Chemical composition of upper Cenozoic at DSDP Leg 70 Holes

The hydrothermal deposits that we analyzed from Leg 70 are composed of ferruginous green clays and fragments of manganese-hydroxide crust. Data from X-ray diffraction, IR-spectroscopy, electron diffraction, and chemical analyses indicate that the hydrothermal green clays are composed of disordered mixed-layer phases of celadonite-nontronite. Electron diffraction shows that the parameters of the unit cells and the degree of three-dimensional ordering of mixed-layer phases with 80% celadonite interlayers are very close to Fe-micas of polymorphic modification IM-celadonite. In some sections, there is a tendency for the number of celadonite layers to increase with depth. The manganese-hydroxide crust fragments are predominantly composed of todorokite (buserite). An essential feature of hydrothermal accumulation is the sharp separation of Fe and Mn. Ba/Ti and Ba/Sr ratios are typical indicators of hydrothermal deposits. Sediments composing the hydrothermal mounds were deposited from moderately heated waters, which had extracted the components from solid basalts in environments where there were considerable gradients of temperature, eH, and pH. The main masses of Fe and Mn were deposited in the late Pleistocene. Postsedimentary alteration of deposited hydrothermal sediments led to their slight recrystallization and, in the green clays, to celadonitization. Further, factor analysis (by Varentsov) of chemical components from these hydrothermal deposits revealed paragenetic assemblages. Green clays corresponding to a definite factor assemblage were formed during the main stage of hydrothermal mineral formation. Manganese hydroxide and associated components were largely accumulated during an early stage and at the end of the main stage.

Occurrence and chemistry of microtektites of ODP Site 121-758

The Toba lake event, the Australasian microtektite event, and the Cretaceous/Paleogene boundary were analyzed on the basis of foraminifers, carbonate content, trace elements, and spherules (microtektites). The Toba ash event, recovered in Hole 758C, may have had minor influences on the foraminiferal populations. The Australasian tektite event has probably some influence on foraminiferal ecology, because the larger specimens become scarce just above the microtektite layer. Microtektites recovered from Hole 758B closely resemble spherules recovered from several Cretaceous/Paleogene boundary localities in North America. The Cretaceous/Paleogene spherules, however, are usually larger and are completely altered to goyazite in the terrestrial environment and to smectite in a marine environment. The Cretaceous/Paleogene boundary of Hole 752B does not show obvious anomalous trace-element concentrations, and iridium concentrations are below our detection limits. The trace-element pattern is dominated by the alternation of chalk with volcanic ash layers above the Cretaceous/Paleogene boundary.

Geochemistry at DSDP Holes 80-550 amd 80-548

At Sites 548 and 550 of DSDP Leg 80 several condensed sedimentary sections contain various types of polymetallic crusts. The relationships between mineralogic and geochemical data in the sections have been studied in the context of the biostratigraphic and sedimentologic results. The diagenetic evolution during periods of low accumulation rate varies according to depth and sedimentary environment. At Site 548 on the continental margin, the phosphatic and manganiferous crusts are similar to those related to upwelling influences before Late Cretaceous deposition. At Site 550 the upper Paleocene cherts, deposited directly on oceanic crust, are overlain by pelagic brown clays containing diagenetic manganiferous concretions characterized by very high Sr and Ba contents. The origin of these small nodules is probably related to the authigenesis of fecal pellets. The upper Eocene indurated section is made up of authigenic zeolites, clays, and Fe-Mn phases and is similar to the volcanic-sedimentary deposits described in deep basins and seamounts of the Pacific. These crusts and a polynucleated nodule within the overlying sediments have geochemical characteristics (high Ni, Co, and Cu contents) similar to those formed in the deep ocean under volcanic influences during periods of low sedimentation rates or sedimentary hiatuses. Volcaniclastic material is ubiquitous and peculiarly abundant in Eocene sections and can be related to the volcanic formation of Iceland in the North Atlantic.

