Continuous GPS and broad-scale deformation across the Rhine Graben and the Alps     

Magdala Tesauro  Christine Hollenstein  Ramon Egli  Alain Geiger  Hans-Gert Kahle 《International Journal of Earth Sciences》2005,94(4):525-537

In order to study the ongoing tectonic deformation in the Rhine Graben area, we reconstruct the local crustal velocity and the strain rate field from GPS array solutions. Following the aim of this work, we compile the velocities of permanent GPS stations belonging to various networks (EUREF, AGNES, REGAL and RGP) in central western Europe. Moreover, the strain rate field is displayed in terms of principal axes and values, while the normal and the shear components of the strain tensor are calculated perpendicular and parallel to the strike of major faults. The results are compared with the fault plane solutions of earthquakes, which have occurred in this area. A broad-scale kinematic deformation model across the Rhine Graben is provided on the basis of tectonics and velocity results of the GPS permanent stations. The area of study is divided into four rigid blocks, between which there might be relative motions. The velocity and the strain rate fields are reconstructed along their borders, by estimating a uniform rotation for each block. The tectonic behaviour is well represented by the four-block model in the Rhine Graben area, while a more detailed model will be needed for a better reconstruction of the strain field in the Alpine region.

Magdala TesauroEmail:

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Assessment of long term change in sediment condition after organic enrichment: defining recovery     

Macleod CK  Crawford CM  Moltschaniwskyj NA 《Marine pollution bulletin》2004,49(1-2):79-88

Sediment condition at an Atlantic salmon (Salmo salar) culture site in S.E. Tasmania, Australia was evaluated to determine the rate and extent of recovery after removal of farmed fish. By local standards the cage sediment at the start of this survey was markedly degraded but comparison with results from impact studies in Scotland, Canada and Norway suggests that the sediments were considerably less impacted than in northern temperate areas. The impact at the cages diminished rapidly with both time and distance; after only 2 months conditions were markedly improved. The macrobenthos indicated a slower recovery than chemical measures, after 36 months the benthic faunal community structure under the cages still differed from reference conditions even though other sediment measures had recovered. This study highlighted two other key issues in relation to monitoring and management of sediment recovery. First, techniques used to determine impact may not be appropriate for evaluation of recovery. Second, establishment of local baseline standards is extremely important to ensure appropriate evaluation of both impact and recovery.  相似文献   

Evaluation of short-term fallowing as a strategy for the management of recurring organic enrichment under salmon cages     

Macleod CK  Moltschaniwskyj NA  Crawford CM 《Marine pollution bulletin》2006,52(11):1458-1466

Rotation of cages within fish farm leases and the subsequent fallowing of areas of seabed is commonly used to allow recovery of infaunal communities following periods of organic enrichment. To investigate the effect of different background environmental conditions on recovery response, two Atlantic salmon (Salmo salar) fish farm sites in southeast Tasmania were sampled over two commercial fallowing cycles. Despite similar stocking levels and feed input there were significant differences in the way in which sediment at each farm responded to the cessation of fish stocking. Sediments at both farms showed some improvement in the community structure over a three month fallow period, but the community structure only recovered to that present before stocking not to that at the reference sites. The similarity of the impact sites to the reference sites increased from ca. 25% to 31% at one site and 11% to 27% at the other after fallowing. Rate and extent of recovery were affected by farm location, initial impact of the sediments, and length of fallow period. Initial recovery was faster at the more sheltered site than at the more exposed site, possibly reflecting differences in environmental resilience with the more sheltered location better able to assimilate organic inputs. Accordingly general fallowing management protocols may need to be adapted to reflect differences between sites. The findings of this study suggest that the recovery response of benthic communities can be predicted once baseline conditions are understood.  相似文献   

Analysis of the Devonian (Frasnian) platform from Belgium: a multi‐faceted approach for basin evolution reconstruction     

Anne‐Christine Da Silva  Frédéric Boulvain 《Basin Research》2012,24(3):338-356

This study undertakes a multi‐disciplinary approach (sedimentology, carbon isotopes, magnetic susceptibility and thickness distribution) to improve understanding of a major Palaeozoic carbonate platform, the Frasnian platform of Belgium. These combined techniques are used to reconstruct the platform history, which evolved in two main steps. During the first phase, the basin was strongly influenced by faulting, producing notable thickness and facies variations, with open ocean conditions, with good water circulation and no/or limited barrier reef. The second phase of platform development was less influenced by differential subsidence, as indicated by homogeneous facies distribution. However, this platform developed under restricted waters, with low circulation which is likely related to the development of a barrier reef.  相似文献   

Lunar meteorite LaPaz Icefield 04841: Petrology,texture, and impact‐shock effects of a low‐Ti mare basalt     

Eddy HILL  Lawrence A. TAYLOR  Christine FLOSS  Yang LIU 《Meteoritics & planetary science》2009,44(1):87-94

