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This study evaluates the effect of climate on facies, grain size, and sedimentation rates using sedimentology, geochronology, and stable isotope geochemistry for Miocene-Pliocene deposits in the Angastaco basin (Eastern Cordillera, northwest Argentina). U-Pb zircon data from ash layers constrain the transition between the finer grained fluvial-lacustrine Palo Pintado Formation and the coarser grained fluvial-alluvial San Felipe Formation to ca. 5.2 Ma and the first deposition of sediment derived from the present-day orographic barrier to ca. 4 Ma. [delta][sup.13]C values from pedogenic carbonate nodules range from -15.4[per thousand] to -10.2[per thousand] for the Palo Pintado Formation and from -9.5[per thousand] to -8.2[per thousand] for the San Felipe Formation; this can be best explained by increased, sustained aridity since ca. 5 Ma. The [delta][sup.18]O values range from -9.6[per thousand] to -5.9[per thousand] for the Palo Pintado Formation and from -6.1[per thousand] to -5.2[per thousand] for the San Felipe Formation, corroborating this interpretation. The shift toward more arid conditions correlates with a significant increase in grain size but no significant change in sedimentation rate. Because aridity precedes the development of an orographic effect, we interpret the grain size increase in the Angastaco basin since ca. 5 Ma to be a response of the sedimentary system to aridification resulting from regional climate change. doi: 10.1130/G30532.1

Byline: Olga C. Penalba (1), Federico A. Robledo (1,2) Abstract: We analyzed trends, interdecadal variability, and the quantification of the changes in the frequency of daily rainfall for two thresholds: 0.1 mm and percentile 75th, using high quality daily series from 52 stations in the La Plata Basin (LPB). We observed increases in the annual frequencies in spatially coherent areas. This coherence was more marked in austral summer, autumn, and spring, during which the greatest increases occurred in southern Brazil, especially during extreme events. In winter, the low and middle basins of the Rio Uruguay and Rio Parana showed negative trends, some of which were significant. Interdecadal variability is well defined in the region with more pronounced positive jumps west of the basin between 1950 and 2000. This variability was particularly more marked during periods of extreme rainfall in summer, autumn, and spring, unlike in winter when extreme daily rainfall in the lower Rio Parana basin decreased by up to 60%. The changes in the past century during extreme rainfall produced modifications in the annual rainfall cycle. The annual cycle of both indices was broader during the last period which is mainly explained by the strong decreases in winter. Author Affiliation: (1) Departamento de Ciencias de la Atmosfera y los Oceanos, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428, Buenos Aires, Argentina (2) Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires, Argentina Article History: Registration Date: 17/09/2009 Received Date: 23/06/2008 Accepted Date: 03/08/2009 Online Date: 27/10/2009

The results of detrital zircon U-Pb geochronology suggest a maximum depositional age of 485 [+ or -] 7.2 Ma for a glacial diamictite from the Sierra del Volcan in eastern Argentina (Tandilia System). Earlier interpretations associated the deposit with the Neoproterozoic 'snowball Earth' hypothesis. The data allow direct correlation, for the first time, between Early Palaeozoic deposits in both South America and South Africa connecting the glacial deposits from southern Bolivia to central Argentina with those in South Africa (Pakhuis Formation). On the basis of these results, a new distribution map of glacial cover, corresponding to the Hirnantian stage, can be developed. Supplementary material: Sampling and analytical techniques, data, a simplified map and BSE images are available at http://www.geolsoc.org.uk/SUP18384. doi: 10.1144/0016-76492009-023

An Ordovician metamorphic event is recorded by means of conodont paleothermometry in the slope sedimentary sequences of the Western Precordillera. Allochthonous conodonts from reworked deposits of the eastern carbonate platform with CAI 4.5-5 and autochthonous conodonts from the olistostrome matrix with CAI 3 allow for constraining the metamorphic age within the Paltodus deltifer and Lenodus variabilis zones (i.e., ca. 480-465 Ma). The conodont data support an Ordovician instead of an alternative Devonian collision for the Cuyania terrane with the proto-Andean margin of Gondwana, which is consistent with the earlier proposed, but still contentious, microcontinent model. In the latter scenario, the collision of the Cuyania terrane caused unroofing and cannibalism of the leading edge of the carbonate succession and basement rocks. The erosion of these rocks supplied detritus and metamorphosed conodonts to the deeper basinal settings of the Western Precordillera. As the deformation front migrated into the peripheral foreland of the Eastern and Central Precordillera, nonmetamorphosed conodonts were eventually incorporated into the west-prograding synorogenic clastic wedge. The occurrence of allochthonons and autochthonous conodonts in the slope facies of the Western Precordillera provides a time constraint for the early accretion of the Cuyania terrane and its transition to an evolving foreland mountain system in the Ordovician period.

The penguin skeleton studied here constitutes the fourth partial skeleton found in Patagonia, and the third one with an associated humerus and tarsometatarsus. The finding of this partial skeleton identified with certainty as Palaeospheniscus patagonicus Moreno and Mercerat, 1891 (Ayes, Sphenisciformes) allows the first description of elements other than the tarsometatarsus. The material comes from the basal sector of the Gaiman Formation (Early Miocene), located along the Atlantic coast of Chubut Province, south of Rawson city. This unit comprises a succession of shales, fine tufts, sandstones, tuffaceous sandstones, and coquinas deposited in a shallow marine environment. These beds contain abundant marine vertebrates (sharks, dolphins, rays, birds), mollusk casts, and oyster beds. The skeleton includes: rostrum, two thoracic vertebrae, right coracoid without the distal end, left humerus, right femur, right tarsometatarsus, left fragmentary scapula, left coracoid, left radius without the distal end, proximal portion of left ulna, proximal end of left femur, and preacetabular part of the synsacrum. P. patagonicus would have been a medium-sized penguin weighing about 5 kg that inhabited the breeding colonies established in the nearby Bryn Gwyn area during the early Miocene. Despite the abundance of penguin remains known for Argentina, and the fact that they are among the birds with a better fossil record, this skeleton is an exceptional case. This finding allows a readjustment of the taxonomic criteria applicable to fossil and living species.

