What status for the Quaternary?   总被引：3，自引：0，他引：3  

PHILIP L. GIBBARD  ALAN G. SMITH  JAN A. ZALASIEWICZ  TIFFANY L. BARRY  DAVID CANTRILL  ANGELA L. COE  JOHN C. W. COPE  REW S. GALE  F. JOHN GREGORY  JOHN H. POWELL  PETER F. RAWSON  PHILIP STONE  COLIN N. WATERS 《Boreas: An International Journal of Quaternary Research》2005,34(1):1-6

The status of the Quaternary, long regarded as a geological period effectively coincident with the main climatic deterioration of the current Ice Age, has recently been questioned as a formal stratigraphic unit. We argue here that it should be retained as a formal period of geological time. Furthermore, we consider that its beginning should be placed at the Gauss-Matuyama magnetic chron boundary at about 2.6 Ma, rather than at its current position at about 1.8 Ma. The Quaternary would be formally subdivided into the Pleistocene and Holocene epochs. The global chronostratigraphical correlation table proposed is enclosed at the back of this issue.  相似文献   

Quantifying velocity and turbulence structure in depositing sustained turbidity currents across breaks in slope   总被引：2，自引：0，他引：2  

THOMAS E. GRAY  JAN ALEXANDER  MIKE R. LEEDER 《Sedimentology》2005,52(3):467-488

Two-dimensional experiments investigating sediment transport and turbulence structure in sustained turbidity currents that cross breaks in slope are presented as analogue illustrations for natural flows. The results suggest that in natural flows, turbulence generation at slope breaks may account for increased sand transport into basins and that the formation of a hydraulic jump may not be necessary to explain features such as the occurrence of submarine plunge pools and the deposition of coarser-grained beds in the bottomsets of Gilbert-type fan deltas. Experimental flows were generated on 0°, 3°, 6° and 9° slopes of equal length which terminated abruptly on a horizontal bed. Two-component velocities were measured on the slope, at the slope break and downstream of the slope break. Flows were depositional and non-uniform, visibly slowing and thickening with distance downstream. One-dimensional continuous wavelet transforms of velocity time series were used to produce time-period variance maps. Peaks in variance were tested against a background red-noise spectrum at the 95% level; a significant period banding occurs in the cross-wavelet transform at the slope break, attributed to increased formation of coherent flow structures (Kelvin–Helmholtz billows). Variance becomes distributed at progressively longer periods and the shape of the bed-normal-velocity spectral energy distribution changes with distance downstream. This is attributed to a shift towards larger turbulent structures caused by wake stretching. Mean velocity, Reynolds shear stress and turbulent kinetic energy profiles illustrate the mean distribution of turbulence through the currents. A turbulent kinetic energy transfer balance shows that flow non-uniformity arises through the transfer of mean streamwise slowing to mean bed-normal motion through the action of Reynolds normal stresses. Net turbulence production through the action of normal stresses is achieved on steeper slopes as turbulence dissipation due to mean bed-normal motion is limited. At the slope break, an imbalance between the production and dissipation of turbulence occurs because of the contrasting nature of the wall and free-shear boundaries at the bottom and top of the flows, respectively. A rapid reduction in mean streamwise velocity predominately affects the base of the flows and steeper proximal slope flows have to slow more at the break in slope. The increased turbulent kinetic energy, limited bed-normal motion and strong mixing imposed by steep proximal slopes means rapid slowing enhances turbulence production at the break in slope by focusing energy into coherent flow structures at a characteristic period. Thus, mean streamwise slowing is transferred into turbulence production at the slope break that causes increased transport of sediment and a decrease in deposit mass downstream of the slope break. The internal effects of flow non-uniformity therefore can be separated from the external influence of the slope break.  相似文献   

Physiological characteristics of arctic tern Sterna paradisaea chicks in relation to egg volume     

JAN EIVIND ØSTNES  CHRIS JENSEN  JOACHIM OSTHEIM  CLAUS BECH 《Polar research》1997,16(1):1-8

The effect of egg volume on body mass, body composition and growth rate in arctic tern Sterna paradisaea chicks was studied at Ny-Ålesund, on Svalbard (78°55'N, 12°00'E), in order to investigate whether differences in egg size influence the physiological characteristics of the hatchlings. The relative content of yolk and albumen in eggs did not vary in proportion to egg volume. Hatchlings from large eggs had larger body masses than hatchlings from small eggs, with 71% of the overall variation in body mass accounted for egg volume. In newly-hatched chicks, water content, lean body and total lipid mass, as well as both leg and pectoral muscles, changed isometrically in proportion to egg volume. Hatchlings from large eggs, however, had disproportionately larger yolk sacs. The leg muscles of small chicks contained a lower proportion of water than the leg muscles of large chicks, indicating that the leg muscles of small hatchlings were functionally more mature. There was a weak, but significant, correlation between egg volume and growth rate. However, a residual analysis made to eliminate the effect of egg volume showed no correlation between hatchling body mass and growth rate. The results of the present study show that Arctic tern hatchlings from large eggs emerge with more yolk sac reserves, enabling them to better withstand periods of food-scarcity. During embryonic growth in small eggs, however, there seems to be a greater relative usage of yolk, resulting in a more developed leg musculature. This may partly compensate for the higher mass-specific heat loss in small hatchlings.  相似文献   

