Search results for " Isotopes"
showing 10 items of 460 documents
The role of trapped fluids during the development and deformation of a carbonate/shale intra-wedge tectonic mélange (Mt. Massico, Southern Apennines,…
2020
Abstract Numerous studies exist on exhumed tectonic melanges along subduction channels whereas, in accretionary wedge interiors, deformation mechanisms and related fluid circulation in tectonic melanges are still underexplored. We combine structural and microstructural observations with geochemical (stable and clumped isotopes and isotope composition of noble gases in fluid inclusions of calcite veins) and U-Pb geochronological data to define deformation mechanisms and syn-tectonic fluid circulation within the Mt. Massico intra-wedge tectonic melange, located in the inner part of the central-southern Apennines accretionary wedge, Italy. This melange developed by shear deformation at the bas…
Bulk carbonate isotope stratigraphy from CRP-3 core (Victoria Land Basin, Antarctica): evidence for Eocene–Oligocene palaeoclimatic evolution
2005
Bulk carbonate isotope compositions and carbonate petrography from upper Eocene and lower Oligocene siliciclastic sediments of the CRP-3 sediment core (Victoria Land Basin, Antarctica) have been investigated with the aim of contributing to reconstruction of the Antarctic Cenozoic palaeoclimate. Most of the carbonate is calcite cement occurring as patches, nodules and horizons and consisting of equant and/or drusy sparry calcite, pervasive blocky calcite and rare poikilotopic calcite spar. 18O-depleted values (from −17 to −8 δ‰) of the CRP-3 carbonates suggest that the precipitating fluids were a mixing between marine and meteoric waters from melting glaciers. The δ18O record exhibits a numb…
Textural features and isotope geochemistry of the Scillato travertine (north-central Sicily): genetic implications.
2015
The travertine deposit, outcropping near the Scillato town (north-central Sicily), was originated by precipitation of calcium carbonate from the Scillato springs, documented as bicarbonate-enriched waters due to dissolution of the Madonie mountains carbonate rocks. This deposit is today well represented by the Travertine Cave, essentially constituted by stalactites and stalagmites in which travertine typically appears laminated with alternation of light and dark laminae. Mineralogical analysis have revealed the almost exclusive presence of calcite and observation under the polarized-light microscope showed different textural features, like presence of debris and porous portions, micritic po…
Calcium transport in rat small intestine in vitro and in vivo
1972
Intestinal calcium (Ca) transport was studied in the rat jejunum by the in vitro perfusion technique of Fisher and Parsons and in the tied loop in vivo. Mucosal uptake and absorption of Ca was examined under the following conditions: rising intraluminal Ca-concentrations (0.5–128 meq/l); inhibition of energy dependent metabolism (2,4-dinitrophenol, N2, low temperature); net water flow, out of or into the intestinal lumen; addition of strontium (Sr); pretreatment with low Ca-diet and with 6-methyl-prednisolone. The concentration-dependent Ca absorption curve rose steeply at low Ca-concentrations but changed to a slowly rising straight line above 16 meq/l Ca++. In contrast, Ca uptake into the…
Excitotoxic Hippocampal Membrane Breakdown and its Inhibition by Bilobalide: Role of Chloride Fluxes
2003
We have previously shown that hypoxia and N-methyl-D-aspartate (NMDA) receptor activation induce breakdown of choline-containing phospholipids in rat hippocampus, a process which is mediated by calcium influx and phospholipase A (2) activation. Bilobalide, a constituent of Ginkgo biloba, inhibited this process in a potent manner (Weichel et al., Naunyn-Schmiedeberg's Arch. Pharmacol. 360, 609-615, 1999). In this study, we used fluorescence microscopy and radioactive flux measurements to show that bilobalide does not interfere with NMDA-induced calcium influx. Instead, bilobalide seems to inhibit NMDA-induced fluxes of chloride ions through ligand-operated chloride channels. In our experimen…
Dibutyryl cyclic AMP and adrenaline increase contractile force and 45Ca uptake in mammalian cardiac muscle
1973
The effects of dibutyryl cyclic AMP (DB-AMP; 10−3M) and adrenaline (2.2×10−6 M) on contractile force, 45Ca uptake, and total myocardial Ca concentration were investigated in electrically driven left auricles isolated from rat hearts. The experiments were performed at an extracellular Ca concentration of 0.45 mM and at low frequency of stimulation (15 beats/min). 45Ca exposure was 5 min. Under the conditions used, both drugs increased contractile force and enhanced 45Ca uptake (expressed as relative specific activity) by about 30% (DB-AMP) and 40% (adrenaline), respectively. Thus, the results provide evidence that the effects of adrenaline on 45Ca uptake in mammalian cardiac muscle can be mi…
Isotopic composition of cattle pancreatic stones: biological and geochemical implications.
1977
Latitudinal variations of the O18/O16-ratios of carbonate and phosphate of cattle pancreatic stones parallel a similar pattern of oxygen isotope values in rain water. C13/C12-ratios were virtually identical for the 7 cases studied. Isotopic measurements of mammalian hard tissues may be used for studying short-term climatic variations through Quaternary.
Oxygen isotope composition of North American bobcat (Lynx rufus) and puma (Puma concolor) bone phosphate: implications for provenance and climate rec…
2015
Feline carnivores are threatened by illegal wildlife trade. Tracing the provenance of unknown felid tissues via stable isotope analysis could provide important information in wildlife crime investigations. The oxygen isotope composition of mammalian skeletal phosphate (δ(18)Op) is widely applied to trace the origin of animal remains and to reconstruct migratory patterns in palaeontological, archaeological, ecological and wildlife forensic applications. Teeth and bones of terrestrial mammals form at constant body temperature in isotope equilibrium with body water, which is predominantly controlled by ingested meteoric water (δ(18)Ow) that varies systematically with latitude, altitude and cli…
Relationship between recruitment and mother plant vitality in the alien species Acacia cyclops A. Cunn. ex G. Don
2014
Acacia cyclops is a widespread invader in Mediterranean-climate regions. However, although its naturalization in the Mediterranean Basin dates back only a few years ago, and the invasion process has not been studied hitherto. We investigated seedlings recruitment strategy adopted by A. cyclops in a small island (Lampedusa, Italy) where its natural regeneration was strictly confined under mother plants canopy. Healthy plants (DCP), plants at incipient senescence (SCP) and dead plants (DP) were distinguished according to vitality and canopy status. Living plants were also characterized in relation to leaf C and N isotope composition. Regeneration pattern (seedlings and saplings abundance) was…
Comparison of δ(13)C and δ(18)O from cellulose, whole wood, and resin-free whole wood from an old high elevation Pinus uncinata in the Spanish centra…
2016
δ(13)C and δ(18)O values from sapwood of a single Pinus uncinata tree, from a high elevation site in the Spanish Pyrenees, were determined to evaluate the differences between whole wood and resin-free whole wood. This issue is addressed for the first time with P. uncinata over a 38-year long period. Results are also compared with published isotope values of α-cellulose samples from the same tree. The differences in δ(13)C and δ(18)O between whole wood and resin-free whole wood vary within the analytical uncertainty of 0.3 and 0.5 ‰, respectively, indicating that resin extraction is not necessary for sapwood of P. uncinata. Mean differences between cellulose and whole wood are 0.9 ‰ (δ(13)C)…