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   

Determination of volatile concentrations in fluorapatite of Martian shergottite NWA 2975 by combining synchrotron FTIR,Raman spectroscopy,EMPA, and TEM,and inferences on the volatile budget of the apatite host‐magma          下载免费PDF全文

Ewa Słaby  Monika Koch‐Müller  Hans‐Jürgen Förster  Richard Wirth  Dieter Rhede  Anja Schreiber  Ulrich Schade 《Meteoritics & planetary science》2016,51(2):390-406

We combined the focused ion beam sample preparation technique with polarized synchrotron‐based FTIR (Fourier transform infrared) spectroscopy, laser‐Raman spectroscopy, electron microprobe analysis (EMPA), and transmission electron microscope (TEM) analysis to identify and quantify structurally bound OH, F, Cl, and CO₃ groups in fluorapatite from the Northwest Africa 2975 (NWA 2975) shergottite. In this study, the first FTIR spectra of the OH‐stretching region from a Martian apatite are presented that show characteristic OH‐bands of a F‐rich, hydroxyl‐bearing apatite. Depending on the method of apatite‐formula calculation and whether charge balance is assumed or not, the FTIR‐based quantification of the incorporated OH, expressed as wt% H₂O, is in variably good agreement with the H₂O concentration calculated from electron microprobe data. EMP analyses yielded between 0.35 and 0.54 wt% H₂O, and IR data yielded an average H₂O content of 0.31 ± 0.03 wt%, consistent with the lower range determined from EMP analyses. The TEM observations implied that the volatiles budget of fluorapatite is magmatic. The water content and the relative volatile ratios calculated for the NWA 2975 magma are similar to those established for other enriched or intermediate shergottites. It is difficult to define the source of enrichment: either Martian wet mantle or crustal assimilation. Comparing the environment of parental magma generation for NWA 2975 with the terrestrial mantle in terms of water content, it displays a composition intermediate between enriched and depleted MORB.  相似文献   

Tidal gravity variations revisited at Vostok Station, Antarctica     

Koichiro Doi  Kazuo Shibuya  Anja Wendt  Reinhard Dietrich  Matt King 《Polar Science》2009,3(1):1-12

In 1969, prior to the discovery of the subglacial Lake Vostok, an Askania Gs-11 gravimeter was operated at Vostok Station (78.466°S, 106.832°E; 3478 m asl) to observe tidal gravity variations. To gain a better understanding of the lake's tidal dynamics, we reanalyzed these data using a Bayesian Tidal Analysis Program Grouping method (BAYTAP-G and -L programs). The obtained phase leads for the semidiurnal waves M2 (6.6 ± 2.1°) and S2 (10.1 ± 4.2°) are more pronounced than those of the diurnal waves, among which the largest phase lead (for K1) was 5.0 ± 0.5°. The obtained δ factor for M2 was 0.890 ± 0.032, significantly less than the theoretical value of 1.16. For three global ocean tide models (NAO99b, FES2004, and TPXO6.2), the estimated load tides on waves Q1, O1, P1, K1, M2, and S2 range from 0.1–0.2 μGal (Q1 and S2) to 0.6–0.7 μGal (K1). The difference in amplitude among the three models is less than 0.14 μGal (M2), and the difference in phase is generally less than 10°. In calculating the residual tide vectors using the ocean models, the TPXO6.2 model generally gave the smallest residual amplitudes. Our result for the K1 wave was anomalously large (1.36 ± 0.25 μGal), while that for the M2 wave was sufficiently small (0.37 ± 0.17 μGal). The associated uncertainty is half that reported in previous studies. It is interesting that the residual K1 tide is approximately 90° phase-leaded, while the M2 tide is approximately 180° phase-leaded (delayed). Importantly, a similar reanalysis of data collected at Asuka Station (71.5°S, 24.1°E) gave residual tides within 0.2–0.3 μGal for all major diurnal and semidiurnal waves, including the K1 wave. Therefore, the anomalous K1 residual tide observed at Vostok Station must be linked to the existence of the subglacial lake and the nature of solid–ice–water dynamics in the region.  相似文献   

