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William C. Schwab Elazar Uchupi Robert D. Ballard Thomas K. Dettweiler 《Geo-Marine Letters》1989,9(3):171-178
SeaMARC side-scan sonographs and Argo video and photographic data suggest that the recent sedimentary environment of the floor
of the Tongue of the Ocean is controlled by an interplay of turbidity current flow from the south, sediment spill-over from
the carbonate platform to the east (windward side), and rock falls from the west carbonate escarpment (lee side). The spill-over
forms a sandy sedimentary deposit that acts as a topographic obstruction to the turbidity current flow from the south. This
obstruction is expressed by the westward migration of a northwest-southeast oriented turbidity-current-cut channel. 相似文献
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P. M. Nikolić S. Ðurić D. M. Todorović D. Vasiljević-Radović V. Blagojević P. Mihajlović J. Elazar K. T. Radulović A. I. Bojičić D. Urošević 《Physics and Chemistry of Minerals》2001,28(1):44-51
Electron transport properties of single crystal and polycrystalline natural mineral galena (PbS) samples from the Trep?a mine, Yugoslavia, were determined using the photoacoustic frequency transmission technique. Their thermal diffusivity (D T≈0.16 × 10?5 m2 s?1), the coefficient of diffusion (D between 0.15×10?2 0.16×10?2 m2 s?1) and lifetime of the excess carrier (τ≈35 μs and the front and rear recombination velocity (s g≈65.5 m s?1 and s b≈66.4 m s?1, respectively), were calculated by comparing the experimental results and the theoretical photoacoustic amplitude and phase signals. The lattice parameter obtained by X-ray work was a?=5.936?Å. The free carrier concentration of these single-crystal samples was measured using the Hall method (N?=?3×1018 cm?3). Measurements of the optical reflectivity of the same samples, as a function of wavelength, in the infrared and far infrared ranges, were performed. In the far infrared range a free electron plasma frequency was observed and numerically analyzed, using the least-squares fitting procedure. The values of optical parameters were calculated and the value of the free carrier concentration obtained by the Hall method was confirmed. 相似文献
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Neogene tectonic activity (Betic Orogeny) along the southern plate boundary of Iberia, as it converged with Africa and the Alboran Plate was inserted between them, propagated along Iberia's west side as far north as Galicia, northwest Spain. As the activity propagated northward, it reactivated structures formed during the Paleozoic (Hercynian), the Early Cretaceous opening of the northern North Atlantic and the Bay of Biscay, and the Paleogene Pyrenean Orogeny when Iberia collided with Eurasia. Recent earthquakes indicate that this tectonism is still active today as far north as northwest Spain. 相似文献
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The morphology of the Gulf of Oman Basin, a 3,400 m deep oceanic basin between Oman and southern Pakistan and southern Iran, ranges from a convergent margin (Makran margin) along the north side, a passive type (Oman margin) along the south side, translation types along the basin's west (Zendan Fault-Oman Line) and east (Murray Ridge) sides and a narrow continental rise and a wide abyssal plain in the centre of the basin. Sediment input into the basin during the Late Quaternary has been mainly from the north as a result of the uplift of the Coast Makran Mountains in the Late Miocene-Pliocene. Today most of this detritrus is deposited on the shelf and upper continental slope and perched basins behind the fold/fault ridges on the lower slope. The presence of fans and channels on the continental rise on the north side of the basin indicate, however, that continental derived debris was, and possibly is, being transported to the deep-sea by turbidity currents via gaps in the ridges on the lower slope. In addition to land derived terrigenous sediments, the basin deposits also contain biogenic (organic matter and calcium carbonate), eolian detritus and hydrates and authigenic carbonates from the tectonic dewatering of the Makran accretionary wedge. The eolian sediment is carried into the Gulf of Oman Basin from Arabia and the Mesopotamia Valley by the northwesterly Shamal winds. This type of detritus was particularly abundant during the glacial arid periods 21,000–20,000 and 11,000 (Younger Dryas) years ago when exposure of the Persian (Arabian) Gulf increased the area of dust entrainment and shifted the position of the source of the eolian sediments closer to the basin. 相似文献
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The geologic history of the passive continental margin off the east coast of North America from New England to Newfoundland is described using all available geological and geophysical information. “Rift” and “drift” phases of the margin's evolution are recognized, with rifting initiated in Late Triassic and completed by Early Jurassic. The plate decoupling process created a complex block-faulted terrain as a result of uplift and tensional fracturing. The approximate plane of continental separation is marked by a “hinge zone” characterized by a pronounced steepening of basement gradients. Since the Early Jurassic, the margin has undergone continual subsidence in response to cooling and sediment loading. This “drift” sequence attains its maximum thickness in the vicinity of the continental slope and thins both landward and seaward. On the shelf, this unit consists of Mesozoic evaporites, carbonates, and deltaic deposits. Overlying these sediments is a prograding wedge of Cenozoic elastics. On the rise, the Mesozoic sediments are evaporites, hemipelagic limestones and shales and carbonaceous clays. The Cenozoic is dominantly terrigenous material. Separating these two sedimentary provinces is the continental slope, a site of major facies changes and a Mesozoic reef complex. 相似文献
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Multichannel seismic reflection profiles recorded in the northern Red Sea show structures that we interpret to be a result of the intrusion of uppermost Miocene salt. We believe that the evaporites are underlaid by attenuated continental crust and the flow of salt is due to renewed faulting of basement in the Pliocene when sea floor spreading began between latitudes 21°N and 15°30°N. 相似文献