An integrated regionalization of earthquake, flood, and drought hazards in China   总被引：10，自引：0，他引：10  

JINFENG WANG  STEPHEN WISE  ROBERT HAINING 《Transactions in GIS》1997,2(1):25-44

Earthquake, flood, and drought data from different sources are combined in a single data set using the same data structure, projection, and scale. The intensity and frequency of each hazard is classified into severe, heavy, modest, and light, producing a classification with 64 combined states for the three kinds of hazard. These classes are then ranked according to severity. The three hazard coverages arc overlaid and the polygons that are produced are coded by the classification system. A map is produced that shows the distribution of these 64 classes in regions and their areas measured from the spatial topological data file in the GIS. Spatial analysis reveals the spatial association among the three hazards and between the three hazards and human factors. There is a brief discussion of the implications of the regionalized map for hazard monitoring.  相似文献   

Experimental turbidity currents entering density-stratified water: analogues for turbidites in Mediterranean hypersaline basins   总被引：2，自引：0，他引：2  

BIANCA RIMOLDI  JAN ALEXANDER†  STEPHEN MORRIS† 《Sedimentology》1996,43(3):527-540

Experimental turbidity currents entering two-layer density-stratified water behave differently from similar currents flowing over the same topography into non-stratified water. Experiments were designed as analogues for flows entering Mediterranean hypersaline pools. In both the hypersaline pools and the experiments, the water density changes abruptly across a pycnocline. Turbidity currents generated on a platform at the level of the pycnocline behaved in one of three ways as they flowed from the platform into deeper stratified water. (1) When the bulk density of the current was less than the dense water layer, the current spread at the pycnocline. The head of the current advanced rapidly when it lost contact with the bed. Grains settling out of the current fell through the dense water layer forming an extensive deposit. In nature this behaviour will lead to ‘turbidites’ with sharp but non-erosive bases, strongly developed grading and no traction features. (2) When the bulk density of the current was greater than the dense water layer, the current continued as an underflow, plunging into the deeper water. Sedimentation lowered the bulk density of the current and the low-density interstitial fluid caused the head to loft. Low-density interstitial fluid convected from the body of the current, lofting particles into the water column. These particles were hydraulically sorted during upward transport and subsequent settling to the floor. The resulting turbidites had a more limited extent than the deposits of either non-lofting underflows or interflows. By inference from the experiments, natural deposits of this type may have local (proximal) erosion and traction features at the base and strongly graded tops. (3) In some of the currents with high bulk density, the rising turbid water reached the pycnocline and spread at that level as a secondary interflow. The tail of the turbidity current, which was less dense than the head and body of the current, flowed above the pycnocline adding momentum to the secondary interflow. The thin non-erosive graded deposit from the secondary interflow may extend beyond the deposits of the primary underflow. In all three cases (but more pronounced in cases 2 and 3) the interaction of the current with the pycnocline displaced that surface and generated a wave that was reflected back and forth from each end of the pool. The waves remobilized sediment on the ramp.  相似文献   

Early Weichselian (MIS 5d and 5c) temperatures and environmental changes in northern Fennoscandia as recorded by chironomids and macroremains at Sokli,northeast Finland     

STEFAN ENGELS  KARIN F. HELMENS  MINNA VÄLIRANTA  STEPHEN J. BROOKS  H. JOHN B. BIRKS 《Boreas: An International Journal of Quaternary Research》2010,39(4):689-704

