Carbonate melting and peperite formation at the intrusive contact between large mafic dykes and clastic sediments of the upper Palaeozoic Saint‐Jules Formation,New‐Carlisle,Quebec     

P. Jutras  A. Macrae  J. V. Owen  J. Dostal  M. Prda  G. Prichonnet 《Geological Journal》2006,41(1):23-48

The base of an upper Palaeozoic graben‐fill in eastern Canada was affected by mafic dyke intrusions shortly after deposition, resulting in the formation of peperite. Complex magma–sediment interactions occurred as the melts mingled with the wet and poorly consolidated clastic material of this sedimentary basin, which is separated from underlying rocks by the Acadian unconformity (Middle Devonian). As a result of these interactions, the mafic rocks are strongly oxidized, albitized and autobrecciated near and above the unconformity, where blocky juvenile clasts of mafic glass and porphyritic basalt have mingled with molten or fluidized sediments of the upper Palaeozoic Saint‐Jules Formation, forming a peperite zone several metres thick. In contrast to most peperite occurrences, the New‐Carlisle peperites are associated with the tip of dykes rather than with the sides of sills or dykes. We argue that more heat can be concentrated above a dyke than above a sill, as the former provides a more efficient and focused pathway for heated waters to invade the poorly consolidated host sediments. Superheated groundwaters that issued from the sides of the dykes appear to have promoted melting of carbonate components in calcareous sedimentary rock clasts of the Saint‐Jules Formation, locally generating carbonate melts that contributed to the mingling of juvenile and sedimentary clasts in the peperite. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Sagged phosphatic Nantgarw porcelain (ca. 1813–1820): Casualty of overfiring or a fertile paste?     

J. Victor Owen  Michelle L. Morrison 《Geoarchaeology》1999,14(4):313-332

Nantgarw phosphatic (bone-ash) porcelain (ca. 1813–1820) is renowned for its translucency and the high quality of its enamel decoration. However, only a small proportion of its wares (perhaps 10%) were successfully fired due to sagging (body distortion) and other problems. This indicates that: (1) In terms of its potential for generating a minimum melt, the Nantgarw paste had an unusually fertile composition, or (2) Nantgarw's staff had difficulties in controlling kiln temperatures, so that its wares tended to be overfired. This issue has been addressed using analytical data for sherds excavated from the factory site. Detailed modal, petrographic, and geochemical data demonstrate that extensively sagged wasters contain a high proportion (∼43–63 vol %) of a former melt phase but are surprisingly porous (7–25 vol % pores). In terms of minimum melt generation, the sagged samples have a more fertile bulk composition than their successfully fired counterparts. Most of the wasters contain subsolidus anorthite (∼An₉₅) enclosed by a melt phase with (once corrected for entrained silica polymorph crystallites) a eutectic (minimum melt) composition. The anorthite, however, was completely resorbed by the melt in some of the sagged samples, which subsequently crystallized liquidus anorthite that displays a quenched morphology. These samples were therefore fired above (T_max <1430°C, as estimated from melt compositions) the eutectic (T∼1290°C) in the anorthite–tricalcium phosphate–silica system. The fact that other wasters contain subsolidus anorthite and a minimum melt shows that firing at the eutectic did not guarantee a successful firing, regardless of the melt fertility of the paste. It is likely that the duration of firing near T_max and character of the object (i.e., flatware vs. hollow-ware) were also important variables in this regard. In addition to producing their well-known phosphatic wares, Nantgarw's proprietors apparently also experimented with silicious pastes with compositions akin to true porcelain. Some of silicious sherds found at the site have a lead-bearing (∼15 wt % PbO) glaze, indicating that they survived an early, high temperature biscuit firing, after which they were fired at lower temperature in the glost kiln (i.e., a “soft-paste type” firing sequence). Evidence that the Nantgarw kiln could achieve temperatures in the order of 1400°C further suggests that these silicious sherds are b.f. wasters. © 1999 John Wiley & Sons, Inc.  相似文献   

Spatial and temporal replicability of meteoric and in situ 10Be concentrations in fluvial sediment          下载免费PDF全文

Veronica Sosa Gonzalez  Amanda H. Schmidt  Paul R. Bierman  Dylan H. Rood 《地球表面变化过程与地形》2017,42(15):2570-2584

