Abstract: We address some predictions derived from the biogeographic model proposed by Luis Borrero (1989-90) in order to analyze the earliest human occupations identified on the north coast of the Beagle Channel (8600-6500 cal. years BP). We examined the chronological, stratigraphic and archaeological information from the basal deposits of Imiwaia I, Binushmuka I and Túnel I to explore the formational processes and temporal structure of the archaeological contexts during the maximum extension of the Holocene marine transgression. Continuous human activity is inferred from 8600 cal. years BP on the southern coast of Tierra del Fuego. The structures of the earliest archaeological deposits indicate low-intensity and discrete occupations over time. The archaeological signal remains weak until the Holocene marine transgression reached its maximum level at approximately 7000 cal. years BP, when the formation of multicomponent archaeological deposits (shell middens) becomes visible in the region. Lastly, we discuss the implications of this information for the colonization of the Fuegian archipelago.

Resumen: Partimos de algunas predicciones derivadas del modelo biogeográfico propuesto por Luis Borrero (1989-90) para analizar las ocupaciones humanas más tempranas identificadas en la costa norte del Canal Beagle (8600-6500 años cal. AP). Examinamos la información cronológica, estratigráfica y la composición de los depósitos basales de Imiwaia I, Binushmuka I y Túnel I con el fin de explorar los procesos de formación y estructura temporal de los contextos arqueológicos en momentos previos al máximo alcance de la transgresión marina del Holoceno. Se observa una actividad humana continua en la costa sur de Tierra del Fuego desde hace al menos 8600 años cal. AP. Las estructuras de los depósitos más tempranos marcan ocupaciones con baja intensidad y discretas en el tiempo. La señal arqueológica se mantiene débil hasta que la transgresión marina del Holoceno alcanzó su máximo nivel en un momento cercano a los 7000 años cal. AP, cuando la formación de depósitos arqueológicos multicomponentes (concheros) comenzó a hacerse visible en la región. Por último, se discuten las implicaciones de esta información para el poblamiento del archipiélago fueguino.

Abstract Microbialites are the most abundant life evidence in Precambrian sedimentary rocks. They are produced by microbial interaction activity and sedimentary processes reflecting paleoenvironmental conditions. The Ediacaran-Cambrian carbonate and siliciclastic successions in the Southern Amazon Craton in Central Brazil, provide a key opportunity to understand how the metazoan life coexisted with the microbial communities. The spatial and temporal distribution of microbialites as well as morphological and paleoenvironmental changes have been assessed, reinterpreting previous works and including new data from the Araras-Alto Paraguai and Corumbá basins. The deposition was controlled by subsidence and sea-level changes that affected these basins, considered extensions of epicontinental seas during the Gondwana assembly. The stromatolites are restricted to coastal deposits and experienced thriving flourishment intervals after the Marinoan Glaciation (635 Ma). Post-glacial transgression was marked by microbial colonization in shallow platforms represented by stratiform and giant domical stromatolites in the Araras-Alto Paraguai Basin. The continuity of the transgression generated a moderately deep aragonite sea at about 622 Ma. A progressive sea-level fall caused the implantation of coastal environments under greenhouse conditions with tidal flat and sabkha settings colonized by centimetric-scale stromatolites. The sea retreat was accompanied by progressive uplift, causing a moderate inversion of the basin and erosion of the succession until ~560 Ma with the deposition of the last preserved tidal flat deposits with the occurrence of thrombolites. The subsiding Corumbá Basin was the site of microbially-induced deposition of carbonates in a shallow platform connected to an offshore setting with the proliferation of metazoan straddling the Ediacaran-Cambrian boundary. Microbial communities were restricted to lagoon deposits during the Lower Cambrian transgression in the Araras-Alto Paraguai Basin and the last phase refers to the sea retreat towards southeast, developing a fluvial system connected with the arid and evaporitic tidal flats colonized by microbialites that lasted until the upper Cambrian. Except for the post-glacial stromatolites, the columnar and domal microbialite indicate that the coastal settings dominated the Ediacaran-Cambrian transition. The preservation of microbialites in the post-glacial intervals can be associated with the Mg-Ca-CO3 oversaturation in dolomitic platforms. The rapid calcification and ability to resist the dissolution and replacement have increased the stromatolites’ preservation potential reported here, where its well-preserved occurrence in tidal flats and sabkha occurs due to intense early diagenetic silicification. The change from carbonate accumulation to siliciclastic-rich environments contributed to the demise of microbially-induced strata. In general, the scarce coexistence between coastal stromatolite and metazoan-bearing marine deposits makes it challenging to establish a competitive relationship between these organisms, as previously postulated.

Abstract Diatom assemblages and coastal sedimentary facies succession in the deltaic plain of the Colorado River (Argentina) were studied in order to reconstruct the environment conditions in response to Holocene eustatic sea-level changes and delta progradation. Samples were selected from a 200˗cm core (39°35’52” S, 62°6’43” W). Chronology was based on radiocarbon datings in bulk samples and mollusk shells. Nine lithological units were recognized where fine and very fine sand predominate. The core sediments were dominated by tychoplanktonic coastal-marine diatoms. The accompanying flora included stable marine-coastal taxa and allochthonous fluvial fresh-brackish species. Three diatom zones (DZ) were established based on cluster analyses. The LCH site was significantly affected by Late Pleistocene and Holocene sea˗level fluctuations, and the progradation of the deltaic lobe during the last ca. 7,000 14C yr. BP. Ancient tidal channels were flooded in the early Holocene postglacial transgression. Erosive and re˗working processes associated with the formation of estuarine channels, affected valves preservation, yielding with barren sections. Tidal flats and marshes have developed in the area during the late Holocene regression phase. The comparison of the sedimentary sequence with deltaic facies evolution models, confirm the presence of a hiatus, which masks the Holocene Maximum and highstand. Argentina (Argentina sealevel sea level 200cm cm 200 39°3552 393552 39°35 52 39 35 (39°35’52 S 62°643 62643 62°6 43 62 6 62°6’43 W. W . W) shells predominate coastalmarine marine diatoms marinecoastal freshbrackish fresh brackish species DZ (DZ analyses fluctuations ca 7000 7 000 7,00 C yr BP transgression reworking re working preservation sections phase models hiatus highstand 20 3552 39°355 39355 3935 39°3 5 3 (39°35’5 643 62°64 6264 626 62° 4 62°6’4 700 00 7,0 2 355 393 39° (39°35’ 64 62°6’ 70 0 7, (39°35 (39°3 (39° (39 (3 (

