Scielo RSS <![CDATA[Latin American journal of sedimentology and basin analysis]]> http://www.scielo.org.ar/rss.php?pid=1851-497920140001&lang=en vol. 21 num. 1 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[Editorial]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1851-49792014000100001&lng=en&nrm=iso&tlng=en <![CDATA[Inorganic composition of suspended sediments in the Acre River, Amazon Basin, Brazil]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1851-49792014000100002&lng=en&nrm=iso&tlng=en The purpose of this study was to determine the chemical and mineralogical composition of suspended sediments from the Acre River, located in the Purus Basin, upper Amazon basin, a region associated with the Fitzcarrald Arch. The elemental and mineralogical compositions of the sediments were assessed by using mass and atomic spectroscopy, and X-ray diffraction. A total of 46 samples were collected between 2008 and 2011 from four sites in the study area during wet and dry seasons. The suspended sediments contained feldspar, kaolinite, illite and quartz as well as the elements Hg, Zn, V, Ti, Si, Pb, Ni, Na, Mn, Mg, K, Fe, Cu, Cr, Cd, Ca, Al, S, and P in different proportions that were associated with the various weathering reactions linked to physical, chemical and biological processes in the region. The obtained results represent the first set of values and relationships regarding the mineralogy and chemical identification of the suspended sediments in the Acre River and can be used as a reference for the geochemical characteristics of the Purus Basin. Such regional studies will become increasingly necessary to observe the impacts of climate change and human activities on the suspended sediment load and composition of the Amazon River. <![CDATA[Aplicación del método de flujo de energía en el litoral de la provincia de Buenos Aires, Argentina]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1851-49792014000100003&lng=en&nrm=iso&tlng=en El objetivo de este trabajo es estimar el potencial transporte longitudinal marino de sedimentos, desde la ciudad balnearia de Monte Hermoso hasta Punta Rasa (Provincia de Buenos Aires), a través del método de flujo de energía (CERC, 2002), utilizando datos de clima de olas de los modelos WAVEWATCH III (NOAA, 2009). El método relaciona la altura de ola significativa, su ángulo de incidencia y otros parámetros característicos de playas, con la tasa de transporte de sedimentos paralela a la costa. Los resultados permitieron generar mapas de flujo de energía y del consiguiente transporte potencial de material sedimentario. A través de la comparación con antecedentes de estudios previos basados en relevamientos in situ se logró verificar la concordancia existente entre el clima de ola y la morfología regional de playas. La aplicación de los modelos de olas brindó continuidad al cálculo a lo largo del área de estudio, aportando un panorama integral al fenómeno de deriva litoral.<hr/>The objective of this work is to estimate the potential longitudinal marine sediment transport from the seaside city of Monte Hermoso to Punta Rasa (Buenos Aires, Argentina), through the Energy Flux method (CERC, 2002) data from WAVEWATCH III wave climate models (NOAA, 2009). The method relates the significant wave height, the angle of incidence and other parameters characteristic of beaches, to the rate of sediment transport along the coast. The results allowed to generate maps of energy flux and the consequent potential transport of sedimentary material. Through comparison with previous in situ studies, it was possible to verify the concordance between wave climate and of regional beaches. The application of wave models to the calculation provided continuity throughout the study area, giving a comprehensive scenario to the phenomenon of longshore drift. <![CDATA[Descripción litofacial e interpretación genética de los metaconglomerados de la Formación San Luis (Proterozoico Superior - Cámbrico), sierra de San Luis, Argentina]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1851-49792014000100004&lng=en&nrm=iso&tlng=en La Sierra de San Luis forma parte de la región austral de las Sierras Pampeanas y está conformada por un basamento ígneo-metamórfico originado durante las orogenias Pampeana y Famatiniana. Las metamorfitas de bajo grado, denominadas Formación San Luis, incluyen metapelitas, meta-areniscas, metaconglomerados y metavolcanitas ácidas. Las mismas afloran en el sur de la Sierra de San Luis, en dos fajas de rumbo NNE-SSO, denominadas Oriental y Occidental, de 50 y 40 km de longitud respectivamente. La compleja estructura de deformación de la Formación San Luis dificulta precisar la potencia original de la secuencia sedimentaria, estimada en un mínimo de 3.500 m sin descomprimir. Esta unidad se habría depositado en una cuenca marina con influencia glaciaria, durante un periodo de tiempo comprendido en el lapso Neoproterozoico Tardío -Cámbrico. El objetivo de este trabajo es la descripción litofacial e interpretación genética del protolito de los metaconglomerados de esta unidad, para lo cual se relevaron 420 m de metasedimentitas distribuidos en tres afloramientos. El Metaconglomerado Cañada Honda (270 m de espesor) aflora en la localidad de Tres Pasos, en el centro de la faja Oriental. Según las facies reconocidas fue dividido en tres intervalos. El intervalo inferior