Yacoraite Formation Research Articles

The impact of microbial mats in promoting record of Maastrichtian crocodylomorph tracks from Yacoraite Formation, Argentina

Here we report tetrapod tracks from a stratigraphic level of Maastrichtian age in the Yacoraite Formation (Maimará ichnosite, Jujuy Province, Argentina). The ichnological material consists of convex hyporeliefs whose formation was induced by growth of microbial mats in an upper subtidal-lower intertidal setting. Ichnological features that are recognized in tracks and traces allowed to include them into the categories of ‘punting tracks’ and ‘buoyancy tracks’. These categories suggest swim behaviours of the producers, which are tentatively interpreted as crocodylomorphs. Reconstruction of the filling process leading to tracks preservation and inclusion into the geological record enabled reconstructing at least two different phases of mats development, one dominated by chemical precipitation and the other by trapping and binding of coated grains and other particles. These two phases of mat growth are related to slightly changing energetic conditions of the palaeoenvironment and further support a marine origin for the unit. Finally, it is suggested that biologically induced, in-situ mineral precipitation promotes fast formation of overtracks through early lithification achieving preservation of tetrapod tracks well before their complete filling.

Structural Inheritance in the Eastern Cordillera, NW Argentina: Low‐Temperature Thermochronology of the Cianzo Basin

AbstractThe present‐day deformation style of the Eastern Cordillera in NW Argentina is strongly influenced by the inversion of pre‐existing Paleozoic and Mesozoic structures. In particular, the extensional faults and lithological contrasts resulting from the Cretaceous–Paleogene Salta Rift phase form heterogeneities that were preferentially reactivated during the Andean orogeny. Constraining the timing and characteristics of reactivation is a key to understanding the interplay between tectonics and inherited crustal anisotropies. In this study, we combine structural and sedimentological field data with a low‐temperature thermochronology data set from the area surrounding the fault‐bounded Cianzo basin. The southeastern boundary is formed by the inverted Hornocal fault, which was the basin‐bounding normal fault of the Lomas de Olmedo sub‐basin (Salta Rift basin). Lacustrine deposits of the Yacoraite Formation overspill on the footwall of this fault and mark tectonic quiescence during the post‐rift phase of the Salta Rift. Apatite (U‐Th‐Sm)/He and fission track ages in the Hornocal fault hanging wall show an onset of rapid cooling interpreted to be concomitant with fault inversion between the latest Oligocene and middle Miocene (∼24–15 Ma). Low‐temperature thermochronology data also constrain the timing of major folding in the eastern limb of the Cianzo syncline to pre‐10 Ma, whereas the western limb started tilting post‐10 Ma. Characterization of exhumation patterns related to fault activity surrounding the Cianzo basin emphasizes the influence of the pre‐existing structural framework on deformation in fold‐and‐thrust belts.

Upside down: Resilience and recolonization of overturned stromatolite from the Maastrichtian-Danian Yacoraite formation (northwestern Argentina)

Stromatolites are organo-sedimentary structures, internally laminated, which grow attached to the substrate. This lamination mirrors the dynamic interaction of environmental and biological factors where its formation takes place. However, some stromatolites from the Yacoraite Formation, from Amblayo locality, in northwestern Argentina, present an unconventional internal structure characterized by bilateral symmetry, where the development of lamination extends towards both sides of an imaginary plane.This contribution reports a multi-scale analysis of these particular stromatolites, with the aim of determining the extent to which environmental factors have influenced their internal structure. In addition to this, a sequence of stages that gave rise to these organo-sedimentary structures will be proposed.Results suggest a microbialitic growth by in-situ biologically induced, carbonate precipitation, which was carried out in a shallow intertidal environment with good luminosity and significant sedimentary input. However, the stromatolitic growth occurred over two stages, interrupted by a stochastic event that generated a overturning of the structure, providing a new colonizing surface for growth of microorganisms and resulting in a bilateral internal structure.The characterization of these stages, including the overturning of the structure, not only provides a highly accurate proxy for reconstructing punctual environmental conditions of the Yacoraite Formation, but also opens up a field of discussion focused on the resilience and recolonization capacity of stromatolite-producing microorganisms after stochastic events.

