Aromatic Biomarkers Research Articles

Chemical compound classes supporting microbial methanogenesis in coal

Microbial generation of coalbed methane (CBM) occurs in numerous basins worldwide. This study identifies specific classes of chemical compounds in two high volatile bituminous coals from the Illinois Basin in southwestern Indiana, USA that are being degraded during methanogenesis. Springfield Coal is rich in vitrinite (92.2vol.% vitrinite in coal) whereas Lower Block Coal contains larger contributions of liptinite and inertinite and contains only 66.2vol.% vitrinite. Anaerobic bioreactors used in the experiments contained a mineral-salts medium, operationally-defined coal extracts, and a microbial inoculum composed of an endemic microbial consortium that was obtained from co-produced water from an active CBM well. Our experiments investigated degradation of organic matter (OM) and concurrent methanogenesis using water-soluble, methanol (CH3OH)-soluble, and dichloromethane (CH2Cl2)-soluble fractions of extracted OM from coal as the sole carbon sources. Only methanol and dichloromethane were found to be effective solvents to extract sufficient OM from coals for biodegradation. The methane yield over time was small (1.7 to 8.7μmol in total headspace) and less than 1% of carbon added to bioreactors in organic extracts was converted into methane. Extracts of vitrinite-rich Springfield Coal yielded relatively more methane than extracts of Lower Block Coal. The preference of methanogenic microbial consortia for extracts from vitrinite-rich Springfield Coal may be related to the fact that the organic matter in vitrinite is rich in functional groups containing organic nitrogen, sulfur and oxygen (NSO) that provide chemical sites with low activation energies to initiate biodegradation. A comparison of the molecular compositions of the initial organic extracts with their biodegraded residues after incubation of the bioreactors for 24weeks indicated that biodegradation of n-alkanes and aromatic hydrocarbons occurred concurrently, whereas hopanes proved to be far more refractory. Our study documents significant biodegradation of n-alkanes (14 to 91% by GC/MS peak intensity) from coal extracts. It is particularly noteworthy that biodegradation also eliminated 6 to 58% of aromatic biomarkers, although the pool of n-alkanes was not exhausted. This significant early biodegradation of aromatic hydrocarbons in coal extracts contrasts starkly with the biodegradation pattern of petroleum where similar aromatic compounds are degraded only after n-alkanes have been severely depleted. This evidence may support the hypothesis that microbial communities engaged in coal biodegradation do not express a strong preference for either aliphatic or aromatic carbon sources, in contrast to biodegradation patterns typical of petroleum. CH3OH‐extracted organic matter from coal was generally more biodegradable than CH2Cl2-extracted organic matter from the same coal, probably because CH3OH extracts contained lower concentrations of longer straight aliphatic chains allowing faster microbial degradation.

Petroleum geochemistry of the Potwar Basin, Pakistan: II – Oil classification based on heterocyclic and polycyclic aromatic hydrocarbons

► Potwar Basin Pakistan contains marine to terrigenous crude oils. ► Aromatic biomarkers reveal oil classification and type of source organic matter. ► Abundance of heterocyclics depends on depositional environments of organic matter. ► Triaromatic/methyl triaromatic steroids show interesting source related distribution. ► Alkyl isomers of naphthalene, phenanthrene, dibenzothiphene, dibenzofuran, fluorene. In a previous study, oils in the Potwar Basin (Upper Indus) of Pakistan were correlated based on the dissimilarity of source and depositional environment of organic matter (OM) using biomarkers and bulk stable isotopes. This study is aimed at supporting the classification of Potwar Basin oils into three groups (A, B and C) using the distribution of alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, alkyldibenzofurans, alkylfluorenes, alkylbiphenyls, triaromatic steroids, methyl triaromatic steroids, retene, methyl retenes and cadalene. The higher relative abundance of specific methyl isomers of naphthalene and phenanthrene and the presence of diagnostic aromatic biomarkers clearly indicate the terrigenous and oxic depositional environment of OM for group A oil. Group B and C oils are of marine origin and the aforementioned heterocyclic and polycyclic aromatic hydrocarbons (HCs) differentiate them clearly into two different groups. The relative percentages of heterocyclic aromatic HCs reveal that the distribution of these compounds is controlled by the depositional environment of the OM. Sulfur-containing heterocyclic aromatic HCs are higher in crude oils generated from source rocks deposited in suboxic depositional environments, while oxygen-containing heterocyclic aromatic HCs in combination with alkylfluorenes are higher in marine oxic and deltaic oils. Biomarker and aromatic HC parameters do not indicate significant differences in the thermal maturity of Potwar Basin oils. Triaromatic and methyl triaromatic steroids support the division of Potwar Basin oils into the three groups and their relative abundances are related to source OM rather than thermal maturity. Significantly higher amounts of C 20 and C 21 triaromtic steroids and the presence or absence of long chain triaromatic steroids (C 25 , C 26 , C 27 , and C 28 ) indicates that these compounds are probably formed from different biological precursors in each group. Different isomers of methyl substituted triaromatic steroids are present only for short chain compounds (C 20 –C 22 ) and the origin of these compounds may be short chain methyl steranes from unknown biological precursors.

