Coarse clast ridge sequences as suitable archives for past storm events? Case study on the Houtman Abrolhos,Western Australia     

Anja M. Scheffers  Sander R. Scheffers  Dieter H. Kelletat  Peter Squire  Lindsay Collins  Yuexing Feng  Jian‐Xin Zhao  Renaud Joannes‐Boyau  Simon Matthias May  Gerhard Schellmann  Heather Freeman 《第四纪科学杂志》2012,27(7):713-724

Prehistoric storm records are relatively scarce in most parts of the world. This article presents storm records derived from coral rubble‐based geological archives of the Houtman Abrolhos Archipelago located off the west coast of Australia, where the southernmost coral reefs of the Indian Ocean are found. Winter storm swell from the circum‐Antarctic ‘Brave Westerlies’, as well as tropical cyclone waves, have left numerous ridge systems on dozens of islands of the archipelago, all composed of coral rubble from adjacent reefs. At three islands, seven ridge systems were dated by three different methods: U‐series (68 dates), radiocarbon (64 dates), electron spin resonance (7 dates); 139 radiometric dates span the last 5500 years of the Holocene. In contrast to the geomorphological interpretation, the age sequences show ‘inversions’, hiatuses and different ages for the same ridge, all pointing to complicated ridge formation processes. Time gaps, some exceeding 1000 years, are interpreted as phases of erosion and not as phases without storm activity. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Insights into rock avalanche emplacement processes from detailed morpho‐lithological studies of the Tschirgant deposit (Tyrol,Austria)          下载免费PDF全文

Anja Dufresne  Christoph Prager  Annette Bösmeier 《地球表面变化过程与地形》2016,41(5):587-602

Large, rapid rockslope failures generate deposits with complex morphologies due to a number of causal and influencing factors. To investigate these, we conducted a detailed case study at the carbonate Tschirgant deposit (Tyrol, Austria). It preserved evidence of simultaneous rock sliding (very large, coherent hummocks) and rock avalanche spreading (smaller, more scattered hummocks and ridges). Motion indicators, such as longitudinal ridges furthermore pinpoint the transition between linear sliding and radial spreading. The lithological distribution in the Tschirgant deposit shows that it retained source stratigraphy despite being split into two accumulation lobes by a high bedrock ridge. Furthermore, lithology had a very strong control on the final deposit morphology in that the different lithologic units form individual deposit surfaces. River erosion has created fortuitous outcrops that reveal the basal rock avalanche contact. The underlying valley‐fill sediments (substrates) have been intricately involved in shaping the rock avalanche morphology and, where entrained, highlight internal rock avalanche deformation features. This study shows that intrinsic dynamic properties of granular media (e.g. tendency for longitudinal alignments), emplacement mode, lithology (and source predisposition), runout path topography, and substrates form the quintet of causal factors that shape rock avalanche morphology. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Dynamic adjustment of training sets (‘moving-window’ reconstruction) by using transfer functions in paleolimnology—a new approach   总被引：1，自引：0，他引：1  

Thomas Hübener  Mirko Dreßler  Anja Schwarz  Kirsten Langner  Sven Adler 《Journal of Paleolimnology》2008,40(1):79-95

This paper presents a new method (moving-windows) that optimizes diatom-based paleolimnological reconstructions of past environmental conditions from supra-regional training sets. The moving-window method identifies the best number of nearest neighbours (window size) from a merged supra-regional EDDI and local (MV) training set (n = 429) for each fossil diatom assemblage and the best type of transfer function (ML, WA-PLS) based on the error statistic of each transfer function (highest cross-validated R ², lowest cross-validated average bias, maximum bias and RMSEP). At first we evaluated the moving-window approach by comparing measured TP-values with inferred TP-values using both the moving-window approach and the WA-PLS method. The relative errors of the moving-window approach were not significantly different for 208 samples that had an error <15 μg/l TP using the WA-PLS method. However, for the remaining 221 samples with errors >>15 μg/l TP using the WA-PLS method, the moving window approach significantly reduced the relative error of the inferred TP levels. Secondly, the moving- window approach was used to reconstruct epilimnetic total phosphorous (TP) for Lake Dudinghausen, Lake Rugensee, Lake Tiefer See and Lake Drewitzer See (Northern Germany) using both the supra-regional EDDI training set and a local training set from Northern Germany (MV training set). The moving-window inferred TP-levels of the four study lakes were compared with published reconstructed TP-values and with inferred TP-values based on the local MV training set. Overall, the moving-window and the published TP-trends agree well with each other. However, the moving-window reconstructions generally indicated lower TP-levels throughout the past ∼5,000 to 12,000 years, including past maxima. Thus, the moving-window method seems to generate more realistic absolute TP levels due to the optimized window size (highest number of modern analogues, best error statistics). The identification of more realistic absolute historic TP-values is important for the validation of reference conditions for inland waters. This study also demonstrates that a robust local training set may, similar to moving-window training sets, also lead to reliable reconstructions, if the geological settings of the local training set lakes and the study lakes are similar.  相似文献   

