Cuencas triásicas del Oeste argentino: origen y evolución

The Triassic basins of western Argentina and northern Patagonia are located along fhe Pacific margin of Southwest Gondwana. They are narrow and elongated depressions oriented NW-SE, floored by a thick continental crust composed of Precarnbrian and Lower Palaeozoic magmatic rocks, and an Upper Palaeozoic plutonic-volcanic complex (Gondwana Magmatism). These basins are associated with the Choiyoi Magmatic Province, the Central Patagonian Batholith and the Comallo Volcanic Complex. For the Triassic of western Argentina the following stages are recognised: Barrealian (Early to Mid Triassic), Cortaderitian (Mid to early Late Triassic) and Florian (Late Triassic). During the Barrealian severa1 passive rfts are opened (Ischigualasto - Villa Unión, Marayes, Las Salinas - Beazley, Cuyo and the short-lived San Rafael basins). They are characterised by a synrift phase related to the activity of the main fracture systems along the active flank of the half-grabens, high accommodation space and frequent coarsegrained sediment supply (usually vocaniclastic) from the active margins. Intercalations of basic lava flows are common. In the Cortaderitian protracted extension, maximum regional development of the Triassic bgsins occurred. Most basins were controlled by thermal-tectonic subsidence. High accommodation space, limited coarse-grained cbntributions and high lacustrine base levels are the more characteristic conditions for basin sedimentary infill. In the Florian stagelthe Ischigualasto-Villa Unión, the Marayes and the Cuyo basins are characterised by fluvial-dominated red-bed successions, related to a transtensional stage of evolution. Several half-grabens (Malargüe, Paso Flores and Chacaico) are opened as precursors of the Neuquén Basin. In northwestern Patagonia, the combInation between regional strike-slip displacement along the Gastre Fault System and protopacific subduction, causes the development of the arc magmatism represented by the Central Patagonian Batholith and the thick volcano-sedimentary Comallo complex

The Cambrian-Ordovician siliciclastic platform of the Balcarce Formation (Tandilia System, Argentina) : Facies, trace fossils, palaeoenvironments and sequence stratigraphy

The Lower Palaeozoic sedimentary cover of the Tandilia (Balcarce Formation) is made up of thick quartz arenite beds together with kaolinitic claystones and thin fine-grained conglomerates. The Balcarce Formation was formed in the nearshore and inner shelf environments of a tide-dominated and storm influenced open platform. It shows many features suggesting tidal sedimentation. Coarse-grained facies were formed by sand bar migration and accretion. Heterolithic packages are interpreted as interbar (swale) deposits. Subordinated HCS sandstones indicate storm events. The recognition of thick progradational clinoforms allows to confirm that the Balcarce sea was open to the south, as suggested years ago through palaeocurrent interpretation. The great abundance and variety of trace fossils is among the most outstanding characteristics of this unit. The ichnotaxa that have been recognised so far are: Ancorichnus ancorichnus, Arthrophycus alleghaniensis, Arthrophycus isp., Bergaueria isp., Cochlichnus isp., Conostichus isp., Cruziana furcifera, Cruziana isp., Daedalus labeckei, Didymaulichnus lyelli, Didymaulichnus isp., Diplichnites isp., Diplocraterion isp., Herradurichnus scagliai, ?Monocraterion isp., Monomorphichnus isp., Palaeophycus alternatus, Palaeophycus tubularis, Palaeophycus isp., Phycodes aff. pedum, Phycodes isp., Plagiogmus isp., Planolites isp., Rusophycus isp., Scolicia isp. and Teichichnus isp. Trace fossils have traditionally been used to assign the Balcarce Formation to the Lower Ordovician, due to the presence of Cruziana furcifera. However, Plagiogmus is typical of Cambrian successions world-wide

Quantitative Kinematic Characterization of Reaching Impairments in Mice After a Stroke

