Fossil manganese deposits buried within DSDP/ODP cores, Legs 1-126

Probable in-situ manganese deposits larger than 1 cm in diameter buried in ODP/DSDP cores were selected for study after examining previous descriptions of the manganese deposits in site reports and the ODP data base. Most of the selected samples from 11 cores occur at or just above sedimentary hiatuses or in slowly deposited sediments and are overlain by rapidly deposited sediments of biogenic, terrigenous or volcanogenic origin. The changes in sedimentation recorded in the lithostratigraphic sections around these deposits are closely related to changes in tectonic evolution, deep water circulation or biological productivity at the sites. The similarity in composition and structure of the buried deposits to those of the modern manganese nodules and crusts with no evidence of post-depositional change suggest that buried manganese deposits may be used as indicators of past sedimentary conditions during which they formed. Their major components are hydrogenetic and earlydiagenetic manganese minerals as well as detrital minerals. The characteristics of these manganese deposits suggests that similar processes of deposition have taken place since the Paleogene or older.

Chemical, isotope and mineral composition of hydrothermally altered upper oceanic crust drilled at ODP Site 129-801C

ODP Hole 801C penetrates >400 m into 170-Ma oceanic basement formed at a fast-spreading ridge. Most basalts are slightly (10-20%) recrystallized to saponite, calcite, minor celadonite and iron oxyhydroxides, and trace pyrite. Temperatures estimated from oxygen isotope data for secondary minerals are 5-100°C, increasing downward. At the earliest stage, dark celadonitic alteration halos formed along fractures and celadonite, and quartz and chalcedony formed in veins from low-temperature (<100°C) hydrothermal fluids. Iron oxyhydroxides subsequently formed in alteration halos along fractures where seawater circulated, and saponite and pyrite developed in the host rock and in zones of restricted seawater flow under more reducing conditions. Chemical changes include variably elevated K, Rb, Cs, and H2O; local increases in FeT, Ba, Th, and U; and local losses of Mg and Ni. Secondary carbonate veins have 87Sr/86Sr = 0.706337 - 0.707046, and a negative correlation with d18O results from seawater-basalt interaction. Carbonates could have formed at any time since the formation of Site 801 crust. Variable d13C values (-11.2? to 2.9?) reflect the incorporation of oxidized organic carbon from intercalated sediments and changes in the d13C of seawater over time. Compared to other oceanic basements, a major difference at Site 801 is the presence of two hydrothermal silica-iron deposits that formed from low-temperature hydrothermal fluids at the spreading axis. Basalts associated with these horizons are intensely altered (60-100%) to phyllosilicates, calcite, K-feldspar, and titanite; and exhibit large increases in K, Rb, Cs, Ba, H2O, and CO2, and losses of FeT, Mn, Mg, Ca, Na, and Sr. These effects may be common in crust formed at fast-spreading rates, but are not ubiquitous. A second important difference is that the abundance of brown oxidation halos along fractures at Site 801 is an order of magnitude less than at some other sites (2% vs. 20-30%). Relatively smooth basement topography (<100 m) and high sedimentation rate (8 m/Ma) probably restricted the access of oxygenated seawater. Basement lithostratigraphy and early low-temperature hydrothermal alteration and mineral precipitation in fractures at the spreading axis controlled permeability and limited later flow of oxygenated seawater to restricted depth intervals.

Biogenic and mineral composition and foraminiferal stratigraphy of sediment cores obtained in northern Germany

