Depositional Environment Of Organic Matter Research Articles

Biomarker signatures and depositional environment of ore-bearing black shale in the Luishia Cu–Co deposit, Democratic Republic of Congo: Implications for regional copper mineralization

The Central African Copperbelt is a globally important sediment-hosted stratiform copper cluster, with regional Cu–Co deposits controlled by Neoproterozoic rift basin. Ore formation in the Copperbelt involves multiple stages of mineralization during diagenesis, basin inversion, and collisional orogeny. Understanding the depositional environment of ore-hosting rocks is crucial for revealing the geological settings and pre-orogenic ore genesis. This paper presents a biomarker study focusing on the ore-bearing black shale in the Luishia Cu–Co deposit, Democratic Republic of Congo. The research investigates thermal maturity, source, and depositional environment of organic matter through rock organic carbon and pyrolysis analysis, chloroform bitumen “A” group component analysis, as well as saturated hydrocarbon gas chromatography-mass spectrometry (GC-MS) analysis. The results indicate significant thermal maturation of organic matter in Luishia black shale. Bacteria are identified as the primary source of organic matter followed by red algae and green algae. The sedimentary environment is characterized by a restricted rift basin under shallow marine conditions with a stratified water column. The processes of bacterial sulphate reduction (BSR) and thermochemical sulphate reduction (TSR) significantly influence the mineralization during diagenesis and basin inversion, respectively. Enhanced thermal maturity promotes methane generation which plays a role in reducing anhydrite and subsequently precipitating ore minerals. The findings have important implications for regional exploration strategies.

Analysis of redox-sensitive trace elements to the reconstruction of the depositional paleoenvironment of the Ponta Grossa Formation in southern Brazil

In the Devonian period, several intense climatic changes occurred on Earth, such as global cooling and intense volcanic eruption events, increasing the amount of organic matter in water bodies and forming a bituminous sedimentary material containing redox-sensitive trace elements, called shale. Among the places with this type of rock formation from the Devonian period, one of them is the Ponta Grossa region, located in the Paraná Basin, southern Brazil, which lacks studies that use metals to understand the depositional environment of its formation. Therefore, this study aims to analyze the redox-sensitive trace elements together with the total organic carbon to understand the depositional environment at the time of the formation of these shales. For this, outcrop samples were collected and analyzed regarding the total organic carbon and the redox-sensitive trace elements, generating ratios between them. From the results obtained, it was observed that the environment was warmer and humid, with very low salinity, a greater tendency to anoxia, periods of greater primary productivity, and marine transgressions. Thus, it was possible to know the depositional environment of organic matter that later originated the shale deposits in this region of the planet.

Significance of infrared spectroscopic branching factor for investigation of structural characteristics of alkanes, geochemical properties and viscosity of oils

A detailed investigation of significance of the infrared (IR) spectroscopic branching factor (??2/??3; the ratio of methylene and methyl group peak heights at 2917?2921 and 2951?2954 cm-1, respectively in the IR spectra) for characterization of alkane structure, geochemical properties and viscosity of 76 oil samples was performed. These oils, originating from 13 Serbian oil fields in SE Pannonian Basin, differ according to source and depositional environment of organic matter (OM), as well as by thermal maturity and biodegradation stage. Methylene and methyl asymmetric stretching peak absorbances were used for the branching factor calculation. CH2 peak positions exhibited 3?4 cm-1 red shift with increasing the CH2/CH3 ratio, due to a greater contribution of trans vs. gauche rotamers in aliphatic chains. Comparing IR spectra of the oils and model n-alkanes, it was established that the average (CH2)n methylene chain length per ??3 group varied from n = 3.5 to 6.5. The CH2/CH3 ratio showed significant concordance with geochemical parameters, enabling clear distinction of the oils according to source and depositional environment of OM. At the same time, dependence of the CH2/CH3 ratio on oil maturity in the range from immature to mature was not observed, allowing for an accurate determination of oil genetic types irrespective of maturity. The CH2/CH3 ratio showed good accordance with oil biodegradation scale and oil viscosity.

