Organic Geochemistry

Long-term changes in the carbohydrate composition of 5 dierent vascular plant tissues, including black mangrove leaves and wood (Avicennia germinans), cypress needles and wood (Taxodium distichum) and smooth cordgrass (Spartina alterni¯ora), were measured as these tissues decomposed over a 4 yr period under sub-aqueous conditions. Carbohydrate composition was measured using a molecular-level analysis for neutral sugars and a modi®ed version of the MBTH (3-methyl-2-benzothiazolinone hydrazone hydrochloride) method for colorimetric determination of total carbohydrate yields. Minimal cross contamination from non-carbohydrate vascular plant constituents indicated the MBTH method was highly speci®c for carbohydrates. The dierence between total carbohydrate yields using the MBTH method and total neutral sugar yields revealed a substantial carbohydrate fraction (7±23% of the total plant carbon) in fresh and senescent tissues that was not identi®ed at the molecular level. The molecularly uncharacterized fraction of carbohydrates probably consisted of ketoses, uronic acids and amino sugars.

Frequent charcoal ®ndings together with black carbon concentrations in the soil organic matter (SOM) of up to 35% provided evidence that black carbon is important for the SOM stability in Terra Preta soils. This paper aims to investigate whether black carbon is additionally stabilised by organo-mineral complexation. For this purpose black carbon was analysed in density fractions using benzenecarboxylic acids as molecular markers. Density fractions were also studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. Concentrations and total amounts of black carbon were generally highest in the light fraction indicating that a major part of black carbon is not chemically stabilised but intrinsically refractory. On the other hand, a large part of black carbon was also found in the heavier fractions, where it was partly embedded within plaques of iron and aluminium oxides on mineral surfaces. The major part of black carbon in the medium fraction seemed to be organo-mineral complexed because we found amounts of black carbon in this fraction by wet chemical analysis but not by scanning electron microscopy and energy dispersive X-ray spectroscopy. The spectroscopic analysis can only detect particulate black carbon. Black carbon was particularly enriched in 30±40 cm soil depth, and in all fractions of Terra Preta soils compared to adjacent Oxisols. The occurrence of particulate black carbon together with potsherds in the subsoil horizons of Terra Preta soils indicate that this might be due to turbation processes or the soils were covered by earthworm or termite activities. Further research, however, is needed to clarify the transport mechanisms of black carbon into deeper soil horizons. #

Series of C37-C39 di-and triunsaturated ketones and methyl and ethyl esters of hexatriacontadienoic acid (C3~,: 2) have been previously identified in marine sediments and the coccolithophorid Emiliania huxleyi. These compounds have now been found in four further species of the Isochrysidales (Prymnesiophyta) which are not known to bear coccoliths, suggesting that they are more widely distributed in living algae than previously thought. In addition, the ketones have been recognised in sediments of Eocene age (ca 45 Ma) which greatly extends their known geological time range and increases their potential as molecular markers for algal input. Heptatriacontatetraen-2-one (C37 : 4), octatriacontatetraen-3-one (C38 : 4), methyl and ethyl esters of hexatriacontatrienoic acid (C3¢, : 2) and the ethyl ester of hexatriacontatetraenoic acid (C36 : 4) have also been identified in varying amounts in thesc algae by gas chromatography and computerised gas chromatography-mass spectrometry.

Sedimentary basins are significant deposits for both fossil energy sources and metallic ore deposits. It has been reported in numerous studies that a close relationship exists between oil and gas reservoirs and metallic ore deposits. Besides, in many studies, it has been determined that both source rocks and petroleum resources have a high amount of metal concentrations. In ore deposits, for hand specimens and on a microscopic scale, metallic ores are spatially associated with hydrocarbons. Organic matter in sediments can occur in different forms such as kerogen, bitumen, solid carbon, hydrocarbon gas, and more, in fractures and inclusions in significant amounts of free oil. On a regional scale, both metallic ore deposits and hydrocarbon reservoirs or seeps are generally bounded by the same tectonic units of the basin and controlled by the similar structures (especially regional anticlines, domes or paleo-highs). The results of the study show that hydrocarbons and metals derived from sediment pores during diagenesis are deposited by the co-transportation process by the same hydrothermal fluid and so, ore and organic matter in host rocks have a common source. In other words, organic- and metal-rich sediments in a sedimentary basin are used as a source for both metallic ore deposits and hydrocarbon reservoirs. Metal- and hydrocarbon-rich fluids derived from sediments consolidated as a result of topographic uplift and the compression of the basin laterally migrate along aquifers and head towards the boundaries of the basin and paleo-highs through the faults in the main- and sub-basin. Thus, they constitute metallic ore deposits and hydrocarbon reservoirs characterized by different deposition and trapping mechanisms in different compartments. Metallic ores are deposited in faults, fracture zones, and unconformity surfaces in areas where ore fluids encounter appropriate geochemical barriers. Hydrocarbons accumulate in stratigraphic, lithological, and structural traps. Within the scope of the study, the usage of metallic ore deposits as an indicator in hydrocarbon exploration are investigated in the regions where there are no surface hydrocarbon shows (outcrop of source rocks, oil or gas seeps, oil or gas fields), but there are the metallic ore deposits in operable scales. For this purpose, the results of the studies performed in four different regions of Turkey where there are the metallic ore deposits in operable-sizes have been presented. As a result of the study, it has been inferred that, in the regions where especially economic metallic ore deposits are located, they can be utilized as a shallow and reliable indicator for oil and gas exploration.

