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151.
In January of 1982 we measured a microwave spectrum of CO in the Martian atmosphere utilizing the rotational J = 1 → 2 transition of CO. We have analyzed data and reanalyzed the microwave spectra of R. K. Kakar, J. W. Waters, and W. J. Wilson, (Science196, 1090–1091, 1977, measured in 1975) and J. C. Good and F. P. Schloerb, (Icarus47, 166–172, 1981 measured in 1980) in order to constrain estimates of the temporal variability of CO abundance in the Martian atmosphere. Our values of CO column density from the data of Karar et al., Good and Schloerb, and our own are 1.7 ± 0.9 × 1020, 3.0 ± 1.0 × 1020, and 4.6 ± 2.0 × 1020cm?2, respectively. The most recent estimate of CO column density from the 1967 infrared spectra of J. Connes, P. Connes, and J.P. Maillard, (Atlas de Spectres Infarouges de Venus, Mars, Jupiter, et Saturne, Editions due Centre National de la Recherche Scientifique, Paris, 1969), is 2.0 ± 0.8 × 1020 cm?2 (L.D.G. Young and A.T. Young, Icarus30, 75–79, 1977). The large uncertainties given for the microwave measurements are due primarily to uncertainty in the difference between the continuum brightness temperature and atmospheric temperatures of Mars. We have accurately calculated the variation among the observations of the continuum (surface) brightness temperature of Mars, which is primaroly a function of the observed aspect of Mars. A more difficult problem to consider is variability of global atmospheric temperatures among the observations, particularly the effects of global dust storms and the ellipticity of the orbit of Mars. The large bars accompanying our estimates of CO column density from the three sets of microwave measurements are primarily caused by an assumed uncertainty of ±10°K in our atmospheric temperature model due to possible dust in the atmosphere. A qualitative consideration of seasonal variability of global atmospheric temperatures among the measurements suggests that there is not strong evidence for variability of the column abundance of CO on Mars, although variability of 0–100% over a time scale of several years is allowed by the data set. The implication for the variability of Mars O2 is, crudely, a factor of two less. We found that the altitude distribution of CO in the atmosphere of Mars was not well constrained by any of the spectra, although our spectrum was marginally better fitted by an altitude increasing profile of CO mixing ratios. 相似文献
152.
A sample of flares detected in 1980 with the Bent Crystal Spectrometer and the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission satellite has been analysed to study the upward motions of part of the soft X-ray emitting plasma. These motions are inferred from the presence of secondary blue-shifted lines in the Ca XIX and Fe XXV spectral regions during the impulsive phase of disk flares. Limb flares do not show such blue-shifted lines indicating that the direction of the plasma motion is mainly radial and outward. The temporal association of these upward motions with the rise of the thermal phase and with the impulsive hard X-ray burst, as well as considerations of the plasma energetics, favour the interpretation of this phenomenon in terms of chromospheric evaporation. The two measureable parameters of the evaporating plasma, emission measure and velocity, depend on parameters related to the energy deposition and to the thermal phase. The evaporation velocity is found to be correlated with the spectral index of the hard X-ray flux and with the rise time of the thermal emission measure of the coronal plasma. The emission measure of the rising plasma is found to be correlated with the total energy deposited by the fast electrons in the chromosphere by collisions during the impulsive phase and with the maximum emission measure of the coronal plasma. 相似文献
153.
The data such as the H-spectrum-spectroheliographic (SSHG) observations, the H-chromospheric observations, etc., of a flare loop prominence which occurred on the western solar limb on 1981 April 27 have been obtained at Yunnan Observatory. The distribution of the internal motions and the macroscopical motion of the flare loop prominence with time and space in the course of its eruption and ascension is derived from the comprehensive analysis of the data. The possible physical pictures and the instability of the motions of the loop are inferred and discussed. 相似文献
154.
P. Kaufmann F. M. Strauss J. E. R. Costa B. R. Dennis A. Kiplinger K. J. Frost L. E. Orwig 《Solar physics》1983,84(1-2):311-319
Simultaneous microwave and X-ray observations are presented for a solar flare detected on May 8, 1980 starting at 19:37 UT. The X-ray observations were made with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and covered the energy range from 28–490 keV with a time resolution of 10 ms. The microwave observations were made with the 5 and 45 foot antennas at the Itapetinga Radio Observatory at frequencies of 7 and 22 GHz, with time resolutions of 100 ms and 1 ms, respectively. Detailed correlation analysis of the different time profiles of the event show that the major impulsive peaks in the X-ray flux preceded the corresponding microwave peaks at 22 GHz by about 240 ms. For this particular burst the 22 GHz peaks preceded the 7 GHz by about 1.5 s. Observed delays of the microwave peaks are too large for a simple electron beam model but they can be reconciled with the speeds of shock waves in a thermal model. 相似文献
155.
