Raised Coral Terraces at Malakula, Vanuatu, Southwest Pacific, Indicate High Sea Level During Marine Isotope Stage 3   总被引：2，自引：0，他引：2  

Guy Cabioch  Linda K Ayliffe   《Quaternary Research》2001,56(3)

The occurrence of a series of raised coral reefs from the uplifted island of Malakula (Vanuatu, SW Pacific) provide an opportunity to examine sea-level fluctuations over at least the past 120,000 years. Thirteen fossil coral samples from Malakula were analyzed by the thermal ionization mass spectrometry (TIMS) U/Th dating technique, yielding information on sea levels during late marine isotope stage 3 and early stage 4. Our findings are in good agreement with sea-level estimates from raised coral terraces in Papua New Guinea and the recent sea-level reconstruction from the deep-sea sedimentary δ¹⁸O records. In particular, our coral data appear to confirm that sea levels at about 45,000–50,000 yr B.P. were only 30 to 60 m below the present level. Combined with other evidence of sea-level change, our data provide a strong case for much higher sea levels and therefore markedly reduced continental ice volume at 47,000 to 49,000 years ago.  相似文献   

Pavement Deformation Monitoring in a Rolling Load Facility     

Jon P. Mills  Ian Newton  & Guy C. Peirson 《The Photogrammetric Record》2001,17(97):07-24

This paper describes work undertaken to measure deformation of a pavement within the Newcastle University Rolling Load Facility (NUROLF). Precise three dimensional measurements of the pavement have been produced from stereo-imagery taken with diVerent cameras, using both analytical and digital photogrammetric instrumentation. The photogrammetric measurements, and those from the existing system consisting of an array of linear voltage displacement transducers, have been compared with measurements produced using a digital level. Encouraging results have been achieved and photogrammetry has been shown to be capable of producing a similar accuracy to the existing system. There are many advantages associated with a photogrammetric survey but attempts to establish a permanent, automated photogrammetric system for the rolling load facility at a reasonable cost have so far been unsuccessful. It is anticipated that, with the falling cost of high resolution digital sensors, such a system will soon be possible.  相似文献   

The effects of FeO on the system CMAS at low pressure and implications for basalt crystallization processes     

Ping Shi  Guy Libourel 《Contributions to Mineralogy and Petrology》1991,108(1-2):129-145

The common occurrence of olivine, clinopyroxene and plagioclase in natural basalts may suggest that crystallization of these phases exerts important controls on the evolution of natural basalts at low pressure. In order to understand the effects of such an assemblage on the evolution of basalt, an experimental study of the divariant assemblage 1+an+cpx+ol in the system CMAS + FeO was undertaken at 1 bar and under very reducing conditions. Experiments have been performed along three isothernal sections. Detailed electron microprobe data have been collected on all the coexisting phases. Combining these data with available data in the system CMAS, the compositions of all the coexisting phases have been described as functions of temperature and CaO content in the melt by applying a multiple linear regression method. This allows a quantitative characterization of the divariant assemblage 1+an+epx+ol in the system CMAS + FeO, from 1275°C to 1160°C, with liquid compositions ranging from mg#=1 to mg#=0.28. Knowing the composition-temperature relationships, the basic T-X configuration of the assemblage 1+an+cpx+ol has been analysed, and mass balance calculations have been performed to examine the FeO effect on different crystallization processes. Addition of FeO to the system CMAS transforms the thermal divide in the assemblage 1+an+cpx+ol to a thermal ridge, and shifts the spine of the thermal ridge towards SiO₂-poor compositions with decreasing temperature. This indicates that tholeiitic basalts can be relatively silica-poor, and evolve towards slightly more silica-poor compositions. With increasing FeO content, pigeonite replaces ortheonstatite as a crystallizing phase along the silica-rich boundary of the assemblage 1+an+cpx+ol. In some iron, and silica rich composition, olivine possibly terminates its crystallization or even starts resorption prior to pigeonite precipitation; this suppresses silica enrichment in the melt. Crystallization paths of the assemblage 1+an+cpx+ol are determined by the detailed T-X relations of the thermal ridge with the melt evolving away from the spine. The liquid evolution trend depends strongly on the initial compositions. A tholeiitic liquid can follow a moderate silica enrichment path at the same very reducing condition of there is a high modal proportion of olivine. ‘A Fenner mechanism therefore is at work at the same place as a Bowen mechanism’.  相似文献   

