81 



be among the coarsest on the shelf, and (2) moderately-and 

 poorly=sorted sediments occur among the relic sands and 

 sediments containing an abundance of authigenic minerals and 

 shell fragments. 



The nearshore relic materials, which are both red sands 

 and rock fragment sands, often contain significant amounts of 

 gravel or silt and clay. Both cause a wider spread of the 

 grain-size distribution and create the areas of moderately- 

 sorted sediment o The moderate sorting of these sediments 

 caused by gravel is inherited from their original period of 

 deposition. The sorting value resulting from the silt and 

 clay may have either originated during the last stages of 

 deposition, or as a result of the accumulation more recently 

 of a thin cover of fine-grained detritus over the relic 

 material. Moderate and poor sorting in the offshore sedi- 

 ments containing relic sands or gravels are probably due to 

 the same reasons. Poorly-and moderately-sorted sediments on 

 the outer shelf ha-ve coarse fractions composed of authigenic 

 minerals and shell fragments and a patchy distribution similar 

 to that observed in sediment size. Any processes which tend 

 to concentrate coarse material, such as winnowing away of fine 

 material or removal of this material from highs and subsequent 

 deposition in depressions, create "depression" sediments which 

 are poorly-and moderately-sorted, and "high" sediments which 

 may be well-or moderately-sorted. The intervening purely 

 detrital sediments on the central shelf and those on the shelf 

 off the Malibu coast are all well-sorted. 



