cordillera Oriental across the Cambrian-Ordovician transition. Further, this study is placed in a broader context incorporating adjacent basins.

Fig. 5
figure 5

Detailed stratigraphic sections encompassing the Cambrian-Ordovician boundary. Sequence stratigraphic and biostratigraphic correlations among localities are shown. Pad., Padrioc Formation; N.f.a., Neoparabolina frequens argentina; J.k., Jujuyaspis keideli; K., Kainella; K.m., Kainella meridionalis

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Biostratigraphy

Trilobites provide temporal control as this is the most accurate fossil group for the studied interval (Fig. 4). The earliest trilobite-bearing strata correspond to the base of the Lampazar Formation and the Casa Colorada Member (Figs. 4 and 5) recording the first appearance datum (FAD) of Neoparabolina frequens argentina (Vaccari et al. 2010). One isolated remain of Neoparabolina frequens argentina has been found in the uppermost strata of the Padrioc Formation at Angosto del Moreno (Moya and Monteros 2000). The Cambrian-Ordovician boundary is identified in our studied area by the FAD of Jujuyaspis keideli (Figs. 4 and 5). According to Vaccari et al. (2010, 2018), the classic fossil distribution through the Jujuyaspis keideli biozone starts with the FAD of Jujuyaspis keideli followed by the FAD of Saltaspis steinmanni. At Angosto del Moreno, only Saltaspis steinmanni was found, therefore lacking the lower interval of the J. keideli biozone. The early Tremadocian (Tr1; Early Ordovician) consists of the Jujuyaspis keideli, Kainella andina, and Kainella meridionalis biozones (e.g., Vaccari et al. 2010 and references therein). The upper limit of the Kainella meridionalis biozone corresponds to the Tr1—Tr2 boundary, and is marked by the FAD of Kaninella teiichii.

Results

The Santa Rosita Formation and the Guayoc Chico Group chiefly consist of muddy siltstone interbedded with medium- to very fine-grained sandstone. Thirteen sedimentary facies gathered into the four facies assemblages previously listed (i.e., Estuary, Foreshore-Shoreface, Delta-front, and Offshore; Table 1), were identified.

Table 1 Sedimentary facies characteristics and facies assemblages
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Estuary

Description

This facies assemblage consists of three sedimentary facies (E1, E2, E3; Table 1; Fig. 6). E1 is composed of unbioturbated fine- to medium-grained sandstone units (individual beds > 1 m thick) with irregular bases. Sandstone commonly displays trough-cross bedding and some bed surfaces shown mudstone intraclasts (Fig. 6a). This facies occurs in the Tilcara Member in Quebrada de Trancas. E2 consists of trough cross-bedded fine- to medium-grained sandstone (Fig. 6c). Single and double mudstone drapes occur on the foreset of the cross-stratified sandstone (Fig. 6c). Units may reach up to several meters thick, are poorly bioturbated, and have an overall lenticular geometry (Fig. 6b). The axes of E2 sandbodies are oriented south/north (Fig. 6b). E3 comprises heterolithic packages exhibiting wavy-, flaser- and lenticular-bedded sandstone layers alternating with muddy-siltstone. E3 is also poorly bioturbated. In some localities, ladderback ripples (Fig. 6d) on bed tops were observed, as well as syneresis cracks. Both E2 and E3 are present in the Pico de Halcón Member in Quebrada de Trancas and Quebrada de Moya, as well as in the Padrioc Formation in Sierra de Cajas and in Angosto del Moreno.

Fig. 6
figure 6

Estuary facies zone. a Mudstone pebble on the top of the surface of a sandstone bed (E1); Tilcara Member; Quebrada de Trancas. mp: mudstone pebble. b Sandstone beds reflecting the infill of tidal channels (E2); Pico de Halcón Member; Quebrada de Moya. Person for scale is 1.75 m. c Trough cross-stratified sandstone and associated mudstone drapes (E2); Pico de Halcón Member; Quebrada de Trancas. sm, single mudstone drap; dm, double mudstone drapes. d Ladder-back ripples (E3); Padrioc Formation; Sierra de Cajas. Dashed line highlights the crests of ladder-back ripples

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Interpretation

Trough cross-stratification indicates a unidirectional tractional flow and migration of 3D dunes. The associated mudstone intraclasts suggest the interplay of fluvial and tidal processes along the fluvial to the marine transition zone, where high-energy currents (tidal and fluvial) were capable of reworking previously deposited mudstone layers (e.g., Gugliotta et al. 2018). The absence of bioturbation suggests strongly brackish to freshwater conditions, preventing colonization by the infauna (Mángano and Buatois 2003). Together, these observations suggest deposition in fluvial-tidal channels. Paleocurrent data from 3D dunes show a northward progradation. Sandstone beds displaying trough cross-bedding (E2) and mudstone drapes point to subaqueous dunes that migrated northward in tidal channels (Dalrymple and Choi 2007). Heterolithic facies (E3) intervals reflect deposition in tidal flats (Buatois and Mángano, 2003; Buatois et al. 2006), and resemble similar deposits elsewhere (e.g., Collinson et al. 2006; Dalrymple and Choi 2007). The association of the three sedimentary facies points to estuarine environments (Buatois and Mángano 2003; Buatois et al. 2006).