Modelling the coupled heterogeneities of the lacustrine microbialite-bearing carbonate reservoir of the Yacoraite Formation (Salta, Argentina)

The Yacoraite Formation is a complex lacustrine microbialite-bearing carbonate formation whose heterogeneity is due to different sedimentary facies associations and several microbialite geobodies. The bi-variate plurigaussian geostatistical method is applied to simulate in parallel these two types of heterogeneity in a 3D reservoir-scale geological model. Each variable is simulated by a complete plurigaussian method based on geological interpretation and field observations and quantifications. They are coupled through the occurrence of the microbialites within the sedimentary facies and associated into combined facies giving a one-glance representation of the reservoir heterogeneity, then used to constrain the porosity simulation.

Constructing high-resolution stratigraphic frameworks by the application of signal analysis techniques: Example of Balbuena IV sequence, Yacoraite formation, Salta Basin

One of the most essential and valuable applications of high-resolution sequence stratigraphy is reservoir zonation and characterization. Establishing a hierarchical chronostratigraphic framework comprising sequences at multiple scales is crucial to identify main reservoir heterogeneities that compartmentalize the fluid flow in the subsurface. In this context, this paper proposes a workflow that integrates different signal analysis techniques to identify sequences of multiple hierarchies from a series of stratigraphic data. The Continuous Wavelet Transform (CWT), Detrend Error Log (DTEL), and Integrated Detrend Error Log (INDTEL) techniques are utilized to process gamma-ray data obtained from outcrops of the Yacoraite Formation, which are conventionally employed as analogs for reservoir characterization. Our results suggest that CWT fits better with higher frequency cycles, while INDTEL shows a good fit with medium frequency cycles. In addition to these techniques, Hidden Markov Models were also applied, predicting T-R cycles as hidden states from the facies transition matrix and possible occurrence of missed beats. All these methods were scripted in the Python programming language, enabling the generation of fast and interactive outputs. This approach brings parameters that can guide the construction of stratigraphic models by automated processes.

Depositional controls in an ancient, closed lake system: A high-resolution and multi-scalar case study from the Yacoraite Formation (Salta Basin, Argentina)

The Yacoraite Formation (Cretaceous–Paleogene) is a mixed carbonate–siliciclastic microbialite-bearing lacustrine succession deposited in the intra-continental Salta rift basin (Argentina). In the northern sub-basin of Tres Cruces, the spectacular exposures and high lateral continuity of the outcrops provide a suitable setting to investigate and reconstruct the paleoenvironments of deposition and the resulting facies architecture of this closed, saline lake system. The Yacoraite Formation deposited in a predominantly shallow-water ramp-like lake system, characterized by eighteen main facies, classified within four main facies associations, each defining a particular depositional environment along the lake profile. From proximal (shallow) to distal: i) Palustrine Facies Association; ii) Littoral Facies Association; iii) Sub-littoral Facies Association; and lastly iv) Profundal Facies Association. In the Yacoraite paleo-lake extensive fringing mud-flat environments surrounded the lake margins, while the littoral marginal areas hosted extensive wave-dominated oolitic–bioclastic grainstones forming shoals and bars parallel to the lake margins and provided a sheltered environment in the back-shoals that allowed prolific microbialite development. In proximity to river inputs, shallow-water deltas and shoreline sandstones accumulated in the littoral margins. In the sub-littoral zone, mud-supported carbonates such as ostracod wackestones and mudstones deposited below the fair-weather wave base, and in the profundal settings deep-water organic-rich shales deposited. The Yacoraite paleo-lake evolved from a relatively stable and perennial lake system (lake stage 1) into a rapidly fluctuating ephemeral lake system (stage 2), as a result of progressively changing environmental and climatic conditions toward more arid settings. Climate control is also critical in the facies architecture, with the development of short-term cyclicity, represented by meter-scale transgressive–regressive (T–R) cycles being the result of lacustrine expansion–contraction cycles. The regressive hemicycles represent shallowing-upward succession of sub-littoral and littoral carbonate-dominated facies, whereas the transgressive hemicycles are mostly represented by sub-littoral and profundal mudstones and shales. Stacking of short-term cycles resulted in the development of medium- and long-term cyclicity at the scale of tens of meters, which represent the long-term evolution of the lake system. Lastly, a comparison with two well-documented closed lake systems highlights the role of allogenic factors acting at a regional scale (e.g., climate and tectonics) in controlling the lake-basin type, facies association and the resulting architecture. Factors at the lake-basin scale (e.g., lake margin profile, bathymetry) modulate the expression of facies and cyclicity. Ultimately, the characterization of the kilometer-scale outcrops of the Yacoraite paleo-lake provides a reference analog study to support the characterization of similar depositional systems and reservoirs of other ancient, closed lake systems, including the Pre-Salt Carbonates of the South Atlantic.

