Vertebrate tracks from the Paso Córdoba fossiliferous site (Anacleto and Allen formations,Upper Cretaceous), Northern Patagonia,Argentina: Preservational,environmental and palaeobiological implications     

《Cretaceous Research》2018

The Paso Córdoba fossiliferous site (Río Negro, Northern Patagonia) is one of the first Mesozoic fossiliferous localities studied in Argentina. There, turtle, crocodile and dinosaur remains as well as dinosaur and bird tracks have been recorded. Recently, a new locality with vertebrate tracks, the Cañadón del Desvío, has been discovered in Paso Córdoba. Six track-bearing layers were located in outcrops belonging to the Anacleto (lower to middle Campanian, Neuquén Group) and Allen (middle Campanian-lower Maastrichtian, Malargüe Group) formations. The Cañadón del Desvío locality reveals that vertebrate trace fossils are distributed in two distinct environments, floodplains of a meandering fluvial to shallow lacustrine system and a wet interdune deposit that is associated to an aeolian setting. Also, in the logged section several soft sediment deformation structures were found. In regard of this, a sedimentary facies analysis is provided in order to assess the palaeoenvironmental implications of this new record. The analysed tracks are preserved in cross-sections, on bedding-planes and as natural casts. When it is possible, the tracking surface, true tracks, undertracks and overtracks/natural casts have been identified and the track preservation and the formation history of the tracksite are discussed. Only two tracks preserve enough anatomical details to relate them with their trackmakers, in this case hadrosaurid dinosaurs. The stratigraphical, facial and palaeoenvironmental data of this study support the idea of a transitional passage between the Anacleto and Allen Formation in Paso Córdoba. The presence of hadrosaurid dinosaur tracks suggests that the upper part of the log, where this kind of tracks were found, likely belong to Allen Formation due to this dinosaurs appear in the Southern Hemisphere in this epoch. The sum of osteological and ichnological remains improve the Paso Córdoba palaeofaunistic knowledge. The presence of six different levels in which the trackmakers walked reflects the abundance of vertebrates in the transition between Anacleto and Allen formations.  相似文献   

Geochemistry of waters and brines from the Salinas Grandes basin,Córdoba,Argentina. I. Geomorphology and hydrochemical characteristics     

R. M. Dargám 《International Journal of Salt Lake Research》1994,3(2):137-158

This paper reports on hydrochemical features of diluted waters in the source areas and the brine end-members dominant in the playa of the Salinas Grandes Basin, Córdoba, Argentina. Special emphasis was placed on the study of the relationship between geomorphology and the resulting hydrochemical fractionation. Inflow is from springs and mountain streams which disappear before reaching the saline complex. The playa and intermittent saline lakes are mainly fed by groundwater flow and a few moderately saline and perennial springs. Conversely, ephemeral lakes are fed by atmospheric precipitation and groundwater, whereas small ponds are only fed by atmospheric precipitation. The absence of a clear linkage between geomorphological units and water types was evident in the source areas. Up to four types of water were recognized in a given geomorphological unit. From the sandflat downward towards the playa, the correspondence between geomorphological units and water types was clear, coinciding with a decreased hydrochemical heterogeneity. In this subenvironment, I have recognized two dominant types of water (SO ₄ ^2– –Cl^––HCO ₃ ^– –Na⁺ and Cl^––SO ₄ ^2– –HCO ₃ ^– –Na⁺), which can be considered the original members of the neutral brine in the playa (Cl^––SO ₄ ^2– –Na⁺ where Ca²⁺+Mg²⁺ do not surpass 5 meq per cent), and an intermediate type in the mudflat (Cl^––SO ₄ ^2– –Na⁺ where the contribution of Ca²⁺+Mg²⁺ reaches up to 15 meq per cent). It seems evident that in the zone between the source areas and the sandflat, hydrochemistry is governed by chemical weathering. In stream floodplains and in the distal alluvial plain, close to the saline complex, the increase in water types as well as the increase of HCO ₃ ^– with respect to SO ₄ ^2– , were explained by the mixture of aquifers controlled by the Salinas Grandes-Salinas de Ambargasta fracture. In the saline complex, the more concentrated end-members are the result of evaporation of the two more frequent water-types in the sandflat subenvironment, and salt dissolution of ancient evaporite deposit.  相似文献   

Changes in the ionic composition of a saline lake,Mar Chiquita,Province of Córdoba,Argentina     