Foreshore-Shoreface (FS)

Description

This facies assemblage consists of four sedimentary facies (FS1, FS2, FS3, FS4; Table 1, Fig. 7). FS1 comprises low-angle planar-laminated unbioturbated fine- to medium-grained sandstone (i.e., swash cross-stratification) with aligned pores with a millimeter-scale diameter (Fig. 7a). FS2 are sandstone having symmetrical to asymmetrical ripples and rare trace fossils (Fig. 7a). FS1 and FS2 occur only at Sierra de Cajas at the top of the Angosto del Moreno Formation. These beds exhibit normal contacts but have lateral thickness variations, reaching up to ca. 12 m thick. FS3 comprises up to 1-m thick, hummocky cross-stratified to trough cross-stratified very fine- to fine-grained sandstone (Fig. 7b) with symmetrical (Fig. 7c) to asymmetrical ripples (Fig. 7d), occurring in all localities in the Lampazar and Angosto del Moreno formations, and in the Alfarcito and Rupasca members (Fig. 5). Individual beds are stacked forming up to 10 m thick stratigraphic packages and bioturbation is scarce typically represented by Skolithos linearis. This facies is present in all localities. FS4 corresponds to unbioturbated erosionally based, poorly-sorted, matrix-supported breccia forming beds up to 80 cm thick (Fig. 7e). FS4 was only identified at Quebrada de Trancas at the base of the Alfarcito Member (Fig. 7e). Breccia is characterized by a sandy matrix with pebble-to cobble-sized sandstone to siltstone clasts (Fig. 7e).

Fig. 7
figure 7

Foreshore-shoreface facies zone. a Sandstone bed displaying low-angle planar stratification (in orange; FS1) alternated with thinner sandstone levels exhibiting small-scale symmetrical and asymmetrical ripples (in yellow; FS2); Sierra de Cajas, Angosto del Moreno Formation. Note that rippled intervals have a very limited lateral extension. b Trough cross-stratified sandstone (FS3) with superimposed wave ripples (wr); Alfarcito Member; Quebrada de Moya. c Sandstone (FS3) with aggrading symmetrical ripples suggesting high sedimentation rate; Sierra de Cajas, Angosto del Moreno Formation. d Sandstone (FS3) with wave and combined-flow cross-lamination; Quebrada de Trancas; Alfarcito Member. e Poorly sorted, matrix-supported breccia (FS4) corresponding to the basal levels of Alfarcito Member at Quebrada de Trancas

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Interpretation

Planar bedding in FS1 likely reflects high-energy, upper-flow regime processes (e.g., Perillo et al. 2014). The associated aligned pores are considered as keystone vugs formed by air-bubble trapped in the sediment by swash processes (e.g., Dunham 1970; Reineck and Singh 1980). Symmetrical and asymmetrical ripples in FS2 reflect oscillatory to combined-flow processes, which are likely formed by the interplay of wave and tide processes. The stacking pattern of FS1 and FS2 reflects deposition in a wave-dominated, tidally modulated foreshore, where surf-swash processes (at low tide; FS1) alternated periodically with oscillatory processes (at high tide; FS2) (e.g., Vaucher et al. 2017, 2018). FS3 exhibits sedimentologic features pointing to deposition from permanent, nearshore oscillatory, unidirectional and combined-flow currents acting at the water–sediment interface and punctuated by storm events in shoreface environments as discussed in previous studies in these strata (Buatois and Mángano 2003; Buatois et al. 2006) and elsewhere (e.g., Hampson and Storms 2003; Clifton 2006). The presence of vertical burrows of suspension feeders (i.e., Skolithos linearis) indicates high-energy conditions and organic particles in suspension in the water column, consistent with deposition in agitated nearshore areas (Mángano et al. 2005). Breccia beds of FS4 reflect high-energy deposition and pass vertically to offshore deposits (see “Offshore (O)”). FS4 potentially records wave-ravinement processes during a transgressive phase (e.g., Cattaneo and Steel 2003; Buatois et al. 2012; Zecchin et al. 2018).