Background and Objective. Kinematic analysis of reaching movements is increasingly used to evaluate upper extremity function after cerebrovascular insults in humans and has also been applied to rodent models. Such analyses can require time-consuming frame-by-frame inspections and are affected by the experimenter's bias. In this study, we introduce a semi-automated algorithm for tracking forepaw movements in mice. This methodology allows us to calculate several kinematic measures for the quantitative assessment of performance in a skilled reaching task before and after a focal cortical stroke. Methods. Mice were trained to reach for food pellets with their preferred paw until asymptotic performance was achieved. Photothrombosis was then applied to induce a focal ischemic injury in the motor cortex, contralateral to the trained limb. Mice were tested again once a week for 30 days. A high frame rate camera was used to record the movements of the paw, which was painted with a nontoxic dye. An algorithm was then applied off-line to track the trajectories and to compute kinematic measures for motor performance evaluation. Results. The tracking algorithm proved to be fast, accurate, and robust. A number of kinematic measures were identified as sensitive indicators of poststroke modifications. Based on end-point measures, ischemic mice appeared to improve their motor performance after 2 weeks. However, kinematic analysis revealed the persistence of specific trajectory adjustments up to 30 days poststroke, indicating the use of compensatory strategies. Conclusions. These results support the use of kinematic analysis in mice as a tool for both detection of poststroke functional impairments and tracking of motor improvements following rehabilitation. Similar studies could be performed in parallel with human studies to exploit the translational value of this skilled reaching analysis

The Cambrian-Ordovician siliciclastic platform of the Balcarce Formation (Tandilia System, Argentina): Facies, trace fossils, palaeoenvironments and sequence stratigraphy

The Lower Palaeozoic sedimentary cover of the Tandilia (Balcarce Formation) is made up of thick quartz arenite beds together with kaolinitic claystones and thin fine-grained conglomerates. The Balcarce Formation was formed in the nearshore and inner shelf environments of a tide-dominated and storm influenced open platform. It shows many features suggesting tidal sedimentation. Coarse-grained facies were formed by sand bar migration and accretion. Heterolithic packages are interpreted as interbar (swale) deposits. Subordinated HCS sandstones indicate storm events. The recognition of thick progradational clinoforms allows to confirm that the Balcarce sea was open to the south, as suggested years ago through palaeocurrent interpretation. The great abundance and variety of trace fossils is among the most outstanding characteristics of this unit. The ichnotaxa that have been recognised so far are: Ancorichnus ancorichnus, Arthrophycus alleghaniensis, Arthrophycus isp., Bergaueria isp., Cochlichnus isp., Conostichus isp., Cruziana furcifera, Cruziana isp., Daedalus labeckei, Didymaulichnus lyelli, Didymaulichnus isp., Diplichnites isp., Diplocraterion isp., Herradurichnus scagliai, ?Monocraterion isp., Monomorphichnus isp., Palaeophycus alternatus, Palaeophycus tubularis, Palaeophycus isp., Phycodes aff. pedum, Phycodes isp., Plagiogmus isp., Planolites isp., Rusophycus isp., Scolicia isp. and Teichichnus isp. Trace fossils have traditionally been used to assign the Balcarce Formation to the Lower Ordovician, due to the presence of Cruziana furcifera. However, Plagiogmus is typical of Cambrian successions world-wide

Protonation effect on the excited state behaviour of some aza-analogues of EE-distyrylbenzene

The photobehaviour of four aza-analogues ofEE-distyrylbenzene bearing the heteroatom in the two side rings [1,4-di-(2-pyridylethenyl)benzene] or in the central ring [2,5-di-(phenylethenyl)pyridine, 2,6-di(phenylethenyl)pyridine and the corresponding diene, 2,6-di(phenylbutadienyl)pyridine] has been investigated in aqueous solutions at pH 2 and 9, where the molecules are in mono-protonated and neutral forms, respectively. The type of conjugation, linear for the first two compounds and crossed for the others, is particularly important in determining the spectral and photochemical properties. The main effects of the protic solvent are a reduction of the radiative deactivation, prevalent in the corresponding hydrocarbons, and an increase of the reactive deactivation, very modest in the hydrocarbons. The increase in photoreactivity to detriment of fluorescence, observed in protic medium with respect to non-polar solvents, is drastically emphasized in acid medium where the fluorescence quantum yield decreases by an order of magnitude leading to high values of theEE→ZEphotoisomerization quantum yield. The presence of conformational isomerism (two main conformers were detected) has been observed in both basic and acid media for compounds with crossed conjugation and for the linearly conjugated 2,5 substituted pyridine. The results obtained give a picture of the different photobehaviour of the neutral and protonated species and indicate the experimental conditions to favour a specific relaxation pathway

