Composition of sedimentary rocks from the Mountainous Crimea and the Northwestern Caucasus

Detailed data obtained on chemistry of sedimentary rocks from the Mountainous Crimea and the Northwestern Caucasus that were dated at the Cenomanian/Turonian boundary and formed during Oceanic Anoxic Event 2 make it possible to calculate dissolved oxygen concentration in bottom waters of the sedimentation basin. Enrichment factors of trace elements in black shales are revised and an explanation is suggested for genesis of the rocks with regard for unusual climatic changes.

Sedimentary mineralogy of argillaceous sediments at DSDP Legs 56-57 Holes

Mineral assemblages of DSDP Holes 436 and 438A and the upper section of Hole 439 (871.5-911.0 m sub-bottom) resemble each other and are composed of montmorillonite (probably a small portion of montmorillonite/illite mixed-layer clays), illite, chlorite, kaolinite, quartz, plagioclase, hornblende, calcite, dolomite, siderite, gypsum, pyrite, and halite. In the middle section of Hole 439 (933.5-1041.0 m), clinoptilolite is also found. In the lower section of Hole 439 (1077.5-1150.0 m), montmorillonite is not confirmed, and clinoptilolite and mixed-layer illite are found. These assemblages, which also contain detrital kaolinite, are generally found in sediments from brackish-water environments. At Site 439, more than 1000 meters of sediment might have been removed by erosion at the base.

Sediment properties, contents and accumulation rates of Hg in cores of Upper Quaternary sediments from the Deryugin Basin, Okhotsk Sea

The Hg distribution and some mineralogical-geochemical features of bottom sediments up to a depth of 10 m in the Deryugin Basin showed that the high and anomalous Hg contents in the Holocene deposits are confined to a spreading riftogenic structure and separate fluid vents within it. The accumulations of Hg in the the sediments were caused by its fluxes from gas and low-temperature hydrothermal vents under favorable oceanological conditions in the Holocene. The two mainly responsible for the high and anomalous Hg contents are infiltration (fluxes of hydrothermal or gas fluids from the sedimentary cover) and plume (Hg precipitation from water plumes with certain hydrochemical conditions forming above endogenous sources). The infiltration anomalies of Hg were revealed in the following environments: (1) near gas vents on the northeastern Sakhalin slope, where high Hg contents are associated only with Se and were caused by the accumulation of gases ascending from beneath the gas hydrate layer; (2) in the area of inferred occasionally operating low-temperature hydrothermal seeps in the central part of the Deryugin Basin, in which massive barite chimneys, hydrothermal Fe-Mn crusts, and anomalous contents of Mn, Ba, Zn, and Ni in sediments develop.

Geochemical characterization of black shales from the Tarfaya Basin

Organic geochemical and petrological investigations were carried out on Cenomanian/Turonian black shales from three sample sites in the Tarfaya Basin (SW Morocco) to characterize the sedimentary organic matter. These black shales have a variable bulk and molecular geochemical composition reflecting changes in the quantity and quality of the organic matter. High TOC contents (up to 18wt%) and hydrogen indices between 400 and 800 (mgHC/gTOC) indicate hydrogen-rich organic matter (Type I-II kerogen) which qualifies these laminated black shale sequences as excellent oil-prone source rocks. Low Tmax values obtained from Rock-Eval pyrolysis (404-425 MC) confirm an immature to early mature level of thermal maturation. Organic petrological studies indicate that the kerogen is almost entirely composed of bituminite particles. These unstructured organic aggregates were most probably formed by intensive restructuring of labile biopolymers (lipids and/or carbohydrates), with the incorporation of sulphur into the kerogen during early diagenesis. Total lipid analyses performed after desulphurization of the total extract shows that the biomarkers mostly comprise short-chain n-alkanes (C16-C22) and long-chain (C25-C35) n-alkanes with no obvious odd-over-even predominance, together with steranes, hopanoids and acyclic isoprenoids. The presence of isorenieratane derivatives originating from green sulphur bacteria indicates that dissolved sulphide had reached the photic zone at shallow water depths (~100m) during times of deposition. These conditions probably favoured intensive sulphurization of the organic matter. Flash pyrolysis GC-MS analysis of the kerogen indicates the aliphatic nature of the bulk organic carbon. The vast majority of pyrolysis products are sulphur-containing components such as alkylthiophenes, alkenylthiophenes and alkybenzothiophenes. Abundant sulphurization of the Tarfaya Basin kerogen resulted from excess sulphide and metabolizable organic matter combined with a limited availability of iron during early diagenesis. The observed variability in the intensity of OM sulphurization may be attributed to sea level-driven fluctuations in the palaeoenvironment during sedimentation.

