346 THE DEEP SEA 



surface, of green gray color from locally developed reducing 

 conditions. 



Some deep-sea or abyssal deposits, even though distant from 

 continents or islands, seem properly excluded from the pelagic 

 type. These include the glacial-marine, and the turbidity current 

 deposits. These are more rapidly accumulated and thus less 

 oxidized, and are likewise more similar to the hemipelagic and 

 continental sediments In llthology, mineralogy, and thus in chemi- 

 cal composition. 



Some of the deposits composed largely of the remains of plankton 

 may also be excluded, not only because these were accumulated 

 near or even on the continents, but also normally accumulate more 

 rapidly and lack the characteristic of highly oxidized components. 

 These might be termed planktonic deposits except for confusion 

 of such with those of the typical pelagic deposits composed largely 

 of plankton remains. It Is, however, this distinct kind of deposit 

 of plankton remains, lacking the highly oxidized character of 

 pelagic deposits, such as some In the Gulf of California, which 

 form the usual and perhaps only plankton accumulations known 

 in the ancient strata on the continents. Their much greater rate 

 of accumulation is commonly reflected In their thickness relative 

 to probable time, and rather than being highly oxidized like 

 pelagic sediments, these are normally high In organic matter 

 content. A thick deposit, for the amount of upper Eocene time, is 

 known as the Oceanic formation in Barbados, B.W.I., because of 

 the abundance and variety of marine planktonic remains, including 

 many Radlolaria. It lacks, however, the pelagic sediment feature 

 of slow accumulation with the highly oxidized character of the 

 iron minerals. The reported red clay in this formation has proved 

 to be limited only to weathering of some present day exposures of 

 the rocks. 



Depth of water, though normally great. Is not a factor of 

 particular significance for pelagic deposits, as Globigerina ooze on 

 guyots and banks shows the typical characteristics of pelagic 

 sediments even where accumulated at hundreds rather than 

 thousands of meters. Here it commonly shows better than average 

 sorting In grain size, but a similar relation of sorting to topography 

 is apparent In some pelagic sediments at great depths. 