Constraining depositional evolution and reservoir compartmentalization in a mixed carbonate-siliciclastic lacustrine system: The Yacoraite formation, Salta Group, NW Argentina

The mixed carbonate-siliciclastic Yacoraite Formation, Salta Group in northern Argentina has been interest of recent studies searching for potential analogues for the South Atlantic pre-sal carbonates. Microbial lacustrine carbonates are important reservoir systems and their characteristics and stratigraphic packaging are a major factor impacting compartmentalization. This study provides sedimentological and facies analyses combined with petrographical, isotope geochemical and petrophysical analyses of lacustrine clastics and carbonates using an example from the Yacoraite Formation (Salta Group) in northern Argentina (Tres Cruces sub-basin).The Yacoraite Formation records the evolution of a lacustrine system responding to basin scale tectonic processes and climatic conditions and is interpreted as a microbially-related mixed carbonate clastic lacustrine system comprising 8 main Facies types, deposited in either a perennial or an ephemeral system. The most dominant architectural elements are: Sandstones with interbedded shales (F1), Shales with interbedded sandstones and siltstones (F2), Thick-bedded oolitic grainstone (F5), Thin-bedded oolitic grainstone-packstone (F6) and Stromatolite boundstone (F8). These facies types allow to differentiate two types of lacustrine environments: Perennial (Stage I) vs Ephemeral (Stage II) intercalated with episodes of continental plains deposition, arranged in three depositional sequences (Yacoraite I, II and III), each recording either transgressive or a regressive-transgressive trend.Carbonate and clastics are arranged in cycles during the Perennial l Stage suggesting that the depositional system responded in patterns attributable to reciprocal sedimentation, whereas, during the Ephemeral Stage 2, spatial coexistence of clastic and carbonate seem to be the case rather that cyclic vertical superposition.Thick-bedded oolitic grainstone and Stromatolites (F5 and F8 respectively) of the perennial lacustrine system show laterally continuous and thick beds with the best reservoir properties. Furthermore, the Sandstones with interbedded shales (F1) are characterized by intermediate values of porosity and permeability, which would not result in permeability barriers. On the other hand, Thin-bedded oolitic grainstone-packstone (F6) of the ephemeral lacustrine system are characterized by a high degree of heterogeneity due to their limited areal distribution and their complex spatial variability with Shales with interbedded sandstones and siltstones (F2).

A mid-latitude Maastrichtian palynological record from the Yacoraite Formation (Salta Group), northwestern Argentina

A palynological assemblage from one sample of the Yacoraite Formation outcrops (Maastrichtian–Danian of the Salta Basin) at the Valle del Tonco, Salta Province, Argentina, is described. The flora is distinctly continental and dominated by angiosperms, accompanying ferns and gymnosperms, along with few freshwater algae, bryophytes and fungi. The presence of taxa such as Aquillapollenites magnus, Gabonisporis vigorouxii and Crassitricolporites brasiliensis, together with the absence of typical taxa of the Danian Mtchedlishvilia saltenia Zone, allow to propose a late Maastrichtian age for this palynoflora. Due to its location at mid-latitudes, the palynoflora from the Yacoraite Formation is within a transitional or mixed flora zone with closer affinity to the equatorial Palmae Province. Therefore, the recorded flora has a good potential to understand the transition between the floras of low and high latitudes and to know the floristic composition of the area before the K-Pg extinction event.

