Mixed Organic Matter Research Articles

Organic Geochemistry and Thermal Maturity Assessment of Cretaceous Balambo Formation from Selected Sites, Kurdistan, NE Iraq

The Cretaceous Balambo Formation from three sections in Kurdistan Region of Northern Iraq was studied. The selected sections are located in the Zagros Fold -Thrust Belt. Eleven rock samples were analyzed by means of the organic geochemical method, Bitumen extraction method, and gas chromatography/mass spectrometry to determine the bitumen and hydrocarbon content, kerogen types, origin of organic matter, thermal maturity level, and depositional environment. The analyzed samples are considered to have an excellent potential in Baranan-1.G1 and Sazan sections, with poor to fair potential in Baraw section. The Baranan-1.G1 source rocks are of type II kerogen (oil prone), whereas Sazan and Baraw samples are of type II/III (oil/ gas prone). Detailed distribution analysis of biomarkers such as normal alkane, isoprenoids, sterane and terpane was performed on saturated hydrocarbons. The mode of n-alkanes and isoprenoids distribution in all analyzed samples is similar, with a unimodal distribution that indicates non-biodegraded hydrocarbons, with the same range of alkane compounds between C13-C34 alkanes. The results of n-C17, pristane, n-C18 and phytane, and regular steranes show that the source rocks of Balambo Formation in Baranan-1.G1 are mainly rich with algal marine organic matter deposited under a reducing environment, while Baraw and Sazan sections are composed of mixed marine organic matter that refers to terrestrial land plants input deposited under reducing anoxic/dysoxic environments. Thermal maturation appraisal is deduced from Pristane/n-C17 versus Phytane/n-C18 diagram, Carbon Preference Index (CPI), C29 ββ/ (ββ+αα), C29 20S/ (20S +20R), C32 22S/ (22S+22R), and Ts/ (Ts+Tm). All these parameters indicate that the analyzed samples are mature and have entered the oil window (early to peak oil window). Biomarker ratios of C22/C21, C24/C23 and C26/C25, C31R/C30H show that the Balambo Formation is composed mostly of carbonates with less shale beds.

Organic geochemical characteristics of Zeit source rock from Red Sea Basin and their contribution to organic matter enrichment and hydrocarbon generation potential

Organic-rich shale intervals in the Miocene Zeit Formation were collected from seven wells in the Red Sea basin for compilation of organic geochemical and petrological methods. The current study evaluated the paleo-oxygenation conditions regarding the preservation and the organic-rich sedimentation. The type of organic facies and their relation to hydrocarbon generation potential were also studied. Most of the Zeit shale samples are organically rich and include favorable source rocks, as indicated by the high TOC content of up to 1 wt%. The shale samples also have hydrogen index (HI) values between 58 and 595 mg HC/g TOC, resulting in two dominant organic facies of Types II-III, and III kerogen, with little Type II, and thereby contributing to generate both oil and gas. Biomarker fingerprints, including of n-alkanes, isoprenoids, terpanes, and steranes reveal that the Zeit shales contain mixed organic matter, with a high contribution of marine plankton/algal and microorganisms. The presence of the phytoplankton algae i.e. Chlorococcales and Tasmanites in the Zeit shales further suggests reducing conditions during deposition, thus, enhanced growth of algae and marine microorganisms owing to the presence of nutrients and contribute to good preservation of organic matter. According to maturity indicators of geochemical Tmax (≥430 °C) and vitrinite reflectance (VRo) values (0.52–0.98%), the analyzed Zeit shales are in a mature stage of oil window equivalent to early-mature and peak-mature. This implies that the Zeit shales were reached a sufficient maturity level for commercial oil generation.