Differential transportation and deposition of terrestrial biomarkers in middle Eocene fluvial to estuarine environments, Hokkaido, Japan

Abstract Higher plants constitute a significant portion of sedimentary organic matter in middle Eocene fluvial–floodplain–estuarine sedimentary rocks exposed in the Bibai region of central Hokkaido, Japan. The differential transportation and deposition of terrestrial biomarkers were studied in this area. The distribution of higher plant and fungal biomarkers in the Bibai non-marine sedimentary rocks was constrained by sedimentary facies and lithology. Claystones and siltstones lacking coaly fragments tended to be rich in angiosperm biomarkers, whereas coal and coaly mudstones were comparatively rich in gymnosperm biomarkers. Perylene, a possible fungal biomarker, was detected in fine-grained floodplain deposits. Facies and lithologic controls on terrestrial biomarker distribution can be attributed to the differential transportation and deposition of organic debris and degradation products derived from higher plants and fungi. Redox potential of the depositional environment is another important factor for the formation and preservation of terrestrial aromatic biomarkers. Reconstruction of land-based paleovegetation from terrestrial biomarkers in non-marine sediments requires careful consideration of the differential transportation and preservation of precursory terrestrial organic compounds.

Geochemical characteristics of Tertiary coal-bearing source rocks in Xihu depression, East China Sea basin

This study aims at investigating hydrocarbon generation potential and biological organic source for the Tertiary coal-bearing source rocks of Pinghu Formation (middle-upper Eocene) in Xihu depression, East China Sea shelf basin. Another goal is to differentiate coal and mudstone with respect to their geochemical properties. The coal-bearing sequence has a variable organofacies and is mainly gas-prone. The coals and carbonaceous mudstones, in comparison with mudstones, have a higher liquid hydrocarbon generation potential, as reflected by evidently higher HI values (averaging 286mg HC/g C) and H/C atomic ratios (round 0.9). The molecular composition in the coal-bearing sequence is commonly characterized by unusually abundant diterpenoid alkanes, dominant C29 sterane over C27 and C28 homologues and high amount of terrigenous-related aromatic biomarkers such as retene, cadalene and 1, 7-dimethylphenanthrene, indicating a predominantly terrigenous organic source. The source rocks show high Pr/Ph ratios ranging mostly from 3.5 to 8.5 and low MDBTs/MDBFs ratios (<1.0), indicating deposition in an oxic swamp-lacustrine environment. The coals and carbonaceous mudstones could be differentiated from the grey mudstones by facies-dependent biomarker parameters such as relative sterane concentration and gammacerane index and carbon isotope composition. Isotope and biomarker analysis indicate the genetic correlation between the Pinghu source rocks and the oils found in Xihu depression. Moreover, most oils seem to be derived from the coal as well as carbonaceous mudstone.

