D . Carbonate Constituents 



The most important sand-size or larger constituents of the carbonate fraction 

 are foraminifera tests. Even in many of the continental shelf sediments, foraminifera 

 dominate the carbonate fraction. Next in abundance are calcareous chunks and 

 fragments which cannot be positively identified . Many appear to be fragments of 

 foraminifera tests; others are probably windblown grains of limestone or dolomite. 

 Mollusks ore found in appreciable quantities only in continental shelf sediments. 

 Radiolaria vary considerably in importance, ranging from to 40 percent of the total 

 coarse fraction . They are more abundant at depths below 1,000 fathoms, particularly 

 in the southeast basin. Abundant calcareous pellets were noted on the Indian outer 

 shelf in the aforementioned carbonate-rich band. These pellets are slightly phosphotic, 

 and range in size from fine to medium sand and in color from salmon to dark blue gray. 

 Some pellets strongly resemble phosphate grains. 



E . Light Minerals 



In the process of coarse fraction analysis, the quartz content of the material of 

 sand size was determined. More accurately, the "quartz" fraction includes all light- 

 colored non-carbonate minerals of which quartz is the most important constituent . 

 Plotting these percentages (Fig . 10) reveals an interesting pattern of oreol distribu- 

 tion . Northwest of the Murray Ridge, except for the inner Gulf of Oman, the deep- 

 sea sediments contain much quartz (between 14 and 70 percent) in the coarse fraction . 

 The coarse fractions of the Arabian Sea Basin sediments contain "between and 4 per- 

 cent quartz; in fact, about one-half of the samples contained no sand-size quartz. 

 It is significant that this quartz occurs on the ridge as well as in abyssal plain sediments, 



Inner continental shelf sediments generally contain significant amounts of sand- 

 size quartz; however, outer shelf sediments of the Indian and Pakistan coast contain 

 mainly calcium carbonate and generally less than 5 percent quartz of this size . 



Most samples contain an insufficient amount of light mineral, non-carbonate 

 fraction of sand-size to justify quantitative mineral determinations . It was possible, 

 however, to determine the quartz and feldspar content of the non-carbonate sand 

 fraction of eight samples. The results of these determinations are shown in Table 1 . 

 Indian shelf samples Nos . 45 and 46 are from the Gulf of Combay, and sample No. 

 89 was collected near the Gulf of Kutch (Fig. 2). The remaining five samples are 

 deep-sea sediments from the southwestern corner of the study area near the Arabian 

 coast . In every sample, quartz is more abundant than both of the feldspars combined, 

 and plagioclase is more common than orthoclase. The two samples from the Gulf of 

 Combay exhibit unusually high plagioclase contents^ 35 and 36 percent, as compared 

 to values between 14 and 21 percent for the remaining samples . The orthoclase con- 

 tent is less variable and ranges between 5 and 12 percent for all samples. 



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