Delta-Front (DF)

Description

This facies assemblage contains two sedimentary facies (DF1, DF2; Table 1; Fig. 8). DF1 consists of fine-grained sandstone forming packages of ca. 2–10 m thick (Fig. 8a– c, e, f). DF1 is characterized by planar bedding with local bed pinch-out, planar lamination, and asymmetrical ripples. Soft-sediment deformation structures are found near the sandstone bases (Fig. 8c). DF1 is laterally discontinuous and shows an overall lobate geometry (Fig. 8a, e, f). This facies pinches out westwards and eastwards into DF2 siltstone intervals at the scale of hundreds of meters (Fig. 8a, e). DF2 is composed of thick, continuous, homogeneous siltstone intervals (Fig. 8a), locally intercalated with cross-laminated very fine-grained sandstone (Fig. 8d). Body and trace fossils are scarce and poorly diverse in DF1 and DF2. Both facies are only present in the Alfarcito Member at Quebrada de Trancas (Fig. 5).

Fig. 8
figure 8

Delta-front facies zone in Quebrada de Trancas; Alfarcito Member. a Lobe sandstone complex (DF1) with the axis toward the north laterally pinching out into a siltstone interval (DF2). b Fine-grained sandstone (DF1) displaying current-ripples and planar-laminations. c Soft-sediment deformation structures near the bottom of a sandstone bed. d Siltstone interval (DF2) with intercalated cross-laminated fine-grained sandstone (pointed out by the white arrows). e Stacking pattern highlighting the vertical relationship between proximal (DF1) and distal (DF2) delta-front and the lobate geometry of DF1. f Central view of a lobate sandstone package (DF1) showing the lateral relationship with the adjacent siltstone interval (DF2)

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Interpretation

Lobe morphologies suggest the dominance of unidirectional flows likely driven by river processes combined with a high rate of sedimentation without substantial reworking of material by strong waves (e.g., Reading and Collinson 1996; Bhattacharya and Giosan 2003; Bhattacharya et al. 2006). Only a few oscillatory structures were observed, suggesting limited wave/storm influence. The sandstone units likely reflect deposition in more proximal settings, whereas siltstone intervals suggest more distal emplacement. Lateral pinchouts between the two facies are evidence of northward progradation. The lobate shape of sandstone bodies suggests that adjacent siltstone intervals record deposition away from major terrestrial inputs. Furthermore, the combined reduced fossil content and the scarce bioturbation could reflect stressed environments related to freshwater input and high sediment concentration in the water column (e.g., MacEachern et al. 2005). This facies assemblage points to a river-dominated, wave-affected proximal (DF1) to distal (DF2) delta front (e.g., Orton and Reading 1993; Olariu and Bhattacharya 2006; Coates and MacEachern 2007).

Offshore (O)

Description

This facies assemblage is composed of four sedimentary facies (O1, O2, O3, O4; Table 1; Fig. 9). O1 consists of laterally persistent poorly bioturbated to unbioturbated, sharp-based, meter-thick mudstone and siltstone packages (Fig. 9a), interbedded with centimetre-thick, very fine-grained sandstone layers displaying parallel stratification, combined-flow cross-lamination, as well as symmetrical ripples. O2 comprises unbioturbated bioclastic grainstone (sensu Lokier and Al Junaibi 2016). It consists of decimetre-thick fossil-rich (mostly trilobite and echinoderm remains), wavy sandy limestone layers that can form up to 2 m-thick packages. O3 consists of siltstone packages interbedded with discrete hummocky to microhummocky cross-stratified, very fine-grained sandstone, in places displaying interference ripples (Fig. 9b–d). O4 comprises regularly interbedded discrete hummocky cross-stratified very fine- to fine-grained sandstone and thin siltstone intercalations (Fig. 9e). Both O3 and O4 include sandstone layers with sharp bases contact showing flute and gutter casts and flame structures. Gutter casts are all oriented north–south (Fig. 9d), and flute casts indicate a northward direction of the paleoflow (Fig. 9f). With the exception of O2, only found at the base of the Lampazar Formation in Sierra de Cajas, all the sedimentary facies that composed this facies assemblage are the most commonly found at the different localities and are present in the Lampazar and the Pupusa formations, and in the Casa Colorada, the Alfarcito and the Rupasca members (Fig. 5). Overall, this facies assemblage contains abundant and diverse trace fossils. Body fossils are mainly represented by trilobites and brachiopods.