Origin of light volatile hydrocarbon gases in mud volcano fluids, Gulf of Cadiz — Evidence for multiple sources and transport mechanisms in active sedimentary wedges     

Marianne Nuzzo  Edward R.C. Hornibrook  Fiona Gill  Christian Hensen  Richard D. Pancost  Matthias Haeckel  Anja Reitz  Florian Scholz  Vitor H. Magalhes  Warner Brückmann  Luis M. Pinheiro 《Chemical Geology》2009,266(3-4):359-372

Widespread mud volcanism across the thick (≤ 14 km) seismically active sedimentary prism of the Gulf of Cadiz is driven by tectonic activity along extensive strike–slip faults and thrusts associated with the accommodation of the Africa–Eurasia convergence and building of the Arc of Gibraltar, respectively. An investigation of eleven active sites located on the Moroccan Margin and in deeper waters across the wedge showed that light volatile hydrocarbon gases vented at the mud volcanoes (MVs) have distinct, mainly thermogenic, origins. Gases of higher and lower thermal maturities are mixed at Ginsburg and Mercator MVs on the Moroccan Margin, probably because high maturity gases that are trapped beneath evaporite deposits are transported upwards at the MVs and mixed with shallower, less mature, thermogenic gases during migration. At all other sites except for the westernmost Porto MV, δ¹³C–CH₄ and δ²H–CH₄ values of ~ − 50‰ and − 200‰, respectively, suggest a common origin for methane; however, the ratio of CH₄/(C₂H₆ + C₃H₈) varies from ~ 10 to > 7000 between sites. Mixing of shallow biogenic and deep thermogenic gases cannot account for the observed compositions which instead result mainly from extensive migration of thermogenic gases in the deeply-buried sediments, possibly associated with biodegradation of C₂₊ homologues and secondary methane production at Captain Arutyunov and Carlos Ribeiro MVs. At the deep-water Bonjardim, Olenin and Carlos Ribeiro MVs, generation of C₂₊-enriched gases is probably promoted by high heat flux anomalies which have been measured in the western area of the wedge. At Porto MV, gases are highly enriched in CH₄ having δ¹³C–CH₄ ~ − 50‰, as at most sites, but markedly lower δ²H–CH₄ values < − 250‰, suggesting that it is not generated by thermal cracking of n-alkanes but rather that it has a deep Archaeal origin. The presence of petroleum-type hydrocarbons is consistent with a thermogenic origin, and at sites where CH₄ is predominant support the suggestion that gases have experienced extensive transport during which they mobilized oil from sediments ~ 2–4 km deep. These fluids then migrate into shallower, thermally immature muds, driving their mobilization and extrusion at the seafloor. At Porto MV, the limited presence of petroleum in mud breccia sediments further supports the hypothesis of a predominantly deep microbial origin of CH₄.  相似文献   

Single-crystal polarized FTIR spectroscopy and neutron diffraction refinement of cancrinite     

Giancarlo Della Ventura  G. Diego Gatta  Gunter J. Redhammer  Fabio Bellatreccia  Anja Loose  Gian Carlo Parodi 《Physics and Chemistry of Minerals》2009,36(4):193-206

