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31.
Janne Liebmann Bryant Ware Michael I.H. Hartnady Christopher L. Kirkland Nicholas E. Timms Noreen J. Evans 《Geostandards and Geoanalytical Research》2023,47(3):637-655
Lead isotopes are a powerful and versatile tool to elucidate fundamental geological problems related to the formation and evolution of continental crust. K-feldspar is a popular target for Pb isotope measurement as it is prevalent in many rock types and tends to capture the initial Pb isotope composition of its parental magma. We present data for a new Pb isotope reference material: Albany K-feldspar; as well as updated data for Shap K-feldspar. Results of Pb double-spike TIMS for Albany K-feldspar are 206Pb/204Pb = 16.7872 ± 0.0062, 207Pb/204Pb = 15.5640 ± 0.0056, and 208Pb/204Pb = 36.6600 ± 0.0168 (2s). TIMS measurement results for Shap K-feldspar indicate two isotopically distinct Pb populations. LA-MC-ICP-MS, with a spatial resolution as high as 15 μm, indicates a homogeneous Pb isotopic composition in Albany K-feldspar. In accord with previous studies, our results show that scatter in the measured Pb isotope ratios, related to the low natural isotopic abundance of 204Pb, along with the effect of isobaric 204Hg-204Pb interference, increases at lower count rates. However, the mean Pb isotope ratios measured via LA-MC-ICP-MS using a range of spot sizes are in excellent agreement with TIMS results thus highlighting the feasibility of Pb isotope determination via LA-MC-ICP-MS to access geological information preserved in small crystals, including mineral inclusions. 相似文献
32.
Christopher P. Francis Stefan Engels Ian P. Matthews Adrian P. Palmer Rhys G. O. Timms Anne-Lise Jourdan Ian Candy 《第四纪科学杂志》2021,36(3):325-338
Three clearly defined abrupt cooling events (ACEs) can be observed within Greenland Interstadial (GI)-1 in the Greenland ice-core records. However, the spatial variation in amplitude and timing of these ACEs is poorly understood due to the paucity of well-dated records with quantified temperature reconstructions. This study presents high-resolution chironomid-inferred July air temperature (TJul) and oxygen isotope (δ18O) records from Crudale Meadow (Orkney Isles, UK). Three centennial-scale ACEs punctuate the Windermere Interstadial at Crudale Meadow. The largest ACE shows an amplitude of 5.4 °C and a 1% isotopic decline and is centred on ~14.0 ka bp , consistent with the timing of the GI-1d event in the Greenland stratigraphy. The two other observed ACEs are of smaller magnitude and are centred on ~13.6 ka bp and ~13.2 ka bp , with these smaller magnitude events tentatively correlated with the GI-1cii and GI-1b events, respectively, but lack sufficient chronological constraint to fully assess their timing. When comparing the Crudale Meadow record with other locations in the British Isles a strong relationship can be observed between the magnitude of TJul cooling and latitude, with a reduced signal in more southerly locations, indicating that oceanic forcing may be a key driver of the ACEs. 相似文献
33.
Sample 73235 is one of several aphanitic impact melt breccias collected by the Apollo 17 mission at stations 2 and 3 on the slopes of the South Massif. This study presents a detailed investigation of internal structures and U-Pb ages of large zircon grains from this breccia sample. New data combined with the results of previous studies of zircon grains from the same location indicate that most zircon clasts in breccias from stations 2 and 3 formed during multiple magmatic events between 4.37 and 4.31 Ga, although the oldest zircon crystallized at about 4.42 Ga and the youngest at 4.21 Ga. In addition, zircons from the aphanitic breccias record several impact events prior to the ∼3.9 Ga Late Heavy Bombardment. The results indicate that the zircons probably crystallized at different locations within the Procellarum KREEEP Terrane and were later excavated and modified by several impacts and delivered to the same locality within separate ejecta blankets. This locality became a source of material that formed the aphanitic impact melt breccias of the South Massif during a ∼3.9 Ga impact. However, the zircons, showing old impact features, are not modified by this ∼3.9 Ga impact event suggesting that (i) this common source area was located at the periphery of excavation cavity, and (ii) the > 3.9 Ga ages recorded by the zircon grains could date large (basin-forming) events as significant as major later (∼3.9 Ga) collisions such as Imbrium and Serenitatis. 相似文献
34.
