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281.
282.
Gas in sediments has become an important subject of research for various reasons. It affects large areas of the sea floor
where it is mainly produced. Gas and gas migration have a strong impact on the environmental situation as well as on sea floor
stability. Furthermore, large research programs on gas hydrates have been initiated during the last 10 years in order to investigate
their potential for future energy production and their climatic impact. These activities require the improvement of geophysical
methods for reservoir investigations especially with respect to their physical properties and internal structures. Basic relationships
between the physical properties and seismic parameters can be investigated in shallow marine areas as they are more easily
accessible than hydrocarbon reservoirs. High-resolution seismic profiles from the Arkona Basin (SW Baltic Sea) show distinct
‘acoustic turbidity’ zones which indicate the presence of free gas in the near surface sediments. Total gas concentrations
were determined from cores taken in the study area with mean concentrations of 46.5 ml/l wet sediment in non-acoustic turbidity
zones and up to 106.1 ml/l in the basin centre with acoustic turbidity. The expression of gas bubbles on reflection seismic
profiles has been investigated in two distinct frequency ranges using a boomer (600–2600 Hz) and an echosounder (38 kHz).
A comparison of data from both seismic sources showed strong differences in displaying reflectors. Different compressional
wave velocities were observed in acoustic turbidity zones between boomer and echosounder profiles. Furthermore, acoustic turbidity
zones were differently characterised with respect to scattering and attenuation of seismic waves. This leads to the conclusion
that seismic parameters become strongly frequency dependent due to the dynamic properties of gas bubbles. 相似文献
283.
Another Revision of the Saprobic Index ‐ Why and What For? The 1990 revision of the German standard DIN 38410 “Determination of the Saprobic Index in Running Waters” had to be revised again in the course of a periodical updating due to the DIN regulations. Thus, practical experience can be taken into account as well as scientific development and the legal requirements. In this work, modifications of the standard are explained as far as it is not done within DIN 38410. Additionally, emerged suggestions and critiques are discussed. The necessity of quality assurance is especially emphasized. An essential part of the revision is the considerable enlargement of the list of indicators (macro‐ and microorganisms). Beside this, type‐specific ranges of the saprobic index are presented for the reference status in all types of German rivers. Consequently the saprobic system may be used as a metric for the biological assessment with the benthic fauna within the implementation of the European Water Framework Directive. Moreover, many details of the standard have been tightened up. The methods for further enlargements of these lists will also be described, especially the proceeding for the inclusion of neozoic organisms as indicators within the saprobic system. A formula concerning the statistical securing of the saprobic index is not given anymore, mainly because of the high variability of habitats and biocoenses in pristine environments. Further information for quality assurance is given as well. 相似文献
284.
285.
Dr. Friedrich Lippmann 《Contributions to Mineralogy and Petrology》1954,4(1-2):130-134
Zusammenfassung Durch röntgenographisehe und differentialthermoanalytische Untersuchungen wurde in einem roten Keuperton (km 3) von Zaisersweiher bei Maulbronn ein quellfähiges chloritisches Mineral (Corrensit) als Hauptbestandteil gefunden, das sick durch doppelten Basisabstand (28 Å) auszeichnet. Daneben treten Illit (Glimmer) und Quarz auf. Nebengemengteile sind Hämatit und Feldspat.Herrn Professor Dr.Carl W. Correns zum 60. Geburtstag gewidmet. 相似文献
286.
Magnetic mineralogy of Chinese loess and its significance 总被引:19,自引:0,他引:19
Xiuming Liu John Shaw Tungsheng Liu Friedrich Heller Baoyin Yuan 《Geophysical Journal International》1992,108(1):301-308
287.
288.
289.
Friedrich Leyden 《International Journal of Earth Sciences》1922,13(1):18-40
Ohne Zusammenfassung 相似文献
290.
A geochemical rock- and soil-sampling program was carried out in the vicinity of eight concealed “Cyprus type” deposits, occurring in marginal mafic to intermediate metapillow lavas of the Troodos Ophiolite Complex. The mineralization of massive and stockwork sulfide ore is characterized by the predominance of pyrite, intergrown with less chalcopyrite and minor amounts of sphalerite.Background values of Hg are in the range of 8–12 ppb for soils and 3–6 ppb for surface rocks. Anomaly/background ratios of 10:1 (soils) and 5:1 (rocks) have been found only, where Hg migrated along channels formed by faults cutting shallow-seated mineralization. Here, Hg sometimes shows significant correlations with Cu, Zn, Ba and exceptionally with Co. However in one case an Hg anomaly in soils and surface rocks was detected directly over a deposit. The use of Hg as indicator element for these types of deposits is therefore limited. Buried mineralization may be delineated more distinctly by Cu, Zn and Ba. 相似文献