**4. Orán Group**

#### **4.1. Metán Subgroup (Río Seco, Anta, and Jesús María formations)**

The basal contact of the Metán Subgroup deposits corresponds to a regional unconformity and is generally associated with the Lumbrera Formation (Santa Bárbara Subgroup, Salta Group). In the eastern part of the basin (Umbral de Los Gallos [53]), this subgroup lies on different units of the postrift deposits of the Salta Group, such as the Lumbrera, Maíz Gordo, Mealla, and Yacoraite formations (**Figure 7**). Although the distribution of the Metán Subgroup is broader than that of the Salta Group, its depocenters are generally the same as those exist‐ ing during the accumulation of the Salta Group [54].

In this basin, a zircon fission‐track sample from an intercalated tuff at Alemanía yielded an age of 14.5 ± 1.4 Ma and hornblende crystals from a tuff collected in the lower part of the Anta Formation at Río Piedras produced a 40Ar/39Ar date of 13.95 ± 0.72 Ma. The age of the low‐ est exposed Anta Formation beds is 15.2 Ma at Río Piedras and 17.3 Ma at Río Metán based on magnetic stratigraphy [55, 56]. Other authors have placed the contact with the overlying Guanaco Formation at 12.3 Ma (Arroyo Piedra Blanca), 13.5 Ma (Río Metán), 13.1 Ma (Río Piedras), and 9.7 Ma (Arroyo González) [56, 57] (**Figure 7**). The paleomagnetic ages obtained from the contacts at the base and top of the Metán Subgroup vary in different parts of the basin, from between 17.3 and 12 Ma to between 15 and ∼9 Ma (**Figure 7**). These data reveal that an elongated initial depocenter developed parallel to the uplift zone at ∼17 Ma, migrated toward the eastern edge of the recent basin at ∼15 Ma and continued to fill with sediment until ∼12 Ma, when new basin structuring and the erosion of the Metán Subgroup deposits began.

#### *4.1.1. Facies and depositional architecture of the Metán Subgroup*

The Río Seco, Anta, and Jesús María formations present interfingering stratigraphic relation‐ ships (**Figure 11**). The deposits of the Metán Subgroup (Río Seco and Jesús María formations) are characterized by a succession of lithofacies from fine‐grained to very coarse‐grained sand‐ stone, often with pelitic clasts (**Table 3**) and have been interpreted as the product of ephemeral flows that deposited sand sheet under high‐flow regime conditions (**Figures 10** and **11**, **Table 3**).

The deposits of the Río Seco and Jesús María formations have been interpreted as accumulates in a paleoenvironment of a "sandy ephemeral fluvial system associated with dune fields" under arid climatic (**Figure 11**) [54, 56].

The Anta Formation is primarily composed of brown, green, and yellow mudstone and medium‐ to fine‐grained sandstone. Gypsum layers, gypsum nodules, and pyroclastic layers are common throughout the basin. The oolitic limestones with foraminifera are found in the south‐eastern sector of the basin. These limestones have been assigned to the Paraná marine ingression with 14.9 Ma in age, based on paleomagnetic data collected at the Piedras river (Miliolidos, **Figure 10**) [54, 56].

**4. Orán Group**

began.

**4.1. Metán Subgroup (Río Seco, Anta, and Jesús María formations)**

and b) braided fluvial fan and river system of San Felipe Formation with its architectural elements.

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

ing during the accumulation of the Salta Group [54].

