Grain Size Distribution, Coarse Fraction & Mineralogy of Sediments from Five Areas in the Equatorial & Southwest Pacific

173-179Preliminary results on the grain size distribution, coarse fraction and mineralogy of a limited number of deep-sea sediments from 4 areas in a N-S transect across the equatorial Pacific (Areas C, D, F and G) and I in the southwest Pacific (Area K) are reported. The sediments have been classified according to the Folk classification. Area C sediments are generally mud and in composition siliceous ooze to siliceous mud. The median grain size normally lies between 8.7 and 9.3 φ and the acid soluble (CaCO3) content between 3.1 and 15.9%. Sample 5 KG is a siliceous debris-bearing nanno/foram ooze with a carbonate content of 88.9%. Area D sediments are sandy mud and in composition siliceous debris-bearing nanno/foram ooze with ~n acid soluble content of 91.2%. The median grain size of these sediments is 8 φ. Area F sediments are sandy silt and in composition siliceous debris-bearing nanno/foram ooze with an acid soluble content of 95.5%. The median grain size of these sediments is 7.25 φ. Area G sediments are mud and in composition siliceous debris-bearing foram/nanno ooze with an acid soluble content of 58.6%. The median grain size of these sediments is 7.75 φ. Area K sediments are mud and in composition nanno/foram bearing red clay with an acid soluble content of 14.4%. The median grain size of these sediments is 8.95 φ. Very poorly sorted sediments are encountered in Areas D and F which lie near to the equatorial high carbonate zone and are characterised by high carbonate contents. The sorting of the sediments improves away from the equatorial region due to lower carbonate contents in the sediments. In the coarse fraction ( > 63 µm), radiolaria/siliceous matter predominates in the siliceous ooze sediments from Area C whereas foram/calcareous matter is the dominant constituent of the sediments from Areas D, F and G. Micronodules are the main constituents of the coarse fraction of the red clay sediments from Area K. Fish teeth are observed in sediments from Areas C and K while sediments from Areas D, F and G are devoid of fish teeth. The abundance of fish teeth may be related to carbonate contents of .the sediments which acts as a diluent. Mineralogically, Area C sediments are generally characterised by quartz and smectite with lesser amounts of chlorite + kaolinite, illite and plagioclase. Areas D, F and G sediments are dominated by calcite ( > 80%) with low percentages of quartz, smectite, chlorite + kaolinite, illite and plagioclase. Area K sediments are dominantly quartz and smectite. Chlorite + kaolinite, plagioclase, illite and calcite are present in moderately high percentages. Quartz, chlorite + kaolinite, illite and feldspar appear to be detrital and eolian in origin. Smectite may be authigenic in origin