The geochemistry and mineralogy of some N.W.Indian Ocean D.S.D.P. cores (sites 222 and 223, leg 23, deep-sea drilling project)

Deep-sea cores recovered from the N.W. Indian Ocean during Leg 23 of the Deep-Sea Drilling Project were subjected to geochemical and mineralogical analysis. The examined core material was from Sites 222 and 223. Site 223 was drilled on the margin of the Owen Basin on the west side of the Owen Fracture Zone (O.F.Z.), representing a near-shore environment of deposition. The pre-Late Paleocene basaltic basement was reached at this site; the sediments ranging from Late Paleocene to Late Pleistocene in age. Site 222 was drilled within the Indus cone, being dominated by terrigenous material. No basaltic basement was reached; the sediments ranging in age from Late Miocene to Late Pleistocene.The strongly altered basaltic samples recovered from O.F.Z. (six from 223 and one from 224) do riot represent typical mid-ocean ridge basalts (M.O.R.B.). They are transitional ocean island basalts with strong affinities towards alkaline basalts. Most probably the nature of these basalts is reflected by the role of O.F.Z. as an active transform fault at the boundaries of the Indian and African plates. The alteration is predominantly low-temperature, as commonly observed elsewhere, although some hydrothermal effects were identified in the lower cones.The sediments from both studied sites are dominated by terrigenous components, mainly as the result of their near-shore nature. Thusi) most of the major and trace elements are controlled by terrigenous minerals, ii) the average percentage contribution made to the total element content by the lattice held lithogenous fraction of the sediments is, for most of the studied elements, high (> 65%). Mn, Ca, Sr and Na are exceptions; and iii) authigenic Fe-Mn oxides are practically absent. Sediments from the upper part of Site 223 and from Site 222 (post-middle Miocene) show the typical characteristics of non-pelagic anoxic sediments.The terrigenous material reaching the upper part of Site 223 is especially rich in mafic and ultramafic detritus, mainly derived from the Oman ophiolites, whilst the terrigenous matter reaching Site 222 approaches the usual composition of near-shore muds. An aeolian mode of transportation for the detrital material is quite significant for Site 223, whilst a fluvial mode (Indus River) dominates in Site 222.The lower part of the sedimentary sequence at Site 223 is more pelagicin nature, but is dominated by terrigenous minerals which control the abundance of most major and trace elements. However, a significant proportion of hydrogenous minerals, i.e. smectite, clinoptilolite and probably palygorskite exist, together with an opal-cristobalite-tridymite assemblage. These most probably result from the combined effect of the solution of basaltic material and the existence of siliceous organisms. Illite(mica) is the most prominent detrital clay mineral, together with mixed layers illite/smectite(I/Sm), palygorskite (mainly in Site 223), chlorite and kaolinite. Quartz, feldspars (mainly plagioclase), dolomite and several heavy minerals make up the detrital assemblage. Smectites, clinoptilolite, opal-CT (in Site 223), pyrite and calcite (in both sites) are the most significant authigenic minerals.