Modeling Hydrocarbon Generation of Deeply Buried Type Ⅲ Kerogen: A Study on Gas and Oil Potential of Lishui Sag, East China Sea Shelf Basin

The hydrocarbon generation model and hydrocarbon potential are investigated in the Lishui Sag, based on gold-tube pyrolysis experiments of deeply buried type Ⅲ kerogen. From this, we discuss the classification of kerogen types of source rocks with mixed organic matter sources. The hydrocarbon generated from the source rocks of the Lingfeng Formation and Yueguifeng Formation is dominated by natural gases with little oil in the West subsag, and the hydrocarbon generation model of the Lingfeng Formation is similar to that of Yueguifeng Formation, but the gas potential of Lingfeng Formation is higher than that of Yueguifeng Formation. The hydrocarbon potential of the Yueguifeng Formation in the East subsag is much higher than the West subsag, and it has considerable oil potential. Macerals diversity of source rocks is responsible for the difference of hydrocarbon generation characteristics for type Ⅲ kerogen in the Lishui Sag. It is not rigorous to evaluate the hydrocarbon potential of kerogen only based on pyrolysis parameters. Application of kerogen type index (KTI) can improve the accuracy of the classification of kerogen types with mixed organic matter sources. According to the classical kerogen classification template, the selected samples belong to type III kerogen. In this article, the selected samples were further subdivided into type III and type II/III based on the KTI value. Type III kerogen (0.5 ≤ KTI < 1.5) mainly produces gas, and type II/III kerogen (1.5 ≤ KTI < 5) mainly produces gas, but its oil potential is higher than that of type III.

Use of rare earth elements and internal transition elements for characterization of the depositional paleo environment in samples of the experience of the Pimenteiras Formation, Parnaíba Basin, Brazil

The quality of the organic matter together with the conditions of the depositional paleoenvironment at the top of the Pimenteiras Formation (Devonian), were geochemically characterized using 11 (eleven) samples of shales collected from meter to meter in outcrop located on the western edge of the Parnaíba Basin, the northeast region of Brazil. The inorganic geochemical characterization was carried out through the analysis of rare earth elements and uranium, and transition elements (Ni, V, Co, and Mo) by ICP OES for Ni and V. For the rest of the elements, the determinations were made by ICP MS. The transition elements allowed to evaluate the origin of the organic matter using the diagram of the concentration ratio between the Ni/Co elements versus the concentration ratio for the V/Ni elements and the depositional paleoenvironment using the V concentration versus Ni concentration diagram. The uranium and molybdenum relationships established the presence or not of sulfides (euxinic or non-euxinic environment). The first group consists of samples from the lower third (base) of the outcrop, which has mixed organic matter, predominantly terrestrial, with the contribution of fresh/brackish water organisms, deposited under paleoenvironmental conditions from oxic to suboxide. The second group consists of samples collected in the upper third (top) of the outcrop containing mixed organic matter with a predominance of marine organic matter and little terrestrial contribution, deposited under anoxic paleoenvironmental conditions. The sum of the concentrations of rare earth elements suggested the existence of two sets of samples containing organic matter from different sources. The organic geochemical characterization was performed using analytical techniques to evaluate the percentage of total organic carbon, total sulfur, Rock-Eval pyrolysis data, and for diagnostic reasons of saturated biomarkers. The shales of the first group poor in total organic carbon (TOC), have the sum of the concentrations of rare earth elements lower than the second group, which are rich in organic matter. According to analyzes of the saturated biomarkers, about the depositional paleoenvironment of the Pimenteiras Formation in the area of that outcrop, the organically poorest shales of the first group were deposited in a transitional depositional paleoenvironment, with a large supply of continental organic matter, while the most enriched in organic matter. organic matter represents a marine flood surface, where the organic material is predominantly marine.

Organic petrological and geochemical appraisal of the Upper Jurassic Naokelekan Formation, Kurdistan, Iraq