Geochemical characteristics and paleodepositional setting of coal-bearing strata in Konya-Karapınar Basin, Central Anatolia, Turkey

The Neogene coals of the Hotamış Formation in the Konya-Karapınar basin were examined, and the organic matter type, thermal maturity, paleodepositional environment, and Rock-Eval pyrolysis characteristic of coal samples obtained from boreholes. The total organic carbon (TOC) values of coal vary between 15.2 wt% and 47.0 wt% and the yield of extractable organic matter (EOM) values varies between 0.5% and 1.0% indicating a limited hydrocarbon production potential. Bitumen index (BI) and Quality index (QI) values were calculated for coal samples and vary from 1 to 13 mg HC/g TOC and from 75 to 260 mg HC/g TOC, respectively. Due to BI and QI values, coal samples have limited gas generation potential. The type of organic matter was determined as Type III kerogen according to Rock-Eval data. The coal samples have Tmax values between 414 and 443 °C, and huminite reflectance values with 0.20%–0.41% Ro indicating that they are in the immature-early mature stage. This is supported by biomarker maturity parameters 20S/(20S + 20R) (C29) sterane (0–0.59), ββ/(αα + ββ) (C29) sterane (0–0.58), MPI-1 (0.18, 0.31) and MPI-1* (0.21, 0.37). The relative abundance of C27–C28–C29 normal steranes and aromatic steroids and the abundance of partially low carbon number tricyclic terpanes of the Konya-Karapınar coals showed that the organic matter consisted of terrestrial higher plants with a small contribution of algae and microorganisms. Homohopane distributions, V/(V + Ni), V/Sc ratios show that organic matter accumulated in an environment that varies between oxic-anoxic conditions and that medium-high gammacerane index, C27–C28–C29 sterane distributions, and low DBT/P ratios are compatible with the weak brackish water-fresh water depositional environment of organic matter.

A comparative study of the molecular and isotopic composition of biomarkers in immature oil shale (Aleksinac deposit, Serbia) and its liquid pyrolysis products (open and closed systems)

The molecular and isotopic composition of biomarkers in initial bitumen isolated from immature (0.41% Rr) oil shale samples (Aleksinac deposit) and liquid products obtained by pyrolysis in open (OS) and closed (CS) systems are studied. The influence of pyrolysis type and variations of kerogen type on biomarkers composition and their isotopic signatures in liquid products is determined. The applicability of pyrolysis type, numerous biomarkers and carbon isotopic compositions (δ13C) of n-alkanes in liquid pyrolysates is established. Pyrolysis experiments were performed on two selected samples that showed high content of total organic carbon and hydrocarbon generation potential, but also certain variations in sources/depositional environment of organic matter (type I and mixed type I/II kerogen) within previous research of the oil shales sample set. The biomarker signatures were evaluated using gas chromatography-mass spectrometry (GC-MS) and δ13C of individual n-alkanes in bitumen and liquid pyrolysates. The molecular composition of liquid pyrolysates from the OS is very similar to those in initial bitumen, independently on kerogen type, confirming algal origin of organic matter (OM) deposited in lacustrine environment, even more apparently than results of initial bitumen. Therefore, OS can be useful for assessment of source and depositional environment of OM. Pyrolysis in the CS caused more intense thermal alterations, therefore the source fingerprints sometimes notably disappear. The liquid pyrolysates from the CS have the distributions of biomarkers similar to those in crude oils. The biomarker maturity parameters showed slightly higher values in the CS pyrolysate of mixed type I/II kerogen in relation to type I kerogen. δ13C of n-alkanes in liquid pyrolysates from the OS are isotopically lighter in comparison to bitumen, independently on kerogen type. Oppositely, in liquid pyrolysates from the CS, they become heavier than in bitumen, indicating the thermal influence on δ13C signatures, with more pronounced difference for type I kerogen.

