Phylogeny, diet, and habitat of an extinct ground sloth from Cuchillo Curá, Neuquén Province, southwest Argentina     

Michael Hofreiter  Julio L. Betancourt  Alicia Pelliza Sbriller  Vera Markgraf  H. Gregory McDonald 《Quaternary Research》2003,59(3):364-378

Advancements in ancient DNA analyses now permit comparative molecular and morphological studies of extinct animal dung commonly preserved in caves of semiarid regions. These new techniques are showcased using a unique dung deposit preserved in a late glacial vizcacha (Lagidium sp.) midden from a limestone cave in southwestern Argentina (38.5° S). Phylogenetic analyses of the mitochondrial DNA show that the dung originated from a small ground sloth species not yet represented by skeletal material in the region, and not closely related to any of the four previously sequenced extinct and extant sloth species. Analyses of pollen and plant cuticles, as well as analyses of the chloroplast DNA, show that the Cuchillo Curá ground sloth browsed on many of the same herb, grass, and shrub genera common at the site today, and that its habitat was treeless Patagonian scrub-steppe. We envision a day when molecular analyses are used routinely to supplement morphological identifications and possibly to provide a time-lapse view of molecular diversification.  相似文献   

On the Solar Origins of Intense Geomagnetic Storms Observed During 6–11 March 1993     

Srivastava  Nandita  Gonzalez  Walter D.  Gonzalez  Alicia L.C.  Masuda  Satoshi 《Solar physics》1998,183(2):419-434

Intense geomagnetic storms with DST index -100 nT were recorded on 9 March and 11 March 1993 associated with solar activity on 6 March and 9-10 March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6 March 1993 and in the other case, to two large filament disruptions on the disk during 9-10 March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here.  相似文献   

Groundwater chemical pollution risk: assessment through a soil attenuation index     

Olga Susana Heredia  Alicia Fernández Cirelli 《Environmental Geology》2008,53(6):1345-1351

Aquifer vulnerability is frequently estimated through methodologies that don’t consider most physical and chemical soil parameters. A soil attenuation index is proposed to estimate groundwater chemical pollution risk, that takes into account organic carbon content, pH, cation exchange capacity, clay content, phreatic depth and landscape position. The attenuation index is constructed by a methodology similar to that developed for water quality index. P, Mn and Zn concentrations in groundwater from selected places were used to validate the proposed index.  相似文献   

Grain size and depositional environment as predictors of permeability in coastal marine sands     

Alicia M. Wilson  Markus Huettel  Stephen Klein 《Estuarine, Coastal and Shelf Science》2008

More than half of the surface sediments covering the continental shelves are sandy, which may permit substantial sub-seafloor pore water advection. Knowledge of sediment permeability is required for quantifying advection and associated solute transport, but studies of marine sediments typically report grain size analyses rather than permeability. Here data from 23 studies were examined to determine the range in permeabilities reported for sublittoral marine sands and to assess the utility of permeability–grain size relationships in this setting. In the resulting database, the permeability of small (∼30 cm) undisturbed cores collected from the sea floor all fell between 2 × 10⁻¹² and 4 × 10⁻¹⁰ m², a range where advective transport induced by wave and current action should be pervasive. The range in grain size was very similar for near-shore (<10 m water depth) and continental shelf samples (>10 m water depth), but the permeability of the continental shelf samples was consistently lower for the same median grain size. Empirical permeability–grain size relationships generated a poor fit (r² = 0.35) for the aggregate data, but separate relationships for near-shore and continental shelf samples were significantly better, r² = 0.66 and 0.77, respectively. Permeability–grain size relationships thus may be useful for sublittoral sands, but a larger database needs to be accumulated before reliable fit parameters and variability can be predicted. Thus it is recommended that permeability be routinely determined when characterizing sedimentological properties of marine sand deposits. Concurrent determinations of sediment bulk density and porosity may further improve estimates of permeability.  相似文献   

Comparison of marine and river water humic substances in a Patagonian environment (Argentina)     

María del Carmen Scapini  Víctor Hugo Conzonno  Vilma Teresa Balzaretti  Alicia Fernández Cirelli 《Aquatic Sciences - Research Across Boundaries》2010,72(1):1-12