Engels, S., Helmens, K. F., Väliranta, M., Brooks, S. J. & Birks, H. J. B. 2010: Early Weichselian (MIS 5d and 5c) temperatures and environmental changes in northern Fennoscandia as recorded by chironomids and macroremains at Sokli, northeast Finland. Boreas, Vol. 39, pp. 689–704. 10.1111/j.1502‐3885.2010.00163.x. ISSN 0300‐9483. A 25‐m‐long sediment record spanning the time from the Eemian to the Holocene was recovered from Sokli, northeast Finland. This study focuses on a 6‐m‐long sediment interval that is dated to the Early Weichselian period (MIS 5d and 5c) and consists of lacustrine and fluvial deposits. Using chironomid remains, botanical and zoological macroremains as well as sediment lithology, we were able to reconstruct past changes in the environment, including climate. The results indicate that the site was situated on a flood‐plain during the latter stages of MIS 5d (Herning Stadial) and that summer temperatures might have been ～6 °C lower than at present. Although this value should be treated with caution, as numerical analysis shows that it has a very poor fit‐to‐temperature, this low reconstructed value concurs with several other reconstructions that are available from western Europe. During MIS 5c (Brørup interstadial), the depositional environment changed into a lake system, initially with stratification of the water and subsequently with complete mixing and a strong influence of streams. Both chironomid‐based and macroremain‐based temperature inferences indicate past July air temperatures that were significantly higher than at present. This result is in contrast to other (low‐resolution) reconstructions from northern Fennoscandia that indicate past temperatures 6–7 °C lower than present using fossil coleopteran assemblages. However, several central European sites indicate that there was a phase during the Brørup interstadial that was characterized by high summer temperatures, and a comparison between the high‐resolution reconstructions from western Europe and the results presented in this study suggests that the north–south July air temperature gradient between the mid‐ and high‐latitudes was much weaker during the Brørup interstadial than it is at present. High solar insolation values (particularly the obliquity) during the Brørup interstadial might explain the low summer temperature gradient over the European continent. A return to fluvial conditions occurred in the upper parts of the sediment sequence, and, after a brief interval of gyttja deposition under cooling conditions, the site became glaciated during MIS 5b.  相似文献   

The Perseverance Ultramafic Complex, Western Australia: The Product of a Komatiite Lava River   总被引：3，自引：0，他引：3  

BARNES  STEPHEN J.; HILL  ROBIN E. T.; GOLE  MARTIN J. 《Journal of Petrology》1988,29(2):305-331

The Perseverance ultramafic complex is a body of olivine-richkomatiitic rocks spatially associated with the Agnew nickeldeposit, in the Agnew-Wiluna greenstone belt of the ArchaeanYilgarn Block in Western Australia. The complex consists ofa central lenticular body, up to 700 m thick, of olivine adcumulates,flanked by laterally extensive sheet-like bodies of olivineorthocumulates and spinifextextured komatiite flows. Rocks progressivelyfurther away from the central lens have chemical compositionsreflecting higher original proportions of komatiite liquid tocumulus olivine. Parent liquids had MgO contents between 25and 32% MgO, approximately chondritic Al/Ti ratios and HREEpatterns, and moderate depletion in LREE. Olivines within the adcumulate lens show a progressive increasein forsterite content from Fo₉₃ at the bottom to Fo_94?5, atthe top. Calculated original olivine compositions in the flankingrocks are similar to those at the base of the central lens.Original olivine nickel contents show a symmetrical variationfrom maximum values of 3500 ppm at the top of the central lens,through minimum values of 1000 ppm at the base and margins ofthe central lens to intermediate values in the distal rocks.The complex as a whole shows evidence for nickel depletion relativeto other komatiite suites. These observations are explained in terms of prolonged eruptionand flow of komatiitic lava down a major flow channel or lavariver. Adcumulates crystallized on the floor and sides of thecentral channel, which was formed at an early stage by thermalerosion of floor rocks. Episodic overflow of the central channelproduced distal ‘flood plain’ rocks consisting ofolivine orthocumulates and layered flows. Lavas became moremagnesian and nickel-rich with time, giving rise to the observedspatial variation in primary olivine composition. Nickel depletionof the earliest lavas is attributed to pre-eruption segregationof large volumes of immiscible Fe-Ni-sulfide, which were concentratedto form the underlying Agnew nickel deposit.  相似文献   

