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1.
Rocks from the vicinity of Bosumtwi crater, Ghana, and a repre-sentative collection of Ivory Coast tektites have been analyzed mass spectrometrically for rubidium, strontium, and strontium isotopic composition. The data from the rocks of the crater area yield an age of 1.97 x 10(9) years (lambda(gb) = 1.47 chi 10(-11) year(-1)). The data for the Ivory Coast tektites fall on this isochron. This identity of age values for the Ivory Coast tektites and the Birrimian basement rocks of West Africa strongly supports the hypothesis of terrestrial formation for these tektites. The evidence available at present suggests that the Ivory Coast tektites are most probably the fusion products of meteoritic impact at the Bosumtwi crater site. 相似文献
2.
Measurement of rhenium (Re) and osmium (Os) concentrations and Os isotopic compositions in Ivory Coast tektites (natural glasses with upper crustal compositions that are ejected great distances during meteorite impact) and rocks from the inferred source crater, Lake Bosumtwi, Ghana, show that these tektites incorporate about 0.6 percent of a meteoritic component. Analysis of elemental abundances of noble metals alone gives equivocal results in the detection of meteoritic components because the target rocks already have relatively large amounts of noble metals. The Re-Os system is ideally suited for the study of meteorite impacts on old continental crust for three reasons. (i) The isotopic compositions of the target rocks and the meteoritic impactor are significantly different. (ii) Closed-system mixing of target rocks and meteorites is linear on Re-Os isochron diagrams, which thus permits identification of the loss of Re or Os. (iii) Osmium isotopic compositions are not likely to be altered during meteorite impact even if Re and Os are lost. 相似文献
3.
Elemental abundance (20 trace elements, 3 major elements) comparisons for Ivory Coast microtektites and Australasian microtektites indicate that there are distinct chemical similarities between microtektites and nearby tektites. Several trace element abundances in microtektites are quite different from those observed in Apollo 11 and Apollo 12 samples. 相似文献
4.
The Australasian and Ivory Coast deep-sea microtektites have fission track ages of 0.71 and 1.09 million years, respectively. These ages are in good agreement with the ages of deposition of the microtektites determined from paleomagnetic data. Both the fission track ages and ages of deposition of the microtektites agree with the potassium/ argon and fission track ages of tektites from the respective tektite strewn fields. 相似文献
5.
Glass BP 《Science (New York, N.Y.)》1968,161(3844):891-893
Glassy objects of spherical, oval, dumbbell, teardrop, and irregular shapes have been found in a deep-sea sediment core taken off the Ivory Coast. They occur in a layer of sediment that was apparently deposited about 800,000 years ago. Their geographic location, appearance, and physical properties suggest that they are microtektites and that they are related to the tektite-strewn field of the Ivory Coast. 相似文献
6.
Carbon and oxygen isotope analysis through a 30-year (1944 to 1974) growth of Montastrea annularis from Hen and Chickens Reef (Florida Keys) shows a strong yearly variation in the abundances of both carbon-13 and oxygen-18 and a broad inverse relationship between the two isotopes. Normal annual dense bands are formed during the summer and are characterized by heavy carbon and light oxygen. "Stress bands" are formed during particularly severe winters and are characterized by heavy carbon and heavy oxygen. The isotopic effect of Zooxanthellae metabolism dominates the temperature effect on the oxygen-18/oxygen-16 ratio. The isotopic results on the deep-sea solitary coral Bathypsammia tintinnabulum, where Zooxanthellae are nonexistent, indicates that the abundance of the heavy isotopes carbon-13 and oxygen-18 is inversely related to the growth rate, with both carbon and oxygen approaching equilibrium values with increasing skeletal age. 相似文献
7.
M Stuiver 《Science (New York, N.Y.)》1968,162(857):994-997
Freshwater lake marl and mollusks from Indiana show variations in ratios of oxygen-18 to oxygen-16 of a few per mil during the Postglacial. For the last 9000 years these variations are about 1 per mil for properly selected lake sediments. Thus the oxygen isotope composition of atmospheric precipitation appears relatively stable over this interval, indicating stationary atmospheric circulation patterns over the Great Lakes region. A reduction in oxygen-18 content around 10,000 years ago corresponds with the climate change indicated by pollen profiles. Large systematic differences were found between carbon-13 and oxygen-18 content of marl and mollusks. 相似文献
8.
Discovery of shock-metamorphosed material establishes the impact origin of Lonar Crater. Coarse breccia with shatter coning and microbreccia with moderately shocked fragments containing maskelynite were found in drill holes through the crater floor. Trenches on the rim yield strongly shocked fragments in which plagioclase has melted and vesiculated, and bombs and spherules of homogeneous rock melt. As the only known terrestrial impact crater in basalt, Lonar Crater provides unique opportunities for comparison with lunar craters. In particular, microbreccias and glass spherules from Lonar Crater have close analogs among the Apollo specimens. 相似文献
9.
A study has been made of carbon-13 and oxygen-18 variations in Greek marbles from the ancient quarry localities of Naxos, Paros, Mount Hymettus, and Mount Pentelikon. Parian, Hymettian, and Pentelic marbles can be clearly distinguished by the isotopic relationships; Naxian marbles fall into two groups characterized by different oxygen-18/oxygen-16 ratios. Ten archeological samples were also analyzed; the isotopic data indicate that the "Theseion" is made of Pentelic marble and a block in the Treasury of Siphnos at Delphi is probably Parian marble. 相似文献
10.