B. N. Abramov 《Lithology and Mineral Resources》2008,43(1):37-43
The maturity of terrigenous material of the Paleoproterozoic Udokan copper-bearing sedimentary complex is considered. The average values of hydrolyzate module (HM), alumina-silica module (AM), and Pettijohn’s coefficient of maturity appreciably vary throughout the Udokan Complex. Among cupriferous sandstones, rocks of the Aleksandrovka Formation are characterized by the highest maturity, whereas rocks of the Chitkanda Formation are distinguished by the lowest maturity. The maturity of cupriferous sandstones of the Sakukan Formation corresponds to that of host rocks. The maturity of cupriferous sandstones from the Aleksandrovka Formation is much higher than that of host rocks. In the Chitkanda Formation, the cupriferous sandstones are much less mature than host rocks. Climatic conditions in provenances estimated from the Nesbitt index of chemical weathering or chemical index of alteration (CIA) may be characterized as temperate ones without prominent climatic features. Most CIA values range from 46 to 66. The formation of copper-bearing sediments was closely related to the periods of volcanic activity. 相似文献
156.
B. Hou L.A. Frakes M. Sandiford L. Worrall J. Keeling N.F. Alley 《Sedimentary Geology》2008,203(1-2):112-130
The Eucla Basin including the vast Nullarbor Plain lies on the margins of the Yilgarn, Musgrave and Gawler cratons in southern Australia and owes its distinctive landscape to a unique set of interactions between eustatic, climatic and tectonic processes over the last ~ 50 Ma. Understanding of the history of the basin and the palaeovalleys that drained from the surrounding cratons are important because they contain major mineral deposits, and the sediments derived from them contain remobilised gold, uranium, and heavy minerals. In particular, a remarkably preserved palaeoshoreline sequence along the north-eastern margin of the Eucla Basin is highly prospective for heavy mineral placer deposits. The record of marine, marginal marine, estuarine, fluvial and lacustrine environments, as constrained mainly by an extensive borehole dataset, reflects major depositional events during the Palaeocene–Early Eocene, Middle–Late Eocene, Oligocene–Early Miocene, Middle Miocene–Early Pliocene and Pliocene–Quaternary. These events reflect the key role of eustatic sea-level variation which, during highstands, inundated the craton margins, flooding palaeovalleys to up to 400 km inboard of the present coastline. However, a systematic eastward migration of the depocentre across the Eucla Basin during the Neogene, together with apparent flow reversals in a number of palaeovalley systems draining the Gawler Craton, suggest that the Eucla Basin has also been subject to differential vertical movements, expressed as a west-side up, east-side down tilting of ~ 100–200 m. This differential movement forms part of a broader north-down–southwest-up dynamic topographic tilting of the Australian continent associated with relatively fast (6–7 cm/yr) northward plate motion since fast spreading commenced in the Southern Ocean at ~ 43 Ma. We suggest that the evolving dynamic topography field has played a key role in facilitating development of placer deposits, largely through multistage, eastward reworking of near-shore sequences during highstand transgressive cycles on a progressively tilting platform under the influence of persistent westerly weather systems. 相似文献
157.
Giant groove casts have been found in the upper Proterozoic to Lower Cambrian Phe Formation (Haimanta Group), a siliciclastic sandstone/shale succession in the Tethyan Zone of the Higher Himalaya tectonic unit. The grooves are among the largest linear erosion structures related to submarine mass-movements observed in the geologic record. They are up to 4 m wide, about 0.2 m deep and can be traced for more than 35 m without changing their character. The grooves are straight, subparallel to cross-cutting striations with shallow semi-circular cross-sections and well-defined superimposed minor ridges and grooves. Groove casts exist on the soles of several sandstone beds within a 73 m thick logged section, commonly associated with flute casts. Their characteristics were compared with several other types of ancient and modern submarine linear erosion structures. A sand-rich, non-channelized basin floor depositional environment is inferred from the lithofacies, the combination of sedimentary structures, the lack of coarse-grained pebbly facies, the lateral continuity of beds, and the lack of channel structures. The grooves probably formed by laminar debris flows/concentrated density flows dragging blocks of already lithified sediment across the basin floor. When the bedding is structurally rotated back to horizontal, the groove casts show consistent North–South oriented palaeocurrent trends, with South-directed palaeocurrent directions indicated by flute casts. These palaeocurrent orientations contrast with previous palaeogeographic reconstructions of this area, which propose sediment delivery from the South. We therefore suggest a new “double provenance” model for the spatial relationship of late Proterozoic to Early Cambrian strata of the Himalaya, in which Lesser and Tethyan Himalayan age-equivalent sediment was deposited in a connected basin, where the former received detritus from the South, and the latter from a hitherto unknown source in the North. One possible candidate for this northern source is the South China Block and an associated Neoproterozoic volcanic arc. 相似文献
158.