[1] The Puna is part of the larger Puna-Altiplano Plateau (also known as the Central Andean Plateau), characterized by high elevation, low relief, and aridity, located in the central Andes of Bolivia and Argentina. Tertiary sedimentary rocks preserved within the Puna contain a unique archive of information regarding the paleogeography, depositional environments, and timing of sediment source exhumation during the early stages of Andean mountain building. The Eocene Geste Formation in the Salar de Pastos Grandes area (within the central Puna of northwestern Argentina) consists of deposits that are the result of confined to unconfined flows in a sandy to gravelly, braided fluvial system and alluvial fans proximal to the source terrane. Paleocurrent data document an overall eastward flow direction. Up-section coarsening of the Geste Formation suggests that topographic relief in the source area increased through time, possibly owing to enhanced tectonic activity and source terrane unroofing. Sandstone petrography and conglomerate clast-count data document quartzose and phyllitic compositions typical of Ordovician rocks preserved just west of the Salar de Pastos Grandes area. Paleocene-Eocene detrital apatite fission track age populations (P1: ~35-52 Ma; P2:~52-65 Ma) of the Geste Formation and their consistent trends up-section suggest moderate to rapid (~0.4 mm/a to >1 mm/a) exhumation of western sediment sources during the early to mid-Tertiary stages of Andean mountain building. Sedimentation rates increase up-section from ~0.1 mm/a to 1 mm/a. Our data, when combined with other structural, stratigraphic and seismic evidence from surrounding regions, suggest that the Geste Formation was deposited in response to crustal shortening and resulting erosion and sedimentation, which started as early as Cretaceous in the Chilean Cordillera de Domeyko and in the Salar de Pastos Grandes area by Eocene time. The Geste Formation could be interpreted either as a local wedge-top accumulation on the eastward propagating central Andean orogenic wedge, or as a local intermontane basin. The similarities between wedgetop deposits preserved in Bolivia and Eocene deposits in northwestern Argentina, south of ~25[degrees]S, lead us to favor the wedge-top scenario for the Geste Formation. If correct, this implies that the deformation front of the Andean orogenic wedge incorporated both thin- and thick-skinned structures as it migrated, possibly unsteadily, from the Cordillera de Domeyko during the Cretaceous-Paleocene to areas within the Puna and Eastern Cordillera by mid-late Eocene time. Contemporaneously, a regional-scale foreland basin system developed over an along-strike distance of at least 650 km. Citation: Carrapa, B., and P. G. DeCelles (2008), Eocene exhumation and basin development in the Puna of northwestern Argentina, Tectonics, 27, TC1015, doi:10.1029/ 2007TC002127.

[1] During the Cretaceous-Eocene interval a system of intracontinental rift basins, the Salta group rift, evolved in northwestern Argentina. Individual segments of the rift later suffered different degrees of inversion during Cenozoic shortening. The Tres Cruces subbasin, on the west side of the Eastern Cordillera, was strongly deformed, being now part of a thickskinned thrust belt with a predominantly N-S structural trend. On its eastern border, tilting due to folding and thrusting and subsequent erosion have produced exceptional outcrops of preserved east-trending extensional structures including half grabens, rollover anticlines, and extensional fault-propagation folds. Farther west, the synrift succession is only intermittently exposed, although the interference of north- and easttrending structures as well as peculiar, dome-shaped anticlines with spur-like extensions suggest that north-and east-trending Cretaceous faults were reactivated, particularly near their intersections. Compilation of published data and analysis of our new data focused on the Salta rift indicates three main factors favoring the contractional reactivation of normal faults: dip angles lower than approximately 60[degrees], especially for faults striking roughly normal to contraction; strikes no closer to the contraction direction than approximately 30[degrees]; and low downdip fault curvatures. Occasional dip-slip reactivation of east-trending faults does not match the present and long-term Andean stress regimes and presents an unresolved problem. Citation: Monaldi, C. R., J. A. Salfity, and J. Kley (2008), Preserved extensional structures in an inverted Cretaceous rift basin, northwestern Argentina: Outcrop examples and implications for fault reactivation, Tectonics, 27, TC 1011, doi: 10.1029/2006TC001993.