Geochemical characterization of an oil seep from the Bagua Basin, north-central Peru

Oil hosted in a rock taken from a seep exposed by a road cut in north-central Peru was studied by geochemical means. The oil is classified as heavy paraffinic (waxy) by liquid chromatography. The oil appears to be highly mature, showing evidence of chemical and/or biological degradation. This is further supported by relatively high yields of polar fractions (resins and asphaltenes), partial depletion of n-alkanes below C16, and a relative enrichment of isoprenoid hydrocarbons. The n-alkane distribution obtained by whole-oil gas chromatography (GC) also points to mature, waxy oil. Pristane/phytane and isoprenoid ratios suggest that Type II kerogen deposited in low-oxygen (dystrophic) environment was likely the source of the oil. Biomarker fingerprints of the saturate fraction obtained by gas chromatography–mass spectrometry (GC–MS) and other characteristic ratios indicate the high level of thermal maturation of the oil and suggest that the oil was derived from a clay-rich source rock rich in bacterial-derived organic matter deposited in suboxic conditions. Aromatic biomarker data confirm the high level of thermal maturity of the oil and point to a mixed shale/carbonate source rock deposited in a sulfate-poor marine environment. The parent oil most likely has a pre-Cretaceous source due to the absence of 18 α (H) oleanane and the fact that the C28 αββ/C29 αββ steranes and the C28 αββ/C29 αββ sterane vs. C27 αββ/C29 αββ sterane ratios are both comparable to values reported for oils derived from the Jurassic Pucara Formation source rock in the nearby Marañon Basin.

Bioaccumulation of petroleum hydrocarbons in arctic amphipods in the oil development area of the Alaskan Beaufort Sea

An objective of a multiyear monitoring program, sponsored by the US Department of the Interior, Bureau of Ocean Energy Management was to examine temporal and spatial changes in chemical and biological characteristics of the Arctic marine environment resulting from offshore oil exploration and development activities in the development area of the Alaskan Beaufort Sea. To determine if petroleum hydrocarbons from offshore oil operations are entering the Beaufort Sea food web, we measured concentrations of hydrocarbons in tissues of amphipods, Anonyx nugax, sediments, Northstar crude oil, and coastal peat, collected between 1999 and 2006 throughout the development area. Mean concentrations of polycyclic aromatic hydrocarbons (PAH), saturated hydrocarbons (SHC), and sterane and triterpane petroleum biomarkers (StTr) were not significantly different in amphipods near the Northstar oil production facility, before and after it came on line in 2001, and in amphipods from elsewhere in the study area. Forensic analysis of the profiles (relative composition and concentrations) of the 3 hydrocarbon classes revealed that hydrocarbon compositions were different in amphipods, surface sediments where the amphipods were collected, Northstar crude oil, and peat from the deltas of 4 North Slope rivers. Amphipods and sediments contained a mixture of petrogenic, pyrogenic, and biogenic PAH. The SHC in amphipods were dominated by pristane derived from zooplankton, indicating that the SHC were primarily from the amphipod diet of zooplankton detritus. The petroleum biomarker StTr profiles did not resemble those in Northstar crude oil. The forensic analysis revealed that hydrocarbons in amphipod tissues were not from oil production at Northstar. Hydrocarbons in amphipod tissues were primarily from their diet and from river runoff and coastal erosion of natural diagenic and fossil terrestrial materials, including seep oils, kerogens, and peat. Offshore oil and gas exploration and development do not appear to be causing an increase in petroleum hydrocarbon contamination of the Beaufort Sea food web.

Application of Light Petroleum Biomarkers for Forensic Characterization and Source Identification of Spilled Light Refined Oils