Wave Energy from the North Sea: Experiences from the Lysekil Research Site     

Mats Leijon  Cecilia Boström  Oskar Danielsson  Stefan Gustafsson  Kalle Haikonen  Olivia Langhamer  Erland Strömstedt  Magnus Stålberg  Jan Sundberg  Olle Svensson  Simon Tyrberg  Rafael Waters 《Surveys in Geophysics》2008,29(3):221-240

This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider? buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.  相似文献   

Holocene tephra deposits in the northern Okinawa Trough     

LIU Yanguang  OLE Bjφrslev Nielsen  ZHANG Deyu  DU Dewen  JAN Heinemeier  WU Yonghua 《海洋学报(英文版)》2006,25(1):78-89

1 Introduction Volcanic activities have played an important role in the process of global climatic changes. Being good stratigraphic markers, widespread tephra layers in ma- rine sediments can provide reliable evidences for the regional paleoceanographic …  相似文献   

Paleogeography of the Early Badenian connection between the Vienna Basin and the Carpathian Foredeep     

Rostislav Brzobohaty  Zdeněk Stráník 《Central European Journal of Geosciences》2012,4(1):126-137

The paleogeographic reconstruction for an early Badenian connection of the Vienna Basin and the Carpathian Foredeep in the Mikulov area (Mikulov Gate) based on paleontological (otoliths) and geological (regional geology, tectonics) data has been provided. The ecologically homogenous deep water associations of otoliths in the most NW tip of the Vienna Basin (Sedlec HJ-2 Borehole) links up bathymetrically with nearly adequate otolith assemblages in the southernmost Moravian part of the foredeep. Ten meso- and bathypelagic teleost species have been identified in the Vienna Basin for the first time. Geological analyses proved inversion processes of recurrent nature along old faults of the NW-SE direction in the Dyje (Thaya) Depression. In the early Badenian the Mikulov Gate resulted from the sagging block of the Waschberg Zone. This marine channel was relatively deep (> 200m, as indicated by otoliths) and in all probability flooded an entire front of the nappes in this area.  相似文献   

Crater morphology in sandstone targets: The MEMIN impact parameter study     

Anja DUFRESNE  Michael H. POELCHAU  Thomas KENKMANN  Alex DEUTSCH  Tobias HOERTH  Frank SCHÄFER  Klaus THOMA 《Meteoritics & planetary science》2013,48(1):50-70

Abstract– Hypervelocity (2.5–7.8 km s^?1) impact experiments into sandstone were carried out to investigate the influence of projectile velocity and mass, target pore space saturation, target‐projectile density contrast, and target layer orientation on crater size and shape. Crater size increases with increasing projectile velocity and mass as well as with increasing target pore space saturation. Craters in water‐saturated porous targets are generally shallower and larger in volume and in diameter than craters from equivalent impacts into dry porous sandstone. Morphometric analyses of the resultant craters, 5–40 cm in diameter, reveal features that are characteristic of all of our experimental craters regardless of impact conditions (I) a large central depression within a fragile, light‐colored central part, and (II) an outer spallation zone with areas of incipient spallation. Two different mechanical processes, grain fragmentation and intergranular tensile fracturing, are recorded within these crater morphologies. Zone (I) approximates the shape of the transient crater formed by material compression, displacement, comminution, and excavation flow, whereas (II) is the result of intergranular tensile fracturing and spallation. The transient crater dimensions are reconstructed by fitting quadric parabolas to crater profiles from digital elevation models. The dimensions of this transient and of the final crater show the same trends: both increase in volume with increasing impact energy, and with increasing water saturation of the target pore space. The relative size of the transient crater (in percent of the final crater volume) decreases with increasing projectile mass and velocity, signifying a greater contribution of spallation on the final crater size when projectile mass and velocity are increased.  相似文献   

SBAS orbit and satellite clock corrections for precise point positioning   总被引：2，自引：0，他引：2  