Atypical ooid diversity in the Upper Cretaceous Yacoraite Formation, Argentina

AbstractThis study reports on ooid diversity from different lithotypes of the Yacoraite Formation (Salta Group basin) in the Central Andes of north‐west Argentina. The ooids display a variety of internal and external morphologies that may be deployed as proxies for seawater chemistry and hydrodynamic processes. A short review of nomenclature problems is first discussed, followed by presentation of a two‐fold quantitative and qualitative methodology. Our proposed classification addresses internal and external ooid characters in order to understand growth in response to various environmental processes at an individual particle level. This classification allows discrimination between a variety of morphologies, but also evaluation of the complexity of the processes involved in ooid formation as seen in the fossil record. This study evaluates whether the ooids present within the Yacoraite Formation share similarities with ooids formed in marine versus marine lagoon and/or lacustrine environments. A possible lacustrine interpretation finds its origin in the diverse assemblage of ooid morphotypes present, which exceeds the variations described for marine ooids. However, growth paths and occurrence of various compound morphologies point to intense marine recycling, suggesting little accommodation. Together with other sedimentological characteristics, for example, bi‐directional cross‐bedding, tidal shoals, hummocky cross‐stratification and exposure surfaces, these features suggest that marine processes had an impact on the sediments. Therefore, the ooid assemblage of the Cretaceous Yacoraite Formation was most likely formed in a shallow coastal lagoon in the framework of an epicontinental sea that at times experienced marine flooding events. A detailed evaluation of processes involved in oolite formation is needed in order to improve the stratigraphic and palaeoenvironmental understanding of ooid formation through time. This includes examining alternating constructive and destructive stages, early binding and cementation, reworking, recycling and averaging processes.

Depositional age models in lacustrine systems from zircon and carbonate U‐Pb geochronology

AbstractThe Yacoraite Formation (Salta rift, Argentina) consists of Maastrichtian–Danian lacustrine carbonate and siliciclastic deposits with interbedded volcanic ash layers, organized in four third‐order stratigraphic sequences. It offers the exceptional opportunity to jointly apply in situ zircon and carbonate U‐Pb geochronology that resulted in two distinct depositional age depth models. Ages of the youngest zircon population from ash layers were linearly interpolated to derive a zircon depositional age depth model. A carbonate depositional age depth model was instead obtained from dated carbonate phases including microbialites, ooids, oncoids of calcitic and dolomitic mineralogy as well as early lacustrine calcite cements. Mean ages were defined from different carbonate phases belonging to the same layer and then linearly interpolated. Sedimentation rates were calculated from both depth models between pairs of dated samples and used to estimate the age of sequence boundaries, as well as the duration of the four stratigraphic sequences. The zircon and carbonate depositional age depth models agree with biostratigraphic constraints and exhibit excellent consistency. The onset and end of sedimentation were estimated at 68.2 ± 0.9 Ma and 62.3 ± 0.6 Ma (duration ca 5.7 Ma) via zircon geochronology and at 67.9 ± 1.7 Ma and 61.9 ± 1.3 Ma (duration ca 6.0 Ma) via carbonate geochronology. Results from this study show that with suitable samples and a newly implemented working strategy, in situ U‐Pb dating of depositional and early diagenetic carbonates represent a valuable chronostratigraphic tool for estimating sedimentation rate and duration in poorly time‐framed depositional systems.

Ostracods from upper Yacoraite Formation (Danian), Salta Basin, Western Argentina: Taxonomy and paleoenvironmental indicators of climatic signals in lacustrine deposits

This paper presents the first study of nonmarine ostracods recovered from the Danian of the upper Yacoraite Formation (Balbuena IV sequence) Salta Basin. Six species were identified: Ilyocypris triebeli, Ilyocypris argentiniensis, Neuquenocypris (Alleniella)? sp. 1; Neuquenocypris (Alleniella)? sp. 2; Penthesilenula sp. and four indeterminate species. The ostracod fauna shows fluctuations in abundance, diversity, and preservation associated with different phases of the paleolake evolution. This distribution, clearly delineated by the depositional facies, corroborates previous geochemical analyses and high-resolution sequence stratigraphy developed for the section. In general, the most abundant occurrences of ostracods coincide with high-frequency transgressive tracts of the lake system, which form long-term wettest interval of the upper Yacoraite Formation.