Light petroleum biomarkers such as bicyclic sesquiterpanes and diamondoids are ubiquitous components of crude oils and ancient sediments, and are also widely found in intermediate petroleum distillates and many finished petroleum products. These compounds are relatively resistant to biodegradation and light-to-medium evaporation weathering, thus particularly useful in oil-source correlation and differentiation for those cases where the traditional tri- to pentacyclic biomarkers are absent. This work utilized sesquiterpanes and diamondoids for fingerprinting and identification of light oils spilled on water. The gas chromatography/flame ionization detection (GC/FID) analysis and distribution profiles of polycyclic aromatic hydrocarbon (PAHs) and conventional biomarkers suggest that the spilled oils are mixtures of mainly gasoline and light diesel type fuel. Since potential source oil candidates were not available, and a large part of the hydrocarbons in gasoline and diesel co-eluted in chromatographic analysis, it is a challenge to quantify the gasoline and diesel in spill samples. It has been known from previous studies that the bulk concentrations of C14 to C16 sesquiterpanes are in the range of approximately 6,000 to 9,000 μg/g for many light diesel fuels, while little or no sesquiterpanes were detected in gasoline, light kerosene and heavy-end lubricating oils. The target sesquiterpanes in the spilled oil samples were determined to be in quite high concentrations: approximately 4,000 μg/g oil. Therefore, it was estimated that these spilled oil samples consist of approximately half gasoline and half light diesel. To verify the estimation, spilled samples were simulated by mixing a fresh gasoline and a light diesel with a similar carbon range as the spilled oils. Results from comparison of GC/FID chromatograms of the spilled oils with the simulated spill samples are consistent with that obtained from sesquiterpane analysis.

Applications of Polycyclic Aromatic Hydrocarbons to Assess the Source and Thermal Maturity of the Crude Oils from the Lower Indus Basin, Pakistan

A suite of six crude oils from Lower Indus Basin, Pakistan, were analyzed for geochemical characterization of source organic matter (OM) and thermal maturity. Distribution of polycyclic aromatic hydrocarbons (PAHs), alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, and aromatic biomarkers were reported from aromatic fractions of the crude oils. The aromatic hydrocarbons parameters revealed a higher thermal maturity of OM of source rock-generated Lower Indus Basin oils. Calculated vitrinite reflectance values from the methylphenanthrenes index 1 (MPI-1) and methyldibenzothiophene ratio (MDR) indicate that most of the oils reached a late oil generation window of thermal maturity. PAH distributions revealed the oils of two different origins are present in the Lower Indus Basin; two oil samples indicate aquatic source of OM and the aromatic biomarker distributions of retene, 1-MP, and 1,7-DMP indicate a significant contribution of land plant OM in the other four oils. This is the first study to report the distribution of aromatic hydrocarbons from Lower Indus Basin crude oils.

Aliphatic and aromatic biomarkers from Carboniferous coal deposits at Dunbar (East Lothian, Scotland): Palaeobotanical and palaeoenvironmental significance

Carboniferous (Viséan) coals from Dunbar, East Lothian, Scotland, contain well-preserved miospore and megaspore assemblages suggesting a lycopod-dominated forest ecosystem with some ferns, sphenopsids and pteridosperms. The low rank of the coals and the well defined microflora permit assessment of the palaeoenvironmental significance of lipid biomarkers during the Early Carboniferous. Rock-Eval, petrographic, and lipid analyses indicate a fully terrestrial depositional environment. Although we also present and discuss a wide diversity of other lipid biomarkers (alkanes, hopanoids, steroids), we focus on the terrestrial-derived biomarkers. Combustion-derived PAHs pyrene, fluoranthene, benzo[a]anthracene, chrysene and triphenylene indicate the occurrence of forest fires in the study areas during Early Carboniferous times. Alkyldibenzofurans are considered to derive from lichen-biomass. Retene, cadalene, simonellite, tetrahydroretene and kaurane are poorly specific and can derive from a variety of early Palaeozoic land plants. Abietane, phyllocladane, ent-beyerane and 4β(H)-eudesmane, as well as bisnorsimonellite, diaromatic totarane, diaromatic sempervirane and 2-methylretene, however, as yet had only been reported from conifers, which do not appear in the fossil record until the Late Carboniferous. Within the lower Carboniferous forest ecosystem, arborescent lycopsids and pteridosperms are proposed as alternative sources for these compounds.

