The lllite-chlorite-mlnor monlrnorlllonite province is largely/ but not entirely, 

 restricted to the Arabian Sea Basin and nearby shelf areas of India and Pakistan to 

 the northeast. These are probably largely Indus River sediments. 



The illite-chlorite-no montmorillonite assemblage is generally restricted to the 

 northwest basin, including the Gulf of Oman . KaoHnite was observed as a minor 

 constituent in only five samples in the entire study region. 



H . Carbonate Mineralogy 



Quantitative analyses of the carbonate fraction mineralogy could be obtained 

 on only four samples by the techniques used (Table 2) . All of the sediments repre- 

 sented in Table 2 are from the carbonate-rich band of the outer Indian shelf. With 

 one exception, mineral percentages of these samples are typical of continental shelf 

 non-reef carbonates wherein the unstable minerals, aragonlte and high Mg calcite, 

 are dominant. The exception is sample No. 87 in which low Mg calcite makes up 

 51 percent of the carbonate fraction . 



Semi-quantitative analysis of the carbonate fraction of the other Indian shelf 

 samples indicates that low Mg calcite is usually more abundant than high Mg calcite 

 and aragonite. Deep water sediments contain mostly low Mg calcite in the carbonate 

 fraction . 



Dolomite is present In variable amounts In almost all samples. The presence of 

 dolomite was verified by both microscopic observation and x-ray diffraction analysis . 

 In general, dolomite Is more abundant In the Arabian Sea Basin and particularly on 

 the Indian continental shelf. Dolomite Is usually found in silt-size grades, but In 

 eight samples (Nos . 45, 47, 50, 51, 63, 85, 89, and 92) grains were noted in the 

 •062 to . 125 mm . size fraction . The amount of dolomite was not quantitatively de- 

 termined, but for the most part, it Is present In only trace amounts and probably never 

 makes up more than 5 or 10 percent of the carbonate fraction . Wei I -formed rhombs 

 are rare and many dolomite grains are rounded, a fact which rules out an authigenic 

 origin for this mineral . 



VI. DISCUSSION 



The northern Arabian Sea is an area of dominant terrigenous sedimentation, as 

 might be expected because of the close proximity of land on three sides and the ab- 

 sence of barriers or sediment traps near the continental margins . 



Within the deep-sea basin, the Murray Ridge has a strong influence on sedi- 

 mentation . The most obvious effect of the ridge Is Its role In damming or containing 

 the Indus cone, thus preventing deposition of Indus River materials in the Gulf of 

 Oman Basin . This effect It demonstrated by the presence of the two abyssal plains 



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