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Processes |
Atlantic Oceanographic Laboratory, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, B2Y 4A2 Canada
Detailed sampling using a very small sample size and grain-size analysis with a Coulter Counter of three fine-grained turbidites enabled a distinction to be made between the well-sorted single-grain Stokes’-deposited and unsorted ‘whole suspension’ floc-deposited grain-size populations. The results indicate that each turbidite is a continuous sequence deposited from the same source suspension. Particles settle to the bottom as flocculated masses. Initially flocs are broken up by near-bottom shear forces and only the coarsest silt and sand remains on the bed. The remaining mud forms a temporary mud suspension near the bottom which reflocculates and intermittently deposits at some critical concentration producing mud interlayers between silt laminae. Decrease in current velocity eventually allows simultaneous deposition of single grains and flocs with the latter becoming progressively more abundant resulting in formation of graded beds. Eventually, all deposition occurs in the form of mud flocs and a massive sediment results. The study essentially confirms the basic mechanism of the fine-grained turbidite deposition model proposed by Stow & Bowen (1978).
