Scielo RSS <![CDATA[Revista de la Asociación Argentina de Sedimentología]]> http://www.scielo.org.ar/rss.php?pid=1853-636020040002&lang=en vol. 11 num. 2 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.ar/img/en/fbpelogp.gif http://www.scielo.org.ar <![CDATA[Hacia una verdadera integración latinoamericana en la sedimentología]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1853-63602004000200001&lng=en&nrm=iso&tlng=en <![CDATA[Stratigraphic control in the preservation of vertebrates remains in the Cerro Barcino Fm (Cenomanian), Chubut Province]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1853-63602004000200002&lng=en&nrm=iso&tlng=en En este trabajo son analizados los factores que controlaron la concentración de restos de vertebrados en niveles estratigráficos del Miembro Cerro Castaño de la Formación Cerro Barcino. (Cenomaniano). El hallazgo de vertebrados se limita a bancos de areniscas guijarrosas correspondientes a canales fluviales de geometría tabular y bases no erosivas. Los depósitos asociados de planicies de inundación, y otros tipos de canales intercalados en la secuencia, no han provisto hasta la fecha restos paleontológicos de interés. Con el objeto de analizar el origen de la concentración de los restos de vertebrados, la secuencia fue dividida en seis facies sedimentarias que incluyen depósitos de canal (CHmt, CHsl y CHsw) y de planicie de inundación (Pd, Pp y Pc). Los canales del tipo CHmt resultan multiepisódicos, de geometría tabular y son los que muestran la concentración de restos óseos aquí analizados. Los del tipo CHsl aparecen como canales de relleno simple (mono o biepisódicos), de geometría lentiforme o lenticular y base ligeramente erosiva. Finalmente, los del tipo CHsw son monoepisódicos, fuertemente lenticulares y confinados. En lo que respecta a las planicies de inundación, incluyen depósitos de desbordes fluviales Pd (areniscas limosas macizas), horizontes de paleosuelos Pp (arcilitas y limolitas con frecuentes pedotúbulos) y niveles de caída Pc (chonitas y tobas vítreas). La secuencia aquí considerada fue depositada por cursos fluviales fuertemente condicionados por la eruptividad, pudiéndose reconocer tres tipos principales: 1) sineruptivos, 2) posteruptivos tempranos y 3) posteruptivos tardíos. Los primeros incluyen a canales del tipo CHsl, asociados a facies de desborde (Pd) y depósitos de caída (Pc). En los segundos la red fluvial incidió fuertemente las facies sineruptivas, formando canales del tipo CHsw asociados a terrazas y planicies con paleosuelos (Pp). Finalmente, los períodos posteruptivos tardíos están registrados en canales del tipo CHmt (que contienen a los restos óseos aquí estudiados), los que pasan lateralmente a depósitos de desborde (Pd) y niveles edáficos (Pp). La información aquí reunida lleva a suponer que la concentración de vertebrados en los canales del tipo CHmt fue consecuencia tanto de factores depositacionales (ambientales) como postdepositacionales (diagenéticos). Desde el punto de vista ambiental, el sistema fluvial posteruptivo tardío es el que habría mostrado las mejores condiciones para la vida. Esto habría llevado a la acumulación de abundantes restos óseos tanto en las planicies como en los canales. Sin embargo, la prolongada exposición subaérea de los huesos en planicies sujetas a una baja tasa de agradación, unida a las transformaciones diagenéticas sufridas por las rocas de grano fino, no favorecieron la preservación de restos de vertebrados en las áreas intercanal. Por el contrario, el más rápido sepultamiento de los restos óseos en los canales, unido a una importante fase de cementación temprana carbonática que bloqueo el sistema diagenético, contribuyó a la preservación y concentración del material óseo en los canales del tipo CHmt.<hr/>The factors that controlled the differential concentration of vertebrates remains in specific stratigraphic intervals of Cerro Castaño Member are considered in this paper (Fig. 1). The finding of vertebrates is only limited to pebbly sandstone beds that form fluvial channels with non erosive bases and tabular geometry. The closely associated alluvial plains, and other types of channels intercalated in the sequence, have not yielded significant paleontological remains. In order to analyze the origin of the differential concentration of vertebrates, the sequence was divided in six sedimentary facies (Figs. 2 and 4, Table 1), including different kinds of channel (CHmt, CHsl y CHsw) and flood plain (Pd, Pp y Pc) deposits. CHmt facies is composed of cross-bedded sandstones and conglomerates forming tabular multistorey channel complex bounded by non erosive bases (Fig. 4). Sandstones comprise lithoarenites and feldslithoarenites with low matrix percentage (less than 4 %), high