*4.1.1. Facies and depositional architecture of the Metán Subgroup*

The basal contact of the Metán Subgroup deposits corresponds to a regional unconformity and is generally associated with the Lumbrera Formation (Santa Bárbara Subgroup, Salta Group). In the eastern part of the basin (Umbral de Los Gallos [53]), this subgroup lies on different units of the postrift deposits of the Salta Group, such as the Lumbrera, Maíz Gordo, Mealla, and Yacoraite formations (**Figure 7**). Although the distribution of the Metán Subgroup is broader than that of the Salta Group, its depocenters are generally the same as those exist‐

**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,

In this basin, a zircon fission‐track sample from an intercalated tuff at Alemanía yielded an age of 14.5 ± 1.4 Ma and hornblende crystals from a tuff collected in the lower part of the Anta Formation at Río Piedras produced a 40Ar/39Ar date of 13.95 ± 0.72 Ma. The age of the low‐ est exposed Anta Formation beds is 15.2 Ma at Río Piedras and 17.3 Ma at Río Metán based on magnetic stratigraphy [55, 56]. Other authors have placed the contact with the overlying Guanaco Formation at 12.3 Ma (Arroyo Piedra Blanca), 13.5 Ma (Río Metán), 13.1 Ma (Río Piedras), and 9.7 Ma (Arroyo González) [56, 57] (**Figure 7**). The paleomagnetic ages obtained from the contacts at the base and top of the Metán Subgroup vary in different parts of the basin, from between 17.3 and 12 Ma to between 15 and ∼9 Ma (**Figure 7**). These data reveal that an elongated initial depocenter developed parallel to the uplift zone at ∼17 Ma, migrated toward the eastern edge of the recent basin at ∼15 Ma and continued to fill with sediment until ∼12 Ma, when new basin structuring and the erosion of the Metán Subgroup deposits

The Río Seco, Anta, and Jesús María formations present interfingering stratigraphic relation‐ ships (**Figure 11**). The deposits of the Metán Subgroup (Río Seco and Jesús María formations)

**Figure 10.** Stratigraphic correlation of the deposits of Metán Subgroup (base of Orán Group).

**Figure 11.** Description of the palaeoenvironment with architectural elements illustrated using schematic diagrams of Metán Subgroup a) 1 ‐ proximal ephemeral sandy fluvial system associated with wind deposits, 2‐ distal ephemeral sandy fluvial system, 3‐ playa lake; b) 1‐ alluvial fan deposits, 2‐ sandy plain, 3‐ dry mud flat, 4‐ ephemeral saline lake; c) 1‐ proximal ephemeral fluvial system and, 2‐ distal ephemeral fluvial system.


**Table 3.** Code of the major architectural elements defined for the Orán Group with their characteristic lithofacies.

The deposits of the Anta Formation have been defined as accumulates in a playa lake paleoen‐ vironment, in which the following features have been recognized: sand flats, arid mud‐flats, ephemeral saline lakes, and permanent saline lakes [54] (**Figure 11**).

The presence of zeolites (analcime) in the facies of laminated green pelite indicates that it formed in an environment such as alkaline lake in an arid to semiarid condition. In these basins with little or no drainage, evaporation would have increased the alkalinity of the waters and the reaction between the water and volcanic ash falling intermittently into the lake would have caused the zeolitization of the volcanic glass [56, 57].

The provenance of the Metán Subgroup in the area of maximum subsidence (Piedra Blanca, Río Metán, Arroyo González, **Figure 10**) most probably came from the west with sediments of the Salta Group, the Puncoviscana Formation, and granite from the border of Puna as a result of first‐ or second‐order fluvial systems connected to the Calchaquí Basin.

The presence of *Riella* sp. (phylum Bryophyta, class Hepaticae, family Riellaceae) in the Anta Formation suggest that it is the only genus of the class Hepaticae whose present representa‐ tives develop in both purely alkaline salt waters and fresh water. Associated with *Pediastrum* sp. and *Phaeceros* sp., they are formed in lacustrine environments and reflect stenohaline con‐ ditions that are alkaline and rich in nutrients [54, 58].