Upper Jurassic Naokelekan Formation, being part of the intercepted strata of the well-known Miran oilfield in Kurdistan region of Northern Iraq, has been previously extensively evaluated as a potential/effective source rock, mainly by means of organic geochemistry. In the present study, a total of 60 samples were collected from four Naokelekan Fm. outcrops, those of Banik, Galy-Derash, Barsarin and Dwawa, in order to conduct organic petrographical study and organic geochemical assessment, including both biomarker and Rock-Eval analyses. The average recorded TOC content for Banik, Galy-Derash, Barsarin and Dwawa section is considerable to very high, corresponding to values of 27.5, 9.0, 3.5 and 5.2 wt%, respectively, with the highest values representing the notably organic-rich bottom part of the Formation, known as “coal layer”. According to the petrographical analysis, solid migrabitumens comprise the predominant component for all the analysed samples, whereas the maceral groups of vitrinite, liptinite and/or inertinite showcase a minor to trace occurrence. In terms of organic geochemistry, each of the four sections of interest shows a different biomarker profile. Nevertheless, a number of calculated parameters related to kerogen type and depositional conditions, including the isoprenoids/n-alkanes ratios, suggest a mixed terrestrial-marine organic matter. Furthermore, as indicated by the Ro (%) measurements along with Rock-Eval parameters and the vitrinite reflectance equivalent based on aromatic compounds, the maturity level is marginally mature in the cases of Banik and Galy-Derash, whereas in the cases of Dwawa and Barsarin sections it is mature to post-mature. A synthesis of the organic petrography and geochemical appraisal applied in the present study, suggests that the reported solid hydrocarbons in Naokelekan Fm., particularly at its basal layers are non-indigenous/migrated and the precursor organic matter was deposited in a marine environment, under oscillating conditions ranging from euxinic to well‑oxygenated. Accordingly, the organic features of the notably bitumen-rich “coal-bed” fit the profile of a reservoir and/or migration path.

N-Alkane Characteristics of Thawed Permafrost Deposits Below a Thermokarst Lake on Bykovsky Peninsula, Northeastern Siberia

Rapid permafrost thaw by thermokarst mobilizes previously frozen organic matter (OM) down to tens of meters deep within decades to centuries, leading to microbial degradation and greenhouse gas release. Late Pleistocene ice-rich Yedoma deposits that thaw underneath thermokarst lakes and refreeze after lake drainage are called taberal sediments. Although widespread, these have not been the subject of many studies. To study OM characteristics and degradability in thawed Yedoma, we obtained a 31.5 m long core from beneath a thermokarst lake on the Bykovsky Peninsula, northeastern Siberia. We reported radiocarbon ages, biogeochemical parameters (organic carbon (OC) content and bulk carbon isotopes) and n-alkane distributions. We found the most degraded OM in frozen, fluvial sediments at the bottom of the core, as indicated by the lowest n-alkane odd-over-even predominance (OEP; 2.2). Above this, the thawed Yedoma sediments had an n-alkane distribution typical of emergent vegetation, suggesting a landscape dominated by low-centered polygons. These sediments were OC poor (OC content: 0.8 wt%, 60% of samples <0.1 wt%), but the OM (OEP~5.0) was better preserved than in the fluvial sediments. The upper part of the Yedoma reflected a transition to a drier, grass dominated environment. Furthermore, this unit’s OM was least degraded (OEP~9.4). The thermokarst lake that formed about 8 cal ka BP thawed the Yedoma in the talik and deposited Holocene lake sediments containing well-preserved OM (OEP~8.4) with the highest n-alkane concentrations (20.8 μg g-1 sediment). Old, allochthonous OM was found in the thawed Yedoma and frozen fluvial deposits. Using an n-alkane endmember model, we identified a mixed OM input in all units. In our study, the thawed Yedoma sediments contained less OC than reported in other studies for still frozen Yedoma. The Yedoma OM was more degraded compared to previous biomarker research on frozen Yedoma. However, this signal is overprinted by the input signal. The fluvial deposits below the Yedoma contained more OM, but this OM was more degraded, which can be explained by the OM input signal. Continued talik deepening and expansion of this thermokarst lake and others similar to it will expose OM with heterogeneous properties to microbial degradation.