Fig. 9
figure 9

Offshore facies zone. a Overview of the siltstone-dominated intervals (O1); Quebrada de Moya; Alfarcito Member. b Siltstone interbedded with hummocky cross-stratified sandstone; Quebrada de Moya; Alfarcito Member (O3). c Close-up of b showing intercalated sandstone and siltstone layers at centimeter-scale. d Hummocky cross-stratified sandstone displaying a steep-sided gutter cast, Quebrada de Trancas, Alfarcito Member (O3). e Hummocky cross-stratified sandstone intercalated within sandy siltstone (O4), Quebrada de Trancas, Alfarcito Member. e North-directed flute casts at the base of a sandstone bed (O4), Quebrada de Moya; Alfarcito Member

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Interpretation

This facies assemblage records deposition below the FWWB in open marine offshore environments, reflecting low-energy suspension fall-out conditions punctuated by storm events at various depths (e.g., Heward 1981; Buatois et al. 2006; Clifton 2006; Vaucher et al. 2017). According to the previously described facies zone (i.e., Delta-front), a prodeltaic setting for some siltstone intervals displaying very thin fine-grained sandstone layer cannot be excluded (e.g., Coates and MacEachern 2007; Bhattacharya and MacEachern 2009). The sandy limestone intervals exclusively composed of shelly remains (mostly trilobite) seem to reflect low sedimentation rates during a transgressive phase (e.g., Beckvar and Kidwell 1988; Botquelen et al. 2004). Ichnologic information supports deposition in fully marine, distal settings (Mángano et al. 2005), which is consistent with body-fossil data.

The Cambrian-Ordovician unconformity

In Quebrada de Trancas, the lowermost Ordovician strata consist of shallow-marine deposits (base of Alfarcito Member; Figs. 5, 10a and b) that truncate the underlying estuarine Cambrian deposits (Pico de Halcón Member), suggesting that up to 25 m of strata are missing. The erosion surface is overlain by breccias of FS4 (Fig. 7e) that grade upward into offshore deposits (Fig. 5). At this locality, Lower Ordovician deposits onlap the underlying Cambrian strata (Fig. 10a). Measured dips of the beds above and below the erosion surfaces are 60° and 50°, respectively, suggesting an angular unconformity. On the southern flank of the Angosto del Moreno (Fig. 10c), three upper Cambrian sandstone units (foreshore-shoreface deposits of the Angosto del Moreno Formation) are juxtaposed against the Lower Ordovician siltstone unit (offshore deposits of the Pupusa Formation). In the northern part (Fig. 10c), the upper Cambrian foreshore-shoreface deposits (Angosto del Moreno Formation) are sharply overlain by Lower Ordovician offshore deposits (Pupusa Formation), suggesting that up to 60 m of strata were removed along the surface. Contrarily to Quebrada de Trancas, no breccia was found at the contact between Cambrian and Ordovician rocks.

Fig. 10
figure 10

Cambrian-Ordovician unconformity. a Satellite view from Quebrada de Trancas highlighting the discordant and erosional contact between the upper Cambrian Pico de Halcón Member with the overlying lower Tremadocian Alfarcito Member. b Field observation of the wave ravinement surface (wrs) between Pico de Halcón and Alfarcito members. Person for scale is 1.7 m. c Satellite view from Angosto del Moreno showing the wave ravinement surface. The northern part shows a conformable contact between upper Cambrian and Lower Ordovician strata, while in the southern flank three upper Cambrian units are juxtaposed to Lower Ordovician siltstone. Satellite images are from Bing Maps ©

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The erosive and unconformable stratigraphic surface, separating the marginal-marine units below (i.e., Pico de Halcón Member at Quebrada de Trancas / Angosto del Moreno Formation at Angosto del Moreno) from the overlying deeper-water, fully marine deposits (i.e., Alfarcito Member at Quebrada de Trancas/Pupusa Formation at Angosto del Moreno), is interpreted as a wave ravinement surface (Cattaneo and Steel 2003; Zecchin et al. 2018 and references therein). In a high-energy context, erosion by wave ravinement is commonly able to remove up to 10–20 m of sediment (e.g., Cattaneo and Steel 2003; Zecchin et al. 2018). However, ~ 25 m and ~ 60 m have been removed in Quebrada de Trancas and Angosto del Moreno, respectively (Fig. 10a, c). This suggests a slow landward retreat of the shoreline, allowing longer time for waves to remove the underlying sediment (Zecchin et al. 2018). The angular relationship observed in Quebrada de Trancas suggests that the wave ravinement surface was formed on a steep profile, implying uplift that tilted the Pico de Halcón Member prior to deposition of the Alfarcito Member. Deposits associated with wave ravinement are commonly millimeter to decameter thick. However, the unusual thickness (~ 80 cm) of the breccia beds found at Quebrada de Trancas suggests a high-gradient topography (e.g., Hwang and Heller 2002; Zecchin et al. 2018), also supporting a cliff-like configuration of tilted Cambrian sedimentary strata prior to the formation of the wave ravinement surface. In the two other studied localities, Sierra de Cajas and Quebrada de Moya, the absence of outcrop continuity prevent closer examination of the stratal geometries associated with the Cambrian-Ordovician boundary.