Geochemistry of interstitial waters of Lau Backarc Basin sediment samples

Interstitial water samples from Sites 834 through 839, drilled during Ocean Drilling Program Leg 135 in the backarc Lau basin (Southwestern Pacific), have been analyzed for major elements, manganese, copper, strontium, barium, vanadium, and 87Sr/86Sr isotopic composition values. The concentration-depth profiles of the major chemical components show almost straight concentration gradients at all sites, and seem to reflect slight alteration of volcanic material. However, in the lower part of the sedimentary cover, where volcanogenic material is abundant and where diagenetic minerals occur, systematic decreases in calcium, strontium, manganese, copper, and vanadium concentrations are observed. A downwelling flow of bottom seawater, which affected the diagenetic chemical signature of the interstitial water, is probably responsible for the recorded chemical features. This hypothesis is supported by strontium isotope data obtained from interstitial water samples at Site 835. It is also in accordance with data from heat flow and physical properties.

Mineral and chemical compositions of authigenic carbonates from the northern Deryugin Basin, Sea of Okhotsk

Mineral and chemical compositions of authigenic carbonates are studied by several methods in a sediment core collected in the axial zone of the Deryugin riftogenic basin. Manganese carbonates (kutnahorite, rhodochrosite) associated with manganiferous calcite, manganiferous pyrite, and nontronite are firstly identified in the Sea of Okhotsk. Manganese carbonates in Holocene diatomaceous ooze were presumably formed due to diagenetic transformation of sedimentary manganese hydroxides, organic matter, and biogenic silica, while those found in the underlying turbidites precipitated owing to the intermittent influx of endogenic fluids migrating along sand interbeds.

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).

Geochemistry of interstitial gases in sedimentary deposits at DSDP Leg 64 Holes

We analyzed interstitial gases from holes at Sites 474, 477, 478, 479, and 481 in the Gulf of California, using gas chromatography and stable isotope mass spectrometry to evaluate their composition in terms of biogenic and thermogenic sources. The hydrocarbon gas (C1-C5) concentrations were comparable to the shipboard data, and no olefins could be detected. The ?13C data for the CH4 confirmed the effects of thermal stress on the sedimentary organic matter, because the values were typically biogenic near the surface and became more depleted in 12C versus depth in holes at Sites 474, 478, and 481. The CH4 at Site 477 was the heaviest, and in Hole 479 it did not show a dominant hightemperature component. The CO2 at depth in most holes was mostly thermogenic and derived from carbonates. The low concentrations of C2-C5 hydrocarbons in the headspace gas of canned sediments precluded a stable carbon-isotope analysis of their genetic origin.

Chemical and mineral compositions of sedimentary deposits and magmatic rocks from DSDP Legs 41, 45, 48, and 49

This collective monography by a group of lithologists from the Geological Institute of the USSR Academy of Sciences summarizes materials of the Deep-Sea Drilling Project from the Atlantic Ocean. It gives results of processing materials on the sequences drilled during DSDP Legs 41, 45, 48 and 49. These studies were based on lithological-facial analysis combined with detailed mineralogical-petrographic description. Its chapters give a number of ideas on formation of the Earth sedimentary cover, which can be used for compilation of regional and global schemes of ocean paleogeography, reconstruction of history of some structures in the World Ocean, correlation between sedimentary processes on continents and in oceans, estimation of perspectives for oil and gas fields and ore formation.

Composition of bottom sediments from the Central Basin of the Indian Ocean

A study of petrographic and mineral compositions of 26 sediment cores from the western part of the Central Basin of the Indian Ocean has identified biogenic, terrigenous, volcanogenic, and authigenic sediment types formed in certain facies conditions. On the basis of bio- and paleomagnetic stratigraphy data from the cores sedimentation rates of different sediment types have been calculated. Modern and Pliocene-Pleistocene positions of the main facies boundaries (the critical depth of carbonate accumulation, the geochemical boundary between hemi- and miopelagic zones, the frontal boundaries of the equatorial belt of biogenic silica accumulation) have been determined. It has been shown that the sedimentary process during Pliocene-Quaternary had cycle variations characterized by successive changes of different sedimentation types - hemipelagic, miopelagic, and biogenic.

Magnetic observation of ODP Site 152-919 in the Irminger Basin, North Atlantic

Component natural remanent magnetizations derived from u-channel and 1-qcm discrete samples from ODP Site 919 (Irminger Basin) indicate the existence of four intervals of negative inclinations in the upper Brunhes Chronozone. According to the age model based on planktic oxygen isotope data, these "excursional" intervals occur in sediments deposited during the following time intervals: 32-34 ka, 39-41 ka, 180-188 ka and 205-225 ka. These time intervals correspond to polarity excursions detected elsewhere, known as Mono Lake, Laschamp, Iceland Basin and Pringle Falls. The isotope-based age model is supported by the normalized remanence (paleointensity) record that can be correlated to other calibrated paleointensity records for the 0-500 ka interval, such as that from ODP Site 983. For the intervals associated with the Mono Lake and Laschamp excursions, virtual geomagnetic poles (VGPs) reach equatorial latitudes and mid-southerly latitudes, respectively. For intervals associated with the Iceland Basin and Pringle Falls excursions, repeated excursions of VGPs to high southerly latitudes indicate rapid directional swings rather than a single short-lived polarity reversal. The directional instability associated with polarity excursions is not often recorded, probably due to smoothing of the sedimentary record by the process of detrital remanence (DRM) acquisition.