N. E. Timms 《Journal of Metamorphic Geology》2003,21(9):853-873
Detailed 3‐D analysis of inclusion trails in garnet porphyroblasts and matrix foliations preserved around a hand‐sample scale, tight, upright fold has revealed a complex deformation history. The fold, dominated by interlayered quartz–mica schist and quartz‐rich veins, preserves a crenulation cleavage that has a synthetic bulk shear sense to that of the macroscopic fold and transects the axis in mica‐rich layers. Garnet porphyroblasts with asymmetric inclusion trails occur on both limbs of the fold and display two stages of growth shown by textural discontinuities. Garnet porphyroblast cores and rims pre‐date the macroscopic fold and preserve successive foliation inflection/intersection axes (FIAs), which have the same trend but opposing plunges on each limb of the fold, and trend NNE–SSW and NE–SW, respectively. The FIAs are oblique to the main fold, which plunges gently to the WSW. Inclusion trail surfaces in the cores of idioblastic porphyroblasts within mica‐rich layers define an apparent fold with an axis oblique to the macroscopic fold axis by 32°, whereas equivalent surfaces in tabular garnet adjacent to quartz‐rich layers define a tighter apparent fold with an axis oblique to the main fold axis by 17°. This potentially could be explained by garnet porphyroblasts that grew over a pre‐existing gentle fold and did not rotate during fold formation, but is more easily explained by rotation of the porphyroblasts during folding. Tabular porphyroblasts adjacent to quartz‐rich layers rotated more relative to the fold axis than those within mica‐rich layers due to less effective deformation partitioning around the porphyroblasts and through quartz‐rich layers. This work highlights the importance of 3‐D geometry and relative timing relationships in studies of inclusion trails in porphyroblasts and microstructures in the matrix. 相似文献
35.
S. J. Timms N. M. Lynn M. E. Mount Y. Sivintsev J. M. Warden 《Marine pollution bulletin》1997,35(7-12):365-373
In progressing its work for the International Arctic Seas Assessment Project (IASAP), under the auspices of the International Atomic Energy Agency (IAEA), the Source Term Working Group has developed a FORTRAN model to predict a radiation release profile into the Kara Sea from reactor fuel and activated components of the nuclear icebreaker Lenin. The model accounts for the degradation of containment materials through corrosion and other mechanisms, and predicts annual release rates to 4500 years into the future. Version I of the model was developed as a spreadsheet program from the original data gathered by the Working Group and the results were published by Timms et al. (1994); revised information on the method of disposal necessitated a change to the program, which is presented in this paper as Version II. The model is being applied to other marine reactors dumped in the Kara Sea in a programme of work for the IASAP aimed at assessing the collective release profile from all significant dump sites in this region. 相似文献
36.
Brian V. Timms 《International Journal of Salt Lake Research》1998,7(2):113-132
Lake Wyara lies on a tertiary fault, but is much modified geomorphologically by wind and subsequent wave action from the west, so that the eastern shore is smoothed and lined by beaches at various levels, but there is no lunette. When full and overflowing, which has occurred 4–5 times in the last 108 years, it is 3400 ha in area and ca 6m in depth. Most overflows are due to floodwaters from the adjacent Paroo catchment entering the lake via its outflow and then returning again back to the river. During 1987–96, it completely filled and dried once, salinity varying from 2.8 to 350 g L-1. Water was clear, alkaline and strongly dominated by Na and Cl-ions. Macrophytes grew abundantly offshore at lower to moderate salinities, fish were few in variety and limited to low salinities, and waterbirds were usually both diverse and numerous. During the 10 years of study, only 13 zooplankter species and 23 species of littoral inverbebrates (with 3 ostracods common to both lists) were encountered; most lived at lower salinities (<30 g L-1) and none was found >60 g L-1. Dominants were mainly crustaceans and included Boeckella triarticulata and Daphnia angulata when hyposaline, and Daphniopsis queenslandensis, Moina baylyi, Diacypris spp., and Mytilocypris splendida at higher salinities. Insects were generally limited to hyposaline conditions, but Micronecta sp., and Tanytarsus barbitarsis were euryhaline. Overall, the invertebrate fauna is depauperate by comparison with saline lakes elsewhere in Australia, but similar to that in other large saline lakes in the semi-arid and arid zones of central and eastern Australia. This is related to the lake's episode nature which provides an unreliable and unpredictable habitat and therefore not encouraging speciation and also to a relatively homogenous habitat throughout the lake due to strong wind action smoothing shorelines vertically and horizontally. 相似文献
37.
