**3. Calchaquí Basin**

Group (Valle Calchaquí) and the Orán Group (Lerma Valley, Sianca Valley, Santa Bárbara

The structural evolution of the Andean foreland basin was mainly controlled by the inver‐ sion of the extensional basins of the Cretaceous rift of the Salta Group, which overlaps with the general migration of the deformation toward the foreland. Some authors describe this as "broken foreland basin," a view with widespread consensus today [13, 14], while others refer

The Cenozoic Andean foreland basin provides an excellent opportunity to define the rela‐ tionships between tectonism and sedimentation because its geologic history is closely linked to the tectonic activity over the evolution of the river system in the basin. In this study, the paleoenvironmental characteristics, the types of contacts between units, the provenance of the deposits, and the geochronologic and paleomagnetic ages of the stratigraphic units in each basin are presented. The integration of these data has improved our understanding of the

In Cordillera Oriental, the upper Neoproterozoic La Paya Formation basement unit contains low‐grade metamorphosed sandstones and mudstones [15, 16] that grade southward into schists, gneisses, and migmatites [17, 18] in the Sierra de Quilmes and Cumbres Calchaquíes

Marine quartzites of the Meson Group are arranged in angular unconformity on top of the

The marine deposits of the Silurian‐Devonian basin are represented by deposits of an exten‐ sive marine platform environment whose greater thicknesses are developed east of the

The sedimentary succession that overlaps the Neoproterozoic to lower Paleozoic basement corresponds to the Cretaceous‐Paleogene strata of the Salta Group [21] and the Paleogene‐

The Salta Group, in Cordillera Oriental and Santa Bárbara System, is present in three subba‐ sins: Metán, Alemanía, and Pucará‐Brealito (**Figure 3**). The Salta Group deposits are divided into the following three subgroups (from base to top): Pirgua [22], Balbuena, and Santa Bárbara [23]. The Pirgua Subgroup is composed of sandstones, conglomerates, and siltstones at almost all localities and represents the syn‐rift fill. The Balbuena Subgroup, which accumulated dur‐ ing the Maastrichtian to Early Paleocene, represents the early postrift stage and is composed of white sandstones (Lecho Formation) and gray to yellow limestones in the upper part (Yacoraite Formation). The Santa Bárbara Subgroup consists of the Mealla, Maíz Gordo, and Lumbrera formations [23] and is dominated by fine‐grained red sandstone, siltstone, and green mudstone. The Lumbrera Formation [23], which represents the uppermost part of the Salta Group (**Figure 2**) is composed of claystones and siltstones and is always reddish‐brown to red. In the

System, and Sierra de Zapla) accumulated (**Figures 1** and **2**).

132 Seismic and Sequence Stratigraphy and Integrated Stratigraphy - New Insights and Contributions

to it as a "foreland basin system" [6, 7].

basin evolution during the Andean orogeny.

previous deposits [19] (middle to upper Cambrian).

Neogene strata of the Payogastilla Group and Orán Group.

**2. The pre‐Andean basement**

(**Figures 2** and **3**).

Cordillera Oriental [20].

#### **3.1. Los Colorados Formation**

The middle to upper Eocene deposits of the Payogastilla Group, including the Los Colorados Formation, represents the initial stage in the evolution of the Andean foreland basin of north‐western Argentina (**Figure 2**). The area of Tin Tin, Tonco, and Calchaquí valleys fea‐ ture outcrops with well‐documented, complete profiles of the Los Colorados Formation (**Figure 4**).

The first episode of filling of the basin started with the deposition of the Los Colorados Formation in the middle to upper Eocene [33, 34]. A clear second‐order subaerial unconfor‐ mity Type 2 [35, 36] is located between the Lumbrera Formation and Los Colorados Formation. This unconformity is also found in the Luracatao and Pucará valleys [13, 14, 31, 34].

Based on the fossil record, the initial development of the foreland basin, at least in the Luracatao Valley, occurred during the middle Eocene [34]. Sedimentary filling of the basin began with the deposition of the Los Colorados Formation and was characterized by sheet‐ flood ephemeral fluvial deposits formed by unconfined and confined channels within dune fields in an arid region. In some parts of the basin, aeolian deposits interfinger with ephemeral fluvial systems, such as those in the Tonco Valley (Sequences I and III).

