Late Quaternary mass movement events in Lake El′gygytgyn,North‐eastern Siberia     

OLAF JUSCHUS  MARTIN MELLES  A. CATALINA GEBHARDT  FRANK NIESSEN 《Sedimentology》2009,56(7):2155-2174

Lake El′gygytgyn is situated in a 3·6 Myr old impact crater in North‐eastern Siberia. Its sedimentary record probably represents the most complete archive of Pliocene and Quaternary climate change in the terrestrial Arctic. In order to investigate the influence of gravitational sediment transport on the pelagic sediment record in the lake centre, two sediment cores were recovered from the lower western lake slope. The cores penetrate a sub‐recent mass movement deposit that was identified by 3·5 kHz echo sounding. In the proximal part of this deposit, deformed sediments reflect an initial debris flow characterized by limited sediment mixture. Above and in front of the debrite, a wide massive densite indicates a second stage with a liquefied dense flow. The mass movement event led to basal erosion of ca 1 m thick unconsolidated sediments along parts of its flow path. The event produced a suspension cloud, whose deposition led to the formation of a turbidite. The occurrence of the turbidite throughout the lake and the limited erosion at its base mainly suggest deposition by ‘pelagic rain’ following Stokes’ Law. Very similar radiocarbon dates obtained in the sediments directly beneath and above the turbidite in the central lake confirm this interpretation. When applying the depositional model for the Late Quaternary sediment record of Lake El′gygytgyn, the recovered turbidites allow reconstruction of the frequency and temporal distribution of large mass movement events at the lake slopes. In total, 28 turbidites and related deposits were identified in two, 12·9 and 16·6 m long, sediment cores from the central lake area covering approximately 300 kyr.  相似文献   

A job in mud logging: is it worth it?     

MARTIN HOUSTON 《Geology Today》1985,1(2):59-60

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About the concepts of continuum and age     

MARTIN KIRKBRIDE 《Boreas: An International Journal of Quaternary Research》1989,18(1):87-88

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Radiolarites et sédiments hypersiliceux océaniques: une comparaison     

M. STEINBERG  A. DESPRAIRIES  J. F. FOGELGESANG†  A. MARTIN  D. CARON†  R. BLANCHET‡ 《Sedimentology》1977,24(4):547-563

The mineralogical and chemical composition of Jurassic radiolarian cherts has been studied in Morocco (Rif), Italy (Lombardy basin and Apennines), Greece (Pindus zone and Vourinos Massif), some in close association with ophiolites. We have compared these samples with Cretaceous cherts from the NW Pacific (Leg 32) and with Cenozoic diatomaceous oozes from the Sea of Japan (Leg 31). The silica in the radiolarian cherts is quartz or chalcedony. Most of these rocks also contain feldspars and hematite while the clay fraction is composed of illite and/or chlorite generally associated with swelling clays and, locally, with kaolinite. In oceanic sediments all mineralogical species of silica have been detected (from opal to quartz), the clays generally being the same as those of the radiolarian cherts, the feldspars also being present. Based on the chemical composition of the radiolarian cherts, three facies can be distinguished: massive cherts, pelitic radiolarites and ferruginous radiolarites, the latter occurring only near the contact with volcanic basement. The chemical composition of cherts and diatom oozes from the Pacific is very close to the composition of radiolarian cherts. Although the mineralogy of radiolarian cherts can be related to several models (detrital, diagenesis of pelagic clays etc.) the detrital origin of part of the clay fraction seems certain. The origin of silica and its relation to the palaeolatitudes and the relatively confined nature of the Tethys oceans as well as the influence of volcanic inputs are evaluated, Chemical and mineralogical composition of radiolarian cherts shows that the diagenesis of the clay fraction is not a significant source of silica. Accumulation of diatom oozes in the Sea of Japan and in other areas, shows that the distance from continents and very deep seas are not essential to the development of siliceous sedimentation.  相似文献   

