Four seep sites located within an ∼20km2 area offshore Georgia (Batumi seep area, Pechori Mound, Iberia Mound, and Colkheti Seep) show characteristic differences with respect to element concentrations, and oxygen, hydrogen, strontium, and chlorine isotope signatures in pore waters, as well as impregnation of sediments with petroleum and hydrocarbon potential. All seep sites have active gas seepage, near surface authigenic carbonates and gas hydrates. Cokheti Seep, Iberia Mound, and Pechori Mound are characterized by oil-stained sediments and gas seepage decoupled from deep fluid advection and bottom water intrusion induced by gas bubble release. Pechori Mound is further characterized by deep fluid advection of lower salinity pore fluids. The Pechori Mound pore fluids are altered by mineral/water reactions at elevated temperatures (between 60 and 110°C) indicated by heavier oxygen and lighter chlorine isotope values, distinct Li and B enrichment, and K depletion. Strontium isotope ratios indicate that fluids originate from late Oligocene strata. This finding is supported by the occurrence of hydrocarbon impregnations within the sediments. Furthermore, light hydrocarbons and high molecular weight impregnates indicate a predominant thermogenic origin for the gas and oil at Pechori Mound, Iberia Mound, and Colkheti Seep. C15+ hydrocarbons at the oil seeps are allochtonous, whereas those at the Batumi seep area are autochthonous. The presence of oleanane, an angiosperm biomarker, suggests that the hydrocarbon source rocks belong to the Maikopian Formation. In summary, all investigated seep sites show a high hydrocarbon potential and hydrocarbons of Iberia Mound, Colkheti Seep, and Pechori Mound are predominantly of thermogenic origin. However, only at the latter seep site advection of deep pore fluids is indicated.

Ulrich Berner, Thomas Pape, Anja Reitz, Mark Schmidt, Michael K. Ivanov, and Gerhard Bohrmann 1 Federal Institute for Geosciences and Natural Resources, Hannover, Germany 2 MARUM Center for Marine Environmental Sciences, University of Bremen, Germany 3 IfM-GEOMAR Leibniz-Institute of Marine Sciences, Kiel, Germany 4 UNESCO MSU Center for Marine Geology and Geophysics, Moscow State University, Russia

The Timber Peak of North Victoria Land, Antarctica, exposes, embedded between two 150 m thick Early Jurassic mafic sills, 80 m of Late Triassic sediments of the Beacon Supergroup. The sediments comprise fluvial channel sandstones interbedded with lacustrine and palustrine deposits containing Dicroidium-dominated floras. The sandstones show a thin fused margin at the contact to the sills. During the German Antarctic North Victoria Land Expedition IX (2005/2006) an approximately 3.5 m thick section of carbonaceous mudstones and coals, 12 m above the lower sill, was sampled for organic geochemical and petrographical analyses in order to better describe the depositional environment and to investigate whether the sill intrusions are responsible for thermal alteration processes of the sedimentary organic matter. Hydrogen and oxygen indices of RockEval pyrolyses suggest that the sediments contain degraded terrestrial organic matter (Type IV). Carbon isotope ratios of aliphatic and aromatic fractions show typical values related to land plant dominated material. Varying abundances of C27to C29-steranes reveal mixtures between land plant and aquatic organic matter, which in turn suggests that the sediments were likely deposited in swamp-like and/or lacustrine environments. Copyright © AAPG. Serial rights given by author. For all other rights contact author directly. Sterane isomerisation parameters indicate that the sediments have reached maturities of the oil window, which is supported by vitrinite reflectance data. We observe a general increase of vitrinite reflectance (VR) values from the top to the lower parts of the analyzed section. The increase of approximately 0.4 %-VR over a depth interval of 3.5 m is unusual and cannot be explained through subsidence processes, but must be related to an abnormal heat flow related to the sill intrusions. The maturity data suggests that the underlying sill had a greater thermal influence on the sediments than the overlying one. This assumption seems plausible as the vertical distance between the sample positions and the lower sill is 12 m compared to 65 m towards the upper sill. The increase of reflectance values, however, is not uniform and the observed scattering of the data might be attributed to the influence of the variability of the thermal conductivity of different sediment types. References Berner, U., E. Faber, G. Scheeder, and D. Panten, 1997, Primary cracking of algal and landplant kerogens: kinetic models of isotope variations in methane, ethane and propane: Chemical Geology, v. 126/3, p. 233-245. Berner, R.A. and R. Raiswell, 1983, Burial of organic carbon and pyrite sulfur in sediments over Phanerozoic time: A new theory: Geochimica et Cosmochimica Acta, v. 47/5, p. 855-862. Espitalie, J., J.L. Laporte, M. Madec, F, Marquis, P. Leplat, J. Paulet, and A. Boutefeu, 1977, Rapid method for source rock characterization, and for determination of their petroleum potential and degree of evolution: Revue de l'Institut Francais du Petrole et Annales des Combustibles Liquides, v. 32/1, p. 23-42. Lafargue, E., F. Marquis, and D. Pillot, 1998, Rock-Eval 6 Applications in Hydrocarbon Exploration, Production and Soils Contamination Studies: Oil & Gas Science and Technology, v. 53/4, p. 421-437. Peters, K. E., C.C. Walters, and J.M. Moldowan, 2005, The Biomarker Guide; Volume 1: Biomarkers and Isotopes in the Environment and Human History. 2ed., 471 p., ISBN: 0-521-78158-2. Peters, K E., C.C. Walters, and J.M. Moldowan, 2005, The Biomarker Guide; Volume II: Biomarkers and Isotopes in Petroleum Systems and Earth History. 2ed., p. 475-1155., ISBN: 0-521-83762-6. Sofer, Z., 1984, Stable carbon isotope compositions of crude oils; application to source depositional environments and petroleum alteration: AAPG Bulletin, v. 68/1, p. 31-49.