The Ratekau boring ended in clays of the so-called Asterigerina-Zone; these clays have shallow-water features in the uppermost samples. The clays are overlain by deep-water clays with pteropods; this formation is split into two parts by a shallow-water deposit. The fossiliferous series ends upward in sandy deposits with shallow-water fossils. The question is raised whether the two deep-water deposits might correspond to the Lower Doberg Beds (Eochattian) and the Upper Doberg Beds (Neochattian) at the Doberg hill, closer to the rim of the basin. All fossiliferous samples from this boring are thought to be of Late Oligocene age; the boundary towards the Middle Oligocene, however, could not be ascertained. The Vaale boring ended in rather typical Septaria clay of the Middle Oligocene. This clay is capped by some metres of unfossiliferous glauconite clays, which in turn are overlain by silts and silty clays with planktonic fossils identical to those found at Dingden locality. These deposits are tentatively dated as Early Miocene. The next higher series of samples consists of sands and clays deposited in shallower waters. They contain a rich fauna of benthic molluscs, which, according to the current notion in stratigraphy, would have a Reinbek Age. In addition, they contain a set of planktonic fossils which differs from the 'Lower Miocene' assemblages. These sands and clays are overlain by a thick series of marine sands very poor in fossils. Finally, four metres of clay with foraminifera, having Younger Miocene affinities, form the top of the fossiliferous sequence. The borings at Wulksfelde and Langenhorn were not far apart and their sediments are easily correlated. Both wells start below in continental 'Lignite Sands' and contain overlying shallow water sands and clays. These yielded Hemmoor benthic mollusca, supposed to indicate Lower Miocene in the relevant literature; however, we encountered their planktonic foraminifera in the uppermost Miocene as well. The same planktonic species were found in all samples of both borings. These deposits under discussion furthermore contain a particular pteropod species. They are overlain by a thick series of gypsiferous clays, with scarce fossils. The uppermost fossiliferous clays (probably Langenfelde Age) contain another pteropod species, not met with in other samples. The discrepancies between the plankton zonation and the traditional subdivision according to benthic molluscs in the borings of Vaale, Wulksfelde and Langenhorn (and in samples from Twistringen, Dingden and Antwerp localities as well) renders the time-stratigraphic value of the denominations Reinbek and Hemmoor rather doubtful. The samples of the Westerland boring can be placed in the Gram and Sylt stages of local chronostratigraphy on the strength of the Astarte series established by HINSCH. The Gram samples contain a typical pteropod species; both groups of samples contain the same planktonic foraminifera as the borings Wulksfelde and Langenhorn. Our material did not bring the problem of the Miocene-Pliocene boundary in this region any closer to a solution. In conclusion, it can be claimed that this investigation provides strong arguments that the usual recognition of Hemmoor and Reinbek does not correspond to well-defined chronostratigraphical units. A better chronostratigraphic subdivision has to be based on the examination of many more samples, and on a better understanding of the paleoecology of the fossils involved.

Description, geochemistry and mineral composition of ODP Site 193-1189 jasperoids, PACMANUS field

Bright red "jasperoids" were recovered at three positions during Leg 193 drilling below Roman Ruins (Site 1189) in the PACMANUS hydrothermal field. These do not represent fossil exhalative oxide deposits equivalent to those associated with sulfide chimneys at the Roman Ruins seafloor. Rather, they constitute an integral, relatively early stage involving oxidized fluids in the development of veins and breccias that characterize the mostly sulfidic stockwork zone intersected below Roman Ruins in Hole 1189B. They formed by growth of quartz in open spaces created by hydrofracturing, the characteristic feature being mostly euhedral cores dusted by tiny hematite flakes. In one occurrence there are also frondlike aggregates and possible earlier cavity linings of hematite, overgrown by quartz, that potentially formed by maturation of ferruginous gels first deposited in the openings. The trace element geochemistry of the jasperoids, apart from minor enrichment in uranium, provides no indication that they represent subsurface conduits for fluids that deposit Fe-Mn-Si at the seafloor, though this remains a possibility for some such deposits.

Chemistry of sulfide deposits from ODP Site 106-649

In Snake Pit massive sulfide fragments and friable, unconsolidated material recovered during ODP Leg 106, isocubanite and pyrite are generally the predominant phases, followed by marcasite, chalcopyrite, sphalerite, and pyrrhotite. Detailed analyses of paragenetic relations of minerals indicate that isocubanite first precipitated together with pyrrhotite. With decreasing temperature, chalcopyrite and sphalerite precipitated, and at the latest stage colloform sphalerite-pyrite (or colloform marcasite) formed. Isocubanite usually has exsolution lamellae of chalcopyrite and less commonly of pyrrhotite. The average bulk chemical composition of the friable, unconsolidated material indicates that it is rich in copper, reflecting the dominance of isocubanite in the specimens, and is characterized by high Co, low Pb, and Ag contents. Sulfur isotope ratios are very uniform, ranging in d34S from +1.2 to +2.8 per mil. The obtained values are apparently low, compared to those for the eastern Pacific sulfide samples, reflecting a smaller contribution of seawater sulfate in the Snake Pit sulfide deposit.

Mineral and chemical compositions of sedimentary and volcano-sedimentary rocks drilled in DSDP Legs 43 and 44

Sedimentary cover on the bottom of the Northwest Atlantic Ocean is underlain by Late Jurassic - Cretaceous tholeiite-basalt formation. It consists of come sedimentary formations with different lithologic features and age. Their composition, stratigraphic position and, distribution are described on materials of deep-sea drilling. Mineralogical and geochemical studies of DSDP Leg 43 and Leg 44 holes lead to new ideas about composition and genesis of some sediment types of and their associations. High metal contents in the chalk formation of black clays on the Bermuda Rise probably result from exhalations. Connection of red-colored and speckled deposits with hiatuses in sedimentation is shown. Main stages of geological history of the North American Basin are reflected in accumulation of the followed formations: ancient carbonate formation (Late Jurassic - Early Cretaceous), formation of black clays rich in organic matter (Cretaceous), formation of speckled clays (Late Cretaceous), siliceous-clayey turbidite formation (Eocene), hemipelagic and pelagic clayey formation (Neogene), and terrigenous turbidite formation (Pleistocene).

