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261.
262.
Hemmo A. Abels Stefaan Van Simaeys Frits J. Hilgen Ellen De Man Noël Vandenberghe 《地学学报》2007,19(1):65-73
Our results prove that glacio‐eustatic sea level oscillations in the early Oligocene were dominantly obliquity controlled with additional influence of the ∼100‐ and 405‐kyr eccentricity cycles. This was derived from spectral analysis of resistivity records from an extended downhole section of the Boom Clay succession in Belgium, that reveals a prevailing obliquity control on the laterally persistent metre‐scale alternations of shallow marine silt‐ and claystones in the Rupelian historical stratotype succession. These direct measurements of sea level variations in a shallow marine setting corroborate that variations with similar frequencies in benthonic oxygen isotope records from the open ocean indeed reflect, at least partly, ice volume change. A very tentative astronomical tuning has been established for the Boom Clay succession which awaits future confirmation with the addition of more accurate age calibration points. 相似文献
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264.
A. Claverie G. R. Isaak C. P. McLeod H. B. Van Der Raay T. Roca Cortès 《Solar physics》1981,74(1):51-57
The discrete structure in the 5 min velocity oscillations of the solar surface has been confirmed by a re-analysis of data obtained between 1976 and 1979, and in addition a preliminary analysis of 1980 data show excellent consistency of the determined frequencies over the five year period. It is further shown that atmospheric transparency, as measured by the power in the solar intensity fluctuations, shows no correlation with the measured amplitude of the velocity fluctuations, over 2 orders of magnitude.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands. 相似文献
265.
Solar Physics - Vertically propagating traveling waves have been observed in the solar photosphere. These waves have a period of 278 ± 41 seconds and a vertical phase velocity of about 2 km... 相似文献
266.
267.
The onset of coronal transients 总被引:2,自引:0,他引:2
W. Van Tend 《Solar physics》1979,61(1):89-93
A model for the motion of transients in the high corona, recently given by Anzer (1978), is extended to include also the onset of a transient, associated with prominence destabilization. A comparison is made with flare instabilities, and some relevant observations are considered. 相似文献
268.
Stephen E. Kesler Michael J. Issigonis Jon C. Van Loon 《Journal of Geochemical Exploration》1975,4(2):235-245
Analysis of the chlorine, fluorine and water content of approximately 200 samples from a total of fourteen mineralized and ten barren intrusive rocks from the Caribbean and Central America indicates that abundances of these constituents fail to distinguish mineralized rocks from barren rocks. Variations in background abundances arise from the increase in halogen content of potassium-rich rocks and from the depletion of halogens in altered and porphyritic rocks. A particularly well developed potassium-fluorine covariance is observed in tin-bearing granites, but such a covariance cannot be used to distinguish intrusive rocks associated with porphyry copper mineralization. 相似文献
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270.
We constructed a detailed relative sea-level rise curve for the last 1500 years using a novel approach, i.e. charting the rate of relative sea-level rise using microfaunal and geochemical data from a coastal salt marsh sequence (Clinton, CT, USA). The composition of benthic foraminiferal assemblages and the iron abundance in peats were used to describe shifts in marsh environment through time quantitatively. The resulting sea-level rise curve, with age control from 14C dating and the onset of anthropogenic metal pollution, shows strong increases in the rate of relative sea-level rise during modern global warming (since the late nineteenth century), but not during the Little Climate Optimum (ad 1000–1300). There was virtually no rise in sea-level during the Little Ice Age (ad 1400–1700). Most of the relative sea-level rise over the last 1200 years in Clinton appears to have occurred during two warm episodes that jointly lasted less than 600 years. Changes from slow to fast rates of relative sea-level rise apparently occurred over periods of only a few decades. We suggest that changes in ocean circulation could contribute to the sudden increases in the rate of relative sea-level rise along the northeastern USA seaboard. Relative sea-level rise in that area is currently faster than the worldwide average, which may result partially from an ocean surface effect caused by hydrodynamics. Our data show no unequivocal correlation between warm periods (on a decaal to centennial time-scale) and accelerated sea-level rise. One period of acclerated sea-level rise may have occurred between about ad 1200 and 1450, which was the transition for the Little Climate Optimum to the Little Ice Age, i.e. a period of cooling (at least in northwestern Europe). Local changes in tidal range might also have contributed to this apparent increase in the rate of relative sea-level, however. The second period of accelerated sea-level rise occurred during the period of modern global warming that started at the end of the last century. 相似文献