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111.
The concentrations and isotopic compositions of lithium, beryllium, and boron, analyzed in situ by ion microprobe in 66 spots of a type B1 Ca-Al-rich inclusion (CAI 3529-41) from the Allende meteorite, are reported. Large variations are observed for both the Li and the B isotopic ratios with 7Li/6Li ranging from 9.2 ± 0.22 to 12.22 ± 0.43 (a ≈250‰ range in δ7Li values) and 10B/11B ranging from 0.2468 ± 0.0057 to 0.4189 ± 0.0493 (a 410‰ range in δ11B values). The very low Li concentrations (<1 ppb) observed in several anorthite and fassaite grains require that a correction for the contribution of spallogenic Li produced during irradiation of the Allende meteoroid by galactic cosmic rays (GCR) be made (after this correction 7Li/6Li ranges from 9.2 ± 0.22 to 13.44 ± 0.56, i.e., a ≈350‰ range in δ7Li values). In 3529-41, the 10B/11B ratios are positively correlated with 9Be/11B in a manner indicating the in situ decay of short-lived 10Be (half-life = 1.5 Ma) with a 10Be/9Be ratio at the time of formation of the CAI of 8.8 ± 0.6 × 10−4, which is in agreement with previous findings [McKeegan, K.D., Chaussidon, M., Robert, F., 2000. Incorporation of short-lived 10Be in a calcium-aluminum-rich inclusion from the Allende meteorite. Science289, 1334-1337]. The present detailed investigation demonstrates that only minor perturbations of the 10Be-10B system are present in 3529-41, contrary to the 26Al/26Mg system for which numerous examples of isotopic redistribution following crystallization were observed [Podosek, F.A., Zinner, E.K., MacPherson, G.J., Lundberg, L.L., Brannon, J.C., Fahey, A.J., 1991. Correlated study of initial 87Sr/86Sr and Al-Mg systematics and petrologic properties in a suite of refractory inclusions from the Allende meteorite. Geochim. Cosmochim. Acta55, 1083-1110]. Petrographically based criteria were developed to identify within the 66 analyzed spots in 3529-41, those where post-magmatic perturbation of the Li and Be distributions occurred. Li and Be concentrations measured in different analytical spots are compared with those predicted by using experimentally determined partition coefficients according to a model of closed-system crystallization of the CAI melt. These criteria show that 56% of the spots in melilite, 38% in anorthite, and 8% in fassaite suffered post-crystallization perturbations of Li and/or Be distributions. In the remaining spots, which do not show obvious indication of redistribution of Li or Be, the 7Li/6Li isotopic variations (corrected for GCR exposure) are positively correlated with9Be/6Li suggesting the in situ decay of now-extinct 7Be. The derived isochron implies that at the time of its formation, the CAI melt had a 7Be/9Be ratio of 0.0061 ± 0.0013 and a 7Li/6Li ratio of 11.49 ± 0.13. In contrast, all the spots in 3529-41, which do show evidence for post-magmatic redistribution of Li and Be, have relatively constant 7Li/6Li, averaging 11.72 ± 0.56, which is consistent with mass balance calculations for Li isotopic homogenization in the CAI after the decay of 7Be. The incorporation of live 7Be in 3529-41 requires, because of the very short half-life of this nuclide (53 days), that it be produced essentially contemporaneously with the formation of the CAI. Therefore, the irradiation processes responsible for production of 7Be must have occurred within the solar accretion disk. Calculations developed in the framework of the x-wind model [Gounelle, M., Shu, F.H., Shang, H., Glassgold, A.E., Rehm, E.K., Lee, T., 2004. The origin of short-lived radionuclides and early Solar System irradiation (abstract). Lunar Planet. Sci.35, 1829] reproduce the 7Be and 10Be abundances observed in 3529-41. The correlated presence of 7Be and 10Be in 3529-41 is thus a strong argument that 10Be, which is observed rather ubiquitously in CAIs, is also a product of irradiation in the early solar system, as might be a significant fraction of other short-lived radionuclides observed in early solar system materials. 相似文献
112.
The devastating 1999 Marmara and Düzce earthquakes led to a significant increase in the earthquake studies in Turkey in geological,
engineering and financial aspects. Extreme Value Theory (EVT) has a range of applications from stock market changes to natural
disasters like floods and hurricanes. Here EVT is fitted to the ordinary and earthquake reinsurance claims of Turkey. 相似文献
113.
114.
Fabrice Ardhuin François-Régis Martin-Lauzer Bertrand Chapron Philippe Craneguy Fanny Girard-Ardhuin Tanos Elfouhaily 《Comptes Rendus Geoscience》2004,336(12):1121-1130
We model the drift velocity near the ocean surface separating the motion induced by the local current, itself influenced by winds and waves, and the motion induced by the waves, which are generated by local and remote winds. Application to the drift of ‘tar balls’, following the sinking of the oil tanker Prestige-Nassau in November 2002, shows that waves contribute at least one third of the drift for pollutants floating 1 m below the surface, with a mean direction about 30° to the right of the wind-sea direction. Although not new, this result was previously obtained with specific models, whereas the formalism used here combines classical wave and circulation forecasting models. To cite this article: F. Ardhuin et al., C. R. Geoscience 336 (2004). 相似文献
115.
