Iron-Rich Basal Sediments from the Eastern Equatorial Pacific: Leg 16, Deep Sea Drilling Project

Abstract

Iron-rich sediments chemically similar to those forming at present on the crest of the East Pacific Rise have been found just above basement at widely separated drill sites in the eastern equatorial Pacific, including three sites of Leg 16 of the Deep Sea Drilling Project. These sediments were probably formed when the basement was at the crest of this rise and have moved to their present location as a result of sea-floor spreading.

The hydrothermal alteration of oceanic basalts by seawater

“…von der Borch and Rex, 1970;von der Borch ct al, 1971;Cook, 1971;Cronan et al 1972;Cronan, 1973Cronan, , 1974Horowitz and Cronan, 1976). These represent ancient hydrothermal deposits that were precipitated at the ridge crest and have moved to their present positions as a result of sea-floor spreading, suggesting that hydrothermal circulation at the mid-ocean ridges has been a geologically continuous process.…”

“…The concept of sea-floor spreading requires that these sediments move away from the ridge and are gradually overlain by pelagic sediments. This leads to the formation of a metal-enriched basal sediment layer which has been sampled in several areas of the ocean by the Deep Sea Drilling Project (von der Borch and Rex, 1970;von der Borch et al, 1971;Cronan et al, 1972;Cronan, 1973;Horowitz and Cronan, 1976). A few examples of the chemical composition of these sediments are listed in Table 4-1.…”

Basal Ferruginous Sediments Cored during Leg 16, Deep Sea Drilling Project

“…The low iron values in this core probably reflect its dilution by opaline silica. Recalculation of the analyses on a biogenous-silica-free basis (Cronan et al, 1972) gives an approximate value of 13 to 14 per cent iron in these sediments. There seems to be no iron enrichment at DSDP 163.…”

Chert and Porcellanite from Deep Sea Drilling Project Site 436, Northwest Pacific

“…Small, reddish-brown spherules and rounded aggregates of amorphous iron oxide are common in both the silicified and unsilicified rocks and sediments from Site 436 (Cores 39-42). These particles are found in comparable sediments from the Pacific basin (Pimm et al, 1971;von der Borch and Rex, 1970;von der Borch et al, 1971;Cronan et al, 1972), and similar aggregates occur in jasper beds in the Caballos Formation of Texas Folk, 1977, p. 1267) and in cherts and associated red shales of the Franciscan complex of California (Davis, 1918;Bailey et al, 1964).…”