Abstract— Found during the 2004 U.S. Antarctic Search for Meteorites season, LaPaz Icefield (LAP) 04841 represents an addition to the LaPaz lunar basalts suite and brings the total mass collected to 1.93 kg. The presence of FeNi grains, troilite, and the anorthositic composition of plagioclase are evidence for the lunar origin of this meteorite. Pyroxene and olivine Mn/Fe values plot along the trend set for lunar basalts. Analyses of chromite grains provide a V/(Al + Cr) ratio of 1.33 ± 13, translating to an fO₂ one log unit below the IW buffer, in accordance with previous fO₂ estimates for lunar basalts. Application of the Zr‐cooling speedometer, for ilmenite and ulvöspinel pairs, gives a cooling rate of 5.2 °C/day, matching previous estimates of cooling rates for the LaPaz lunar meteorites and Apollo mare basalts. Mineral modes and chemistries, as well as trace‐element patterns, provide compelling evidence for pairing of this meteorite to others in the LaPaz lunar basalt suite.  相似文献   

The use of Auger spectroscopy for the in situ elemental characterization of sub‐micrometer presolar grains     

Frank J. STADERMANN  Christine FLOSS  Maitrayee BOSE  A. Scott LEA 《Meteoritics & planetary science》2009,44(7):1033-1049

Abstract— Presolar grains are small samples of stardust that can be found at low abundances in some of the most unaltered types of extraterrestrial materials. While earlier laboratory studies of stardust mainly focused on grain types that can be extracted from bulk meteorites by acid dissolution techniques, such as silicon carbide and graphite, recent analyses of presolar silicates rely on isotope imaging searches for locating these grains in situ. Since presolar silicates are generally less than a micrometer in diameter and represent at best only a few hundred ppm of their host materials (e.g., primitive meteorites or interplanetary dust particles), locating and studying these particles can be analytically challenging. Recently, we began using scanning Auger spectroscopy for the in situ elemental characterization of presolar silicate grains as a complement to NanoSIMS isotopic studies for obtaining spatially matched compositional data. Auger spectroscopy is a well‐established analytical technique for elemental characterizations in the material sciences, but has not been widely used in geological applications. We discuss the application of this technique to sub‐micrometer sized silicate grains and address practical issues such as sample preparation, measurement settings, spatial resolution, data processing, and elemental quantification.  相似文献   

Comparison of ladderane phospholipid and core lipids as indicators for anaerobic ammonium oxidation (anammox) in marine sediments   总被引：2，自引：0，他引：2  

Andrea Jaeschke  Christine Rooks  Joanna C. Nicholls  Stefan Schouten 《Geochimica et cosmochimica acta》2009,73(7):2077-2088

We investigated anaerobic ammonium oxidation (anammox) in continental shelf and slope sediments of the Irish and Celtic Seas by using anammox specific ladderane biomarker lipids. We used the presence of an intact ladderane phospholipid as a direct indicator for living anammox bacteria, and compared it with the abundance of ladderane core lipids derived from both living and dead bacterial biomass. All investigated sediments contained ladderane core lipids as well as the intact ladderane phospholipid, in agreement with ¹⁵N-labeling experiments, which revealed anammox activity at all sites. Ladderane core lipid and intact ladderane phospholipid concentrations were significantly correlated (R² = 0.957 and 0.464, respectively) with anammox activity over the transect of the continental shelf and slope sediments. In the Irish Sea (50-100 m water depth) highest abundances of the intact ladderane phospholipid were found in the upper 2 cm of the sediment, indicating a zone of active anammox. A sharp decline further down-core suggested a strong decrease in anammox biomass and rapid degradation of the intact lipids. In comparison, ladderane core lipids were 1-2 orders of magnitude higher in concentration than the intact ladderane phospholipid and accumulated as dead cell remnants with depth. In the slope sediments of the Celtic Sea both ladderane core lipids and the intact ladderane phospholipid were found in sediments at water depths ranging from 500 to 2000 m. Here, anammox seemed to be active at greater depths of the sediment (>2 cm). Mean abundances of both intact and core ladderane lipids in whole sediment cores increased downslope, indicating an increasing importance of anammox in deeper slope sediments.  相似文献   

A late Holocene paleoclimatic history of Lake Tanganyika, East Africa     

J. Curt Stager  Christine Cocquyt  Constanze Weyhenmeyer 《Quaternary Research》2009,72(1):47-56

A nearshore core (LT03-05) from the north basin of Lake Tanganyika provides diatom, pollen, and sedimentary time series covering the last ca. 3800 yr at 15-36 yr resolution. A chronology supported by 21 AMS dates on terrestrial and lacustrine materials allows us to account for ancient carbon effects on ¹⁴C ages and to propose refinements of the region's climatic history. Conditions drier than those of today were followed after ca. 3.30 ka by an overall wetting trend. Several century-scale climate variations were superimposed upon that trend, with exceptionally rainy conditions occurring 1.70-1.40 ka, 1.15-0.90 ka, 0.70-0.55 ka, and 0.35-0.20 ka. Around 0.55-0.35 ka, during the Spörer sunspot minimum, drier conditions developed in the northern Tanganyika basin while more humid conditions were registered at Lakes Victoria and Naivasha. This indicates significant variability in the nature and distribution of near-equatorial rainfall anomalies during much of the Little Ice Age.  相似文献   

