Petrochemistry of Basalts D/V Glomar Challenger, Leg 45 Holes 395 and 396

Results describe the chemical composition of post-Jurassic sediments penetrated by Deep Sea Drilling Project Hole 464 (northern Hess Rise), peculiar features in the distribution of chemical components through the section, and modes of their occurrence determined by factor analysis and from the data on mineralogy, lithology, and accumulation rates of sediments and chemical components.Three main stages in the geochemical history of sedimentation in the region are outlined: I. Late Mesozoic stage (Early Albian-Cenomanian). la. Early phase (Late Aptian-Early Albian). This early phase is characterized by accumulation of dark-red and brown, calcareous silica-clay oozes, considerably enriched by volcanogenic (mostly hyalopelite basalt volcaniclastic) material. High accumulation rates of sediments (22.5 mm 10~3yr -1 ) and chemical components are noted. Ib. Late phase (late Albian-Cenomanian). Accumulation of relatively light-colored, calcareous, essentially silicic sediments took place at that time. The amount of volcaniclastic material, iron, and other heavy metals in these sediments is much less than in the early Albian deposits. Relatively high accumulation rates of sediments (17.9 mm 10~3yr~') and of some of the components (SiO 2 , A1 2 O 3 , etc.) were recorded. The obtained data are in good correlation with the model which implies that in the Albian the northern part of Hess Rise was in the equatorial zone, with high biological productivity, while the Pacific Plate moved northward. II. Late Cretaceous (Early Turonian?-Middle Miocene). During that time, relatively local accumulation of fine volcaniclastic material (ash) took place; this material was transformed into clay (montmorillonite-hydromica) enriched by ferric hydroxide, and to a lesser degree by Mnhydroxide and associated heavy metals. III. Late Cenozoic stage (upper Miocene-Pleistocene) was the time of accumulation of clay-silica, mostly radiolarian oozes, in chemical composition and accumulation rates similar to the typical clay-silica sediments of the modern open ocean at depths below the level of carbonate compensation. The outlined stages, phases of geochemical history of sedimentation in the region, represent the evolution of sediment accumulation in the basin.

Section: Methodsmentioning

confidence: 99%

Geochemical History of Post-Jurassic Sedimentation in the Central Northwestern Pacific, Northern Hess Rise, Deep Sea Drilling Project Site 464

Варенцов¹,

Sakharov²,

Rateev³

1981

“…Geochemical study of the deposits was carried out on the basis of lithological-mineralogical data. Determination of chemical components of the sediments was made in the laboratory of the Geological Institute of the U.S.S.R. Academy of Sciences: main components by the method of bulk analysis, heavy metals by optical emission spectroscopy (Zolotarev and Choporov, 1978). The analytical data were evaluated by EC-1022 in the laboratory of mathematical methods (by D. A. Kazimirov and P. K. Ryabushkin) by factor analysis (Davis, 1973;Harman, 1967).…”

Section: Methodsmentioning

confidence: 99%

Composition and Conditions of Genesis of Sedimentary Rocks in the Lower Part of Site 462, Deep Sea Drilling Project Leg 61

Timofeev¹,

Vi²,

Im³

et al. 1981

Cretaceous volcaniclastic rocks from the lower part of Deep Sea Drilling Project Hole 462 (Cores 14-80) were studied under the microscope. X-ray study of clay minerals and authigenic zeolites and amphiboles was also made. Altered hyalobasalts and palagonitized (or replaced by Fe-Mg-smectite) sideromelanic glass are predominant in the rock composition. Acid to basic plagioclases, basic volcanic glass, biotite, pyroxene, hornblende, and olivine were recognized in sediments. Accumulation of sediments took place in relatively deep-water environments, whereas transportation of volcaniclastic material was by turbidite flows. In the zone of doleritic sills, the volcaniclastic rocks were subjected to hydrothermal and contact-metasomatic alteration, resulting in formation of authigenic zeolites (analcime, wairakite [?], thomsonite) and monoclinic amphiboles (tremolite, actinolite). Geochemical study of volcaniclastic sediments shows them to be products of transportation of tholeiitic basalt material which interacted with sea water. An increase in content of Fe 3+ , K, Mn, and heavy metals (Cu, Ni, Co, V) is observed in this succession: tholeiitic basalts, their hyaloclastites, smectitic clays. A similar tendency is observed in a transitional zone from the lower horizons of the sequence (Barremian) to the upper ones (Cenomanian).

“…A detailed description of methods was given in the paper on Site 463 (Varentsov et al, this volume). It should be emphasized that the chemical analyses of sediments were made at the Geological Institute of the U.S.S.R. Academy of Sciences, main components by methods of bulk analysis, heavy metals and trace elements by optical emission spectroscopy, by comparison with international reference standards (Zolotarev and Choporov, 1978;Kirkpatrick, 1979).…”

Section: Methodsmentioning

confidence: 99%

Geochemical History of Post-Jurassic Sedimentation in the Central Northwestern Pacific, Southern Hess Rise, Deep Sea Drilling Project Site 466

Varentsov¹

1981

Deep Sea Drilling Project Hole 466 was drilled in a small structural depression on southern Hess Rise, about 50 km northeast of Site 465. Identification of the stages in geochemical history of sedimentation in the region of Site 466 is based on interpretation of data on distribution of main components and heavy metals and forms of their occurrences (results of factor analysis and mineralogy), and rates of component accumulation, within the general context of information on these deposits. Late Albian (early-oceanic). The remarkable geochemical feature of this stage is that the major part of the main components and heavy metals accumulated as basaltic volcaniclastics and clay products of their alteration. The volcaniclastic material is closely bound to sapropelic organic matter. Shallow-water carbonate turbidite sediments play a geochemically insignificant part. The sediments accumulated in a shallow-water basin with stagnant bottom waters. There is hiatus from Upper Albian to upper Turonian. Late Cretaceous (Turonian/Coniacian-early Maastrichtian). Within this stage were accumulated nannofossil carbonate oozes similar in their geochemistry to pelagic oceanic sediments. The increased rates of sedimentation during the late Turonian-early Santonian can be explained by the model suggesting that the region at that time was situated within the equatorial zone of high biological productivity, during northward movement of the Pacific Plate (Lancelot and Larson, 1975; Lancelot, 1978; van Andel, 1974). Tertiary-Quaternary. There is a hiatus from late Maastrichtian to early Eocene. In the middle to late Eocene were accumulated pelagic nannofossil carbonate sediments with high contents of materials which remained after dissolution: Mn hydroxides, A1 2 O 3 , and P compounds. There is a hiatus from early Oligocene to late Miocene. Pelagic nannofosil oozes accumulated during the early Pliocene to Pleistocene have relatively high concentrations of SiO 2 , A1 2 03, Fe, Mn, and associated heavy metals, increasing towards the Pleistocene because of intensification of island volcanism. The geochemical stages of post-Jurassic sedimentation in the region concerned, as for some other areas of the northwestern Pacific, reflect the evolution of the basin, from relatively shallow-water environments with essential influence of volcanism during early stages to pelagic conditions of the open ocean.