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171.
It is proposed that Akasofu's substorm parameter be interpreted as the electromagnetic power flux which enters the magnetosphere from the solar wind. 相似文献
172.
Camerlenghi Angelo Domack Eugene Rebesco Michele Gilbert Robert Ishman Scott Leventer Amy Brachfeld Stefanie Drake Allison 《Marine Geophysical Researches》2001,22(5-6):417-443
We present the results of a marine geophysical investigation of the northern Prince Gustav Channel. By comparative analysis of multibeam bathymetric data, single channel seismic reflection profiles, underway chirp sonar data, ADCP current data and sediment coring, we define the main morphological elements of the area. In particular we define the glacial morphogenesis in relation to the excavation of inner shelf basins and troughs along structural discontinuities and lithologic boundaries. We identify streamlined surfaces that testify to the grounding of ice and past ice flow directions. These glacial forms are found only on glacial tills preserved in the deepest part of the basins, while net erosion to bedrock has occurred elsewhere. Since the Last Glacial Maximum (LGM), the relict glacial morphology has been draped by hemipelagic and diatomaceous mud, and bottom currents have played a major role in focusing sedimentation within small depocentres, that we define as contouritic drifts. Based on shallow sediment architecture and supported by direct measurements, we propose that the direction of bottom water flow is from the outer shelf into the Prince Gustav channel as a result of a combination of tidal currents and ice shelf-related thermohaline circulation. 相似文献
173.
Detailed analysis of the morphology of Bacino Bannock, a deep-sea basin filled by a hypersaline brine, shows with unusual
detail the effect on the ocean floor topography of the deformation and dissolution of a salt body under tectonic stress. Although
salt diapirism occurs in the central part of the investigated area, the major cause of basin formation is dissolution of subsurface
evaporites which creates negative relief that exceeds by about one order of magnitude the positive relief. The true shape
of the deformed salt deposit is preserved as a result of the absence of a thick post-evaporites sedimentary cover. 相似文献
174.
Ana María Sato Hugo Tickyj Eduardo Jorge Llambías Miguel Angelo Stipp Basei Pablo Diego Gonzlez 《Gondwana Research》2004,7(4):1077-1087
The Las Matras Block in Central Argentina constitutes the southernmost part of the Cuyania terrane, which was accreted to the southwestern margin of Gondwana during the Early to Mid Ordovician Famatinian orogeny. The Grenville-aged rocks of the Las Matras Block are represented by the tonalitic to trondhjemitic Las Matras pluton. A new U-Pb conventional zircon age of 1244±42 Ma confirms previous Sm-Nd and Rb-Sr isochron ages of this pluton. Mineral composition data are consistent with the tonalitic-trondhjemitic character of the pluton, and constrain its emplacement level to 1.9 to 2.6 kb. This shallow level of emplacement and the undeformed character of the pluton are distinctive features of this southernmost basement. A regional comparison indicates that the igneous-metamorphic evolution of the Grenville-aged basement rocks of the Cuyania terrane occurred over a period of more than 200 million years, with ages older than 1200 Ma up to those close to 1000 Ma. The shallowest crustal level is found in Las Matras, suggesting a southward shallowing of the exposed level of basement. The deformation and metamorphism associated with the collisional Famatinian orogeny affect both the Cuyania terrane and the adjacent western margin of Gondwana, and the Gondwana margin was also the locus of the related arc magmatism, but the compressive effects of the collision decrease in intensity toward the south. The Famatinian metamorphism and magmatism continue even further south into the Patagonia region, but the southern continuity of the Cuyania terrane into this region remains uncertain. 相似文献
175.
Marco Murru Concetta Ferrara Stefania Da Pelo Angelo Ibba 《Comptes Rendus Geoscience》2003,335(2):227-238
The Palaeocene of southern Sardinia includes a continental ferruginous sedimentation, with a high content of Al and Fe, indicative of a subhumid tropical climate. The subsequent microcodium carbonated detrital microcodium levels, containing an abundant quartzose fraction, rather suggest semiarid conditions. In SW Sardinia, the marine deposits, referred to Late Thanetian–Lower Ypresian (=Ilerdian) times, are limestones including larger foraminifers and contain significant amounts of quartz. A lower content of detrital kaolinite points a sediment source from the surrounding areas with a semiarid climate. The occurrence, at the top of this unit, of small trochospiral rotaliids and larger amount of detrital kaolinite suggests a transition to a rainy tropical climate in the adjacent areas. These limestones pass gradually to carbonate sediments characterized by large amounts of detrital kaolinite and intercalated coal layers, with pollen of tropical palms, attributed to the Late Ypresian (=Cuisian)–Early Lutetian and referred to a humid-subhumid tropical climate. 相似文献
176.
177.
Within observational accuracy, the radiation pressure 1/3aT
4 at the effective solar temperature is equal to the coronal gas pressurenkT. This suggests a radiative-gas discontinuity between optically thick and optically thin regions. Ideal transitions of this nature are studied and the applicability of this model to the Sun is explored. Further empirical corroboration is obtained if the gas pressure anomalies of Gulyaev are resolved by postulating a corrective gradient of radiation pressure possibly caused by Lyman- opacity. 相似文献
178.
A. Camerlenghi 《Marine Chemistry》1990,31(1-3)
A brief review of the geological knowledge on the anoxic basins of the eastern Mediterranean is presented. Anoxic basins have been discovered in two different geological settings in the eastern Mediterranean. Bannock Basin belongs to the compressional style of the Mediterranean Ridge, and Tyro and Poseidon Basins belong to the transcurrent tectonic style of the Strabo Trench. The origin of the basins is subsurface salt dissolution triggered by tectonic deformation of the sediments on the Mediterranean Ridge, and tectonic subsidence (pull-apart mechanism) in the Strabo Trench. The onset of a deep-sea brine lake is always related to the outcrop of Messinian salts on the side-walls of the basin. The rate of basin subsidence controls the evolution of the brine lakes, which can also be completely diluted by bottom water circulation. 相似文献
179.