Near Bordeaux (France), the Oligocene aquifer is a potential target for drinking water supply. A high-resolution seismic campaign and several exploration wells helped to clarify the geometry of this formation and, as a consequence, the Medoc Tertiary aquifers. The major information extracted from these new data is the existence of a soft deformation inducing two different deposit areas, showing different hydrogeological characteristics (thickness, type, hydraulic properties, etc.). The presence of an erosional gap area affecting the Oligocene formations lead us to propose a new image of groundwater flow in the area, in the context of a predicted intensive exploitation of this resource. To cite this article: F. Larroque, A. Dupuy, C. R. Geoscience 336 (2004). 相似文献
116.
The highly aromatic structure of the macromolecular organic matter (OM) of the Murchison and Orgueil meteorites was recently shown to contain free organic radicals which are concentrated in micro-regions in contrast with terrestrial samples which always show an homogeneous distribution of radicals. An additional signature is revealed, in the present study, by the evolution of the radical concentration with temperature. Whereas in terrestrial samples, this concentration is independent of temperature (Curie magnetism), a significant increase is observed above 150 K in the two meteorites. Based on the electronic structure of organic radicals, calculated by Extended Hückel and Density Functional methods, this behavior was assigned to the occurrence of diradicaloid moieties hosted by aromatic structures of 10 to 15 rings and having a quinoidal structure. They represent 40 and 25% of the total radicals in Orgueil and Murchison, respectively. The search for the cosmochemical interpretation of this unique observation should open a new field of experimental investigations. 相似文献
117.
From outwash to coastal systems in the Portneuf–Forestville deltaic complex (Québec North Shore): Anatomy of a forced regressive deglacial sequence 下载免费PDF全文
Pierre Dietrich Jean‐François Ghienne Mathieu Schuster Patrick Lajeunesse Alexis Nutz Rémy Deschamps Claude Roquin Philippe Duringer 《Sedimentology》2017,64(4):1044-1078
Deglacial sequences typically include backstepping grounding zone wedges and prevailing glaciomarine depositional facies. However, in coastal domains, deglacial sequences are dominated by depositional systems ranging from turbiditic to fluvial facies. Such deglacial sequences are strongly impacted by glacio‐isostatic rebound, the rate and amplitude of which commonly outpaces those of post‐glacial eustatic sea‐level rise. This results in a sustained relative sea‐level fall covering the entire depositional time interval. This paper examines a Late Quaternary, forced regressive, deglacial sequence located on the North Shore of the St. Lawrence Estuary (Portneuf Peninsula, Québec, Canada) and aims to decipher the main controls that governed its stratigraphic architecture. The forced regressive deglacial sequence forms a thick (>100 m) and extensive (>100 km2) multiphased deltaic complex emplaced after the retreat of the Laurentide Ice Sheet margin from the study area ca 12 500 years ago. The sedimentary succession is composed of ice‐contact, glaciomarine, turbiditic, deltaic, fluvial and coastal depositional units. A four‐stage development is recognized: (i) an early ice‐contact stage (esker, glaciomarine mud and outwash fan); (ii) an in‐valley progradational stage (fjord head or moraine‐dammed lacustrine deltas) fed by glacigenics; (iii) an open‐coast deltaic progradation, when proglacial depositional systems expanded beyond the valley outlets and merged together; and (iv) a final stage of river entrenchment and shallow marine reworking that affected the previously emplaced deltaic complex. Most of the sedimentary volume (10 to 15 km3) was emplaced during the three‐first stages over a ca 2 kyr interval. In spite of sustained high rates of relative sea‐level fall (50 to 30 mm·year?1), delta plain accretion occurred up to the end of the proglacial open‐coast progradational stage. River entrenchment only occurred later, after a significant decrease in the relative sea‐level fall rates (<30 mm·year?1), and was concurrent with the formation and preservation of extensive coastal deposits (raised beaches, spit platform and barrier sands). The turnaround from delta plain accretion to river entrenchment and coastal erosion is interpreted to be a consequence of the retreat of the ice margin from the river drainage basins that led to the drastic drop of sediment supply and the abrupt decrease in progradation rates. The main internal stratigraphic discontinuity within the forced regressive deglacial sequence does not reflect changes in relative sea‐level variations. 相似文献
118.