The Generation of Granitic Magmas by Intrusion of Basalt into Continental Crust   总被引：49，自引：15，他引：49  

HUPPERT  HERBERT E.; SPARKS  R. STEPHEN J. 《Journal of Petrology》1988,29(3):599-624

When basalt magmas are emplaced into continental crust, meltingand generation of silicic magma can be expected. The fluid dynamicaland heat transfer processes at the roof of a basaltic sill inwhich the wall rock melts are investigated theoretically andalso experimentally using waxes and aqueous solutions. At theroof, the low density melt forms a stable melt layer with negligiblemixing with the underlying hot liquid. A quantitative theoryfor the roof melting case has been developed. When applied tobasalt sills in hot crust, the theory predicts that basalt sillsof thicknesses from 10 to 1500 m require only 1 to 270 y tosolidify and would form voluminous overlying layers of convectingsilicic magma. For example, for a 500 m sill with a crustalmelting temperature of 850 ?C, the thickness of the silicicmagma layer generated ranges from 300 to 1000 m for countryrock temperatures from 500 to 850?C. The temperatures of thecrustal melt layers at the time that the basalt solidifies arehigh (900–950?C) so that the process can produce magmasrepresenting large degrees of partial fusion of the crust. Meltingoccurs in the solid roof and the adjacent thermal boundary layer,while at the same time there is crystallization in the convectinginterior. Thus the magmas formed can be highly porphyritic.Our calculations also indicate that such magmas can containsignificant proportions of restite crystals. Much of the refractorycomponents of the crust are dissolved and then re-precipitatedto form genuine igneous phenocrysts. Normally zoned plagioclasefeldspar phenocrysts with discrete calcic cores are commonlyobserved in many granitoids and silicic volcanic rocks. Suchpatterns would be expected in crustal melting, where simultaneouscrystallization is an inevitable consequence of the fluid dynamics. The time-scales for melting and crystallization in basalt-inducedcrustal melting (10²–10³ y) are very short compared tothe lifetimes of large silicic magma systems (>10⁶ y) orto the time-scale for thermal relaxation of the continentalcrust (> l0⁷ y). Several of the features of silicic igneoussystems can be explained without requiring large, high-level,long-lived magma chambers. Cycles of mafic to increasingly largevolumes of silicic magma with time are commonly observed inmany systems. These can be interpreted as progressive heatingof the crust until the source region is partially molten andbasalt can no longer penetrate. Every input of basalt triggersrapid formation of silicic magma in the source region. Thismagma will freeze again in time-scales of order l0²–10³y unless it ascends to higher levels. Crystallization can occurin the source region during melting, and eruption of porphyriticmagmas does not require a shallow magma chamber, although suchchambers may develop as magma is intruded into high levels inthe crust. For typical compositions of upper crustal rocks,the model predicts that dacitic volcanic rocks and granodiorite/tonaliteplutons would be the dominant rock types and that these wouldascend-from the source region and form magmas ranging from thosewith high temperature and low crystal content to those withhigh crystal content and a significant proportion of restite.  相似文献   

Late Pleistocene mixing zone dolomitization, southeastern Barbados, West Indies     

STEPHEN J. BURNS  VICTOR ROSSINSKY Jr 《Sedimentology》1989,36(6):1135-1137

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Formation of ¹⁸O-depleted dolomite within a marine evaporitic sequence, Triassic Reichenhall Formation, Austria     

