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Many of the fundamental characteristics of abyssal plain turbidites may be traced in the modern calcareous turbidites of the Tongue of the Ocean. However, less broad areas of coverage and greater diversity of the constituents are evident from the Tongue of the Ocean than would be expected in abyssal plain deposits. This difference reflects a narrower depositional basin and several localized sources, each with its own materials.
The abyssal plain deposits are laterally transported cyclic-graded beds of terrigenous sand, silt, and clay alternating with possibly minor layers of true pelagic sediment consisting of the vertically (particle by particle) settled clay components characteristic of red clays. The cyclic units are monotonously similar, with no outstanding distinctions between them except for thickness and maximum grain size, and are of broad areal extent.
The Tongue of the Ocean deposits are also cyclic, but the turbidites consist of bioclastics, pteropods, foraminiferal sands, and calcareous silts and clays; the pelagic beds between are homogeneous calcareous clayey silts (calcilutites) with varying amounts of Foraminifera and pteropods. The sediments are primarily calcareous silts in contrast to the terrigenous clays of the abyssal plain. Cyclic units vary in composition and are only locally distributed.
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