The diffusion of oxygen labeled with oxygen-18 through cores of wet soil increased significantly when roots of growing corn seedlings penetrated the cores. The increase was small or absent when roots grew through a layer of soft wax or a layer of water-saturated 0.5-mm glass beads, indicating that the diffusion increase was a joint effect of the roots and airfilled pores in the soil. A possible mechanism is suggested. 相似文献
11.
The ratios of oxygen-18 to oxygen-16 and of carbon-13 to carbon-12 in the early shell and septa of two Nautilus specimens are interpreted for the early ontogeny of the animals. Changes in the carbon isotope content are tentatively correlated with the end of the embryonic period and with environmental changes. Variations in the oxygen isotope content are in part ascribed to migrations from warm to cooler water after a certain stage of development. The size of the body chamber of the young animals can be determined by comparison of the isotope contents in outer shell and septa. 相似文献
12.
Volcanic glasses collected on the rim of Shorty Crater in the Apollo 17 area were formed 3.63 x 10(9) years ago. The amounts of xenon-136 produced by neutron-induced fission of uranium-235 indicate that the glasses resided on the lunar surface for about 38 million years before they were deeply buried. The glass spherules were reexcavated by the impact that formed Shorty Crater 17 million years ago, and remained undisturbed until they were collected. 相似文献
13.
The oxygen isotope compositions (delta(18)O) of eclogitic xenoliths from the Roberts Victor kimberlite range from 2 to 8 per mil relative to SMOW (standard mean ocean water). This surprising variation appears to be due to fractional crystallization: the eclogites rich in oxygen-18 represent early crystal accumulates; the eclogites poor in oxygen-18 represent residual liquids. Crystal-melt partitioning probably exceeded 3 per mil and is interpreted to be pressure-dependent. Anomalous enrichment of oxygen-18 in cumulate eclogites relative to ultramafic xenoliths suggests that crystal-melt partitioning increased after melt-formation but prior to crystallization. 相似文献
14.
The ratios of oxygen-18 to oxygen-16 ( (18)O/(16)O) of cellulose purified from two sets of wheat plants grown under conditions similar in all respects except for a large difference in the (18)O/(16)O ratios of the carbon dioxide supplied to them differ by only a small amount. The difference in the (18)O/(16)O ratios of the cellulose is similar to that observed for the (18)O/(16)O ratios of the water present in the plants. These results indicate that the oxygen derived from carbon dioxide undergoes complete exchange with the oxygen of the water in the plant during the synthesis of cellulose and that the (18)O/(16)O ratio of the water inside the plant is the primary influence on the (18)O/(16)O ratio of cellulose in terrestrial plants. 相似文献
15.
Atmospheric gases trapped in polar ice at the firn to ice transition layer are enriched in heavy isotopes (nitrogen-15 and oxygen-18) and in heavy gases (O(2)/N(2) and Ar/N(2) ratios) relative to the free atmosphere. The maximum enrichments observed follow patterns predicted for gravitational equilibrium at the base of the firn layer, as calculated from the depth to the transition layer and the temperature in the firn. Gas ratios exhibit both positive and negative enrichments relative to air: the negative enrichments of heavy gases are consistent with observed artifacts of vacuum stripping of gases from fractured ice and with the relative values of molecular diameters that govern capillary transport. These two models for isotopic and elemental fractionation provide a basis for understanding the initial enrichments of carbon-13 and oxygen-18 in trapped CO(2), CH(4), and O(2) in ice cores, which must be known in order to decipher ancient atmospheric isotopic ratios. 相似文献
16.
Seasonal variations in the oxygen-18/oxygen-16 ratio of calcite shells of living planktonic foraminifera in the Sargasso Sea off Bermuda are a direct function of surface water temperature. Seasonal occurrence as well as depth habitat are determining factors in the oxygen isotopic composition of planktonic foraminifera. These relationships may be used to determine the seasonal temperature contrast of oceans in the past. 相似文献
17.
A new method measures the oxygen-isotopic composition of dissolved sulfate ions and barium sulfate. Sulfate ions in the oceans are enriched in oxygen-18 by 9.5 per mille relative to mean ocean water and show only minor variations, probably because the exchange rate with water is slow enough to prevent local equilibrium with surface waters. Sulfate ions in saline lakes and brines have oxygen-18 enrichment of from 7 to 23 per mille relative to mean ocean water;the value of the highest enrichment observed is about the same as that of atmospheric oxygen. 相似文献
18.
The mean oxygen-18 content of continental ice sheets during the last glacial maximum is estimated to deltaO(18)=-30 per mille or less, and the consequent change in the isotopic composition of the oceans at that time to 1.2 per mille or more. This means that at least 70 percent of the oxygen-18 variations found in shells of planktonic foraminifera from deep-sea cores between times of glacial maximums and minimums are due to isotopic changes in ocean water, and at most 30 percent to changes in ocean surface temperature. Hence, Emiliani's "paleotemperature" curve rather depicts the amount of ice on the continents in excess of that present today. In this sense it may be renamed a "paleoglaciation" curve. 相似文献
19.
A study of the evolution of the oxygen-18/oxygen-16 ratio of the oceans suggests that this ratio is unlikely to have remained constant with time. Our models suiggest that early formation of the oceans is more likely than linear growth. 相似文献
20.
Atmospheric oxygen has been found to be enriched in oxygen-18 by 23.5 +/- 0.3 per mil relative to average ocean water (SMOW). Oxygen dissolved in seawater is further enriched in oxygen-18 by 0.85 per mil at 0 degrees C. The temperature dependence of the solubility enrichment is given by epsilon (per mil) = 0.85- 0.010 t ( degrees C). This result is in good agreement with earlier measurements of the solubility effect in distilled water. 相似文献