Abundance and chemical and mineral compositions of nodules from the Pacific Ocean

The monograph highlights extensive materials collected during expeditions of P.P. Shirshov Institute of Oceanology. We consider facial conditions of nodule formation, regularities of their distribution, stratigraphic position, petrography, mineral composition, textures, geochemistry of nodules and hosting sediments. Origin of iron-manganese nodules in the Pacific Ocean is considered as well.

Geochemistry at DSDP Leg 70 Holes

The hydrothermal mounds on the southern flank of the Galapagos Spreading Center are characterized by the following main features: 1) They are located over a young basement (0.5 to 0.85 m.y. of age) in a region known for its high sedimentation rate (about 5 cm/10**3 y.) because it is part of the equatorial high biological productivity zone. 2) They are located in a region with generally high heat flow (8 to 10 HFU). The highest heat-flow measurements (up to 10**3 HFU) correspond to mound peaks (Williams et al., 1979), where temperatures up to 15°C were measured during a dive of the submersible Alvin (Corliss et al., 1978). 3) They are often located on small vertical faults which displace the basement by a few meters (Lonsdale, 1977) and affect the 25- to 50-meter-thick sediment cover. Most of these characteristics have also been observed in the other three known cases of hydrothermal deposits with mineral parageneses similar to that of the Galapagos mounds. However, the case of the hydrothermal mounds south of the Galapagos Spreading Center is unique because of the unusual thickness of the hydrothermal deposits present. The mounds are composed of several, up to 4.5-meter-thick, layers of green clays which, in one case (Hole 509B), are overlain by about 1.4 meters of Mn-oxide crust. We suspect that such a large accumulation of hydrothermal products results from the "funnelling" of the hydrothermal solutions exiting from a highly permeable basement along the faults. This chapter reports a preliminary study of those green clays collected by hydraulic piston coring of the Galapagos mounds during Deep Sea Drilling Project (DSDP) Leg 70 of the D/V Glomar Challenger. Green clays have also been reported from three presently or recently active hydrothermal areas in or close to spreading centers.

Geochemistry of phosphate and glauconites of ODP Leg 128 samples

Glauconites and phosphates have been detected in almost all investigated samples at Sites 798 (uppermost Miocene or lower Pliocene to Pleistocene) and 799 (early middle Miocene to Pleistocene). Autochthonous occurrences appear in very minor quantities (generally below 0.2%) throughout the drilled sequences, whereas allochthonous accumulations are limited to the lower Pliocene or uppermost Miocene sequence at Site 798 (glauconites) and to the upper and middle Miocene sequence at Site 799 (upper and middle Miocene: glauconites; middle Miocene: phosphates). X-ray fluorescence, microprobe, and bulk chemical analyses indicate high variabilities in cations and anions and generally low oxide totals. This is probably related to the substitution of phosphate and fluoride aniors by hydroxide and carbonate anions in phosphates and to the depletion of iron, aluminum, and potassium cations and the enrichment in hydroxide and crystal water in glauconites. Gradients in pore-water contents of dissolved phosphate and fluoride at Sites 798 and 799 suggest a depth of phosphate precipitation between 30 and 50 mbsf, with fluoride as the limiting element for phosphate precipitation at Site 798. Phosphate and fluoride appear to be balanced at Site 799. Crude extrapolations indicate that the Japan-Sea sediments may have taken up approximately 7.2*10**10 g P total/yr during the Neogene and Pleistocene. This amount corresponds to approximately 0.3% of the estimated present-day global transfer of phosphorus into the sediments and suggests that the Japan Sea constitutes an average sink for this element. The two main carriers of phosphorus into the present Japan Sea are the Tshushima and the Liman currents, importing approximately 6.6*10**10 g P and 5.7*10**10 g P per year, respectively. Bulk chemical analyses suggest that at least 36% of P total in the sediments is organically bound phosphorus. This rather high value, which corresponds to the measured Japan-Sea deep-water P organic/P total ratios, probably reflects rapid transport of organic phosphorus into the depth of the Japan Sea.