Physical properties, mineral and chemical compositions, and accumulation rates of Holocene and Upper Pleistocene bottom sediments from the Sea of Okhotsk

Mineral and chemical compositions and physical properties of diatomaceous clayey-siliceous sediments from the Sea of Okhotsk are studied. Accumulation rates of silica are determined. Their compositional model based on silica content is similar to that of Late Jurassic and Olenekian-Middle Anisian cherts from the Sikhote Alin region. Thickness of Holocene siliceous unit and accumulation rates of siliceous deposits depended on bioproductivity in the upper water layer and seafloor topography. Accumulation rates of amorphous SiO2 (0.05-5.7 g/cm**2/ka) and free SiO2 (0.5-11.6 g/cm**2/ka) are minimal on seamounts and maximal in depressions near foothills. These values match accumulation rates of free SiO2 in Triassic and Late Jurassic basins of the Sikhote Alin region (0.33-3 g/cm**2/ka). Comparison of composition and accumulation rates of silica shows that Triassic and Late Jurassic siliceous sequences of Sikhote Alin could accumulate in a marginal marine basin near a continent.

Pelagic, turbiditic, and contouritic sequential deposits on the Cape Verde Plateau

On the Cape Verde Plateau, Neogene deposits are composed of major pelagic and hemipelagic sediments. These sediments show climatic sequences composed of two lithologic terms that differ in their siliciclastic and carbonate contents. Several turbiditic and contouritic sequences are interbedded in these deposits. Turbidite sequences are fine grained and thin bedded with a very low frequency (about 12 sequences during the Neogene). They are composed of quartz-rich siliciclastic or volcaniclastic sediments. Quartz-rich turbidites originated from the Senegalese margin. Their slightly higher frequency during the early Pliocene indicates that the stronger turbidity currents, and probably the most abundant continental inputs, occur at that period. Volcaniclastic turbidites are only present in the early Miocene (about 17 Ma) and the early Pleistocene (1 Ma). They have flown from adjacent Cape Verde Islands and reflect two episodes of high volcanic activity in this area. Contourite sequences, composed of biogenic sandy silts, represent less than 5% of the sediment pile and seem to have been mainly deposited during the late Pleistocene. These different sequences show clay mineral variations throughout Neogene time. Kaolinite is predominant in the Miocene and lower Pliocene deposits; this mineral decreases thereafter, with an increased trend of illite in the uppermost Pliocene and Pleistocene sediments, suggesting a change in sediment sources on the Saharan continent at about 2.6 Ma.

Mineral quantification of a Jordan Cretaceous outcrop (Section GM3, Ghawr Al Mazar, Ghor al Mazrar)

Cyclic fluctuations in global sea level during epochs of warm greenhouse climate have remained enigmatic, because absence or subordinate presence of polar ice during these periods precludes an explanation by glacio-eustatic forcing. An alternative concept suggests that the water-bearing potential of groundwater aquifers is equal to that of ice caps and that changes in the dynamic balance of aquifer charge versus discharge, as a function of the temperature-related intensity of the hydrological cycle, may have driven eustasy during warm climates. However, this idea has long been neglected for two reasons: 1) the large storage potential of subsurface aquifers was confused with the much smaller capacity of rivers and lakes and 2) empirical data were missing that document past variations in the hydrological cycle in relation to eustasy. In the present study we present the first empirical evidence for changes in precipitation, continental weathering intensity and evaporation that correlate with astronomically (long obliquity) forced sea-level cycles during the warmest period of the Cretaceous (Cenomanian-Turonian). We compare sequence-stratigraphic data with changes in the terrigenous mineral assemblage in a low-latitude marine sedimentary sequence from the equatorial humid belt at the South-Tethyan margin (Levant carbonate platform, Jordan), thereby avoiding uncertainties from land-ocean correlations. Our data indicate covariance between cycles in weathering and sea level: predominantly chemical weathering under wet climate conditions is reflected by dominance of weathering products (clays) in deposits that represent sea-level fall (aquifer charge > discharge). Conversely, preservation of weathering-sensitive minerals (feldspars, epidote and pyroxenes) in transgressive sediments reflects decreased continental weathering due to dryer climate (aquifer discharge > charge). Based on our results we suggest that aquifer-eustasy represents a viable alternative to glacio-eustasy as a driver of cyclic 3rd-order sea-level fluctuations during the middle Cretaceous greenhouse climate, and it may have been a pervasive process throughout Earth history.

