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Abstract

Submarine slopes are distinctive depositional environments because of their gradients and their setting between sediment source locales at their upper level and areas more favorable for preservation on basin floors beyond. The model for slope sedimentation must incorporate such factors as structural framework, gradient, dissection,type and rate of sediment input, and transport processes. Slopes are most often envisioned as inclined planes reflecting depositional instability, i.e., temporary resting places for sediments during their passage to depositional sites in deeper, more distal environments. Sediments are, however, preserved in a multiple set of slope subenvironments, and there are criteria for recognizing most of these.

The dominant slope assemblage comprises fine-grained pelagic deposits, hemipelagic materials influenced by bottom current activity (ana often entirely reworked by benthic organisms), turbidites with their mixed faunas andmineralogy, contorted slumped units, and large allochthonous slices. Distinguishing paleoslope from paleobasin deposits is generally difficult because of the merging of sedimentary facies in the two environments. Marine geological investigations have shed light on the three-dimensional geometry, vertical-lateral facies relationships, sedimentary properties and processes on modern slopes. These studies, combined with investigations of paleoslopedeposits in certain Cretaceous and Tertiary flysch basins in the Alps and Carpathians, allow more precise paleogeographic interpretations.

Channel deposits, coarse fills of submarine canyons and valleys answering the description of fiuxolurbidiles, are important in this respect. The shoe-string bodies migrate downslope and incise pelagic and bottom-current transported units and turbidite bundles. These fills of former sedimentary funnels are well developed on lower slopes, subsea fans and rises, and can be traced well into basins; they need not necessarily be geographically proximal to source. Associated primary structures indicate that traction and grain-flow processes are significant in the deposition of submarine channel units.

In association with these channels, wedges of pebbly mudstone often occur at the base of the slopes and, where concentrated, signal the position of a predominent decrease in gradient. Large, often rounded, blocks and boulders enrobed in contorted mud suggest conditions of rapid sedimentation, as off river mouths or along rapidly eroded coastlines where materials are periodically moved across narrow shelves and then en masse, onrelatively steep slopes, in and between canyons. The assemblage of channel, pebbly mudstone, and slump deposits define paleoslope and basin trends, pin-point source input along ancient basin margins, and serve to distinguishlateral from longitudinal dispersal patterns.

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