R. Scott Anderson Renata B. Jass Jaime L. Toney Craig D. Allen Marcey Hess Julianna Fessenden 《Quaternary Research》2008,69(2):263-275
Chihuahueños Bog (2925 m) in the Jemez Mountains of northern New Mexico contains one of the few records of late-glacial and postglacial development of the mixed conifer forest in southwestern North America. The Chihuahueños Bog record extends to over 15,000 cal yr BP. An Artemisia steppe, then an open Picea woodland grew around a small pond until ca. 11,700 cal yr BP when Pinus ponderosa became established. C/N ratios, δ13C and δ15N values indicate both terrestrial and aquatic organic matter was incorporated into the sediment. Higher percentages of aquatic algae and elevated C/N ratios indicate higher lake levels at the opening of the Holocene, but a wetland developed subsequently as climate warmed. From ca. 8500 to 6400 cal yr BP the pond desiccated in what must have been the driest period of the Holocene there. C/N ratios declined to their lowest Holocene levels, indicating intense decomposition in the sediment. Wetter conditions returned after 6400 cal yr BP, with conversion of the site to a sedge bog as groundwater levels rose. Higher charcoal influx rates after 6400 cal yr BP probably result from greater biomass production rates. Only minor shifts in the overstory species occurred during the Holocene, suggesting that mixed conifer forest dominated throughout the record. 相似文献
159.
Haydon P. Mort Thierry Adatte Gerta Keller David Bartels Karl B. Fllmi Philipp Steinmann Zsolt Berner E.H. Chellai 《Cretaceous Research》2008,29(5-6):1008
With a multi-proxy approach, an attempt was made to constrain productivity and bottom-water redox conditions and their effects on the phosphorus accumulation rate at the Mohammed Plage section on the Tarfaya coast, Morocco, during the Cenomanian-Turonian Anoxic Event (OAE 2). A distinct δ13Corg isotope excursion of +2.5‰ occurs close to the top of the section. The unusually abrupt shift of the isotope excursion and disappearance of several planktonic foraminiferal species (e.g. Rotalipora cushmani and Rotalipora greenhornensis) in this level suggests a hiatus of between 40–60 kyrs at the excursion onset. Nevertheless, it was possible to determine both the long-term environmental history as well as the processes that took place immediately prior to and during OAE 2. TOC% values increase gradually from the base of the section to the top (from 2.5% to 10%). This is interpreted as the consequence of a long-term eustatic sea-level rise and subsidence causing the encroachment of less oxic waters into the Tarfaya Basin. Similarly a reduction in the mineralogically constructed ‘detrital index’ can be explained by the decrease in the continental flux of terrigenous material due to a relative sea-level rise. A speciation of phosphorus in the upper part of the section, which spans the start and mid-stages of OAE 2, shows overall higher abundances of Preactive mass accumulation rates before the isotope excursion onset and lower values during the plateau. Due to the probable short hiatus, the onset of the decrease in phosphorus content relative to the isotope excursion is uncertain, although the excursion plateau already contains lower concentrations. The Corg/Ptotal and V/Al ratios suggest that this reduction was mostly likely caused by a decrease in the available bottom oxygen content (probably as a result of higher productivity) and a corresponding fall in the phosphorus retention ability of the sediment. Productivity appears to have remained high during the isotope plateau possibly due to a combination of ocean-surface fertilisation via increased aridity (increased K/Al and Ti/Al ratios) and/or higher dissolved inorganic phosphorus content in the water column as a result of the decrease in sediment P retention. The evidence for decreased P-burial has been observed in many other palaeoenvironments during OAE 2. Tarfaya's unique upwelling paleosituation provides strong evidence that the nutrient recycling was a global phenomenon and therefore a critical factor in starting and sustaining OAE 2. 相似文献
160.
K. K. Singh R. P. Patel J. Singh B. Kumar A. K. Singh R. P. Singh B. L. Koul Lalmani 《Journal of Earth System Science》2008,117(3):219-225
In this paper, we report observations of unusual whistlers recorded at Jammu (geomag. lat. = 22°26′N; L = 1.17), India on March 8, 1999 during the daytime. They are interpreted as one-hop ducted whistlers having propagated along
higher L-values in closely spaced narrow ducts from the opposite hemispheres. After leakage from the duct, the waves might have propagated
in the earth-ionosphere waveguide towards the equator in surface mode. Tentative explanation of the dynamic spectra of these
events is briefly presented. 相似文献