Foraminiferal study of ODP Hole 189-1171

Sequence boundary ages determined in shallow-water sediments obtained from ODP (Ocean Drilling Program) Leg 189 Site 1171 (South Tasman Rise) compare well with other stratigraphic records (New Jersey, United States, and northwestern Europe) and d18O increases from deep-sea records, indicating that significant (>10 m) eustatic changes occurred during the early to middle Eocene (51-42 Ma). Sequence boundaries were identified and dated using lithology, bio- and magnetostratigraphy, water-depth changes, CaCO3 content, and physical properties (e.g., photospectrometry). They are characterized by a sharp bioturbated surface, low CaCO3 content, and an abrupt increase in glauconite above the surface. Foraminiferal biofacies and planktonic/benthic foraminiferal ratios were used to estimate water-depth changes. Ages of six sequence boundaries (50.9, 49.2, 48.5-47.8, 47.1, 44.5, and 42.6 Ma) from Site 1171 correlate well to the timings of d18O increases and sequence boundaries identified from other Eocene studies. The synchronous nature of sequence boundary development from globally distal sites and d18O increases indicates a global control and that glacioeustasy was operating in this supposedly ice-free world. This is supported by previous modeling studies and atmospheric pCO2 estimates showing that the first time pCO2 levels decreased below a threshold that would support the development of an Antarctic ice sheet occurred at ca. 51 Ma. Estimates of sea-level amplitudes range from ~20 m for the early Eocene (51-49 Ma) and ~25 m to ~45 m for the middle Eocene (48-42 Ma) using constraints established for Oligocene d18O records.

Carbonate, organic carbon, pyrolysis and composition of the extracts at DSDP Holes 76-534A and 44-391

The geochemical studies of Sites 534 and 391 and their comparison allow us to improve the chemical characterization of different geological formations dating from the early Callovian to the Maestrichtian along the continental margin of eastern North America. Three of the formations are favorable for the preservation of organic matter: (1) the unnamed formation (middle Callovian to Oxfordian), (2) the Blake-Bahama Formation (Berriasian to Barremian), and (3) the Hatteras Formation (Aptian to Cenomanian). The organic matter is mainly detrital, except for a few organic-rich layers where a contribution of aquatic material occurs. In these organic-rich layers, the petroleum potential is medium to good. Maturation has not quite reached the beginning of the oil window even for the deepest organic material.

Calcium carbonate, isotopes and Rock-Eval pyrolysis at DSDP Holes 77-535 and 77-540

At DSDP Sites 534 (Central Atlantic) and 535 and 540 (Gulf of Mexico), and in the Vocontian Basin (France), Lower Cretaceous deposits show a very pronounced alternation of limestone and marl. This rhythm characterizes the pelagic background sedimentation and is independent of detritic intercalations related to contour and turbidity currents. Bed-scale cycles, estimated to be 6000-26,000 yr. long, comprise major and minor units. Their biological and mineralogic components, burrowing, heavy isotopes C and O, and some geochemical indicators, vary in close correlation with CaCO3 content. Vertical changes of frequency and asymmetry of the cycles are connected with fluctuations of the sedimentation rate. Plots of cycle thickness ("cyclograms") permit detailed correlations of the three areas and improve the stratigraphic subdivision of Neocomian deposits at the DSDP sites. Small-scale alternations, only observed in DSDP cores, comprise centimetric to millimetric banding and millimetric to micrometric lamination, here interpreted as varvelike alternations between laminae that are rich in calcareous plankton and others rich in clay. The laminations are estimated to correspond to cycles approximately 1,3, and 13 yr. in duration. The cyclic patterns appear to be governed by an interplay of continental and oceanic processes. Oceanic controls express themselves in variations of the biogenic carbonate flux, which depends on variations of such elements as temperature, oxygenation, salinity, and nutrient content. Continental controls modulate the influxes of terrigenous material, organic matter, and nutrients derived from cyclic erosion on land. Among the possible causes of cyclic sedimentation, episodic carbonate dissolution has been ruled out in favor of climatic fluctuations with a large range of periods. Such fluctuations are consistent with the great geographic extension shown by alternation controls and with the continuous spectrum of scales that characterizes limestone-marl cycles. The climatic variations induced by the Earth's orbital parameters (Milankovitch cycles) could be connected to bed-interbed alternations.

