To estimate properties with some reliability, the designer must 

 know some marine sedimentology . Fortunately, the basic concepts are 

 simple. First, one must determine whether the sediments are land- 

 derived (terrigenous) or ocean-derived (pelagic). Figure 2-1 gives an 

 overall view of the ocean sediment distribution throughout the world. 



2.3.1 Near- Shore Areas 



One may assume that all continental shelves and slopes are ter- 

 rigenous; also, virtually all seafloor features labeled "abyssal plains" 

 have basically terrigenous components.* In a few areas of the world 

 (North Atlantic or the far Northwest Pacific), other significant terrige- 

 nous deposits may well be found beyond the continental slope as a 

 result of being downwind from major deserts . An engineer working in 

 these areas should consult an expert from a nearby oceanographic 

 institution for local information, the literature of marine geology, and 

 ocean engineering research institutions, such as the Civil Engineering 

 Laboratory. This consultation should be for all areas and for all initial 

 searches by ocean engineers with little background in geotechnology . 



2.3.2 Deep Ocean Areas 



The sediments of the deep ocean basins far from land are deter- 

 mined by two factors: (1) sea surface biological productivity and 

 (2) dissolution of calcium carbonate. Where productivity is high (such 

 as the northern Pacific near the Aleutians, equatorial Pacific, and the 

 region surrounding Antarctica), one finds siliceous ooze, a sediment 

 composed of the remains of organisms whose hard parts are opaline 

 silica. In those areas where calcium carbonate dissolution is less than 

 the carbonate supply, calcareous ooze (a sediment composed of the 

 remains of organisms whose hard parts are calcium carbonate) may be 

 found. At water depths shallower than the calcite compensation depth 

 (CCD), calcareous sediments are almost always found. The sediment is 

 defined as a calcareous ooze if its calcium carbonate content is more 



*These were probably brought down by turbidity currents. 



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