A suite of gas samples obtained from gas pockets and sediments of the Nankai accretionary prism (Site 808) has been analyzed for their gas composition and carbon and hydrogen isotope ratios. Gases collected from gas pockets between 10 and 555 mbsf consist of CH4 and CO2. Stable carbon isotope ratios of these two components point to a bacterial formation of methane via CO2-reduction that is also supported by D/H ratios of methane. Methane desorbed from sediments by a vacuum/acid treatment is of bacterial and thermal origin. Mixing between these gas types is indicated by molecular composition and carbon isotope ratios. Diagenetic processes at low temperatures can explain ethane to pentane concentrations from 0 to 850 mbsf. Between 850 mbsf and the basaltic basement hydrocarbon occurrences are related to catagenetic processes at elevated temperatures. Thermal alteration of organic matter is reflected through different gas parameters. Propane carbon isotope values of a sample from the zone of the frontal thrust indicate that the gas likely migrated from sediments of a higher maturity into the immature sediments at 366 mbsf.

The analysis of various factors influencing mineral availability documents future short-and long-term mineral-commodity supply trends. The lifetime of reserves, the development of the relative importance of production centres and the forecasting of the depletion of a resource base are mainly geological factors, although the category “reserves”, in contrast to “resources”, is determined by technical and economical aspects. These three factors govern the short-and long-term supply of mineral commodities. The intensity-of-use factors and the growth rate of consumption are variables related to the demand of mineral commodities. They influence the decision of companies for certain commodities as targets for exploration and investment in production centres. Both factors control the short-to medium-term mineral supply. Finally, the lead time to production is a technical variable, although influenced by ore deposit type, and controls short-term mineral availability.

Pyrolyses experiments (dry, open-system) on algal kerogens and landplant material (Berner et al., 1995) have shown that carbon isotopic variations of methane, ethane and propane obtained from laboratory simulations mimic isotope variations of natural thermal gases. These isotope variations can be approximated through kinetic models (Berner et al., 1995). Also, maturity parameters like vitrinite reflectance and Rock-Eval Tmax are reliably calculated from kinetic models that are based on pyrolysis experiments. User-friendly versions of isotope/maturity models for methane, ethane and propane were obtained from application of statistical curve-fitting procedures to the results of instantaneous kinetic models of Berner et al. (1995). The resulting simple empirical functions relate carbon isotopic variations of light hydrocarbons directly to source rock maturity and can be applied where gases have accumulated instantaneously. They allow flexible calculations that account for carbon isotopic variability of precursor sites of the individual gases. Application of the model enables detection of mixing between bacterial and thermal gases, as well as mixing between thermal gases of different maturities. The application of the proposed models is demonstrated in two case studies (Green Tuff Basin, Japan; Cooper Basin, Australia) with data taken from the literature (Rigby and Smith, 1981; Sakata, 1991).

