Abstract The final consolidation of southwestern Gondwana during the Ediacaran–Cambrian resulted in the formation of a large landmass originally surrounded by the newborn Panthalassic Ocean. The Río de la Plata Craton is one of the last pieces that complete the geotectonic puzzle along the austral part of this supercontinent. However, the sedimentary record corresponding to the interval between the consolidation of SW Gondwana until the initial deposition in a large Ordovician cratonic basin is apparently missing. In this context, the Ediacaran–Cambrian epiclastic shallow-marine ramp of the Cerro Negro Formation, the uppermost unit of La Providencia Group, Tandilia System, is envisaged as the first known stratigraphic record of the hidden pericratonic basins of Gondwana. Geochronological and provenance data, coupled with robust stratigraphic and sedimentologic background, support that this unit keeps more tectono-sedimentary affinity with the Ordovician Balcarce Formation than the Neoproterozoic Sierras Bayas Group. The presence of similar Neoproterozoic source areas for both units, the absence of any metamorphism and deformation related to the Brasiliano cycle, and shallow marine deposition strongly suggest that the paleogeography and physiography of the original southernmost continental platform of Gondwana were similar to the Ordovician ones. Thus, the Cerro Negro Formation appears as the missing link between the ultimate stages of the Brasiliano Orogenic Cycle and the final stabilization of the continental platform from the SW part of Gondwana. EdiacaranCambrian Ediacaran Cambrian Ocean supercontinent However context shallowmarine Group System data background tectonosedimentary tectono units cycle ones Thus

Abstract The terminal Ediacaran fossil record includes microbial mats and body fossils characterized by simple morphologies, which represents a challenge to understand several aspects related to the paleoecology of the emerging complex life. The marine siliciclastic deposits of the Cerro Negro Formation (~560–550 Ma) contain evidence of different styles of microbially induced sedimentary structures (MISS) and discoidal forms associated with them. Different types of MISS, such as Kinneyia and wrinkle structures, elephant skin, and Arumberia, are reported and related to shallow marine depositional environments. These morphologies are commonly associated with the high quality of preservation of body fossils in Ediacaran deposits. The preservation of Aspidella discoidal holdfast is related to biotic and abiotic processes involving substrate sealing by microbial mats, fluidization, and probably organic matter decay. Both abiotic factors (tidal currents and waves, added to liquefaction and sand injection) and biotic factors (substrate biostabilization by microbial mats favoring sediment cohesion) are considered the main ones responsible for the preservation style in the Cerro Negro Formation. This formation constitutes a remarkable example in SW-Gondwana of how preservation dynamics took place on a seabed sealed by microbial mats and is an important deposit conserving diverse Ediacaran forms of life in South America. ~560–550 560550 560 550 (~560–55 Ma MISS (MISS them skin Arumberia environments fluidization decay tidal waves injection cohesion SWGondwana SW Gondwana America ~560–55 56055 56 55 (~560–5 ~560–5 5605 5 (~560– ~560– (~560 ~560 (~56 ~56 (~5 ~5 (~ ~ (

ABSTRACT The objective of this work is to discuss the paleoenvironment and age of the Los Monos Formation, in outcrop and subsurface, along a regional transect (west-east) in the southern sector of the Tarija basin. The lithofacies and ichnofacies of the Alarache, Angosto del Pescado and Balapuca outcrops and core-intervals of the Aguas Blancas xp-13, Ramos x-12, Tartagal x-1 and Tonono x-1 boreholes were analyzed. The definition of lithofacies and ichnofacies allowed us to interpret a shallow to outer shelf paleoenvironment (from the offshore-transition, offshore and shelf). Towards the top of the Tonono Formation, the equivalent of the Los Monos Formation in the Chaco-Salteño was defined as a brackish-waters marginal-marine paleoenvironment. The mineralogy of the mentioned sections plus the Vespucio x-1 borehole was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), thus the majority elements in clay minerals were also determined from EDAX. Authigenic and detrital clays from SEM-EDAX were recognized. Four clay mineral assemblages were defined (I+Ch; Ch+I; I+K; K+I), where I+K and K+I assemblages characterize the transgressive events within the basin. The palynofacies of the Balapuca, Alarache and Angosto del Pescado outcrops and samples from the Ramos xp-1002, Ramos xp-1011 and Ramos xp- 1012 boreholes were defined, the dominance of terrestrial palynomorphs was identified with variable participation of marine palynomorphs, according to a shallow marine paleoenvironment with shoreline shifts. Two transgressive events were recognized during the late Eifelian-early Givetian and the late Givetian-early Frasnian, which are characterized by an increase in marine components and clay assemblages of I+K and K+I. The palynological associations point to a late Eifelian-early to middle Givetian age for the Los Monos Formation in the study area. The analysis of illite crystallinity and expansive layers in the mixed-layer IS indicated advanced diagenesis for the unit, from late mesodiagenesis (Tonono x-1 and Vespucio x-1) to telodiagenesis (Balapuca and Ramos), according to the final stage of oil generation window to gas generation window, respectively. Finally, based on the mineral composition with a predominance of quartz (>70% in average) and low content of clays (<20% in average), thermal maturity in oil and gas window, the important thickness in the subsurface (700-1000 meters) and significant lateral continuity (>100 km2), the unit has some of the attributes to be considered as a potential shale-type unconventional reservoir.