Cosmogenic isotopes, short‐lived radionuclides, elemental concentrations and thermochronometric indicators are measured in river sand to quantify erosion rates and trace sediment sources, and/or infer erosional processes. Interpretations of detrital sediment analyses are often based on the rarely tested assumption of time‐invariant tracer concentration. A better understanding of when and where this assumption breaks down and what sampling strategies minimize temporal and small‐scale spatial variance will improve science done using detrital river sediment. Here, we present new and previously published spatial and temporal replicates measured for in situ and meteoric ¹⁰Be (¹⁰Be_i and ¹⁰Be_m, respectively). Our new data include 113 replicate pairs, taken from agricultural and/or tectonically active watersheds in China months to millennia apart and spatial replicates taken up to 2 km apart on the same day. The mean percentage difference is 10% (?122% to 150%) for both systems considered together; the mode is close to 0% for both systems; and 36% of pairs of samples replicate within our analytical accuracy at 2σ . We find that ¹⁰Be_i replicates better than ¹⁰Be_m (p < 0.01). ¹⁰Be_i replicability is worse in steeper basins, suggesting that stochastic processes (i.e. landslides) affect reproducibility. ¹⁰Be_m replicability is worse in larger basins, suggesting non‐conservative behavior of ¹⁰Be_m as sediment moves downstream. Our results are consistent with the few previously published replicate studies. Considering all replicate data in a wide range of landscapes, in areas with deep erosional processes, replicability is poor; in other areas, replicability is good. This suggests that, in steep, tectonically active, and/or agricultural landscapes, individual detrital sediment measurements do not represent upstream rates as well as larger populations of samples. To ensure that measurements are representative of the upstream watershed, our data suggest that samples be amalgamated either over time or from several places close by in the same channel. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Quaternary alluvial fans in the Gobi of southern Mongolia: evidence for neotectonics and climate change     

L. A. Owen  B. F. Windley  W. D. Cunningham  J. Badamgarav  D. Dorjnamjaa 《第四纪科学杂志》1997,12(3):239-252

Alluvial fans in southern Monglia occur along a group of narrow discontinuous mountain ranges which formed as transpressional uplifts along a series of strike-slip faults. They provide information on the nature of neotectonic activity in the eastern Gobi Altai range and on palaeoclimate change. Alluvial fan formation was dominated by various geomorphological processes largely controlled by climatic changes related to an increase in aridity throughout late Quaternary times. Their sedimentology shows that initially they experienced humid conditions, when the sedimentary environments were dominated by perennial streams, followed by a period of increasing aridity, during which coarse fanglomerates were deposited in alluvial fans by ephemerial streams and active-layer structures were produced by permafrost within the alluvial fan sediments. With climatic amelioration during early Holocene times, the permafrost degraded and fan incision and entrenchment dominated. Sedimentation was then confined to the upper reaches of the fans, adjacent to steep mountain slopes, and within the entrenched channels. The alluvial fans have been neotectonically deformed, faulted and their surface warped by small thrust faults that propagate from the mountain fronts into their forelands. Localised uplift rates are in the order of 0.1 to 1 m Ka⁻¹. © 1997 John Wiley & Sons, Ltd.  相似文献   

Dangerous Earth: an introduction to geological hazards     

Lewis A. Owen 《第四纪科学杂志》1998,13(4):358-358

  相似文献   

Reanalysis of Solar Observing Optical Network Sunspot Areas     

Owen Giersch  John Kennewell  Mervyn Lynch 《Solar physics》2018,293(10):138

We address recent concerns that the sunspot-area measurements performed by the United States Air Force (USAF) Solar Observing Optical Network (SOON) have been underestimating sunspot areas. We examine briefly the history of SOON, and we perform an analysis of a three-decade time series of SOON measurements. By remeasuring USAF sunspot areas, we find that sunspot areas are being underestimated by between 8% and 17% due to the measuring techniques employed by SOON analysts. In particular, the SOON practice of rounding down limb-area correction factors results in some individual regions having areas reported by up to 50% less than their true values. This does not, however, account for the full discrepancy in sunspot areas between SOON and other observatories, which, in recent years, may be as high as a 50% discrepancy.  相似文献   

Hydrological functioning of a beaver dam sequence and regional dam persistence during an extreme rainstorm     

Cherie J. Westbrook  Amanda Ronnquist  Angela Bedard-Haughn 《水文研究》2020,34(18):3726-3737

It is becoming increasingly popular to reintroduce beaver to streams with the hopes of restoring riparian ecosystem function or reducing some of the hydrological impacts of climate change. One of the risks of relying on beaver to enhance ecosystem water storage is that their dams are reportedly more apt to fail during floods which can exacerbate flood severity. Missing are observations of beaver dam persistence and water storage capacity during floods, information needed to evaluate the risk of relying on beaver as a nature-based flood solution. A June rainstorm in 2013 triggered the largest recorded flood in the Canadian Rocky Mountains west of Calgary, Alberta. We opportunistically recorded hydrometric data during the rainfall event at a beaver-occupied peatland that has been studied for more than a decade. We supplemented these observations with a post-event regional analysis of beaver dam persistence. Results do not support two long-held hypotheses—that beaver ponds have limited flood attenuation capacity and commonly fail during large flood events. Instead we found that 68% of the beaver dam cascade systems across the region were intact or partially intact after the event. Pond fullness, in addition to the magnitude of the water-sediment surge, emerged as important factors in determining the structural fate of dam cascade sequences. Beaver ponds at the instrumented site quickly filled in the first few hours of the rain event and levels were dynamic during the event. Water storage offered by the beaver ponds, even ones that failed, delayed downstream floodwater transmission. Study findings have important implications for reintroducing beaver as part of nature-based restoration and climate change adaptation strategies.  相似文献   

