2,608 research outputs found
Penecontemporaneous partial disaggregationand/or resedimentation during the formation and deposition of subglacial till
Glacier ice has been always considered to be the geologic agent that forms and deposits till. However, the reality is more complex: meltwater and gravity participate to various degrees at the formation, deposition and penecontemporaneous redeposition of till, even though the glacier is the principal agent and thedeposition of till takes place in contact or near-contact with glacier ice. Boulton's (1980) and Lawson's (1981) cntena for the differentiation of "tills" from "nontills" are tested here, by using mainly their own data on glacial sedimentation and penecontemporaneous resedimentation at Breidamerkurjokull, Iceland, and Matanuska Glacier, Alaska, but re-interpreting some of their conclusions or pointing out some discrepancies in their own conclusions. A strict adherence to some of Boulton's (1980) and Lawson's (1981) critetia would not permit calling most of Matanuska Glacier's melt-out tills, and the Breidamerkurjokull, lodgement till, particularly its dilated top portion, a true till. However, they may be considered tills, if the broad definition of: "Till is a sediment that has been transported and subsequently deposited by or from glacier ice, with little or no sorting by water" is applied instead
Lake Arkona-Whittlesey and Post-Warren Radiocarbon Dates from "Ridgetown Island" in Southwestern Ontario
Author Institution: Department of Geology, University of Western OntarioThree radiocarbon dates from raised beaches along the "Ridgetown Island" support the age assignment of 13,000 years B.P. for the beginning of Lake Whittlesey in Ohio, and the termination of Lake Warren before 12,000 years B.P., as concluded from post-Warren data in Ontario
Penecontemporaneous partial disaggregationand/or resedimentation during the formation and deposition of subglacial till
Glacier ice has been always considered to be the geologic agent that forms and deposits till. However, the reality is more complex: meltwater and gravity participate to various degrees at the formation, deposition and penecontemporaneous redeposition of till, even though the glacier is the principal agent and thedeposition of till takes place in contact or near-contact with glacier ice. Boulton's (1980) and Lawson's (1981) cntena for the differentiation of "tills" from "nontills" are tested here, by using mainly their own data on glacial sedimentation and penecontemporaneous resedimentation at Breidamerkurjokull, Iceland, and Matanuska Glacier, Alaska, but re-interpreting some of their conclusions or pointing out some discrepancies in their own conclusions. A strict adherence to some of Boulton's (1980) and Lawson's (1981) critetia would not permit calling most of Matanuska Glacier's melt-out tills, and the Breidamerkurjokull, lodgement till, particularly its dilated top portion, a true till. However, they may be considered tills, if the broad definition of: "Till is a sediment that has been transported and subsequently deposited by or from glacier ice, with little or no sorting by water" is applied instead
Alpha-chloralose poisoning in cats: clinical findings in 25 confirmed and 78 suspected cases
Objectives The aim of this study was to describe the clinical picture in cats with alpha-chloralose (AC) intoxication and to confirm AC in serum from suspected cases of AC poisoning. Methods Suspected cases of AC poisoning were identified in patient records from a small animal university hospital from January 2014 to February 2020. Clinical signs of intoxication described in respective records were compiled, the cats were graded into four intoxication severity scores and hospitalisation time and mortality were recorded. Surplus serum from select cases in late 2019 and early 2020 was analysed to detect AC with a quantitative ultra-high performance liquid chromatography tandem mass spectrometry analysis, and the AC concentration was compared with the respective cat's intoxication severity score. Results Serum from 25 cats was available for analysis and AC poisoning was confirmed in all. Additionally, 78 cats with a clinical suspicion of AC intoxication were identified in the patient records, most of which presented from September to April. The most common signs of intoxication were ataxia, tremors, cranial nerve deficits and hyperaesthesia. The prevalence of clinical signs and intoxication severity differed from what has previously been reported, with our population presenting with less severe signs and no deaths due to intoxication. The majority had a hospitalisation time <48 h, irrespective of intoxication severity score. Conclusions and relevance This study describes the clinical signs and prognosis in feline AC intoxication. There were no mortalities in confirmed cases, indicating that AC-poisoned cats have an excellent prognosis when treated in a timely manner. Recognition of AC intoxication as a differential diagnosis for acute onset of the described neurological signs in areas where AC exposure is possible may influence clinical decision-making and help avoid excessive diagnostic procedures. A severe clinical picture upon presentation could be misinterpreted as a grave prognosis and awareness about AC poisoning may avoid unnecessary euthanasia
Anomalous luminescence of subglacial sediment at Haut glacier d'Arolla, Switzerland - a consequence of resetting at the glacier bed?
<p>Luminescence has the potential to elucidate glacial geomorphic processes because primary glacial sediment sources and transport pathways are associated with contrasting degrees of exposure to light. Most notably, sediment entrained from extraglacial sources should be at
least partially reset, whereas sediment produced by glacial erosion of subglacial bedrock should retain substantial luminescence commensurate with a geological irradiation history.</p>
<p>We set out to test the validity of this assumption at Haut Glacier dâArolla, Switzerland using sediment sampled extraglacially and from the glacier bed. Contrary to our expectations, the subglacial samples exhibited natural signals that were substantially lower than those of other sample groups, and further (albeit limited) analyses have indicated no obvious differences in sample group luminescence characteristics or behaviour that could account for this observation. For glaciological reasons, we can eliminate both the possibility that the subglacial sediment has been extraglacially-reset or exposed in situ to heat or light. We therefore advocate investigation of possible resetting processes related to subglacial crushing and grinding, and speculate that such processes, if more generally present, may enable the dating of subglacially-deposited tills using luminescence-based techniques.</p>
Subduction metamorphism of serpentiniteâhosted carbonates beyond antigorite-serpentinite dehydration (NevadoâFilĂĄbride Complex, Spain)
I. MartĂnez Segura and M. J. RomĂĄn Alpiste are thanked for their kind assistance during sample preparation and SEM operation, and M. T. GĂłmezâPugnaire and A. Jabaloy for early work on Almirez ophicarbonates. We are grateful to the Sierra Nevada National Park for providing permits for fieldwork and sampling at the Almirez massif. We further acknowledge the editorial handling by D. Whitney and D. Robinson and the reviews of M. Galvez and T. Pettke, whose comments and constructive criticism helped to improve the manuscript.
