14 



MARINE BOTTOM SAMPLES OF LAST CRUISE OF CARNEGIE 



clay may be defined as a fine-grained deposit, ordinari- 

 ly of reddish or brownish color, in which the CaC03 

 content is less than 30 per cent and the content of detri- 

 tal or volcanic minerals and of organic remains is usu- 

 ally small. Sediments in which there are large amounts 

 of pelagic organisms are called pelagic oozes regardless 

 oftheir color or content of unaltered minerals. Normally, 

 however, as may be seen from the average values given 

 in the table and from the descriptions on preceding pag- 

 es, pelagic oozes are reddish brown to white in color, 

 and contain only small amounts of relatively coarse- 

 grained unaltered minerals. When the CaCOs content is 

 greater than 30 per cent, the deposit is usually either a 

 Globigerina or pteropod ooze. When the CaCOs content 

 is less than about 30 per cent and siliceous organic re- 

 mains are present in large amounts, the deposit is a 

 diatom or radiolarian ooze. In the Antarctic diatom 

 oozes the average content given in the table for mineral 

 particles greater than 0.05 mm in diameter is compara- 

 tively large, but this is owing to the inclusion of a few 

 samples of high mineral content. Of the seventeen dia- 

 tom oozes described in the Valdivia report, twelve con- 

 tain less than 5 per cent mineral particles of sand size. 

 As will be shown later, the remaining five samples more 

 appropriately may be designated as diatom muds. 



Terrigenous deposits called sands and muds, as 

 identified by Murray, may be distinguished by one or 

 more of the following characteristics: (1) notable 

 amounts of unaltered minerals or minerals characteris- 

 tic of diagenesis under near-shore conditions; (2) nota- 

 ble amounts of neritic organic remains; (3) less than 

 about 30 per cent of pelagic organic remains; (4) a blu- 

 ish, blackish, gray, or greenish color. Blue muds, for 

 example, are normally characterized by a bluish, black- 

 ish, gray, or greenish color, a relatively low content of 

 CaC03 and of pelagic organic remains, and the presence 

 of considerable amounts of detrital minerals. A reddish 

 or brown color, the presence of large amounts of detri- 

 tal minerals, and the absence of more than 30 per cent of 

 pelagic organic remains distinguish a red mud. A high 

 CaC03 content and the presence of large amounts of ne- 

 ritic organic remains characterize calcareous (coral) 

 muds. Green muds and volcanic muds are characterized 

 by the presence, in notable amounts, of glauconite or ■ 

 volcanic material, respectively, together with the ab- 

 sence of more than 30 to 40 per cent of pelagic organic 

 remains. In two of the Challenger samples of green mud 

 (numbers 149 and 236), however, no glauconite is record- 

 ed. 



Difficulties of the Accepted 

 C lassification 



The fundamental validity of much of the Murray 

 classification of deep-sea sediments becomes more and 

 more apparent on close consideration, and is shown well 

 by the wide applicability of the classification and by the 

 fact that it can usually be expressed in terms of the 

 physical properties and composition of the sediments. 

 There are, however, certain weaknesses in the present 

 system. 



The two basic criteria employed to distinguish pe- 

 lagic and terrigenous deposits, namely (1) the amount of 

 pelagic organic remains, and (2) the character and com- 



position of the inorganic constituents, are often contra- 

 dictory. For example, ten samples are listed by Murray 

 and Chumley which they themselves state might have 

 been called either Globigerina ooze because of the pres- 

 ence of pelagic organisms, or blue mud because of the 

 bluish gray color and the presence of detrital minerals. 

 Five samples are described by these authors which 

 might have been called either Globigerina ooze or vol- 

 canic mud from the presence of large amounts of both 

 pelagic foraminifera and volcanic material. Similarly, 

 several of the Challenger red muds from off the South 

 American coast contained, in addition to large amounts 

 of detrital mineral grains, large amounts of pelagic or- 

 ganisms, and Murray and Renard state that they might 

 equally well have been called either Globigerina ptero- 

 pod oozes, or red muds. Three cases are given by Mur- 

 ray and Chumley in which Globigerina ooze is said to 

 overlie blue mud. This has been interpreted by some 

 workers to mean that terrigenous deposits are here 

 overlain by pelagic ones, whereas in fact, aside from 

 the difference in the amount of CaC03, the deposits are 

 quite similar. From their color and content of detrital 

 minerals, the overlying Globigerina oozes might proper- 

 ly also be described as blue muds. Certain samples col- 

 lected by the Albatross off the western coast of South 

 America, which were called diatom oozes by Murray 

 and Lee because of their high content of siliceous organ- 

 isms, might also have been designated as blue or green 

 muds, judging by their color. They are quite dissimilar 

 to the typical Antarctic diatom oozes which were proba- 

 bly deposited at a much slower rate under oxidizing con- 

 ditions. Many sediments collected in the region south- 

 east of Japan contain large quantities of both pelagic 

 foraminifera and fresh volcanic material. Some of these 

 would be designated in the Murray system as volcanic 

 mud, others as Globigerina ooze, even though they appar- 

 ently form a continuous series, the relatively low CaCOs 

 content of which is not owing to depth or other physical 

 factors but merely to dilution by volcanic materials. 



The color terms used in the description of some of 

 the types of terrigenous deposits are occasionally anom- 

 alous or misleading. To illustrate, there are many 

 green-colored sediments occurring off the west coasts 

 of North and South America which appear to contain no 

 glauconite and therefore would be called blue muds in 

 the Murray system, even though they are similar in ev- 

 ery other respect to the glauconite-bearing sediments of 

 the same region which are called green muds. Likewise, 

 Stetson (1933) was obliged to describe certain deposits 

 from the Arctic as blue mud, because of the presence of 

 minerals of continental type, even though the deposits 

 are chocolate brown in color. 



The simple deposit types of Murray and Renard hold 

 quite satisfactorily for deposits made up of pure materi- 

 als. The fact is, however, that many deep-sea deposits 

 are not pure but contain a number of constituents of var- 

 ious origins. Thus two sediments, whose major constit- 

 uents are the shells of pelagic foraminifera and which 

 consequently would be called simply Globigerina ooze in 

 the Murray system, may differ widely with respect to 

 the physical characters and composition of their other 

 constituents, and these differences may indicate that the 

 two sediments were formed under dissimilar conditions. 

 It is desirable, therefore, to take such differences into 

 account by subdividing many of the Murray deposit types. 



