Early Triassic (Induan–Olenekian) conodont biostratigraphy,global anoxia,carbon isotope excursions and environmental perturbations: New data from Western Australian Gondwana     

I. Metcalfe  R.S. Nicoll  R. Willink  M. Ladjavadi  K. Grice 《Gondwana Research》2013,23(3):1136-1150

The Early Triassic Induan–Olenekian Stage boundary (Dienerian–Smithian sub-stage boundary) has been identified at a depth of 2719.25 m in the petroleum exploration well Senecio-1 located in the northern Perth Basin, Western Australia. Conodont faunas represent three conodont zones in ascending order, the Neospathodus dieneri Zone, the Neospathodus waageni eowaageni Zone and the Neospathodus waageni waageni Zone. The Induan–Olenekian (Dienerian–Smithian) boundary is placed at the base of the Neospathodus waageni eowaageni Zone equivalent to the first appearance of Neospathodus ex. gr. waageni utilised elsewhere and adopted by the IUGS ICS Triassic Subcommission to define the base of the Olenekian. Bulk kerogen δ¹³C carbon isotopes define a positive peak of c. 4 per mille that essentially coincides with the Induan–Olenekian boundary as seen in proposed Global Stratotype Sections and Points (GSSPs) in South China and Spiti, India demonstrating the global utility of this level for correlation. An anoxic zone is recognised in the lower part of the Senecio-1 core and the upper limit of this zone is dated as late Induan (late Dienerian). Temporal and spatial mapping of marine anoxia and dysoxia globally demonstrates that pulses of dysoxia/anoxia affected shallow-marine zones at different times in different locations. Dysoxia/anoxia in the shallow-marine environment appeared in the latest Permian at the extinction level, later than in the deep-marine environment, and appears to be largely restricted to the Induan (Griesbachian and Dienerian) and early Olenekian (Smithian). Temporally and geographically restricted upwelling of an oxygen minimum zone into the ocean surface layer due to environmental perturbations including extreme global warming, increased terrestrial chemical weathering intensity and continental erosion, sea level rise, and changes in marine nutrient inventories and productivity rates, is interpreted as a likely cause of observed variation in shallow-marine dysoxia/anoxia in the Early Triassic.  相似文献   

The Jinshajiang suture zone: tectono-stratigraphic subdivision and revision of age   总被引：2，自引：0，他引：2  

WANG Xiaofeng  Ian Metcalfe  JIAN Ping  HE Longqing  WANG Chuanshang 《中国科学D辑(英文版)》2000,43(1):10-22

Integrated study of rock assemblage, tectonic setting, geochemical feature, fossil contained and isotopic geochronology on the metamorphic mixed bodies, exposed in the Jinshajiang suture zone, suggests that one informal lithostratigraphic unit, the Eaqing Complex, and three tectono-stratigraphic units, the Jinshajiang ophiolitic melange, the Gajinxueshan Group and the Zhongxinrong Group, can be recognized there. It is first pointed out that the redefined Eaqing Complex might represent the Meso- to Neo-Proterozoic remnant metamorphic basement or mi-crocontinental fragment in the Jinshajiang area. The original rocks of it should be older than (1627 ±192) Ma based on the geochronological study. The zircon U-Pb age of plagiogranites within the Jinshajiang ophiolitic assemblage is dated for the first time at (294 ± 3) Ma and (340 ± 3) Ma respectively. The Jinshajiang ophiolite is approximately equivalent to the Ailaoshan ophiolite in the formation age, covering the interval from the Late Devonian to the Carboniferous. Dating of U-Pb age from basalt interbeds indicates that the redefined Gajinxueshan Group and Zhongxinrong Group may be considered Carboniferous to Permian and latest Permian to Middle Triassic in age. In geotectonic terms the Jinshajiang suture zone is thought to be a back-arc basin in the eastern margin of the Paleo-Tethys. This back-arc basin started in the Late Devonian, and formed in the Devonian-Carboniferous. The collision event around the Permian/Triassic boundary to the Middle Triassic led to the closure of the back-arc basin and formation of suture.  相似文献   