quantities of cement (up to 21 %), open fabric, scarce diagenetic alteration and almost absent porosity. Three different types of cements have been distinguished in these rocks: 1) rim-type zeolite cement, 2) poikilitic calcite and 3) microcristalline and poikilitic analcime (Fig. 5d,e). CHsw facies forms simple lenticular channels with erosive bases deeply incised into floodplain deposits (Fig. 4). The lowermost part of each channel shows lenses of intraformational conglomerates covered by massive and cross-bedded medium- and fine-grained sandstones. CHsw facies is dominated by lithoarenites showing moderate to high matrix content (up to 20 %), mainly zeolitic cement and frequent formation of pseudomatrix (Fig. 5f). The last type of channel deposits correspond to CHsl facies that form thin lentiform channels (up to 0.5 m thick) encapsulated into floodplain facies (Fig. 4). These channels comprise coarse-grained sandstones showing low proportions of matrix, relatively open fabric and scarce diagenetic transformations (Fig. 5a,b). Zeolites forming both rim and granular cements predominate (Fig. 6). Pd facies are the coarsest deposits identified in the alluvial plain area. They comprise pyroclastic-rich silty sandstones stratified in centimetric to decimetric massive tabular beds. Frequently, Pd facies occurs either interstratified with vitric tuff belonging to the Pc facies or associated to mudstones and chonites forming paleosoils (Pp facies). The analyzed section of the Cerro Barcino Fm was deposited in different kinds of allociclycally controlled fluvial environments. Even though the area was located rather far away from the volcanic segment, the recurrent ash falls exerted a hard control on sedimentation. Moreover, as the eruptivity was changing throughout time, periods dominated by high amounts of pyroclastic sedimentation can be distinguished from others where ash falls were almost totally absent. Figure 8 shows the three types of fluvial systems recognized in this paper: 1) sineruptive, 2) early posteruptive and 3) late posteruptive. Following this model, it is very likely that during high eruptivity periods large amounts of ash falls had produced rapid agraddation of the alluvial plains. These sineruptive fluvial system would have favored the formation of shallow braided channels (CHsl facies) laterally associated to fine sandstones (Pd facies) and vitric tuffs (Pc facies). When eruptivity ceased, and consequently the pyroclastic input, channels began to evolve towards its equilibrium profile eroding earlier flood plain deposits. This stage is represented in the here named early posteruptive fluvial system (Fig. 8), characterized by deeply incised lenticular channels (CHsw facies) that laterally pass to bioturbated chonites and mudstones (Pp facies). After some time, the fluvial system reached quasi-equilibrium conditions (late posteruptive stage) forming multistorey tabular channels (CHmt) that laterally pinched out into muddy fine sandstones (Pd facies) and bioturbated mudstones (Pp facies). Both depositional (environmental) and postdepositional (diagenetic) factors are likely to have controlled the high concentration of vertebrates in specific stratigraphic levels of the Cerro Barcino Fm. The fact that vertebrate remains only appear in CHmt channels can be explained by the favorable conditions that prevailed during the late posteruptive stage when pyroclastic falls ceased and a flood plain was stabilized (Fig. 9). Moreover the early carbonate cementation affecting channel sandstones closed the diagenetic system and favored bone preservation. On the contrary, early carbonate cementation was not found in the associated alluvial plains deposits; therefore, compactation and chemical diagenesis processes were not inhibited and the transformation-dissolution of bones was favored in these rocks. The lack of vertebrates in syneruptive deposits (only microscopic bones have been found) could be explained as the consequence of recurrent pyroclastic falls that limited the formation of vegetated soils and consequently the number of living vertebrates. Finally, neither environmental nor diagenetic conditions would have been the best for vertebrates preservation during the early posteruptive stage. The extremely low agradational rate of the alluvial plain promoted the chemical, physical and biological alteration of bones. Moreover, early diagenetic cementation has not been identified in this interval; on the contrary, closed fabrics as well as pseudomatrix formation and autigenesis of clay minerals features were frequently found in these sandstones. In conclusion, the high bone concentration in some stratigraphic levels of the Cerro Barcino Fm results from the combination of favorable environmental conditions