#### **4.2. Guanaco Formation (base of Jujuy Subgroup)**

**Formation Code Architectural elements Principal lithofacies** Piquete SG Sandy bedforms Gcm ‐ Sm ‐ St ‐ Sp

**Figure 11.** Description of the palaeoenvironment with architectural elements illustrated using schematic diagrams of Metán Subgroup a) 1 ‐ proximal ephemeral sandy fluvial system associated with wind deposits, 2‐ distal ephemeral sandy fluvial system, 3‐ playa lake; b) 1‐ alluvial fan deposits, 2‐ sandy plain, 3‐ dry mud flat, 4‐ ephemeral saline lake;

Guanaco GB Gravel bars Gmg ‐ Gi ‐ Gt ‐ Sm

Jesús FF Foodplain deposits Fl ‐ Fm ‐ Fo ‐ Po María LS Laminated sand sheets Sl ‐ Fm ‐ Fl ‐ Se

Anta FF Mud Flat Fl ‐ Fg ‐ Fgr

**Table 3.** Code of the major architectural elements defined for the Orán Group with their characteristic lithofacies.

Río Seco LS Laminated sand sheets associated with aeolian deposits

CH Channel

c) 1‐ proximal ephemeral fluvial system and, 2‐ distal ephemeral fluvial system.

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

GB Gravel bars Gmg ‐ Gi ‐ Gt ‐ Sm

SB Sandy bedforms Gcm ‐ Sm ‐ St ‐ Sp FL Saline lake Fl ‐ Fm ‐ Co

SB Sand Flat Sm ‐ St ‐ Sp ‐ Sm FF Foodplain deposits Fl ‐ Fm ‐ Fo ‐ Po

SB Sandy bedforms Gcm ‐ Sm ‐ St ‐ Sp

Sl ‐ Fm ‐ Fl ‐ Se

SB Sandy bedforms St ‐ Sm ‐ Fm

The Jujuy Subgroup is widely distributed in the central and southern sector of the Cordillera Oriental and in the Santa Barbara System. It exhibits a general increasing grain‐size trend, with cycles of 50–200 m in thickness and lateral extents of tens of kilometers. The cycles rep‐ resent the progradation of the sediments at times of reduced accommodation space, whereas the cycles of decreasing grain‐size represent periods of vertical aggradation associated with greater accommodation space [59] (**Figure 12**).

The basal contact between the Jesús María or older deposits and Guanaco formations is a paraconformity or unconformity and the contact at the top is an unconformity with the Piquete Formation or Quaternary deposits (**Figure 12**).

The Guanaco Formation has garnetiferous glassy tuff layers and is linked to the La Pava‐ Ramadas Caldera, whose volcanic activity has been dated to 8.73 ± 0.25 Ma (K/Ar; [60]). Records of these tuffs have been found in San Antonio de los Cobres, Lerma Valley, and the valleys of Rio Grande of Jujuy and Juramento‐Metán.

The Guanaco Formation was deposited between ∼9 and <6.9 Ma [60], near Coronel Moldes, and it has an age of 9.31 ± 0.31 Ma [57]. The thickness of the preserved Guanaco Formation deposits ranges between 0 and 900 m in the Cordillera Oriental and more is more than 2000 m in the Santa Bárbara System (**Figure 12**) [59, 61]. This variation reflects a deformation episode after the formation was deposited and a previous structuring at ∼10 Ma [31, 62].

#### *4.2.1. Facies and depositional architecture of the Guanaco Formation*

The Guanaco Formation is characterized by alluvial fans deposits dominated by: (1) conglom‐ erate and sabulite with channeled bases and an upward fining arrangement, constituting

**Figure 12.** Stratigraphic correlation of the deposits of Jujuy Subgroup (top of Orán Group).

deposits of gravel bars; (2) facies of conglomerates accumulated by hyperconcentrated depos‐ its; and (3) conglomerate sandstone with trough and planar stratification corresponding to lateral bar deposits and dune migration [59] (**Table 3**, **Figure 13a**).

This fluvial system is associated with an alluvial fan paleoenvironment dominated by braided stream. The proximal deposits are located in the western zone (the Lerma Valley) and the Integrated Stratigraphy of the Cenozoic Andean Foreland Basin (Northern Argentina) http://dx.doi.org/10.5772/intechopen.69985 147

**Figure 13.** Description of the paleoenvironment with architectural elements illustrated using schematic diagrams of Jujuy Subgroup. a) 1‐ alluvial fan deposits and, 2‐ braided fluvial systems deposits of Guanaco Formation, b) 1‐ and 2‐ alluvial fan deposits with braided fluvial systems of Piquete Formation.

middle and distal sectors are located in the central and distal zones [59] (**Figures 12** and **13**), which are associated with a large river system.