Concentration of organic compounds in slush, under-ice water, and the snow-ice fast-ice cover of the southeast sector of the Antarctic in April 2008

Data are presented on concentration of hydrocarbons (HC) relative to concentrations of suspended matter, lipids, organic carbon, and chlorophyll a in surface waters and snow-ice cover of the East Antarctic coastal areas. It was shown that growth of concentrations of aliphatic HC (AHC) to 30 µg/l in surface waters takes place in frontal zones and under young ice formation. AHC concentration in snow increases with growth of aerosol concentration in the atmosphere. In the lower part of ice, at the boundary with seawater, despite low temperatures, autochthonous processes may provide high AHC concentrations (up to 289 µg/l). Within the snow-ice cover on fast ice, concentration co-variations of all the compounds considered take place.

Composition of organic matter from water, suspended matter, and bottom sediments of Nha Trang Bay, South China Sea

This research has been carried out in the Nha Trang Bay (Southern Vietnam, South China Sea) at a section from the estuary of the Cai River to the marine part of the bay, as well as in the area of coral reefs. River- and sea waters, suspended matter, and bottom sediments are studies. Data on dissolved organic carbon and total nitrogen in water are obtained. Organic carbon concentration is estimated in suspended matter; organic carbon and molecular and group compositions of n-alkanes are determined in bottom sediments. Molecular and group compositions of n-alkanes in bottom sediments of the landfill made it possible to identify three types of organic matter (OM): marine, mixed, and mainly of terrigenous origin. All these types of OM are closely related to specificity of sedimentation and hydrodynamics of waters in this area.

Magnetic properties of basalts at DSDP Hole 83-504B

We have studied the magnetic properties of 22 samples from DSDP Leg 83 to determine the origin of remanence and its relationship to such problems as the tectonic and chemical evolution of the section, the depth of the magnetized layer, and the applicability of magnetic properties of ophiolites to the marine crust. The magnitude of natural remanence has fairly typical values in the uppermost part of the section, falls two to three orders of magnitude in the transition zone, and returns to values slightly less than the upper part in the dike complex. This behavior reflects, for the most part, variations in the amount of magnetic minerals present. Directional behavior is highly variable throughout the section and often shows complexity even on the level of a single sample. Curie temperature measurements and preliminary opaque petrography indicate that the remanence is chemical in origin and probably involves a resetting of the original thermal remanent magnetization (TRM) direction. Selective destructive demagnetization of four breccia samples shows that the remanence of the clasts was acquired prior to consolidation and did not change significantly thereafter. There are also indications that some of the remanence may be carried by secondary magnetic phases. A comparison of these samples with comparable ophiolite rocks is equivocal, with similarities in remanence characteristics but differences in magnetic mineralogy. As for magnetic anomalies, the transition zone is too weakly magnetized to contribute significantly. The available data on the dike complex are inconclusive and their contribution is still open to debate.

Methane and microbiological processes in the Barents Sea

Biogeochemical cycle of methane in the Barents Sea was studied using isotope geochemistry to determine rates of microbial methane oxidation. It was established that microbiological processes (glucose consumption, 14CO2 assimilation, sulfate reduction, and slow methane oxidation) in oxidized surface and weakly reduced sediments are marked by only insignificant change in SO4 concentration and absence of notable increase of total alkalinity and N/NH4 downward sediment cores. Microbial methane productivity was 0.111x10**6 mol/day. Taking into account volume of the water column, microbial methane consumption therein can be as much as 1.8x10**6 mol/day.