Global industrial systems — a case study of the clothing industry     

Guy P.F. Steed 《Geoforum》1978,9(1):35-47

Recent rapid changes in comparative advantage have led to serious stresses through market disruption of the industries of many developed countries. The paper views the global industrial geography of the clothing industries as a form of adaptive, purposeful system in which governments respond to stress through the negotiation of “voluntary” export restraints, reversion to “escape clauses” or safeguards offering protection, or the application of adjustment assistance. It contrasts the stresses and mechanisms of adjustment of the Netherlands, West Germany, Sweden, the United States and Japan.  相似文献   

Composition and evolution of the eucrite parent body: evidence from rare earth elements     

Guy J. Consolmagno  Michael J. Drake 《Geochimica et cosmochimica acta》1977,41(9):1271-1282

Eucrites are extraterrestrial plagioclase-pigeonite basalts. Experimental studies suggest that they were produced by partial melting of an olivine (Fo₆₅)-pigeonite (Wo₅En₆₅)-plagioclase (An₉₄)-spinel-metal source region. Quantitative modeling of the evolution of REE abundances in the eucrites indicates that the main group of eucrites (e.g. Juvinas) may be produced by approximately 10% equilibrium partial melting of a source region with initial REE abundances which were chondritic relative and absolute. Other eucrites appear to represent greater (e.g. Sioux County—15%) or smaller (e.g. Stannern—4%) degrees of melting. Moore County and Serra de Magé appear to be cumulates of pyroxene and plagioclase produced by fractional crystallization of a Juvinas-like melt. Nuevo Laredo may represent a residual liquid after such fractional crystallization. Our calculations are consistent with the conclusion that the eucrites were derived from a single type of source region. The close correspondence of the age of the eucrites (? 4.6 AE) to the age of the solar system appears to preclude the possibility of extensive chemical differentiation of the eucrite parent body prior to the event which produced the eucritic melts. Thus our calculations have yielded not only the mode of the source region but, assuming homogeneous accretion, the mode and hence the bulk composition of the eucrite parent body as well. We are unable to estimate quantitatively the ratio of metal to olivine in the parent body. If no metal is present, the bulk composition (in oxide wt%) is Na₂O—0.04, MgO—29.7, Al₂O₃—1.8, SiO₂—39.0, CaO—1.2, FeO—28.3. If, in contrast, the parent body contained 30% metal, the bulk composition of the silicate portion of the eucrite parent body is Na₂O—0.06, MgO—28.0, Al₂O₃—2.6, SiO₂—41.3, CaO—1.9, FeO—26.3. Relative abundances of the meteorites suggest that the eucrite parent body is still intact. The solar system object most closely resembling the eucrites is asteroid 4 Vesta. Because Vesta is unique among the asteroids, we have license to conclude that it is the source of the eucrites and its bulk composition is close to the analyses given above.  相似文献   

Simulation of the geochemical transformations of sterols: superacid effect of clay minerals     

Odette Sieskind  Guy Joly  Pierre Albrecht 《Geochimica et cosmochimica acta》1979,43(10):1675-1679

The heating of cholestanol 2a with kaolinite (140°C, 16 hr) mainly leads to a mixture of steranes (40%) and sterenes (35%). The major compounds which are formed have been identified as 5α(H)- and 5β(H)-cholestanes, 4a and 4b, the diacholestenes, 5, the diacholestanes, 6, and the D-homodiacholestanes 7. With the exception of the latter, these compounds have all been observed previously in ancient sediments and crude oils. Several of these compounds are identical or bear structural similarities with those obtained from cholestanol at low temperature in acidic or superacidic conditions. The comparison with the results obtained using other minerals (montmorillonite, talc, alumina, polyphos-phate-treated montmorillonite) shows that the observed transformations are catalysed by superacid sites which are present in kaolinite and montmorillonite.  相似文献   

Shore protection structures: Effects on recession rates and beaches from the 1870s to the 1970s along the Ohio shore of lake Erie     