Geochemical Characterization of the Eocene Coal-Bearing Source Rocks, Xihu Sag, East China Sea Shelf Basin, China: Implications for Origin and Depositional Environment of Organic Matter and Hydrocarbon Potential

Eocene coal-bearing source rocks of the Pinghu Formation from the W-3 well in the western margin of the Xihu Sag, East China Sea Shelf Basin were analyzed using Rock-Eval pyrolysis and gas chromatography–mass spectrometry to investigate the samples’ source of organic matter, depositional environment, thermal maturity, and hydrocarbon generative potential. The distribution patterns of n-alkanes, isoprenoids and steranes, high Pr/Ph ratios, abundant diterpanes, and the presence of non-hopanoid triterpanes indicate predominant source input from higher land plants. The contribution of aquatic organic matter was occasionally slightly elevated probably due to a raised water table. High hopane/sterane ratios and the occurrence of bicyclic sesquiterpanes and A-ring degraded triterpanes suggest microbial activity and the input of microbial organisms. Overwhelming predominance of gymnosperm-derived diterpanes over angiosperm-derived triterpanes suggest a domination of gymnosperms over angiosperms in local palaeovegetation during the period of deposition. The high Pr/Ph ratios, the plot of Pr/n-C17 versus Ph/n-C18, the almost complete absence of gammacerane, and the distribution pattern of hopanes suggest that the samples were deposited in a relatively oxic environment. Generally, fluctuation of redox potential is coupled with source input, i.e., less oxic conditions were associated with more aquatic organic matter, suggesting an occasionally raised water table. Comprehensive maturity evaluation based on Ro, Tmax, and biomarker parameters shows that the samples constitute a natural maturation profile ranging from marginally mature to a near peak oil window. Hydrogen index and atomic H/C and O/C ratios of kerogens suggest that the samples mainly contain type II/III organic matter and could generate mixed oil and gas.

Investigation of aliphatic hydrocarbons in core sediments of Brunei Bay, East Malaysia

The distribution of aliphatic hydrocarbons in three sediment cores from Brunei Bay was investigated in order to understand their sources and the biogeochemical processes of these hydrocarbons. The total concentrations of C15 to C37n-alkanes ranged from 0.70 to 16.5 μg g−1. Traces of hopanes with C29–C31 carbon homologs were detected in the study area. The carbon preference index (CPI15–37) ranged from 1.23 to 3.42 coupled with the natural n-alkane ratio (NAR19–32) ratios (1.52 to 5.34), and the presence of unresolved complex mixtures and hopanes, suggested slight contamination by anthropogenic hydrocarbons, presumably derived from activities along the coasts. The presence of C27 trisnorhopene and diploptene, as well as their association with long-chain and short-chain n-alkanes, revealed a depositional environment of organic matter in the sediment cores.

Petrographic, palynofacies and geochemical characteristics of organic matter in the Saouef Formation (NE Tunisia): Origin, paleoenvironment, and economic significance

Saouef lignite layers and carbonaceous shales are studied in order to reconstruct the origin and depositional environment of organic matter (OM), as well as to evaluate their economic potential. The study is based on organic compositions, bulk geochemical parameters, biomarker data, and carbon isotope composition of OM (δ13C). Lignite samples, collected next to the Saouef village, were macroscopically identified as stratified matrix coal or as humic coal. Rock Eval pyrolysis and the palynofacies analysis indicate the predominance of Type-III-IV kerogen (OM). The depositional environment fluctuated between terrestrial environments with a low water table to the limnic environment. The OM is derived from higher land plant remains (e.g. wood, root, bark) from a mixed vegetation including conifers and angiosperms, and emerged macrophytes. The dominance of huminite over liptinite and intertinite maceral groups, along with the phytoclasts, confirms the woody origin of the OM. A high bacterial activity is evidenced by the abundance of hopanoids in the extractable OM as well as by the amorphous OM content. The high measured TOC values exceeding 20wt% in some samples may give an economic value of the organic layers of Saouef Formation. However, a Tmax<435°C and Rr<0.5% induce the immaturity of the samples despite the presence of expelled bitumen in one sample.

Geochemical investigation of trace elements in crude oils from two different depobelts in the Niger Delta basin, Nigeria

ABSTRACTThe concentrations of trace elements in crude oil samples from the Northern and Central swamps depobelts in the Niger Delta basin were investigated using Flame Atomic Absorption Spectrometer. The origin, source facies, and depositional environment of organic matter that produced the oils were determined based on the trace elements concentrations. The concentrations of the trace elements (Cr, Cu, Fe, Mn, Ni and V) ranged from 0.04 to 5.71 ppm. Iron is the most abundant element in the samples while Cr has the least concentration. The results from trace metal geochemistry showed that the Niger Delta oils were derived predominantly from terrestrial organic matter deposited in the oxic depositional environment. The concentrations and ratios of nickel and vanadium grouped the oils into two distinct families reflecting the depobelt the oils belong. This observation indicates that the source rocks in the two depobelts were formed from organic matter of different source facies.