Origin and migration of oil and natural gas in the central part of the Ukrainian outer Carpathians: Geochemical and geological approach

The generation and migration processes, as well as the influence of secondary processes, on oil and natural gas accumulated in Lower Cretaceous–lower Miocene strata of the central part of the Ukrainian outer Carpathians are discussed. Type II and II/III kerogens from the Oligocene–lower Menilite beds of the Boryslav-Pokuttya nappe generated oil and natural gas mainly during the middle stage of the oil window. These hydrocarbons accumulated in the fields of the Boryslav-Pokuttya and Skiba nappes. Water washing is the dominant secondary process occurring in many accumulations, regardless of reservoir rock, whereas biodegradation is insignificant and is clearly evident only in natural gas from one seep in the abandoned Starunia ozocerite mine. All hydrocarbon gases are thermogenic and were generated from mixed organic matter containing various proportions of type II and III kerogens. Only one natural gas accumulation in the Pivnichna Dolyna field contains some microbial hydrocarbon contribution. Carbon dioxide mainly originated from thermogenic kerogen decarboxylation and sporadically from microbial processes. Molecular nitrogen was mainly generated during low-temperature thermal transformation of organic matter and could also partly originate from NH4-rich illites of the clayey facies of the Oligocene–lower Miocene Menilite beds. The integration of the geochemical data with geological setting and maturation history of source rocks enabled us to reconstruct hydrocarbon migration paths, revealing the complicated trap-filling process.

Thermogenic gas generation from organic-rich shales in the southeastern Say'un-Masila Basin, Yemen as demonstrated by geochemistry, organic petrology, and basin modeling

The current study aimed to explore the gas-generating potential and oil-to-gas conversion in the Madbi oil-source rock system based on data from deep well within the Say'un-Masila Basin using both geochemical and petrological methods as well as basin models. Biomarker results for the bitumen from analyzed shale samples indicate mixed organic matter, with mainly phytoplankton, bacteria, and some terrigenous land plants, deposited under relatively anoxic marine environmental conditions. The terrigenous organic matter, and rich in lipids from phytoplankton and bacteria, suggests Types II and II/III as the original organic matter during deposition. Such findings are not consistent with the significant amounts of vitrinite and inertinite that found under microscope and the low current hydrogen index (HI) values of 43–282 (Types III/IV and III/II kerogen) of the analyzed shale samples. The chemical and optical maturity indicators show that the Madbi shales throughout the studied well section are at different thermal maturity stages, consistent with late-mature stage of the oil window to gas-generation window. Therefore, this high thermal maturation is the critical factor that significantly modifies the original organic matter.Based on the basin models of the single well studied (Ghayl Bin Yumain-01), the initial conversion of kerogen to oil, occurring between the Late Cretaceous and Late Eocene (75–38 Ma), corresponding to peak-oil window (0.70–1.00 Easy %Ro). Furthermore, the oil was expelled during the Late Eocene to Early Oligocene; hence, the late-mature stage of the oil window (1.00–1.30 Easy %Ro) commenced during this time, with transformation ratios (TR) of 50–70%. Subsequently, the cracking of the retained oil into gas has occurred from the Early Oligocene through the present and is attributed to the high thermal maturation of the gas window (>1.30 Easy %Ro), with maximum TRs of 70–97%.

Distribution and geochemical significance of dibenzofurans, phenyldibenzofurans and benzo[b]naphthofurans in source rock extracts from Niger Delta basin, Nigeria

