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71.
Reflux stratabound dolostone and hydrothermal volcanism-associated dolostone: a two-stage dolomitization model (Jurassic, Lebanon) 总被引:2,自引:0,他引:2
The Kesrouane Formation, which is characterized by pervasive dolomitization, has a stratigraphic thickness that exceeds 1000 m. It is part of a broad carbonate platform deposited in the Levant region and represents 60% of the Lebanese Jurassic rocks. Two genetically distinct dolostones are recognized within this unit: (1) fine‐to‐medium crystalline non‐planar grey dolostone; and (2) coarse‐crystalline planar beige dolostone. The former is stratabound and of Early Jurassic age (87Sr/86Sr = 0·707455). This dolostone locally exhi‐bits pseudomorphs of evaporite nodules, pointing towards seepage‐reflux dolomitization by hypersaline‐ to marine‐related fluids. Exposures of the coarse‐crystalline dolostone are associated with regional pre‐Cretaceous faults, along which Late Jurassic volcanics also occur. Sedimentological and diagenetic considerations coupled with microthermometry support a hydrothermal origin for this dolostone, with TH values of primary inclusions between 50 and 80 °C. The related dolomitizing fluids are mesosaline (3·5–12·0 eq. wt% NaCl), and are believed to result from the mixing of evaporative brines and sea water. Dolomitization is thus believed to have occurred in two stages, whereby fluids invaded the host rocks first by seepage‐reflux, explaining the resulting Early Jurassic stratabound dolostone, and later through fracture flow along the faults associated with the Late Jurassic volcanism, explaining the coarse‐crystalline hydrothemal dolostone. 相似文献
72.
Microbial communities flourish at gas hydrate occurrences in ocean sediments. Studies are reported in this paper on the laboratory production, separation, characterization and hydrate catalysis of biosurfactants from cultures of the Bacillus subtilis bacterium associated with Gulf of Mexico gas-hydrate accumulations. The B. subtilis bacterium from ATCC 21332 species was cultured anaerobically with glucose as carbon-source to produce surfactin, one of the more potent surface active agents known. The surface-active agent was removed from the broth in foam created by bubbling inert gas through the mixture, and biosurfactant was then recovered from the collapsed-foam distilled water solution by acid precipitation and dichloromethane extraction. According to HPLC spectra, five surfactin isomers were identified in the sample of laboratory-generated biosurfactant. Recovered surfactin was then used to perform gas-hydrate formation studies in porous media saturated with the surfactin-water solution. Gas-hydrate induction time and formation rate determinations showed that the anaerobically-produced biosurfactants catalyzed hydrate formation markedly. The tests suggest prolific surfactin production by the B. subtilis bacterium and of other species under prevailing anaerobic conditions around seafloor gas hydrates that promotes hydrate formation and the propensity of the bioproduct to be dispersed in the porous media by natural gas vents. 相似文献
73.
This study is based on the morphosedimentary analysis of the cliff-top storm deposits accumulated on the coast of Banneg Island located in the archipelago of Molène (Brittany, France). These CTSDs comprise large, tabular clasts quarried from the upper part of the cliff and the backing scoured platform by giant oceanic storm waves impacting directly the western coast of the island. An analysis of the distribution and the geomorphology of these accumulations were carried out using the DGPS topographic surveys. Most of the clasts are organised into imbricate boulder clusters or ridges deposited between 7.5 and 14.5 masl. 52 accumulations were inventoried from the north to the south of the island, representing a global volume of 1000 m3. The median size of the clasts calculated is equivalent to 0.8 × 0.6 × 0.4 m and a weight of 0.6 t. The largest one measuring 5.3 × 3.9 × 0.5 m (≈ 32 t) is located in the centre of the island (ridge #28). It has been deposited 14 m inland from the edge of the cliff at the elevation of 9 m. Sediment analysis shows that clast sizes become smaller with increasing distance from the shoreline, but there is no relationship between the sorting and the distance inland. A study of the hydrodynamic conditions inducing clast transport was undertaken by an analysis of the wave data from the 1989 to the 1990 winter storms. Models of wave runup indicate that their highest water levels may have reached up to 19 masl, 5 to 10 m higher than the top of the cliff. Submersion by giant storm waves has been more important and frequent in the centre and the south of the island. Wave data over the 1979 to the 2007 period shows that no events as powerful as those of the 1989 to the 1990 winter were recorded during the last 30 years. Yet, it appears that the 1979–1990 decade was characterized by important morphogeneous events while the following period (1990–2007) has experienced a sharp decrease in storm events. These variations could be attributed to the inversion from a negative towards a positive phase in the North Atlantic Oscillation index. 相似文献