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KROON NORRIS KLAUS IAN T. ALEXANDER LEON PAUL BARDOT CHARLES E. BARKER JEAN-PIERRE BELLIER CHARLES D. BLOME LEON J. CLARKE JOCHEN ERBACHER KRISTINA L. FAUL MARY ANNE HOLMES BRIAN T. HUBER MIRIAM E. KATZ KENNETH G. MACLEOD SANDRA MARCA FRANCISA C. MARTINEZ-RUIZ ISAO MITA MUTSUMI NAKAI JAMES G. OGG DOROTHY K. PAK THOMAS K. PLETSCH JEAN M. SELF-TRIAL NICHOLAS J. SHACKLETON JAN SMIT WILLIAM USSLERIII DAVID K. WATKINS JOEN WIDMARK & PAUL A. WILSON 《Geology Today》1998,14(6):222-226
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Synsedimentary faulting and palaeocurrent patterns in the Triassic sandstones of the High Atlas (Morocco) 总被引：1，自引：0，他引：1
The influence of syndepositional fault patterns on palaeocurrents is demonstrated in fluvial to shallow-marine sandstones of Upper Triassic basins in the High Atlas. The synsedimentary nature of faults is deduced from hydroplastic slickensides, thickness variations due to block tilting and dislocation of layers next to the fault scarp. On a regional scale, it is shown that the major normal fault trend of N050–070° controlled the overall palaeocurrent pattern which was directed towards the west-southwest, i.e. in the direction of the future Atlantic ocean. Some anomalies in the palaeocurrent pattern could be related to an increase in subsidence which induced a general coarsening of sediment towards the top of the Triassic. 相似文献
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The Oligocene basanites from Montferrier near Montpellier containvarious ultramafic xenoliths, predominantly spinel-lherzoliteslocally rich in amphibole, and a unique garnet-clinopyroxenite.The sulfide content of spinel-lherzolites is unusually highfor xenoliths and approaches that of MORB mantle sources. Thegarnet-clinopyroxenite, now consisting of recrystallized cpx+ garnet + opx + sp assemblage, results from subsolidus evolutionof a primary subcalcic clinopyroxene (plus minor spinel) compositionallysimilar to those experimentally obtained during high-pressurecrystallization of MORB; such an origin is also attested bythe Ni/Cu ratio of the coexisting sulfide component which isclose to 1. The spinel lherzolites display generally fine-grained porphyroclastictextures with varying proportions of porphyroclasts and neoblasts,and more rarely granuloblastic textures. Within each singlesample, the cores of the pyroxene and spinel porphyroclastshave nearly constant compositions. Significantly inhomogeneouschemical changes appear at the extreme edges of some large crystals,as well as in the fine-grained pyroxenes and spinel, whereasolivine composition is invariable. Such compositional variationsresult from the superimposed effects of two episodes of deformationand recrystallization. Geothermometric determinations show that all the spinel lherzolitesand the garnet-pyroxenite attained an equilibrium state around950?C. From a discussion on the origin of relict opx–cpx–spclusters and relatively high sulfide contents in peridotites,on the reconstructed primary paragenesis of the garnet-pyroxenite,and from a comparison with the North Pyrenean ultramafic associations,it is inferred that this equilibration occurred at the end ofan episode involving partial melting, crystallization, and subsolidusrecrystallization consequent on plastic deformation. Sulfideswere probably retained as sulfide melt early in this episodewhile metasomatism responsible for the crystallization of amphiboleoccurred late. This event is ascribed to a diapiric uplift upto a 45–50 km depth in relation with Oligocene riftingwhich started 35–40 m.y. ago in the Languedoc area. The compositional disequilibrium observed in a number of lherzolitesis related to a second episode of shearing deformation responsiblefor generating porphyroclastic textures, grading locally intomylonites. As a consequence of a concomitant cooling, Al andCr contents decrease in both pyroxenes, and Na content alsodecreases in clinopyroxene. The main chemical change of spinelconsists of a systematic substitution of MgAl2O4 by FeCr2O4,linked to the development of a porphyroclastic texture, i.e.to the degree of shearing deformations imposed upon the peridotites.The temperature decrease down to 750?C resulted from the ascentof previously equilibrated mantle blocks into colder parts nearthe Moho. This event occurred a few millions years before thecollection of xenoliths by the Montferrier basanites, probablyas the Cevennes fault zone below Oligocene grabens was reactivedat depth. 相似文献