The conglomerate facies of the Guanaco Formation contain more than 15% high‐grade meta‐ morphic clasts (migmatites) and granitoids associated with paleocurrent directions from the west. These characteristics have been interpreted that the provenance sediments is from the eastern edge of the Puna.

The characteristics of the sedimentary paleoenvironment, the provenance data, and the paleocurrent directions from the west suggest that, between ∼9 and 6 Ma, the foreland basin evolved independently from the Calchaquí Valley Basin and that the connection of first‐ and second‐order fluvial systems transported material from the eastern edge of the Puna and from the El Toro Lineament.

#### **4.3. Piquete Formation (top of Jujuy Subgroup)**

deposits of gravel bars; (2) facies of conglomerates accumulated by hyperconcentrated depos‐ its; and (3) conglomerate sandstone with trough and planar stratification corresponding to

This fluvial system is associated with an alluvial fan paleoenvironment dominated by braided stream. The proximal deposits are located in the western zone (the Lerma Valley) and the

lateral bar deposits and dune migration [59] (**Table 3**, **Figure 13a**).

**Figure 12.** Stratigraphic correlation of the deposits of Jujuy Subgroup (top of Orán Group).

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

The Piquete Formation is widespread in the Cordillera Oriental, the Santa Bárbara System, and the Sierra de Zapla (**Figures 3** and **12**). The base is characterized by an erosional uncon‐ formity or paraconformity on the deposits of the Guanaco Formation in the Santa Bárbara System [63]. In other areas, these units are separated by an angular unconformity, as in the Cordillera Oriental [59, 64] (**Figure 12**).

The measured partial thickness varies from 190 to over 2000 m. This unit features deposits of whitish, fine‐grained vitrocrystalline, rhyodacitic to dacitic tuffs with thicknesses of 1.80 to 3 m. The Pliocene deposits of the Piquete Formation accumulated in response to the strong structuring that produced the upheaval of the Subandean ranges, the Santa Bárbara System, and part of the Cordillera Oriental, which also resulted in the formation of intermontane basins, such as the Lerma Valley and the Siancas Valley.

Paleomagnetic studies and ages from fission track dating in apatite from one tuff (Coronel Moldes) in the basal section of this unit yielded an age of 5 Ma [33, 57]. The upper third was dated based on a tuff that yielded an age of 1.3 ± 0.2 Ma [65].

### *4.3.1. Facies and depositional architecture of the Piquete Formation*

The paleoenvironment of the Piquete Formation has been interpreted as relatively small allu‐ vial fans distributed on the flanks of structural depressions and dominated by debris flows (**Table 3**). If these alluvial fans would have been more, had developed in the eastern sector, and away from the thrust fronts, flood plains with small lake systems would have developed [59] (**Figure 13**).

The conglomerates in the Piquete Formation contain slabs of limestone from the Yacoraite Formation, slate from the Precambrian basement of the Puncoviscana Formation, and clasts of reddish sandstone and limestone from the Salta Group. The change in the conglomeratic clast composition from the Guanaco Formation to the Piquete Formation suggests that between ∼5 and 2 Ma, thick sediments from the eastern edge of the Puna were trapped in the intermon‐ tane Calchaquí Basin [42, 59].

The paleontological content of the Piquete Formation at present is very limited and includes fragmentary remains of vertebrates, notably including abrocomid rodents and plates of Dasypodidae. In the Xibi Xavi river, in the city of Jujuy, complete remains of a glyptodont (*Cranithlastus xibiensis*) and megatherium teeth [66] have been found. Alligatoroid remains from Rosario de la Frontera (south of Salta province), assigned to the species *Caiman latirostris* based on its morphology [67], have also been found.