Galaxy clustering in the Herschel Deep Field     

H. J. McCracken  †  T. Shanks  N. Metcalfe  R. Fong  A. Campos 《Monthly notices of the Royal Astronomical Society》2000,318(3):913-924

  相似文献   

Accuracy of tretyakov precipitation gauge: Result of wmo intercomparison     

Daqing Yang  Barry E. Goodison  John R. Metcalfe  Valentin S. Golubev  Esko Elomaa  Thilo Gunther  Roy Bates  Timothy Pangburn  Clayton L. Hanson  Douglas Emerson  Voilete Copaciu  Janja Milkovic 《水文研究》1995,9(8):877-895

The Tretyakov non-recording precipitation gauge has been used historically as the official precipitation measurement instrument in the Russian (formerly the USSR) climatic and hydrological station network and in a number of other European countries. From 1986 to 1993, the accuracy and performance of this gauge were evaluated during the WMO Solid Precipitation Measurement Intercomparison at 11 stations in Canada, the USA, Russia, Germany, Finland, Romania and Croatia. The double fence intercomparison reference (DFIR) was the reference standard used at all the Intercomparison stations in the Intercomparison. The Intercomparison data collected at the different sites are compatible with respect to the catch ratio (measured/DFIR) for the same gauge, when compared using mean wind speed at the height of the gauge orifice during the observation period. The Intercomparison data for the Tretyakov gauge were compiled from measurements made at these WMO intercomparison sites. These data represent a variety of climates, terrains and exposures. The effects of environmental factors, such as wind speed, wind direction, type of precipitation and temperature, on gauge catch ratios were investigated. Wind speed was found to be the most important factor determining the gauge catch and air temperature had a secondary effect when precipitation was classified into snow, mixed and rain. The results of the analysis of gauge catch ratio versus wind speed and temperature on a daily time step are presented for various types of precipitation. Independent checks of the correction equations against the DFIR have been conducted at those Intercomparison stations and a good agreement (difference less than 10%) has been obtained. The use of such adjustment procedures should significantly improve the accuracy and homogeneity of gauge-measured precipitation data over large regions of the former USSR and central Europe.  相似文献   

Changing patterns in rainfall extremes in South Australia     

Kamruzzaman  Mohammad  Beecham  Simon  Metcalfe  Andrew V. 《Theoretical and Applied Climatology》2017,127(3-4):793-813

Theoretical and Applied Climatology - Daily rainfall records from seven stations in South Australia, with record lengths from 50 to 137 years and a common period of 36 years, are...  相似文献   

Climate change at the monsoon/Westerly boundary in Northern Mexico   总被引：1，自引：0，他引：1  

S. E. Metcalfe  A. Bimpson  A. J. Courtice  S. L. O‘Hara  D. M. Taylor 《Journal of Paleolimnology》1997,17(2):155-171

Northern Mexico lies close to the present day boundary between mid-latitude (Westerly) and tropical (monsoonal) sources of moisture. Studies from the adjacent southwest USA have shown major changes in lake levels and vegetation distributions over the late Quaternary which have been interpreted in terms of significant variations in the relative strengths and positions of these climate systems. Palaeoclimatic data from this area have, however, left a number of unresolved questions which can only be answered by extending work into northern Mexico, closer to the major source of summer (monsoonal) rain, the Gulf of Mexico. Studies of palaeolake sediments from a series of hydrologically closed lake basins across a range of altitudes (1280 to 2200 m a.s.l.) in northern Chihuahua are in progress using geochemical, mineral magnetic, diatom and plant microfossil analyses. Preliminary results are presented from the Alta Babícora and Encinillas basins. The sites provide records of lacustrine deposition between >11000 and about 2500 yr BP. The diatom record from Babíora provides clear evidence for a deep water lake in this basin in the late glacial which persisted into the early Holocene. A dry episode coinciding with the timing of the Younger Dryas is recorded in Alta Babícora. Conditions wetter than present are indicated up to at least 7000 yr BP.  相似文献   