CHRISTOPH SPÖTL  STEPHEN J. BURNS 《Sedimentology》1991,38(6):1041-1057

Dark grey, bituminous dolostones interbedded with marine-derived anhydrite horizons occur in the Triassic Reichenhall Formation of western Austria. Fossils are rare and indicate a hostile, hypersaline depositional environment. The dolomites are finely crystalline, fairly stoichiometric, well ordered and non-ferroan. Closely spaced samples (94 in total) of individual dolomite units have been analysed for their carbon and oxygen isotopic composition. The data indicate surprisingly low δ¹⁸O values (-5.7 to -2.1%₀ PDB), whereas the δ¹³C values are comparable to the contemporary Triassic seawater (+0.2 to +2.6%₀ PDB). Sedimentological evidence, including (i) lack of any evidence for extensive dissolution, (ii) distinct oxygen and carbon isotope ratios of individual dolomite units, (iii) covariance of carbon and oxygen isotopes within some dolomite layers and (iv) inclusions of celestite in dolomite, indicates a nearly closed system after early diagenesis. Combining this information with water-rock interaction calculations suggests that the lightest oxygen isotope compositions are the result of freshwater influx into the basin during very early dolomite formation. A secondary factor may be dolomite recrystallization at elevated temperatures during burial.  相似文献   

The application of cathodoluminescence to interpreting the diagenesis of an ancient calcrete profile   总被引：1，自引：0，他引：1  

STEPHEN T. SOLOMON  GORDON M. WALKDEN 《Sedimentology》1985,32(6):877-896

A laterally extensive calcrete profile has been identified in the Late Asbian (Lower Carboniferous) shallow marine shelf limestones of the Llangollen area, North Wales. The upper surface of the profile is defined by a laterally discontinuous palaeokarstic surface and by laminated calcareous crusts which developed within the underlying limestone. The profile contains a unique series of early pore-filling vadose cements which only occur down to 1 m below the palaeokarstic surface. Cathodoluminescence reveals that these cements pre-date the late pore-filling meteoric phreatic cements which occur throughout local Asbian lithologies. A spar cement stratigraphy has been established for the calcrete profile. Subaerial vadose cements comprise two generations of non-luminescent cement, followed by a brightly luminescent generation which occasionally shows an acicular habit. This needle-fibre calcite represents the final stage of vadose cementation. Precipitation of vadose cements was contemporary with subaerial alteration and micritization of the limestone. Textures, visible only with cathodoluminescence, provide evidence of recurrent periods of fabric dissolution. The most extensive phase of dissolution occurred immediately after the precipitation of the non-luminescent subaerial vadose cements. Several different textures have been recorded, each reflecting the morphology of a partially dissolved substrate. Dissolution textures are generally confined to the walls of the larger pores and to early brecciation fractures. These probably acted as fluid pathways in the calcrete during early subaerial diagenesis. Much of the non-marine micrite in the calcrete profile appears as needle-fibre calcite under cathodoluminescence. This acicular calcite was probably formed in response to localized supersaturation of meteoric pore fluids caused by periods of near-surface evaporation. Since needle-fibre luminescence is strongly variable, these ambient conditions are not believed to have directly controlled the activator ion concentrations of cementing pore waters. Needle-fibre calcite is considered to be a cement precipitate which has almost completely recrystallized to micrite, probably during the late stages of subaerial diagenesis. Two generations of subaerial micrite which define a ‘micrite stratigraphy’, have been distinguished under cathodoluminescence. Reconstructing the diagenetic history of this ancient calcrete profile has revealed that subaerial alteration was multistaged, with many diagenetic processes acting simultaneously during a single phase of emergence.  相似文献   

Crustal Anatexis and Granite Petrogenesis During Low-pressure Regional Metamorphism: The Trois Seigneurs Massif, Pyrenees, France   总被引：2，自引：5，他引：2  

