Dill 



Small objects, such as tin cans, are covered by a deposit of fine- 

 grained sediment, showing that although larger objects cause scour, 

 smaller ones do not. The sediment cover shows that, in general, the 

 continental slope at the present time is an environment of deposition. 



Fine-grained sediment, brought to the shoreline by rivers, form 

 clouds of dense, dirty water that slowly spread seaward along the bot- 

 tom as a turbid layer (Moore, 1960; Vernon, 1965). This material is 

 kept is suspension by bottom currents and swell-induced surge as it 

 crosses the continental shelf. When these suspended particles 

 encounter the relatively quiet waters over the gently sloping contin- 

 ental slope (less than 10 degrees) they are no longer kept in suspen- 

 sion by storm surges and bottom currents, and build up as a prograd- 

 ing sedimentary deposit (Moore and Curray, 1963). The occurrence 

 of relatively thick deposits of sediment have been verified by sub- 

 bottom acoustic profiles across most of the continental slopes of the 

 world. It is then very important to note that the terraces and sea 

 cliffs discussed herein are not covered by such sediments. They must 

 be older than the sediment covering most of the continental slope and 

 yet young enough not to have been covered. In most instances the 

 fine-grained sediments are capable of being deposited on relatively 

 steep slopes. Submersible observations in areas of sub-bottom 

 acoustic profiles have shown stable sedimentary deposits up to ten 

 or even hundreds of feet thick develop on slopes of over 40 degrees, 

 a value much greater than the average continental slope. The lack 

 of a sedimentary cover on the terrace and sea cliffs therefore indi- 

 cates there has not been a large enough supply or sufficient time to 

 bury these features. Youth must be the other criteria for the exist- 

 ence of the terraces; the late Pleistocene age of associated fossils 

 support this contention. 



Significance of Terraces and Sea Cliffs 



Geologically speaking, we are looking at a slope that has been 

 formed in the last 'few minutes" of earth time. A world-wide cor- 

 relation of the terraces at similar depths would indicate that tectonic 

 (mountain building) forces have not had time to warp and modify the 

 continental edge since their formation. The occurrence of shallow- 

 water fossils, those that lived in depths of less than 60 feet, in 

 water ten times that depth, must indicate a greatly lowered sea 

 level. We know that the great ice sheets that covered much of the 

 continents during the Late Pleistocene lowered sea level; however, 

 the deepest proposed lowering until now has been about 480 feet 

 (Curray, 1960, 1965; Donn, et al. , 1962; Shepard, 1964; Garrison 

 and McMaster, 1966). The wide-spread, 600-foot terrace indicates 

 a greater lowering of sea level than heretofore suspected. 



Large numbers of bottom fish are associated with the rocky 

 areas. They do not venture far from the protection of the ledges 

 and, at high frequencies, would constitute a definite, false- echo 

 problem because of their air bladders. Large schools of an unknown 



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