This paper constitutes the first monographical study of the rich brachiopod faunas from the Early Ordovician Suri and Molles Formations of the central Famatina Range, which form a nearly continuous, more than 2,000 m thick succession of fossiliferous clastic and volcaniclastic rocks. Conodonts from the brachiopod-rich levels of the upper third of the Suri Formation and Los Molles Formation indicate the upper part of the Oepikodus evae Biozone (mid-Arenig). The systematic study of brachiopod faunas reveals the presence of 22 species belonging to 19 genera, three of which are new. The new genera recognized are the orthid Suriorthis, the hesperonomiid Mollesella, and the rectostrophiid Trigonostrophia. The following 12 new species and subspecies are described and illustrated: the clitambonitoidean Tritoechia mollesensis; the skenidioideans Crossiskenidium? stelzneri and Skenidioides kayseri; the orthoideans Paralenorthis suriensis, Paralenorthis riojanus brevis, Panderina? ambigua, Productorthis angulensis, Hesperonomiella arcuata, and Monorthis transversa; the plectorthoideans Ffynnonia famatinensis and Desmorthis? bifurcata; and the porambonitoidean Rugostrophia protoandina. Associated forms are Tritoechia sp., Pinatotoechia acantha Benedetto, 200lb; Protoskenidioides cf. revelata Williams, 1974; Hesperonomia orientalis Benedetto, 1998a; Paralenorthis riojanus (Levy and Nullo, 1973), Famatinorthis turneri (Levy and Nullo, 1973); and Camerella sp. Brachiopods from the Famatina Range display strong affinities with Welsh and Central Newfoundland, Maine and New Brunswick volcanic assemblages forming with them a statistically well defined Celtic cluster. Faunal evidence suggests that the Famatina volcanic belt continues northward into the western Puna belt.

We studied the diving behavior of Red-legged Cormorants (Phalacrocorax gaimardi) in Patagonia, Argentina, using VHF radio-transmitters deployed during incubation. Red-legged Cormorants made foraging trips in inshore waters less than 15 m deep. Mean dive duration was 26.8 + 2.0 sec while mean time at surface was 9.2 [+ or -] 0.9 sec (n = 2217 dives). The birds spent 74% of their foraging time underwater. Diving efficiency was different among individuals, and was among the highest reported for the Phalacrocoracidae. Dive variables were correlated with the height of the tide, suggesting that the birds forage on the seabed. Red-legged Cormorants were efficient divers, investing most of their feeding time underwater and foraging in shallow waters, maximizing bottom time. Our results are consistent with the hypothesis that Red-legged Cormorant diving behavior is strongly influenced by a combination of environmental variables (bottom heterogeneity and high tide width) characteristic of the south coast of Patagonia. Key words: diving behavior, Phalacrocorax gaimardi, radio-telemetry, Red-legged Cormorant.

We present laser-ablation microprobe inductively coupled-mass spectrometry analyses of Y, Yb, Er, Dy, and Gd in garnet crystals from high-grade metamorphic and migmatitic rocks from the Sierras Pampeanas of Argentina. These rocks contain large garnet porphyroblasts ([greater than or equal to] 4 mm) that are compositionally zoned. Rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores. A notable feature of this zonation is the inversion of Yb/Er and Yb/Dy ratios, from >1 in the cores to Keywords: Rayleigh fractionation, garnet, heavy rare earth clements, melting.

Copahue volcano erupted altered rock debris, siliceous dust, pyroclastic sulfur, and rare juvenile fragments between 1992 and 1995, and magmatic eruptions occurred in July-October 2000. Prior to 2000, the Copahue crater lake, acid hot springs, and rivers carried acid brines with compositions that reflected close to congruent rock dissolution. The ratio between rock-forming elements and chloride in the central zone of the volcano-hydrothermal system has diminished over the past few years, reflecting increased water/rock ratios as a result of progressive rock dissolution. Magmatic activity in 2000 provided fresh rocks for the acid fluids, resulting in higher ratios between rock-forming elements and chloride in the fluids and enhanced Mg fluxes. The higher Mg fluxes started several weeks prior to the eruption. Model data on the crater lake and river element flux determinations indicate that Copahue volcano was hollowed out at a rate of about 20 000-25 000 [m.sup.3]/yr, but that void space was filled with about equal amounts of silica and liquid elemental sulfur. The extensive rock dissolution has weakened the internal volcanic structure, making flank collapse a volcanic hazard at Copahue. Keywords: hydrothermal fluids, volcanic processes, hydrochemistry, limnology, eruptions.

Megaspore and microspore massulae of Paleoazolla patagonica gen. et sp. nov. are described from the Upper Cretaceous of La Colonia Formation, Chubut Province, Argentina. The new fern possesses megaspore complexes with three to four glochidiate floats attached directly to the megaspore; a columella-like structure appears to be absent. The megaspore wall consists of a two-layered exine that is smooth to irregularly perforate, a two-layered perine with a spongy, densely packed endoperine, and a loosely organized exoperine. Infrafilosum hairs cover the exoperine. Microspore massulae are irregular in size and shape and bear multibarbed glochidia that generally have anchor-shaped tips. A comparison with other azollaceous and salviniaceous genera, particularly Azolla, is provided, together with a discussion of some evolutionary trends within the family. Key words: Argentina; Azollaceae; heterosporous ferns; Paleoazolla patagonica; Upper Cretaceous.

Two rhizobial populations with pronounced differences in their acid tolerance and symbiotic properties were found to be present in alfalfa-nodulating rhizobia from acid soils of different locations in Central Argentina and Uruguay. The 15 acid-tolerant isolates were able to grow at pH 5.0 and formed nodules in alfalfa with a low rate of nitrogen fixation. They also share a genetic background closely related to that of Rhizobium sp. Or191 recovered from an acid soil in Oregon. Results demonstrate that similar populations of acid-tolerant alfalfa-nodulating rhizobia exist in geographically distant regions where soil acidity is a common characteristic.

The Quebrada del Toro and Quebrada de las Conchas in the Cordillera Oriental of northwestern Argentina are notable for repeated landsliding and damming of major drainages. Both areas correspond to displacement transfer zones along major thrust systems that developed during the Neogene uplift of the central Andes. During this period, displacement transfer zones were areas of subdued relief that localized where rivers cross the fault systems. However, neotectonic deformation converted the transfer zones into restraining bends along strike-slip systems, resulting in enhanced uplift at river crossings. The antecedent streams responded by rapidly downcutting into the ascending hanging-wall blocks, producing precipitous local relief. The extreme local relief that was controlled by the kinematic evolution of faulting in both areas provides an effective precondition for landsliding, which may have been ultimately triggered by seismicity and gravitational failure aided by enhanced undercutting during past humid conditions.