Detrital zircons from the town of Angastaco have been dated to 37.6 ± 1.2 Ma [37] and the apatites from Monte Nieva have been dated to 28.7 ± 1.9 Ma [6]. This deposit is ∼300 m thick and contains basal sandstone and siltstone facies of an ephemeral fluvial system and is associ‐ ated with aeolian deposits [38]. A tuff horizon intercalated in the aeolian deposits in the Tin Tin section has provided an age of 21.0 ± 0.8 Ma (U‐Pb) [39].

#### *3.1.1. Facies, depositional architecture, and sequence stratigraphy of the Los Colorados Formation*

The Los Colorados Formation is an unconformity‐bounded depositional sequence that cor‐ responds to a major stratigraphic cycle in the evolution of the foreland basin in the Calchaquí

**Figure 4.** Correlation of Los Colorados Formation based on the sequence stratigraphy analysis.

Valley. The entire Payogastilla Group corresponds to a first‐order sequence [35, 36], i.e., it is associated with one distinct tectonic setting. Hence, according to the hierarchy based on the magnitude of base‐level changes that resulted in the formation of the sequence, the Los Colorados Formation can be assigned to a second‐order level of stratigraphic cyclicity. In this context, the three depositional sequences that form its stratigraphic subdivisions can be con‐ sidered third‐order sequences. The correlations reveal that the deposits are separated at the base and top by second‐order subaerial unconformities [35, 36].

The lower boundary of the Los Colorados Formation is marked by an increase in the grain size, by a paleoenvironmental change from the mud flat deposits of the Lumbrera Formation to ephemeral fluvial systems with conglomerates and by a marked change in the sedimentary provenance. This unconformity is very clear in the northern part of Amblayo Valley. The controversial upper boundary is an erosional unconformity (Tonco Valley) and represents a change in depositional paleoenvironment from distal sandy ephemeral fluvial system and clay playa deposits or aeolian accumulations to a braided fluvial system (**Figures 4** and **5**).

The Los Colorados Formation deposits were identified as facies of an ephemeral fluvial sys‐ tem with flashy discharge, calcic paleosols, and dune fields, which are characteristic of arid regions.

Sequence stratigraphic concepts are applicable, with modifications, to the successions that are entirely nonmarine in origin, even where there are no marine surfaces with which to cor‐ relate them, such as in the Payogatilla Group basin. In a fully nonmarine environment, fluvial accommodation is created and destroyed by the following: (a) differential tectonic movement between basin and source areas, which can modify the amount of sediment supply and the gradient of the landscape profile and (b) cycles of climate change, which can alter the balance between fluvial discharge and sediment load [40].

#### **3.2. Angastaco Formation**

north‐western Argentina (**Figure 2**). The area of Tin Tin, Tonco, and Calchaquí valleys fea‐ ture outcrops with well‐documented, complete profiles of the Los Colorados Formation

The first episode of filling of the basin started with the deposition of the Los Colorados Formation in the middle to upper Eocene [33, 34]. A clear second‐order subaerial unconfor‐ mity Type 2 [35, 36] is located between the Lumbrera Formation and Los Colorados Formation.

Based on the fossil record, the initial development of the foreland basin, at least in the Luracatao Valley, occurred during the middle Eocene [34]. Sedimentary filling of the basin began with the deposition of the Los Colorados Formation and was characterized by sheet‐ flood ephemeral fluvial deposits formed by unconfined and confined channels within dune fields in an arid region. In some parts of the basin, aeolian deposits interfinger with ephemeral

Detrital zircons from the town of Angastaco have been dated to 37.6 ± 1.2 Ma [37] and the apatites from Monte Nieva have been dated to 28.7 ± 1.9 Ma [6]. This deposit is ∼300 m thick and contains basal sandstone and siltstone facies of an ephemeral fluvial system and is associ‐ ated with aeolian deposits [38]. A tuff horizon intercalated in the aeolian deposits in the Tin

*3.1.1. Facies, depositional architecture, and sequence stratigraphy of the Los Colorados Formation*

The Los Colorados Formation is an unconformity‐bounded depositional sequence that cor‐ responds to a major stratigraphic cycle in the evolution of the foreland basin in the Calchaquí

This unconformity is also found in the Luracatao and Pucará valleys [13, 14, 31, 34].

fluvial systems, such as those in the Tonco Valley (Sequences I and III).

