Geologic Significance of Seismic Reflectors in the Deep Western North Atlantic Basin*
Brian E. Tucholke, 1981. "Geologic Significance of Seismic Reflectors in the Deep Western North Atlantic Basin", The Deep Sea Drilling Project: A Decade of Progress, John E. Warme, Robert G. Douglas, Edward L. Winterer
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Several major seismic horizons in the deep basin of the western North Atlantic Ocean have been calibrated according to age and physical and lithologic character by JOIDES drilling. Three horizons are discussed that are representative of the spectrum of stratigraphic relations in the basin. Horizon which ranges from Hauterivian to Barremian in age, correlates with a sharp upward transition from limestones to black clays coincident with a rise in the calcite compensation depth. In Eocene time, sediments enriched in biogenic silica were widely deposited, and subsequent diagenesis formed chert beds; the upper Lower to lower Middle Eocene surface of these cherts correlates with Horizon Ac which is one of the strongest and most widespread reflectors in the basin. Widely distributed borehole data indicate that both Horizon β and Horizon Ac normally occur within continuously deposited sedimentary sections. Beneath the continental rise, Horizon Au correlates with a major unconformity eroded between Late Eocene and Early Miocene time by southward-flowing abyssal currents. The reflector may have limited chronostratigraphic significance because of lateral migration of the abyssal current system with time. Several simple models are used to assess potential age significance of the seismic and lithologic boundaries and are compared to borehole data.
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At the present the Glomar Challenger has drilled over 500 holes over the world ocean, involving hundreds of scientists from dozens of countries. This volume is intended as a review of some of theimportant results from the most comprehensive, ambitious and successful earth-bound geologic project ever undertaken. The symposium upon which this volume originated was held April 4, 1979 at the SEPM/AAPG Annual Meeting in Houston. No comprehensive synthesis of all aspects of the DSDP has appeared, and the topic coverage in this volume is biased towards the sediments and fossils, and their significance for certain aspects of earth history – paleogeography, bathymetry, climatology, oceanography, ecology, environments – all in keeping with the audience of sedimentary geologists.