An exploration of Argentina's geological history is presented, focusing on the formation of the Precordillera. Theories include its origin as a part of the Texas plateau versus its origin as an open ocean outboard from the Ouachita facies.

Over much of its length, the Andean orogen is characterized by a generally east-vergent geometry and a progressive eastward (cratonward) migration of individual arc-orogenic elements. A departure from this model occurs in the Sierras Pampeanas region of central western Argentina where a terrane of active basement uplifts is currently developing to the east of the main Cordillera. Apatite fission-track data from uplifted Precambrian and Phanerozoic basement rocks of the Sierras Pampeanas constrain the tectonic development of this terrane and indicate that deformation associated with exhumation may have propagated broadly westward since the late Miocene. Two pre-Andean cooling events - during the Carboniferous-Permian (ca. 300-280 Ma) and the early Jurassic-middle Jurassic (ca. 200-174 Ma) - have been identified. The onset of Andean deformation is represented by a cooling event during the late Paleocene-middle Eocene. This cooling was followed by a period of middle Miocene-late Miocene reheating, during foreland basin-style sedimentation. Exhumation, and possible westward migration of the exhumation 'front' in the Sierras Pampeanas, commenced during the late Miocene-Pliocene to the east of the dominantly east-vergent Precordillera fold-and-thrust belt. The apparent convergence of deformation in these two terranes and the progressive closure of Miocene-Pliocene intermontane basins in the Sierras Pampeanas may reflect the early stages of Andean plateau uplift. The relative timing of plateau development along strike suggests that lateral thickening of the orogen is progressing southward at least from the latitude of central Bolivia (ca. 20[degrees]S). Furthermore, the time-space coincidence between basement uplift and flattening of the subducted slab beneath the Sierras Pampeanas suggests that a relationship exists between westward displacement of the terrane and the dynamics of plate interaction.

Research was conducted to characterize the rhizobial populations naturally associated with wild beans in various areas in the Southern Andes in northwest Argentina. Results suggest that the rhizobial populations nodulating wild beans in virgin field soils of Northwest Argentina are not the only R. etli and R. leguminosarium bv. phaseoli isolates in those soils that are able to associate with Phaseolus vulgaris L. Both the high densities of type I rhizobia induce speculation that P. vulgaris in this center of origin might have coevolved in the symbiosis with Rhizobium spp.

We assessed differences in breeding bird assemblages and vegetation structure between a natural forest edge and the adjacent forest interior in an old-growth Chaco forest of Argentina. The edge had a dense cover of thin stems at low heights and high species richness of woody plants, whereas the interior had high canopy cover, high tree density, high density of thick stems, and a more heterogeneous vertical profile. We used mist-net and point-count surveys to sample bird assemblages, capturing 374 birds during 3,553 net hours and detecting 826 individuals during point counts. Overall, we recorded a total of 74 bird species. Bird species richness and bird abundance appeared to be higher in the edge, although differences between habitats were not entirely consistent for mist-net and point-count data. Several early successional bird species were closely associated with edge, and other species occurred exclusively in the interior of the forest. At the guild level, frugivores, terrestrial granivores, arboreal granivores, terrestrial insectivores, and long-flight insect-hunters were more abundant at the edge than in the interior, whereas the reverse was true for bark insectivores and short-flight insectivores. Our results indicate that edge and interior bird assemblages are different. The distribution of birds between these habitats appeared to reflect constraints on habitat use imposed by vegetation structure, and also could be related to differential distribution of food resources, especially fruit.

Breeding and non-breeding barn owls close to the southern limit of their distribution in Argentina commonly prey on small rodents but occasionally feed on various vertebrates. Selectively, they consume large rodents when there is abundant prey during the breeding season. Consumption of female rodents is higher by fall-winter, which is attributed to behavioral and body mass differences between sexes of prey. The prey consumption of barn owls also differ between the breeding season, when there is higher food consumption, and the non-breeding season.

The world's largest breeding colony of Magellanic penguins is located on the southern coast of Argentina at a place called Punto Tombo. It is there that the penguins first began to be slaughtered in 1982 for commercial purposes. Soon thereafter Argentines became outraged by the senseless slaughter of these harmless creatures and forced the government to pass a law prohibiting their killing and call for a scientific study of the penguins instead.

Geochronological, bulk-rock geochemical and mineralogical data were obtained for samples taken from the Achala batholiths in Argentina to elucidate the petrogenesis of the area. The results provide evidence that the biotite-apatite-rich enclaves were not restites from a Precambrian source nor xenoliths of Precambrian wall rocks. The results further suggested that the enclaves are magmatic segregations, with the fluorine-rich characteristics of the biotites and apatites pointing to the high fluorine content of their magma origin.

