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This report synthesizes X-ray mineralogy data from Sites 194, 195, 196, 198, and 199 of Leg 20 in the far western Pacific. The discussion attempts to characterize the mineralogy of various lithostratigraphic horizons insofar as sample material permits. In view of the intermittent coring, a high degree of sample disturbance, and low core recovery, it is not certain whether the samples are representative of the sedimentary section at the sites drilled. Hence, our conclusions must be viewed as tentative. Ewing et al. (1968) have identified four acoustic layers in north Pacific deep-sea sediments. These layers are (1) the upper transparent layer, (2) the opaque layer, (3) the lower transparent layer, and (4) the lower opaque layer (also called Horizon B). These sedimentary intervals overlie a rugged, acoustic basement. This generalized acoustic stratigraphy was recognized in the far western Pacific by Leg 20 scientists. One of the objectives of Leg 20 was to obtain a general understanding of the age and lithology of these major acoustic intervals. Portions of the upper transparent and opaque intervals were drilled at Sites 194, 195, 196, and 198. Shipboard scientists separated the upper transparent interval into two sedimentary suites: (1) a Holocene to late Miocene volcaniclastic silty clay sequence overlying (2) an early Tertiary to Late Cretaceous pelagic clay sequence. The volcaniclastic sediments form a wedge which thins to the east and south, away from the western Pacific island arcs, and which overlaps the pelagic sediments. Shipboard scientists attributed the origin of the volcaniclastic wedge to volcanic arcs in the western Pacific. Sediments from the volcaniclastic suite were X-ray analyzed from Sites 194, 195, and 196. The underlying pelagic clays were sampled for X-ray analyses at Sites 196 and 198. Pelagic clays of the upper transparent interval gradationally overlie the acoustically opaque interval. The opaque interval was found to consist of Cretaceous clays and calcareous clays frequently interbedded with chert. No samples were submitted for X-ray analyses from the opaque interval, although samples were submitted from the transitional interval between the upper transparent layer and the opaque layer at Site 198. No samples were submitted from the lower transparent or lower opaque intervals. Site 199, in the Caroline Basin, does not exhibit the characteristic succession of transparent and opaque acoustic layers. Instead, Site 199 consists of a thick sequence of volcanic-ash-rich acoustically transparent sediments. Hence, Site 199 is discussed apart from other Leg 20 sites.

X-Ray Mineralogy of Sediments from the Far Western Pacific, Leg 20, DSDP