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1.
The southern Central Andes of Argentina and Chile (27–40°S) are the product of deformation, arc magmatism, and basin evolution above a long-lived subduction system. With sufficient timing and provenance constraints, Andean stratigraphic and structural records enable delineation of Mesozoic-Cenozoic variations in subsidence and tectonic regime. For the La Ramada Basin in the High Andes at ∼31–33°S, new assessments of provenance and depositional age provided by detrital zircon U-Pb geochronology help resolve deformational patterns and subsidence mechanisms over the past ∼200 Myr. Marine and nonmarine clastic deposits recorded the unroofing of basin margins and sediment contributions from the Andean magmatic arc during Late Triassic to Early Cretaceous extension, thermal subsidence, and possible slab rollback. Subsequent sediment delivery from the Coastal Cordillera corresponded with initial flexural accommodation in the La Ramada Basin during Andean shortening of late Early Cretaceous to Late Cretaceous age. The architecture of the foreland basin was influenced by the distribution of precursor extensional depocenters, suggesting that inherited basin geometries provided important controls on later flexural subsidence and basin evolution. Following latest Cretaceous to early Paleogene tectonic quiescence and a depositional hiatus, newly dated deposits in the western La Ramada Basin provide evidence for a late Paleogene episode of intra-arc and proximal retroarc extension (development of the Abanico Basin, principally in Chile, at ∼28–44°S). Inversion of this late Paleogene extensional basin system during Neogene compression indicates the southern Central Andes were produced by at least two punctuated episodes of shortening and uplift of Late Cretaceous and Neogene age.  相似文献   
2.
This work is part of a project aimed to the development and application of hydrogeological, hydrogeochemical and geological methodologies for the study of the geothermal system of Rosario de La Frontera (NW Argentina).The surface thermal manifestations of this area, whose temperatures range from 22.6 to 92.6 °C, are mainly located in the northern sector of Sierra de la Candelaria anticline. This regional structure crops out between the provinces of Salta and Tucuman (NW Argentina), at the foothills of the central Andean retro-wedge.The present investigation focuses on hydrogeological and structural data, and isotopic compositions (18O, D and 3H) of thermal springs.Preliminary results allowed to define: i) the meteoric origin of spring water and their long (more than 50 years) residence time at depth, ii) a positive water balance, ranging between 2 and 4 millions of m3/yr, and iii) a conservative geothermal reservoir volume of about 39 km3, iv) a geothermal potential with Er = 5.6*1018 J and Ef = 0.8*1018 J.  相似文献   
3.
An understanding of paleonvironmental and paleoceanographic evolution of the Southwestern Atlantic Ocean during the Palaeogene is prevented by the lack of precise tools to date and correlate the sedimentary units. Palynological samples collected in the upper portion of the Man Aike Formation, which crops out southern Lago Argentino area, in the southwest of the Austral Basin (50°21′45″S–72°14′30″W), contain well preserved marine organic dinoflagellate cysts, which are potentially important biostratigraphic and paleoenvironmental indicators. Herein we describe the composition of the Man Aike Formation's dinoflagellate cyst assemblages and compare them to similar assemblages collected in the same basin in the upper member of the Río Turbio Formation using Compositional Statistical Analysis. The dinoflagellate cyst assemblages from the upper part of the Man Aike Formation are highly correlated to the assemblages from the upper member of the Río Turbio Formation from outcropping sections (51°31′13″S–72°15′11″W) and with the lower part of sediment cores drilled by Yacimientos Carboníferos Fiscales in the Río Turbio Formation area. These dinoflagellate cyst assemblages show a very low correlation with the assemblages from the upper part of the Yacimientos Carboníferos Fiscales's cores. The comparison of our results with the high-resolution Southern Pacific Ocean dinoflagellate cyst zonation for the late Palaeocene to late Eocene allow us to date some of the dinoflagellate events recorded in formations of southwestern Patagonia. The assemblages from the Man Aike Formation and the lower part of the upper member of the Río Turbio Formation relate to the zones SPDZ11 and SPDZ12 and are assigned to the mid-middle Eocene (late Lutetian to early Bartonian). The biostratigraphy proposed herein constrains the age of the Man Aike Formation and equivalent units based on calcareous microfossil data, mollusks affinities and 87Sr/86Sr isotopic values to an age ranging between ∼42 and 39 Ma. The assemblages from the upper part of the upper member of the Río Turbio Formation relate to the SPDZ13 Zone, which corresponds to the late Eocene (early Priabonian). The dinoflagellate cyst assemblages indicate that they were under the influence of relatively warm, marine open waters in an inner-shelf environment for the lower part of the sections. In the upper part of the sections, the assemblages suggest shallow marine waters associated with coastal areas and high trophic levels, possibly as a result of freshwater inputs.  相似文献   
4.