tiene 60 m de potencia y está conformado por paraconglomerados masivos con matriz fangosa (Cfm) intercalados con delgados niveles de pelitas masivas (Fm). Esta asociación de facies vertical (Cfm-Fm) se interpreta como depósitos de flujos de detritos cohesivos, que culminan con la depositación de remanentes suspendidos sobre los mismos. El segundo intervalo tiene 40 m de potencia y está conformado por lentes de sabulitas con gradación normal (Sg) y fangolitas masivas (Fm). Esta asociación de facies vertical (Sg-Fm) se considera como el producto de flujos turbidíticos desacelerantes y de densidad decreciente. El intervalo superior tiene 170 m de potencia y está conformado por paraconglomerados masivos con matriz areno-fangosa de fábrica abierta (Caa) y cerrada (Cac), delgados niveles de vaques finas (Vf) y fangolitas laminadas (Fl). Se reconocen las asociaciones de facies Caa-Vf-Fl y Cac-Vf-Fl, interpretadas como el producto de flujos hiperconcentrados con distinto grado de dilución que culminan con la depositación de remanentes suspendidos sobre los mismos. El conjunto de asociaciones de facies reconocidas en el Metaconglomerado Cañada Honda se habría depositado en un cañón desarrollado en la zona proximal de un sistema de talud - llanura abisal. El Metaconglomerado Arroyo Curtiembre (115 m de espesor) y el Metaconglomerado Cerro Blanco (35 m de espesor) se localizan en el sector norte y central, respectivamente, de la faja Occidental. El primero se compone de fangolitas laminadas (Fl) y fangolitas guijarrosas laminadas (FGl), mientras que en el segundo las fangolitas laminadas alternan con fangolitas sabulíticas laminadas (FSl). Las asociaciones de facies de estas dos unidades metasedimentarias (Fl-FGl y Fl-FSl) son interpretadas como depositadas a partir de decantación continua de material suspendido en plumas de baja densidad, asociada a eventos de lluvia de detritos transportados por icebergs y mantos de hielo marino en la zona de máximo proglacial. Se considera entonces que los metaconglomerados Arroyo Curtiembre y Cerro Blanco corresponden al mismo intervalo estratigráfico; por lo que este último representaría posiciones más distales respecto del frente glaciario, dado que presenta menor espesor y disminución en la fracción dominante de su esqueleto.<hr/>The Sierra de San Luis is part of the southern region of Sierras Pampeanas and it is composed of an igneous-metamorphic basement, mostly generated during the Pampean and Famatinian orogenies. The low-grade metamorphic rocks belong to the San Luis Formation (Prozzi & Ramos, 1988), and they include phyllites, slates, metapsammites, metaconglomerates and acid metavolcanic rocks. This unit is exposed in the south-central sector of the Sierra de San Luis, across two NNE - SSW elongated outcrops called Eastern and Western Belts, which are 50 and 40 km long, respectively (Fig. 1) (Ortiz Suárez et al., 1992). The complex deformational structure of the San Luis Formation hinders its original thickness, estimated at a minimum of 3500 m without decompaction (von Gosen and Prozzi, 1996). According to different dating techniques, the age of the San Luis Formation would span between the Late Neoproterozoic to the Cambrian (Söllner et al., 2000; Drobe et al., 2009, 2011; Casquet et al., 2014). The aim of this paper is to describe and interpret the preserved sedimentological features of coarse-grained units within the San Luis Formation (metaconglomerates), in order to shed light into depositional processes and systems. This research is particularly important due to the little knowledge available about the protolite sedimentologic and stratigraphic characteristics of the unit. Additionally, metaconglomerates might constitute a relevant element of stratigraphic correlation between different exposures of the San Luis Formation, thus providing time lines that are not possible to obtain by other means. Three main metaconglomerates are reported in this study, one for the Eastern Belt, and two for the Western Belt (Fig. 2). Conventional sedimentological information was collected in the field while logging stratigraphic section. The mineralogy and petrology of the coarse clastic fraction were studied in the field and samples of mudstones and sandstones were collected for microscopic analysis (Table 1). Cañada Honda Metaconglomerate (Prozzi, 1990). This unit is exposed in the Eastern Belt, at Tres Pasos locality (Figs. 1, 3). This metasedimentite is 270 m thick and 10 km along strike. Here, this metaconglomerate has been divided into three sections. The lower section is 60 m thick and consists of disorganized, matrix-supported paraconglomerates (Cfm) (Fig. 4), with up to 30% of framework of pebbles to boulders, and over 70% of muddy matrix with low proportion of sand. Beds commonly have irregular geometries, probably due to the metamorphic deformation, and are thick to very thick bedded. They are interbedded with massive mudstones (Fm), which are up to 0.5 m thick. The second section is 40 m thick and is composed of lenses of normal-graded sabulites (Sg) with erosive bases and scarce lateral development, interbedded with massive mudstones (Fm) (Fig. 5). The upper section is 170 m thick and comprises two paraconglomerates. One of them (Caa) has a 40% of disorganized framework of pebbles and a mud-rich sandy matrix dominated by fine to coarse sand. The other