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Late Cryogenian glaciation in South Australia:Fluctuating ice margin and no extreme or rapid post-glacial sea-level rise

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Geoscience Frontiers 2019年第4期10卷 1397-1408页

作者： George e.williams Victor A.Gostin Department of earth Sciences University of Adelaide

Postulated extreme sea-level rise of up to 1-1.5 km with the late Cryogenian Ghaub deglaciation in Namibia is contentious,as is the great rapidity(<104 yr)of the sea-level *** extreme glacioeustatic events,if real,wou... 详细信息

Postulated extreme sea-level rise of up to 1-1.5 km with the late Cryogenian Ghaub deglaciation in Namibia is contentious,as is the great rapidity(e sea-level *** extreme glacioeustatic events,if real,would have been global and affected all *** South Australia,up to six glacial advances and retreats during the late Cryogenian elatina glaciation indicate a fluctuating ice *** latter stage of the elatina glaciation and the immediate post-glacial environment are examined here for evidence of extreme and rapid sea-level *** the central Adelaide Rift Complex,diamictite with faceted and striated clasts occurs at the top of the elatina Formationeneath the early ediacaran Nuccaleena Formation’cap carbonate’.One hundred kilometres to the south,~30 m of siltstone and sandstone followed by^6 m of clast-poor diamictite with clasts 10+cm long occur between tidal rhythmites and the cap *** hundred kilo metres further south,~70 m of siltsto ne,dolo mitic siltstone and minor dolomite separate tidal rhythmites and early ediacaran *** the rhythmites were deposited during a high stand(interstadial or interglacial),not during post-glacial sea-level ***-generated erosional surfaces within tidal rhythmites at Warren Gorge indicate intermittent rhythmite deposition,and water depth and other palaeoenvironmental factors are uncertain,casting doubt on a published estimate of rapid sea-level rise during rhythmite *** lack of late Cryogenian deeply incised valleys and thick valley-fill deposits in South Australia and central Australia argues against extreme sea-level variations.A hiatus occurred between elatina deglaciation and deposition of the Nuccaleena cap carbonate,and three palaeomagnetic polarity chrons identified in the cap carbonate imply slow deposition spanning 10^5-10^6 *** is supported by independent evidence from magnetic chronostratigraphy for ediacaran strata in South Australia and Califo

关键词： Late Cryogenian glaciation Sea level Adelaide Rift Complex elatina Formation Nuccaleena Formation

Shuram-Wonoka carbon isotope excursion:ediacaran revolution in the world ocean's meridional overturning circulation

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Geoscience Frontiers 2018年第2期9卷 391-402页

作者： George e.williams Phillip W.Schmidt Department of earth Sciences University of Adelaide Magneticearth

The late ediacaran Shuram-Wonoka excursion, with δ^(13)C_(carb) values as low as-12‰(PDB) in marineshelf deposits and spanning up to 10 Myr, is the deepest and most protracted δ^(13)C_(carb) negative anomaly recognised in earth history. The excursion formed on at least four continents in low(≤32°) palaeolatitudes, and in China is associated with a major phosphogenic event. Global and intrabasinal correlation, magnetostratigraphy, isotope conglomerate tests and further geochemical data are consistent with a primary or syn-depositional origin for the excursion. Continental-margin phosphorites are generated by oceanic upwelling driven by surface winds, and δ^(13)C_(carb) negative anomalies are explicable by oceanic upwelling of 13 C-depleted deep oceanic waters, arguing that a feature common to these exceptional ediacaran events was unprecedented perturbation of the world ocean. These events occurred during the transition from an alien Proterozoic world marked by low-palaeolatitude glaciation near sea level and strong seasonality to the familiar Phanerozoic earth with circum-polar glaciation and temperate climate, suggesting that the Shuram-Wonoka excursion is related to this profound change in earth's climate system. Of various hypotheses for Proterozoic low-palaeolatitude glaciation, only the high obliquity(>54°) hypothesis, which posits secular decrease in obliquity to near the present-day value(23.5°) during the ediacaran, predicts an unparalleled revolution in the ediacaran world ocean. The obliquity controls the sense of the world ocean's meridional overturning circulation, which today is driven by the sinking of cold, dense water at the poles and upwelling driven by zonal surface *** the decreasing obliquity passed the critical value of 54° during the ediacaran the meridional temperature gradient reversed, with the equator becoming warmer than the poles and Hadley lowlatitude(eric zonal circulation reversing. This reversal of the temperat

