Age, origin and significance of a new middle MIS 3 tephra horizon identified within a long-core sequence from Les Echets, France     

DANIEL VERES  SIWAN M. DAVIES  BARBARA WOHLFARTH  FRANK PREUSSER  STEFAN WASTEGÅRD  LINDA AMPEL  ANNE HORMES  GÖRAN POSSNERT  JEAN-PAUL RAYNAL  GÉRARD VERNET 《Boreas: An International Journal of Quaternary Research》2008,37(3):434-443

A new tephra has been identified within a long core (EC 3) sequence recovered from Les Echets, near Lyon, France. This visible tephra was discovered as part of a high resolution multiproxy re-investigation of the Les Echets sequence. Independent chronological information suggests that the tephra is c . 2 000–45 000 years old, and geochemical analysis indicates that it is of basanitic composition. The latter suggests a possible origin in the Eifel; however, as yet, no other volcanic events or deposits can be correlated to the Les Echets tephra. New sedimentological and chronological data are presented indicating that the tephra falls within an interval that most likely correlates with Dansgaard–Oeschger events 12-9. Thus, this tephra could potentially be an important middle MIS 3 marker horizon in central Europe if it can be traced in other palaeorecords.  相似文献   

Deciphering the depositional environment of the laminated Crato fossil beds (Early Cretaceous,Araripe Basin,North‐eastern Brazil)     

ULRICH HEIMHOFER  DANIEL ARIZTEGUI  MARC LENNIGER  STEPHEN P. HESSELBO  DAVID M. MARTILL  ARISTOTELES M. RIOS‐NETTO 《Sedimentology》2010,57(2):677-694

The laminated limestones of the Early Cretaceous Crato Formation of the Araripe Basin (North‐eastern Brazil) are world‐famous for their exceptionally well‐preserved and taxonomically diverse fossil fauna and flora. Whereas the fossil biota has received considerable attention, only a few studies have focused on the sedimentary characteristics and palaeoenvironmental conditions which prevailed during formation of the Crato Fossil Lagerstätte. The Nova Olinda Member represents the lowermost and thickest unit (up to 10 m) of the Crato Formation and is characterized by a pronounced rhythmically bedded, pale to dark lamination. To obtain information on palaeoenvironmental conditions, sample slabs derived from three local stratigraphic sections within the Araripe Basin were studied using high‐resolution multiproxy techniques including detailed logging, petrography, μ‐XRF scanning and stable isotope geochemistry. Integration of lithological and petrographic evidence indicates that the bulk of the Nova Olinda limestone formed via authigenic precipitation of calcite from within the upper water column, most probably induced and/or mediated by phytoplankton and picoplankton activity. A significant contribution from a benthonic, carbonate‐secreting microbial mat community is not supported by these results. Deposition took place under anoxic and, at least during certain episodes, hypersaline bottom water conditions, as evidenced by the virtually undisturbed lamination pattern, the absence of a benthonic fauna and by the occurrence of halite pseudomorphs. Input of allochthonous, catchment‐derived siliciclastics to the basin during times of laminite formation was strongly reduced. The δ¹⁸O values of authigenic carbonate precipitates (between ?7·1 and ?5·1‰) point to a ¹⁸O‐poor meteoric water source and support a continental freshwater setting for the Nova Olinda Member. The δ¹³C values, which are comparatively rich in ¹³C (between ?0·1 and +1·9‰), are interpreted to reflect reduced throughflow of water in a restricted basin, promoting equilibration with atmospheric CO₂, probably in concert with stagnant conditions and low input of soil‐derived carbon. Integration of lithological and isotopic evidence indicates a shift from closed to semi‐closed conditions towards a more open lake system during the onset of laminite deposition in the Crato Formation.  相似文献   

An accurate interpolating scheme for semi-Lagrangian advection on an unstructured mesh for ocean modelling     

DANIEL Y. LE ROUX  CHARLES A. LIN  ANDREW STANIFORTH 《地球，A辑:动力气象学与海洋学》1997,49(1):119-138

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Ancient oceans and continental margins of the Alpine-Mediterranean Tethys: deciphering clues from Mesozoic pelagic sediments and ophiolites   总被引：1，自引：0，他引：1  