It is crucial to date continental landforms to quantify processes involved in terrestrial surface evolution, especially in regions affected by active tectonics. Andean Quaternary alluvial fan surfaces affected by the El Tigre strike-slip fault have been studied using combined geomorphic and 10Be exposure age approaches. Field observations and SPOT (French acronym for 'Satellite for Observation of the Earth') image analysis enable the identification of six alluvial fan units. Measurements of in situ-produced cosmogenic 10Be concentrations in quartzite boulders exposed on the top of fan surfaces show that the depositional periods ended during successive major interglacial stages. The calculated minimum exposure ages date the abandonments of the alluvial fan surface from 41 000 [+ or -] 8500 yr for the youngest to 670 000 [+ or -] 140 000 yr for the oldest unit. When linked to the measured maximum cumulative right-lateral displacement of stream channels, the exposure ages yield a horizontal slip rate of about 1 mm/yr on the El Tigre fault. This study shows that for arid regions, where fan surface erosion is minimal, in situ-produced 10Be can be used to constrain the age of stratigraphically separate alluvial fan surfaces. These fan surface exposure ages can be further used to calculate slip rates on active faults and infer depositional periods correlative with climatic events.

In Ordovician time, Gondwana in the area of northwestern Argentina and northern Chile had a west-facing active margin. The evolution of this margin culminated in the Ocloyic orogeny at the end of Ordovician time. This orogeny was caused by the collision of the allochthonous Arequipa-Antofalla terrane with this margin. The early Paleozoic evolution of northwestern Argentina and northern Chile contrasts markedly with the accretionary history of central Argentina and central Chile, where the Precordillera and Chilenia terranes docked in the Late Ordoviclan and Late Devonian periods, respectively. An inspection of the available stratigraphic and geochronological data on sedimentary, volcanic, and plutonic units of the southern Central Andes of northern Chile and northwestern Argentina reveals a lull in magmatic and metamorphic activity lasting for [approximately]100 m.y., from Early Silurian to early Late Carboniferous time. This is interpreted as corresponding to a tectonic scenario in which the present Andean margin was a passive margin of Gondwana. This passive margin developed in response to the rifting off of a part of the Arequipa-Antofalla terrane; the present location of this block is unknown. Late Carboniferous time marks the renewed onset of subduction, initiating the Andean plate tectonic setting still prevalent today. Recently proposed models explain the Late Ordovician orogeny by the collision of Laurentia with western South America during Laurentia's clockwise motion around South America and away from its position in the Neoproterozoic supercontinent. In its present form, this pothesis is difficult to reconcile with the Paleozoic tectonostratigraphic evolution of the southern Central Andean region.

The Agrio Formation of the Neuquen Basin, Argentina, contains an extensive sequence of ammonite faunas, most of which are monogeneric. Detailed collecting through 15 sections across the basin has facilitated a major revision of the ammonite zonation. Formerly embracing four broad zones, the Agrio Formation is now divided into nine zones, the lowest four of which are divided into a total of 11 subzones. The new zonation provides a standard against which other South American faunas can be compared. The degree of subdivision now achieved is comparable to that for the 'standard' sequences of the West Mediterranean region. Although it is not possible to correlate the two regions in detail, the occurrence of some widely distributed genera (Olcostephanus, Karakaschiceras, Oosterella, Spitidiscus and Crioceratites) at well-defined levels in the Neuquen Basin provides some crucial links. Thus the approximate positions of the Lower/Upper Valanginian, Valanginian/Hauterivian and Lower/Upper Hauterivian boundaries can be determined.

Integration of sequence stratigraphy, magnetostratigraphy, Ar/Ar dating, and paleontology considerably advances knowledge of the Late Cretaceous-early Paleogene chronostratigraphy and tectonic evolution of Bolivia and adjacent areas. The partly restricted marine El Molino Formation spans the Maastrichtian and Danian ([approximate]73-60.0 Ma). Deposition of the alluvial to lacustrine Santa Lucia Formation occurred between 60.0 and 58.2 Ma. The widespread erosional unconformity at the base of the Cayara Formation is 58.2 Ma. This unconformity separates the Upper Puca and Corocoro supersequences in Bolivia, and is thus coeval with the Zuni-Tejas sequence boundary of North America. The thick overlying Potoco and Camargo formations represent a late Paleocene-Oligocene foreland fill. The onset of shortening along the Pacific margin at [approximate]89 Ma initially produced rifting in the distal foreland. Santonian-Campanian eastward-onlapping deposits indicate subsequent waning of tectonic activity along the margin. Significant tectonism and magmatism resumed along the margin at [approximate]73 Ma and produced an abrupt increase in subsidence rate and other related phenomena in the basin. Subsidence was maximum between [approximate]71 and [approximate]66 Ma. Due to the early Maastrichtian global sea-level high, marine waters ingressed from the northwest into this underfilled basin. Subsidence decreased during the Late Maastrichtian and was low during the Danian. It increased again in the latest Danian, for which a slight transgression is recorded, and peaked in the early Selandian. Tectonism between 59.5 and 58.2 Ma produced a variety of deformational and sedimentary effects in the basin and correlates with the end of emplacement of the Coastal batholith. The subsequent 58.2 Ma major unconformity marks the onset of continental foreland basin development, which extended into Andean Bolivia during the late Paleocene-Oligocene interval. This basin underwent internal deformation as early as Eocene time in the Altiplano and Cordillera Oriental. These early structures, previously assigned to the late Oligocene-early Miocene orogeny, probably accommodated observed tectonic rotations in the Eocene-Oligocene.

Silicified material from the Early Caradoc part of the Las Aguaditas Formation in San Juan Province, Argentina, includes a nearly complete growth series for a new species of the tropidocoryphid Stenoblepharum Owens, 1973. Cladistic analysis of Stenoblepharum species indicates that S. astinii new species is most closely allied to the Early Caradoc S. strasburgense (Cooper, 1953) from Virginia. Chinese species of Stenoblepharum are sister group to a Baltic/Laurentian clade. A single adult-like protaspid stage occurs in the life cycle of S. astinii, closely resembling the protaspis of Decoroproetus. It is preceded by a non-adult-like first protaspid instar that appears to be characteristic of Proetoidea in general but contrasts markedly with the early larval stages of other taxa in Proetida.