D. E. Martinez 《International Journal of Salt Lake Research》1995,4(1):25-44

Mar Chiquita is the largest water-body in Argentina according to area. This ranges from 2,000 km² in dry periods to 5,000 km² in humid ones. Its very high salinity ranged this century from 200 to 300 g/L, but an increase in the average rainfall in the basin since 1973 has led to a rise in lake level and the dilution of its waters to 78 g/L in 1978 and about 30 g/L in the late 1980s. Ionic strength decreased from 6.61 in 1970 to 0.541 in 1986. The composition of the water also changed, with increases in the proportions of sulphate, calcium and magnesium concentrations. The most important processes taking place in solution are calcite and gypsum equilibrium, formation of clay minerals, and sulphate reduction in the interstitial waters of the bottom sediments. The thermodynamic state of the solutions for different years has been obtained. Results show that the solution shifted from gypsum oversaturation in 1970 to gypsum equilibrium in 1978, and to gypsum undersaturation since 1982. A geochemical simulation of the composition of the solution from its origin from mean tributary composition, following a modified Hardie-Eugster model, has been developed using PHRQPITZ. The results agree with empirical observations.  相似文献   

Post glacial lacustrine event sedimentation in an ancient mountain setting: Carboniferous Lake Malanzán (Western Argentina)     

Luis Alberto Buatois  Maria Gabriela Mángano 《Journal of Paleolimnology》1995,14(1):1-22

Lacustrine deposits of the Malanzán Formation record sedimentation in a small and narrow mountain paleovalley. Lake Malanzán was one of several water bodies formed in the Paganzo Basin during the Late Carboniferous deglaciation. Five sedimentary facies have been recognized. Facies A (Dropstones-bearing laminated mudstones) records deposition from suspension fall-out and probably underflow currents coupled with ice-rafting processes in a basin lake setting. Facies B (Ripple cross-laminated sandstones and siltstones) was deposited from low density turbidity currents in a lobe fringe environment. Facies C (Massive or graded sandstones) is thought to represent sedimentation from high and low density turbidity currents in sand lobes. Facies D (Folded sandstones and siltstones) was formed from slumping in proximal lobe environments. Facies E (Wave-rippled sandstones) records wave reworking of sands supplied by turbidity currents above wave base level.The Lake Malanzán succession is formed by stacked turbidite sand lobe deposits. These lobes were probably formed in proximal lacustrine settings, most likely relatively high gradient slopes. Paleocurrents indicate a dominant direction from cratonic areas to the WSW. Although the overall sequence shows a regressive trend from basin fine-grained deposits to deltaic and braided fluvial facies, individual lobe packages lack of definite vertical trends in bed thickness and grain size. This fact suggests aggradation from multiple-point sources, rather than progradation from single-point sources. Sedimentologic and paleoecologic evidence indicate high depositional rate and sediment supply. Deposition within the lake was largely dominated by event sedimentation. Low diversity trace fossil assemblages of opportunistic invertebrates indicate recolonization of event beds under stressed conditions.Three stages of lake evolutionary history have been distinguished. The vertical replacement of braided fluvial deposits by basinal facies indicates high subsidence and a lacustrine transgressive episode. This flooding event was probably linked to a notable base level rise during postglacial times. The second evolutionary stage was typified by the formation of sand turbidite lobes from downslope mass-movements. Lake history culminates with the progradation of deltaic and braided fluvial systems  相似文献   

Cosmogenic nuclide measurements in southernmost South America and implications for landscape change     

M.R. Kaplan  A. Coronato  N.R.J. Hulton  J.O. Rabassa  P.W. Kubik  S.P.H.T. Freeman 《Geomorphology》2007,87(4):284-301

We measured in situ ¹⁰Be, ²⁶Al and³⁶Cl on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand boulder and moraine and, by inference, landscape changes. Nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraine ages are themselves constrained by previously obtained ⁴⁰Ar/³⁹Ar ages on interbedded lava flows or U-series and amino acid measurements on related (non-glacial) marine deposits. We suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories, despite the fact that some moraine landforms are demonstrably 1 Myr old. We hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials. Comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi-arid Patagonia imply different geomorphic processes operating in southernmost South America. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter.  相似文献   

Factors affecting arsenic concentration in groundwaters from Northwestern Chaco-Pampean Plain,Argentina     

María Gabriela García  Ondra Sracek  Diego Sebastián Fernández  Margarita del Valle Hidalgo 《Environmental Geology》2007,52(7):1261-1275

The concentration of arsenic measured in groundwater from three aquifers in the study area located in the Eastern Tucuman province, Argentina, mostly depends on the lithology, but the spatial and temporal variations of concentrations seem to be also controlled by pH changes, climatic factors, and human perturbations. The highest concentrations of As (more than 1,000 μg L⁻¹) were found in the shallow aquifer, made of As-rich loess, while the lowest concentrations were measured in the deep confined aquifer, consisting of alternating layers of alluvial sands/gravels and clays. Intermediate values were measured in the semiconfined aquifer made of the fluvial sediments deposited in the Salí River valley, that alternate in the upper part of the sedimentary sequence with layers of loess. Because most of As in the loess is considered to be adsorbed onto Fe-oxyhydroxide coatings, the increase of pH in the flow direction (west-east) leads to increasing arsenic concentrations towards the eastern border of the study area. The decomposition of organic wastes poured into the Salí River or associated with local and diffuse sources of contamination in the eastern part of the study area depletes dissolved oxygen, which leads to the reductive dissolution of Fe and Mn oxyhydroxides, and to the subsequent release of the adsorbed and co-precipitated As. This process mainly affects shallow groundwater and the upper part of the semiconfined aquifer. Geochemical and hydrological data also suggest that rising water table levels at the end of the wet season may also lead to reductive dissolution of As-rich Fe oxyhydroxides in the shallow aquifer.  相似文献   