Structural aspects of humic substances (HSs) in marine waters of Engaño Bay (Atlantic Ocean) and water from the Chubut River (Patagonia, Argentina) were compared. The HSs were isolated, purified, and analyzed using a multiple-method approach for structural characterization: elemental analysis, nuclear magnetic resonance (¹³C and ¹H NMR), infrared spectroscopy (FTIR), UV-visible absorption and fluorescence. Similarities between the marine and freshwater components were evaluated on the basis of N and O contents, H/C and C/N atomic ratios, infrared bands from nitrogen-containing and carboxylic groups, percentage of functional groups obtained from NMR spectra, spectral slope coefficient of absorption spectra, absorbance ratios at 250 and 365 nm (E ₂/E ₃), aromaticity, excitation–emission matrices and fluorescence quantum yield. Both the Engaño Bay and Chubut River waters have HSs that are mainly composed of fulvic acids (FAs); although they are very similar, they may be distinguished from one another. Similarities include the predominance of aliphatic carbon content (low aromatic content); however, the water bodies differed in their content of proteins and carboxylic acids. The Engaño Bay FAs have mainly an aquatic origin; although the Chubut River FAs suggest a similar aquagenic origin, there is also evidence of contributions from pedogenic FAs.  相似文献   

A New LA‐ICP‐MS Method for Ti in Quartz: Implications and Application to High Pressure Rutile‐Quartz Veins from the Czech Erzgebirge          下载免费PDF全文

Alicia M. Cruz‐Uribe  Regina Mertz‐Kraus  Thomas Zack  Maureen D. Feineman  Glenn Woods  Dorrit E. Jacob 《Geostandards and Geoanalytical Research》2017,41(1):29-40

Experimental determination of the pressure and temperature controls on Ti solubility in quartz provides a calibration of the Ti‐in‐quartz (TitaniQ) geothermometer applicable to geological conditions up to ~ 20 kbar. We present a new method for determining ⁴⁸Ti mass fractions in quartz by LA‐ICP‐MS at the 1 μg g^?1 level, relevant to quartz in HP‐LT terranes. We suggest that natural quartz such as the low‐CL rims of the Bishop Tuff quartz (determined by EPMA; 41 ± 2 μg g^?1 Ti, 2s) is more suitable than NIST reference glasses as a reference material for low Ti mass fractions because matrix effects are limited, Ca isobaric interferences are avoided, and polyatomic interferences at mass 48 are insignificant, thus allowing for the use of ⁴⁸Ti as a normalising mass. Average titanium mass fraction from thirty‐three analyses of low temperature quartz from the Czech Erzgebirge is 0.9 ± 0.2 μg g^?1 (2s) using ⁴⁸Ti as a normalising mass and Bishop Tuff quartz rims as a reference material. The 2s average analytical uncertainty for individual analyses of ⁴⁸Ti is 8% for 50 μm spots and 7% for 100 μm spots, which offers much greater accuracy than the 21–41% uncertainty (2s) incurred from using ⁴⁹Ti as an analyte.  相似文献   

P-T conditions of earliest Late Cretaceous metamorphism in the Western Sonobari Complex,northwestern Mexico: tectonic implications     

Ricardo Vega-Granillo  Alicia Sarmiento-Villagrana  Sergio Salgado-Souto  Elizabeth Araux-Sánchez 《International Geology Review》2017,59(7):812-828

The Western Sonobari Complex in northwestern Mexico consists of metamorphosed rocks mostly derived from Palaeozoic (?) sedimentary and Mesozoic igneous protoliths. Rocks of this complex display amphibolite facies orogenic metamorphism, pervasive foliation, migmatization, and four folding phases. These features are ascribed to a contractional tectonic event with NNW–SSE shortening direction, which caused thrusting, thickening of the crust, and sinking of the lithological units. U–Pb geochronology of migmatitic leucosome bands indicates that peak metamorphic conditions were reached between ~93 and 89 Ma. Post-tectonic Late Cretaceous peraluminous aplite-pegmatite dikes transect the metamorphic foliation. Traditional thermobarometry in the metamorphic rocks yields average pressures and temperatures of 9.0–7.1 kbar and 745–663°C, typical of intermediate P/T Barrovian metamorphism. On the basis of its age and contractional character, the thickening event originating the metamorphism may be related to collision of the Alisitos island arc against crustal blocks of Mexico. Thermobarometric data of post-tectonic intrusives including Late Cretaceous granodiorite and Eocene gabbro indicate emplacement within an overthickened crust, while P-T conditions of post-tectonic dikes point towards an almost isothermal decompression path along the amphibolite facies field. Rock units of similar age and metamorphic character are discontinuously exposed from the Islas Marias offshore the Nayarit coast to the Peninsular Ranges batholith of Baja California, and even extend north into the Sierra Nevada batholith and the Sevier hinterland. This extensive belt of Barrovian metamorphic rocks thus provides a record of middle Cretaceous shortening and crustal thickening related to arc-continent collision followed by subduction resuming.  相似文献   