Aliphatic and aromatic biomarkers from Gondwanan sediments of Late Ordovician to Early Devonian age: An early terrestrialization approach

Twenty one core samples of Late Ordovician to Early Devonian age from sections in southern Tunisia, North African Platform (Gondwana) and containing marine and terrestrial organic matter with microbial input were investigated to link the aliphatic and aromatic hydrocarbon distributions with the terrestrial and marine palynomorph content (e.g. acritarchs, prasinophytes, chitinozoans, cryptospores and trilete spores). In addition to several biomarkers of algal/bacterial origin, long chain n-alkanes that might be derived from land plants, as well as the terrestrial diterpane, norabietane, were found. Several land plant-derived biomarkers, such as retene, cadalene, simonellite, tetrahydroretene and C 19 isohexylalkyl naphthalene were observed in the aromatic fractions. While these terrestrial biomarkers could be clearly recognized in the middle Silurian–lower Devonian samples, their presence in the upper Ordovician–lower Silurian sediments is more doubtful, because of much lower relative abundances. The land plant biomarkers show a fairly good correlation with the occurrence and abundance of cryptospores and trilete spores, derived from bryophytes and tracheophytes, which covered the emerged areas around the Ghadamis Basin during the Silurian and Devonian. The early tracheophytes (e.g. Cooksonia, lycophytes and zosterophylls) are therefore suggested as a new terrestrial source for most of the saturated and aromatic biomarkers found in sediments of Middle Silurian to Early Devonian age.

Vegetation Effects on Soil Organic Matter Chemistry of Aggregate Fractions in a Hawaiian Forest

We examined chemical changes from leaf tissue to soil organic matter (SOM) to determine the persistence of plant chemistry into soil aggregate fractions. We characterized a slow (Dicranopteris linearis) and fast-decomposing species (Cheirodendron trigynum) and surface (O), and subsurface (A-horizon) SOM beneath each species using pyrolysis-gas chromatography/mass spectrometry (py-GC/MS), with and without derivatization. The live tissues of Dicranopteris had greater lignin content whereas Cheirodendron had a greater lipid, N-bearing, and polysaccharide component. Despite this difference in leaf chemistry, SOM chemistry was similar between soil aggregate fractions, but different between horizons. The O-horizon contained primarily lignin and polysaccharide biomarkers whereas the A-horizon contained polysaccharide, aromatic, and N-derived compounds, indicating considerable microbial processing of plant litter. The soils beneath Cheirodendron inherited a greater lipid signal composed of cutin and suberin biomarkers whereas the soils beneath Dicranopteris contained greater aromatic biomarker content, possibly derived from plant lignins. The soils beneath both species were more similar to root polysaccharides, lipids, and lignins than aboveground tissue. This study indicates that although plant-derived OM is processed vigorously, species-specific biomarkers and compound class differences persist into these soils and that differences in plant chemical properties may influence soil development even after considerable reworking of plant litter by microorganisms.

Improved understanding of mixed oil in Nigeria based on pyrolysis of asphaltenes

Crude oil from reservoirs in the onshore Niger Delta is a mixture of low and high maturity charge. Aromatic biomarkers in these oils, such as alkylphenanthrenes and alkylnaphthalenes, show relatively high thermal maturity, whereas the saturated sterane and hopane biomarkers indicate lower maturity close to the peak of the oil window. The high predicted maturity of the crude oils based on alkylphenanthrene and alkylnaphthalene indices is probably caused by mixing of high maturity condensate with less mature black oil. This correlates with the gas washing phenomenon of studied Nigerian oils caused by migrating condensate stream. The results of our study indicate that asphaltenes can be used to infer the organofacies of the low maturity petroleum charge in mixed crude oils. Compositional characteristics of the asphaltene pyrolysates indicate an origin of the related oils from Type II/III or Type III source rock kerogen. The n-alkyl-chain length distributions of the asphaltene pyrolysates predict source rocks that generated high wax paraffinic–naphthenic–aromatic oils or paraffinic oils. The n-alkyl-chain length of asphaltene pyrolysates changes in proportion to oxicity and the relative input of terrigenous organic matter to the source rock.