关键词： ediacaran Shuram-Wonoka carbon isotope excursion Oceanic meridional circulation Atmospheric circulation Proterozoic paleoclimate Obliquity of the ecliptic

Steel slag carbonation in a flow-through reactor system:The role of fluid-flux

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Journal of environmental Sciences 2015年第1期27卷 266-275页

作者： eleanor J.Berryman Anthony e.williams-Jones Artashes A.Migdisov Department of earth and Planetary Sciences McGill University Technische Universitat Berlin Los Alamos National Laboratory

Steel production is currently the largest industrial source of atmospheric CO2. As annual steel production continues to grow, the need for effective methods of reducing its carbon footprint increases correspondingly. The carbonation of the calcium-bearing phases in steel slag generated during basic oxygen furnace（BOF） steel production, in particular its major constituent, larnite {Ca2SiO4}, which is a structural analogue of olivine {（MgFe）2SiO4}, the main mineral subjected to natural carbonation in peridotites, offers the potential to offset some of these emissions. However, the controls on the nature and efficiency of steel slag carbonation are yet to be completely understood. experiments were conducted exposing steel slag grains to a CO2–H2O mixture in both batch and flow-through reactors to investigate the impact of temperature, fluid flux, and reaction gradient on the dissolution and carbonation of steel slag. The results of these experiments show that dissolution and carbonation of BOF steel slag are more efficient in a flow-through reactor than in the batch reactors used in most previous studies. Moreover, they show that fluid flux needs to be optimized in addition to grain size, pressure, and temperature, in order to maximize the efficiency of carbonation. Based on these results, a two-stage reactor consisting of a high and a low fluid-flux chamber is proposed for CO2 sequestration by steel slag carbonation,allowing dissolution of the slag and precipitation of calcium carbonate to occur within a single flow-through system.

关键词： CO2sequestration Steel slag carbonation Flow-through reactor Fluid flux

In the presence of danger: the extracellular matrix defensive response to central nervous system injury

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Neural Regeneration Research 2014年第4期9卷 377-384页

作者： Lyn B.Jakeman Kent e.williams Bryan Brautigam Department of Physiology and Cell Biology Ohio State University Wexner Medical CenterColumbusOHUSA Neuroscience Graduate Studies Program Ohio State University Wexner Medical CenterColumbusOHUSA Biomedical Research Graduate Program Ohio State University Wexner Medical CenterColumbusOHUSA OSU Center for Brain and Spinal Cord Repair Ohio State University Wexner Medical CenterColumbusOHUSA

Glial cells in the central nervous system （CNS） contribute to formation of the extracellular matrix, which provides adhesive sites, signaling molecules, and a diffusion barrier to enhance efficient on and axon potential propagation. In the normal adult CNS, the extracellular matrix （eCM） is relatively stable except in selected regions characterized by dynamic remodeling. However, after trauma such as a spinal cord injury or cortical contusion, the lesion epicenter becomes a focus of acute neuroinflammation. The activation of the surrounding glial cells leads to a dramatic change in the composition of the eCM at the edges of the lesion, creating a perilesion environment dominated by growth inhibitory molecules and restoration of the peripheral/ central nervous system border. An advantage of this response is to limit the invasion of damaging cells and diffusion of toxic molecules into the spared tissue regions, but this occurs at the cost of inhibiting migration of endogenous repair cells and preventing axonal regrowth. The following review was prepared by reading and discussing over 200 research articles in the field published in PubMed and selecting those with significant impact and/or controversial points. This article highlights structural and functional features of the normal adult CNS eCM and then focuses on the reactions of glial cells and changes in the perilesion border that occur following spinal cord or contusive brain injury. Current research strategies directed at modifying the inhibitory perilesion microenvironment without eliminating the protective functions of glial cell activation are discussed.

关键词： nerve regeneration glial scar proteoglycan axon growth spinal cord injury contusion inhibitory inflammation astrocyte macrophage neural regeneration

Strongly seasonal Proterozoic glacial climate in low palaeolatitudes:Radically different climate system on the pre-ediacaran earth

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Geoscience Frontiers 2016年第4期7卷 555-571页

作者： George e.williams Phillip W.Schmidt Grant M.Young Department of earth Sciences University of AdelaideSA 5005Australia CSIRO Mineral Resources Flagship PO Box 52North RydeNSW 16FOAustralia Department of earth Sciences University of Western OntarioLondonOntario N6A 5B7Canada