Age of samples from the sedimentary cover of the Primorye continental slope and from the submarine Bogorov Rise

Results of a complex study of the sedimentary cover (continuous seismic profiling and diatom analysis) in the northeastern Sea of Japan including the Bogorov Rise an adjacent part of the Japan Basin and the continental slope, are presented. Two varied-age complexes were distinguished in the sedimentary cover of the continental slope of Primorye: Middle Miocene and Late Miocene - Pleistocene. These complexes formed in a stable tectonic setting with no significant vertical movements. A depression in the acoustic basement is located along the continental slope and it is divided from the Japan Basin by a group of volcanic structures, the most uplifted part of which forms the Bogorov Rise. The depression probably formed before Middle Miocene. In Middle Miocene the Bogorov Rise was already at depths close to modern ones. In the sedimentary cover near the Bogorov Rise buried zones were found. Probably they were channels for gas transportation in pre-Pleistocene. Deformations of sediments that occurred in the beginning of Pleistocene are established in the basin.

Sedimentology of ODP sites in the Cape Basin, southeast Atlantic Ocean

Middle/late Miocene to early Pliocene sedimentary sequences along the continental margin of southwest Africa have changes that correspond to the carbonate crash (12-9 Ma) and biogenic bloom events (~7-4 Ma) described in the equatorial Pacific by Farrell et al. (1995, doi:10.2973/odp.proc.sr.138.143.1995). To explore the origins of these changes, we analyzed the carbon and coarse fraction contents of sediments from ODP Sites 1085, 1086, and 1087 at a time resolution of 5 to 30 kyr. Several major drops in CaCO3 concentration between 12 and 9 Ma are caused by dilution from major increases in clastic input from the Oranje River during global sea level regressions. Abundant pyrite crystals and good preservation of fish debris reflect low oxygenation of bottom/pore waters. Regional productivity was enhanced during the time equivalent to the carbonate crash period. Higher benthic/planktic foraminiferal ratios indicate that CaCO3 dissolution at Site 1085 peaked between 9 to 7 Ma, which was after the global carbonate crash. This period of enhanced dissolution suggests that Site 1085 was located within a low-oxygen water mass that dissolved CaCO3 more easily than North Atlantic Deep Water, which began to bathe this site at 7 Ma. At 7 to 6 Ma, the onset of the biogenic bloom, increases and variations in total organic carbon and benthic foraminiferal accumulation rates show that paleoproductivity increased significantly above values observed during the carbonate crash period and fluctuated widely. We attribute the late Miocene paleoproductivity increase off southwest Africa to ocean-wide increases in nutrient supply and delivery.

Sedimentary and subsidence history of ODP Sites 135-840 and 135-841

Sedimentary sections recovered from the Tonga platform and forearc during Ocean Drilling Program Leg 135 provide a record of the sedimentary evolution of the active margin of the Indo-Australian Plate from late Eocene time to the Present. Facies analyses of the sediments, coupled with interpretations of downhole Formation MicroScanner logs, allow the complete sedimentary and subsidence history of each site to be reconstructed. After taking into account the water depths in which the sediments were deposited and their subsequent compaction, the forearc region of the Tofua Arc (Site 841) can be seen to have experienced an initial period of tectonic subsidence dating from 35.5 Ma. Subsidence has probably been gradual since that time, with possible phases of accelerated subsidence, starting at 16.2 and 10.0 Ma. The Tonga Platform (Site 840) records only the last 7.0 Ma of arc evolution. However, the increased accuracy of paleowater depth determinations possible with shallow-water platform sediments allows the resolution of a distinct increase in subsidence rates at 5.30 Ma. Thus, sedimentology and subsidence analyses show the existence of at least two, and possibly four, separate subsidence events in the forearc region. Subsidence dating from 35.5 Ma is linked to rifting of the South Fiji Basin. Any subsidence dating from 16.2 Ma at Site 841 does not correlate with another known tectonic event and is perhaps linked to localized extensional faulting related to slab roll back during steady-state subduction. Subsidence from 10.0 Ma coincides with the breakup of the early Tertiary Vitiaz Arc because of the subduction polarity reversal in the New Hebrides and the subsequent readjustment of the plate boundary geometry. More recently, rapid subsidence and deposition of a upward-fining cycle from 5.30 Ma to the Present at Site 840 is thought to relate to rifting of the Lau Basin. Sedimentation is principally controlled by tectonic activity, with variations in eustatic sea level playing a significant, but subordinate role. Subduction of the Louisville Seamount Chain seems to have disrupted the forearc region locally, although it had only a modest effect on the subsidence history and sedimentation of the Tonga Platform as a whole.