Samples of an algae-rich kerogen and a xylite were subjected to an open-system pyrolysis that allows a simulation of primary cracking (temperatures: 20 to 810 degrees C, heating rate: 5 degrees C/min, helium flow: 21 ml/min) within the (measured) maturity range 0.3 to 5.4% vitrinite reflectance. Gases collected during pyrolysis were analyzed for their molecular composition and the carbon isotope ratios of methane, ethane and propane. With increasing maturity of the algae-rich kerogen, we observe an increase of the carbon isotope ratios of produced light hydrocarbons. Carbon isotope values of methane derived from xylite, however, show significant inversions with increasing maturity, that indicate an isotopic inhomogeneity of the precursors from which methane is generated. Hydrogen isotope values of methane from Kukersite vary between - 211 and - 84 parts per thousand, whereas, hydrogen isotope ratios of methane from xylite increase from - 314 to - 164 parts per thousand. The data of the pyrolysis experiments have been used to develop kinetic models of hydrocarbon generation that are combined with Rayleigh-distillation models to describe the isotope fractionation between organic matter and light hydrocarbons. Carbon isotope fractionation factors between kerogens and individual gas components are high for Kukersite (alpha(CH4-Kuk)=1.017, alpha(C2-Kuk)=1.009, alpha(C3-Kuk)=1.005) and low for xylite (alpha(CH4-Xyl)=1.0042, alpha(C2-Xyl)=1.003, alpha(C3-Xyl)=1.001). Hydrogen isotope fractionation factors are lower for Kukersite and higher for xylite (alpha(CH4-Kuk)=1.1, alpha(CH4-Xyl)=1.2) Gas generation and isotope models are combined with kinetic models of thermal kerogen alteration. The results of the calculations are compared to measured data of natural samples from the Delaware and Val Verde basins (U.S.A.).

Methane concentrations and stable carbon isotope ratios of water samples from the East Pacific Rise (EPR) at 21°S and the Arabian Sea (24°N, 65°E) have been determined. EPR surface water is in equilibrium (ca. 50 nl/L and −50

In order to estimate the isotope fractionation effect between coals and methane during coalification a maturity-related fractionation model has been developed for coals and reservoir gases of NW Germany which is based on empirical data. Assuming that observed isotope shifts of the convertible carbon of coals of different maturities are related to a loss of methane during coalification and that this shift can be described by a Rayleigh distillation process, functions with preselected fractionation factors were fitted to measured isotope data of the convertible carbon of coals. The best approximation of theoretical and measured data was achieved with a low fractionation factor (αc= 1.003). Using this model theoretical methane carbon isotope data were determined and compared to the isotopic composition of reservoir methanes of NW Germany. Although the methane isotope data of reservoir gases and the related maturity of the coals show a slight scatter, the theoretical data plot within the same range and follow the increase of the 13C concentration of reservoir gases with increasing maturity of the coals.

The combination of multiple sediment sources and varying rates of sediment accumulation in the Celebes and Sulu seas have had significant impact on the processes of diagenesis, mineralization, and pore-fluid flow.Isotopic and mass-balance calculations help elucidate the various reactions taking place in these western Pacific basins, where ash alteration and basalt-seawater interactions are superimposed on the effects of sulfate oxidation of organic carbon and biogenic methane and of dolomitization of biogenic carbonates.Based on the shape of the calcium and magnesium depth profiles, two major reactive zones have been identified.The first is located near the zone of sulfate depletion and is characterized by carbonate recrystallization, dolomitization and ash alteration reactions at both Ocean Drilling Program Sites 767 and 768.The second reactive zone corresponds to the bottom of the sedimentary sequence and is characterized by alteration reactions in the basement (Site 767) and in the pyroclastic deposits beneath the sediment column (Site 768).

Paleo‐temperature gradients for Site 768 are determined by modelling organic maturities. It is found that the measured maturity of the organic matter cannot be attributed to the present‐day thermal gradient of 130°C/KM. From a comparison between modelled and measured maturities a high paleogradient of 250°C/KM is derived.

Thermal hydrocarbons found in natural oil and gas deposits frequently represent gas mixtures, the differentiation of which can be difficult or impossible. A mathematical model has been developed to predict gas-mixtures from two known end-members. The basis for the model are the relationships between carbon isotope ratios of methane through propane, the molecular gas composition and the maturity of the organic precursor materials (sapropelic kerogen). Applying the model, it is possible to estimate the isotopic composition of mixed hydrocarbon gases from the maturities of the related source rocks.