Pre-Tremadocian conodonts and trilobites and Tremadocian conodonts are reported from the Cambrian and Ordovician La Silla Formation in the Cerro La Silla section in east-southeast Jachal, San Juan Province, Argentina. A shallow marine conodont fauna contains elements of Clavohamulus hintzei Miller, a common species in North America, but reported for the first time from the early Paleozoic platform carbonates of the western Argentine Precordillera. The presence of this species suggests a correlation with the Clavohamulus hintzei conodont subbiozone of the Cordylodus intermedius conodont biozone in North America, considered Early Ordovician (Skullrockian Stage, Ibexian Series) in North America, but by South American and European standards, this biozone would be of latest Cambrian age. C. hintzei and associated conodonts of the La Silla Formation are typical of the tropical faunas of the North American Midcontinent Faunal Province; Late Cambrian trilobites from lower in the formation also are typical North American taxa. The presence of these faunas in the platform carbonates is consistent with plate reconstructions suggesting that the Precordillera was in a tropical or subtropical position close to Laurentia during the late Precambrian and early Paleozoic. These new paleontological data provide one more argument for recent models of the Precordillera as a displaced terrane derived from the Ouachita Embayment at the southern margin of Laurentia.

Stratigraphic analysis of Pleistocene non-marine bedded evaporites in northwest Argentina elucidates the effect that episodic saline lake expansion and contraction have on the stratigraphic completeness of units deposited and preserved in a continental saline environment. Stratigraphic successions in these rocks contain features that relate uniquely to fluctuations in saline lake level. Bounding the top of each succession is a surface with evidence for an abrupt increase in water depth. Because sediment accumulation and stratal preservation vary spatially as a function of lake level, the degree of stratigraphic completeness varies among locations. These results have implications for attempts to extract the record of continental climate change from saline lake strata. Bedded evaporites in these strata accumulated in a saline lake characterized by a marginal zone of gypsum and ulexite with clastic interbeds and an accumulation of halite in the saline lake center. Four internally conformable successions of genetically related lithofacies assemblages are recognized. Each succession consists of a basal sandstone that is the initial accumulation of the lake-level rise and lake highstand. Overlying this sandstone are cyclic evaporite and fine-grained clastic deposits of the lake-level fall. These units are modified by desiccation-related processes resulting from lake contraction and desiccation around the lake margins. Subsequent lake-level rise resulted in subaqueous mechanical erosion of clastics and dissolution of interbedded evaporites. In more basinward regions, dissolution of evaporites occurred prior to accumulation of lake highstand units. In the saline lake center, the lake never dried up entirely, and evidence for partial lake desiccation is equivocal.

The seismic history of extra-Andean South America is poorly documented. Between lat 26 [degrees] S and 33 [degrees] S, about 375 km east of the fold-and-thrust belt that marks the present orogenic front, the block-faulted crystalline basement uplifts of the Sierras Pampeanas in Argentina reveal extensive Quaternary reverse faulting. 14C dates of 1080 [+ or -] 70 and 1310 [+ or -] 40 yr B.P. have been determined on organic material from colluvium on the footwall of the east-dipping Los Molinos branch of the Comechingones fault. They indicate at least 2.1 m of slip, probably coseismic, during the past 1300 yr in an area for which no significant deformation has been reported in association with historical earthquakes.

A new species of Andalgalomys is described from the Monte Desert-Chacoan thorn-scrub region of Argentina. This genus previously was known in Argentina only near Andalgala, Catamarca Province, from a single isolated valley; specimens of the new species are the first documentation of the genus outside the province. Specimens from localities in Catamarca and San Luis provinces are reported. The distribution of the genus is extended southward ca. 500 km. The diploid number of chromosomes is 60. Key words: Andalgalomys, Argentina, Graomys, morphology, phyllotine rodents, South America, systematics, taxonomy

Synorogenic deposits preserved near the thrust front zone and thrust belt of the Precordillera fold and in the Bermejo foreland basin in central Argentina were analyzed to trace the evolution of deformation during the last 5 Myr and to study the trust system kinematics. The seismic lines across the region indicate progressive and instantaneous limb rotations. The Niquivil thrust in the Central Precordillera's easternmost thrust plate was found to have experienced episodic motion in a first thrust movement as a fault-propagation fold and in a second movement as a high-angle anticlinal breakthrough fault after a period of quiescence.

The Argentine Precordillera is a continental fragment rifted from the Ouachita embayment of the southern margin of Laurentia (North America) during Cambrian time [about 515 million years ago (Ma)] and accreted to the western margin of Gondwana (South America) during Ordovician time (about 455 Ma). Similarities of Cambrian stratigraphic successions and faunas, Grenville basement rocks, and dimensions link the Argentine Precordillera to the Ouachita embayment. Evidence of rifting during Cambrian time and of a wide ocean basin during Ordovician time indicates that the Precordillera traveled as an independent microcontinent to collide with Gondwana., The rifted continental margin of Laurentia (now North America) records continental breakup and the opening of the lapetus Ocean in latest Precambrian to earliest Paleozoic time (1). Collisions during later [...]

Fecal analysis were made to determine the diet of wild greater rheas for the design of appropriate conservation measures. The rheas diet consisted of 90% green material, 9% of seeds and 1% of fragments of invertebrates. The green material consisted mainly of alfalfa and wild dicots which constitutes the diet of rheas for a great part of the year. Diet of rheas were found compatible to incorporate in areas used for cattle ranching.