one (Cac) has up to 70% of framework and a mud-rich sandy matrix dominated by fine to coarse sand, with disorganized fabric and uncommon inverse gradation in the first 10 cm of some thick beds. Moreover, coarse pebbles and cobbles (5 to 20 cm long) are commonly observed protruding from the top of the beds (Fig. 7b). Both massive paraconglomerates (Caa and Cac) have tabular geometries with thick to very thick beds. They have flat to slightly erosive bases and transitional tops to fine-grained wackes (Vf) (Fig. 8), which are mostly tabular, thin- to medium-bedded layers. These facies are capped by thin, laminated mudstones (Fl). Four facies associations are recognized in the Cañada Honda Metaconglomerate (Fig. 13a-d). Association Cfm-Fm is interpreted as deposits from cohesive debris flows (Lowe, 1982; Mulder and Alexander, 2001), ending with settling processes associated with residuary particles suspended above those flows (Fig. 13a). Association Sg-Fm is interpreted to reflect deposition from waning turbidity currents with decreasing density (Lowe, 1982) (Fig. 13b). Associations Cac-Vf-Fl and Caa-Vf-Fl are interpreted as deposits of hyperconcentrated cohesionless flows (Mulder and Alexander, 2001), ending with settling processes associated to residuary particles suspended above those flows (Fig. 13c, d). All together, the four facies associations of this metaconglomerate would have deposited in the canyon area of a slope depositional system. Arroyo Curtiembre Metaconglomerate (Ramos et al., 1996). This unit is exposed in the headwaters of the homonymous creek in the northern sector of the Western Belt, where it attains 115 m in thickness and it extends over 2 km along strike (Fig. 9). It is composed of laminated pebbly mudstones (FGl), with 15% of framework of coarse pebbles and 85% of muddy matrix (Fig. 10). The clasts disturb the lamination at their bases and are interpreted as dropstones (Fig. 11a). Beds have tabular geometry and are medium- to thick-bedded. They are typically interbedded with laminated mudstones (Fl) in strata of similar thickness, with transitional contacts (Fig. 11b). Systematic vertical relationship between facies Fl and FGl (Fig. 13e) is inferred to reflect deposition from rain-out of debris, from icebergs and seasonal sea-ice, associated with continuous settling of suspended sediment in low-density plumes, in the maximum proglacial zone. Cerro Blanco Metaconglomerate (new name). This coarse-grained unit is exposed in the eastern side of the homonymous hill in the Western Belt, where it is 35 m thick and no more than 300 m wide. It is composed of laminated pebbly mudstones (FSl) with up to 15% of framework of granules to coarse pebbles (0.2 - 3 cm) and over 85% of muddy matrix (Fig. 12). As in the previous case, the clasts slightly disturb the lamination at their bases, and are, thus, interpreted as dropstones (Fig. 12). Beds are tabular, less than to 2 m thick, and they vertically grade into laminated mudstones (Fl). The close relationship between facies FSl and Fl (Fig. 13f) suggests that this association was formed by the same processes that accumulated the sediments of the Arroyo Curtiembre metasedimentite; that is to say rain-out of debris from icebergs with season fluctuations. In this location, however, there are a lower proportion of pebbles versus matrix and, in average, a smaller grain size (granules vs. pebbles). Considering the marked similarity in facies between Cerro Blanco Metaconglomerate and Arroyo Curtiembre Metaconglomerate, we conclude they would represent the same stratigraphic interval. <![CDATA[Seismic sequence stratigraphy of a foreland unit inthe Magallanes-Austral Basin, Dorado Riquelme Block, Chile: Implications for deep-marine reservoirs]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1851-49792014000100005&lng=en&nrm=iso&tlng=en This contribution presents geological data that provides a sequence-stratigraphic-based exploration model for Oligocene units in the central Magallanes-Austral Foreland Basin, and identifies the related sedimentary deposits that constitute basin-floor fan reservoirs. The study area is located in the Magallanes Region, Chile, and it was discovered in 2009-2010 by the joint venture of the National Oil Company of Chile and Methanex group at Dorado Riquelme Block. Seismic stratigraphic analysis of the Magallanes-Austral Foreland Basin enabled the definition of four evolutionary stages using 3D seismic information from a 91.6 km long section, as well as lithostratigraphic and biostratigraphic records and wireline logs. The clinoforms observed in the Foreland III stage of the Magallanes-Austral Foreland Basin are the focus of this study. Six seismic units (SU-1 to SU-6) and twenty-five depositional sequences were identified there, based on temporal affinity and genetic mechanisms. The youngest four seismic units comprise alternating forestepping and downstepping prograding patterns, while the fifth seismic unit is characterized by a backstepping pattern, which is followed by a sixth seismic unit in which forestepping patterns are again developed. The most important reservoirs were identified in seismic unit SU-2, and they are associated with sandstone-prone deposits accumulated in basin-floor fans. Their development is associated in this contribution with periods of relative sea-level fall during forced regressions.