for life (reached during late posteruptive stage) coupled with early carbonatic cementation that closed the diagenetic system. <![CDATA[Grain-size analysis of down-river bottom sediments within the «Pampa Ondulada», Buenos Aires Province, Argentina]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1853-63602004000200003&lng=en&nrm=iso&tlng=en La dinámica de los procesos actuantes en la depositación de materiales en los lechos de los cursos de agua superficiales reviste importancia en los estudios ambientales ya que este compartimento puede ser el posible sumidero de contaminantes, actuando como agente de retención y/o de transporte. Este proceso está, a nivel inorgánico, fundamentalmente regulado por las propiedades físico-químicas de las partículas más finas. La permanencia de las mismas en suspensión posibilita una mayor dispersión de contaminantes hacia cursos colectores mayores, afectando la calidad ambiental de áreas más alejadas. Se estudiaron muestras de sedimentos de fondo de la cuenca inferior en siete de cursos de agua de la Pampa Ondulada (Arroyos del Medio, Ramallo, Tala, Arrecifes, Areco en el sector norte y Carnaval- Martín, del Gato y Pescado en el sector sur). El análisis granulométrico de los testigos (subdivididos en nivel superior e inferior) no mostró diferencias notables cuando se analizaron las medidas de tendencia central (media y mediana). Las medidas de dispersión (selección, asimetría y curtosis) en cambio son dispares. Resultan útiles, en especial, los diagramas C-M (primer percentil vs mediana). A través de estos parámetros se discriminaron dos tipos de cursos de agua con identidad propia por sus características texturales y procesos sedimentarios dominantes: los cursos de características netamente «fluviales» con subpoblaciones de tracción, saltación y suspensión (C muy distinto de M) que sugieren variaciones notables del régimen hidráulico en regiones de mayor pendiente regional, y los cursos de tipo fangoso (fracción limo dominante) y mejor seleccionados, con escasas variaciones en su régimen hidráulico (C muy parecido a M), donde los procesos de suspensión-decantación predominan sobre los de tracción en regiones de menor pendiente local. La procedencia de estos sedimentos se vincula, en el primer caso, a una mezcla de aportes de materiales producto de la erosión hídrica y eólica en cuencas extensas de la llanura pampeana, mientras que para el segundo caso, la procedencia es a partir de sedimentos (limos) eólicos escasamente retrabajados. Todas estas rocas sedimentarias se incluyen dentro del modelo de depositación del Loess Tipo Pampeano de edad cuaternaria tardía, acarreado por vientos derivados del campo de hielo de la Cordillera Patagónica al SW, que formaron un gran mar de arena y una faja de loess detrás. Las rocas fuentes de estos sedimentos son la Cordillera Andina y las Sierras Pampeanas.<hr/>The dynamics of bottom fluvial sediments play an important role in environmental studies, considering specially the fact that they may act as natural sinks of pollutants, and also as transporting agents. In this way, the transit of these finer sediments may result in a danger to the environmental quality of downcurrent areas of a basin. The size of the component particles is then, one of the fundamental textural characteristics of all fragmented deposits and their lithified equivalents (Passega, 1957, 1977, Day, 1965, Carver, 1971). In this contribution, bottom sediments sampled in equivalent distal positions of seven different fluvial basins of the Pampa Plains (Pampa Ondulada) of Argentina have been studied (Fig. 1). All the rivers flow from west to east within the Province of Buenos Aires reaching either the Paraná River or the Río de la Plata Estuary (Fidalgo and Martinez, 1983). Listed from north to south they are: del Medio, Ramallo, Tala, Arrecifes, Areco (northern sector) and Carnaval-Martín, del Gato and del Pescado (southern sector) (see also Fig. 2). Grain size determination of cores, taken at a water depth of 1 m in both margins, have been analysed (Fig. 3). The cores were divided in an upper layer (0-10 cm) and a lower layer (10-20 cm). Statistical parameters do not show large differences; the mean and the median are similar corresponding from coarse to very coarse silt (5-6 to 4-5 φ). In spite of this, most of the differences are shown in the percentile one (C) values (silts and sands), poor to moderate sorting (standard deviation), high kurtosis (concentration of peakness of the distribution) and positive skewness (Limarino and Martinez, 1992, Tripaldi, 2002) (Table 1). In this respect, the C-M diagram is specially usefull to discriminate different types of fluvial environments considering textural parameters and sedimentary procesess. From this