The Kalkowsky Project - Chapter III. Significance of primary radial fabrics associated with ancient partly leached or recrystallized calcareous ooids

Calcitic ooids and bothryoids from the Yacoraite Formation in the provinces of Jujuy and Salta (Argentina) display radial fabrics pointing to their primarily high-Mg calcite (HMC) nature. The present publication documents some specimens that are partly or fully leached or recrystallized, which raises fundamental questions about the validity of some concepts, such as the very existence of the so-called "two-phase"/"bimineralic" ooids. It is assumed here that the organic content in the oolitic cortices (and, subsequently, its degree of oxidation) is the key to explaining some differential diagenetic alterations.

Microbialitic deposits of the Yacoraite Formation, NW Argentina: distribution, environments, paleoecology, and economic implications

The Yacoraite Formation (NW Argentina) displays important microbialitic deposits of varied features throughout its six sub-basins. With the discovery of important microbialitic hydrocarbon reservoirs and the interest in lacustrine systems due to recent hydrocarbon finds in the pre-salt Cretaceous series of the South Atlantic, the importance of these organo-sedimentary structures has increased considerably. Because of this, in the past decade, numerous works in Yacoraite Formation have focused on its microbialites. In this study, we provide an updated summary of the existing background and state of knowledge of the microbialites in the Yacoraite Formation, which occupy different stratigraphic positions in diverse sub-basins separated by several kilometers. Due to this, these structures have developed under diverse conditions, giving rise to a great variety of structures and morphologies, useful as reliable and high-resolution proxies for paleoenvironmental studies and to discuss important ecological paradigms. In addition, microbialites of Yacoraite Formation show promising petrophysical conditions to be evaluated as reservoir rocks. Based on the large number of deposits mentioned throughout this work, and the morphological and structural variety of their microbialites, we can highlight Yacoraite Formation as one of the most important microbialite-bearing units in Argentina and South America.

Ostracods from Upper Yacoraite Formation (Danian), Salta Basin, Western Argentina: Taxonomy and Paleoenvironmental Indicators of Climatic Signals in Lacustrine Deposits

Ostracods from Upper Yacoraite Formation (Danian), Salta Basin, Western Argentina: Taxonomy and Paleoenvironmental Indicators of Climatic Signals in Lacustrine Deposits

Three-dimensional stromatolites from Maastrichtian–Danian Yacoraite Formation, Argentina: modelling and assessing hydrodynamic controls on growth patterns

AbstractStromatolites are biogenic sedimentary structures formed by the interplay of biological (microbial composition) and environmental factors (local hydrodynamic conditions, clastic input and/or water chemistry). Well-preserved, three-dimensional (3D) fossil stromatolites are key to assessing the environmental factors controlling their growth and resulting morphology in space and time. Here, we report the detailed analysis of well-exposed, highly informative stromatolite build-ups from a single stratigraphic horizon within the Maastrichtian–Danian Yacoraite Formation (Argentina). This study focuses on the analysis of depositional processes driving intertidal to shallow subtidal stromatolites. Overall depositional architecture, external morphology and internal arrangement (mega, macro, meso and microstructures) of stromatolite build-ups were analysed and combined with 3D photogrammetric models, allowing us to decipher the links between stromatolite structure and tidal dynamics. Results suggest that external morphology and architecture of elongated and parallel clusters grew under the influence of run-off channels. The internal morphology exhibits columnar structures where the space between columns is interpreted as recharge or discharge channels. This work supports the theory that stromatolites can be used as a high-resolution tool in the assessment of water dynamics, and provides a new methodological approach and data for the dynamic reconstruction of intertidal stromatolite systems through the geological record.

New record of Late Cretaceous vertebrate tracks from the Yacoraite Formation (Juella, Quebrada de Humahuaca, northwestern Argentina): aerial drone survey, preservation and sedimentary context