Coastal processes and environmental hazards: the Buenos Aires (Argentina) and Venetian (Italy) littorals   总被引：1，自引：0，他引：1  

Jorge Pousa  Luigi Tosi  Eduardo Kruse  Dardo Guaraglia  Maurizio Bonardi  Andrea Mazzoldi  Federica Rizzetto  Enrique Schnack 《Environmental Geology》2007,51(8):1307-1316

The Buenos Aires (Argentina) and Venice (Italy) coastlands have experienced significant saltwater contamination of the phreatic aquifer, coastal erosion, hydrodynamic changes and relative sea level rise processes due to natural and man-induced factors. These factors expose coastal areas to morpho-hydro-geological hazards, such as soil desertification, frequency and degree of flooding, littoral erosion, and the silting of river mouths and channels. Man-made interventions and actions, such as beach mining, construction of coastal structures and exploitation of aquifers without an adequate knowledge of the hydrology setting and an adequate management program, worsen these natural hazards. Uncontrolled human activity induces environmental damage to the overall coastal plains. The coastal plains play an important role in the social/economic development of the two regions based on land use, such as agriculture, horticulture, breeding, and tourism, as well as industry. Results of investigations on saltwater contamination, sea level rise and morphological changes recently performed in these two coastal areas are presented here.  相似文献   

Groundwater contamination: risk management and assessment for landfills in Mar del Plata, Argentina   总被引：3，自引：0，他引：3  

E. Bocanegra  H. Massone  D. Martínez  E. Civit  M. Farenga 《Environmental Geology》2001,40(6):732-741

 This study presents a program for risk management in the contamination of groundwater resulting from leachate in landfills at Mar del Plata (Argentina). The program includes prediction, prevention, monitory observation and mitigation as actions that must be taken prior to, during, and after contamination occurs. This routine aids in the identification of weak points and failures of the program for those who are in charge of making decisions, and will allow better use of limited financial and technical resources based on planning, thus minimizing disconnected determinations. Results of the prediction stage were confirmed through monitoring. The presence of a plume of contamination more than 100 m from the landfill was shown, thus proving that implementation of a monitoring plan to follow the development of the contaminated plume must be implemented, particularly in populated areas which depend on residential wells for their water supply. Received: 8 May 2000 · Accepted: 14 August 2000  相似文献   

Geochemistry of groundwater in the alluvial plain of Tucumán province, Argentina   总被引：3，自引：0，他引：3  

Gabriela M. García  Margarita del V. Hidalgo  Miguel A. Blesa 《Hydrogeology Journal》2001,9(6):597-610

The Salí River hydrogeological basin is one of the most productive artesian basins in Argentina. It is located in the southeastern part of the province of Tucumán, northwestern Argentina, and its groundwater resources are developed for water supply and irrigation. The chemical composition of the water is strongly influenced by the interaction with the basinal sediments and by hydrologic characteristics such as the flow pattern and time of residence. Three hydrochemical zones are defined in the study area and the processes that control the chemical composition of the water are manifestly different in each zone. The dissolution of halite, sodium sulphate, and gypsum explains part of the contained Na⁺, K⁺, Cl^–, SO₄ ^2–, and Ca²⁺, but other processes, such as cation exchange, calcite precipitation, weathering of aluminosilicates, and gas exchange with the atmosphere, also contribute to the water composition. The assessment of contamination indicators, such as pH, dissolved organic matter, dissolved oxygen, phosphate, and nitrate, indicates that the groundwater is suitable for human consumption. However, biological contamination has been detected in samples from some wells, especially those near the Salí River. Electronic Publication  相似文献   

Lateral heterogeneities in the upper and mid-mantle conductivity in Argentina     

Ana Osella  Alicia Favetto  Patricia Martinelli 《Pure and Applied Geophysics》1993,141(1):139-156

Regional studies of Sq variations measured at five permanent observatories in Argentina were performed to estimate the distribution of the electrical conductivity of the upper and mid-mantle, reaching a depth of approximately 800 km. After separating the total field into its parts of external and internal origin, the in duced field was modeled, applying two-dimensional techniques. Additionally, induction arrows and an equivalent apparent resistivity curve were calculated A north-south heterogeneity was detected, showing an increase of the conductivity of the shallower layers north of the profile, which may be related to the presence of high volcanic activity in the area.Also at CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas).  相似文献