DANIEL BERNOULLI  HUGH C. JENKYNS† 《Sedimentology》2009,56(1):149-190

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GALLIC TRAJECTORIES OF GEOGRAPHY AND THE SELF     

DANIEL W. GADE 《Geographical review》1999,89(1):122-128

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Book reviews     

DANIEL F. L. DORLING 《International journal of geographical information science》2013,27(5):443-450

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GIS-based urban modelling: practices,problems, and prospects     

DANIEL Z. SU 《International journal of geographical information science》2013,27(7):651-671

This paper reviews the practices, problems, and prospects of GISbased urban modelling. The author argues that current stand-alone and various loose/tight coupling approaches for GIS-based urban modelling are essentially technology-driven without adequate justification and verification for the urban models being implemented. The absolute view of space and time embodied in the current generation of GIS also imposes constraints on the type of new urban models that can be developed. By reframing the future research agenda from a geographical information science (GISci) perspective, the author contends that the integration of urban modelling with GIS must proceed with the development of new models for the informational cities, the incorporation of multi-dimensional concepts of space and time in GIS, and the further extension of the feature-based model to implement these new urban models and spatial-temporal concepts according to the emerging interoperable paradigm. GISci-based urban modelling will not only espouse new computational models and implementation strategies that are computing platform independent but also liberate us from the constraints of existing urban models and the rigid spatial-temporal framework embedded in the current generation of GIS, and enable us to think above and beyond the technical issues that have occupied us during the past ten years.  相似文献   

Geomorphology of carbonate platform‐marginal uppermost slopes: Insights from a Holocene analogue,Little Bahama Bank,Bahamas     

EUGENE C. RANKEY  DANIEL F. DOOLITTLE 《Sedimentology》2012,59(7):2146-2171

As the product of a variety of sediment sources and sedimentation (and re‐sedimentation) and erosion processes, the geomorphology and sedimentology of carbonate slopes are highly variable. The purpose of this study is to describe sub‐bottom profiles and side‐scan sonar, multibeam and optical data acquired by an autonomous underwater vehicle to explore variability in geomorphological and sedimentological character of the present‐day platform‐marginal, uppermost slope environments (< 240 m water depth) on the north, open‐ocean facing flank of Little Bahama Bank, Bahamas. Although at time scales of greater than 100 ka this margin is progradational, the data illustrate a complex juxtaposition of erosional and depositional processes and features. Erosion is evidenced by two prominent escarpments (70 m and 120 m) that expose eroded, bedded rocky outcrops. These escarpments are interpreted to represent relict features, related to past sea‐level positions, although they still may be shedding debris. Aside from erosional remnants, sedimentation and active transport is indicated by several features, including active bedforms (especially above the 70 m escarpment, but ripples occur to depths of ca 200 m), several mass transport complexes that overlie and cover the lower escarpment, gravity flow deposits and rare slump features. Similarly, a thick (up to 20 m) onlapping sediment wedge, interpreted to be Holocene in age, suggests lateral accretion of the slope by more than 75 m in this period. Data illustrate that this open‐ocean margin is distinct from windward margins in the Bahamas, which typically include near‐vertical walls of erosion or bypass, flanked downdip by rubble and talus, and leeward margins, which have onlapping muddy wedges, but that lack marked terraces or escarpments. Collectively, the results provide perspectives into the nature and controls on complex geomorphological patterns of erosion and deposition in Holocene uppermost slope systems, concepts potentially applicable to ancient analogues.  相似文献   

Blanket mire formation at the Cross Lochs, Sutherland, northern Scotland     

DANIEL J. CHARMAN 《Boreas: An International Journal of Quaternary Research》1992,21(1):53-72

A brief review of the genesis of blanket peats is presented, together with detailed analyses of basal peats from northern Scotland. Particular attention is paid to local factors affecting peat growth and the problems of sampling and interpretation arising from them. Macrofossil and loss-on-ignition analyses of four peat-mineral interfaces solve many of the terminological problems of such profiles and indicate that interpretations based on field stratigraphy alone are uncertain. Pollen analyses of two profiles from contrasting microtopographic situations show well-defined vegetational change associated with early peat development. Fully organic ombrotrophic peat is present from 6805 ± 50 BP at one site, following anthropogenic burning from c . 7500 BP and partial recovery of the open birch woodland. A change from birch woodland to Calluna heath occurs at approximately the same time on a more freely drained site with much later peat development, following further burning from 4890 ± 65 BP. Anthropogenic activity is clearly associated with changes in soil and vegetation preceding peat formation, and the role of climatic factors remains equivocal.  相似文献   

