Physical Properties of Sedimentary Provinces, North Pacific and North Atlantic Oceans
The North Pacific and North Atlantic Oceans are sites of very slow and relatively rapid deposition respectively. In this brief account we describe the lithologic, textural and physical properties of sediment cores and define geographic limits of provinces of similar sediment. Values of mean grain size, wet density, moisture content, and porosity are presented.
Red clays of the North Pacific are slightly coarser than their Atlantic equivalents but have similar bulk properties. Radiolarian oozes of the North Pacific are the most porous, water-laden materials of any ocean floor. Diatomaceous sediments have bulk properties between those characteristic of red clay and radiolarian ooze. Carbonate oozes of the North Atlantic have a wider range of properties than their North Pacific counterparts. This is explained by the location of the former along the Mid-Atlantic Ridge where there is ample evidence in cores of winnowing of fines by currents. Deposits of the equatorial Pacific accumulate in a quiet deep-water environment.
Turbidites of the northeast Pacific grade from clay (Mz = 1μ) to sand (Mz — 128μ). In the North Atlantic they are far more widespread and coarser-grained. They grade from clay (Mz — 1μ) to sand (Mz — 136μ) and rarely to gravel (Mz — 1526μ). Ash layers of the North Pacific average 6 cm in thickness and have a Mz = 26μ. Hemipelagites have properties which are the same for both oceans, but ranges of textural parameters of these terrigenous sediments are greater in the North Atlantic.
Interest in physical properties of the ocean floor is experiencing something of a revival today. Mining companies, faced with problems related to exploitation of ferromanganese nodules, are studying the seabed in order to understand its nature and to assure proper design of dredge hardware. Environmentalists demand careful evaluation of all aspects of ocean mining in order to avoid possible damage to organisms living in the water column or on the sea floor. Settling properties of abyssal clays are not well understood. Additional research is needed to determine the effects of large-scale resuspension of these tiny grains on the physical and biological framework of the oceans.
The United States Navy (Naval Ship Systems Command) has shown considerable foresight by supporting investigations related to use of the sea floor as an acoustic interface. Systems analysts in military oceanography need information on the distribution of layered and uniform marine deposits along with their physical characteristics. These data are fundamental to accurate prediction of levels of sound reflection at the water-sediment interface.
This report briefly summarizes some of the results of a five-year analytical program directed at definition of physical and textural properties of ocean sediments in the Northern Hemisphere.
KeywordsOcean Floor Turbidity Current Abyssal Plain Manganese Nodule Ferromanganese Nodule
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