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31.
Ji&#x;í Bruthans Michal Filippi Milan Ger&#x;l Mohammad Zare Jaroslava Melkov Anna Pazdur Pavel Bosk 《第四纪科学杂志》2006,21(8):843-857
Slightly inclined Holocene marine terraces cover parts of two circular salt diapirs (Hormoz and Namakdan) in the Persian Gulf. Their relative altitude above present sea level results from a combination of general marine transgression/regression affecting the whole area, and of local uplift related to salt diapirism. Differential uplift rate of the studied diapirs in centre‐to‐rim profiles was calculated from results based on: (i) radiocarbon ages of skeletal remains of benthic faunas (19 samples), which originally grew close to sea level; (ii) original altitude of samples, estimated from general sea‐level oscillation curves for the last 10 kyr, and (iii) present sample altitude measured in the field. Calculated uplift rates increase from rim to centre on both diapirs in the range from: 2 mm yr?1 at the rim to 5–6 mm yr?1 at the interior of Hormoz, and 1–3 mm yr?1 at the rim to 3–5 mm yr?1 at the interior of Namakdan. Such uplift rate distributions fit into the parabolic profile of Newtonian fluid rather than to profiles typical for pseudoplastic fluids. The increase in uplift rate with distance from rim to centre of diapirs is gradual as demonstrated also by generally smooth surface of marine terraces. No tectonic dissections were found. The depositional history on both salt diapirs is similar although they are situated more than 100 km apart. Marine sedimentation started at about 9.6k cal. yr BP on Hormoz and at 8.6k cal. yr BP on Namakdan. Owing to rapid transgression, the sea partially truncated both salt diapirs and rapidly deepened, and carbonate mud was deposited on the peripheries of both salt diapirs. Between 7 and 5k cal. yr BP beach deposition replaced carbonate mud. Soon after 5k cal. yr BP, the sea retreated from most of the marine terraces on both salt diapirs. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
32.
Salt exposures and weathering residuum on several salt diapirs in different geographic/climatic settings were studied. Anhydrite,
gypsum, hematite, calcite, dolomite, quartz, and clay minerals are the main constituents of the weathering residuum covering
the salt diapirs in various thicknesses. Erosion rates of residuum as well as of rock salt exposures were measured at selected
sites for a period of 5 years by plastic pegs as benchmarks. Recorded data were standardized to a horizontal surface and to
long-term mean precipitation. For the rock salt exposures the following long-term denudation rates were determined of 30–40 mm a−1 for coastal diapirs and up to 120 mm a−1 for mountain salt diapirs. Long-term mean superficial denudation rate measured on weathering residuum of low thickness reached
3.5 mm a−1 on coastal diapirs. The total denudation rate estimated for the thin residuum is close to 4–7 mm a−1 based on apparent correlation with the uplift rate on Hormoz and Namakdan diapirs. Denudation of rock salt exposures is much
faster compared to parts of diapirs covered by weathering residuum. The extent of salt exposures is an important factor in
the morphological evolution of salt diapirs as it can inhibit further expansion of the diapir. Salt exposures produce huge
amounts of dissolved and clastic load, thus affecting the surrounding of the diapir. 相似文献
33.
Christian Anibas Abebe Debele Tolche Gert Ghysels Jiri Nossent Uwe Schneidewind Marijke Huysmans Okke Batelaan 《Hydrogeology Journal》2018,26(3):819-835
Among the advances made in analytical and numerical analysis methods to quantify groundwater/surface-water interaction, one methodology that stands out is the use of heat as an environmental tracer. A large data set of river and riverbed temperature profiles from the Aa River in Belgium has been used to examine the spatial-temporal variations of groundwater/surface-water interaction. Exchange fluxes were calculated with the numerical heat-transport code STRIVE. The code was applied in transient mode to overcome previous limitations of steady-state analysis, and allowed for the calculation of model quality. In autumn and winter the mean exchange fluxes reached ?90 mm d?1, while in spring and early summer fluxes were ?42 mm d?1. Predominantly gaining conditions occurred along the river reach; however, in a few areas the direction of flow changed in time. The river banks showed elevated fluxes up to a factor of 3 compared to the center of the river. Higher fluxes were detected in the upstream section of the reach. Due to the influence of exchange fluxes along the river banks, larger temporal variations were found in the downstream section. The exchange fluxes at the river banks seemed more driven by variable local exchange flows, while the center of the river was dominated by deep and steady regional groundwater flows. These spatial and temporal differences in groundwater/surface-water exchange show the importance of long-term investigations on the driving forces of hyporheic processes across different scales. 相似文献
34.