134 Seismic and Sequence Stratigraphy and Integrated Stratigraphy - New Insights and Contributions

**Figure 4.** Correlation of Los Colorados Formation based on the sequence stratigraphy analysis.

Tin section has provided an age of 21.0 ± 0.8 Ma (U‐Pb) [39].

(**Figure 4**).

The thickness of the Angastaco Formation varies considerably between the sections in which it is fully exposed (e.g., from 4450 m at the Calchaquí River to 1500 m in the Tonco Valley, **Figure 6**). The depocenter of the basin between ∼13.7 and 10 Ma was located in the area of Angastaco.

**Figure 5.** Palaeoenvironment with architectural elements illustrated using schematic diagrams of Los Colorados Formation. a) LAST (e g. Sequence II), proximal ephemeral confined (SB element) in the base, b) unconfined ephemeral – mud flat (LS element) associated with aeolian deposits (HAST).

**Figure 6.** Stratigraphic correlation of the Los Colorados and Angastaco formations (base of Pavogastilla Group).

The structures are located on the western edge of the basin and are similar to those that cre‐ ated local accommodation space in other broken foreland settings [10, 13, 14, 41, 42].

#### *3.2.1. Facies and depositional architecture of the Angastaco Formation*

Several fluvial systems have been recognized based on the lithofacies and stratigraphic archi‐ tectural. The lithofacies were characterized based on the deposits' properties (**Table 1**) and on the stratigraphic analysis (**Figure 7**, **Table 2**).

Integrated Stratigraphy of the Cenozoic Andean Foreland Basin (Northern Argentina) http://dx.doi.org/10.5772/intechopen.69985 137

**Figure 7.** Description of the palaeoenvironment with architectural elements illustrated using schematic diagrams of Angastaco Formation. a) Gravel‐bed braided river system associated with gravity flow deposits, Angastaco Formation of the middle part of the deposits with its architectural elements, b) Deep gravel‐bed braided river at the top Angastaco Formation, with its architectural elements.


The structures are located on the western edge of the basin and are similar to those that cre‐

Several fluvial systems have been recognized based on the lithofacies and stratigraphic archi‐ tectural. The lithofacies were characterized based on the deposits' properties (**Table 1**) and on

ated local accommodation space in other broken foreland settings [10, 13, 14, 41, 42].

**Figure 6.** Stratigraphic correlation of the Los Colorados and Angastaco formations (base of Pavogastilla Group).

*3.2.1. Facies and depositional architecture of the Angastaco Formation*

136 Seismic and Sequence Stratigraphy and Integrated Stratigraphy - New Insights and Contributions

the stratigraphic analysis (**Figure 7**, **Table 2**).


**Table 1.** Major lithofacies identified in the Payogastilla Group and Oran Group (modified from Ref. [47]).


**Table 2.** Codes of the major architectural elements defined for the Payogastilla Group with their characteristic lithofacies.

The Angastaco Formation conglomerates in the western part of the basin contain substan‐ tial amounts of plutonic rocks from the Oire Eruptive Belt. In the eastern part of the study area (Tonco profile), however, slates, phyllites, and schists from the Puncoviscana Formation are present. There are fewer paleovolcanic clasts from the Eruptive Belt of the eastern Puna (Calchaquí River) and neovolcanics in the San Lucas River and the Tonco south area, which are associated with paleocurrent directions from the north‐west and west. In the San Lucas and the Tonco south River area, a small but significant component of red sandstone clasts from the Formation and gray sandstones from the Maíz Gordo Formation represent the Salta Group. These data suggest the tectonic uplift of the Sierra León Muerto in the eastern study area (**Figures 3** and **6**) [43].