Depositional model

Late Cambrian (Furongian)

The oldest depositional units of the studied interval correspond to the Tilcara Member and the Padrioc Formation (late Cambrian; Furongian; Figs. 4 and 5), which overlie the Mesón Group. Both units reflect proximal estuarine environments characterized by fluvial-tidal channels (Figs. 5 and 6a; Table 1), corresponding to a lowstand systems tract (LST) and an early transgressive systems tract (TST; Buatois et al. 2006), open to the north, as suggested by paleocurrent data showing a south-to-north tidal transport.

The TST is recorded by offshore environments identified by a siltstone-dominated interval interbedded with storm-induced deposits (O1; O3; O4; Figs. 5 and 9). This TST corresponds to the Lampazar Formation and the coeval Casa Colorada Member (Figs. 4 and 5). The base of these units is mostly coincident with the FAD of Neoparabolina frequens argentina (Figs. 4 and 5). A long-term retrogradational trend characterized the Cambrian interval but is punctuated by a first regressive pulse that mostly delineates the tops of both the Lampazar Formation (at 192 m in Sierra de Cajas; at 200 m in Angosto del Moreno; Fig. 5) and the Casa Colorada Member (at 82 m in Quebrada de Trancas; Fig. 5). The Casa Colorada Member is not present in Quebrada de Moya, because the Pico de Halcón Member has a faulted contact with the underlying Mesón Group.

By the end of the Cambrian, a major regressive phase took place as reflected by the deposition of the highstand systems tract (HST) sandstone-dominated Angosto del Moreno Formation at both Sierra de Cajas and Angosto del Moreno. This HST phase is characterized by the emplacement of foreshore-shoreface environments (Figs. 5 and 7). In Quebrada de Trancas and Quebrada de Moya, the estuarine Pico de Halcón Member represents the subsequent LST and TST displaying a northward orientation of the system as exhibited by axes of incision of the estuarine channels (Figs. 5 and 6). The estuarine Pico de Halcón Member fills an incised valley (Buatois et al. 2006). This implies that the underlying deposits (i.e., Angosto del Moreno Formation) were eroded in Quebrada de Trancas and Quebrada de Moya. In Sierra de Cajas, sharp-based shoreface to foreshore parasequence sets are observed (Fig. 5). At this locality, the Angosto del Moreno Formation commonly displays mostly offshore to lower shoreface deposits that are abruptly overlain by foreshore sandstones (Fig. 5). Such a stratigraphic pattern suggests a forced regression, which corresponds to a falling stage systems tract (FSST) (e.g., Clifton 2006). In the Angosto del Moreno, the Angosto del Moreno Formation almost exclusively displays shoreface deposits (Fig. 5), suggesting slightly deeper-water settings of deposition in comparison with Sierra de Cajas. The Angosto del Moreno Formation and the Pico de Halcón Member are the upper stratigraphic units belonging to the Neoparabolina frequens argentina biozone (Figs. 4 and 5), thus marking the end of Cambrian record.

Early Ordovician (Tr1)

The beginning of the Ordovician was characterized by a major transgressive phase during which the TST of the Pupusa Formation and the Alfarcito Member were deposited; both correspond to the base of Jujuyaspis keideli biozone (Figs. 4 and 5). The facies assemblage in the lower part of Tr1 (between 157 and 188 m; Fig. 5) indicates that wave-dominated conditions prevailed (foreshore-shoreface to offshore environments; Quebradas de Trancas and Moya; Figs. 5 and 11a), while coeval strata suggest offshore environments (Sierra de Cajas and Angosto del Moreno; Figs. 5 and 11a). A rapid change from wave-dominated conditions (lower shoreface—offshore deposits; TST) to river-dominated (distal to proximal delta-front environments; HST; at 188 m Fig. 5) is revealed by the presence of the siltstone-to-sandstone lobate interval (DF1 and DF2) of the delta-front facies assemblage (Figs. 5 and 7) in Quebrada de Trancas. This change is apparent several meters above the base of the Jujuyaspis keideli biozone, continuing up to the middle of the Kainella andina biozone (Fig. 5). In order to preserve the delta-front lobate sandstone (Fig. 8e, f) of the Alfarcito Member between 188 to 380 m (in Quebrada de Trancas; Fig. 5), reduced incoming wave energy is suggested (e.g., Reading and Collinson 1996; Bhattacharya and Giosan 2003; Bhattacharya et al. 2006).

