80 HISTORY OF THE OCEANS 



parent that present rates vary between 0.4 to a little over 1 cm/ 

 1000 years for calcareous material and from 0.05 to 0.5 cm '1000 

 years for clay. These ranges might be used as a first approximation 

 in estimating time in thickness computations. After computations 

 have been made of the amounts of original deposits in any specific 

 locality, the application of any generalized rate of deposition will 

 yield an estimated age for the deposit. 



Obviously any age computations based on these rates are 

 nebulous in that ancient rates of sedimentation are, at best, 

 only poor estimates. The results of this method, however, when ap- 

 plied to various localities, fall into the category of evidence which 

 indicates ancient age of the ocean basins, namely Paleozoic to 

 pre- Paleozoic. 



Summary 



A very important job is to be done in computing the volume of 

 sediments presently in the ocean basins of the world. To do this 

 properly it will be necessary to have at hand a much more compre- 

 hensive seismic survey coverage of the ocean basins; the surv^eys 

 will have to be classified by environment into basins, ridges, con- 

 tinental shelves and slopes, and similar areas which contain varying 

 thicknesses of sediments owing to their location and sedimentary 

 history. It must also be decided whether or not the lower layers 

 are the lithified equivalents of the upper layers and /or other 

 different sediments deposited under different conditions. 



The concepts of this paper will not apply to all sections measured 

 seismically in the oceans. As more and more evidence is deri\'ed 

 about the sea floor, we realize that generalizations are likely to 

 be untenable. Near volcanic islands and ancient drowned islands, 

 the sediments of the archipelagic aprons are likely to be thick and 

 composed of pyroclastics, erosional debris, lava flows, and clay 

 and organic material settling from the upper waters. The seismic 

 picture is undoubtedly complicated in many areas by volcanic 

 effusions building up into seamounts, seaknolls, or intruded into 

 the sediment column. Fractured zones and areas of slumping and 

 lack of accumulation are further complicating problems. Some areas 



