VII. BOTTOM SEDIMENTS 



A. General 



The distribution of bottom sediments appears to be related in a 

 general way to distance from the Antarctic Continent and depth of water. 

 The sediments sampled in depths less than 500 fathoms are principally of 

 terrigenous origin and may be classified as a marine glacial till with 

 two important exceptions: (l) the volcanic ash deposits of McMurdo 

 Sound and in the vicinity of Ross Island, Peter I Island, and other 

 volcanic features, and (2) the predominantly biological sediments with 

 an irregular and undertermined distribution. Varying amounts of organic 

 constituents are associated with the terrigenous sediments; the most 

 frequent being siliceous sponge spicules. The features common to all of 

 these sediments are the lack of chemical weathering and their poor sort- 

 ing. Ice rafting is presumably the most effective transporting agent. 



In water deeper than 500 fathoms, the few botton sediments collected 

 are composed generally of sufficient planktonic micro-organisms to be 

 classed as organic deposits, except where local conditions prevail. 

 These local variations are found in the vicinity of islands and at the 

 base of the Antarctic Contentinental Slope. Part of these sediments 

 appear to be the result of ice rafting, as well as other transporting 

 agents . 



Identifications and percentages of organic and inorganic constituents 

 are only gross approximations of the major elements comprising the sand 

 and larger fractions. In particular, any volcanic derivative is grouped 

 under volcanic glass, and pyroxene includes all ferrornagnesium minerals 

 such as augite and horneblende. Also, the percentages given for plank- 

 tonic micro-organisms, particularly at the top of cores and in grab 

 samples, are probably low since some of these constituents, especially 

 diatoms, are evidently lost during sampling and laboratory processing. 

 However, mlcro-scopic examination of the silts and comparison with the 

 coarser fractions of about one-third of the samples agreed reasonably 

 well in the diatom estimates. Perhaps the delicate forms do not occur 

 in appreciable percentages in many of the sediments since the only diatoms 

 seen in the sand fractions were two large, thick walled species of 

 Cos cinodi s cus ♦ 



B. Areal Description 



1. Ross Sea Area 



a. McMurdo Sound - The terrigenous sediments sampled in the Ross 

 Sea are divisible into two provinces depending on their source. Those 

 derived from Ross Island and associated volcanics are one of these. 

 Fifteen cores of predominantly volcanic glass and feldspar were obtained 

 by EASTWIND in McMurdo Sound. In some few cases, rock fragments or 

 organic remains comprise the primary components. 



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