Fig. 11
figure 11

Southeast-northwest cross-sections between Sierra de Cajas (SC) and Quebrada de Trancas (QT) showing the evolution at different time frames during the early Tremadocian. a Initiation of deformation during the Cambrian-Ordovician transition. The deformation started inducing both local uplift (blue arrow) and subsidence (red arrow). Physiographical changes were still weak, allowing the establishment of open wave-dominated environments during the transgressive phase at the beginning of the Jujuyaspis keideli biozones. b The intensity of deformation increased, accentuating local uplift and subsidence, and forming a high relief in SC. The latter acted as a hydrodynamic barrier dissipating incoming wave energy that winnowed sediment in this locality. Thus, SC created protected environments southward, allowing the development of the lobe-shaped deltaic deposits in QT from Jujuyaspis keideli to Kainella andina biozones. A–A’ transect refer to Fig. 12. c The physiography remained as it was in b and the distal to proximal delta-front progressively filled the inherited topography up to SC. Once the topography was filled, open wave-dominated environments set up from the middle of Kainella andina biozone. Yellowish color corresponds to sandstone-dominated deposits, whereas the greenish one corresponds to mudstone-dominated deposits

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The lower Tremadocian interval in Sierra de Cajas consists of two biozones (Jujuyaspis keideli and Kainella andina) identified in the much thinner Pupusa Formation (25 m thick in Sierra de Cajas and 165 m thick in Quebrada de Trancas; Fig. 5). Even though the Pupusa Formation is thinner in Sierra de Cajas compared to Angosto del Moreno, both Jujuyaspis keideli and Saltaspis steinmanni occur, which is not the case southward at Angosto del Moreno where only Saltaspis steinmanni was found. Therefore, the absence of Jujuyaspis keideli at Angosto del Moreno suggests that the TST at the base of the Pupusa Formation is diachronic with a north to south transgressive trend. Hence, to explain the reduced thickness of the Pupusa Formation in Sierra de Cajas and the absence of Jujuyaspis keildeli, an uplift at Angosto del Moreno and further in Sierra de Cajas is proposed. The uplift should have occurred prior to the deposition of the Pupusa Formation at Angosto del Moreno, thus exposing the Angosto del Moreno Formation during the Cambrian-Ordovician transition (Fig. 10c). Afterward, uplift took place in Sierra de Cajas, whereas the transgression continued, forming an extensive wave ravinement surface and leading to deposition of the transgressive Pupusa Formation at Angosto del Moreno (Fig. 10c). The uplift at Sierra de Cajas may have formed a high relief acting as a hydrodynamic barrier dissipating the incoming wave energy (Beji and Battjes 1993). This barrier allowed the preservation of lobate-shaped deposits (DF1 and DF2) in a protected southern area (Fig. 11b). During the uplift in Sierra de Cajas, the establishment of strong currents is proposed. These currents may have prevented sedimentation and/or removed sediments, therefore explaining the reduced thickness of the Pupusa Formation. In Sierra de Cajas, the contact between the Jujuyaspis keideli and Kainella andina biozones represents a sedimentary hiatus (Figs. 5 and 11b). Foreshore-shoreface sedimentation prevailed in Quebrada de Moya during the emplacement of the lobe deltaic (DF1) complex in Quebrada de Trancas. Quebrada de Moya is located slightly to the northeast of Quebrada de Trancas, but was under the influence of more energetic processes (i.e., fair-weather and storm waves). Therefore, Quebrada de Moya contributed to produce a protected environment in Quebrada de Trancas. Such conditions very likely happened during the deposition of the deltaic lobes (i.e. up to the middle of Kainella andina biozone; at 380 m on Fig. 5) until the topography was filled (Fig. 11c). In Quebrada de Trancas at 380 m, there is a shift from a parasequence set dominated by river processes (i.e., delta-front; from 188 to 280 m) to a wave-dominated parasequence set (i.e., foreshore-shoreface and offshore; from 280 to 624 m). Such a switch of processes (i.e., from the river- to wave-dominated) and renewal of sedimentation in Sierra de Cajas (Kainella andina biozone) suggest that the previously created topographic high, preventing wave processes to occur in Quebrada de Trancas is not active anymore. This is probably due to the infill of the topographic low by DF1 and DF2 deposits (Fig. 11b, c). Thus, wave propagation was no longer blocked and wave-dominated settings were established (Fig. 11c).

Previously, it was proposed that this sedimentary basin had an east-to-west prograding trend (e.g., Astini 2003). However, this trend is not consistent with the sandstone deltaic lobe progradation (Fig. 10a, b, d), the geometrical organization of the stratigraphic units (Fig. 11) or the paleocurrent indicators (i.e., flute casts, gutter casts; see Fig. 9d, f), which all point to a south-to-north trend of deposition. Therefore, it is more consistent with the northward orientations proposed by Buatois and Mángano (2003) and Buatois et al. (2006).