ABSTRACT Laguna Las Vueltas (LLV) area retains the morphology of a late Pleistocene watershed that was flooded during a mid-Holocene marine transgression. Sediments associated with a paleosol dated at 22,582 cal yr BP reflect subaerial exposure of the area prior to the submergence during the marine transgression. This transgression produced an extensive tidal flat near the mouth of the former LLV watershed by 7,477 cal yr BP. Subsequent decoupling of the Las Vueltas valley from the sea occurred through the growth of a baymouth barrier and a beach-ridge plain to the east. This decoupling turned the lagoon into a pan environment in which subsequent lake-level fluctuations were controlled by climate. A lunette dune developed at the pans in the former lagoon, providing a narrow corridor where humans trapped, killed and processed guanacos as early as 3,402 cal yr BP Changes in aeolian sedimentation hint at increased aridity during the past 500 years.

RESUMEN El área de Laguna Las Vueltas (LLV) conserva la morfología de una cuenca hídrica del Pleistoceno tardío que fue inundada durante la transgresión marina del Holoceno medio. Los sedimentos asociados con un paleosuelo datado en 22.582 cal yr AP reflejan la exposición subaérea del área con anterioridad a la transgresión marina. Esta transgresión provocó hacia 7.477 cal yr AP una extensa planicie de marea en la zona baja de la cuenca de la LLV. La subsecuente desvinculación del valle de la LLV con el mar ocurrió a partir del desarrollo de una barrera litoral y una planicie de cordones de playa hacia el este. Este desacople convirtió a la albufera en una laguna somera (pan), donde las subsiguientes fluctuaciones de nivel del agua estuvieron controladas por el clima. Una duna de tipo “lunette” se desarrolló en el área de la antigua albufera, dando lugar a un corredor angosto donde los grupos humanos atraparon, mataron y procesaron guanacos desde al menos 3.402 años cal yr AP. Los cambios en la tasa de sedimentación eólica sugieren un incremento de la aridez en los últimos 500 años.

ABSTRACT There are several organic matter-rich shale geologic formations in Mexico that could be considered non-conventional potential oil reservoirs; one of those formations is the Eagle Ford Formation (Late Cenomanian - Turonian), aim of this study. The Eagle Ford Formation is located within the Sabinas paleobasin and along the Burros-Peyote paleoplatform, in the Coahuila State. This formation has been previously described as a transgression system deposited in a shallow marine environment with a total organic carbon between 0.5 to 8% with type II organic matter. For these reasons, it could be considered a potential source for non-conventional hydrocarbons. Therefore, it is considered that a reservoir of shale gas must have certain requirements, such as: 1) high total organic carbon (> 2% of COT), 2) presence of types II and III kerogen, 3) vitrinite reflectance values greater than 1.2% Ro (0.7% for shale oil), 4) thickness greater than 30 m and large extension, 5) fracturability (<40% clays or absence of expandable clays) or the presence of a microcracking system, 6) overpressure, 7) adequate depth, 8) heterogeneity, and others. A systematic sampling was carried on outcrops of Coahuila State with the goal to determine the thermal maturity degree of the Eagle Ford Formation using a detailed stratigraphic analysis of three columns (CSI, CSII and CSV) and micro-thermometric of fluid inclusions. Our results indicate that the Eagle Ford Formation is a sedimentary sequence rich in organic matter, locally composed of carbonaceous carbonate shale in laminar stratification alternating with shaly limestone (mudstone-wackestone) and clastic o bioclastic limestone (packstone-grainstone). Regarding the diagenetic alteration, primary porosity is affected by compaction and cementation processes. However, it was also observed a secondary micro-porosity development due to neomorphism, dolomitization, fracturing and stylolitization processes. Measured homogenization temperatures (Th) in fluid inclusions are between 65 °C and 125 °C, reaching the temperature window to generate oil and humid gas. The thermal evolution through its facies changes in the basin is not homogeneous. Our results indicate that the Eagle Ford Formation is a sedimentary sequence rich in organic matter, locally composed of carbonaceous carbonate shale in laminar stratification alternating with shaly limestone (mudstone-wackestone) and clastic o bioclastic limestone (packstone-grainstone).