Anne Claude Naki Akçar Susan Ivy-Ochs Fritz Schlunegger Philippe Rentzel Christine Pümpin Dmitry Tikhomirov Peter W. Kubik Christof Vockenhuber Andreas Dehnert Meinert Rahn Christian Schlüchter 《Swiss Journal of Geoscience》2017,110(3):793-809
The Quaternary stratigraphy of the Alpine Foreland consists of distinct terrace levels, which have been assigned to four morphostratigraphic units: Höhere (Higher) Deckenschotter, Tiefere (Lower) Deckenschotter, Hochterrasse (High Terrace) and Niederterrasse (Lower Terrace). Here, we focus on the terrace gravels at Hohle Gasse, SSE of Pratteln near Basel, which are mapped as Tiefere Deckenschotter. Petrographic and morphometric data established from clasts allowed to infer the transport mechanisms and sources of the gravels. Sedimentological analyses indicate that the gravels were transported by a braided river and deposited in a distal glaciofluvial setting. In addition, it can be shown that the majority of the clasts display multiple reworking and only a minority maintained a distinct glaciofluvial shape. Cosmogenic multi-isotope dating using 10Be and 36Cl allowed direct dating of the sediments at the study site. A depth-profile age of \(2 70_{ - 1 90}^{ + 8 30}\) ka for 10Be was achieved for the deposits at Hohle Gasse. Unfortunately, no age could be modelled from the 36Cl concentrations as the blank correction was too high. Furthermore, this age proves that the studied terrace level should be assigned to the morphostratigraphic unit Hochterrasse. 相似文献
119.
Stanislav Frančišković-Bilinski Mladen Juračić Darko Tibljaš 《Environmental Earth Sciences》2011,64(7):1755-1761
Surface sediments (fraction <63 μm) from the source to the mouth of the Rječina, short (18.3 km) karst allogenic river in
Croatia, which is an important source of drinking water, were studied to investigate their mineral (by XRD) and chemical (by
ICP-MS) composition to check possible anthropogenic influence at the lower course due to paper industry and mills, and in
the prodelta area from untreated municipal sewage and the large harbor of Rijeka town. In all analyzed sediment samples and
in the sandstone source, rock quartz is a major mineral, while feldspar and mica group minerals are less abundant. Chlorite
is a minor or trace mineral in all samples. Calcite and dolomite are abundant in the river prodelta, reflecting changes in
bedrock lithology from flysch to carbonates. In river sediments, Fe is the most abundantly analyzed element, while Ca is the
most abundant in prodelta sediments. Concentrations of Al, Mn, Ni, Cr, Co, La and Nd decrease downstream, while Mg, S, Na,
B, Pb, Zn, As, Sn, U, Mo, Hg and Ag have relatively higher concentration in prodelta sediments. The results are compared with
sediments of other rivers in the area: Raša, Rižana and Dragonja, as well as with those of the Rosandra Creek (Italy). Sediments
in the Raša River showed similar behavior as those in the Rječina, as the highest concentration of metals was found in the
restricted upper part of the estuary, characterized by rapid deposition of clay particles and terrestrial sedimentary organic
matter. The comparison also showed that the most contaminated were the sediments from the Rižana, followed by those from the
Rječina and Rosandra Creek, which had similar results. Among the studied elements, As was present in all sediment samples
at concentrations >6 ppm that might have the lowest toxic effects. At the lower Rječina and in prodelta sediments, Pb was
also present at slightly elevated concentrations (>31 ppm) that could cause such effects. Concentrations of Zn in the prodelta
correspond to those occurring in moderately polluted sediments (90–200 ppm). In the prodelta sediments, Hg is slightly below
toxicity threshold (1 ppm), while Ag is present at toxicity threshold (0.5 ppm) or close to it. Rječina River could act as
a good illustrative example for behavior of toxic metals in allogenic karstic rivers, in which accumulation of anthropogenically
introduced pollutants usually occurs in their estuaries, as a result of transport and deposition of fine particles. 相似文献
120.
Marc Antoine Couillard Gilbert Cabana Jean François Dery Gaétan Daigle Julian John Dodson 《Estuaries and Coasts》2011,34(6):1234-1245
Tomcod (Microgadus tomcod) in the St. Lawrence estuarine transition zone (ETZ) undergo an ontogenetic habitat shift. Older age classes, characterised
by a male-dominated sex ratio, disperse downstream over the summer months to occupy the colder more saline waters of the estuary.
Significant differences in length and mass along the salinity gradient were observed in September with upstream fish of any
given age class generally exhibiting greater growth. These differences were not seen in early summer. Benthic amphipod δ
34S signatures were strongly correlated with salinity and served to demonstrate that tomcod δ
34S signatures were not in isotopic equilibrium in the more saline waters of the ETZ. Seasonal distributional patterns, growth
dynamics and isotopic disequilibrium all indicate that the observed habitat shift may occur on an annual basis, following
winter aggregation in warmer, less saline waters. Tomcod located in the downstream parts of the ETZ, predominantly males,
were significantly more sexually developed than upstream tomcod for a given age. On the other hand, greater growth early in
life is insured by occupying warmer, upstream waters during the summer months. 相似文献