Chromian Spinel-Silicate Chemistry in Ultramafic Rocks of the Jijal Complex, Northwest Pakistan   总被引：3，自引：1，他引：3  

JAN  M. QASIM; WINDLEY  BRIAN F. 《Journal of Petrology》1990,31(3):667-715

The approximately 150 km² Jijal complex occupies a deep-levelsection of the Cretaceous Kohistan are obducted along the Indussuture. The complex consists of mafic garnet granulites, anda > 10 km ? 4 km slab of pyroxenites (diopsidite > websterite;? olivine), dunite, and subordinate peridotite, all of whichare devoid of plagioclase. These contain chromite either inlenses, layers, and veins or as disseminated grains. The chromiteis mostly medium grained, subhedral to euhedral, shows pull-aparttexture, and may contain inclusions of associated silicates.Chromite grains within thin sections of chromitite are generallyhomogeneous in composition, but dunite and pyroxenite samplescommonly contain chromite grains of variable composition. Thesegregated chromite has higher Cr₂O₃ wt%, cr-number, and mg-number,and lower fe'-number than the accessory chromite. These variationsare mainly attributed to subsolidus exchange of Mg and Fe betweenchromite and associated olivine or pyroxene, and to inheritancefrom a magmatic source, but other factors may also be responsible.In general, the chromite grains are altered along margins andfractures to ferritchromit that is enriched in cr-number (andgenerally Fe³⁺, Mn, and Ti) and impoverished in mg-number comparedwith the parent grains. Chromian chlorite (clinochlore, penninite,with up to 7?3 wt.% Cr₂O₃) is commonly associated with the alteration,as is serpentine in most silicate rocks and some chromitites.The chlorite shows considerable compositional variation fromgrain to grain and in some cases within a single grain. Clinopyroxene is low-Al, -Na and high-Ca diopside. Orthopyroxeneranges from En₉₁ to En₈₂ and olivine from Fo₉₈ to Fo₈₄ (ignoringone analysis each). The mg-number of these minerals is higherin chromitites than in dunites and pyroxenites. Several aspectsof the petrogenesis of the ultramafic rocks (e.g., the abundanceof diopsidite) are not clear, but they seem to have passed througha complex history. The high cr-numbers (>60) in the chromiteindicate that the rocks may have originated from some form ofoceanic lithosphere-island are interaction. Petrography andmineral compositional data suggest that the rocks are ultramaficcumulates derived from an are-related (?primitive) high-Mg tholeiiticmagma, possibly at pressures in excess of 8 kb.There also aresmall ultramafic bodies in the form of conformable layers andemplaced masses within the garnet granulites. These containmagnetite and pleonaste with < 10 wt.% Cr₂O₃, and less magnesianolivine and pyroxene than the principal ultramafic mass. Thesealso have the characteristics of island are plutonic rocks,but it is not clear whether the garnet granulites constitutea continuous sequence of are cumulates with the principal ultramaficmass or the two are produced from different source magmas.  相似文献   

The origin and tectonic significance of asymmetrical meander-belts     

MIKE R. LEEDER  JAN ALEXANDER 《Sedimentology》1987,34(2):217-226

In the Hebgen lake area of SW Montana, the Madison and South Fork Rivers occupy the northeast sides of their respective meander-belts. The form of the abandoned meander-loops within these asymmetric meander-belts indicates that they were produced by gradual northeast migration of the active channels. This progressive migration can be related to tectonic tilting produced by regional extensional faulting at a high angle to the original channel-belt axis which ran down a gently sloping outwash cone. Asymmetric channel sandstone bodies in the rock record can be recognized by the preferred dip of successive lateral accretion units in meander loops. Together with soft sediment deformation, facies and thickness variations they may indicate tectonic deformation of the sedimentary surface.  相似文献   

Amino acid ratios in Quaternary molluscs and foraminifera from western Norway: correlation, geochronology and paleotemperature estimates     

GIFFORD H. MILLER  HANS PETTER SEJRUP  JAN MANGERUD  BJØRN G. ANDERSEN 《Boreas: An International Journal of Quaternary Research》1983,12(2):107-124