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SANDA BALESCU MICHEL LAMOTHE JEAN-PIERRE LAUTRIDOU 《Boreas: An International Journal of Quaternary Research》1997,26(1):61-72
The infrared stimulated luminescence (IRSL) dating method is applied to alkali feldspar coarse grains from the two distinct Middle Pleistocene interglacial estuarine deposits of Tourville, located along the Seine Valley. The upper deposit (unit D), previously dated at 200 ka by ESR on in situ shells and correlated with a stage 7 high sea-level stand (186–245 ka), yields a measured IRSL age of 176 ± 21 ka. The lower deposit (unit B) assigned to a distinctly older high sea-level event (stage 9: 303–339 ka) yields a measured IRSL age of 273 ± 28 ka. The nearby stage 7 raised beach of Sangatte, in Northwestern France, previously dated by TL on quartz (229 ± 18 ka) yields a measured IRSL age of 186 ± 19 ka. These IRSL age estimates systematically underestimate the expected geological ages. This could be due to the long-term fading or instability of the luminescence signal in alkali feldspars. The correction for long-term fading has been tested on these samples. At Tourville, it yields corrected IRSL ages of 196 ± 23ka and 314 ± 32ka, for the upper and lower units respectively and, at Sangatte, a corrected IRSL age of 206 ± 20 ka. These corrected IRSL age estimates are in better agreement with the expected geological ages. This study demonstrates the potential of the feldspar luminescence dating method to provide chronological information on Middle Pleistocene interglacial estuarine sediments within the North Sea-English Channel Basin. 相似文献
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研究钻孔DGKS-9602位于冲绳海槽中部,岩芯长度为931 cm,钻孔年代覆盖了氧同位素1～4阶段,年代可追溯至距今73 ka.孢粉分析结果证明,孢粉带与氧同位素阶段有较好的对应关系,其中松属花粉与蒿属花粉比值(P/A)与海平面变化曲线相互吻合.应用非相似性类比法将钻孔孢粉样品与陆地表土孢粉样品进行欧氏距离计算,从而... 相似文献
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A semi-empirical model has been developed to reproduce glacial–interglacial changes of continental dust and marine sodium concentrations (factor of ∼50 and ∼5, respectively) observed in inland Antarctic ice cores. The model uses conceptual pathways of aerosols within the high troposphere; assumes the dry deposition of impurities on the Antarctic surface; uses estimates of aerosol transit times taken independent of climate; assumes a temperature-dependent removal process during aerosol pathways from the mid-latitudes. The model is fitted to the data over the last four climate cycles from Vostok and EPICA Dome C Antarctic sites. As temperature is cooling, the aerosol response suggests different modes of climate couplings between latitudes, which can be continuous or below temperature thresholds for sodium and dust, respectively. The model estimates a southern South America dust source activity two to three times higher for glacial periods than for the Holocene and a glacial temperature over the Southern Ocean 3–5 °C cooler. Both estimates appear consistent with independent observations. After removal of temperature effects, dust and sodium residuals for both sites show orbital frequencies in opposite phase at the precession timescale. Such long-term insolation-related modulation of terrestrial and marine aerosol input, could provide a chemical pacemaker useful for refining ice core chronologies. 相似文献
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Fabric characteristics of subaerial slope deposits 总被引：1，自引：0，他引：1
The clast fabrics of certain types of terrestrial slope deposits are reviewed and compared, including the deposits of rockfalls, solifluction, debris flows, dry grain flows, frost-coated clast flows and run-off. The analysis is based on modern deposits in active environments. The study shows that fabric characteristics allow discrimination between ‘collective’and individual movement of rock particles. The individual particle movement generally results in a random clast orientation, whereas the processes of ‘collective’movement typically create distinct preferred orientations. The highest fabric strengths together with low values of spherical variance are found in solifluction deposits. A survey of Pleistocene slope deposits indicates, however, that clast fabric has to be used with caution in the identification of past slope dynamics, because significant post-depositional changes may occur during ageing and burial of deposits. The diagnostic significance of fabric characteristics may also be low due to the overlap of the statistical values that typify different processes. 相似文献