C. H. Carter  D. J. Benson  D. E. Guy Jr 《Environmental Geology》1981,3(6):353-362

Shore-protection structures—largely groins and seawalls—have increased in number along the 300-km-long mainland Ohio shore of Lake Erie from about 60 in 1876–77, to about 1,400 in the late 1930s, to about 3,600 in the mid 1970s. Recession rates, on the other hand, have decreased from the early period (1876–1877 to the late 1930s) to the later period (late 1930s to 1973). Forexample, the length of shore that receded at the intermediate rate (0.3 to 0.9 m/yr) decreased from 76 to 54 km and the length of shore that receded at the lowest rate (less than 0.3 m/yr) increased from 151 to 171 km. Beach widths also have decreased; the length of shore fronted by wide (greater than 15 m) beaches decreased from 64 km to 35 km between 1876–1877 and 1968. Furthermore, the length of shore without a beach increased from 84 km in 1876–1877 to 112 km in 1968. The decreases in recession rates have been caused by the shore-protection structures, which have directly armored the shore from waves (seawalls) or reduced the wave energy reaching the shore by trapping sand (groins). Moreoever, because the shore is a major source of sand for the beaches, the decrease in recession has led to a reduced sand supply and narrower beaches. Ironically, by protecting the shore, the structures apparently have more than compensated for the loss of the best natural form of shore protection, beach sand.  相似文献   

Equivalence of equations describing trace element distribution during equilibrium partial melting     

Guy J. Consolmagno  Michael J. Drake 《Geochimica et cosmochimica acta》1976,40(11):1421-1422

The mathematical equivalence of several equations used to calculate the evolution of trace element abundances during equilibrium partial melting is demonstrated.  相似文献   

The influence of clouds on solar radiation at sea     

Prof. Guy A. Franceschini 《Ocean Dynamics》1968,21(4):162-168

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Sedimentology and palaeogeomorphology of four large valley systems incising delta plains, western Canada Foreland Basin: implications for mid-Cretaceous sea-level changes     

A. Guy Plint  Jennifer A. Wadsworth 《Sedimentology》2003,50(6):1147-1186

The mid-Cenomanian Dunvegan Formation represents a delta complex deposited on a foreland basin ramp over about 2 my. The Dunvegan is divided into 10 transgressive–regressive allomembers, labelled J–A in ascending order, each defined by regional marine transgressive surfaces. Parasequences within allomembers show an aggradational to offlapping stacking pattern that reflects alternate generation and removal of accommodation. The upper surfaces of allomembers H–E are incised by extensive valley systems traceable for up to 320 km and over about 50 000 km². Valley depths range up to 41 m and can change significantly over short distances. However, the average depth of incision (mean 21 m) shows no systematic variation in longitudinal profiles and no evidence of headward shallowing. Valleys are typically 1–2 km wide, but locally widen to about 8 km. Widening is sometimes associated with confluence zones, but elsewhere it is not. Updip reaches of valleys are dominated by cross-bedded fluvial sandstone forming multistorey point-bar deposits. Sandstones contain widespread but uncommon paired carbonaceous drapes recognizable as tidal bundles. Inclined heterolithic stratification is locally well developed at the top of the valley fill. Downdip reaches of valleys, typically within 50 km of the lowstand shoreline, have a sandstone-dominated lower part and, locally, a mud-rich upper portion consisting of a variety of laminated heterolithic facies with a clear tidal signature. These heterolithic deposits may represent central basin, tidal flat, bayhead delta and point-bar environments. Valley filling took place mainly during the transgressive systems tract (TST) when tidally influenced environments migrated upvalley. Semi-diurnal tidal backwater effects extended at least 30 km landward of the regional maximum transgressive marine shoreline. The aggradational late TST and highstand systems tract (HST) includes deltaic and coastal plain deposits comprising lake and anastomosed river deposits that suggest a very low gradient (≈ 1:3000). Delta parasequences of the falling stage systems tract (FSST) offlap seaward and have no equivalent coastal plain deposits. The FSST has an average width of 60 km and an inferred gradient of 1:2500. The upper surfaces of the HST and FSST are extensively incised by valleys. The lowstand systems tract (LST) is subtly aggradational, lacks valleys and is characterized by large delta lobes fed by major distributaries. The width and inferred slope of the FSST, coupled with the thickness of aggradational TST and HST deposits on the coastal plain, suggest a vertical accommodation of about 35 m per transgressive event. About 11 m of this is attributed to isostatic subsidence resulting from water and sediment loads; the residual 24 m is attributed to eustatic rise. This sea-level change is of the same order of magnitude as the valley depths. The length of valleys, however, does not seem to be explicable solely in terms of downstream forcing by sea-level change, and an additional, upstream-forcing mechanism, possibly related to precipitation cycles in the Milankovitch band, might be inferred.  相似文献