Proterozoic （pre-ediacaran） glaciations occurred under strongly seasonal climates near sea level in low palaeolatitudes. Metre-scale primary sand wedges in Cryogenian periglacial deposits are identical to those actively forming, through the infilling of seasonal （winter） thermal contraction-cracks in perma- frost by windblown sand, in present-day polar regions with a mean monthly air temperature range of 40 ~C and mean annual air temperatures of -20 ~C or lower. Varve-like rhythmites with dropstones in Proterozoic glacial successions are consistent with an active seasonal freeze-thaw cycle. The seasonal （annual） oscillation of sea level recorded by tidal rhythmites in Cryogenian glacial successions indicates a significant seasonal cycle and extensive open seas. Palaeomagnetic data determined directly for Prote- rozoic glacial deposits and closely associated rocks indicate low palaeolatitudes： Cryogenian deposits in South Australia accumulated at 〈10% most other Cryogenian deposits at 〈20~ and Palaeoproterozoic deposits at 〈15~ palaeolatitude. Palaeomagnetic data imply that the Proterozoic geomagnetic field approximated a geocentric axial dipole, hence palaeolatitudes represent geographic latitudes. The Cry- ogenian glacial environment included glacier-flee, continental permafrost regions with ground frozen on a kyr time-scale, aeolian sand-sheets, extensive and long-lived open seas, and an active hydrological cycle. This palaeoenvironment confiicts with the ＇snowball earth＇ and ＇slushball earth＇ hypotheses, which cannot accommodate large seasonal changes of temperature near the equator. Consequently, their proponents have attempted to refute the evidence for strong seasonality by introducing Popperian ＇auxiliary assumptions＇. However, non-actualistic arguments that the Cryogenian sand wedges indicate diurnal or weakly seasonal temperature changes are based on misunderstandings of periglacial pro- cesses. Modelling of a strongly seasonal climate for a frozen-over ear

关键词： Proterozoic Glaciation Periglacial structures Varves Paleoclimate Paleomagetism

east African topography and volcanism explained by a single,migrating plume

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Geoscience Frontiers 2020年第5期11卷 1669-1680页

作者： Rakib Hassan Simon e.williams Michael Gurnis Dietmar Muller School of Geosciences Room 412Madsen Building F09 Eastern AvenueThe University of SydneyNSW2006Australia Seismological Laboratory California Institute of TechnologyPasadenaCA91125USA Now at Geoscience Australia GPO Box 378CanberraACT2601Australia State Key Laboratory of Continental Dynamics Department of GeologyNorthwest UniversityXi’an 710069China

Anomalous topographic swells and Cenozoic volcanism in east Africa have been associated with mantle *** models involving one or more fixed plumes beneath the northeastward migrating African plate have been suggested to explain the space-time distribution of magmatism in east *** devise paleogeographically constrained global models of mantle convection and,based on the evolution of flow in the deepest lower mantle,show that the Afar plume migrated southward throughout its *** models suggest that the mobile Afar plume provides a dynamically consistent explanation for the spatial extent of the southward propagation of the east African rift system(eARS),which is difficult to explain by the northeastward migration of Africa over one or more fixed plumes alone,over the last≈45 *** further show that the age-progression of volcanism associated with the southward propagation of eARS is consistent with the apparent surface hotspot motion that results from southward motion of the modelled Afar plume beneath the northeastward migrating African *** models suggest that the Afar plume became weaker as it migrated southwards,consistent with trends observed in the geochemical record.

关键词： Numerical mantle flow models Deep mantle flow LLSVP morphology Plume dynamics Plume motion Dynamic topography

Decoding earth’s plate tectonic history using sparse geochemical data

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Geoscience Frontiers 2020年第1期11卷 265-276页

作者： Michael G.Tetley Zheng-Xiang Li Kara J.Matthews Simon e.williams R.Dietmar Müller earthByte Group School of GeosciencesUniversity of SydneyNSWAustralia Seismological Laboratory California Institute of TechnologyPasadenaCAUSA Data61 CSIROAustralian Technology ParkNSWAustralia earth Dynamics Research Group The Institute for Geoscience Research(TIGeR)School of Earth and Planetary SciencesCurtin University of TechnologyGPO Box U1987PerthWA 6845Australia