In biological wastewater treatment, bacteria tend to aggregate by forming flocs, biofilms and even granules. A large part of the floc structure in activated sludge is composed of extracellular polymers. The extracellular polymeric substances (EPS) are mainly responsible for the structural and functional integrity of biofilms/flocs and they are considered to be important for the physico‐chemical properties of activated sludge. This review considers the composition of EPS and proportion between the constituents. Moreover it includes the relationship between the EPS constituents and sludge properties such as sludge retention time, hydrophobicity and surface charge. 相似文献
35.
Two seismic agencies reported a very low double-couple percentage (DC%) of the Amfilochia earthquake, of about 30% and 60%,
by Schweizerischer Erdbebendienst and Mediterranean Very Broadband Seismographic Network, respectively. Near-regional waveforms,
carefully analyzed in this paper for the DC%, suggested a higher DC%, ranging from 75 to 100, dependent on the uncertainty
of the source position (optimum value DC% = 93). Using a statistical F test, forward modeling of the near-regional data with a single-event low-DC% source yields a significantly worse waveform
match. The fit of near-regional data can be further improved (although at the 90% significance level only) when considering
a speculative two-event model. The same model, when viewed at the very-low frequency range, reaches the very low DC% values.
However, two features make the two-event model unlikely: The two subevents strongly differ in their focal mechanism, and their
mutual separation (3.5 s) is larger than the expected duration of this earthquake. Therefore, the two-source model appears
to be nothing but an interesting equivalent representation of the non-DC model, providing some insight into the possible origin
of the apparently low DC%. Preference is given to the simple interpretation, most clearly supported by the near-regional data,
that the Amfilochia earthquake was an almost pure-shear event. 相似文献
36.
Lucie Novakova Milan Broz Jiri Zaruba Karel Sosna Jan Najser Lenka Rukavickova Jan Franek Vladimir Rudajev 《应用地球物理》2016,13(2):315-325
Underground storage systems are currently being used worldwide for the geological storage of natural gas (CH4), the geological disposal of CO2, in geothermal energy, or radioactive waste disposal. We introduce a complex approach to the risks posed by induced bedrock instabilities in deep geological underground storage sites. Bedrock instability owing to underground openings has been studied and discussed for many years. The Bohemian Massif in the Czech Republic (Central Europe) is geologically and tectonically complex. However, this setting is ideal for learning about the instability state of rock masses. Longterm geological and mining studies, natural and induced seismicity, radon emanations, and granite properties as potential storage sites for disposal of radioactive waste in the Czech Republic have provided useful information. In addition, the Czech Republic, with an average concentration radon of 140 Bq m?3, has the highest average radon concentrations in the world. Bedrock instabilities might emerge from microscale features, such as grain size and mineral orientation, and microfracturing. Any underground storage facility construction has to consider the stored substance and the geological settings. In the Czech Republic, granites and granitoids are the best underground storage sites. Microcrack networks and migration properties are rock specific and vary considerably. Moreover, the matrix porosity also affects the mechanical properties of the rocks. Any underground storage site has to be selected carefully. The authors suggest to study the complex set of parameters from micro to macroscale for a particular place and type of rock to ensure that the storage remains safe and stable during construction, operation, and after closure. 相似文献
37.