Biotic variation in coastal water bodies in Sussex, England: Implications for saline lagoons     

Chris B. Joyce  Cristina Vina-Herbon  Daniel J. Metcalfe 《Estuarine, Coastal and Shelf Science》2005,65(4):633-644

Coastal water bodies are a heterogeneous resource typified by high spatial and temporal variability and threatened by anthropogenic impacts. This includes saline lagoons, which support a specialist biota and are a priority habitat for nature conservation. This paper describes the biotic variation in coastal water bodies in Sussex, England, in order to characterise the distinctiveness of the saline lagoon community and elucidate environmental factors that determine its distribution. Twenty-eight coastal water bodies were surveyed for their aquatic flora and invertebrate fauna and a suite of exploratory environmental variables compiled. Ordination and cluster analyses were used to examine patterns in community composition and relate these to environmental parameters. Biotic variation in the coastal water body resource was high. Salinity was the main environmental parameter explaining the regional distribution of taxa; freshwater and saline assemblages were evident and related to sea water ingress. Freshwater sites were indicated by the plant Myriophyllum spicatum and gastropod mollusc Lymnaea peregra, while more saline communities supported marine and brackish water taxa, notably a range of chlorophytic algae and the bivalve mollusc Cerastoderma glaucum. Site community differences were also related to bank slope and parameters describing habitat heterogeneity. A saline lagoon community was discerned within the matrix of biotic variation consisting of specialist lagoonal species with associated typically euryhaline taxa. For fauna, the latter were the molluscs Abra tenuis and Hydrobia ulvae, and the crustaceans Corophium volutator and Palaemonetes varians, and for flora they were the algae Ulva lactuca, Chaetomorpha mediterranea, Cladophora spp. and Enteromorpha intestinalis. One non-native polychaete species, Ficopomatus enigmaticus, also strongly influenced community structure within the lagoonal resource. The community was not well defined as specialist and associated taxa were distributed throughout the spectrum of sites surveyed. Implications for the identification and conservation of saline lagoons are discussed.  相似文献   

Assessing the impact of distributed snow water equivalent calibration and assimilation of Copernicus snow water equivalent on modelled snow and streamflow performance     

Andy D. Beaton  Ming Han  Bryan A. Tolson  James M. Buttle  Robert A. Metcalfe 《水文研究》2024,38(2):e15075

Accuracy of the Copernicus snow water equivalent (SWE) product and the impact of SWE calibration and assimilation on modelled SWE and streamflow was evaluated. Daily snowpack measurements were made at 12 locations from 2016 to 2019 across a 4104 km² mixed-forest basin in the Great Lakes region of central Ontario, Canada. Sub-basin daily SWE calculated from these sites, observed discharge, and lake levels were used to calibrate a hydrologic model developed using the Raven modelling framework. Copernicus SWE was bias corrected during the melt period using mean bias subtraction and was compared to daily basin average SWE calculated from the measured data. Bias corrected Copernicus SWE was assimilated into the models using a range of parameters and the parameterizations from the model calibration. The bias corrected Copernicus product agreed well with measured data and provided a good estimate of mean basin SWE demonstrating that the product shows promise for hydrology applications within the study region. Calibration to spatially distributed SWE substantially improved the basin scale SWE estimate while only slightly degrading the flow simulation demonstrating the value of including SWE in a multi-objective calibration formulation. The particle filter experiments yielded the best SWE estimation but moderately degraded the flow simulation. The particle filter experiments constrained by the calibrated snow parameters produced similar results to the experiments using the upper and lower bounds indicating that, in this study, model calibration prior to assimilation was not valuable. The calibrated models exhibited varying levels of skill in estimating SWE but demonstrated similar streamflow performance. This indicates that basin outlet streamflow can be accurately estimated using a model with a poor representation of distributed SWE. This may be sufficient for applications where estimating flow is the primary water management objective. However, in applications where understanding the physical processes of snow accumulation, melt and streamflow generation are important, such as assessing the impact of climate change on water resources, accurate representations of SWE are required and can be improved via multi-objective calibration or data assimilation, as demonstrated in this study.  相似文献   