diagram two types of rivers are recognized based on the characteristics of their bottom sediments (Figs. 4-6). River sandy bottom sediments with a tipically fluvial inprint, rolling-sliding, saltation and suspension populations are well defined (C different from M), suggesting important changes in the hydraulic regime. These rivers (del Medio, Arrecifes, Areco, Martín-Carnaval, and del Gato) are located within areas with stepper regional slopes and show complex provenance. In river silty bottom sediments that show finer textures, only well developed saltation and suspension populations are present (C similar to M), with moderate sorting, suggesting a steady flow and slow hidraulic regimes, where settling procesess dominate. These rivers (mainly del Tala, and some samples from Ramallo and del Pescado) are associated with areas with smaller local slopes and show generally a simple provenance. The provenance of these sediments is interpreted, in the former, as complex source produced by both water and wind erosion in an extense basins within the Pampa Plains, while in the latter, the source is poorly reworked eolian material (lime) (Ahlbrant, 1979, Pye, 1987, Bidart, 1992, 1996). All these sedimentary rocks are included within the depositional model of the Pampa Type Loess, where winds derived from the Patagonian ice field in the SE, during the Late Quaternary, formed a large sand sea and a loess belt behind it. The source rocks of these sediments are both the Andean Cordillera and the Pampean Range (Iriondo, 1987, Iriondo and Kröhling, 1996, Kröhling and Orfeo, 2002). <![CDATA[Sedimentologic aspects of eolian sands from the Late Pleistocene-Holocene of the La Pampa Province]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1853-63602004000200004&lng=en&nrm=iso&tlng=en El objetivo general de este trabajo es analizar la procedencia, génesis y dinámica de transporte de los depósitos eólicos arenosos del centro-este de la provincia de la Pampa. Para ello, se analizaron el marco geológico-geomorfológico y los aspectos estratigráficos de tres sectores considerados como sendos estudios de casos: cordón medanoso La Pastoril-Santa Isabel, cordón medanoso Toay y cordón medanoso General Acha. Estos cordones se caracterizaron sedimentológicamente (granulometría, mineralogía) a través del análisis de 20 muestras. Se identificaron dos unidades eólicas asociadas a dos ciclos de sedimentación, informalmente denominadas inferior (Pleistoceno tardío-Holoceno medio) y superior (originado por acción antrópica durante el siglo XX) relacionados con vientos del cuadrante O-NO en Santa Isabel y del S y SO en General Acha. Los resultados obtenidos sugieren que la topografía sería un factor de control importante en la distribución de los sedimentos, además de la distancia al sistema fluvial, que determinaría su tamaño de grano. Los análisis mineralógicos indicarían un aporte mixto de materiales, tanto distal (sistema fluvial del Bermejo-Desaguadero-Salado-Curacó), como local (afloramientos rocosos de la provincia).<hr/>The main goal of this paper is to analyze the provenience of sandy eolian deposits of the central eastern part of La Pampa Province. Considering present eolian models proposed by different authors, the hypothesis tested in this paper is that eolian sediments are the result of deflation of alluvial deposits from the Bermejo-Desaguadero-Salado-Curacó fluvial system. With this purpose in mind, three case studies were selected (La Pastoril-Santa Isabel, Toay and General Acha) (Fig. 1). The analysis was made following the concept of spatial scale hierarchy which considered the geological and general environmental setting of the studied areas along with fundamental geomorphological features of the analyzed dune systems. This was complemented by the stratigraphic survey of selected sections from which 20 samples were collected for sedimentological analysis (grain-size and mineralogy). Also, due to the lack of information, three samples were collected from the present Desaguadero fluvial system for general characterization. At the regional scale two main geoforms were identified: an extensive plain and the paleovalley of the Desaguadero fluvial system. The plain grades eastward and includes several longitudinal depressions (longitudinal valleys). A sandy silt mantle is covering the plain, whereas the main dune system is located along the longitudinal depressions and the Desaguadero paleovalley (Fig. 1). In the three studied areas two eolian units, informally named lower and upper, were identified. These units, separated by a buried soil, were generated by winds from the W-NW in Santa Isabel and from the S and SW in General Acha. Wind directions coincide with present wind systems. The upper part of the lower unit is