Isoleucine epimerization (alle/Ue) ratios in the pelecypod Mya truncata and benthic foraminifer Cibicides lobalulus from emerged marine units in western Norway allow construction of a regional relative chronostratigraphy for the Ecmian and Weichselian. Two in situ interglacial sections are considered correlative by the similar biostratigraphy and alle/Ile ratios in C. lobalulus. Overlying sediments at the two sites are of both marine and glacial origin. Neither site contains a complete Weichselian record, but allelic ratios, lithostratigraphy and fauna! changes suggest at least four stadial and three interstadial events occurred along the western Norwegian coast during Early and Middle Weichselian time. Kinetic data defining the relationship between the isoleucine epimerization rate constant and temperature for the species studied allow the estimation of paleotemperatures for samples of known age. Accepting published age estimates for the Eemian interglacial beds, the average Weichselian temperature in western Norway is calculated to have been ca. 4°C below the average Holocene temperature, whereas the last interglacial was 1 to 2°C warmer that the Holocene. The limited temperature depression over this region during the Weichselian implies that coastal western Norway was ice-covered only about 30% of this period, and that Atlantic water, although not necessarily in a warm surface current as today, entered the Norwegian Sea during much of marine isotope stage 5 and intermittently during stage 3. Interpolated amino acid ages date interstadial events at ca. 94 ka, 78 ka and 52 ka, B.P., whereas glacial events are dated ca. 103 ka and bracketed by limiting dates between 78 and 89 ka, between 52 and 63 ka and less than 36 ka B.P.  相似文献   

Potassic Magmatism in Western Sichuan and Yunnan Provinces, SE Tibet, China: Petrological and Geochemical Constraints on Petrogenesis   总被引：31，自引：1，他引：30  

GUO  ZHENGFU; HERTOGEN  JAN; LIU  JIAQI; PASTEELS  PAUL; BOVEN  ARIEL; PUNZALAN  LEA; HE  HUAIYU; LUO  XIANGJUN; ZHANG  WENHUA 《Journal of Petrology》2005,46(1):33-78

Potassic volcanism in the western Sichuan and Yunnan Provinces,SE Tibet, forms part of an extensive magmatic province in theeastern Indo-Asian collision zone during the Paleogene (40–24Ma). The dominant rock types are phlogopite-, clinopyroxene-and olivine-phyric calc-alkaline (shoshonitic) lamprophyres.They are relatively depleted in Na₂O, Fe₂O₃, and Al₂O₃ comparedwith the late Permian–early Triassic Emeishan continentalflood basalts in the western part of the Yangtze craton, andhave very high and variable abundances of incompatible traceelements. Primitive mantle-normalized incompatible element patternshave marked negative Nb, Ta and Ti anomalies similar to thoseof K-rich subduction-related magmas, although the geodynamicsetting is clearly post-collisional. Spatially, some incompatibletrace element abundances, together with inferred depths of meltsegregation based on the Mg-15 normalized compositions of thesamples, display progressive zonation trends from SW to NE withincreasing distance from the western boundary of the Yangtzecraton. Systematic variations in major and trace element abundancesand Sr–Nd–Pb isotope compositions appear to havepetrogenetic significance. The systematic increases in incompatibletrace element abundances from the western margin to the interiorof the Yangtze craton can be explained by progressively decreasingextents of partial melting, whereas steady changes in some incompatibletrace element ratios can be attributed to changes in the amountof subduction-derived fluid added to the lithospheric mantleof the Yangtze craton. The mantle source region of the lamprophyresis considered to be a relatively refractory phlogopite-bearingspinel peridotite, heterogeneously enriched by fluids derivedfrom earlier phases of late Proterozoic and Palaeozoic subductionbeneath the western part of the Yangtze craton. Calculationsbased on a non-modal batch melting model show that the degreeof partial melting ranges from 0·6% to 15% and the proportionof subduction-derived fluid added from0·1% to 0·7%(higher-Ba fluid) or from 5% to 25% (lower-Ba fluid) from theinterior to the western margin of the Yangtze craton. Some pre-existinglithospheric faults might have been reactivated in the areaneighbouring the Ailao Shan–Red River (ASRR) strike-slipbelt, accompanying collision-induced extrusion of the Indo-Chinablock and left-lateral strike-slip along the ASRR shear zone.This, in turn, could have triggered decompression melting ofthe previously enriched mantle lithosphere, resulting in calc-alkalinelamprophyric magmatism in the western part of the Yangtze craton. KEY WORDS: Tibet; potassic magmatism; lithospheric mantle; metasomatism  相似文献   