Resumen En México existen unidades geológicas compuestas por sedimentos de grano cfmuy fino y ricas en materia orgánica, que podrían considerarse como recursos potenciales de hidrocarburos. Entre ellas se encuentra la Formación Eagle Ford (Cenomaniano Tardío-Turoniano), la cual es el objeto de estudio en este trabajo. Dicha formación está localizada dentro de la Paleocuenca de Sabinas y sobre la Paleoplataforma Burro-Peyotes, en el estado de Coahuila. Anteriormente se ha definido que representa un sistema transgresivo depositado en un ambiente marino nerítico-medio con valores de carbón orgánico total (COT) entre 0.5 y 8% y con materia orgánica del tipo II predominante, por lo que podría considerarse como un posible recurso de hidrocarburos no convencional. Para ello se considera que un reservorio de lutitas gasíferas (shale gas) debe cumplir con ciertos requisitos, como: 1) Riqueza orgánica (>2% de COT), 2) tipo de kerógeno II o III, 3) valores de reflectancia de la vitrinita mayor a 1.2% Ro (0.7% para shale oil), 4) espesor mayor a 30 m y gran extensión, 5) fracturabilidad (<40% de arcillas o ausencia de arcillas expandibles) o la presencia de un sistema de microfisuras, 6) sobrepresión, 7) profundidad adecuada, 8) heterogeneidad, entre otras. Con el objetivo de determinar el grado de madurez térmico de esta formación, se realizó un muestreo sistemático en afloramientos del estado de Coahuila para el análisis de estratigrafía a detalle (columnas CSI, CSII, CSV) y microtermometría de inclusiones fluidas. Los resultados ratifican que la Formación Eagle Ford es una secuencia sedimentaria rica en materia orgánica, compuesta localmente por lutita calcárea carbonosa con estratificación laminar que alterna a caliza arcillosa (mudstone-wackestone) y caliza clástica- bioclástica (packstone-grainstone). Respecto a las alteraciones diagenéticas, la porosidad de origen primario se ve afectada por los procesos de compactación y precipitación de cementos, también se generó una microporosidad secundaria debido al desarrollo de neomorfismo, dolomitización, fracturas y estilolitización. Además, se determinó que las temperaturas de homogeneización (Th) de inclusiones fluidas que alcanzó esta formación varían entre los 65 °C y 125 °C, lo que la sitúa en la etapa catagenética de la generación de petróleo y gas húmedo. Asimismo, se observó que la evolución térmica de inclusiones fluidas en la cuenca no es homogénea.

Abstract Marine invertebrate fossils have long been considered important tools for age dating and stratigraphic interpretation of the Paleogene deposits of Central Asia, however information has not yet been provided from the Kopet-Dagh Basin (NE Iran). In this research, fossiliferous horizons of the Chehelkaman Formation at the Sheikh and Ghaleh-Zou sections (which have never been recognized previously), both in the Sheikh Syncline area, are discussed. These sedimentary beds overlay the terrestrial siliciclastic Pesteligh Formation and are the first evidence of marine flooding of the Paleogene transgression in the central Kopet-Dagh. Systematic paleontological studies of molluscan fossils in this succession led to the identification of ten genera, twelve species and two subspecies of bivalves and five genera and five species of gastropods. The assemblage belongs to four different fossilif-erous horizons: (1) Turritellidae Dominated Assemblage (TDA), (2) Pycnodonte - Turkostrea horizon, (3) Cordiopsis-Cardium horizon and (4) Globularia shell beds in the Sheikh section and only TDA horizon in the Ghaleh-Zou section. The age of the whole succession, based on Cordiopsis subathooensis - Turritella subathooensis Zone cooccurrence with nannofossil zones NP12 and NP13, is Late Ypresian (early middle Cuisian). The TDA in both sections confirms the abundance of nutrients and their bimodal orientation demonstrates effects of oscillatory waves rather than unidirectional paleo-currents. High rates of bioerosion, encrustation, fragmentation, disarticulation and corrosion of the shells in the Pycnodonte - Turkostrea horizon reveals high volumes of nutrients and energy-rich conditions. This interval, overlain by the Cordiopsis - Cardium horizon in a pavement arrangement, represents the stable conditions after a storm. The Globularia shell beds inter-bedded with marly beds indicate stability and a deepening trend of the environment, terminating to deeper marine shales and marls of the Khangiran Formation.

Resumen Los fósiles de invertebrados marinos se han considerado herramientas importantes para la recolecta de datos por edades y la interpretación estratigráfica de los depósitos de paleógenos de Asia Central, sin embargo, aún no se ha proporcionado información de la cuenca de Kopet-Dagh (NE Irán). En esta investigación, se discuten los horizontes fosilíferos de la Formación Chehelkaman en las secciones Sheikh y Ghaleh-Zou (que nunca antes se habían reconocido), ambos en el área Sheikh Syncline. Estos lechos sedimentarios se superponen a la Formación de Pesteligh siliciclástica terrestre y son la primera evidencia de inundación marina de la transgresión del Paleógeno en el centro de Kopet-Dagh. Los estudios paleontológicos sistemáticos de fósiles de moluscos en esta sucesión condujeron a la identificación de: diez géneros, doce especies, dos subespecies de bivalvos, cinco géneros y cinco especies de gasterópodos. El conjunto pertenece a cuatro horizontes fosilíferos diferentes: (1) Conjunto Dominado por Turritellidae (TDA), (2) Pycnodonte-Turkostrea horizonte, (3) Cordiopsis - Cardium horizonte, (4) Camas de concha Globularia en la sección Sheikh y solo horizonte TDA en la sección de Ghaleh-Zou. La edad de toda la sucesión es Ypresian tardío (Cuisian medio temprano). Ésta edad está basada en Cordiopsis subathooensis - Turritella subathooensis co-ocurrencia de la zona con las zonas de nannofósiles NP12 y NP13. El TDA en ambas secciones confirma la abundancia de nutrientes y su orientación bimodal demuestra los efectos de las ondas oscilatorias en lugar de las paleocorrientes unidireccionales. Las altas tasas de bioerosión, incrustación, fragmentación, desarticulación y corrosión de las conchas en Pycnodonte - Turkostrea horizonte revela altos volúmenes de nutrientes y condiciones ricas en energía. Este intervalo, cubierto por la Cordiopsis - Cardium horizonte en una disposición de pavimento, representa las condiciones estables después de una tormenta. Los lechos de conchas de Globularia intercalados con lechos de marga, indican estabilidad y una tendencia cada vez más profunda del medio ambiente terminando en lutitas y margas más profundas de la Formación Khangiran.