Aromatic biomarkers as indicators of source, depositional environment, maturity and secondary migration in the oils of Cambay Basin, India

Aromatic biomarkers have been analysed for source, depositional environment, maturity and secondary migration in crude oils from different formations of Paleocene to Eocene age in the Ahmedabad–Mehsana Block of North Cambay Basin and the Broach Block of South Cambay Basin. North Cambay Basin oils are characterized by a high abundance of 1,2,5- and 1,2,7-trimethylnaphthalenes (TMN) and low to medium ratio of dibenzothiophene/phenanthrene and low ratio of pristane/phytane indicates that these oils have been derived from a source containing predominantly higher plants, and that the organic matter was deposited in restricted marine or lacustrine environments in anoxic to suboxic conditions. The relative abundance of 1,2,7-TMN suggests that it was derived from the structural degradation of oleanane type triterpenoids present in angiosperms. South Cambay Basin oils are less abundant in 1,2,5- and 1,2,7-TMNs and low ratio of dibenzothiophene/phenanthrene and high ratio of pristane/phytane indicating that the oils were derived from higher plant source organic matter deposited under marine or fluvial deltaic environment in oxic conditions. Maturity sensitive ratios based on phenanthrene, naphthalene, dibenzothiophene and their alkyl substituted isomers have been used to calculate the equivalent vitrinite reflectance. These parameters indicate a wide range of thermal maturity of the oils ranging from 0.60% to 0.93% VRc. Methylphenanthrene index and methyldibenzothiophene ratios indicate that the maturity of North and South Cambay Basin oils are different. The North Cambay Basin oils are less mature than South Cambay Basin oils. Pyrrolic nitrogen distribution indicates that the alkylated carbazoles and benzocarbazoles are more abundant in South Cambay Basin oils as compared to North Cambay Basin oils. These data indicate that North Cambay Basin oils are less migrated compared to South Cambay Basin oils. This systematic investigation of the aromatic biomarkers in oils of Cambay Basin has resulted in a new generation, migration, and entrapment model that has led to the development of new exploration leads.

Origin and occurrence of crude oil in the Niger delta, Nigeria

Ten crude oils samples from onshore and offshore Niger delta were characterized based on their biomarkers and isotopic composition by Gas chromatography–Mass spectrometry and Isotope mass spectrometry. Abundance of pentacyclic triterpanes of hopane and oleanane skeletons and C 27–C 29 steranes in the oils indicates that they were formed from a mixed source (marine and terrestrial kerogen). The oleanane concentrations permit source grouping of the oils into three families. Various maturity parameters computed for the oils, especially those of aromatic biomarkers and aromatic sulfur compounds (thiophenes) to some extent reveal an increasing thermal maturity with increasing reservoir depths. The carbon isotope values lacked sufficient variation to distinguish maturity differences in the oils. This observation is quite revealing in that oils whose associate gases had earlier revealed a consistent increase in maturity with increasing depths, also have similar maturity values. The implication of this is that the oils and associated gases might have been formed at different levels of thermal maturity before being pooled together during migration into their present habitat.

Typing/correlation of Nigerian crude oils using saturates and aromatic biomarkers

Typing/correlation of Nigerian crude oils using saturates and aromatic biomarkers

Polar aromatic biomarkers of Miocene-aged Chukurovo resinite and correlation with a progenitor macrofossil

Abstract Functionalised aromatic constituents of Chukurovo resinite are compared here with the chemical composition of a macrofossil assigned paleobotanically as Taxodium dubium ( Sternb .) Heer. Terpenoids and lipids of fossil wood tissue embedded in a clay sediment were extracted and analyzed for comparison. The information was interpreted in relation to the biomarker compositions of different conifer families, as well as to the effects of contamination by inward migration of organic matter from the adjacent sediments. Many of identified geolipids, i.e., alkanes, alkanols, alkan-2-ones, and steranes/triterpanes have no chemosystematic value because they are ubiquitous in the plant kingdom. Ferruginol, sugiol, and products of their diagenetic transformations were identified as the dominant specific biomarkers in the resinite. Ferruginol and its analogues were the most abundant diterpenoids in Taxodium dubium sample. Thus, the biomarker composition of the extractable matter of the resinite strongly suggests that species of Cupressaceae contributed significantly to the Chukurovo paleoenvironment.