WICKHAM  STEPHEN M. 《Journal of Petrology》1987,28(1):127-169

Detailed mapping of Hercynian basement rocks exposed in theTrois Seigneurs Massif, Pyrenees, France, has demonstrated acontinuous metamorphic sequence developed in Palaeozoic peliticsediments, ranging from chlorite-grade phyllites, through andalusiteand sillimanite mica schists to a zone of migmatites and ultimatelya heterogeneous, peraluminous, biotite- and cordiente-bearinggranitoid (ranging in composition from biotite granite to quartzdiorite) at the deepest tectonic levels exposed. In additionto this ‘deep’ pluton, a syn-metamorphic leucogranitesuite forms pods and sills within the migmatites and mica schistsand a post-metamorphic, homogeneous biotite granodiorite intrudes(and superimposes a contact aureole on) the metasediments. Despitepost-metamorphic deformations, it is clear that the small ({smalltilde} 3 km) separation of low- and high-grade rocks impliesthe existence of very high temperature gradients (80–100?C km ^–1) during Hercynian metamorphism. Extensive meltingoccurred at {small tilde} 700 ?C at 10–12 km depth, indicatedby the metamorphic mineral assemblages and metamorphic reactionsoccurring in the mica schists. Whole rock XRF analyses of 50 rock samples, including all themain lithologies, indicate that leucogranite compositions areuniform and identical to those of migmatite leucosomes; theyare also close to the major-element composition of experimentallygenerated partial melts of pelitic rocks from the Trois SeigneursMassif. Taken with field relationships, this implies that allleucogranites were generated by partial fusion of pelitic material(< 40 wt. per cent) from the metamorphic sequence, with rapidremoval of the melt by segregation and intrusion to higher structurallevels. The deep biotite granite was probably generated by partialmelting and homogenisation of the same source material, withthe addition of a small magmatic component that was not derivedlocally from the pelites. The late granodiorite was not generatedby anatexis of pelitic material as observed in the metamorphicsequence, and was probably derived by melting of the lower crustat deeper levels than any contemporary exposure of Hercynianbasement in the Pyrenees. Petrological analysis of the metamorphic sequence suggests thatwater activity was externally buffered to high values throughoutthe ‘high-level’ anatexis observed in the TroisSeigneurs sequence. Evidence for this is provided by metacarbonateand metapelite mineral equilibria, by the sequence of metamorphicisograds and by their sharp definition. Moreover, ‘wet’melting conditions are required in order to generate the observedlarge quantities(> 40 wt. per cent) of granitic melt frompelitic material over the small (< 30 ?C) temperature increaseimplied by the section through the migmatite zone. Anatexisof pelitic metasediment was thus promoted by an influx of hydrousfluid into the melting zone. Stable-isotope studies suggestthat this influx was derived from the ground surface, allowingmelts to be continuously saturated as they were generated, andimplying that groundwater infiltration was primarily responsiblefor large-scale anatexis of metasediment at such shallow depths.  相似文献   

Lobal interactions and rheologic superposition in subglacial till near Bradtville, Ontario, Canada   总被引：1，自引：0，他引：1  

STEPHEN R. HICOCK 《Boreas: An International Journal of Quaternary Research》1992,21(1):73-88

Structural, stratigraphic, and lithologic data from a section 69 m long of Catfish Creek drift (north shore of Lake Erie) tell a complex story of two competing glacial lobes. Stone surface features and orientations indicate that stones rotated in viscously deforming, fine-medium textured subglacial till prior to final emplacement. Fractures, shears, and attenuated sediment lenses in tills reveal that they experienced some brittle shear superposed on ductile shear during till dewatering and stiffening. The Huron-Georgian Bay lobe advanced first from the northwest, deforming interstadial sediments and depositing subglacial till. Next, southward confluent flow of the Huron, Georgian Bay, and Erie lobes carved subglacial troughs into sediments and deposited (then deformed) bouldery deformation till by squeeze flow. The northwest flowing Erie lobe then prevailed, depositing deformation till, subglacial aquatic sediments, and mudflows. Finally, a pavement-bearing, hybrid deformation-lodgement till covered the section. Till formation was mainly by subglacial viscous flow with minor lodgement superposed as water content decreased and some fines were probably winnowed. This implies that till deformation probably accounted for much of the glacier movement. Therefore, rapid ice flow could have occurred over the section, along the southern margin of the Laurentide Ice Sheet.  相似文献