The Maastrichtian shallow marine deposits exposed at the south margin of the Lago Argentino within the Austral-Magallanes Basin are known as the Calafate Formation. In order to interpret the depositional systems and reconstruct the sequence stratigraphic architecture for this unit at its type locality (Cerro Calafate), we acquire new data from seven stratigraphic sections. We recognized six facies associations (FA-1 to FA-6) corresponding to shallow marine deposits, which are organized vertically displaying a transition from shallower to deeper conditions, representing a ~90 m thick transgressive succession. The Calafate Formation deposits are differentiated into a lower wave-dominated coast (FA1, FA2 and FA3) and an upper tide-dominated coast (FA4, FA5 and FA6), each marked by the dominance of wave and tidal sedimentary processes, respectively. The Calafate Formation overlies the fluvial deposits of the Chorrillo Formation by a transgressive surface (TS), which is overlaid by a transgressive marine succession characterized by a retrogradational stacking pattern. The latter is finally covered by offshore transition marine deposits marking a progressive deepening of the depositional system that culminates with the maximum flooding surface (MFS). From here, an aggradational stacking pattern dominates the upper sandstones of the unit representing the highstand systems tract (HST), which is interpreted to be the cause of short-term periods when the accommodation space rate was nearly equaled to the sediment supply rate during the Maastrichtian.

ABSTRACT The Ipubi Formation represents the Aptian-Albian siliciclastic-evaporitic succession of Araripe Basin, NE Brazil. This succession comprises siliciclastic rocks (bituminous shales and claystones) and evaporites (gypsum and secondary anhydrite) and represents part of the lacustrine-shallow marine post-rift phase I. This study used sequence stratigraphy concepts to define the relations between changes in the relative lake level and the formation of Ipubi deposits. Results show that the organic-rich shales of the Ipubi Formation formed during a transgressive pulse that covered large areas of the proximal domains. These deposits overlie a regional unconformity that marks the end of the deposition of the underlying Crato Formation. A High Stand stage that followed the transgression influenced the formation of evaporitic deposits. Climate conditions played a major role in influencing the triggering and stopping of evaporite deposition. Thus, a new relative lake level fall event caused the exposure of the Ipubi Formation deposits, and created another regional subaerial unconformity accompanied by widespread karstification of evaporite beds. A posterior transgression caused the deposition of siliciclastic rocks of the Romualdo Formation over the Ipubi Formation strata, and also promoted a new event of karstification of the Ipubi upper evaporite beds.

RESUMO: Neste artigo, apresentamos novas evidências sobre a transgressão ocorrida Estágio Isotópico 3 (MIS3) na costa do sudeste do Brasil (Baixada Santista). Dados coletados por meio de um ensaio de penetração em solo (SPT) revelam a ocorrência de sedimentos mixohalinos entre 45.000 e 41.000 anos a.P. Uma sequência mais profunda, que mostra clara transição de ambiente continental para um mixohalino, foi associada ao Estágio Isotópico 5e (MIS5e). Marcadores orgânicos e inorgânicos foram usados para reconhecer as variações dos ambientes terrestre/mixohalino/marinho, bem como inferir sobre o clima e a energia do ambiente deposicional. Uma mudança ambiental, que poderia corresponder a um pico do nível do mar ou à ocorrência de condições mais secas, foi reconhecida entre 43.000 e 42.000 anos a.P. Os resultados reforçam a necessidade de futuros trabalhos sobre a variabilidade do MIS3 na costa atlântica sul-americana.

ABSTRACT: In this paper, we present new evidence regarding a Marine Isotope Stage 3 (MIS3) transgression on the south-eastern Brazilian coast (Baixada Santista coastal plain). Data collected from a Standard Penetration Test (SPT) drilling reveal the occurrence of myxohaline sediments between cal BP 45,000 and 41,000. A deeper sequence, which shows a clear transition from terrestrial to a myxohaline environment, was associated with MIS5e. Organic and inorganic proxies have been used to recognize the variations on the terrestrial/myxohaline/marine deposits, as well as to infer about climate and energy of the depositional environment. Environmental change, which could correspond to a sea-level peak or the occurrence of drier conditions, was recognized between 43,000 and 42,000 cal BP. The results reinforce the need for future works on MIS3 variability on the South American Atlantic coast.

ABSTRACT We present evidence of late Berriasian sedimentation which records the presence of Spiticeras correardi, whose stratigraphic range is not well established. Located at Cuencamé de Ceniceros, Durango State, northern Mexico, a section belonging to the Taraises Formation is here presented to show our results. Furthermore, the sampled ammmonite assemblage -herein constituted by Fauriella cf. boissieri, Berriasella cf. calisto, Spiticeras correardi, and Kilianiceras praegratianopolitense- is attributed to the upper Berriasian standard Mediterranean ammonite Zone Fauriella boissieri. It is worth noting that B. cf. calisto hasstrong biostratigraphic significance, due to the fact that it is restricted to the upper part of the aforementioned Fauriella boissieri Zone (Tirnovella alpillensis and Thurmanniceras otopeta subzones).

RESUMEN Presentamos evidencia de sedimentación del Berriasiano tardío que registra contenido de Spiticeras correardi, cuyo rango estratigráfico hasta ahora no se encuentra bien establecido. Nuestros resultados se señalan en una sección estratigráfica correspondiente a la Formación Taraises, ubicada en Cuencamé de Ceniceros, en el Estado de Durango, norte de México. La asociación de ammonoideos en la sección -formada por Fauriella cf. boissieri, Berriasella cf. calisto, Spiticeras correardi, y Kilianiceras praegratianopolitense- se atribuye aquí a la Zona Fauriella boissieri, del Berriasiano superior del estándar Mediterráneo. Vale la pena señalar que la especie B. cf. calisto tiene un fuerte significado bioestratigráfico, pues se encuentra restringida a la parte superior de la mencionada Zona Fauriella boissieri (Subzonas Tirnovella alpillensis y Thurmanniceras otopeta).

