Traces of historical tropical cyclones and tsunamis in the Ashburton Delta (north‐west Australia)          下载免费PDF全文

Simon Matthias May  Dominik Brill  Max Engel  Anja Scheffers  Anna Pint  Stephan Opitz  Volker Wennrich  Peter Squire  Dieter Kelletat  Helmut Brückner 《Sedimentology》2015,62(6):1546-1572

Although the north‐western coast of Western Australia is highly vulnerable to tropical cyclones and tsunamis, little is known about the geological imprint of historic and prehistoric extreme wave events in this particular area. Despite a number of site‐specific difficulties such as post‐depositional changes and the preservation potential of event deposits, both tropical cyclones and tsunamis may be inferred from the geomorphology and the stratigraphy of beach ridge sequences, washover fans and coastal lagoons or marshes. A further challenge is the differentiation between tsunami and storm deposits in the geological record, particularly where modern deposits and/or historical reports on the event are not available. This study presents a high‐resolution sedimentary record of washover events from the Ashburton River delta (Western Australia) spanning approximately the last 150 years. A detailed characterization of event deposits is provided, and a robust chronostratigraphy for the investigated washover sequence is established based on multi‐proxy sediment analyses and optically stimulated luminescence dating. Combining sedimentological, geochemical and high‐resolution optically stimulated luminescence data, event layers are assigned to known historical events and tropical cyclone deposits are separated from tsunami deposits. For the first time, the 1883 Krakatoa and 1977 Sumba tsunamis are inferred from sedimentary records of the north‐western part of Western Australia. It is demonstrated that optically stimulated luminescence applied in coastal sedimentary archives with favourable luminescence characteristics can provide accurate chronostratigraphies even on a decadal timescale. The results contribute to the data pool of tropical cyclone and tsunami deposits in Holocene stratigraphies; however, they also demonstrate how short‐lived sediment archives may be in dynamic sedimentary environments.  相似文献   

Time series assessment on landslide occurrences in an area undergoing development          下载免费PDF全文

Norbert Simon  Michael Crozier  Mairead de Roiste  Abdul Ghani Rafek  Rodeano Roslee 《Singapore journal of tropical geography》2015,36(1):98-111

This study assesses the influence of development on landslide occurrences in a rapidly developing area, Kota Kinabalu in Sabah Malaysia, across three assessment years (1978, 1994 and 2010). Two development indicators, land use and road density, were used to measure the influence of development on landslide occurrence. Land use was classified into four categories (barren, forest, developed and other), and road density was classified into low (< 50 m/40 000 m²), moderate (50–150 m/40 000 m²) and high (> 150 m/40 000 m²). Landslide density analysis was used to calculate the concentration of landslide for the different land use and road density categories. The number of landslides in developed areas increased from 19 landslides/100 km² in 1978, to 29 landslides/100 km² in 1994 and to 50 landslides/100 km² in 2010, mirroring an increase in land use for development purposes from 8 per cent in 1978 to 27 per cent in 2010. Landslide density also gradually increased in the high road density class from 10 landslides/100 km² in 1978, to 30 landslides/100 km² in 1994 and 62 landslides/100 km² in 2010. These results show that road construction activities influence landslide occurrences.  相似文献   

Crystallization and Degassing in the Basement Sill, McMurdo Dry Valleys, Antarctica     