Brian V. Timms 《International Journal of Salt Lake Research》1996,5(4):287-313
Bloodwood Station, 130 km NW of Bourke, NSW, has a diverse array of intermittently flooded wetlands raging from salinas to fresh waters, either clear, opaque or very turbid, and from relatively large (820 ha) to quite small (<1 ha). A study during 1995 followed the filling of 22 wetlands after heavy rain in January to subsequent drying or recession, and looked at the relationship between physicochemical features, aquatic plants, zooplankton, littoral invertebrates, tadpoles, and waterbirds. Wetlands were delineated into two major groups: saline and fresh, with the latter subdivided into five types — clear fresh waters, artificial tanks, vegetated pans, turbid pans, and miscellaneous. The saline lakes developed extensive beds of macrophytes some months after filling which attracted large number of waterbirds. Later, abundant Zooplankton were feed for many Pink-eared Duck. Most of the fresh waters developed large initial populations of phyllopodous crustaceans, Zooplankton and tadpoles, but these waters attracted few waterbirds. Clearer fresh waters later grew macrophytes which attracted many waterbirds, but the turbid claypans remained unattractive to waterbirds during their existence, despite harbouring a host of invertebrates. The vegetated pans, artificial tanks and miscellaneous sites attracted only a few waterbirds, but the tanks along with the persistent clear fresh waters become important as feeding and resting sites as other wetlands dried towards the year end. Few waterbirds bred on these wetlands during 1995. However, many were important as major feeding sites and formed part of a mosaic of intermittent wetlands for Australia's inland waterbirds. 相似文献
38.
In-situ hydraulic conductivity and specific storage measurements are derived from an analysis of pore-water pressure changes in a nest of piezometers installed in a 40-m-thick succession of smectitic clay on the Liverpool Plains of northern New South Wales, Australia. The cumulative response to the rainfall events that typically occurs during winter or early spring is propagated through the clay with measurable loss of amplitude and increasing phase lag. Five major rainfall events occurred over the four years of detailed monitoring. The phase lag at the base of the clay varied between 49 and 72 days. Barometric efficiency (BE) measurements for the clay sequence (BE = 0.07) and the underlying confined aquifer (BE = 0.10) were used, with a known porosity of 0.567, to derive specific storage values of 3.7×10–5 and 6.8×10–6 m–1 respectively. Vertical hydraulic conductivity (Kv) of the clay sequence derived from observed amplitude and phase changes, resulted in an average value of 2.8×10–9 m/s. These in-situ-derived values indicate that previous estimates of vertical hydraulic conductivity of the clays, made on core samples, are unrealistically high. The instantaneous response to individual rainfall events transmitted through the clay succession (tidal efficiency of 0.93) is also described.
Resumen Se han derivado mediciones in-situ de conductividad hidráulica y almacenamiento específico a partir de un análisis de cambios de presión intersticial en una red de piezómetros instalados en una secuencia gruesa de 40 m de arcilla esmectítica en las Planicies Liverpool del norte de Nueva Gales del Sur, Australia. La respuesta acumulativa de los eventos de lluvia que típicamente ocurren en invierno y principio de primavera se propaga a través de la arcilla mediante pérdida de amplitud y un incremento en retraso de fase. Durante los cuatro años de monitoreo detallado ocurrieron cuatro eventos de lluvia principales. El retraso de fase en la base de la arcilla varió de 49 a 72 días. Las mediciones de eficiencia barométrica (BE) para la secuencia arcillosa (BE = 0.07) y el acuífero confinado subyacente (BE = 0.1) se utilizaron, con una porosidad conocida de 0.567, para derivar valores de almacenamiento específico de 3.7×10–5 y 6.8×10–6 m–1, respectivamente. La conductividad hidráulica vertical (Kv) de la secuencia arcillosa derivada de cambios observados en amplitud y fase dio por resultado un valor promedio de 2.8×10–9 m/s. Estos valores derivados in-situ indican que los estimados previos de conductividad hidráulica vertical de las arcillas, hechos en muestras de núcleo, son muy altos y poco confiables. También se describe la respuesta instantánea de eventos de lluvia individuales transmitidos a través de la secuencia arcillosa (eficiencia de marea de 0.93).
Résumé Des mesures in-situ de conductivité hydraulique et demmagasinement spécifique sont obtenues à partir de lanalyse de la variation des pressions interstitielles telles que mesurées au droit dun nid de piézomètres interceptant une épaisseur de 40 m dargile smectique dans les plaines de Liverpool, région nord du New South Wales, Australie. La réponse cumulative aux évènements pluviométriques qui surviennent typiquement durant lhiver ou le début du printemps, se propage dans les argiles suite à une diminution damplitude (des pressions interstitielles) et à un accroissement du pas de temps.. Cinq évènements pluviométriques sont survenus lors dun suivi détaillé effectué sur quatre (4) années. Le pas de temps à la base de largile a varié de 49 à 72 jours. Les mesures defficience barométrique (EB) de lassemblage argileux (BE = 0.07) et de la nappe aquifère confinée sous-jacente (BE = 1.10) ont été utilisées, avec une porosité connue de 0,567, afin dobtenir des valeurs demmagasinement spécifique de respectivement 3.7×10–5 et 6.6×10–6 m–1. La conductivité hydraulique verticale (Ky) de lassemblage argileux a été déterminée à partir de la mesure des variations damplitudes ainsi que des pas de temps, permettant la détermination dune valeur moyenne de 2.8×10–9 m/s. Ces valeurs obtenues in-situ montrent que les estimations de conductivité hydraulique verticale des argiles telles quobtenues à partir déchantillons non remaniés sont surestimées. La réponse instantanée à des évènements pluviométriques individuels transmis au travers de la succession dargile (facteur defficacité de marée de 0.93) est également décrite.相似文献
39.