Abstract Geological studies in the northern sector of the Chaco foreland Basin, Bolivia, yielded new fossils coming from late Oligocene-late Miocene of the Petaca Formation. Few fossil mammals were known from the Subandean Region of Bolivia. We report a partially complete mandible of a hegetotheriid Hegetotheriinae (Notoungulata, Typotheria) from Abapó (Río Grande River). The specimen (YPFB-LIT-PAL-005) is very close in size and dental morphology to the late Oligocene (Deseadan South American Land Mammal Age, SALMA) — Santacrucian (early Miocene) Prohegetotherium schiaffinoi (Kraglievich 1932) from Fray Bentos (Uruguay and Argentina), Salla (Bolivia), Divisadero Largo-Potrerillos and Quebrada Fiera (Argentina). However, mandibular characteristics, as the shape with a marked change in height along its length, increasing towards the back, a prominent masseteric crest, a deep mandibular groove, and a remarkable thickening of the ventral rim of the mandible, indicate differences between this specimen and Prohegetotherium schiaffinoi and the other Hegetotheriinae. The affinity of YPFB-LIT-PAL-005 with P. schiaffinoi suggests a late Oligocene to early Miocene for the upper bearing horizon of the Petaca Formation (in Abapó), an older age than previously assigned to the top of this unit (late Miocene), and confirms the taxon distribution between ∼ 36 ° to ∼ 17 ° south latitude.

The sedimentary infill of the Austral-Magallanes Basin since the onset of its foreland stage in the Lago Argentino region is dominated by deep-marine and coastal deposits. However, during the Late Cretaceous the basin accumulated a thick and poorly known continental sedimentary succession, which has received different lithostratigraphic names. The aim of this work is to characterize the here defined Uppermost Cretaceous Continental Deposits (UCCD) from a detailed facies and architectural analysis, as well as the resulting stacking pattern. Seven Facies Associations (FAs) were discriminated in order to define the sedimentary paleoenvironments: FA1, gravelly sheet bodies; FA2, tabular bodies of conglomerates with mud rip-up clasts; FA3, complex tabular sandy bodies; FA4, simple tabular sandy bodies; FA5, tabular bodies of structureless sandstones; FA6, heterolithic deposits; and FA7, fine-grained deposits. Three different fluvial styles were recognized: meandering systems dominated by avulsion and meander abandonment processes (fluvial style a), braided systems (fluvial style b), and meandering systems dominated by overbank flood processes (fluvial style c). The stacking pattern of the FAs allowed to divide the UCCD into two major depositional stages related to the accommodation space vs sediment supply (A/S) ratio. Stage I is characterized by the alternation of fluvial styles a and b, while the Stage II is represented by the alternation of fluvial styles c and b, and the Stage III is characterized entirely by fluvial style c deposits. Although the UCCD are considered as a whole within a framework of low A/S ratio, several high frequency variations were recognized. The Stage I records seven high frequency intervals of which four are characterized by high A/S ratio interrupted by three events of low A/S. While the stage II is represented by six high frequency periods of low A/S ratio and other five high frequency events of high A/S ratio. The Stage II is considered as deposited in a relative higher A/S context in comparison with the Stage I, based on the behavior of the moderate to high sinuosity meander fluvial systems. Finally, the Stage III is represented entirely by a high frequency low A/S ratio event.