Coastal dunes are recognized in most of the world coasts, but are particularly common on dissipative beach systems, with low beach slopes, allowing the development of extensive areas of sand supply which provides optimal conditions for their development. The relationship between the beach environments and the coastal dunes regulates the dynamic balance in these types of coasts. Sand supply reduction between the beach-dune system commonly enhances erosion processes on beaches and promotes coastline retreat. The purpose of this paper is to characterize the evolution of the aeolian landforms along a field of transgressive coastal dunes at micro and mesoscale, to estimate natural and human induced causes of modification. The models reconstructing the development of aeolian landforms derived from this study will be useful to predict future trends on the coastal dune field and for setting tools for environmental management. San Antonio cape is a sand barrier spit that has progradated northward during the Holocene, integrating a depositional sedimentary sequence related to a marine transgression after the last maximum sea level about 6000 years ago (Violante et al., 2001). It extends along the shorefront from Punta Rasa to Punta Médanos and is located in the northeast sector of Buenos Aires province, Argentina (Fig. 1). Geomorphological interpretation is developed using field information and aerial photographs of 1964 (Naval Hydrographic Service) because it shows minimum anthropogenic modifications. Landscape evolution is determined comparing photographs of 1956 (Military Geographical Institute), 1964 (Naval Hydrographic Service), and 1991 (Punta Indio air base) and images from Google Earth. The dune field is developed over a beach ridge plain that reaches a maximum height of 2.5 m. The maximum development of this dune field is at the southern sector of the study area, near Punta Médanos, where it reaches 4 km wide. The dune field width decreases northward having a minimum development near Punta Rasa (Fig. 1). Beaches are sandy, dissipative and with low slope. They can be uni or multibarred and between 40 and 200 m width. Dune fields are recognized according to their stability: inactive and active. The first type is composed of complex parabolic and blowout dunes. The second one develops seaward, has higher sand transport rates and not many species of vascular plants. Eolian landforms in active dune fields are barchan, barchanoid ridges, and foredunes (Table 1). Foredune in San Antonio occupies a strip parallel to the coast of about 20 to 70 m wide. It is 1 to 10 m high, seaward slopes range from 3 to 7º, while continental slope varies from 7 to 18º. Foredune sediments are composed of well to very well sorted fine sand, with unimodal and symmetrical or slightly negative skewness distibutions. Mean grain size varies from 2 to 2.72 Ø, more than 80% of the sediment is transported by saltation (Table 3). Coarser grain size and more poorly sorted distributions are observed in the southward foredune sediments of Punta Médanos, in response to higher wave energy and the presence of a dissipative to intermediate beach profile (Masselin y Short, 1993) Natural dune environments are characterized by incipient (Fig. 2) and transgressive foredunes (Fig. 3, 4). Foredunes are divided in natural and degraded dunes (Table 2), according to their conservation. The last ones are divided into forest (Fig. 5a and b), forest and fragmentated (Fig. 5c) and razed foredunes (Fig 5d). Where the coastline has curvatures or inflections sand deposition increases on the beach, promoting sediment availability for the beach - dune interaction and favoring the generation of transgressive dunes. However, the analysis of the coastline behavior shows that the coast is retrating between Mar de Ajo and Las Toninas at a rate 1.45 m/year during the last 50 years (López, 2010) and consequently the foredune tends to be degraded and stabilized. The urban process that occupied the coast of Cabo San Antonio began in 1935 resulting in a rapid degradation of the coast (Fig. 6). Human degradation of the dune systems was mainly afforestation, beach and dune mining, building of avenues and houses on the seafront, artificial runoff to the sea and surface impermeabilization. By 1984, a substantial change in the coastal system affected 50% of the active coastal foredune (Fig. 6a). It was estimated a tendency of degradation along the coastal dune system of about 650 m/yr (Fig. 6c) from 1935 to 2000. If this trend continues in the future, the coastal dunefield would be completely degraded by 2030. It is demonstrated that the coastal dune stabilization with exotic plants and tree species, as well as the total or partial devastation for housing, sea front buildings, avenues design, piers construction, and beach resorts have increased vulnerability to the coastal erosion.

Las dunas costeras son reconocidas en la mayoría de las costas del mundo, pero son más comunes en las costas disipativas, como las del Cabo San Antonio, provincia de Buenos Aires (Argentina), donde la baja pendiente de las playas permite el desarrollo de áreas de generación extensas que proveen condiciones óptimas para su formación. Las dunas costeras del Cabo San Antonio se desarrollan en una faja paralela a la costa, con un ancho que varía entre 20 y 70 m. Las alturas oscilan entre escasos metros a 10 m. Las pendientes de las mismas en el sector costero varían entre 3 y 7º y del sector continental de 7 a 18º. En el presente trabajo se ha caracterizado la sedimentología y geomorfología de las dunas costeras del Cabo San Antonio, evaluando los cambios temporales entre los años 1935 y 2000, y se analizaron las causas y consecuencias de la degradación provocada por las actividades antrópicas. Los análisis sedimentológicos realizados en los 7 sitios de muestreo de las dunas costeras presentaron distribuciones unimodales, con valores de asimetría casi simétricos o levemente negativos y selección entre buena y muy buena de los sedimentos. Los valores de media comprenden un rango entre 2 y 2,72 Ø, las distribuciones acumulativas no presentan truncamientos internos y más del 80% de las partículas son transportadas por saltación. Las muestras entre Mar de Ajó y San Clemente no presentan una variación significativa en sus características texturales, sin embargo las dunas costeras de Punta Médanos presentan mayor tamaño de grano y menor selección debido a la presencia de playas intermedias a disipativas y mayor energía de oleaje. Se diferenciaron dos categorías de dunas costeras, las naturales y las degradadas. Dentro del primer grupo se reconocen dunas incipientes, formadas a partir del establecimiento de las primeras plantas vasculares (Sporobolus coarctata y Panicum racemosum) y las dunas costeras propiamente dichas, en las cuales los factores físicos como el viento, la humedad y la disponibilidad de sedimentos tienen mayor incidencia en la dinámica de su desarrollo. La acción de fijación de la duna costera con especies alóctonas, así también como el arrasamiento total o parcial para el trazado de avenidas costaneras o construcción de edificios, casas o balnearios, provoca alteraciones y tiene una relación directa con el aumento de la vulnerabilidad a la erosión marina del sector costero. La urbanización a la que se sometió el litoral del Cabo San Antonio desde 1935 generó una rápida degradación, que para 1984 ya modificaba sustancialmente el 50% del cordón de dunas costeras. Se determinó la tendencia de la velocidad de degradación del cordón costero, de aproximadamente 650 m.a-1. De mantenerse esta tendencia para mediados de la década del 2030, no existirán áreas relativamente importantes del cordón costero natural.