Turkey Lakes Watershed,Ontario, Canada: 40 years of interdisciplinary whole-ecosystem research     

Kara L. Webster  Jason A. Leach  Paul W. Hazlett  Robert L. Fleming  Erik J. S. Emilson  Daniel Houle  Kara H. Y. Chan  Fariborz Norouzian  Amanda S. Cole  Jason M. O'Brien  Karen E. Smokorowski  Stephanie A. Nelson  Shelagh D. Yanni 《水文研究》2021,35(4):e14109

The Turkey Lakes Watershed (TLW) study is a federal, interdepartmental study established in 1979 to investigate the effects of acid rain on terrestrial and aquatic ecosystems. The 10.5 km² watershed, located in the Eastern Temperate Mixed Forest on the Canadian Shield, has been the site of multidisciplinary studies on biogeochemical and ecological processes conducted across plot to catchment scales. The whole-ecosystem investigative approach was adopted from the outset and has allowed research to evolve from its original (and continuing) acidification focus to include investigations on the effects of climate change, forest harvesting and other forest ecosystem perturbations. The extensive scientific and support infrastructure allows for collection of a comprehensive data record essential for understanding long-term environmental trends. Data include atmospheric deposition, meteorology, stream hydrology and chemistry, soil, pore and ground water properties, understory and overstory vegetation, lake and outflow physical and chemical properties, and aquatic macroinvertebrate and fish community composition and abundance. These data have contributed to over 400 published research papers and graduate theses. The watershed has also figured prominently in many continent-wide comparisons advancing fundamental watershed theory. The knowledge gained at TLW has influenced pollutant emission and natural resource management policies provincially, nationally and internationally.  相似文献   

The Asosa region of western Ethiopia: a golden exploration opportunity          下载免费PDF全文

Liam A. Bullock  Owen Morgan 《Geology Today》2018,34(1):31-34

Gold mining has a legendary history in Ethiopia, with Ethiopian mines providing gold to the ancient Egyptian empire and possibly even King Solomon's Mines and the Queen of Sheba. Today, gold occurs in the Pan‐African age schist belt and Tertiary basaltic lavas of the Asosa region of Benishangul‐Gumuz, western Ethiopia. There is widespread artisanal gold production in the Asosa region, with moderate activity by small numbers of local workers producing relatively large amounts of gold. There is a strong relationship between predominantly shear zone‐hosted gold deposits and the Kuluck shear zone, suggesting a structural control on gold accumulation. Gold is also commonly associated with secondary sulphide mineralization and magnetite alteration in Asosa rocks. The source of the gold is thought to be the sub‐volcanic intrusions generated during the subduction of the oceanic crust at the trench island‐arc system, akin to what we see today in epithermal and porphyry type gold systems. Historical workings and anomalous gold concentrations in rock, soil and stream sediments point to a potentially significant untapped gold resource in the Asosa region of western Ethiopia.  相似文献   

A flux transfer event observed at the magnetopause by the Equator-S spacecraft and in the ionosphere by the CUTLASS HF radar   总被引：2，自引：0，他引：2  

D. A. Neudegg  T. K. Yeoman  S. W. H. Cowley  G. Provan  G. Haerendel  W. Baumjohann  U. Auster  K.-H. Fornacon  E. Georgescu  C. J. Owen 《Annales Geophysicae》1999,17(6):707-711

Observations of a flux transfer event (FTE) have been made simultaneously by the Equator-S spacecraft near the dayside magnetopause whilst corresponding transient plasma flows were seen in the near-conjugate polar ionosphere by the CUTLASS Finland HF radar. Prior to the occurrence of the FTE, the magnetometer on the WIND spacecraft ≈226 R_E upstream of the Earth in the solar wind detected a southward turning of the interplanetary magnetic field (IMF) which is estimated to have reached the subsolar magnetopause ≈77 min later. Shortly afterwards the Equator-S magnetometer observed a typical bipolar FTE signature in the magnetic field component normal to the magnetopause, just inside the magnetosphere. Almost simultaneously the CUTLASS Finland radar observed a strong transient flow in the F region plasma between 78° and 83° magnetic latitude, near the ionospheric region predicted to map along geomagnetic field lines to the spacecraft. The flow signature (and the data set as a whole) is found to be fully consistent with the view that the FTE was formed by a burst of magnetopause reconnection.  相似文献