A study of Dolphin Gulls (Larus scoresbii) conducted between 1985 and 1990 at Punta Tombo, Argentina, indicates that their atypical breeding habits are affected by vulnerability to predation and scavenging habits. Location of the colonies changes from year to year. The nest density is high, with clutches generally having two eggs. Incubation time is 24 to 27 days, and the chicks hatch from mid to late Dec. Chicks leave the nesting area within 2-5 days after hatching. Dolphin Gulls are scavengers during the breeding season and eat sea lion excrement and food dropped by Magellanic Penguins and Imperial Cormorants while feeding their young ones.

Conclusions concerning the relation between the early Paleozoic biostratigraphy of the Precordillera of northwest Argentina and the Laurentian craton are discussed. Generally, there is consistency in the relationship although two aspects of the geodynamic model do not agree with the Argentine Precordillera rifting and drifting hypothesis. A detailed analysis of this geodynamic model is presented.

A model of lithosphere shortening that combines flexural isostatic and structural balancing permits the quantitative reconciliation of lithosphere shortening, thrust sheet emplacement, and foreland basin formation. A change in flexural rigidity explains the change in the wavelength of sedimentary deposition over time in the Subandean belt, NW Argentina. Shortening estimates of 110 km generate the foreland stratigraphy, topography and Bouguer anomaly of the Eastern Cordillera and Subandean belt.

Ten species of macruran, anomuran, and brachyuran decapod crustaceans, arrayed in eight families, were collected from seven localities in the Jaguel and Roca Formations, west-central Argentina. All of the decapods were collected from the Maastrichtian Jaquel Formation and a part of the Roca Formation dated as Maastrichtian-Danian. All but one of the taxa, Xanthilites gerthi Glaessner, represent first occurrences in the unit and six had not been described previously from Argentina. Six taxa, Thaumastoplax rocaensis n. sp., Proterocarcinus lophos n. gen. and sp., Lobonotus lobulata n. sp., Glyphithyreus wichmanni n. sp., and Costacopluma australis n. sp. are new. Comparison of the fauna with Cretaceous and Paleogene faunas in Chile, Antarctica, and New Zealand indicates that the Argentinian fauna was strongly influenced by dispersal from lower latitude, Atlantic and Tethyan sources in marked contrast to the high latitude, Pacific affinities of the other faunas. There is no evidence that the Argentinian brachyuran fauna was seriously affected by the K-T extinction event. Seven of the genera from the Roca Formation are known from Cretaceous and Paleogene rocks.

Silurian and Devonian bivalves recovered from the Los Espejos (Silurian to Lower Devonian) and Talacasto (Devonian) Formations of the Northern Precordillera Mountain belt are described and illustrated. The fauna comprises some new nuculoids Deceptrix (Devonodeceptrix) jachalensis n. subgen. and n. sp., Nuculites argentinum n. sp., and Anthracoleda (Pseudoleda) minuta n. subgen. and n. sp., as well as the new pterioid Actinopteria modesta n. sp. Additionally, many poorly known South American bivalves are redescribed and figured. Silurian-Devonian pelecypod faunas from some South American localities show differences both in diversity and in faunal composition. Causes for these differences are briefly discussed. Controls other than latitude are suggested in order to explain biogeographical affinities of the studied fauna.

The Rufous-collared Sparrows in Costa Rica popularly possess individual song repertoires and they do not have the terminal trill. Comparative study with the Argentinian population suggest that songs there are more similar than songs from Costa Rica. The studies from Argentina reveal that the Rufous-collared Sparrows generally have the repertoire of one song per bird.

Ostracodes are described from the 'Cerro del Fuerte Section' and neighboring localities, all in the Precordillera de San Juan (northern Argentina, San Juan Province), and from sparse faunas in Bolivia (Chuquisaca, Tarabuco Province). Additional material comes from the collection of Thomas (1905). This preliminary study gives the first detailed description of ostracode assemblages in the Upper Silurian and Lower Devonian of the South American continent. Records of other abundant lower Paleozoic (Lower Ordovician to Lower Devonian) ostracodes in Argentina, Bolivia, Brazil, Peru, and Venezuela are also reviewed. Twelve different species, belonging to Palaeocopa (Beyrichiacea and Primitiopsacea) and to Binodicopa and Podocopa (Healdiacea, Thlipsuracea, Cypridacea) are described and a new genus is established (Australobollia n. gen.). Ostracode distribution at Cerro del Fuerte attests to the presence of the Siluro-Devonian boundary within the upper Los Espejos Formation and confirms recent stratigraphical attributions mainly based on conodonts and brachiopods (Benedetto et al., 1992). The beyrichiacean Hemsiella indicates a late Ludlow to Pridolian age for the lower part of upper Los Espejos Formation. The non-palaeocope 'Thlipsurella-Phanasymmetria-Ranapeltis' assemblage found in the uppermost part of the formation indicates an Early Devonian (Lochkovian) age. The present study reveals the existence of faunal links at genus (Silurian) and probably species (Early Devonian) level between South America (Argentina, Bolivia), Laurentia, Avalonia-Baltica, and northern Gondwana. For example, close affinities (e.g., Ranapeltis sp. aff. rowlandi and Thlipsurella sp. aff. ellipsoclefta) exist between the uppermost Los Espejos Formation (Argentina) and contemporaneous horizons in the North American Mid-Continent (e.g., Haragan Formation, Oklahoma; Shriver Formation, Pennsylvania). Two types of ostracode assemblages, 'beyrichiacean-dominated' and 'thlipsuracean-bairdiacean-cypridacean dominated,' are recognized in the Late Silurian-Early Devonian of Argentina and discussed relative to other assemblages known in Laurentia, Avalonia-Baltica, and northern Gondwana. Their paleoecological significance in relation to marine bathymetry is addressed.