Velocity and Structural Modeling of Mesozoic Chiltan Limestone and Goru Formation for Hydrocarbon Evaluation in the Bitrisim Area, Lower Indus Basin, Pakistan     

Sarfraz KHAN  Zahid LATIF  Muhammad HANIF  Irfan U. JAN  Shahid IQBAL 《《地质学报》英文版》2016,90(1):258-275

The present study focuses on building a workflow for structural interpretation and velocity modeling and implementing to Jurassic-Cretaceous succession (Chiltan Limestone and Massive sand of the Lower Goru Formation). 2D-Migrated seismic sections of the area are used as data set and in order to confirm the presence of hydrocarbons in the study area, P and S-wave seismic velocities are estimated from single-component seismic data. Some specific issues in the use of seismic data for modeling and hydrocarbon evaluation need to deal with including distinguishing the reservoir and cap rocks, and the effects of faults, folds and presence of hydrocarbons on these rocks. This study has carried out the structural interpretation and modeling of the seismic data for the identification of traps. The results demonstrate existence of appropriate structural traps in the form of horst and grabens in the area. 2D and 3D velocity modeling of the horizons indicates the presence of high velocity zones in the eastern half of the study while relatively low velocity zones are encountered in the western half of the area. Two wells were drilled in the study area (i.e. Fateh-01 and Ichhri-01) and both are dry. Immature hydrocarbons migration is considered as a failure reason for Fateh-01 and Ichhri-01 well.  相似文献   

56 YEARS OF SOLIFLUCTION MEASUREMENTS IN THE ABISKO MOUNTAINS, NORTHERN SWEDEN – ANALYSIS OF TEMPORAL AND SPATIAL VARIATIONS OF SLOW SOIL SURFACE MOVEMENT     

BY HANNA RIDEFELT  JONAS ÅKERMAN  ACHIM A BEYLICH  JAN BOELHOUWERS  ELSE KOLSTRUP  ROLF NYBERG 《Geografiska Annaler: Series A, Physical Geography》2009,91(3):215-232

Solifluction movement rates from 1952 to 2008 for the Abisko region, northern Sweden, have been compiled and analysed through correlation tests and multiple regression. The temporal analysis is based on two datasets ( Lobe11 & gridAB and Line B ) from Kärkevagge. The dataset Lobe11 & gridAB show a strong correlation between movement rates and mean annual air temperature (MAAT) and MAAT is also identified as one of the significant contributing parameters in the multiple regression model. No significant correlations were found for the Line B dataset. The spatial analysis indicates generally higher movement rates in the western part of the region and at lower altitudes mainly between 700 and 900 m a.s.l., but the spatial variability is high. To reduce the influence of the temporal variation the data for the correlation tests of the spatial variations were divided into two parts: 1957 to 1980 and 1981 to 2008. The correlation analysis of the dataset 1957 to 1980 shows a significant negative correlation between annual average movement rates and permafrost probability and altitude. The dataset 1981 to 2008 shows a positive correlation between movement rates and wetness index. It is concluded that movement rates may increase with higher MAAT in the western part of the region (Kärkevagge), the spatial variability of movement rates within the region is very high and that altitude (and/or permafrost) together with wetness index are the main controls on the regional spatial variation. The study highlights the limitations in establishing statistical relationships between movement rates and climate using data from different field empirical studies.  相似文献   

Sedimentology and stratigraphy in the cave Hamnsundhelleren,western Norway     

VIDAR VALEN  JAN MANGERUD  EILIV LARSEN  ANNE KARIN HUFTHAMMER 《第四纪科学杂志》1996,11(3):185-201

The stratigraphy in Hamnsundhelleren is as follows. A basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the Laschamp excursion (43–47 000 yr BP). Angular blocks, bones and clay above this are ¹⁴C dated to the Ålesund Interstadial (28–38 000 yr BP). Another stadial laminated clay following the Ålesund Interstadial includes a palaeomagnetic excursion correlated with Lake Mungo (28 000 yr BP). The newly discovered Hamnsund Interstadial above this consists of frost-weathered clay and scattered angular blocks. It is ¹⁴C dated to 24 500 yr BP on bones mixed into the Ålesund Interstadial. The Hamnsund Interstadial is succeeded by another stadial laminated clay and then a Late-glacial–Holocene mixture of bones and blocks. In Hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice-free–ice-covered cycle have been identified: (i) ice-free phase (deposition of bones and frost-weathered blocks); (ii) subaerial ice-dammed lake phase (sand or silt deposited in a lateral glacial lake); (iii) subglacial ice-dammed lake phase (cave closed by ice, deposition of till, debris flows and laminated clay); (d) ice-plugged phase (cave is plugged by frozen lake water and/or glacial ice, no deposition).  相似文献