The upper cliff of the Santa Cruz River was used to assess the proglacial environments of the Argentino Glacier outlet of Late Pleistocene age. These cliffs show glaciolacustrine, fluvioglacial and till deposits, where only the first one are deformed. Glacial landforms in the area and these structures suggest that the ice mass advanced, topographically controlled, towards the east from the Patagonian Ice Sheet pushing up the proglacial sediments.The spatial arrangement of thrusts and overturned folds, the drumlins-flutes moraine directions and the end moraines shape, allow inferring the dynamic and the Argentino glacier profile. Detailed analyses of the glaciotectonic structures indicate that these have two origins: load in the north with stress transfer to the southeast, and push from the west. Through the analysis of deformed sediments, their thickness and their sedimentary and structural features, three zones of deformations were recognized. Each of these zones was associated to glacial advances because of changes of the regional climate conditions.  相似文献   
5.
This paper analyses the diagenetic evolution of sandstones belonging to the Bajo Barreal Formation (Cretaceous) in the Golfo de San Jorge Basin (Patagonia, Argentina). The Bajo Barreal Formation includes the main reservoirs, which are located along the western area of the basin and is composed of sandstones, conglomerates, mudstones, tuffaceous mudstones and some layers of tuffs. The principal reservoirs comprise medium-to coarse-grained sandstones, which are dominated by feldspathic litharenites and contain minor amounts of litharenites and lithic arkoses. The authigenic minerals include kaolinite, smectite, chlorite, quartz overgrowths, microquartz and calcite, with minor proportions of megaquartz, siderite, analcime, laumontite, feldspar overgrowths and illite/smectite and chlorite/smectite mixed layers. Secondary porosity is much more important than primary porosity and is produced by the dissolution of feldspar, lithic clasts and clay cements. The diagenetic history of the Bajo Barreal sandstones can be divided into seven diagenetic stages, each of which is characterized by a specific assemblage of authigenic minerals and diagenetic processes. Eogenetic conditions occur in stages 1, 2, 3 and 4. Stage 1 corresponds to shallow burial characterized by the physical reduction of primary porosity by compaction; during stage 2, rim clay cements of chlorite, smectite and clinoptilolite, as well as thin quartz overgrowths, were formed. The precipitation of pore-filling cements of kaolinite, chlorite and smectite occurred during stage 3, while stage 4 records the intense dissolution of feldspar, lithic fragments and kaolinite cements. Mesogenesis occurs in diagenetic stages 5 and 6. The former corresponds to a new phase of authigenic kaolinite, while the latter records the significant dissolution of feldspar, lithic clasts and previous cements, which produced the highest values of secondary porosity. Finally, stage 7 corresponds to the highest degree of diagenesis in the Bajo Barreal Formation (mesogenesis), which resulted in the precipitation of cements of zeolites and calcite, as well as quartz and plagioclase overgrowths.  相似文献   
6.
The first Podocarpaceae wood record is described from the Mulichinco Formation (Valanginian, Lower Cretaceous), Neuquén Basin, Argentina. The specimen was directly associated with a middle caudal vertebra of a diplodocid sauropod dinosaur. A new species – Podocarpoxylon prumnopityoides – is proposed based on features that include the presence of abietinean wood type (tracheid radial pitting), plus podocarpoid (cupressoid type) and some dacrydioid (taxodioid type) cross-field pits, diffuse axial parenchyma and low rays. This combination of anatomical characters is comparable to both Prumnopitys and Podocarpus, whereas the type of pits in the cross-fields resembles some members of the extant Prumnopitys. This is the first unequivocal record of the Family Podocarpaceae in the Valanginian of South America and confirms the hypothesis that the divergence between the “Podocarpoid-Dacrydioid” and “Prumnopityoid” clades occurred earlier than the Early Cretaceous.  相似文献   
7.