Paleontologic and stratigraphic evidence points to the early Paleozoic Precordilleran terrane of western Argentina as being the conjugate rift pair of the Appalachians. Stratigraphic similarities of the Cambrian and early Arenig carbonate series and very strong affinities among trilobite, conodont, and brachiopod faunas show their close relationship. The most probable provenance areas are the Appalachian-Ouachita rifted margin and the Newfoundland Appalachians, although the former fits better with geometric and drifting paths suggested by faunal affinities. Increasing Celtic and Baltic brachiopod genera and divergent stratigraphy since the Arenig indicate the drifting of the Precordilleran terrane. Collisional foredeeps developed on collapsed former platform carbonates as flexural subsidence progressed. The collision of the Precordillera with western Gondwana occurred during the mid-Llanvirn to Llandeilo. A magmatic arc related to eastward subduction (present coordinates) was active in the Famatina Range east of the Precordillera. This region of Celtic affinity shows faunal exchange with the Precordilleran terrane since the late Arenig and may represent accreted intra-Iapetus volcanic island-arc complexes. The rifting and drifting stages are consistent with paleoclimatic and paleomagnetic data that show the migration of the Precordilleran terrane from periequatorial to peripolar latitudes between the Cambrian and latest Ordovician. The deep ocean to the west of the Precordillera started to close by the Late Ordovician with the eastward drift of the Chilenian terrane. Absence of volcanic or pyroclastic arc-derived rocks in the Precordillera indicate west-dipping subduction. As Chilenia approached the continental margin, a new forebulge was established on the former collided Precordilleran terrane, developing an erosional unconformity in central Precordillera (Talacasto-Tambolar arch). A Gondwanic signature was fully developed by the Middle Silurian when the Malvinokaffric Clarkeia Fauna flourished. Before then, the Late Ordovician glacial record and associated Hirnantia Fauna were the first clear tie to Gondwana. During the Silurian the marginal basin behaved as a foreland, with lithosphere rheology and eustasy governing the sequence stratigraphy. Wrench faulting along its eastern boundary displaced the Precordillera toward the south. Continued shortening during closure with the Chilenian terrane in the mid-Devonian produced thrust loading of the basin and generated a thick graywacke succession. Final accretion of Chilenia (Late Devonian) generated a regional angular unconformity between the lower and upper Paleozoic. New eastward subduction was initiated west of the accreted Chilenian terrane during the Late Permian-Triassic as indicated by the Choiyoi volcanic complex, which presently outcrops in the Frontal Cordillera.

Chaco Chachalacas (Ortalis canicollis) in the semi-arid Chaco forest region of northern Argentina fed mainly on herbaceous leaves (37% of the dry mass of its diet) and fleshy fruits (25%). Leaves and fruit were consumed year round. The rest of the diet consisted of caterpillars and flowers. The Chaco Chachalaca consumed all the fruit species available to it during this study period. Fruits most frequently eaten were: (1) fruit thickly bunched on the plant with long availability, even though of lower quality and (2) fruit of good quality (judged by pulp and total solids content). Low quality fruits not clumped together were less used in spite of their abundance in the forest., Guans (Penelope) and chachalacas (Ortalis) feed on leaves and fruit and probably are seed dispersers (Delacour and Amadon 1973, Terborgh 1986, Strahl and Grajal 1991). Marion (1976) found that fleshy [...]

Lower Devonian calmoniid trilobites from three localities in San Juan province, Argentina, belong to the new taxa of the Boullia-Paraboulia clade. Morphological differences of two new Argentine species do not conform to the model based on Bolivian taxa. Calmoniids from below the Scaphiocoelia do not exhibit the gradual transformation of an acastomorph ancestor but show fast diversification within the calmoniide. Ghost lineages enhance taxonomic diversity of Lochkovian, suggesting the occurrence of calmoniid radiation in the earliest Devonian.

Anthaspidellid sponges are reported from the La Laja Formation in the Chica de Zonda Range in the Precordillera Oriental, Argentina. These are generically unidentifiable fragments of trabs and more or less well-defined dendroclone spicules. They occur as skeletal elements in small transported fragments and are the only Cambrian occurrence of anthaspidellids known thus far from South America. Walcott (1920) proposed to include an array of dissociated spicules, including triradiate prodiaenes, hexactines, and probable monactine spicules, in the genus Kiwetinokia. Assemblages tentatively identified as Kiwetinokia utahensis? Walcott, 1920, are reported from the Estancia San Martin Formation, of latest Early Cambrian and early Middle Cambrian age from San Isidro Gulch near Mendoza. Similar spicule assemblages occur in the La Laja Formation from the Chica de Zonda Range, in the Precordillera Oriental near San Juan, and in the Los Sombreros Formation in the Tontal Range of the Precordillera Occidental. Sclerites of the sponge-like Chancelloria eros Walcott, 1920, are described from the upper Lower to lower Middle Cambrian La Laja Formation. Chancelloria sclerites are also reported here from rocks of the Middle Cambrian Glossopleura Zone in the San Isidro Formation in Empozada Gulch in the San Isidro area of the Precordillera Austral, west of Mendoza, in Mendoza Province. Sponges and chancelloriids from the Cambrian of Argentina are known basically from dissociated skeletal elements.