Late Miocene hiatuses and related events in the Central Equatorial Pacific : their depositional imprint and paleoceanographic implications

Dorn, Wolfgang Ulrich
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Most studies of Cenozoic hiatuses in deep-sea sediments have been restricted to stratigraphic problems in regions where sedimentation rates are relatively high, carbonate deposition prevails, or the erosional activity of bottom currents had been previously established. This dissertation presents a study of hiatuses recorded in predominantly siliceous, slowly deposited abyssal sequences and concentrates on changes in sedimentological properties across the hiatuses. In Middle-Upper Miocene piston cores K78-5-10 (7.4°N, 169.6°W) and M70-17 (7.5°S, 161.6°W) hiatuses have been identified which, on the basis of integrated radiolarian, diatom, and magnetostratigraphic data, correlate with hiatuses NH3(NH4?), NH5, and NH6 (about 12.6-10.4, 8.9-7.9, and 7.1-6.3 Ma). Both sites lie in the Central Basin of the Equatorial Pacific, below the carbonate compensation depth (5475 m and 4721 m) where sedimentation is dominated by siliceous brown clays that contain radiolarians, authigenic minerals, and volcanic debris. The hiatus intervals occur within the Diartus petterssoni, Didymocyrtis antepenultima, and Didymocyrtis penultima radiolarian zones and are associated with distinct textural, mineralogical, and sedimentological variations detected in X-radiographs, X-ray diffraction analyses, silt-size particle analyses, and compositional analyses of the coarse fraction. Further evidence for the occurrence of distinct depositional changes related to the hiatuses is derived from anisotropy of magnetic susceptibility (AMS) measurements and magnetic grain-size analyses. Intensification of bottom currents seems to be the immediate cause for hiatuses in deep-sea sediments in the Central Basin of the Equatorial Pacific. A comparison of NH6 occurrence with graphic correlation plots of selected DSDP Sites, a recently revised global coastal onlap curve, and stable oxygen and carbon isotope curves, however, points to relative sea-level changes as a potential trigger mechanism. In particular, the data support a relationship between hiatus occurrence and relative sea-level highstands, followed by coastal offlaps, interpreted as indicating falling sea level, and correlating with the cessation of hiatus intervals. Based on data associated with the occurrence of hiatus NH6, a speculative, sea-level dominated depositional model is outlined, which explains the occurrence of marine hiatuses in various depositional environments, regardless of water depth.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1987.
Bibliography: leaves 150-164.
xiii, 164 leaves, bound ill. 29 cm
Marine sediments -- Central Pacific Basin, Paleoceanography -- Central Pacific Basin
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Geology and Geophysics; no. 2151
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