modified by the development of a buried soil showing an A-C horizon sequence. This soil is only buried in areas deeply affected by anthropic activities. Away from these impacted settings, the soil is on the present groundsurface. In Toay, fossil remains of Megatherium americanum were exhumed from the lowermost part of the sampled section which together with regional evidences indicate a late Pleistocene-Holocene age to the lower eolian unit. The upper eolian unit is also restricted to areas deeply modified by human activities, where the vegetation cover was removed and the sediments exposed to eolian reactivation. The occurrence of cultural artifacts (pieces of wire fences, plastic bags) as well as written documents suggest that this eolian reactivation occurred during the XXth century. Based on the stratigraphic results, the sedimentolo-gical analysis was focused on the lower eolian unit. In all three areas the eolian sediments are medium to fine sands with unimodal distribution, transported in saltation and modified saltation or short term suspensions under relatively moderate to high wind shear velocities (Fig. 2; Tables 1 and 2). The most common light components are altered grains (24-56 %), quartz (14-36 %), K-feldspar (2-35 %), volcanic shards (3-23 %) and acid plagioclases (0.5-6 %) (Table 3). Microcline, complex pyroclast (crystals with glass edges) and lithics grains are present in low percentages (up to 3 %). A high percentage of heavy minerals (4.41-36.96 %), is present showing a high variable participation of each component (Table 4). Following the classification by Dott (1964) and modified by Pettijohn et al. (1972), the eolian sediments of Santa Isabel and General Acha may be considered as arkosic sands, those from Toay as lithic sands while the fluvial samples from Santa Isabel and Puelches can be considered as sublithic sands and lithic sands respectively (Fig. 3). However, due to the higher content of volcanic glass shards in most of the samples, the sediments were renamed considering this major component plus their alteration state. Consequently, the sedimentary material is classified as altered arkosic-vitric ash sands and altered lithic-vitric ash sand (Fig. 4). The mineral assemblages of the studied eolian sediments suggest mixed sources of materials, both from distal areas (the Bermejo-Desaguadero-Salado-Curacó fluvial system), and local areas (rock outcrops located in the central part of la Pampa Province). The high degree of roundness shown by the grains, indicates that the transported material was eroded and/or weathered prior to sedimentation, suggesting a policyclic process of reworking and subaereal exposure. Regionally, the areal distribution pattern of sandy eolian deposits with dominance of bedforms (dunes) along the depressions (longitudinal valleys) and paleovalley of the Desaguadero fluvial system suggest a topographic control in the spatial distribution of eolian facies. Likely, these topographic depressions, particularly the longitudinal valleys, acted as wind corridors. At the geographic scale analyzed, the working hypothesis tested oversimplified the complexity of the eolian system. <![CDATA[Enfoque multidisciplinario aplicado al estudio del Paleoceno Inferior del bosque José Ormaechea, Chubut, Argentina]]> http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S1853-63602004000200005&lng=en&nrm=iso&tlng=en El objetivo general de este trabajo es analizar la procedencia, génesis y dinámica de transporte de los depósitos eólicos arenosos del centro-este de la provincia de la Pampa. Para ello, se analizaron el marco geológico-geomorfológico y los aspectos estratigráficos de tres sectores considerados como sendos estudios de casos: cordón medanoso La Pastoril-Santa Isabel, cordón medanoso Toay y cordón medanoso General Acha. Estos cordones se caracterizaron sedimentológicamente (granulometría, mineralogía) a través del análisis de 20 muestras. Se identificaron dos unidades eólicas asociadas a dos ciclos de sedimentación, informalmente denominadas inferior (Pleistoceno tardío-Holoceno medio) y superior (originado por acción antrópica durante el siglo XX) relacionados con vientos del cuadrante O-NO en Santa Isabel y del S y SO en General Acha. Los resultados obtenidos sugieren que la topografía sería un factor de control importante en la distribución de los sedimentos, además de la distancia al sistema fluvial, que determinaría su tamaño de grano. Los análisis mineralógicos indicarían un aporte mixto de materiales, tanto distal (sistema fluvial del Bermejo-Desaguadero-Salado-Curacó), como local (afloramientos rocosos de la provincia).