Organic matter, isotopic composition of calcite veins in basement basalt and pore water at DSDP Leg 78A Holes

Sediments of the Barbados Ridge complex, cored on DSDP Leg 78A, contain low concentrations of acid-insoluble carbon (0.05-0.25%) and nitrogen (C/N 1.5-5) and dispersed C1-C6 hydrocarbons (100-800 ppb). The concentrations of organic carbon and 13C in organic carbon decrease with depth, whereas the concentration of dispersed hydrocarbons increases slightly with depth. These trends may reflect the slow oxidation of organic matter, with selective removal of 13C and slow conversion of the residual organic matter to hydrocarbons. Very minor indications of nitrogen gas were observed at about 250 meters sub-bottom at two of the drilling sites. Basement basalts have calcite veins with d13C values in the range of 2.0 to 3.2 per mil and d18O-SMOW values ranging from 28.5 to +30.6 per mil. Interstitial waters have d18O-SMOW of 0.2 to -3.5 per mil and dD-SMOW of -2 to -15 per mil. The oxygen isotopic composition of the calcite veins in the basement basalts gives estimated equilibrium fractionation temperatures in the range of 11 to 24°C, assuming precipitation from water with d18O-SMOW in the range of +0.1 to -1.0 per mil. This suggests that basalt alteration and precipitation of vein calcite occurred in contact either with warmer Campanian seawater or, later, with pore water, after burial to depths of 200- 300 meters. Pore waters from all three sites are depleted in deuterium and 18O, and dissolved sulfate is enriched in 34S at Sites 541 and 542, but not at Site 543.

C1-C8 hydrocarbons in DSDP Leg 64 Holes sediments

Sediments from the Baja California Continental Margin Transect - Sites 474 and 476 - showed small amounts of C2-C8 hydrocarbons and functionalized compounds (alkenes) typical of organic-rich, Recent, cold (<30°C) marine sediments. In contrast, some samples from Sites 477, 478, 479, and Hole 481A in the Guaymas Basin, an active spreading center, showed the characteristics of thermally generated hydrocarbons. These include an increase (sometimes exponential) in amount and diversity of C2-C8 hydrocarbons and a decrease in alkenes in more thermally mature sediments. The results indicate that the injection of basaltic sills has minimal effect on C2-C8 hydrocarbon generation except in the immediate vicinity of the sill. The absence of light hydrocarbons close to the hottest sills suggests that the compounds distill away as they are formed in these areas of very active hydrothermal circulation. A sample of young sediment exposed to very high temperatures (>300°C) from deeper thermal sources at the hottest site, 477, showed a very limited hydrocarbon distribution, including primarily ethane, benzene, and toluene, together with smaller amounts of propane and butane.

Organic facies of Cenozoic and Cretaceous sediments at DSDP Leg 80 Holes

The organic facies of Cenozoic sediments cored at DSDP Sites 548-551 along the Celtic Sea margin of the northern North Atlantic (Goban Spur) is dominated by terrestrially derived plant remains and charcoal. Similar organic facies also occur in the Lower and Upper Cretaceous sections at these sites. Mid-Cretaceous (uppermost Albian-Turonian) sediments at Sites 549-551, however, record two different periods of enrichment in organic material, wherein marine organic matter was mixed with terrestrial components. The earlier period is represented only in the uppermost Albianmiddle Cenomanian section at the most seaward site, 550. Here, dark laminated marly chalks rich in organic matter occur rhythmically interbedded with light-colored, bioturbated marly chalks poor in organic matter, suggesting that bottom waters alternated between oxidizing and reducing conditions. A later period of enrichment in organic material is recorded in the upper Cenomanian-Turonian sections at Sites 549 and 551 as a single, laminated black mudstone interval containing biogenic siliceous debris. It was deposited along the margin during a time of oxygen deficiency associated with upwelling-induced intensification and expansion of the mid-water oxygen-minimum layer. In both the earlier and later events, variations in productivity appear to have been the immediate cause of oxygen depletion in the bottom waters.

Geochemistry and pyrolysis at DSDP Hole 77-535

There are substantial differences in the character of organic matter contained in the Pleistocene and Cretaceous sedimentary sequences of DSDP Site 535. The argillaceous Pleistocene section contains type III, gas-prone organic matter whereas the calcareous Cretaceous section is dominated by type II, oil-prone organic matter. A more detailed investigation of the Cretaceous section reveals that the finely laminated limestones of Valanginian to Barremian age are of good to excellent source quality. The indigenous organic matter contained within this organically rich section is thermally immature, not having undergone sufficient thermal diagenesis for the generation and expulsion of hydrocarbons. Within this stratigraphic section, however, staining by mature hydrocarbons was detected. These stains are associated with a fractured interval. These fractures may in turn represent potential migration pathways.