Boudreau  Alan; Simon  Adam 《Journal of Petrology》2007,48(7):1369-1386

The Basement Sill is part of the Ferrar Large Igneous Provinceexposed in the McMurdo Dry Valleys, Antarctica. The sill is330 m thick in the Bull Pass area and 450 + m thick in the Daisarea, 12 km to the west, and is characterized by phenocryst-freelower and upper margins and an orthopyroxene-rich central ‘tongue’(opx 1–5 mm in size). Halogen variations in apatite froma suite of samples collected along vertical transects throughthe sill were examined to evaluate the process of crystallization-induceddegassing (i.e. second boiling) and its effects on magma chemistry.Apatite grains from any given sample are generally unzoned withrespect to Cl and F concentrations, but may vary by 20–30mol% in the halogen site between grains. Overall average Cl/Fmass ratios increase with height from the lower margin to thecenter of the sill, and then decrease to near zero towards thetop margin where the rocks are relatively oxide-rich. The Cl/Ftrend parallels those of bulk MgO and grain size. The uppermargin contains abundant mafic pegmatoids and the apatite inthese segregations has lower Cl/F ratios compared with thatin the host-rocks, although REE show no measurable difference.Numerical modeling illustrates that a cooling and crystallizingsill initially develops two separate vapor-saturated zones atthe lower and upper margins owing to the irreversible heat lossto the cooler country rock. Vapor separating from the lowerzone migrates upward into hotter silicate liquid, where it isresorbed, thus increasing the Cl/F mass ratio of the liquid.This process leads to saturation and precipitation of apatitefrom the liquid with a higher Cl/F ratio than would otherwiseoccur. Volatile enrichment can also aid compaction and graingrowth in the central part of the sill. In contrast, the relativelyFe-rich, Cl-poor nature of the upper zone rocks suggests thatthese rocks may have crystallized from more evolved, degassedsilicate liquid, possibly compacted out of the underlying crystalmush. In addition, as vapor sourced from the lower and centralparts of the sill ascends into the cooler upper zone of thesill, the vapor may be localized (along with late interstitialsilicate liquid) to form pegmatoids at temperatures at whichCl is less favored in apatite and can be leached from existingapatite by the ascending vapor, the latter causing the observeddecrease in the Cl/F mass ratio of apatite in the (evolved)pegmatoids. KEY WORDS: Ferrar Igneous Province; halogens; fluid; apatite  相似文献   

The Origin and Evolution of the Kaapvaal Cratonic Lithospheric Mantle   总被引：5，自引：0，他引：5  

Simon  Nina S. C.; Carlson  Richard W.; Pearson  D. Graham; Davies  Gareth R. 《Journal of Petrology》2007,48(3):589-625

A detailed petrological and geochemical study of low-temperatureperidotite xenoliths from Kimberley and northern Lesotho ispresented to constrain the processes that led to the magmaphileelement depletion of the Kaapvaal cratonic lithospheric mantleand its subsequent re-enrichment in Si and incompatible traceelements. Whole-rocks and minerals have been characterized forRe–Os isotope compositions, and major and trace elementconcentrations, and garnet and clinopyroxene for Lu–Hfand Sm–Nd isotope compositions. Most samples are characterizedby Archaean Os model ages, low Al, Fe and Ca contents, highMg/Fe, low Re/Os, very low (< 0·1 x chondrite) heavyrare earth element (HREE) concentrations and a decoupling betweenNd and Hf isotope ratios. These features are most consistentwith initial melting at 3·2 Ga followed by metasomatismby hydrous fluids, which may have also caused additional meltingto produce a harzburgitic residue. The low HREE abundances ofthe peridotites require that extensive melting occurred in thespinel stability field, possibly preceded by some melting inthe presence of garnet. Fractional melting models suggest that30% melting in the spinel field or 20% melting in the garnetfield followed by 20% spinel-facies melting are required toexplain the most melt-depleted samples. Garnet Nd–Hf isotopecharacteristics indicate metasomatic trace element enrichmentduring the Archaean. We therefore suggest a model includingshallow ridge melting, followed by metasomatism of the Kaapvaalupper mantle in subduction zones surrounding cratonic nuclei,probably during amalgamation of smaller pre-existing terranesin the Late Archaean (2·9 Ga). The fluid-metasomatizedresidua have subsequently undergone localized silicate meltinfiltration that led to clinopyroxene ± garnet enrichment.Calculated equilibrium liquids for clinopyroxene and their Hf–Ndisotope compositions suggest that most diopside in the xenolithscrystallized from an infiltrating kimberlite-like melt, eitherduring Group II kimberlite magmatism at 200–110 Ma (Kimberley),or shortly prior to eruption of the host kimberlite around 90Ma (northern Lesotho). KEY WORDS: Kaapvaal craton; lithospheric mantle; metasomatism; Nd–Hf isotopes; Re–Os isotopes  相似文献   

Solute movement in drained fen peat: a field tracer study in a Somerset (UK) wetland     

Andrew J Baird  Simon W Gaffney 《水文研究》2000,14(14):2489-2503

Little is known about solute transport in peats, despite the obvious importance of solute transport on eco‐hydrological processes in both managed and natural peatlands. To address this lack of knowledge, we investigated solute transport processes in an agricultural fen peat using a conservative KBr tracer. The main aim of the study was to elucidate solute transport behaviour in general in this peat, with a more specific aim of investigating whether preferential or bypassing flow occurred. The tracer moved through the peat more rapidly than expected, and the pattern of movement showed clear evidence of plot‐scale bypassing flow. The data also provide evidence that bypassing flow occurs in pores at smaller scales. The implications of this study for management of wetland pastures in the Somerset Moors in south‐west England are discussed. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Natural Environmental Change A. M. MANNION Publisher Routledge,London 1999 (198 pp) £12.99 ISBN 0‐415‐13933‐3 (paperback edition)     

