ALBERT

Description: This site was accidentally spudded on a small basement pinnacle and was abandoned when hard rock was reached within a few meters from the surface. The section penetrated consisted of coarse winnowed calcareous sand over thin chalk ooze resting on a hard crust of ferromanganese oxide presumably covering basalt.

Description: DSDP 159 is one of a series of sites in the eastern equatorial Pacific on the west flank of the East Pacific Rise. It was selected by the Pacific Site Selection Panel on the premise that if hydrothermal processes on the crest of the East Pacific Rise supply the transition metals, a broad zone of such deposits should be present immediately above basement over the entire flank of the Rise.

Description: DSDP 161 is located on the lower west flank of the East Pacific Rise about midway between the Clipperton and Clarion fracture zones which define the boundaries of a large structural block in the eastern Pacific. The site is about 4,000 km west of the present crest of the Rise. It is located near the northern edge of a zone of thick Cenozoic sediments which marks the general location of the equatorial zone of high biological productivity.

Description: DSDP 162 is located due north of DSDP 161 on the lower west flank of the East Pacific Rise about 3900 km west of the crest. It is in the Clarion-Clipperton block, about 80 km south of the Clarion Fracture Zone. The site lies at the extreme northern edge of the zone of thick sediments that parallels the equator in the Pacific and marks the region of high biological productivity.

Description: DSDP 160 forms part of a series of sites in the eastern equatorial Pacific on the west flank of the East Pacific Rise. Earlier legs of the Deep Sea Drilling Project, in particular Legs 5 and 9, have reported sediments rich in oxides of iron and perhaps other transition metals just above basement in the eastern Pacific. These occurrences roughly define a broad zone on the west flank of the rise. Site DSDP 160 lies on this trend and were selected by the Pacific Site Selection Panel to test the extent of such deposits.

Description: At Sites 47 and 48, impenetrable and cherty Upper Cretaceous chalks were found. The upper part of what infer to be lower Cretaceous is even more reflective, and likely to be very cherty (and was found to be cherty in the Vema core). It became clear that basement could only be reached where the Upper Cretaceous and the upper part of the lower Cretaceous are absent. However, west of Site 48, the R/V Argo record showed an area in which the Upper Cretaceous has wedged out down dip, and the Lower Cretaceous is thinning out by loss of the strongly reflective beds at the top. This area appeared to offer the best chance for sampling the lowermost transparent layer. Two holes were drilled: Hole 49.0 and Hole 49.1 after Hole 49.0 stopped at 18 m. Beds near the base of sedimentary sequence revealed by the seismic profiles are found to be of early Cretaceous (Neocomian) or latest Jurassic (Tithonian) age, and of pelagic facies. The crust under the Shatsky Rise is latest Jurassic or older.

Description: Site 49 had been selected to investigate the basal part of the sedimentary sequence as revealed by the acoustic profiles, and to sample the underlying opaque material. However, the cherty nature of the sediments prevented penetration of the section at Site 49, and the only recourse appeared to be to move to a spot of even thinner sedimentary cover. Such a place existed, just downslope from Site 49, where Horizon B' comes very close to the surface, this is where Site 50 was selected.

Description: Having been stopped by chert in the Maestrichtian at Site 47, a site was looked for which would give an adequate Cenozoic thickness for satisfactory spudding-in, yet promised to lead from this into an older part of the section. This is the first record of Middle Maestrichtian in pelagic carbonate facies from the Northwest Pacific and surrounding lands, a matter of paleontologic-biostratigraphic importance.

Description: The sea floor of the western Pacific is covered by five stratigraphic units: (l)an eastward thinning wedge of late Tertiary silty clay, primarily of volcanic origin, (2) a Cretaceous to Tertiary zeolitic red clay, (3) a Late Cretaceous to Tertiary chalk/chert sequence, (4) a Cretaceous clay, and (5) a basal chalk/chert sequence. The basal chalk was deposited on the young crust at the crest of the mid-oceanic ridge, while the upper chalk was deposited beneath the equator, and the abyssal clays were deposited in abyssal depths in mid latitudes. A kinematic model has been constructed that outlines the deposition of these units on growing crust, which not only was displaced westward away from the accretion center of the mid-oceanic ridge, but northward under the equator. The average northward component of motion for the Pacific plate has been 2 cm per year from 0 to 30 m.y. and 4.4 cm per year from 30 to 100 m.y. The deep-sea deposits of the Pacific are basically and systematically time transgressive. Claims of general synchroneity for either lithostratigraphy or acoustostratigraphy are rejected as inconsistent with both the drilling data and the kinematic model of Pacific pelagic stratigraphy. A few more well sampled holes in the ancient Pacific plate combined with an appropriately refined kinematic model should yield a 'rather detailed history of the Pacific plate since the Jurassic.

Description: Sediments from near the basement of a number of Deep Sea Drilling Project (DSDP) sites, from the Bauer Deep, and from the East Pacific Rise have unusually high transition metal-to-aluminum ratios. Similarities in the chemical, isotopic, and mineralogical compositions of these deposits point to a common origin. All the sediments studied have rare-earth-element (REE) patterns strongly resembling the pattern of sea water, implying either that the REE's were coprecipitated with ferromanganese hydroxyoxides (hydroxyoxides denote a mixture of unspecified hydrated oxides and hydroxides), or that they are incorporated in small concentrations of phosphatic fish debris found in all samples. Oxygen isotopic data indicate that the metalliferous sediments are in isotopic equilibrium with sea water and are composed of varying mixtures of two end-member phases with different oxygen isotopic compositions: an iron-manganese hydroxyoxide and an iron-rich montmorillonite. A low-temperature origin for the sediments is supported by mineralogical analyses by x-ray diffraction which show that goethite, iron-rich montmorillonite, and various manganese hydroxyoxides are the dominant phases present. Sr87/Sr86 ratios for the DSDP sediments are indistinguishable from the Sr87/Sr86 ratio in modern sea water. Since these sediments were formed 30 to 90 m.y. ago, when sea water had a lower Sr87/Sr86 value, the strontium in the poorly crystalline hydroxyoxides must be exchanging with interstitial water in open contact with sea water. In contrast, uranium isotopic data indicate that the metalliferous sediments have formed a closed system for this element. The sulfur isotopic compositions suggest that sea-water sulfur dominates these sediments with little or no contribution of magmatic or bacteriologically reduced sulfur. In contrast, ratios of lead isotopes in the metalliferous deposits resemble values for oceanic tholeiite basalt, but are quite different from ratios found in authigenic marine manganese nodules. Thus, lead in the metalliferous sediments appears to be of magmatic origin. The combined mineralogical, isotopic, and chemical data for these sediments suggest that they formed from hydrothermal solutions generated by the interaction of sea water with newly formed basalt crust at mid-ocean ridges. The crystallization of solid phases took place at low temperatures and was strongly influenced by sea water, which was the source for some of the elements found in the sediments.