The Yacoraite Formation is a worldwide known unit due to the diversity and abundance of vertebrate ichnological record. The complex tectono-sedimentary evolution related to the Andean Cycle generated high dip angles of bedding and, consequently, large tracksites are not easily accessible, making hard the ichnological analysis. Here, we describe a new tracksite named “La Banderita”, near Juella town (Quebrada de Humahuaca, Jujuy, Argentina), where abundant vertebrate and invertebrate trace fossils have been identified on different high slope surfaces. A small, portable unmanned aerial vehicle (UAV) equipped with a digital camera was employed to overcome difficulties in studying traces. After the aerial survey, digital photogrammetry was applied to get 3D models of the trampled surfaces (about 7700 m2) and to obtain track distribution maps (more than 100 tracks). As a complement, a detailed 3D model of an easily accessible small area was also made (about 315 m2). Trace fossils were preserved within three facies intervals from subtidal/lower intertidal (Intervals I-II) to intertidal (Interval III) settings. In this last interval, quadrupedal (probably sauropod), bipedal (theropod) and undetermined tracks, differently preserved as undertracks, true tracks and natural casts, are identified. These three modes are product of narrow preservational windows, which have prevented weathering destruction process after original trampling. Ichnological and sedimentological data are coherent with those of other localities from the Yacoraite Formation, and suggest that dinosaurs moved along peritidal settings. This contribution highlights the use of aerial drone survey and 3D photogrammetric models, which besides traditional ichnological and sedimentological techniques, allowed a detailed reconstruction of track formation and preservation, contextualizing the trampled surfaces in their palaeoenvironmental setting.

Dynamic of a lacustrine sedimentary system during late rifting at the Cretaceous–Palaeocene transition: Example of the Yacoraite Formation, Salta Basin, Argentina

AbstractThe architecture of lacustrine systems is the result of the complex interaction between tectonics, climate and environmental parameters, and constitute the main forcing parameters on the lake dynamics. Field analogue studies have been performed to better assess such interactions, and their impact on the facies distribution and the stratigraphic architecture of lacustrine systems. The Yacoraite Formation (Late Cretaceous/Early Palaeocene), deposited during the sag phase of the Salta rift basin in Argentina, is exposed in world‐class outcrops that allowed the dynamics of this lacustrine system to be studied through facies analysis and stratigraphic evolution. On the scale of the Alemania‐Metán‐El Rey Basin, the Yacoraite Formation is organized with a siliciclastic‐dominated margin to the west, and a carbonate‐dominated margin to the east. The Yacoraite can be subdivided into four main ‘mid‐term’ sequences and further subdivided into ‘short‐term’ sequences recording high frequency climate fluctuations. Furthermore, the depositional profiles and identified system tracts have been grouped into two end‐members at basin scale: (a) a balanced ‘perennial’ depositional system for the lower part of the Yacoraite Formation and (b) a highly alternating ‘ephemeral’ depositional system for the upper part of the Yacoraite Formation. The transition from a perennial system to an ephemeral system indicates a change in the sedimentary dynamics of the basin, which was probably linked with the Cretaceous/Tertiary boundary that induced a temporary shutdown of carbonate production and an increase in siliciclastic supply.

Geochemical features of hydrothermal systems in Jujuy Province, Argentina: Hints for geothermal fluid exploration

Fluid primary source(s) and chemical-physical processes controlling water and gas chemistry of thermal springs from Eastern Cordillera, sub-Andean Ranges and Santa Bárbara (Jujuy Province, northern Argentina) were investigated to provide information for a preliminary evaluation of the geothermal potential in these areas. Thermal manifestations in Eastern Cordillera (Reyes) and part of those in the western sector of sub-Andean Range (Aguas Calientes) are fed by shallow aquifers, interacting with Quaternary- Neogene rocks and the upper portion of Pliocene-Miocene formations (Orán Group), whereas the meteoric water recharge area is located at >2500 m a.s.l., corresponding to Chañi hill. Differently, El Jordán thermal spring in the sub-Andean Range is fed by a hydrothermal aquifer hosted within highly porous and fractured formations of the Salta Group (Yacoraite Formation) and recharged by meteoric water from Sierra de Calilegua (∼1500 m a.s.l.). The latter is the recharge area of the La Quinta geothermal waters as well, but these have been fed at higher altitudes (>2500 m a.s.l.) in the range. The hydrothermal reservoir feeding the other thermal springs from the Santa Barbara system (Caimancito, El Palmar, and Siete Aguas) is recharged by meteoric water from Zapla Ranges and Santa Barbara Hill at <2500 m a.s.l. The high-TDS (>16,000 mg/L) Na+-Cl- La Quinta thermal springs are produced by interaction with the evaporite deposits of Salta Group, including halite, whereas the chemistry of El Palmar, El Jordán and Caimancito thermal springs, showing a Na+-SO42-(Cl−) composition, depends on mixing with shallower SO42--rich waters interacting with gypsum deposits of Anta Formation. Dissolved and bubbling gases from all the investigated provinces are related to CO2- and CH4-rich crustal fluids produced by both thermogenic processes occurring within the hydrothermal systems and microbial activity at relatively low depth, with low to negligible mantle contribution, as indicated by the 3He/4He values ≤ 0.21 Ra. The fluid reservoir feeding the Quinta thermal springs shows the highest estimated temperatures (>200 °C), which, considering the depth of Salta Group in the Santa Barbara system (~2000 m), support the idea, suggested by previous authors, of an anomalous geothermal gradient for this area, a promising pre-requisite for future exploitation of the geothermal resource.