Simon G. Lewis 《第四纪科学杂志》2000,15(6):657-657

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Remnants of Earth’s Oldest Continental Crust Formed by Subduction     

GE Rongfeng  ZHU Wenbin  Simon A. WILDE  WU Hailin 《《地质学报》英文版》2020,94(Z1):14-14

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Identification of new low-mass members of the Alpha Persei open cluster by ROSAT. II     

C. F. Prosser  S. Randich  T. Simon 《Astronomische Nachrichten》1998,319(4):215-234

The present investigation examines possible optical counterparts to 130 X-ray sources in the region of the α Persei open cluster (d ∽ 170pc, age ∽ 50 Myr) resulting from the analysis of three 22–25 ksec ROSAT PSPC pointings. In the same manner as for 73 X-ray sources from a raster survey in α Per (Prosser & Randich 1998), CCD photometry is employed to obtain magnitudes and colors for stars/objects close to the X-ray positions, with additional echelle and low-dispersion Hα spectra provided for some stars. For almost 60 X-ray sources, an optical counterpart with photometry acceptable for cluster membership is identified, some of which can be excluded from membership on the basis of discrepant radial velocity or X-ray characteristics. On the order of 30 new members or likely members associated with X-ray sources have been identified based on available data. A photometric rotation period has been obtained for one rapid rotator identified in X-rays.  相似文献   

The structure and sedimentology of relict talus,Trotternish, northern Skye,Scotland     

Simon Hinchliffe  Colin K. Ballantyne  John Walden 《地球表面变化过程与地形》1998,23(6):545-560

Sections up to 3·5 m deep cut through the upper rectilinear segment of relict, vegetated talus slopes at the foot of the Trotternish escarpment reveal stacked debris-flow deposits intercalated with occasional slopewash horizons and buried organic soils. Radiocarbon dating of buried soil horizons indicates that reworking of sediment by debris flows predates 5·9–5·6 Cal ka BP , and has been intermittently active throughout the late Holocene. Particle size analyses of 18 bulk samples from these units indicates that c. 27–30 per cent of the talus deposit is composed of fine (<2 mm) sediment. Sedimentological comparison with tills excludes a glacigenic origin for the talus debris, and the angularity of constituent clasts suggests that in situ weathering has been insignificant in generating fine material. We conclude that the fine sediment within the talus is derived primarily by granular weathering of the rockwall, with syndepositional accumulation of both fine and coarse debris, implying that c. 27–30 per cent of rockwall retreat since deglaciation reflects granular weathering rather than rockfall. The abundance of fines within the talus deposits is inferred to have been of critical importance in facilitating build-up of porewater pressures during rainstorms, leading to episodic failure and flow of debris on the upper parts of the slope. A wider implication of these findings is that the mechanical properties of talus slopes cannot be regarded as those of free-draining accumulations of coarse clasts, and that models that treat talus slopes as such have limited value in explaining their form and evolution. Our findings lend support to models that envisage the upper straight slope on talus accumulations as the product of mass-transport as well as rockfall, and indicate that episodic debris flow has been the primary agent of mass-transport at this site. © 1998 John Wiley & Sons, Ltd.  相似文献   

A method to determine warm and cool steppe biomes from pollen data; application to the Mediterranean and Kazakhstan regions     

Pavel E. Tarasov  Rachid Cheddadi  Joel Guiot  Sytze Bottema  Odile Peyron  Jordina Belmonte  Vittoria Ruiz-Sanchez  Fatima Saadi  Simon Brewer 《第四纪科学杂志》1998,13(4):335-344

An objective method for the assignment of pollen spectra to appropriate biomes has been published recently. The aim of this paper is to improve the distinction between warm and cool steppes, thus refining vegetation and climate reconstruction, particularly during the Last Glacial Maximum. A set of modern pollen spectra from the Mediterranean and Kazakhstan regions, dominated today by open vegetation types, has been analysed statistically in order to relate pollen taxa abundances to warm and cool grass/shrub plant functional types (PFTs). A statistical test using modern pollen data shows that the method is able to distinguish between cool and warm steppe biomes with a high degree of confidence. The method has been applied to two fossil pollen records. The results of this exercise showed that cool steppe dominated in central Greece between 18 000 and 13 000 yr BP, while in western Iran the vegetation was at the boundary between cool and warm steppes. These vegetation types were replaced by warm mixed forest in Greece and warm steppe in Iran after that time span. © 1998 John Wiley & Sons, Ltd.  相似文献