In the upper section, the paleoenvironment changes to more erosional rivers with deep chan‐ nels. The paleocurrents are from the north‐west and are associated with neovolcanic clasts from the volcanic‐sedimentary deposits of the Almagro‐El Toro basin, which has a deposi‐ tional and eruptive age between 14.3 and 6.4 Ma and synorogenic deposits dated at ∼11 Ma [44].

#### **3.3. Palo Pintado Formation**

**Code Lithofacies Interpretation**

138 Seismic and Sequence Stratigraphy and Integrated Stratigraphy - New Insights and Contributions

massive with calcified rhizoliths penetrating down into

Palo LA Lateral‐accretion macroform Gt ‐ Sm

Pintado FF(CH) Abandoned channel fills Fl ‐ Fm

Angastaco GB Gravel bars and bedforms Gh ‐ Gcm

Los Colorados LS Laminated sand sheets

**Table 1.** Major lithofacies identified in the Payogastilla Group and Oran Group (modified from Ref. [47]).

**Formation Code Architectural elements Principal lithofacies** San GB Gravel bars Gmg ‐ Gi ‐ Gt ‐ Sm Felipe SB Sandy bedforms St ‐ Sm ‐ Fm

> DA Downstream – accretion macroform

GB Gravel bars and bedforms Gt ‐ Gm

CS Crevasse splay ‐ Channel Sp ‐ Sl ‐ Sm

FF Foodplain deposits Fl ‐ Fm ‐ Fo ‐ Po SB Sandy bedforms Sl ‐ Sm ‐ Fl GB Gravel bars and bedforms Gh ‐ Sm

SB Sandy bedforms Sm ‐ St ‐ Sp ‐ Sm

SG Sediment gravity flows Gmg

GB Gravel bars and bedforms Gh ‐ Gi ‐ Sm

associated with aeolian

GB Gravel bars and bedforms Gm ‐ Gt

**Table 2.** Codes of the major architectural elements defined for the Payogastilla Group with their characteristic lithofacies.

deposits

SB Sandy bedforms Sl ‐ St ‐ Sp ‐ Fl ‐ Fm

SB Sandy bedforms Gcm ‐ Sm ‐ St ‐ Sp

Fm Massive siltstone and mudstone, very thin beds. Overbank or abandoned channel

Overbank, abandoned channel, or

waning flood deposits.

Swamp and lacustrine in the

Paleosols. The rhizoliths emanate from the bases of damp and wet

Gh ‐ Gi ‐ Gm ‐ Sl ‐ Sm ‐ St

Gh ‐ St

Gh ‐ Gt ‐ Gmg Gh ‐ Gt ‐ Sl

Sl ‐ Fm ‐ Fl ‐ Se

deposits.

floodplain.

interdune units.

Fl Very fine‐grained sandstone, siltstone, and mudstone, fine lamination, desiccation cracks, roots, bioturbation.

Fo Siltstone and mudstone, very small ripples and very thin

Po Very fine‐grained sandstone, siltstone and mudstone,

sandstone of aeolian dune origin.

laminations.

The Palo Pintado Formation is ∼800 m thick and contains a tuff level that has been dated to 10.29 ± 0.11 Ma (K/Ar) [45]. Near the top is another pyroclastic level that has been dated to 5.27 ± 0.28 Ma (206Pb/238U) [46] and 5.98 ± 0.32 Ma [47] (**Figure 7**). The unit comprises thick‐ ening‐ and coarsening‐upward cycles, including matrix‐supported conglomerates, fine‐ to medium‐grained sandstones, and fine‐grained sublithic sandstones ending in green, brown, and gray siltstones levels (**Figure 8a**).

These deposits have been interpreted as wandering sand‐gravel fluvial systems with small lakes [48]. The geometry and the fluvial architectural characteristics are a direct consequence of allogenic controls, such as tectonic activity, under constant climatic conditions.

During the upper Miocene, the uplift of the basin caused an increase in the sedimentary accommodation/deposition (A/D) rate and was also associated with a change in the petro‐ logic composition of the deposits [48]. The resulting orographic barriers produced a warmer and wetter climate [49].

