75 research outputs found
Primer registro de Conopeum gray (Electridae, Bryozoa) en el cretácico superior de la Formación Lefipán (Chubut, Patagonia)
La radiación adaptativa del Orden Cheilostomata (Bryozoa) durante el Cretácico Tardío es de particular interés debido a la rápida expansión y evolución explosiva de innovaciones morfológicas que aparecieron en el grupo. Sin embargo, el conocimiento de briozoos cretácicos es muy escaso globalmente, especialmente en Sudamérica y particularmente en Argentina. En la Formación Lefipán se ha reconocido una fauna monoespecífica de briozoos epifíticos sobre hojas de angiospermos fósiles. La Formación Lefipán es una unidad siliciclástica del Maastrichtiano?Daniano en el ámbito NO de la Cuenca Cañadón Asfalto, la cual completa el ciclo de relleno del rift iniciado a principios del Jurásico. Sus condiciones de sedimentación corresponden a depósitos litorales representados por plataformas someras y deltas dominados por mareas. Asimismo se registra en la unidad la transición K/Pg, aunque en un contexto dinámico afectado por la fase marina transgresiva iniciada a fines del Maastrichtiano. Los ejemplares estudiados corresponden a una nueva especie de queilostomado membraniporiformeasignable al género Conopeum. Briozoos modernos de hábitos de crecimiento membraniporiformes son componentes comunes de ambientes marinos de plataforma somera, intermareal a supramareal con niveles de energía moderada a alta y sustratos duros a flexibles. En la actualidad también se registran formas epifíticas de briozoos caracterizadas por ser fotófilos y por habitar ambientes salobres como albuferas, estuarios y deltas presentando hábitos eurihalinos y adaptados a la naturaleza efímera y flexible del sustrato. Tales condiciones se verifican en la Formación Lefipán, por lo que los briozoos identificados confirman interpretaciones previas.Fil: Taboada, César Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales - Sede Trelew; ArgentinaFil: Pagani, María Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; ArgentinaFil: Cúneo, R.. Museo Paleontológico Egidio Feruglio; ArgentinaReunión de Comunicaciones de la Asociación Paleontológica ArgentinaPuerto MadrynArgentinaCentro Nacional Patagónic
A Paleocene lowland macroflora from Patagonia reveals significantly greater richness than North American analogs
Few South American macrofloras of Paleocene age are known, and this limits our knowledge of diversity and composition between the end-Cretaceous event and the Eocene appearance of high floral diversity. We report new, unbiased collections of 2516 compression specimens from the Paleocene Salamanca Formation (ca. 61.7 Ma) from two localities in the Palacio de los Loros exposures in southern Chubut, Patagonia, Argentina. Our samples reveal considerably greater richness than was previously known from the Paleocene of Patagonia, including 36 species of angiosperm leaves as well as angiosperm fruits, flowers, and seeds; ferns; and conifer leaves, cones, and seeds. The floras, which are from siltstone and sandstone channel-fills deposited on low-relief floodplain landscapes in a humid, warm temperate climate, are climatically and paleoenvironmentally comparable to many quantitatively collected Paleocene floras from the Western Interior of North America. Adjusted for sample size, there are >50% more species at each Palacio de los Loros quarry than in any comparable U.S. Paleocene sample. These results indicate more vibrant terrestrial ecosystems in Patagonian than in North American floodplain environments ∼4 m.y. after the end-Cretaceous extinction, and they push back the time line 10 m.y. for the evolution of high floral diversity in South America. The cause of the dis parity is unknown but could involve reduced impact effects because of greater distance from the Chicxulub site, higher latest Cretaceous diversity, or faster recovery or immigration rates.Facultad de Ciencias Naturales y Muse
Latest Cretaceous, Paleocene and Eocene floras from Patagonia: a critical piece of Gondwana's floral history comes into focus