Anja Heßelbarth  Lambert Wanninger 《GPS Solutions》2013,17(4):465-473

The quality of real-time GPS positions based on the method of precise point positioning (PPP) heavily depends on the availability and accuracy of GPS satellite orbits and satellite clock corrections. Satellite-based augmentation systems (SBAS) provide such corrections but they are actually intended to be used for wide area differential GPS with positioning results on the 1-m accuracy level. Nevertheless, carrier phase-based PPP is able to achieve much more accurate results with the same correction values. We applied SBAS corrections for dual-frequency PPP and compared the results with PPP obtained using other real-time correction data streams, for example, the GPS broadcast message and precise corrections from the French Centre National d’Etudes Spatiales and the German Deutsches Zentrum für Luft- und Raumfahrt. Among the three existing SBAS, the best results were achieved for the North American wide area augmentation system (WAAS): horizontal and vertical position accuracies were considerably smaller than 10 cm for static 24-h observation data sets and smaller than 30 cm for epoch-by-epoch solutions with 2 h of continuous observations. The European geostationary navigation overlay service and the Japanese multi-functional satellite augmentation system yield positioning results with biases of several tens of centimeters and variations larger by factors of 2–4 as compared to WAAS.  相似文献   

Changing patterns of residential and workplace segregation in the Stockholm metropolitan area     

Szymon Marcińczak  Tiit Tammaru  Magnus Strömgren  Urban Lindgren 《Urban geography》2013,34(7):969-992

Immigrant–native segregation is present in the spaces in which individuals from different ethnic/racial groups practice their everyday lives; interact with others and develop their ethnic, social and spatial networks. The overwhelming majority of academic research on immigrant segregation has focused on the residential domain, thus largely overlooking other arenas of daily interaction. The present study contributes to the emerging literature on immigrant residential and workplace segregation by examining changes in patterns of residential and workplace segregation over time. We draw our data from the Stockholm metropolitan region, Sweden’s main port of entry for immigrants. The results suggest a close association between residential and workplace segregation. Immigrant groups that are more segregated at home are also more segregated in workplace neighborhoods. More importantly, we found that a changing segregation level in one domain tends to involve a similar trend in the other domain.  相似文献   

Source‐to‐sink analysis of ancient sedimentary systems using a subsurface case study from the Møre‐Trøndelag area of southern Norway: Part 2 – sediment dispersal and forcing mechanisms     

Tor O. Sømme  Christopher A‐L. Jackson 《Basin Research》2013,25(5):512-531

The composition, volume and stratigraphic organisation of submarine fan systems deposited along continental margins are expected to reflect the landscape from which the sediment was derived. During the Late Cretaceous, the Møre‐Trøndelag margin, Norwegian North Sea was dominated by the deposition of deep‐marine fines; the emplacement of 11 sand‐rich submarine fan systems occurred only during a c. 3 Myr period in the Turonian‐Coniacian. The systems were fed by sediment that was routed through submarine canyons incised into the basin margin; the canyons are underlain by angular unconformities and are interpreted to have resulted from tectonically induced changes in slope physiography and erosion by gravity flows. The areal extent of the onshore drainage catchments that supplied sediment to the fans has been estimated based on scaling relationships derived from modern source‐to‐sink systems. The results of our study suggest that the Turonian fans were sourced by drainage catchments that were up to ca.3600 km², extending more than ca.100 km inland from the palaeo‐shoreline. The estimated inboard catchment extent correlates with the innermost structures of a large, long‐lived, basement‐involved, normal fault complex. On the basis of our analysis, we conclude that increased sediment supply to the Turonian fan systems reflects tectonic rejuvenation of the landscape, rather than eustatic sea‐level or climate fluctuations. The duration of fan deposition is thus interpreted to reflect the ‘relaxation time’ of the landscape following tectonic perturbation, and fan system retrogradation and abandonment is interpreted to reflect the eventual depletion of the onshore sediment source. We demonstrate that a better understanding of the stratigraphic variability in deepwater depositional systems can be gained by taking a complete source‐to‐sink view of ancient sediment dispersal systems.  相似文献