El loess y el problema de la identificación de las loessitas

This paper attempts to discuss the concepts about loess, its main features and origin, as well the possibilities of preQuaternary loess formation and identification. Loess has been defined in different ways. There are two main approaches concerning the meaning of the term: loess = fine grained (silt-size) c1astic rock, and loess = c1astic eolian sedimentary deposit. The second conceptincludes the depositional features ofthe loess, e. g. massive and homogeneous sedimentary bodies of large surficial extent and discrete thickness, with paleosol levels. Loess is a typicál deposit of quite distal sectors of the continental basins;. so its preservation potential is relatively high. Therefore, the controversial point of the geological identification of the loess in pre-Quaternary successions líes in the concept of this term (rock or deposit). If it is considered a sedimentary deposit, the possibilities of identification in the stratigraphic record become greater. As loess formation is conditioned by silt supply, the persistence of surficial winds, and a firm-Iand environment in the periphery of both glacial and desert regions, the term loessite should be used in both genetic and environmental sense, as an equivalent of eolianite, turbidite, tidalite, debrite, etc. Several diagnostic features for the identification of loessites are listed and discussed.Se discuten los conceptos sobre loess, sus atributos principales y origen, así como la posibilidad de su formación e identificación en sucesiones pre-cuaternarias. Elloess ha sido definido de diversas maneras, pero hayal respecto dos conceptos esenciales: 1) loess = roca elástica de grano fino (Iimosa), y 2) loess = depósito sedimentario elástico de origen eólico. Este último concepto ineluye a los rasgos depositacionales del loess, como por ejemplo su carácter homogéneo y macizo en cuerpos de considerable extensión y discreto espesor, con frecuentes niveles de paleosuelos. El loess es un depósito distal de algunas cuencas sedimentarias continentales, por lo que su potencial de preservación es relativamente grande. El aspecto controversial sobre la identificación de loess pre-cuaternario radica en el concepto que se tenga de él (roca o depósito). Si se lo considera un depósito, las posibilidades de diagnosis se hacen mayores. Como la formación delloess depende de: aporte de limo, de la persistencia de los vientos superficiales y de la existencia de un ambiente de tierra firme en la periferia de regiones glaciales o desérticas, el término loessita reúne a conceptos genéticos y ambientales, como ocurre, por ejemplo, con eolianita, turbidita, tidalita, debrita, etc. Finalmente, se presentan diversos criterios para la identificación estratigráfica de las loessitas

Neuroplastic Changes Following Brain Ischemia and their Contribution to Stroke Recovery: Novel Approaches in Neurorehabilitation

Ischemic damage to the brain triggers substantial reorganization of spared areas and pathways, which is associated with limited, spontaneous restoration of function. A better understanding of this plastic remodeling is crucial to develop more effective strategies for stroke rehabilitation. In this review article, we discuss advances in the comprehension of post-stroke network reorganization in patients and animal models. We first focus on rodent studies that have shed light on the mechanisms underlying neuronal remodeling in the perilesional area and contralesional hemisphere after motor cortex infarcts. Analysis of electrophysiological data has demonstrated brain-wide alterations in functional connectivity in both hemispheres, well beyond the infarcted area. We then illustrate the potential use of non-invasive brain stimulation (NIBS) techniques to boost recovery. We finally discuss rehabilitative protocols based on robotic devices as a tool to promote endogenous plasticity and functional restoration

Características y significado sedimentológico de las formas, cuerpos y estructuras originadas por agentes fluidos en sustratos incoherentes.

A review of tractive· sedimentary structures, such as ripples, megaripples and cross-bedding, and the definition of sedimentary bodies and sedimentary forms are considered in this paper. Sedimentary bodies are groups of strata which can be differentiated from adjacent beds beca use of the presence of first order bounding surfaces. Sedimentary forms are features (such as bars, ribbons, crests, ridges, channels, dunes, etc.) originated by the agents of clastic deposition. Sedimentary forms are difficult to recognize in ancient sequences, but they may be inferred by analyzing both the type and distribution of sedimentary structures and sedimentary bodies. Sedimentary bodies are generally the features of sedimentary forms preserved in the geological record. The scale and significance of first, second ancl third order bouncling surfaces developecl in f1uviatile, marine and eolian seclimentary sequences are also treatecl in this contribution.Se efectúa una revision de las principales estructuras sedimentarias (óndubs, megaóndulas y estratos entrecruzados) producidas por procesos tractivos. Además, se desalTollan los conceptos de cuerpo sedimentario y forma sedimentaria. Los cuerpos están constituidos por grupos de estratos reunidos en conjuntos delimitados por importantes superficies de erosión; se dan a conocer las características de los cuerpos de medios fluviales, marinos y eólicos. Las formas son los rasgos morfológicos de acumulación sedimentaria que se aprecian en los ambientes actuales; "también se describen las principales formas desarrolladas en zonas fluviales, marinas y de depositación eólica. La mayoría de los cuerpos sedimentarios representan a formas sedimentarias y por lo tanto pueden ser de gran valor en la interpretación paleoambiental. Por otra parte, se hace un análisis de las discontinuidades de la sedimentación y se reconocen, para diversos tipos de depósitos, superficies de primero, segundo y tercer orden. Las de primer orden delimitan a cuerpos sedimentarios, las de segundo orden aparecen entre estratos sucesivos y las de tercer orden o superficies de reactivación se ubican dentro de la unidad de sedimentación