This contribution presents a characterization of Barremian evaporite facies of the Neuquén Basin (western Argentina) in order to discuss accumulation processes and depositional conditions. The evaporite accumulation is related to a proto-Pacific transgression that followed an Early Barremian widespread desiccation event. These evaporites are known as the Upper Troncoso Member of the Huitrín Formation. They constitute a research topic of great importance, both from the theoretical point of view (stratigraphy, origin, palaeoclimate), as well as from the knowledge of non-renewable natural resources (celestine - barite, anhydrite - gypsum, rock salt, potassium salts and hydrocarbons). The Neuquén Basin is considered an ensialic backarc basin associated with the easterly oriented subduction along the proto-Pacific margin of Gondwana (Figs. 1, 4). A generalised extensional stress regime due to steep subduction angle occurred in the magmatic arc and in the backarc settings, although regional thermal subsidence was punctuated by several episodes of structural inversion. Thus, the Upper Troncoso evaporites represent an unique example of accumulation in a marginal marine basin linked to the active continental margin of western Gondwana (Figs. 3, 4). The Lower Cretaceous deposits of the Huitrín Formation crop out almost continuously for more than 500 km along a north-south oriented belt (Fig. 5), from the latitude of the Aconcagua Mountain (Mendoza Province) up to the vicinity of the city of Zapala (Neuquén Province). Owing to the highest solubility and hygroscopic characteristics of the sediments, combined with the strong tectonic disturbation of the Huitrín Formation, the methodology for the study of the evaporites was largely based on subsurface information (geophysical well-log responses, cutting and cores) taken from oil and potassium salt exploration drill holes. In particular, electric logs allowed to identify electrofacies, and -based on the interpretation of cross-plots- to infer the mineralogy of the evaporites. Together with lithological descriptions of cutting and cores, representative samples of the rocks were studied in thin sections and by X-ray diffractometry. In the latter both whole-rock composition and <2μm clay mineral composition were defined. Lithological sections were elaborated, adjusted and correlated on the basis of this compositional information, and the areal distribution of evaporite salts was represented in a regional map. Geological correlations of the sedimentological record allowed define the geometry of evaporite facies in order to identify the main sedimentary environments. The regional study also involved the quantification of thickness variations in the deposits as well as the changes in evaporite mineralogy. The marine brine associated with the Troncoso evaporites followed successive processes of concentration and dilution. As a result, different salts were accumulated. In this study, these compositional changes are represented by the definition of several evaporite facies (Fig. 6). At the base of the Upper Troncoso Member the Facies Anhidrita was formed (Figs. 7, 8). This unit was covered by a thick salt succession composed of three facies: the lower Facies Salina Concentradora (Figs. 7, 9), the middle Facies de Sales Amargas (Figs. 10, 11), and the upper Facies Salina Terminal (Figs. 12, 13). During Facies Anhidrita deposition (Figs. 7, 8), the evaporite basin reached its maximum expansion (Fig. 14). An extensive salt pan formed from perennial or free brine, in the depocentral sector of the basin. Besides, a sabkha setting subjected to periodic events of flooding and concentration of the brines characterized the marginal areas of the basin. In this marginal belt, sulphate and carbonate microbial mats and siliciclastic muds were accumulated. In the central sectors of the basin, the anhydrite facies is characterized by microcrystalline films (sheets) composed of anhydrite-calcite pairs (Fig. 8), indicating a pelagic sedimentation under an almost stillness environment. A lateral transition from this central sector up to the coastal and supratidal sabkha sectors is recorded by regional correlation. In the lower part of the Facies Salina Concentradora, halite with a crystalline cumulus texture occurs (Figs. 7, 9). It was precipitated from a relatively depth brine and passes upwards to halite with a chevron texture indicating a progressive shallowing of the brine. The stratigraphic record of this facies shows cycles of primary clean halite - recycled halite - anhydrite sheets that repetitively occur. The Facies de Sales Amargas starts with sylvite daughter crystals in halite fluid inclusions, followed by a few crystals of sylvite, passing upwards to two thick beds of sylvinite (Fig. 10). This facies reaches a maximum thickness of 25 meters and represents the evaporite deposits of the Upper Troncoso Member with the smallest areal distribution (Fig. 14). However, they cover a (preserved) area of 3,000 km². These deposits are dominated by sylvinite (sylvite plus halite), which appears as anhedral to subhedral reddish, yellowish and whitish crystal aggregates (Fig. 11). The presence of hematite as fine solid dispersions, suggests that sylvite would result from lixiviation of magnesium chloride from a primary red carnallite. The Facies Salina Terminal represents the dilution of the evaporite basin (Fig. 12). Three successive evaporite cycles are recognized and they are interpreted as the result of flash floods that supplied rainwater from emerged areas. The mix of these waters with the perennial brines in the depocenter allowed precipitation of an anhydrite bed followed by a rhythmic laminated succession of halite with chevron texture alternating with anhydrite. At this time, fine-grained siliciclastics would have been supplied to the evaporite basin through flash floods from emerged areas, as well as from pyroclastic activity in the magmatic arc. This terrigenous material was preferentially accumulated during the dilution of the evaporite brine. The peripheral sectors of the basin are represented by salty mudflat sediments or siliciclastic sabkha deposits, which are interpreted to represent the development of wet salt mudflats in coastal areas and relatively drier mudflats in the more proximal (continental) margins of the basin. Syn-depositional to slightly post-depositional changes occurred in both the central and marginal settings, where underground brines produced precipitation of inter-crystalline passive cement in clean halite, and dissolution - reprecipitation of halite in the chaotic mud salt (Fig. 9c). Early diagenetic processes also involved neoformation of evaporitic minerals (anhydrite by dehydration of gypsum and autigenous sylvite from carnallite). By hyperhalmyrolysis, smectite in fine-grained siliciclastic deposits was transformed in mixed layer clay minerals, namely chlorite and illite. Under the global Cretaceous greenhouse context, the Neuquén Basin supported a dry and windy climate. The magmatic arc would have acted as a topographic barrier to the open proto-Pacific Ocean, and the basin behaved as a partially isolated hydrographically depression below sea level at that time (Fig. 4). Therefore, the evaporites of the upper Troncoso Member are linked to a restricted marine environment; this is an inland hypersaline shallow sea. High temperatures generated strong evaporation rates, which exceeded water supply (runoff, ground water discharge and atmospheric precipitations). These conditions increased salt concentration and caused the precipitation of salts according to their degree of solubility (Fig. 16). Moreover, the continuous evaporation would have created an imbalance in sea level currently stimulating continuous income, although limited, of sea water into the basin (Fig. 17a). In turn, the arc produced partial to total reflux retention in the basin, allowing brine concentration over time (Fig. 17a). A larger positive accommodation space towards the western sector of the depression favoured the connection between the proto-Pacific Ocean with the backarc Neuquén Basin during Facies Anhidrita and Facies Salina Concentradora (Fig.18). In the Facies Sales Amargas and in the Facies Salina Terminal, the evaporitic basin was assimilable to a hydrologically closed basin, with continental recharge of recycled marginal evaporites (Fig. 17b). This contribution identifies and characterizes a group of evapofacies in Barremian evaporites of the Neuquén Basin that allows to answer some questions on the origin, the depositional system, the controls and the evolution of the evaporitic record.