We acknowledge funding from the European Union FP7 MarieâCurie Initial Training Network ABYSS under REA Grant Agreement no. 608001 in the framework of M.D.M.'s PhD project, the Spanish âAgencia Estatal de InvestigaciĂłnâ (AEI) grants no. CGL2016â75224âR to V.L.S.âV and CGL2016â81085âR to C.J.G and C.M and grant no. PCINâ2015â053 to C.J.G. The âJunta de AndalucĂaâ is also thanked for funding under grants no. RNMâ131, RNMâ374 and P12âRNMâ3141. C.M. thanks MINECO for financing a RamĂłn y Cajal fellowship no. RYCâ2012â11314 and K.H. for a Juan de la Cierva Fellowship no. FPDIâ2013â16253 and a research contract under grant no. CGL2016â81085âR. This work and the research infrastructure at the IACT have received (co)funding from the European Social Fund and the European Regional Development Fund.At subâarc depths, the release of carbon from subducting slab lithologies is mostly
controlled by fluid released by devolatilization reactions such as dehydration of antigorite (Atgâ) serpentinite to prograde peridotite. Here we investigate carbonateâsilicate rocks hosted in Atgâserpentinite and prograde chlorite (Chlâ) harzburgite in the
Milagrosa and Almirez ultramafic massifs of the palaeoâsubducted NevadoâFilĂĄbride
Complex (NFC, Betic Cordillera, S. Spain). These massifs provide a unique opportunity to study the stability of carbonate during subduction metamorphism at PâT
conditions before and after the dehydration of Atgâserpentinite in a warm subduction
setting. In the Milagrosa massif, carbonateâsilicate rocks occur as lenses of Tiâclinohumiteâdiopsideâcalcite marbles, diopsideâdolomite marbles and antigoriteâdiopsideâdolomite rocks hosted in clinopyroxeneâbearing Atgâserpentinite. In Almirez,
carbonateâsilicate rocks are hosted in Chlâharzburgite and show a highâgrade assemblage composed of olivine, Tiâclinohumite, diopside, chlorite, dolomite, calcite, Crâ
bearing magnetite, pentlandite and rare aragonite inclusions. These NFC
carbonateâsilicate rocks have variable CaO and CO2 contents at nearly constant Mg/
Si ratio and high Ni and Cr contents, indicating that their protoliths were variable
mixtures of serpentine and Caâcarbonate (i.e., ophicarbonates). Thermodynamic
modelling shows that the carbonateâsilicate rocks attained peak metamorphic conditions similar to those of their host serpentinite (Milagrosa massif; 550â600°C and
1.0â1.4 GPa) and Chlâharzburgite (Almirez massif; 1.7â1.9 GPa and 680°C).
Microstructures, mineral chemistry and phase relations indicate that the hybrid carbonateâsilicate bulk rock compositions formed before prograde metamorphism,
likely during seawater hydrothermal alteration, and subsequently underwent subduction metamorphism. In the CaOâMgOâSiO2 ternary, these processes resulted in a
compositional variability of NFC serpentiniteâhosted carbonateâsilicate rocks along
the serpentineâcalcite mixing trend, similar to that observed in serpentiniteâhosted
carbonateârocks in other palaeoâsubducted metamorphic terranes. Thermodynamic modelling using classical models of binary H2OâCO2 fluids shows that the compositional variability along this binary determines the temperature of the main devolatilization reactions, the fluid composition and the mineral assemblages of reaction
products during prograde subduction metamorphism. Thermodynamic modelling
considering electrolytic fluids reveals that H2O and molecular CO2 are the main fluid
species and charged carbonâbearing species occur only in minor amounts in equilibrium with carbonateâsilicate rocks in warm subduction settings. Consequently, accounting for electrolytic fluids at these conditions slightly increases the solubility of
carbon in the fluids compared with predictions by classical binary H2OâCO2 fluids,
but does not affect the topology of phase relations in serpentiniteâhosted carbonateâ
rocks. Phase relations, mineral composition and assemblages of Milagrosa and
Almirez (meta)âserpentiniteâhosted carbonateâsilicate rocks are consistent with local
equilibrium between an infiltrating fluid and the bulk rock composition and indicate
a limited role of infiltrationâdriven decarbonation. Our study shows natural evidence
for the preservation of carbonates in serpentiniteâhosted carbonateâsilicate rocks beyond the Atgâserpentinite breakdown at subâarc depths, demonstrating that carbon
can be recycled into the deep mantle.Funding from the European Union FP7 MarieâCurie Initial Training Network ABYSS under REA Grant Agreement no. 608001Spanish âAgencia Estatal de InvestigaciĂłnâ (AEI) grants no. CGL2016â75224âR to V.L.S.âV and CGL2016â81085âR to C.J.G and C.M and grant no. PCINâ2015â053 to C.J.GJunta de AndalucĂa Funding under grants no. RNMâ131, RNMâ374 and P12âRNMâ3141MINECO for financing a RamĂłn y Cajal fellowship no. RYCâ2012â11314 and K.H. for a Juan de la Cierva Fellowship no. FPDIâ2013â16253 and a research contract under grant no. CGL2016â81085â
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