Variability of continental depositional systems during lowstand sedimentation: an example from the Kimmeridgian of the Neuquen Basin, Argentina

Several second order lowstand wedges are recognized in the Jurassic-Early Cretaceous sedimentary record of the backarc Neuquén Basin (central-west Argentina). They are distinguished by sharp based continental and marginal marine siliciclastic deposits encased in offshore shales. The Kimmeridgian lowstand wedge was developed slightly after the emergence of the Andean magmatic arc and the tectonic inversion of previous intrabasinal extensional structures. As a result, the Neuquén Basin was compartmentalized into three main depocentres characterised by widespread continental sedimentation under arid to semiarid climatic conditions. A fluvial-dominated system characterised by systematic downstream changes in architectural style is recognized in the Northwestern Depocentre. A gravely and sandy bedload fluvial system was developed in the southern upstream sector, while ticker beds of finer-grained sediments formed in a distal ephemeral fluvial system prevail in the downstream part of the system. The overall fining upward stacking pattern of the sedimentary record in the Northwestern Depocentre accompanied by frequent development of soil horizons and darker deposits suggests a change towards higher accommodation and high water table emplacement. In the Southwestern and Eastern Depocentres, the sedimentary successions show a conspicuous internal transition from fluvial ephemeral fluvial systems to aeolian systems. However, the lowstand deposits of the Eastern Depocentre are characterised by a larger areal distribution and a thicker record of both the fluvial and the aeolian deposits. Marked changes in thickness and in the depositional style of the fluvial and aeolian facies associations within the Southwestern and Eastern depocentres indicate that the sedimentary infill was controlled by systematic variations in accommodation. Low accommodation conditions favoured a high degree of lateral migration of fluvial channels with substantial erosion of fine-grained deposits and the development of sinuous-crested aeolian dunes typically associated with wet interdune deposits. Under higher accommodation conditions the fluvial deposits show a retrogradational stacking with preservation of thick packages of fine-grained sediments, while a large sand sea characterised by amalgamation of dune deposits was developed in the aeolian-dominated uppermost successions. The detailed analysis of the Kimmeridgian lowstand wedge of the Neuquén Basin illustrates how facies and stratigraphic organisation responded to regional and temporal changes in basin configuration, accommodation, sediment supply and water table position. The Kimmeridgian lowstand deposits are geographically distributed as the subsequent transgressive deposits and reveal no major basinward shift during the early stages of sequence stacking. However, they show a much more complicated facies distribution. Consequently, the lowstand wedge deposits better reflect the complex interplay of episodic local tectonism, siliciclastic source area variation and climatic change

Composición normativa y clasificación de rocas pelíticas

A normative classification oi pelitic rocks based on the proportion of major components (SiO" AI,O" Fe,O" MgO, Cao, Na,O, K,O, P,O. and CO,) is presented in this paper. The proposecl procedure includes two models of norm calculation: smectite present and smectite absent. In hoth models the content of K,O can he lIsed to determina te orthoclase  illite. The pelitic rack classificationis based upon the relative contentsin normative clay minerals,quartz and feldspars. Nine compositionalrock-types,which are clearlydefined in a triangulardiagramwere recognized. The importance of chemical compositionstudies in the interpretation of pelitic rocksis also discussed.Se da a conocer un método normativo de clasificación de rocas pelíticas basado en su composición química mayoritaria (SiO" ALO" Fe-..O",MgO, CaO, Na,O, K:O, P,O. y CO,). El procedimiento propuesto presenta dos modelos de norma, con o sin esmectita. En ambos modelos los contenjclos de K,O pueden ser asignados a Oltosa o a illita. La clasificación de las pelitas está basada en las proporciones normativas de argilominerales, cuarzo y fesdespatos. En ella se reconocen nueve variedades composicionales, las que se pueden representar en un diagrama triangular. Se discute el valor de los estudios qlÚmicos composicionales en la interpret'1ción genética de sucesiones y rocas pelíticas