Shocked monazite chronometry: integrating microstructural and in situ isotopic age data for determining precise impact ages 总被引：1，自引：0，他引：1
Timmons?M.?EricksonEmail authorView author&#;s OrcID profile Nicholas?E.?Timms Christopher?L.?Kirkland Eric?Tohver Aaron?J.?Cavosie Mark?A.?Pearce Steven?M.?Reddy 《Contributions to Mineralogy and Petrology》2017,172(2-3):11
Monazite is a robust geochronometer and occurs in a wide range of rock types. Monazite also records shock deformation from meteorite impact but the effects of impact-related microstructures on the U–Th–Pb systematics remain poorly constrained. We have, therefore, analyzed shock-deformed monazite grains from the central uplift of the Vredefort impact structure, South Africa, and impact melt from the Araguainha impact structure, Brazil, using electron backscatter diffraction, electron microprobe elemental mapping, and secondary ion mass spectrometry (SIMS). Crystallographic orientation mapping of monazite grains from both impact structures reveals a similar combination of crystal-plastic deformation features, including shock twins, planar deformation bands and neoblasts. Shock twins were documented in up to four different orientations within individual monazite grains, occurring as compound and/or type one twins in (001), (100), \(\left( 10\bar{1} \right)\), \(~\{110\}\), \(\left\{ 212 \right\},\) and type two (irrational) twin planes with rational shear directions in \([0\bar{1}\bar{1}]\) and \([\bar{1}\bar{1}0]\). SIMS U–Th–Pb analyses of the plastically deformed parent domains reveal discordant age arrays, where discordance scales with increasing plastic strain. The correlation between discordance and strain is likely a result of the formation of fast diffusion pathways during the shock event. Neoblasts in granular monazite domains are strain-free, having grown during the impact events via consumption of strained parent grains. Neoblastic monazite from the Inlandsee leucogranofels at Vredefort records a 207Pb/206Pb age of 2010?±?15 Ma (2σ, n?=?9), consistent with previous impact age estimates of 2020 Ma. Neoblastic monazite from Araguainha impact melt yield a Concordia age of 259?±?5 Ma (2σ, n?=?7), which is consistent with previous impact age estimates of 255?±?3 Ma. Our results demonstrate that targeting discrete microstructural domains in shocked monazite, as identified through orientation mapping, for in situ U–Th–Pb analysis can date impact-related deformation. Monazite is, therefore, one of the few high-temperature geochronometers that can be used for accurate and precise dating of meteorite impacts. 相似文献
40.
Jenni E. Sherriff Keith N. Wilkinson Poppy Harding Hayley Hawkins Rhys G. O. Timms Daniel S. Adler Emily J. Beverly Simon P. E. Blockley Boris Gasparyan Christina J. Manning Darren Mark Samvel Nahapetyan Katie J. Preece 《第四纪科学杂志》2022,37(1):6-27
The significance of the southern Caucasus in understanding Pleistocene hominin expansions is well established. However, the palaeoenvironments in which Palaeolithic occupation of the region took place are presently poorly defined. The Hrazdan river valley, Armenian Highlands, contains a rich Palaeolithic record alongside Middle Pleistocene volcanic, fluvial and lacustrine strata, and thus offer exciting potential for palaeoenvironmental reconstruction. We present the first results of sedimentological, geochemical, tephrostratigraphical and biological (diatoms) study of the sequence of Bird Farm 1, located in the central part of the valley. These data show six phases of landscape development during the interval 440–200 ka. The sequence represents the first quantitative Pleistocene diatom record from the Armenian Highlands and the southern Caucasus, and indicates the persistence of a deep, stratified lacustrine system, with evidence for changing lake productivity that is tentatively linked to climate. Furthermore, major element chemical characterization of visible and crypto-tephra horizons in the sequence enables the first stages of the development of a regional tephrostratigraphy. Together, the evidence from Bird Farm 1 demonstrates the importance of lacustrine archives in the region for palaeoenvironmental reconstruction and highlights the potential for linkages between archives on both a local and regional scale. 相似文献