Trace and rare earth element geochemistry of crude oils and their coexisting water from the Jiyuan Area of the Ordos Basin, N China

The concentration of trace and rare earth elements in 22 crude oil and five oilfield water samples, collected from Triassic Yanchang Formation and Jurassic Yanan Formation reservoirs in the Jiyuan Area of Ordos Basin, N China, was determined using inductively coupled plasma mass spectrometry (ICP‐MS) for the first time. The oil samples were analysed to classify the oils into family and to determine the origin and depositional environment of organic matter that yield the oils using trace elements. The REE chondrite‐normalized distribution patterns of the crude oils show light rare earth element (LREE) enrichment and right‐oblique curves. These patterns could be divided into two distinct types that were consistent with that of the upper continental crust (UCC) and lower continental crust (LCC) characterizing by negative Eu anomalies and positive Eu anomalies, respectively. The REE concentrations in coexisting water samples are less than those in crude oils by a factor of ten. Cluster analysis also classified the oil samples from the Ordos Basin into two main groups. Integrated analysis of Co/Ni, V/Ni and V/ (V + Ni) values suggests that the organic matter have more terrigenous source input and the palaeoenvironment was anoxic and slightly oxic conditions. This study differs from previous studies by using trace element analyses of crude oils to constrain oil‐source rock correlation. The results show that most of the crude oils in north Jiyuan area were derived from Chang 7 mudstones while those from Hongde area may be contributed by Chang 7 oil shales. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Characterisation of lignite lithotypes from the “Kovin” deposit (Serbia) - implications from petrographic, biomarker and isotopic analysis

Four lignite lithotypes (matrix coal, xylite-rich coal, mixture of matrix and mineral-rich coal and mixture of matrix and xylite-rich coal), originating from the Kovin deposit, were investigated in detail. The paper was aimed to determine the main maceral, biomarker and isotopic (?13C) characteristics of investigated lithotypes. Based on these results the sources and depositional environment of organic matter in 4 lithotypes were established. These samples were also used as substrates for investigation of the influence of diagenetic alteration on ?13C signatures of biomarkers, as well as for assessment of the most convenient utilization for each lithotype. The investigated lithotypes differ in accordance with the composition of huminite macerals. Xylite-rich coal notably distinguishes from other lithotypes beacuse of the highest content of conifer resins vs. epicuticular waxes. The mixture of matrix and mineral-rich coal is characterised by the greatest contribution of algae and fungi and the most intense methanotrophic activity at the time of deposition. In all coal lithotypes diagenetic aromatisation influenced isotopic composition of individual biomarkers. Xylite-rich coal has the poorest grindability properties. However, this coal lithotype is the most suitable for fluidized bed gasification, whereas the mixture of matrix and mineral-rich coal has the lowest applicability for this process. The calorific value decreases in order: xylite-rich coal &gt; matrix coal &gt; mixture of matrix and xylite-rich coal &gt; mixture of matrix and mineral-rich coal. The increase of organic carbon content and calorific value is controlled by the increase of contribution of wood vegetation vs. herbaceous peat-forming plants, as well as by stability of water table during peatification.

Determination of Trace Metals and Depositional Environment of Organic Matter from Oil Sands, Ondo, SW Nigeria