The Early Cretaceous (∼135–131 Ma) Paraná-Etendeka continental flood basalts, preserved in bulk in the Paraná basin of southern Brazil and vicinity, have been divided into low-Ti and high-Ti types that govern the southern and northern halves of the basin, respectively. We have examined a new sample set from the southern margin of the northern high-Ti segment of Paraná basalts in Misiones, northeastern Argentina. These basalts are strongly to moderately enriched in TiO2 (2–4 wt.%), have relatively high Ti/Y (300–500), low MgO (3.5–6.5 wt.%), and high Fe (FeO(tot) 12–14 wt.%) and belong to the Pitanga and Paranapanema magma types of Peate et al. (1992). Nd and Sr isotope compositions are quite unvarying with εNd (at 133 Ma) values of −4.6 to −3.6 and initial 87Sr/86Sr of 0.7054–0.7059 and show no variation with fractionation. Compared to high-Ti lavas in the central and northern parts of the Paraná high-Ti basalt segment, the lavas from Misiones are similar to those in the northeastern magin of the basin but less radiogenic in initial Nd isotope composition than those in the central part. This variation probably reflects mixed EM1-EM2 source components in the sublithospheric mantle. A polybaric melt model of a sublithospheric mantle source at the garnet lherzolite-spinel lherzolite transition is compatible with the observed Ti budget of the Pitanga and Paranapanema lavas, regardless of the Nd isotope composition of their purported source.  相似文献   
8.
The alluvial architecture of fine‐grained (silt‐bed) meandering rivers remains poorly understood in comparison to the extensive study given to sand‐bed and gravel‐bed channels. This paucity of knowledge stems, in part, from the difficulty of studying such modern rivers and deriving analogue information from which to inform facies models for ancient sediments. This paper employs a new technique, the parametric echosounder, to quantify the subsurface structure of the Río Bermejo, Argentina, which is a predominantly silt‐bed river with a large suspended sediment load. These results show that the parametric echosounder can provide high‐resolution (decimetre) subsurface imaging from fine‐grained rivers that is equivalent to the more commonly used ground‐penetrating radar that has been shown to work well in coarser‐grained rivers. Analysis of the data reveals that the alluvial architecture of the Río Bermejo is characterized by large‐scale inclined heterolithic stratification generated by point‐bar evolution, and associated large‐scale scour surfaces that result from channel migration. The small‐scale and medium‐scale structure of the sedimentary architecture is generated by vertical accretion deposits, bed sets associated with small bars, dunes and climbing ripples and the cut and fill from small cross‐bar channels. This style of alluvial architecture is very different from other modern fine‐grained rivers reported in the literature that emphasize the presence of oblique accretion. The Río Bermejo differs from these other rivers because it is much more active, with very high rates of bank erosion and channel migration. Modern examples of this type of highly active fine‐grained river have been reported rarely in the literature, although ancient examples are more prevalent and show similarities with the alluvial architecture of the Río Bermejo, which thus represents a useful analogue for their identification and interpretation. Although the full spectrum of the sedimentology of fine‐grained rivers has yet to be revealed, meandering rivers dominated by lateral or oblique accretion probably represent end members of such channels, with the specific style of sedimentation being controlled by grain size and sediment load characteristics.  相似文献   
9.
中国地质调查局与阿根廷地质矿产调查局合作在阿根廷西北部米纳毕戈塔地区进行1︰25万水系沉积物测量,该区属于干旱-半干旱高寒山区,为突出找矿效果,消除或减少风积物干扰,需要确定适合于该区的水系沉积物采样粒度。为此,在该区选择一个有已知矿床的1︰5万图幅进行采样粒度试验,分别选择10~60目、-60目、60~80目、-80目4个粒度级进行粒度试验;根据我国区域地球化学勘查规范,每个粒度分析39种元素。结果表明,大部分元素在4种粒度水系沉积物中的分布形态基本一致,都能够较好地反映出区内已知矿床,说明采用的采样方法可以有效地避免风成砂干扰;金、银、铜、锡等成矿元素在4种粒度中的分布略有差异,10~60目的金、铜和锡异常对已知矿体的反应更清晰准确。因此,本区水系沉积物地球化学测量的最佳采样粒度是10~60目。根据本次试验结果,中-阿地调局在本区联合开展1︰25万水系沉积物地球化学测量时采用了10~60目水系沉积物作为采样介质,取得了很好的效果。这是本区第一次进行水系沉积粒度试验,对本区将来的地球化学调查和研究具有指导意义。  相似文献   
10.
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   
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