El Miembro Troncoso Superior es una unidad evaporítica que forma parte de la Formación Huitrín de edad Barremiana (Cretácico temprano) en la Cuenca Neuquina. El objetivo de este trabajo es presentar un estudio paleoambiental, evolutivo y controles que se dieron en el evento evaporítico huitriniano. El estudio de material e información de sondeos exploratorios de hidrocarburos y de potasio, permitió realizar columnas litológicas, delinear la distribución areal de las sales evaporíticas en el subsuelo y, por medio de correlaciones geológicas, identificar sectores de adelgazamiento y engrosamientos, e inferir la paleotopografía deposicional. La descripción y caracterización petrográfica y por difracción de rayos X permitieron determinar la mineralogía y textura de las unidades litológicas presentes en las evaporitas, lo cual, permitió definir distintas evapofacies o unidades informales. Un horizonte anhidrítico de amplio desarrollo territorial, identificado como Facies Anhidrita se presenta en la base base de la unidad en subsuelo y afloramiento, al cual suprayace un espeso paquete de haluros (halita, silvinita), cuyo registro sedimentario se encuentra hoy solo en el subsuelo de la Cuenca Neuquina. Dentro de este último, se han diferenciado tres facies: la Facies Salina Concentradora en la base, donde la salmuera marina se fue concentrando en sales amargas, que dejó un espeso banco de silvinita intercalado en el tercio superior, referido como Facies de Sales Amargas, la cual constituyó la mayor restricción de la salmuera libre. Culmina la secuencia salina con la dilución de la salmuera, que expandió el área deposicional, y permitió la precipitación de nuevas sales (halita), etapa que se denomina aquí como Facies Salina Terminal. La cuenca evaporítica se vincula a un ambiente marino marginal, separado del Océano proto-Pacífico, por un arco magmático que actuó como una barrera topográfica con el mar abierto, y que permitió el influjo de agua de mar continuo, aunque limitado y, a su vez, habría contribuido con una retención parcial a total del reflujo en la cuenca. Esta condición hidrológica abierta al agua de mar, se habría dado durante la Facies Anhidrita y la Facies Salina Concentradora, cerrándose durante la Facies de Sales Amargas y la Facies Salina Terminal. El espacio de acomodación sedimentaria, mayor en el sector occidental de la cuenca, habría acompañado la vinculación con el ambiente marino proto-Pacífico. El clima habría sido árido y ventoso, en un contexto greenhouse del Cretácico Inferior. La posición de la cuenca a sotavento del arco magmático, habría contribuido con vientos desecantes provenientes del oeste. La depositación de sales en la cubeta con salmuera perenne o libre, siguió un proceso de concentración y dilución evapoquímica. En la faja periférica, que estuvo sujeta a contracciones e inundaciones periódicas de gran escala, se desarrollaron facies de sabkha con matas microbianas bentónicas durante la Facies Anhidrita, mientras que en las facies con haluros, se habrían dado depósitos de barreal salino o de sabkha silicoclástico. Cambios sindeposicionales o ligeramente posdeposicionales, se habrían dado tanto en el ambiente depocentral, como periférico, donde la salmuera subterránea continuó activa modificando los sedimentos.

A shallow marine invertebrate association is reported from a new Early Jurassic locality namely La Casilda, which is situated in the southwestern region of the Chubut Basin (Patagonia, Argentina). The marine deposits of La Casilda are located in the Río Genoa valley and bear a diverse invertebrate fauna including bivalves, gastropods, brachiopods, echinoderms and corals. A preliminary taxonomic analysis of the invertebrate fauna suggests that La Casilda deposits belong to the Mulanguiñeu Formation of late Pliensbachian-early Toarcian age, and may be coeval with those from the marine localities previously sampled in other regions of the Río Genoa valley. The preliminary results of a biodiversity analysis displayed that La Casilda is one of the most diverse localities at the Chubut Basin and could be assigned to the biofacies at the mixed siliciclastic-carbonate ramp proposed for the marine Early Jurassic at the Andean Basin of northern Chile. The evolution of the marine transgression during the early Pliensbachian-early Toarcian is also interpreted here in a time scale based on ammonite faunas, giving a preliminary temporal reconstruction of the entire Chubut Basin.