Glaciers around the world retreated as the climate warmed substantially. For the majority of alpine and arctic areas, however, the lack of meteorological data over a long period makes it difficult to build long-term climate and glacial fluctuation relationships, emphasizing the importance of natural proxy archives. Here we use the 230-year record of stem radial growth of birch trees (Betula ermanii) from the treeline forests above the receding glaciers in eastern maritime Kamchatka to analyse temporal variations of climate as well as glacial advance and retreat. Glaciers in Kamchatka Peninsula represent the southern limit of glaciation in far eastern Eurasia, which makes them prone to global warming. Using instrumental climate data (1930–1996) from local meteorological stations, we find that the July temperature had most prominent positive impact on birch growth. On the contrary, smaller ring increments are associated with the positive summer and net annual ice mass balance of Koryto Glacier. The prevailing trend of higher summer temperatures and lower snowfall over the past 70 years has enhanced tree growth while causing the glacier’s surface to lower by about 35 m and its front to retreat by about 490 m. Assuming these same relationships between climate, tree growth, and glacier mass balance also existed in the past, we use tree rings as a proxy record of climatically induced temporary halts in the glacier’s retreat over the past two centuries, which in total was over 1,000 m. Both direct observations and tree ring proxies indicate several prolonged warm periods (1990s, 1960s, 1930–1940s, 1880–1900s) interspersed with cooler periods (1984–1985, 1970–1976, 1953–1957, 1912–1926, 1855–1875, 1830–1845, 1805–1820 and 1770–1780) when the glacier re-advanced, creating several consecutive terminal moraine ridges. We conclude that birch tree-rings are suitable for assessing tree growth/climate/glacial relationships over a longer timescale in maritime Kamchatka. 相似文献
38.
The Krusné hory (Erzgebirge or Ore Mountains) has been heavily affected by high atmospheric pollutant deposition caused by fossil fuel combustion in an adjacent Tertiary coal basin. Long‐term routine sampling of bulk precipitation (1977–1996) and stream water (1977–1998) in a forested area on the south‐eastern slope of the mountains were used to evaluate trends and patterns in solute concentration and flux with respect to controlling processes. From 1977 to 1996, the annual volume‐weighted Ca2+ and SOconcentrations decreased in bulk precipitation. However, after 1989, when a pronounced and continuous decrease occurred in coal production, annual volume‐weighted concentrations decreased for most solutes, except H+. The concentration decreases were marked, with 1996 levels at or below 50% of those in 1989. The lack of a trend in H+ is attributed to similar decreases in both acid anions and neutralizing base cations. Stream water concentrations of most solutes, i.e. H+, Ca2+, Mg2+, SONOwere highest at the onset of sampling in 1977, decreased markedly from 1977 to 1983 and decreased more gradually from 1983 to 1998. The spruce forest die‐back and removal reduced dry deposition of these solutes by reducing the filtering action, which was provided by the forest canopy. A notable decrease in stream water Ca2+ concentrations occurred after 1995 and may be due to the depletion of Ca2+, which was provided by catchment liming in 1986, 1988 and 1989. Solute flux trends in bulk atmospheric deposition and stream water generally were not significant and the lack of trend is attributed to the large interannual variability in precipitation quantity and runoff, respectively. All solutes except Na+ varied seasonally. The average seasonal concentrations varied between the solutes, but for most solutes were highest in winter and spring and lowest in summer, correlating with the seasonal trend in runoff. For Ca2+, Mg2+ and SOthe concentration minimum occurs in September and the maximum occurs in February or March, correlating with the seasonal baseflow. These solutes are primarily controlled by the contribution of soil water and groundwater to stream flow. During snowmelt, the meltwater generally causes concentrations to decrease as soil water and groundwater are diluted. For NO3 , average minimum concentrations occur in August at the end of the growing season concurrent with the lowest stream flow, and the maximum occurs in February and March with high stream flow during snowmelt. Seasonal stream water NOconcentration variations are large compared with the long‐term decrease. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献