Accurately mapping plate boundary types and locations through time is essential for understanding the evolution of the plate-mantle system and the exchange of material between the solid earth and surface ***,the complexity of the earth system and the cryptic nature of the geological record make it difficult to discriminate tectonic environments through deep *** we present a new method for identifying tectonic paleo-environments on earth through a data mining approach using global geochemical *** first fingerprint a variety of present-day tectonic environments utilising up to 136 geochemical data attributes in any available combination.A total of 38301 geochemical analyses from basalts aged from 5-0 Ma together with a well-established plate reconstruction model are used to construct a suite of discriminatory models for the first order tectonic environments of subduction and mid-ocean ridge as distinct from intraplate hotspot oceanic environments,identifying 41,35,and 39 key discriminatory geochemical attributes,*** training and validation,our model is applied to a global geochemical database of 1547 basalt samples of unknown tectonic origin aged between 1000-410 Ma,a relatively ill-constrained period of earth’s evolution following the breakup of the Rodinia supercontinent,producing 56 unique global tectonic environment predictions throughout the Neoproterozoic and early *** are used to discriminate between three alternative published Rodinia configuration models,identifying the model demonstrating the closest spatio-temporal consistency with the basalt record,and emphasizing the importance of integrating geochemical data into plate *** approach offers an extensible framework for constructing full-plate,deeptime reconstructions capable of assimilating a broad range of geochemical and geological observations,enabling next generation earth system models.

关键词： Plate tectonics Geochemistry Geodynamics Supercontinents Rodinia Big data

Disease spectrum and use of cholecystolithotomy in gallstone ileus

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Hepatobiliary & Pancreatic Diseases International 2012年第5期11卷 553-557页

作者： nicholas e.williams Justin S Gundara Sophia Roser Jaswinder S Samra Upper Gastrointestinal Surgical Unit Royal North Shore HospitalUniversity of SydneySt.LeonardsSydneyNSW 2065Australia

BACKGROUND: Gallstone ileus is a heterogeneous and highly morbid condition that suffers from a lack of consensus regarding the timing and approach to management of the biliary tree and associated fistula. MeTHODS: We report three cases that demonstrate the spectrum of gallstone ileus with classical examples of both Barnard’s and Bouveret’s syndromes. Clinical presentation diagnostic imaging, surgical technique and outcome are discussed. ReSULTS: One patient with Barnard’s syndrome presented with recurrent gallstone ileus. To minimize the risks of complex, definitive biliary surgery and avoid further recurrent episodes, a cholecystolithotomy was performed with effect Two cases of Bouveret’s syndrome were successfully managed with enterolithotomy/cholecystectomy and multivisceral resection respectively, thus highlighting the diverse nature of this disease and management options. CONCLUSIONS: Following enterolithotomy, potentially morbid definitive one-stage surgery in typically compromised, elderly patients needs to be weighed against the risk of recurrence and ongoing biliary pathology. We suggest the use of open cholecystolithotomy for the removal of residual gallstones when the patient is not suitable for definitive biliary surgery.

关键词： cholecystectomy biliary tract disease gallstone ileus biliary tract surgery

Mapping tree canopies in urban environments using airborne laser scanning (ALS):a Vancouver case study

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Forest ecosystems 2018年第4期5卷 429-437页

作者： Giona Matasci nicholas C.Coops David A.R.williams Nick Page Department of Forest Resource Management Unlversity of British Columbia2424Main MallVancouverBC V6T IZ4Canada Vancouver Board of Parks and Recreation 2099Beach AvenueVancouverBC V6G IZ4Canada

Background: The distribution of forest vegetation within urban environments is critically important as it influences urban environmental conditions and the energy exchange through the absorption of solar radiation and modulation of evapotranspiration. It also plays an important role filtering urban water systems and reducing storm water ***: We investigate the capacity of ALS data to individually detect, map and characterize large(taller than15 m) trees within the City of Vancouver. Large trees are critical for the function and character of Vancouver’s urban forest. We used an object-based approach for individual tree detection and segmentation to determine tree locations(position of the stem), to delineate the shape of the crowns and to categorize the latter either as coniferous or ***: Results indicate a detection rate of 76.6% for trees > 15 m with a positioning error of 2.11 m(stem location). extracted tree heights possessed a RMSe of 2.60 m and a bias of-1.87 m, whereas crown diameter was derived with a RMSe of 3.85 m and a bias of-2.06 m. Missed trees are principally a result of undetected treetops occurring in dense, overlapping canopies with more accurate detection and delineation of trees in open ***: By identifying key structural trees across Vancouver’s urban forests, we can better understand their role in providing ecosystem goods and services for city residents.

关键词： Urban forest Large trees Light detection and ranging Airborne laser scanning