Keywords: Oil and gas exploration, Ore deposit, Mineral, Mineralization, Geochemical indicator, Geothermal resources

Bulk (elemental composition, IR, CP/MAS ~3C NMR) and molecular (GC-MS) analyses have been performed on a series of ambers and resins derived from different locations (Dominican Republic, Philippines, Canada, Israel, New Zealand, Chile) having diverse botanical affinities (Araucariaceae, Hymenaea) and variable age (from Holocene to Early Cretaceous). No major differences have been observed from the elemental composition and the spectroscopic data; however, the molecular analyses of the solvent extractable fraction show that a specific mixture of components is present in each sample. These are mainly diterpcnoid products that in general arc also found abundantly in the higher plants from which the ambers and resins originate. Nevertheless, a direct relationship between major terpenoid constituents in fossil resins and precursor plant materials can only be established for the younger samples.

Parent and alkyl PAHs (51 compounds and alkyl homologues) have been quantified in suspended particulates and sediments (345 samples) from the Fraser River system, British Columbia, Canada. The best potential to distinguish natural and anthropogenic sources is exhibited by ratios of the principal mass 178, 202, 228 and 276 parent PAHs, 1,7/ 2,6+1,7-DMP (dimethylphenanthrene), the phenanthrene/anthracene and fluoranthene/pyrene alkyl PAH series and several less commonly applied PAHs (e.g. acephenanthrylene and pentaphene). Using these ratios we infer sources of PAH to the Fraser basin and evaluate the consistency of these source assignments and the suitability of various commonly applied PAH ratios as indicators. PAH ratios and total concentration data reveal a basin lightly impacted by a variety of sources in its remote regions, especially near roads, but heavily impacted in urban areas, particularly near Vancouver. Contamination sources shift from biomass (e.g. wood and grass) burning to vehicle emissions between remote and urban locations. Stormwater and wastewater discharges appear to collect PAH from urban areas and release them as point sources. In contaminated areas ratios are specific for combustion vs. petroleum sources, and some ratios (202 and 276) distinguish biomass or coal from liquid fossil fuel combustion. At lower concentrations multiple sources at times make interpretations based on a single ratio misleading and the higher mass ratios (228 and 276) may be most applicable to urban areas. In all cases the examination of a variety of PAH indicator ratios that encompass a range of masses is necessary for a robust interpretation. #

The geochemical characteristics of 16 oils/condensates/seep oil/oil shows (collectively called oils) from the Eastern Papuan Basin (EPB) and one seep oil from the Western Papuan Basin (WPB) are integrated with data from previous studies of oils, fluid inclusion oils and solid bitumens from the EPB and WPB, Papua New Guinea. The combined set of samples can be divided in two major families of hydrocarbons. The Family A oils, mostly occurring in the WPB region, were generated from clay rich marine source rocks, containing predominantly terrigenous higher plant derived organic matter (OM) deposited in a sub-oxic to oxic environment. Source rock(s) for Family A oils are likely to be of Middle to Upper Jurassic, e.g., the Upper Jurassic Imburu Formation. The Family B oils, distributed mainly in the EPB region, were generated from Cretaceous or younger marine carbonate source rock(s) deposited under anoxic to suboxic conditions, and containing predominantly prokaryotic OM with some terrigenous higher plant inputs. The EPB natural gases analyzed in this study may be co-genetic to the co-occurring Family B oils in the EPB. Both Family A and B oils were generated at similar thermal maturities of 1.0-1.3% vitrinite reflectance equivalent. Although no source interval to date has been firmly identified in the EPB, post-Jurassic strata are a viable option, because (1) Late Cretaceous and Paleogene carbonate and clastic marine sediments including possible source lithologies are present, and (2) this section of the Papuan Basin sustained rapid sedimentation and tectonic loading, particularly in the Cenozoic.

The present work describes the extraction of fulvic acids (FA) from Shilajit and its spectroscopic and mass spectrometric characterization. The spectral features obtained from FT-IR and 1 HNMR were similar to those reported for humic substances from other sources. The molecular elemental composition analysis by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in electrospray negative ion mode resulted in extraordinary high average O/C ratios (0.55) which might be caused by a significant contribution of carbohydrates in Shilajit. A very high average H/C ratio of 1.27 also points to dominant aliphatic or alicyclic structures and relatively low aromaticity. The average molecular formula of the nitrogen free elemental compositions measured by FT-ICR mass spectrometry is C 18.2