Una asociación de invertebrados marinos de aguas someras se registró en una nueva localidad perteneciente al Jurásico temprano denominada La Casilda, la que se sitúa en la región suroeste de la cuenca del Chubut (Patagonia, Argentina). Los depósitos marinos correspondientes a La Casilda se encuentran en el valle del Río Genoa y comprenden una diversa fauna de invertebrados, incluyendo bivalvos, gastrópodos, braquiópodos, equinodermos y corales. Un análisis taxonómico preliminar de dicha fauna sugiere que los depósitos de La Casilda pertenecen a la Formación Mulanguiñeu, cuya edad es Pliensbachiano tardío-Toarciano temprano, y a su vez podrían ser coetáneos con los depósitos marinos de otras localidades muestreados previamente en el valle del Río Genoa. Resultados preliminares de un análisis de biodiversidad muestran que La Casilda es una de las localidades más diversas en la cuenca del Chubut y podría ajustarse a las biofacies correspondientes a la rampa mixta siliciclástica-carbonatada propuesta para la Cuenca Andina del Jurásico temprano marino del norte de Chile. La evolución de la transgresión marina que tuvo lugar durante el Pliensbachiano temprano-Toarciano temprano también se interpreta aquí en una escala de tiempo sobre la base de la fauna de ammonites, dando una reconstrucción temporal preliminar de toda la cuenca del Chubut.

Early Miocene shallow marine deposits in the region of Lago Posadas-Meseta Belgrano (Argentina) represent part of the "Patagoniense" transgression, an Atlantic marine incursion that flooded large part of Patagonia, including the Austral (foreland) Basin (southern Patagonia). These deposits, referred as El Chacay (Argentina) or Guadal (Chile) formations, and the transition to the overlying Santa Cruz Formation were divided into six facies: subtidal sandbars, shallow marine sandy deposits, muddy shelf deposits, estuarine complex deposits, fluvial channels and fluvial floodplains. These are arranged in a general transgressive-regressive cycle, subdivided into two stratigraphic sequences, separated by a major erosional surface. 87Sr/86Sr ages from shell carbonate in eight oysters yielded an age range of 20.3 to 18.1 Ma for these "Patagoniense" deposits. Correlation with other dated "Patagoniense" sections in southern Patagonia, like those at Lago Argentino or Comodoro Rivadavia, indicates that they belong to a single transgression that flooded several Patagonian basins approximately at the same time. Eustasy, flexural subsidence created by tectonic loading in the adjacent fold-and-thrust belt, and basin floor paleo-topography controlled the duration of the depositional event and the sedimentation style of these shallow marine deposits.

Los depósitos marino-someros del Mioceno temprano de la región del Lago Posadas-Meseta Belgano representan parte de la transgresión "Patagoniense", una incursión marina atlántica que invadió gran parte de la Patagonia, incluyendo la Cuenca de antepaís Austral (Patagonia austral). Estos depósitos, referidos como formaciones El Chacay (Argentina) y Guadal (Chile), y su transición a la suprayacente Formación Santa Cruz, fueron divididos en seis facies: barras submareales, depósitos arenosos marino-someros, depósitos fangosos de plataforma, complejo estuarino, canales fluviales y planicie de inundación. Estas facies muestran un arreglo general transgresivo-regresivo, el que puede ser subdividido en dos secuencias estratigráficas separadas por una superficie erosiva. Resultados de ocho edades 87Sr/86Sr de carbonato tomado de valvas de ostras dieron un rango entre 20,3 Ma y 18,1 Ma para estos depósitos Patagonienses. La correlación con sucesiones equivalentes de edad conocida en la Patagonia Austral, como las del Lago Argentino o Comodoro Rivadavia, indican que estas pertenecen a una misma transgresión que inundó gran parte de la Patagonia aproximadamente al mismo tiempo. La eustacia, la subsidencia flexural creada por carga tectónica en la faja corrida y plegada adyacente, y la paleotopografía del fondo de la cuenca, controlaron la duración del evento depositacional y el estilo de sedimentación estos depósitos marino-someros.

The age and stratigraphic subdivisions for the late Oligocene-Miocene, marine deposits of Patagonia (Patagoniense succession) have been largely debated. Most studies for the Comodoro Rivadavia region were focused on its biostratigraphy and stratigraphic relations with the underlying and overlying mammal-bearing terrestrial strata. We report here thirteen new 86Sr/87Sr ages obtained from wellpreserved oyster valves of the Chenque Formation in the classical Patagoniense outcrops around the city of Comodoro Rivadavia (Golfo San Jorge Basin, Argentina). According to these ages, the deposition of the unit in the region occurred between 19.69 and 15.37 Ma (Burdigalian-early Langhian). A lower interval of normal sedimentation rate (Sequences 1 and 2) and an upper interval of high sedimentation rate (Sequence 3) are defined according to these new ages of the Chenque Formation. Subsequently, the depositional age of the Chenque Formation is compared with other well-dated marine successions of southern Patagonia located within the Austral Basin. This analysis suggests that the Austral and Golfo San Jorge basins were flooded by the Atlantic sea at about the same time (~21-20 Ma), inundating what was before a vast continental region of southern Patagonia. A renewed phase of continentalization occurred at about 18 Ma in the Austral Basin and at about 15 Ma in the study region of the Golfo San Jorge Basin. This 3 my difference combined with the elevated sedimentation rate estimated for the upper part of the study interval, suggest that the Golfo San Jorge Basin may have locally experienced relatively high subsidence rates during the early Miocene, allowing prolonged marine sedimentation in the Comodoro Rivadavia area. Consequently, the accumulation of the terrestrial deposits assigned to the Santa Cruz Formation started at about 15 Ma in the study region, later than in other localities of southern Patagonia. This results clearly indicate a remarkable interdigitation between the Santa Cruz and Chenque formations in a west-east transect across central Patagonia.