Sequence stratigraphy

Interpretation in terms of stratigraphic sequences is proposed for the four stratigraphic sections. Identification of long-, medium, and short-term sequences is possible by the facies-zone description established previously (Fig. 5). Short-term sequences are the smallest sequences described in this study (Fig. 5). They vary between ~ 10 and ~ 100 m thick, reflecting the lithological change from siltstone- to sandstone-dominated intervals. Medium-term sequences of ~ 30 to ~ 160 m thick are composed of two small-scale sequences defined by a lower siltstone-dominated short-term sequence and an upper sandstone-dominated short-term sequence (Fig. 5). Long-term sequences consist of two medium-scale sequences and show a thickness of ~ 80 to ~ 180 m. They reflect the transition from siltstone- to sandstone-dominated medium-term sequences (Fig. 5).

The FAD of Neoparabolina frequens argentina corresponds to the FAD of Cordylordus proavus (conodont biozone; Shergold 1988; Waisfeld and Vaccari 2008 and references therein). According to Ogg et al. (2016a, b), the FAD of Cordylordus proavus was estimated at ~ 486.7 Ma. The limit between Kainella meridionalis and Kaninella teiichii biozones corresponds to the limit between Tr1 and Tr2, estimated at ~ 480.2 Ma (Ogg et al. 2016a, b). From the FAD of Neoparabolina frequens argentina to the Tr1–Tr2 boundary, six long-term sequences are recognized, encompassing an estimated duration of ~ 6.4 myr. The proposed duration for a long-term sequence is therefore of ~ 1.28 myr. According to the long-term sequence duration, this can be considered as a third-order cycle (e.g., Strasser et al. 2006). Thus, medium-term and short-term sequences have a respective duration of ~ 642 kyr and ~ 301 kyr. Medium-term sequences would correspond to the fourth-order cycle, and short-term sequences can reflect the long-term of the eccentricity cycle (Strasser et al. 2006). Nevertheless, because unconformities of unknown duration are recognized in the stratigraphic succession, caution should be exercised while considering these estimated durations.

Geodynamic implications

Several authors have characterized the upper Cambrian—Lower Ordovician strata from the Cordillera Oriental as recording long-term relative sea-level fluctuations devoid of tectonically induced deformation during the deposition (Moya 1988, 1997; Astini 2003, 2008; Buatois and Mángano 2003; Buatois et al. 2003; Mángano and Buatois 2004; Buatois et al. 2006). The tectonic setting changed with the development of a volcanic arc to the west and a retro-arc basin in the earliest Ordovician (Pankhurst et al 1998; Bahlburg 1998; Zimmermann and Bahlburg 2003; Zimmermann 2011). This study suggests that major changes in stratigraphic architecture occurred in response to modifications of the basin physiography (Figs. 5, 11 and 12), likely during the Cambrian—Ordovician transition (Fig. 5). As shown previously, the Cambrian strata were uplifted at Sierra de Cajas and Angosto del Moreno, and tilted at Quebrada de Trancas (Fig. 12). These deformations were responsible for changes in hydrodynamic processes and contributed to the development of extensive wave ravinement surfaces and sedimentary hiatus (Figs. 5, 10 and 11). On the west/south-west margin of the basin, the Puna-Famatinian volcanic arc (Fig. 12) developed at the beginning of the Early Ordovician, as a result of northeast-directed subduction, leading to the formation of a retro-arc basin to the east/north-east in the Cordillera Oriental and northward in Bolivia (Fig. 12; Bahlburg 1991; Pankhurst et al. 1998; Zimmermann and Bahlburg 2003; Zimmermann et al. 2010, 2014; Zimmermann 2011). Evidence of the arc activity is first recorded in Puna by felsic volcanic rocks from the volcanoclastic Vicuñas Formation and other Tremadocian successions (Moya et al. 1993; Zimmermann and Bahlburg 2003). Even if the trilobite fauna found in the Vicuñas Formation is suggestive of an Ordovician age, some upper Cambrian fauna was also discovered near the base of the deposits (Moya et al. 1993). According to Pankhurst et al. (1998), the associated magmatic activity commenced prior to the full development of the volcanic arc during the late Cambrian. Development of the volcanic arc drove large-scale deformation of the lithosphere in the retro-arc domain, leading to subsidence in the foredeep area and uplift in the forebuldge (e.g., Jordan 1995). This mechanism very likely explains (1) the forced regression in Sierra de Cajas, as well as the presence of a topographic barrier protecting the southern part of the study area (Figs. 11b and 12); and, (2) the extensive wave ravinement surfaces formed during the early Tr1 over uplifted surfaces at Angosto del Moreno and Quebrada de Trancas.