Paleozoic tectonism on the East Gondwana margin: Evidence from SHRIMP U–Pb zircon geochronology of a migmatite–granite complex in West Antarctica     

Christine S. Siddoway  C. Mark Fanning 《Tectonophysics》2009,477(3-4):262

The Fosdick Mountains migmatite–granite complex in West Antarctica records episodes of crustal melting and plutonism in Devonian–Carboniferous time that acted to transform transitional crust, dominated by immature oceanic turbidites of the accretionary margin of East Gondwana, into stable continental crust. West Antarctica, New Zealand and Australia originated as contiguous parts of this margin, according to plate reconstructions, however, detailed correlations are uncertain due to a lack of isotopic and geochronological data. Our study of the mid-crustal exposures of the Fosdick range uses U–Pb SHRIMP zircon geochronology to examine the tectonic environment and timing for Paleozoic magmatism in West Antarctica, and to assess a correlation with the better known Lachlan Orogen of eastern Australia and Western Province of New Zealand.NNE–SSW to NE–SW contraction occurred in West Antarctica in early Paleozoic time, and is expressed by km-scale folds developed both in lower crustal metasedimentary migmatite gneisses of the Fosdick Mountains and in low greenschist-grade turbidite successions of the upper crust, present in neighboring ranges. The metasedimentary rocks and structures were intruded by calc-alkaline, I-type plutons attributed to arc magmatism along the convergent East Gondwana margin. Within the Fosdick Mountains, the intrusions form a layered plutonic complex at lower structural levels and discrete plutons at upper levels. Dilational structures that host anatectic granite overprint plutonic layering and migmatitic foliation. They exhibit systematic geometries indicative of NNE–SSW stretching, parallel to a first-generation mineral lineation. New U–Pb SHRIMP zircon ages for granodiorite and porphyritic monzogranite plutons, and for leucogranites that occupy shear bands and other mesoscopic-scale structural sites, define an interval of 370 to 355 Ma for plutonism and migmatization.Paleozoic plutonism in West Antarctica postdates magmatism in the western Lachlan Orogen of Australia, but it coincides with that in the central part of the Lachlan Orogen and with the rapid main phase of emplacement of the Karamea Batholith of the Western Province, New Zealand. Emplaced within a 15 to 20 million year interval, the Paleozoic granitoids of the Fosdick Mountains are a product of subduction-related plutonism associated with high temperature metamorphism and crustal melting. The presence of anatectic granites within extensional structures is a possible indication of alternating strain states (‘tectonic switching’) in a supra-subduction zone setting characterized by thin crust and high heat flow along the Devonian–Carboniferous accretionary margin of East Gondwana.  相似文献   

Rapid and cyclic aeolian deposition during the Last Glacial in European loess: a high-resolution record from Nussloch, Germany   总被引：1，自引：0，他引：1  

Pierre Antoine  Denis-Didier Rousseau  Olivier Moine  Stphane Kunesch  Christine Hatt  Andreas Lang  Hlne Tissoux  Ludwig Zller 《Quaternary Science Reviews》2009,28(25-26):2955-2973

This paper reports the results of an investigation of the Weichselian Upper Pleniglacial loess sequences of Nussloch (Rhine Valley, Germany) based on stratigraphy, palaeopedology, sedimentology, palynology, malacology and geochemistry (δ¹³C), supported by radiocarbon, TL and OSL dating. Grain-size and magnetic susceptibility records are taken at 5 cm intervals from the Upper Pleniglacial (UPG) loess. The data indicate cyclic variations in loess deposition between ca 34 and 17 ka, when the sedimentation rate is especially high (1.0–1.2 m per ka for more than 10 m). The grain-size index (GSI: ratio of coarse silt versus fine silt and clay) shows variations, which are assumed to be an indirect measurement of wind intensity. The sedimentation rate, interpreted from the profiles, indicates high values in loess (Loess events LE-1 to LE-7) and low or negligible values in tundra gley horizons G1 to G8. OSL ages from the loess and ¹⁴C dates from organic matter in the loess show that loess deposition was rapid but was interrupted by shorter periods of reduced aeolian sedimentation. Comparison between the data from Nussloch and other European sequences demonstrates a progressive coarsening of the loess deposits between ca 30 and 22 ka. This coarsening trend ends with a short but major grain-size decrease and is followed by an increase to a new maximum at 20 ± 2 ka (“W” shape). Correlation between the loess GSI and the Greenland ice-core dust records, suggests a global connection between North Atlantic and Western European global atmospheric circulation and wind regimes. In addition, the typical Upper Pleniglacial loess deposition begins at ca 30–31 ka, close to Heinrich event (HE) 3, and the main period of loess sedimentation at about 25 ± 2 ka is coeval to HE 2. Correlation of magnetic susceptibility and grain-size records shows that the periods, characterised by high GSI, coincide with an increase in the amount of ferromagnetic minerals reworked from the Rhine alluvial plain. They suggest enhancement in the frequency of the storms from N–NW. These results are integrated within a palaeogeographical model of dust transport and deposition in Western Europe for the Weichselian Upper Pleniglacial (or Late Pleniglacial).  相似文献