Characteristics of deep groundwater flow in a basin marginal setting at Sellafield,Northwest England: Cl and halide evidence     

Richard Metcalfe  Mark B. Crawford  Adrian H. Bath  Anna K. Littleboy  Paul J. Degnan  Hugh G. Richards 《Applied Geochemistry》2007

A number of chemical and physical processes inside and outside a sedimentary basin (e.g. evaporite dissolution and topographic drive, respectively) affect groundwater flow near the basin’s margin. Contrasting formations at the margin, typically basinal sedimentary rocks and basement, are host to the interplay between these processes so that groundwater flows and compositions change within a relatively small volume. To interpret how groundwater flow and geochemistry have evolved, interactions between these processes must be understood. Such interactions were investigated near the margin of the East Irish Sea Basin in NW England, by sampling deep groundwaters (to 1500 m below sea level) from Ordovician volcanic basement rocks and Carboniferous to Triassic sedimentary cover rocks. Variable Br/Cl ratios and Cl concentrations in deep saline waters and brines indicate mixing patterns. Variations in ³⁶Cl/Cl constrain the timing of mixing. Relatively low Br/Cl ratios (ca. 1 × 10⁻³ by mass) characterise brine from the western sedimentary cover and reflect halite dissolution further west. Saline water with relatively high Br/Cl ratios (ca. 2 × 10⁻³ by mass) of uncertain origin occupies the eastern basement. These two waters mix across the area. However, mixing alone cannot explain variable ³⁶Cl/Cl ratios, which partly reflect differing in situ³⁶Cl production rates in different rock formations. Most ³⁶Cl/Cl ratios in groundwater sampled from the eastern metavolcanic basement (mean = 25 × 10⁻¹⁵) and western sedimentary cover (mean = 10 × 10⁻¹⁵) are at or close to equilibrium with in situ³⁶Cl production. These variations in ³⁶Cl/Cl across the site possibly took >1.5 Ma to be attained, implying that deep groundwater flow responded only slowly to the Quaternary glaciation of the site. Interplay between varied processes in basin marginal settings does not necessarily imply flow instability.  相似文献   

Deciphering recent climate change in central Mexican lake records     

Sarah Metcalfe  Sarah Davies 《Climatic change》2007,83(1-2):169-186

Central Mexico contains a large number of lake basins offering opportunities for climatic reconstruction. The area has, however, also been the focus for human settlement since the time of the earliest occupation of the Americas, as well as being subject to tectonic and volcanic activity. A number of methodological issues arise including the susceptibility of common palaeoecological proxies (pollen, diatoms) to multiple forcing factors and problems of obtaining reliable chronologies. Published lake records indicate that the last 1,500 years have been marked by strong climatic variability, superimposed on continuing high levels of anthropogenic impact. Dry conditions, probably the driest of the Holocene, are recorded over the period 1400 to 800 ¹⁴C yr BP (ca. AD 700–1200). Climatic change over the last 1,000 years is not well represented, but there are indications of drier conditions corresponding to the ‘Little Ice Age’ of mid- to high latitudes. A range of mechanisms (e.g. solar cycles, ENSO variability) have been proposed to explain climatic variability over the last 1,500 years, but current lake records are inadequate to test these. The developing dendroclimatology for the Mexican highlands and the rich historical archives of the Hispanic period (from AD 1521) offer new opportunities and challenges to palaeolimnologists.  相似文献