Overgrowth Textures, Disequilibrium Zoning, and Cooling History of a Glassy Four-Pyroxene Boninite Dyke from New Caledonia   总被引：1，自引：0，他引：1  

OHNENSTETTER  DANIEL; BROWN  WILLIAM L. 《Journal of Petrology》1992,33(1):231-271

Pyroxenes in a low-Ca boninite from a dyke show remarkable growthand overgrowth textures and chemical zoning, which are usedto infer crystallization mechanisms and kinetics. The rock comprisesnearly 50 vol.% fresh glass, phenocrysts and glomerocrysts ofclinoenstatite sensu lato ({small tilde}32 vol.%), microphenocrystsof orthopyroxene and Ca-rich clinopyroxene ({small tilde}17vol.%), and microlites of amphibole and oxides ({small tilde}3vol.%). Clinoenstatite, which inverted from protoenstatite,is skeletal with glass and chrome-spinel inclusions and thinovergrowth zones of Ca-rich clinopyroxene and amphibole; thecrystals are occasionally broken. Orthopyroxene is often skeletal,sometimes slightly resorbed with the same inclusions and overgrowthzones. Ca-rich clinopyroxene and amphibole occur mainly in pyroxeneovergrowth zones. Chrome-spinel in contact with glass is overgrownby magnetite-maghemite or amphibole. The rock is andesitic witha high mg-number of 0.78, and is quartz- and strongly hypersthene-and feldspar-normative. The glass is dacitic with an mg-numberof 0.15, strongly quartz- and feldspar-normative, and rich inwater ({small tilde}5.6wt.%). Strong chemical zoning occurs in all minerals, oscillatory zoningoccurring only in clinoenstatite and orthopyroxene. The mg-numberin clinoenstatite sensu lato ranges from 0.95 (clinoenstatitesensu stricto) to 0-68 (clinohypersthene), the largest rangeso far described, and from 0.88 to 0.43 in orthopyroxene. TheWo content of the former (0.21–1.56 with rare higher values)is considerably smaller than and does not overlap that of thelatter (1.36–4.84X Wo generally increasing with Fs. Thecores of both are chromian (up to 0–018 atoms per formulaunit), and Cr falls to or below the detection limit for Fs>25.The Fs-rich zones of clinohypersthene have {small tilde}2wt%A1₂O₃ and (M6wt% TiO₂, whereas those of orthopyroxene reachnearly 10 and 04 wt. %, respectively. Ca-rich clinopyroxenevaries from pigeonite through subcalcic augite and augite toferroaugite, the outer zones reaching 12wt.% A1₂O₃ and 1–8wt% TiO₂. Amphibole is magnesio-hornblende on pyroxene or tschermakitichornblende on oxide. The relative times of nucleation, growth, partial resorption,and fracturing of the crystals were determined from the texturesand the chemistry of the overgrowths. Protoenstatite and chrome-spinelnucleated from the melt and were overgrown in places by allsucceeding minerals. Orthopyroxene nucleated mainly from themelt, whereas the other phases occur only as overgrowths. Orthopyroxenemay show weak resorption at intermediate stages. Protoenstatitecrystals were occasionally broken, the relative times beingshown by the nature of the overgrowths. Minor-element concentrationsvary strongly with the growth stage, chromium soon being usedup in the melt and aluminium and titanium being strongly concentratedin the crystals during the last stages. Plagioclase and quartzare absent because of suppression of their nucleation in a water-richmelt on rapid cooling. Crystallization probably occurred intwo main stages, an early one of moderately fast cooling atlow undercooling probably in a shallow magma chamber (correspondingto the growth of the protoenstatite phenocrysts) and a laterone over a period of less than a day of faster cooling at higherundercooling after uprise and injection into the dyke (correspondingto the fracturing of protoenstatite and growth of the microphenocrystsand microlites).  相似文献