Chemical and mineral composition of rocks and sediments from the Amirante Arc

New geological and geophysical data on the Amirante Arc, which locates to the south of the Seychelles Islands, are presented. These data were obtained by Pacific Oceanological Institute during the 33-rd cruise of R/V Professor Bogorov in 1990. The Amirante Arc represents a seamount chain, which has submeridional strike and total length about 400 km. To the west of the Amirante Arc there are a deep sea trench and a back-arc basin, i.e. this area is characterized by structural elements associated with the subduction zone of Western Pacific type. According to our data the Amirante Arc is composed by tholeiites of ocean plateau type. This facts are evidences that the Amirante Arc differs from typical Pacific island arcs. This gives an opportunity to distinguish a special type of oceanic structures, i.e. non-volcanic (amagmatic) ridges. The Amirante Ridge has been probably formed as a result of oceanic crust heaping due to horizontal displacements of its blocks in the process of spreding ridge formation in the Indian Ocean during Cretaceous-Paleogene.

Mineralogy and geochemistry of latest Miocene deposits in the Tyrrhenian Sea

Late Miocene sediments from ODP Sites 652 and 654, drilled on the Sardinian margin in the Western Tyrrhenian Sea, are investigated through mineralogical, micromorphological, geochemical, and microgeochemical analyses. Clay associations appear to be little controlled by conditions of deposition, and largely depend on pre- and post-depositional conditions. The sedimentary series from Central Mediterranean gives very different geodynamic information, according to the sector considered. While relatively stable conditions, like those encountered in Caltanissetta Basin, Sicily, favor the mineralogical expression of warm-temperate and subarid Messinian climate, the Eastern Sardinia margin (Site 654) clay suites mainly reflect the transition from tectonically active to relaxed conditions. The series deposited at the foot of the same margin above a thinner crust (Site 652) experienced the effects of burial diagenesis, enhanced by strong geothermal gradient.

Composition of hydrothermal massive sulfide deposits from ODP Site 158-957 and Leg 169 sites

Sulfide mineral major and trace element analyses were performed on more than 50 polished slabs representing mineralization from three seafloor hydrothermal massive sulfide deposits. Samples from the Bent Hill and ODP Mound massive sulfide deposits, both on the Juan de Fuca Ridge, can be contrasted with samples from the Trans-Atlantic Geotraverse (TAG) hydrothermal mound on the Mid-Atlantic Ridge. The massive sulfide at Bent Hill is predominantly pyrite and pyrrhotite, with increasing amounts of copper-bearing sulfide minerals at the base of the massive sulfide body and through the stockwork to an interval 200 m below seafloor that hosts high copper mineralization (Deep Copper Zone). ODP Mound contains much more abundant sphalerite and copper-bearing sulfides as compared to either Bent Hill or TAG, which are predominantly pyrite with much less abundant chalcopyrite. Copper-bearing sulfides from the Deep Copper Zone beneath Bent Hill and the lowest sampled interval of ODP Mound are petrographically and chemically similar, but distinct from copper-bearing minerals higher in either sequence.

Geochemistry of ferromanganese deposits from the Wombat Plateau

Ferromanganese crusts, nodules, and ferromanganese-rich sediments were recovered on the Wombat Plateau, northwest Australian continental margin, by dredging during Bureau of Mineral Resources cruise 56 of Rig Seismic and by drilling during ODP Leg 122 of JOWES Resolution. We report here the chemistry and mineralogy of the ferromanganese crusts, nodules, and associated ferromanganese-rich sediments. The ferromanganese deposits from the ODP sites are up to 40 cm thick and probably formed in Late Cretaceous to Eocene times. Those from outcrops usually formed in several phases, and their age is unconstrained except that the substrates are Mesozoic. The samples were recovered from present-day water depths of 2000-4600 m, on the Wombat Plateau adjacent to the Argo Abyssal Plain. Both the nodules and crusts are primarily vernadite (delta-MnO2) and are chemically and mineralogically similar, and not dissimilar from ferromanganese deposits found elsewhere on Australian and other marginal plateaus. They are markedly different from most deep-sea deposits. The only crystalline iron phase identified within the ferromanganese deposits is goethite. Concentrations of metals of potential economic interest are generally low compared to those from vernadite-rich seamount crusts and nodules and from abyssal nodules from areas of high resource potential in the Pacific Ocean. Maximum metal values reach 0.55% Co, 0.58% Ni, and 0.20% Cu in deposits containing 4.8% to 30.9% Fe and 4.4% to 21.1% Mn.