On the influence of the Alps on a cold front   总被引：1，自引：0，他引：1  

KLAUS P. HOINKA  MARTIN HAGEN  HANS VOLKERT  DIETRICH HEIMANN 《地球，A辑:动力气象学与海洋学》1990,42(1):140-164

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Sapphirine+Forsterite and Sapphirine+Humite-Group Minerals in an Ultra-Magnesian Lens from Kuhi-lal, SW Pamirs, Tajikistan: Are these Assemblages Forbidden?   总被引：2，自引：2，他引：0  

GREW  EDWARD S.; PERTSEV  NIKOLAY N.; YATES  MARTIN G.; CHRISTY  ANDREW G.; MARQUEZ  NICHOLAS; CHERNOSKY  JOSEPH V. 《Journal of Petrology》1994,35(5):1275-1293

Sapphirine occurs with humite-group minerals and forsteritein Precambrian amphibole-facies rocks at Kuhi-lal, SW PamirMountains, Tajikistan, a locality also for talc+kyanite magnesiohornblendewhiteschist. Most of these sapphirine-bearing rocks are graphiticand sulfidic (pyrite and pyrrhotite) and contain enstatite,clinohumite or chondrodite, spinel, rutile, gedrite, and phlogopite.A phlogopite schist has the assemblage with X_Fe = Fe/(Fe+Mg)increasing as follows: chlorite (0-003)<phlogopite (0.004–0.005)sapphirine (0.004–0.006) enstatite (0-006)forsterite (0-006–0-007)<spinel (0-014). This assemblage includes the incompatiblepair sapphirine+forsterite, but there is no textural evidencefor reaction. In one rock with clinohumite, X_Fe increases asfollows: clinohumite (0-002) <sapphirine (0-003) <enstatite(0-004–0-006) <spinel (0-010). Ion microprobe and wet-chemicalanalyses give 0-57–0-73 wt.% F in phlogopite and 0-27wt.% F in chlorite in the phlogopite schist; 0-04, 1.5–1.9,and 4.4 wt.% F in forsterite, clinohumite, and chondrodite,respectively; and 0-0-09 wt.% BeO and 0-05–0-21 wt.% B₂O₃in sapphirine. Stabilization of sapphirine+clinohumite or sapphirine+chondroditeinstead of sapphirine+phlogopite is possible at high F contentsin K-poor rocks, but minor element contents appear to be toolow to stabilize sapphirine as an additional phase with forsterite+enstatite+spinel.Although sapphirine+forsterite is metastable relative to spinel+enstatitein experiments conducted at a_H2O=1 in the MgO-Al₂O₃-SiO₂-H₂Osystem, it might be stabilized at a_H2O0.5, P4 kbar, T650–700C.Textures in the Kuhi-lal whiteschists suggest a polymetamorphicevolution in which the rocks were originally metamorphosed atT650C, P 7 kbar, conditions under which sapphirine+clinohumiteand sapphirine+chondrodite are inferred to have formed, andsubsequently affected by a later event at lower P, similar T,and lower a_H2O. The latter conditions were favorable for sapphirine+forsteriteto form in a rock originally containing chlorite+forsterite+spinel+enstatite.  相似文献   

Sediment trend models fail to reproduce small-scale sediment transport patterns on an intertidal beach   总被引：2，自引：0，他引：2  

GERHARD MASSELINK  DANIEL BUSCOMBE  MARTIN AUSTIN†  TIM O'HARE†  PAUL RUSSELL† 《Sedimentology》2008,55(3):667-687

A rigorous test is presented of the application of sediment trend models to an intertidal beach environment characterized by bar morphology. Sediment samples were collected during low tide from a regular grid and their sediment fall velocity distributions, obtained using a settling tube, were analysed using moment analysis. The net sediment transport direction determined from beach surveys, hydrodynamic measurements, wave ripple observations and sediment transport modelling was compared with predictions by sediment trend models based on the spatial distribution of sediment parameters. It was found that the sediment transport pathways and patterns of sedimentation predicted using sediment trend models were at odds with field observations, and varied significantly depending on whether surface or sub‐surface sediment samples were used. The sediment trend models are thought to fail because, in energetic and morphologically variable beach environments, spatial patterns in sediment characteristics are mainly attributed to the presence of different hydrodynamic regions and associated morphology, rather than sediment pathways. The use of sediment trend models cannot replace the collection of morphological, hydrodynamic and sediment transport data in the field to define relationships between flows, forms and sedimentation patterns on a dynamic intertidal beach.  相似文献   