Quantity, provenance, and thermal maturity of organic matter at DSDP Holes 95-612 and 95-613

Using methods of analysis from organic geochemistry and organic petrography, we investigated six Pliocene to Maestrichtian samples from DSDP Site 612 and five Pliocene to Eocene samples from DSDP Site 613 for the quantity, type, and thermal maturity of organic matter. At both sites, organic carbon content is low in the Eocene samples (0.10 to 0.20%) and relatively high in the Pliocene/Miocene samples (0.87 to 1.15%). The Maestrichtian samples from Site 612 contain about 0.6% organic carbon. The organic matter is predominantly terrigenous, as indicated by low hydrogen index values from Rock-Eval pyrolysis and the dominance of long-chain wax alkanes in the extractable hydrocarbons. The organic matter is at a low level of thermal maturity; measured vitrinite reflectance values were between 0.27 and 0.44%.

Organic geochemistry of upper Jurassic-Cretaceous sediments at DSDP Hole 71-511

Cretaceous and Jurassic sediments 435 m thick were drilled at Site 511, in the basin province of the Falkland Plateau, during DSDP Leg 71. The calcareous Unit 3 and the clayey zeolitic Unit 4, both of Senonian age, revealed poorly preserved organic matter indicative of oxidized environments. The same characteristics prevailed for the clayey Unit 5 of Turonian to Albian age. Strictly reducing environments existed for black facies along Unit 6 of earliest Albian to Late Jurassic age and allowed the preservation of a rich organic material that is marine in origin. Besides the transition from reducing conditions in Unit 6 to oxidizing conditions in Unit 5, there are 20 meters of sediments in Cores 56-58 where detrital, nonmarine and then marine organic matter, both implying more or less reducing environments, are interlain by poorly preserved material. In the black shales of the bottom Cores 69 and 70, some nonmarine detritus is mixed with the predominantly marine organic material. An immature stage of evolution can be assigned to all of the samples studied. The chapter also undertakes a comparison with contemporaneous lithologies at adjacent Sites 327 and 330 and attempts some reconstruction of the geography of the eastern Falkland Plateau during the Mesozoic.

Organic geochemical characteristics at DSDP Holes 76-534A and 44-391C

Pyrolysis assay, bitumen analysis, and elemental analysis of kerogen were used to characterize the organic matter of selected core samples from Hole 534A (Leg 76) and Hole 391C (Leg 44) on the Blake-Bahama Plateau. The organic matter throughout the stratigraphic section appears to be principally of a terrestrial origin. The data from several isolated horizons in the Hatteras and Blake-Bahama Formations imply the presence of significant quantities of autochthonous marine organic matter. However, these horizons appear so limited that they cannot be considered potential liquid hydrocarbon source rocks. All the analyzed samples are immature and have not evolved sufficiently to enter into the main stage of hydrocarbon generation. The temporal and spatial restrictions of strata rich in marine organic matter suggest that they do not represent major expansions and contractions of anoxic bottom-water masses, but represent limited occurrences of anoxic conditions.

Organic geochemistry of ODP Leg 135 sediment samples

The average total organic carbon (TOC) content obtained after Rock-Eval/TOC analysis of 156 sediment samples from the eight sites cored during Leg 135 is 0.05%. Hence, the TOC content of Leg 135 sediments is extremely low. The organic matter that is present in these samples is probably mostly reworked and oxidized material. Ten sediment samples were selected for extraction and analysis by gas chromatography and gas chromatography-mass spectrometry. Very low amounts of extractable hydrocarbons were obtained and some aspects of the biomarker distributions suggest that these hydrocarbons are not representative of the organic matter indigenous to the samples. A sample of an oil seep from Pili, Tongatapu was also analyzed. The seep is a biodegraded, mature oil that shows many characteristics in common with previously published analyses of oil seeps from Tongatapu. Biomarker evidence indicates that its source is a mature, marine carbonate of probable Late Cretaceous-Early Tertiary age. The source rock responsible for the Tongatapu oil seeps remains unknown.