Patagonia contains a rich and fairly continuous paleobotanical record from the late Maastrichtian to the middle Eocene, an interval known globally for mass extinction and significant climate changes. From this time interval, we have quantitatively collected and stratigraphically studied over 600 species and 20000 specimens from eight wellpreserved compression macrofloras from north-west and central Patagonia. Cretaceous and early Paleocene floras are from coastal environments, whereas the Eocene floras are from volcaniclastic lake sediments. Several sites and stratigraphic levels in the early Paleocene Salamanca Formation show higher richness than comparable Northern Hemisphere floras, but they are relatively impoverished when compared to those of the upper Maastrichtian Lefipan Formation. Probable middle Paleocene floras from the Peñas Coloradas Formation share most species with the Salamanca Formation, but are preserved in fluvial facies. Bedded tuffs at the Eocene sites have yielded precise Ar- Ar dates of 54.24 ±0.45 Ma for the Pampa de Jones flora, 51.91 ±0.22 Ma for the extremely diverse Laguna del Hunco flora, and 47.46 ±0.05 Ma for the similarly rich Río Pichileufú flora. The history of Patagonian plant diversity in the early Paleogene could be linked to a relatively lower effect of the terminal Cretaceous event and high diversification and immigration during Eocene warming. Although the biogeographic signature of the floras is clearly Gondwanic, during the Paleocene there appears to be greater compositional distinctiveness from coeval Australasian floras than in the Eocene, suggesting some degree of endemism after the K-T. The Eocene floras include beautifully preserved examples of extant Australasian tree genera that are now extinct in South America, including Agathis, Papuacedrus, Dacrycarpus, Eucalyptus, Cassuarinaeceae, and Akaniaceae. Paleoclimate analyses based on the macrofloras indicate subtropical and moist growing conditions; during the Eocene there is evidence for true rainforest conditions. These results contribute a considerably improved framework to understanding the plant evolution in Gondwana.Sesiones libresFinanciado: NSF Grants DEB-0919071 and DEB-0345750Financing: NSF Grants DEB-0919071 and DEB-0345750Financiamento: NSF Grants DEB-0919071 and DEB-0345750Facultad de Ciencias Naturales y Muse
X-ray Spectral and Timing evolution of MAXI J1727-203 with NICER
We present a detailed X-ray spectral and variability study of the full 2018 outburst of MAXI J1727-203 using NICER observations. The outburst lasted approximately four months. Spectral modelling in the 0.3-10 keV band shows the presence of both a soft thermal and a hard Comptonised component. The analysis of these components shows that MAXI J1727-203 evolved through the soft, intermediate and hard spectral states during the outburst. We find that the soft (disc) component was detected throughout almost the entire outburst, with temperatures ranging from ∼0.4 keV, at the moment of maximum luminosity, to ∼0.1 keV near the end of the outburst. The power spectrum in the hard and intermediate states shows broadband noise up to 20 Hz, with no evidence of quasi-periodic oscillations. We also study the rms spectra of the broadband noise at 0.3 - 10 keV of this source. We find that the fractional rms increases with energy in most of the outburst except during the hard state, where the fractional rms remains approximately constant with energy. We also find that, below 3 keV, the fractional rms follows the same trend generally observed at energies >3 keV, a behaviour known from previous studies of black holes and neutron stars. The spectral and timing evolution of MAXI J1727-203, as parametrised by the hardness-intensity, hardness-rms, and rms-intensity diagrams, suggest that the system hosts a black hole, although we could not rule out a neutron star
Discovery of optical outflows and inflows in the black hole candidate GRS 1716-249
We present optical spectroscopy obtained with the GTC, VLT and SALT
telescopes during the decline of the 2016-2017 outburst of the black hole
candidate GRS 1716-249 (Nova Oph 1993). Our 18-epoch data set spans 6 months
and reveals that the observational properties of the main emission lines are
very variable, even on time scales of a few hours. Several epochs are
characterised by P-Cyg (as well as flat-top and asymmetric) profiles in the
H, H and He II (4686) emission lines, implying the
presence of an accretion disc wind, which is likely hot and dense. The wind's
terminal velocity (2000 km s) is similar to that observed in other
black hole X-ray transients. These lines also show transient and sharp
red-shifted absorptions, taking the form of inverted P-Cyg profiles. We argue
that these profiles can be explained by the presence of infalling material at
1300 km s. We propose a failed wind scenario to explain this
inflow and discuss other alternatives, such as obscuration produced by an
accretion-related structure (e.g. the gas stream) in a high inclination system.Comment: Published in MNRAS main journa
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