Abundance anomalies of aromatic biomarkers in the Permian–Triassic boundary section at Meishan, China — Evidence of end-Permian terrestrial ecosystem collapse

Several aromatic biomarkers detected in solvent extracts and kerogen pyrolysates from samples of the Global Stratotype Section and Point (GSSP) for the Permian–Triassic boundary at Meishan, China, show distinctive relative-abundance anomalies that may be related to the end-Permian biotic crisis on land. Enrichment of dibenzofuran homologues across the Permian–Triassic boundary may corroborate the concept of excessive soil erosion following loss of rooted vegetation. Enrichment of alkylphenol entities occurs just below the main marine mass extinction horizon and prior to the characteristic end-Permian δ 13C decline. The alkylphenols were probably derived from lignin and may provide a molecular record of dieback of woody vegetation. Highly decreased relative abundances of dibenzothiophenes could be indicative of excessive supply of Fe 2+. It is suggested that Fe 2+ was land-derived and may have originated from soils. In addition to the Permian–Triassic boundary interval, biomarker abundance anomalies also occur around the Wuchiapingian–Changhsingian boundary in the basal part of the Meishan section.

06/02523 Occurrence and palaeoenvironmental significance of aromatic hydrocarbon biomarkers in Oligocene sediments from the Mallik 5L-38 gas hydrate production research well (Canada)Haberer, R. M. et al. Organic Geochemistry, 2006, 37, (5), 519–538

06/02523 Occurrence and palaeoenvironmental significance of aromatic hydrocarbon biomarkers in Oligocene sediments from the Mallik 5L-38 gas hydrate production research well (Canada)Haberer, R. M. et al. Organic Geochemistry, 2006, 37, (5), 519–538

Study of biodegradation processes along the Carnaubais trend, Potiguar Basin (Brazil) – Part 1

The aim of this study is to estimate hydrocarbon losses in natural reservoirs due to biodegradation processes. A series of 12 non-biodegraded and biodegraded oils were selected in the Potiguar Basin (Brazil). Most biodegraded reservoir oils are located in the southwestern part of the basin (onshore), within the Cretaceous sandstones of the Açu units that occur at shallow depths (<1000 m). Deeper reservoirs, containing non-biodegraded but mature oils, are located in the northeastern area of the basin. Based on the chemical alteration of the saturates and aromatics observed in biodegraded oils, tentative estimates of absolute losses were calculated for the light hydrocarbons (saturates and aromatics) and for the heavy fractions such as C 14+ linear and cyclo-alkanes and C 14+ aromatics. Together with the estimation of losses on global classes, molecular studies clearly show that biodegradation scales based on saturated and aromatic biomarkers can be used as such but do not reflect the loss percentage by biodegradation on global classes.

Occurrence and palaeoenvironmental significance of aromatic hydrocarbon biomarkers in Oligocene sediments from the Mallik 5L-38 Gas Hydrate Production Research Well (Canada)

The aromatic hydrocarbon biomarker distributions of thirty Oligocene sediment samples with different lithology (lignite, clay and sand) from the JAPEX/JNOC/GSC et al. Mallik 5L-38 Gas Hydrate Production Research Well, Canada, were analyzed using gas chromatography–mass spectrometry (GC-MS). The compositions vary with lithology, indicating a change in palaeoenvironmental conditions at the time of deposition. Aromatic diterpenoids of the abietane type are more abundant in the lignite samples than in the clay samples and represent a gymnosperm (e.g., conifer) dominated palaeovegetation. In contrast, in the clay samples aromatic triterpenoids are generally preserved as major constituents, indicating angiosperm dominated vegetation. The sand samples contain only minor amounts of aromatic terpenoids, but show a preference for diterpenoid gymnosperm markers. To recognise gymnosperm versus angiosperm dominated palaeoenvironments a new ratio, termed the angiosperm–gymnosperm aromatic ratio (AGAR), has been developed. Thus, the terpenoid distribution in the deltaic sediments provides information on the compositional changes in the plant community at the Mallik site (lignites) and the hinterland (clays) over time. Concomitantly, the changing dominance in the plant communities allows an insight into varying climatic conditions during the late Oligocene in the area. Additionally, the aromatic biomarker composition has been used to assess the level of thermal maturity of the organic matter in the Mallik samples and indicates a prevailing immature character.