Climatic signals in lacustrine deposits of the Upper Yacoraite Formation, Western Argentina: Evidence from clay minerals, analcime, dolomite and fibrous calcite

AbstractAuthigenic clays are an important control on reservoir quality in lacustrine carbonates but remain challenging to predict. Lacustrine depositional systems respond to climatic variations in rainfall, surface runoff and groundwater input, and evaporation, and result in rapid and frequent changes in lake volume; this is expressed through changing water depth and shoreline position. In the upper portion of the Early Palaeocene Yacoraite Formation of the Salta Basin in Argentina, extensive lacustrine deposits were deposited during the sag phase of rifting. Prior high‐resolution stratigraphic studies have suggested that climatic factors control microbial carbonate sequences within a ‘balanced fill’ lake, with variation in the lake level having a major influence on facies association changes. This study characterizes the evolution of facies and mineralogy within the Yacoraite Formation, focusing on the distribution of clay minerals, making a link between the high, medium and low‐frequency sequence stratigraphic cycles. The low‐frequency transgressive hemicycle of the upper portion of the Yacoraite Formation is comprised of abundant siliciclastic facies, suggesting a wetter period. Microbialites occurring in this interval are coarse‐grained and agglutinated. Detrital clay minerals such as illite and chlorite and associated siliciclastic sediments were input to the lake during high‐frequency transgressive periods. During high‐frequency regressive hemicycles, sedimentation was dominated by carbonate facies with Ca‐rich dolomite and the authigenic clays are comprised of chlorite/smectite mixed‐layers. By contrast, the low frequency regressive hemicycle records fine‐grained agglutinated microbialite with horizons of fibrous calcite, more stoichiometric dolomite, barite and authigenic magnesian smectite. This indicates elevated ion concentrations in the lake under intense evaporation during an arid period. Understanding the conditions that are favourable for formation and preservation of authigenic clays within the lacustrine environment can improve understanding of reservoir quality in comparable economically important deposits.

Fracture network analysis of Yacoraite Formation in the Tres Cruces sub-basin, northwestern Argentina

The Tres Cruces sub-basin, located in Jujuy province, northwestern Argentina, is characterized by intense N-S folding and faulting. These structures were formed as a result of the Cenozoic shortening that produced the tectonic inversion of the Salta Rift Basin normal faults. Some of the main folds and faults show abrupt trend variations, controlled by NW-SE transverse lineaments. We performed a fracture network analysis over the Maastrichtian-Danian limestones of the Yacoraite Formation, at three folds located in the central sector of the sub-basin. A total of 832 planar fractures were measured in different structural domains. Five main fracture sets were identified, trending NW-SE, NE-SW, ENE-WSW, WNW-ESE and N-S to NNW-SSE. Their relative chronology was established based on the observed abutting relationships. The analysis performed suggests that NW-SE, NE-SW and ENE-WSW trending sets are regionally represented and were formed before the initial stages of folding. Set ENE-WSW is sub-parallel to the convergence direction acting during the Neogene. The other two sets are associated with local perturbations of the far-field signal control by the oblique NW-SE lineaments. The origin of the WNW-ESE set remains unclear; its distribution is locally restricted to the San Bernardo domain. Finally, the N-S to NNW-SSE set shows a synfolding origin generated when the surveyed folds were growing. We then place the various identified fracture sets into a single stress field setting, perturbed by the leading NW-SE transverse lineaments that dominate this region.