Set-up of a decision support system to support sustainable development of the Laguna de Bay,Philippines   总被引：2，自引：0，他引：2  

Nauta TA  Bongco AE  Santos-Borja AC 《Marine pollution bulletin》2003,47(1-6):211-218

Over recent decades, population expansion, deforestation, land conversion, urbanisation, intense fisheries and industrialisation have produced massive changes in the Laguna de Bay catchment, Philippines. The resulting problems include rapid siltation of the lake, eutrophication, inputs of toxics, flooding problems and loss of biodiversity. Rational and systematic resolution of conflicting water use and water allocation interests is now urgently needed in order to ensure sustainable use of the water resources. With respect to the competing and conflicting pressures on the water resources, the Laguna Lake Development Authority (LLDA) needs to achieve comprehensive management and development of the area. In view of these problems and needs, the Government of the Netherlands was funding a two-year project entitled 'Sustainable Development of the Laguna de Bay Environment'.A comprehensive tool has been developed to support decision-making at catchment level. This consists of an ArcView GIS-database linked to a state-of-the-art modelling suite, including hydrological and waste load models for the catchment area and a three-dimensional hydrodynamic and water quality model (Delft3D) linked to a habitat evaluation module for the lake. In addition, MS Office based tools to support a stakeholder analysis and financial and economic assessments have been developed. The project also focused on technical studies relating to dredging, drinking water supply and infrastructure works. These aimed to produce technically and economically feasible solutions to water quantity and quality problems. The paper also presents the findings of a study on the development of polder islands in the Laguna de Bay, addressing the water quantity and quality problems and focusing on the application of the decision support system.  相似文献   

An evaluation of glass prisms in boat docks to reduce shading of submerged aquatic vegetation in the lower St. Johns River,Florida     

Alicia?M.?SteinmetzEmail author  Michelle?M.?Jeansonne  Emily?S.?Gordon  John?W.?Burns 《Estuaries and Coasts》2004,27(6):938-944

The effectiveness of glass prisms in boat docks was assessed to determine if shading impacts to submerged aquatic vegetation (SAV), primarilyVallisneria americana, were reduced. Six experimental docks, three with prisms and three without prisms, were constructed in the lower St. Johns River, Florida. SAV percent cover and photosynthetically active radiation (PAR) were monitored under each dock and in an adjacent control area with no experimental docks. Subsurface PAR during the growing season of the first year of the study was not significantly greater beneath docks having prisms than beneath docks without prisms. Postconstruction SAV monitoring (February 2000 to May 2002) revealed no significant differences in SAV percent cover between dock treatments, although coverage declined in both dock treatments and the control area. Declining water quality conditions at the study site clearly impacted the health of the SAV habitat as indicated by the decline in SAV coverage in the control area initially in the study. Given the subsequent resurgence of SAV in the control area, the additional light transmitted through the prisms did not appear to be biologically significant or adequate to counteract effects from larger-scale environmental stressors.  相似文献   

Weathering profiles in granites, Sierra Norte (Córdoba, Argentina)     

Alicia Kirschbaum  Estela Martínez  Gisela Pettinari  Silvana Herrero 《Journal of South American Earth Sciences》2005,19(4):479-493

Two weathering profiles evolved on peneplain-related granites in Sierra Norte, Córdoba province, were examined. Several weathering levels, of no more than 2 m thickness, were studied in these profiles. They had developed from similar parent rock, which had been exposed to hydrothermal processes of varying intensity. Fracturing is the most notable feature produced by weathering; iron oxides and silica subsequently filled these fractures, conferring a breccia-like character to the rock. The clay minerals are predominantly illitic, reflecting the mineral composition of the protolith. Smaller amounts of interstratified I/S RO type are also present, as well as scarce caolinite+chlorite that originated from the weathering of feldspar and biotite, respectively. The geochemical parameters define the weathering as incipient, in contrast to the geomorphological characteristics of Sierra Norte, which point to a long weathering history. This apparent incompatibility could be due to the probable erosion of the more weathered levels of the ancient peneplains, of which only a few relicts remain. Similar processes have been described at different sites in the Sierras Pampeanas. Reconstruction and dating of the paleosurfaces will make it possible to set time boundaries on the weathering processes studied and adjust the paleographic and paleoclimatic interpretations of this great South American region.  相似文献