We relate a single-crystal FTIR (Fourier transform infrared) and neutron diffraction study of two natural cancrinites. The structural refinements show that the oxygen site of the H₂O molecule lies off the triad axis. The water molecule is almost symmetric and slightly tilted from the (0001) plane. It is involved in bifurcated hydrogen bridges, with Ow···O donor–acceptor distances >2.7 Å. The FTIR spectra show two main absorptions. The first at 3,602 cm^?1 is polarized for E ⊥ c and is assigned to the ν₃ mode. The second, at 3,531 cm^?1, is also polarized for E ⊥ c and is assigned to ν₁ mode. A weak component at 4,108 cm^?1 could possibly indicate the presence of additional OH groups in the structure of cancrinite. Several overlapping bands in the 1,300–1,500 cm^?1 range are strongly polarized for E ⊥ c, and are assigned to the vibrations of the CO₃ group.  相似文献   

Field and Laboratory Exposures of Two Moss Species to Low Level Metal Pollution     

Anja H. Tremper  M. Agneta  S. Burton  David E. B. Higgs 《Journal of Atmospheric Chemistry》2004,49(1-3):111-120

Moss transplants of the species Rhytidiadelphus squarrosus and Pleurozium schreberi were used as active biomonitoring organisms as a part of a monitoring study to assess the impact of metals associated with ambient particles on mosses at roadsides.The moss samples were exposed at a semi-urban and roadside site for 3 months for subsequent analysis of metal concentration (Cu, Pb and Zn). This field experiment was carried out to investigate the accumulation of the metals over a period of 0, 4, 8 and 12 weeks at the two sites. The metal concentration in the moss samples generally increased with the length of exposure and was higher at the roadside site. The two species, however, showed slightly different accumulation patterns. In addition to the metal analysis chlorophyll concentrations were analysed as a measure of stress response in the moss samples of the above mentioned field exposures. The chlorophyll concentrations of exposed mosses showed no or only weak correlations to the concentration of the three metals measured in the moss, which suggests that other conditions have a greater influence on the chlorophyll concentration.The effect of a single metal on the moss was studied in laboratory experiments exposing R. squarrosus to the metals copper, lead and zinc at concentrations based on the above field data. At the concentrations used there was a significant reduction in the chlorophyll a concentration after exposure to copper.  相似文献   

Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implications   总被引：1，自引：0，他引：1  

Jens Wendt  Reinhard Dietrich  Mathias Fritsche  Anja Wendt  Alexander Yuskevich  rey Kokhanov  Anton Senatorov  Valery Lukin  Kazuo Shibuya  Koichiro Doi 《Geophysical Journal International》2006,166(3):991-998

In the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30 km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed.
The derived ice flow velocity for Vostok Station is  2.00 m a⁻¹± 0.01 m a⁻¹  . Along the flowline of Vostok Station an extension rate of about 10⁻⁵ a⁻¹ (equivalent to 1 cm km⁻¹ a⁻¹) was determined. This significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4 mm a⁻¹ along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years.  相似文献   

Competition between pelagic and benthic microalgae for phosphorus and light   总被引：2，自引：0，他引：2  

Sabine Flöder  Anja Combüchen  Annika Pasternak  Helmut Hillebrand 《Aquatic Sciences - Research Across Boundaries》2006,68(4):425-433

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Optically stimulated luminescence dating of sublittoral and intertidal sediments from Dubai, UAE: Radioactive disequilibria in the uranium decay series   总被引：1，自引：0，他引：1  

Anja Zander  Detlev Degering  Frank Preusser  Haino Uwe Kasper  Helmut Brückner 《Quaternary Geochronology》2007,2(1-4):123-128

Shallow marine and intertidal shell rich sediments from the low coastal plain of Dubai were dated by optically stimulated luminescence. Combined high-resolution gamma spectrometry and ICP–MS analyses revealed significant disequilibria in the ²³⁸U decay series. Time dependent dose rates were modelled for two scenarios including a closed system and an open system with linear U and Ra uptake. OSL ages that were calculated using the linear uptake model are in good agreement with archaeological evidence and radiocarbon datings on shells and wood. The presented results illustrate that luminescence-dating techniques are suitable to set up a chronostratigraphic frame for calcareous coastal environments if an appropriate model is applied to consider the influence of radioactive disequilibria and time dependent dose rates. A comprehensive radionuclide analysis of the sediments is thought necessary to perform geochemically supported dose rate simulations.  相似文献   

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