<hr/>The main goal of this paper is to analyze the provenience of sandy eolian deposits of the central eastern part of La Pampa Province. Considering present eolian models proposed by different authors, the hypothesis tested in this paper is that eolian sediments are the result of deflation of alluvial deposits from the Bermejo-Desaguadero-Salado-Curacó fluvial system. With this purpose in mind, three case studies were selected (La Pastoril-Santa Isabel, Toay and General Acha) (Fig. 1). The analysis was made following the concept of spatial scale hierarchy which considered the geological and general environmental setting of the studied areas along with fundamental geomorphological features of the analyzed dune systems. This was complemented by the stratigraphic survey of selected sections from which 20 samples were collected for sedimentological analysis (grain-size and mineralogy). Also, due to the lack of information, three samples were collected from the present Desaguadero fluvial system for general characterization. At the regional scale two main geoforms were identified: an extensive plain and the paleovalley of the Desaguadero fluvial system. The plain grades eastward and includes several longitudinal depressions (longitudinal valleys). A sandy silt mantle is covering the plain, whereas the main dune system is located along the longitudinal depressions and the Desaguadero paleovalley (Fig. 1). In the three studied areas two eolian units, informally named lower and upper, were identified. These units, separated by a buried soil, were generated by winds from the W-NW in Santa Isabel and from the S and SW in General Acha. Wind directions coincide with present wind systems. The upper part of the lower unit is modified by the development of a buried soil showing an A-C horizon sequence. This soil is only buried in areas deeply affected by anthropic activities. Away from these impacted settings, the soil is on the present groundsurface. In Toay, fossil remains of Megatherium americanum were exhumed from the lowermost part of the sampled section which together with regional evidences indicate a late Pleistocene-Holocene age to the lower eolian unit. The upper eolian unit is also restricted to areas deeply modified by human activities, where the vegetation cover was removed and the sediments exposed to eolian reactivation. The occurrence of cultural artifacts (pieces of wire fences, plastic bags) as well as written documents suggest that this eolian reactivation occurred during the XXth century. Based on the stratigraphic results, the sedimentolo-gical analysis was focused on the lower eolian unit. In all three areas the eolian sediments are medium to fine sands with unimodal distribution, transported in saltation and modified saltation or short term suspensions under relatively moderate to high wind shear velocities (Fig. 2; Tables 1 and 2). The most common light components are altered grains (24-56 %), quartz (14-36 %), K-feldspar (2-35 %), volcanic shards (3-23 %) and acid plagioclases (0.5-6 %) (Table 3). Microcline, complex pyroclast (crystals with glass edges) and lithics grains are present in low percentages (up to 3 %). A high percentage of heavy minerals (4.41-36.96 %), is present showing a high variable participation of each component (Table 4). Following the classification by Dott (1964) and modified by Pettijohn et al. (1972), the eolian sediments of Santa Isabel and General Acha may be considered as arkosic sands, those from Toay as lithic sands while the fluvial samples from Santa Isabel and Puelches can be considered as sublithic sands and lithic sands respectively (Fig. 3). However, due to the higher content of volcanic glass shards in most of the samples, the sediments were renamed considering this major component plus their alteration state. Consequently, the sedimentary material is classified as altered arkosic-vitric ash sands and altered lithic-vitric ash sand (Fig. 4). The mineral assemblages of the studied eolian sediments suggest mixed sources of materials, both from distal areas (the Bermejo-Desaguadero-Salado-Curacó fluvial system), and local areas (rock outcrops located in the central part of la Pampa Province). The high degree of roundness shown by the grains, indicates that the transported material was eroded and/or weathered prior to sedimentation, suggesting a policyclic process of reworking and subaereal exposure. Regionally, the areal distribution pattern of sandy eolian deposits with dominance of bedforms (dunes) along the depressions (longitudinal valleys) and paleovalley of the Desaguadero fluvial system suggest a topographic control in the spatial distribution of eolian facies. Likely, these topographic depressions, particularly the longitudinal valleys, acted as wind corridors. At the geographic scale analyzed, the working hypothesis tested oversimplified the complexity of the eolian system.