In the Curicó hills (also known as the La China hill), in the Olavarría district, rock art has been discovered on walls and in shelters in the quartzite tabular outcrops of the Balcarce Formation. The paintings are in three sectors and consist of lineal and geometrical motifs painted in red. On the slope of the hill, two stone circular structures were detected, and on the top of the opposite hill an oval stone structure was also found. In this article, the characteristics of this archaeological material are summarised and the results from test pits, excavated in one of these structures is presented. The contemporaneity among the findings is examined as well as its possible tehuelche affiliation. Finally, the symbolic and religion dimensions of the Late Pampean indigenous societies are explored.

En las Sierras de Curicó (también conocidas como de La China) en el Pdo. de Olavarría, se han detectado pinturas rupestres en paredones y reparos de los afloramientos tabulares de cuarcita. Se trata de tres sectores con motivos lineales, geométricos, pintados en rojo. En el faldeo de la misma sierra, se localizaron dos estructuras pequeñas de piedra pircada de forma circular. En la cima de otro afloramiento rocoso, ubicado 500 m al oeste de estas estructuras, se halló una acumulación oval de piedras. En este trabajo se resumen las características del conjunto arqueológico y se presentan los resultados de los sondeos realizados en una de esas estructuras. Se examina la contemporaneidad entre las estructuras y las pinturas rupestres y su posible filiación tehuelche. Se comparan estas pinturas con otras manifestaciones similares de la Región Pampeana. Por último, se exploran aspectos simbólicos y religiosos de las sociedades pampeanas tardías.

Sediments comprising the Agrio Formation (Weaver, 1931) were deposited in the Neuquén Basin (Argentina) during the late Tithonian - early Barremian cycle embracing the Mendoza Group (Stipanicic et al. 1968). This formation extends throughout the Neuquén Basin, and it is characterised by different facies associations. In the Neuquén Province the Agrio sediments are siliciclastic and skeletal sandstones, sandy limestones, micritic limestones and carbonate shales. In the Mendoza Province they are mainly shales, marlstones, mudstones and wackestones; bituminous shale is the most common lithology (Mombrú et al., 1978). The study area is located in the south of Mendoza Province, about 18 km southwest of Malargüe. A detailed section through the Agrio Formation was measured along the Loncoche creek (Fig. 1). Ammonites present throughout the sequence demonstrate its late Valanginian to late Hauterivian age. At this locality, the Agrio Formation overlies oyster bank facies of the Chachao Formation, and it is succeeded by shallow marine limestones of the Chorreado Member (Huitrín Fo

En la sección basal de la Formación Agrio (Cretácico inferior, Cuenca Neuquina, Argentina) se verificó la relación entre las facies, trazas fósiles y evolución del nivel del mar. Por otra parte se introdujo el concepto de asociaciones icnolitológicas, entendiéndose como tal al conjunto genética y espacialmente relacionado de trazas fósiles y facies sedimentarias. En el arroyo Loncoche, al sur de la localidad de Malargüe (provincia de Mendoza), la Formación Agrio (222 m) está compuesta por una sucesión cíclica de pelitas laminadas, margas y calizas micríticas, depositadas en un ambiente marino de rampa externa. Para el intervalo basal de la unidad (77,6 m) se definieron tres asociaciones icnolitológicas: 1- Wackestones masivos con Thalassinoides de relleno grueso, 2- Mudstones con Thalassinoides de relleno fino y 3- Wackestones entrecruzados con Palaeophycus y Teichichnus. Asimismo se observó que la presencia de cada una de ellas responde a condiciones de depositación particulares que pueden vincularse con la evolución del nivel del mar. Utilizando como herramienta las asociaciones icnolitológicas definidas, las variaciones en el apilamiento de facies y en el contenido faunístico se distinguieron cuatro intervalos dentro del tramo de secuencia analizado. El primero está compuesto por wackestones masivos con Thalassinoides de relleno grueso (asociación icnolitológica 1); el segundo por pelitas laminadas sin bioturbación; el tercero por intercalaciones de margas y mudstones con Thalassinoides de relleno fino (asociación icnolitológica 2) y el cuarto por wackestones masivos con Thalassinoides de relleno grueso, mudstones con Thalassinoides de relleno fino y wackestones entrecruzados con Palaeophycus y Teichichnus (asociaciones icnolitológicas 1; 2 y 3 respectivamente) con delgadas intercalaciones de margas. El primer intervalo constituye el cortejo transgresivo, el segundo corresponde a la zona de máxima inundación y los dos últimos conforman el cortejo de mar alto.