944 resultados para parameter instability
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Over 30 first and last occurrence (FO and LO, respectively) planktonic foraminifer datums were recognized from the Oligocene-Miocene section of Ocean Drilling Program (ODP) Site 1148. Most datum levels occur in similar order as, and are by correlation as probably synchronous with, their open-ocean records. Several datum levels represent local bioevents resulting from dissolution and Site 1148's unique paleoceanographic setting in the northern South China Sea. An age of 9.5-9.8 Ma is estimated for the local LO of Globoquadrina dehiscens (257 meters composite depth [mcd]), whereas the local LO of Globorotalia fohsi s.l. (301 mcd) is projected to be at ~13.0 Ma and the local FO of Globigerinatella insueta (367 mcd) is projected to be at ~18.0 Ma. The combined planktonic foraminifer and nannofossil results indicate that the Oligocene-Miocene section at Site 1148 is not complete. Unconformities up to 2-3 m.y. in duration, occurring at and before the Oligocene/Miocene boundary (OHS1, OHS2, OHS3, and OHS4 = MHS1), are associated with slump deposits between 457 and 495 mcd that signal tectonic instability during the transition from rifting to spreading in the South China Sea. Shorter unconformities of <0.5 m.y. duration that truncate the Miocene section were more likely to have been caused by sea-bottom erosion as well as dissolution. A total of 12 Miocene unconformities, MHS1 through MHS12, are mainly affected by dissolution and an elevated carbonate compensation depth (CCD) during Miocene third-order glaciations recorded in deep-sea positive oxygen isotope Mi glaciation events. Respectively, they fall at ~457 mcd (MHS1 = Mi-1), 407 mcd (MHS2 = Mi-1a), 385 mcd (MHS3 = Mi-1aa), 366 mcd (MHS4 = Mi-1b), 358 mcd (MHS5 = MLi-1), 333 mcd (MHS6 = Mi-2), 318 mcd (MHS7 = MSi-1), 308 mcd (MHS8 = Mi-3), 295 mcd (MHS9 = Mi-4), 288 mcd (MHS10 = Mi-5), 256 mcd (MHS11 = Mi-6), and 250 mcd (MHS12 = Mi-7). The correlation of these unconformities with Mi events indicates that some related driving mechanisms have been operating, causing deepwater circulation changes concomitantly in world oceans and in the marginal South China Sea.
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Electron microprobe and thermomagnetic analyses of selected basalt samples from Hole 597C were performed. The main purpose of this work was to investigate and estimate the degree of oxidation of the samples using the ratios of Fe to Ti and the Curie temperatures obtained from thermomagnetic curves. The results show that the magnetic properties of samples from Hole 597C change at a sub-bottom depth of 100 m, and that low-temperature and high-temperature oxidation processes prevailed above and below 100 m, respectively.
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Clay minerals recovered from the Galapagos hydrothermal mounds (Holes 506C, 507D, and 509B) are mainly iron-rich nontronite-like minerals enriched in potassium. Nontronites from Hole 509B show a distinct tendency to become micaceous toward the lower beds of clay sediments. Mn-crusts consist mainly of todorokite or a mixture of todorokite and nontronite. Minerals of clay and Mnrich sediments in the mounds originated from hydrothermal solutions of uncertain origin. Pelagic oozes from hydrothermal mounds and from areas between mounds (Hole 506D) consist mainly of calcite. In the carbonate beds on or near the hydrothermal mounds an admixture of smectite is often found.
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National Highway Traffic Safety Administration, Washington, D.C.
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National Highway Traffic Safety Administration, Washington, D.C.
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Mode of access: Internet.
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"June 1977."
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Mode of access: Internet.
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Federal Highway Administration, Office of Research and Development, Washington, D.C.
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National Highway Traffic Safety Administration, Washington, D.C.
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"HRDI-13/11-08(1M)E"--P. 4 of cover.
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Thesis (M.S.)--University of Illinois.
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"UILU-ENG 77 1714."
