Shallow-Water Limestones in Oceanic Basins as Tectonic and Paleoceanographic Indicators1
Seymour O. Schlanger, 1981. "Shallow-Water Limestones in Oceanic Basins as Tectonic and Paleoceanographic Indicators", The Deep Sea Drilling Project: A Decade of Progress, John E. Warme, Robert G. Douglas, Edward L. Winterer
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Limestones whose constituents were deposited in shallow water are useful indicators of post-depositional uplift, subsidence and latitudinal changes through time. A review of such limestones, drilled at several dozen DSDP sites in all of the major ocean basins, demonstrates their utility in deciphering the geologic history of major structural features and in contributing to our knowledge of paleoceanographic conditions.
Drilling in the northeast Providence Channel of the Bahamas, on the Blake Nose and off the Grand Banks of Newfoundland has extended our knowledge of the Cretaceous reef trends and carbonate shelf margins in the Atlantic passive margin province and has demonstrated subsidence of several kilometers there since Cretaceous time. The Rio Grande Rise and the Walvis Ridge both had Late Cretaceous and Eocene shallow-water histories related to their subsidence as paired aseismic ridges. On Orphan Knoll and Rockall Bank, Jurassic to Paleogene shallow-water sediments containing rich Paleocene bryozoan faunas confirm plate reconstructions for the early opening of the Atlantic. On the aseismic Ninetyeast Ridge in the Indian Ocean shallow-water sediments, including lignite deposits, directly above the basalt basement indicate a progressive subsidence history for the ridge similar to that of an island-seamount chain. In the Pacific Ocean the widespread occurrence of Campanian-Maestrichtian reef faunas from the Line Islands to the Nauru Basin-Marshall Islands leads to an interpretation of central Pacific bathymetric history reminiscent of the Darwin Rise of Menard in that mid-plate volcanism resulted in regional uplift in the central Pacific between ~ 115-110 and 70 m.y.BP. This uplift contributed to the major Cretaceous transgression during that period. Invocation of a spreading rate increase along mid-ocean ridges as the sole explanation for this transgression may not be necessary. The large benthic foraminifers of Late Cretaceous age recovered along the Line Islands and in the Nauru Basin have affinities to those of the Caribbean, indicating that the mid-Pacific atoll scene was not dominated by an Indo-Pacific fauna until Cenozoic time. Further, the Caribbean affinities of the central Pacific Late Cretaceous reef faunas lends credence to earlier suggestions that the Caribbean plate is a relic of the Farallon plate. Analysis of vertical tectonics in the Pacific shows that estimates of paleo-CCD levels should take into account periods of uplift which interrupted normal plate subsidence. Cenozoic reef debris found in turbidite units in deep-water fan deposits adjacent to the Line and Marshall islands chains record global sealevel changes. Drilling on the Emperor Seamounts has revealed Paleogene bryozoan- algal limestones whose latitude of deposition confirms paleomagnetic data from Suiko Seamount which indicate that this seamount did not form at the latitude of the present Hawaiian hot spot.
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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.