#### *3.3.1. Facies and depositional architecture of the Palo Pintado Formation*

The fluvial architectural characteristics and associated lithofacies in the Palo Pintado Formation define a fluvial system with intrachannel and overbank deposits [43]. The intrachannel depos‐ its include gravel bars and bedform deposits (GB) and sandy bedforms comprising trans‐ verse bars and sand waves formed by vertical accretion and downstream flow (SB) (**Table 2**, **Figure 8a**). In contrast, the overbank deposits are represented by three types of features: (a) lateral accretion macroforms, which are characterized by large‐scale, gently dipping second‐ order bounding surfaces that correspond to successive increments of lateral growth, with ero‐ sional bases and gradational tops; (b) small crevasse splay channels resulting from erosion at

**Figure 8.** Stratigraphic correlation of the deposits of Palo Pintado and San Felipe Formations (top of Payogastilla Group).

the borders of the main channel during flood events, which correspond to crevasse channels (CS); and (c) the development of large floodplain deposits (FF) (**Figure 8a**, **Table 2**).

X‐ray diffraction data from floodplain clay minerals revealed the presence of illite, montmo‐ rillonite, magnesium‐rich smectite, and kaolinite generated by hydrolysis under a warm and humid climate [50].

The occurrence of *Caiman* cf*. latirostris* also supports the hypothesis that the climatic con‐ ditions in Valle Calchaquí during the upper Miocene were comparatively wetter than those inferred for contemporaneous units deposited to the east (Guanaco Formation, Orán Group) [51].

The paleomagnetic analysis reflects the increase in the sedimentation rate from 0.41 mm/year at the base, to 0.11 mm/year at the middle, to 0.66 mm/year in the top of the deposits, which is associated with a higher percentage of Salta Group clasts. Paleocurrent directions from the south and the south‐east indicate the tectonic reactivation of the deposition area from the Sierra León Muerto (and its continuation to the north as the Sierra Los Colorados). The exhumation was registered before in the conglomerates of the Angastaco Formation [43, 52].

In the Quebrada Salta, quartzite clasts with *Skolithos* from the Mesón Group (upper Cambrian) and paleocurrents from the north and north‐east suggest a provenance from Quebrada El Toro, where the Mesón Group (upper Cambrian) is well exposed.

#### **3.4. San Felipe Formation**

**Figure 8.** Stratigraphic correlation of the deposits of Palo Pintado and San Felipe Formations (top of Payogastilla Group).

140 Seismic and Sequence Stratigraphy and Integrated Stratigraphy - New Insights and Contributions

The deposits of the San Felipe Formation at the top of the Payogastilla Group are more than 600 m thick in the south‐eastern Calchaquí Valley and are affected by numerous faults and folds. The transition between the Palo Pintado Formation and the San Felipe Formation is sharp and unconformable. The outcrops of San Felipe Formation, present less areal distribution than the previous and are restricted to the south‐eastern sector of the Calchaquí basin (**Figure 8**).

#### *3.4.1. Facies and depositional architecture of the San Felipe Formation*

The San Felipe Formation is characterized by conglomerates deposited in low‐sinuosity channels.

The well‐sorted conglomerates lack of matrix, contain rounded clasts overlapping in thick tabular strata, are 2 to >7 m in thickness, and are found in longitudinal bar deposits (**Table 1**, **Figure 9b**). The unit also contains poorly sorted conglomerates, supported clasts, pseudoplas‐ tic debris flow, and massive coarse‐grained wackes resulting from rapid accumulation and poorly sorted deposition. The origin of the conglomerates in the San Felipe Formation was analyzed in the Quebrada Salta, where there are also elements of the Puncoviscana Formation and the Oire Eruptive Complex. In addition, limestone clasts from the Yacoraite Formation (Salta Group) have been found and clasts from Pirgua Subgroup (Salta Group) in association with paleocurrent directions from the west and south‐west. The San Felipe Formation deposits have been interpreted as braided alluvial fans associated with shallow gravelly braided fluvial system (**Figure 9b**, **Table 2**) [38].

**Figure 9.** Description of the palaeoenvironment with architectural elements illustrated using schematic diagrams. a) meandering fluvial sand‐gravel system with small lakes of the Palo Pintado Formation with its architectural elements, and b) braided fluvial fan and river system of San Felipe Formation with its architectural elements.
