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71.
A.H.F. Robertson 《Earth and Planetary Science Letters》1978,41(3):317-329
The Arakapas fault belt, southern Troodos Massif, which is interpreted as a fossil oceanic fracture zone, contains a sedimentary and volcanic “fill” including basaltic lava breccias, volcaniclastic sandstones, intercalated Fe-rich mudstones, and minor Cu sulphide mineralisation. The volcaniclastic sedimentary rocks were produced by submarine weathering and gravity redeposition of basalt within the transform zone. In contrast, the Fe-mudstones predominantly originated as chemical precipitates from hydrothermal solutions generated by hydrothermal leaching of basalt by seawater. The rare earth elements, and some trace metals, including Co, Ni, Pb, V and Zr, are thought to have been incorporated from seawater into the ferruginous precipitates. Unusually high Fe/Mn ratios of the Fe-mudstones relative to most modern ocean-ridge sediments may reflect deposition in relatively oxygen-depleted waters on the floor of a major bathymetric depression created by the transform faulting; release of acidic thermal waters would have further suppressed Mn precipitation. Contrary to recent suggestions of metallogenesis along oceanic fracture zones, none of the major Cyprus cupriferous sulphide bodies lie along the fossil Arakapas transform zone. 相似文献
72.
73.
Wayne V. Burt 《Boundary-Layer Meteorology》1977,12(4):505-509
Surface winds were measured from anchored buoys at the corners of a 100-km triangle in the Atlantic ocean for three weeks in September 1972. The measurements were part of the British Royal Society Joint Air-Sea Interaction Project, JASIN-72. Peaks were found at a frequency of 0.125 cph (8-h period) in various wind statistics, indicating the presence of the terdiurnal, S
3, component of the atmospheric tides that had previously been extensively studied because it is a prominent component in surface air-pressure records. 相似文献
74.
Thermodynamic calculation of distribution of dissolved aqueous species in the Red Sea geothermal brine provides a model of ore transport and deposition in good agreement with observed accumulations of base metal sulfides, anhydrite, and barite.The Red Sea brine is recirculated seawater that acquires high salinity by low-temperature interaction with Miocene evaporites and is subsequently heated to temperatures in excess of 200°C by interaction with recent rift zone intrusive rocks. At temperatures up to 250°C, NaSO?4 and MgSO04 are the dominant sulfur-bearing species. H2S forms by inorganic sulfate reduction at the higher temperatures but is maintained at a uniform concentration of about 2 ppm by the strength of the sulfate complexes.Chloride complexes solubilize metals at the higher temperatures, and thus sulfide and metals are carried together into the Atlantis II Deep. Below 150°C, the brine becomes supersaturated with respect to chalcopyrite, sphalerite, galena, and iron monosulfide due to chloride-complex dissociation. Sulfide precipitation rates, based on the rate of brine influx, are in good agreement with measured sedimentation rates. Anhydrite precipitates as crystalline fissure infillings from high-temperature inflowing brine. Barite forms from partial oxidation of sulfides at the interface between the lower hot brine and the transitional brine layer. 相似文献
75.
Dating climatic episodes of the Holocene 总被引:2,自引:0,他引:2
Monitoring evidence indicates that the Holocene embraced a sequence of rather discrete climatic episodes. The transitions between these environmental episodes apparently were abrupt and globally synchronous. This paper reports on statistical analyses of radiocarbon dates associated with environmental change and cultural change.Over 800 14C dates associated with pollen maxima and minima, sea level maxima and minima, and top and bottom surfaces of peat beds were simultaneously analyzed to identify times of globally synchronous environmental discontinuities.Some 3700 14C dates associated with 155 cultural continua of the world were collectively analyzed to identify worldwide synchroneities in appearance and termination of the cultures.Significant globally synchronous discontinuities were identified in each independent analysis. The dates of environmental and cultural discontinuities are rather similar, particularly during the recent half of the Holocene. The fact that the cultural discontinuities mostly follow rather closely those of the paleobotanical record suggests that there has been a distinct climatic impact on the cultural history of man. 相似文献
76.
Spectroscopy of thez=2.0763 absorption line system in A2206-199N shows that it has a very large hydrogen column density (5×1020 cm–2) but extremely weak absorption due to heavy elements. We discuss the possibility that the gas cloud causing this absorption system may be exceptionally metal-poor.Paper presented at the IAU Thrid Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
77.
A.H.F. Robertson 《地学学报》1990,2(4):333-339
In northern Euboea (Eastern Greece), Late Cretaceous platform carbonates of the Pelagonian Zone pass depositionally upwards into Maastrichtian hemipelagic limestones, possibly reflecting a rifting event in the adjacent Neotethys. This is followed by a c. 1 km-thick unit of siliciclastic turbidites, debris flows and detached limestone blocks. Thrust intercalations of ophiolitic rocks comprise altered pillow basalts and ultramafic rocks with ophicalcite. Calcite veins in sheared serpentinite contain planktonic foraminifera and the ophicalcite is directly overlain, with a depositional contact, by Globotruncana-bearing pelagic limestones and calciturbidites of Maastrichtian age. The ophiolitic rocks are interpreted as Late Cretaceous oceanic crust and mantle, that formed at a fracture zone, or rifted spreading axis within a Neotethyan, Vardar basin to the east. During the Early Tertiary (Palaeocene–Eocene), the Neotethyan basin began to close, with development of a subduction-accretion complex, mainly comprising sheared, trench-type sandstones, associated with ophiolitic slices. In response to trench/margin collision, the Pelagonian carbonate platform foundered and limestone debris flows and olistoliths were shed into a siliciclastic foreland basin. Suturing of the Neotethyan ocean basin then resulted in westwards thrusting of oceanic units over the foreland basin, thrusting of slices of inferred Late Cretaceous Pelagonian carbonate platform slope and large-scale recumbent folding. 相似文献
78.
Sgubin Giovanni Swingedouw Didier Drijfhout Sybren Hagemann Stefan Robertson Eddy 《Climate Dynamics》2015,45(5-6):1429-1450
Climate Dynamics - The response of the Atlantic meridional overturning circulation (AMOC) to an increase of radiative forcing (ramp-up) and a subsequent reversal of radiative forcing (ramp-down) is... 相似文献
79.
D.A. Robertson 《新西兰海洋与淡水研究杂志》2013,47(2):129-136
Frostfish spawning, as indicated by the presence of planktonic eggs, was observed mainly in north‐eastern, but also in south‐western, New Zealand waters in spring to autumn. Spawning takes place in the afternoon in outer shelf waters 50–200 m deep, with surface temperatures and salinities between 17.5 and 22.0°C and 35.3 and 35.6‰ respectively. Egg and oil droplet diameters ranged from 1.65 to 1.75 mm and 0.40 to 0.43 mm respectively. 相似文献
80.
A drift and pumpback experiment was conducted in a brackish water sandfill. The sandfill was reclaimed from the sea in the eastern part of Singapore and contains sands with low organic and clay/silt contents. The high salinity in the ground water precludes the use of chloride and bromide as tracers in such an environment, and a field experiment was conducted to assess the viability of using fluorescein as a tracer in brackish water aquifers. Nitrate was used as a second tracer to serve as a check. Initial laboratory studies showed that fluorescence was unaffected over the range of electrical conductivity and pH of the ground water. Results from the field experiment show that fluorescein appears to behave conservatively. 相似文献