Skillful Seasonal Forecasts of Summer Surface Air Temperature in Western China by Global Seasonal Forecast System Version 5     

Chaofan LI  Riyu LU  Philip E.BETT  Adam A.SCAIFE  Nicola MARTIN 《大气科学进展》2018,35(8):955-964

Variations of surface air temperature(SAT) are key in affecting the hydrological cycle,ecosystems and agriculture in western China in summer.This study assesses the seasonal forecast skill and reliability of SAT in western China,using the Glo Sea5 operational forecast system from the UK Met Office.Useful predictions are demonstrated,with considerable skill over most regions of western China.The temporal correlation coefficients of SAT between model predictions and observations are larger than 0.6,in both northwestern China and the Tibetan Plateau.There are two important sources of skill for these predictions in western China:interannual variation of SST in the western Pacific and the SST trend in the tropical Pacific.The tropical SST change in the recent two decades,with a warming in the western Pacific and cooling in the eastern Pacific,which is reproduced well by the forecast system,provides a large contribution to the skill of SAT in northwestern China.Additionally,the interannual variation of SST in the western Pacific gives rise to the reliable prediction of SAT around the Tibetan Plateau.It modulates convection around the Maritime Continent and further modulates the variation of SAT on the Tibetan Plateau via the surrounding circulation.This process is evident irrespective of detrending both in observations and the model predictions,and acts as a source of skill in predictions for the Tibetan Plateau.The predictability and reliability demonstrated in this study is potentially useful for climate services providing early warning of extreme climate events and could imply useful economic benefits.  相似文献   

A diatom–conductivity transfer function for reconstructing past changes in the Southern Hemisphere westerly winds over the Southern Ocean          下载免费PDF全文

KRYSTYNA M. SAUNDERS  DOMINIC A. HODGSON  SHELLEY MCMURTRIE  MARTIN GROSJEAN 《第四纪科学杂志》2015,30(5):464-477

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Airborne measurements of dust layer properties, particle size distribution and mixing state of Saharan dust during SAMUM 2006     

By BERNADETT WEINZIERL  REAS PETZOLD  MICHAEL ESSELBORN  MARTIN WIRTH  KATHARINA RASP  KONRAD KANDLER  LOTHAR SCHÜTZ  PETER KOEPKE  MARKUS FIEBIG 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):96-117

The Saharan Mineral Dust Experiment (SAMUM) was conducted in May/June 2006 in southern Morocco. As part of SAMUM, airborne in situ measurements of the particle size distribution in the diameter range 4 nm < D _p < 100 μm were conducted. The aerosol mixing state was determined below D _p < 2.5 μm. Furthermore, the vertical structure of the dust layers was investigated with a nadir-looking high spectral resolution lidar (HSRL). The desert dust aerosol exhibited two size regimes of different mixing states: below 0.5 μm, the particles had a non-volatile core and a volatile coating; larger particles above 0.5 μm consisted of non-volatile components and contained light absorbing material. In all cases, particles larger than 10 μm were present, and in 80% of the measurements no particles larger than 40 μm were present. The abundance of large particles showed almost no height dependence. The effective diameter D _eff in the dust plumes investigated showed two main ranges: the first range of D _eff peaked around 5 μm and the second range of D _eff around 8 μm. The two ranges of D _eff suggest that it may be inadequate to use one average effective diameter or one parametrization for a typical dust size distribution.  相似文献