The oil sands are majorly deposited in the Western Nigeria spans a distance of about 120km, the tar deposits occurring as heavy oil and manifest as seepages and at near surface or at the surface as impregnated sediments at road cuts, cliff faces and river banks and at break of slopes. Samples were collected at Agbabu, Ilubinrin and Loda where open mining is at progress. The asphaltene content was determined and the concentration of a suite of metals mainly the biophiles were determined. The objective of this study is to determine the genetic relationship of these exposed tar sand and seeps based on the fact that Asphaltene have been redefined as micro kerogens bearing in preserved state the features of the original input organic matter. The result indicates that sample obtained from the drilled wellbore (A1) showed an outstanding difference from others. The seep samples (A2, A3, A4, and A6) irrespective of locations showed close relations as represented by the ternary plots. Samples with significant sand content (5.7) also showed similarity. It is suggested that since samples (A2, A3, A4, and A6) were seeps, they could have migrated via structural permeability e.g. faults and fractures while samples 5, 7 could have migrated via pore network in the trapless reservoir sandbody. The %Asphaltene versus Co/Ni ratio groups the samples into tarsands and tar/heavy oil seeps. CPI varies from 0.24 to 1.00 in IREN and 0.16 to 4.13 in LODA showing that LODA attended higher level of maturation as compared to IREN. Pr/Ph ratio (0.78-3.31; 0.87-2.33), Long/Short ratio (0.72-0.77; 1.00-1.60), OEP (0.02-0.68; 0.33- 0.42), Pr/n-C17 (0.84-2.25; 0.19-1.61), Ph/n-C18 (0.04-3.73; 1.00-1.67) and C31/(C31+C29) (1.00-3.40; 1.20-3.60) revealed contributions of marine to terrestrially source of organic matter and dysoxic to marine as depositional environment. Index Terms: Depositional environment, Petroleum geochemistry, Source, Tarsand, Trace metals.

Trace element geochemistry of crude oils and condensates from South African Basins

Crude oil and condensates samples from Bredasdorp and Orange Basins, South Africa were analyzed for trace elements using inductively coupled plasma – optical emission spectrometry. The oil and condensate samples were analyzed to classify the oils into family and to determine the origin of the oils and depositional environment of organic matter that yielded the oils using trace elements. The concentrations of the elements (Co, Cr, Cu, Fe, Mn, Ni, and V) determined ranged from 0.10 to 7364.7 ppb. Iron is the most abundant element in the samples while cobalt is least abundant. Both concentrations and ratios of nickel and vanadium showed two main families of oils; oils of marine origin and oils of terrestrial origin. Oil samples from the Orange Basin are mainly of marine source and their organic matter were deposited under anoxic conditions. Most of the oil samples from the Bredasdorp Basin are of marine origin with a few samples having terrestrial origin. Cluster analysis also classified the oil and condensate samples from the two basins into two main families of marine and terrestrial sources.

The Geochemical Characterization of Sediments from Early Cretaceous Sembar Formation

The soluble organic matter (SOM) and kerogen of sediments contain organic molecules, and can be interpreted in terms of source, generative potential, thermal maturity, and depositional environment of the organic matter. Early Cretaceous sedimentary sequence of Sembar Formation comprising five sediments samples was analyzed. Both SOM and hydrocarbons bound to the kerogen terms as pyrolyzed organic matter (POM) were characterized geochemically. Hydrous pyrolysis was carried out to release hydrocarbons from extracted sediments and fractionated by liquid chromatography. Saturated fractions from both SOM and POM were further analyzed by gas chromatography-flame ionization detector. The study suggested that Cretaceous sequence of Sembar Formation has fair to good hydrocarbon source potential. Thermal maturity parameters indicate onset of oil genesis zone. The presence of even carbon numbered n-alkenes, Pr/Ph and Pr/n-C17 versus Ph/n-C18 plots reveal marine algal source and anoxic depositional environment of organic matter from Sembar Formation.

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.

Fatty Acid Composition between Nuttallia olivacea and Hediste spp. in the Nanakita Estuary, Japan: Estimation of Food Sources

The spatial variability of the food availability in different depositional environments (Nanakita estuary, Japan) was investigated using fatty acid biomarkers. The main objective of the present study was to determine the food availability for Nuttallia olivacea and Hediste spp. in connection with the depositional environment of organic matter (OM). Sandy sediment was mainly occupied by diatoms, bacteria and marine organic matter. Meanwhile, muddy sediment is dominated by diatoms, bacteria and terrestrial organic matter. The main food sources and food availability for N. olivacea were mostly dominated by diatoms, bacteria and dinoflagellates in connection with the depositional environment. Meanwhile, the food utilization characteristics of Hediste spp. may be attributable to the lower food selectivity due to their deposit feeding. From these results, the food availability for N. olivacea was more influenced by the depositional environment in estuarine tidal flat than Hediste spp.