Fig. 12
figure 12

Proposed reconstruction of the studied area during the Early Ordovician Jujuyasips keideli biozone. The basin in opened towards the north, while the physiography of the basin in the retro-arc domain is driven by the onset of the Puna-Famatinian arc to the west

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Southward, at Sierra de Famatina (Fig. 1), the Volcancito Formation has yielded a similar trilobite fauna (Neoparabolina frequens argentina and Jujuyaspis keideli biozones), allowing stratigraphic comparison with the present studied area (Tortello and Esteban 2007). A similar environmental deepening-upward trend is recorded, but in the Volcancito Formation the transgression occurred within the Neoparabolina frequens argentina biozone and not at the beginning of the Jujuyaspis keideli biozone. According to Rapela et al (2018), the onset of the magmatic activity in both the Puna and the Sierra de Famatina was synchronous, and coincided with the Cambrian-Ordovician transition. This suggests that deformation resulting in the deepening trend could reflect the onset of the foredeep subsidence. In the Sierra de Mojotoro (Fig. 2), no Neoparabolina frequens argentina was found (Harrington and Leanza 1957; Balseiro and Waisfeld 2013; Barrientos Ginés et al. 2018), suggesting that there are no coeval strata of the Lampazar Formation and the Casa Colorada Member further south. Indeed, the basal conglomeratic Pedrera Formation (Moya 1998; coeval to the Pupusa Formation and Alfarcito Member) rests directly on top of the Mesón Group. The absence of upper Cambrian deposits yielding Neoparabolina frequens argentina may either reflect non-deposition from emergence in the Sierra de Mojotoro (Fig. 2) or erosion following tectonic uplift at the Cambrian–Ordovician transition. The conglomeratic units in the Salta area may be coeval with the breccias (FS4) of Quebrada de Trancas, but further investigation should be undertaken to assess the provenance of this conglomeratic unit. Other sections exist in the Cordillera Oriental encompassing the same stratigraphic interval (e.g., Astini 2003, Benedetto 2007; Esteban and Tortello 2007; Esteban and Tortello 2009); however, the published stratigraphic intervals are lack of sedimentologic details or are poorly constrained, making comparisons difficult with the present study.

In summary, this study highlights a previously unrecognized episode of basin deformation around the Cambrian-Ordovician transition (Fig. 12). This stratigraphic unconformity was likely concomitant with the onset of the retro-arc basin in the Cordillera Oriental that probably occurred earlier in the western/southwestern foredeep area in the vicinity of the volcanic arc (Fig. 12). Nevertheless, in the foredeep area of the Puna, a strong deepening is expected during the late Cambrian as recognized in the Volcancito Formation further south, in Sierra de Famatina (Tortello and Esteban 2007). As the foredeep is characterized by strong subsidence rates and deepening trends, no wave ravinement is suspected. Further, detailed sedimentologic studies are also required in this area to constrain the evolution and the record of the deformation created by the Puna-Famatinian arc.

Conclusions

The studied upper Cambrian-Lower Ordovician stratigraphic interval of Cordillera Oriental in northwest Argentina was previously interpreted as a sedimentary succession only recording long-term sea-level fluctuations of a different order, with an east-to-west depositional trend, devoid of tectonically induced deformation. This first integrated study highlights a more complex history. Main points are summarized hereafter:

  • Ranging from late Cambrian (Age 10; Neoparabolina frequens argentina biozone) to Early Ordovician (Tr1; Jujuyaspis keideli, Kainella andina, Kainella meridionalis biozones), four main facies assemblages were described: estuarine, foreshore-shoreface, delta-front, and offshore. Correlation was possible due to the recognition of key trilobite taxa. The stacking patterns of facies assemblages suggest five third-order sequences of ~ 1.28 myr in duration.

  • Basin physiographic changes are highlighted by (1) extensive wave ravinement surfaces at the Cambrian-Ordovician transition (at Quebrada de Trancas and Angosto del Moreno), (2) an unconformity between the Pico de Halcón (Cambrian) and Alfarcito (Ordovician) members, (3) a diachronic southward transgression, and (4) a change in coastal processes from river-dominated to wave-dominated across the Jujuyaspis keideli to Kainella andina biozones.

  • The development of the Puna-Famatinian volcanic arc is considered as the driver for the deformation occurring in the basin. The deformation was associated with a change in basin style, from extensional to retro-arc. Therefore, this study confirms the proposal of Bahlburg and Hervé (1997) regarding tectonic disturbance present throughout the stratigraphic successions. This study highlights the complex stratigraphic evolution associated with the onset of a retro-arc basin in the forebuldge area.

  • A revised lithostratigraphic framework is proposed, with newly formally defined formational names, assisting in the correlation between eastern (Quebrada de Trancas and Quebrada de Moya) and western (Sierra de Cajas and Angosto del Moreno) areas of the Cordillera Oriental.