The distribution and geochemical significance of dibenzofurans, phenyldibenzofurans and benzo[b]napthofurans in source rocks from Niger Delta basin, Nigeria, were investigated by Rock–Eval pyrolysis and gas chromatography-mass spectrometry (GC–MS). The data obtained from the source rocks evaluation showed that the rock samples contained type II/III kerogen capable of generating oil and gas and were within immature to early mature stage. The relative abundance of the C0-, C1- and C2-dibenzofurans range from 1.75% to 29.82%, 27.60% to 40.52% and 29.66% to 68.89%, respectively. The dibenzofurans were dominated by C2-dibenzofurans. Among the C1-dibenzofurans, 2-+3-methyldibenzofuran was the most abundant in the rock samples while 1-methyldibenzofuran appeared to be the least. The relative abundance of benzo[b]naphtho[1,2-d]furan ([1,2]BNF), benzo[b]naphtha[2,1-d]furan ([2,1]BNF) and benzo[b]naphtha[2,3-d]furan ([2,3]BNF) in the rock extracts range from 12.01% to 52.58%, 32.61% to 75.21% and 10.27% to 52.43%. The wide range of values recorded for the three isomers of benzo[b]napthofurans in the samples suggest source rocks formed from mixed organic matter. Among the phenyldibenzofuran isomers, 4-phenyldibenzofuran was the most abundant while 1-phenyldibenzofuran was the least. Phenyldibenzofuran ratio-1 (PhFR-1) and phenyldibenzofuran ratio-2 (PhFR-2) values range from 0.13 to 1.20 and 0.11 to 2.11, respectively. The results showed that the relative abundance of PhFR-1 and PhFR-2 increase gradually with increasing burial depth and maturity (VR0 ≤ 0.77%, MPI-1 ≤ 0.62, Tmax ≤ 443 °C), and have a good correlations with calculated vitrinite reflectance, MPI-1 and maximum Temperature (Tmax). This range of values suggested immature to early mature source rocks. The source rocks were found to have shale and coal lithologies and deposited in a lacustrine/fluvial/deltaic settings within immature to early mature stages based on the distribution of dibenzofurans, phenyldibenzofurans and benzo[b]naphthofurans in the source rocks. This study showed that dibenzofurans, phenyldibenzofurans and benzo[b]naphthofurans were effective in determining the origin, depositional environment and thermal maturity of source rocks in Niger Delta basin, Nigeria.

Inorganic geochemistry and petroleum source evaluation of organic black shale in the Mamfe Basin (West Africa)

The shales of the Mamfe basin, West Africa, were studied using inorganic geochemical analysis to investigate the origin of the organic matter, environment of its deposition, paleoproductivity and organic matter preservation, organic matter maturity and petroleum potential. Shale samples from sites 1-7 have V/Ni ratios of: 2.9, 2.36, 3.14, 2.94, 3.04, 1.76 and 2.23 respectively. The V/Ni values of samples from sites 1,2,4, and 7 indicate a mixed terrestrial and marine organic matter origin, while shales from the other three sites have values close to those that represent mixed marine-terrestrial organic matter. Ni/Co, V/Cr and U/Th ratios of the black shales are <3, <2, and <0.75 respectively, indicating organic matter deposition in an oxic environment. The Ba/Al ratios of the studied shales average 64 while the P/Ti ratio averages 1.84 indicating a moderate to high paleoproductivity. The moderate to high paleoproductivity and rapid sedimentation influence the preservation of organic matter in the Mamfe shales. The shales have K/Rb ratios, ranging between 425 and 640, enrichment of LREE over HREE, MREE over HREE, positive Gd, Eu and negative Ce anomalies. These results indicate that the organic matter found in the shales is not yet at the level of maturity to produce petroleum, but may became good petroleum source rocks in the near future.

Organic matter provenance and depositional environment of marine-to-continental mudstones and coals in eastern Ordos Basin, China—Evidence from molecular geochemistry and petrology

Cyclothems, composed of interbedded mudstone, coal and sandstone layers, make up the Taiyuan and Shanxi Formations in the Late Carboniferous to Early Permian in North China under a marine-to-continental depositional environment. The cyclothems act as important fossil energy hosts, such as coalbeds, hydrocarbon source rocks and unconventional natural gas reservoirs. Organic geochemistry and petrology of mudstones and coals in the Taiyuan and Shanxi Formations in the eastern Ordos Basin were studied to reveal the organic matter sources and paleoenvironments. Total organic carbon (TOC) contents vary from 1.1 wt% (mudstone) to 72.6 wt% (coal). The samples are mainly within the oil window, with the Tmax values ranging from 433 to 469 °C. Organic petrology and source biomarkers indicate that the mudstones were sourced from a mixed organic matter input, and terrigenous organic matter predominates over aquatic organic matter. The coals are mostly sourced by terrigenous organic matter inputs. High concentrations of hopanes argue for a strong bacterial input. Some m/z 217 mass chromatograms have peaks at the hopanes' retention times as a result of high hopane to sterane ratios. These hopane-derived peaks do not interfere the identification of the steranes because the hopanes and the steranes have different retention times. Maturity-dependent biomarkers demonstrate that the samples have been thermally mature, which agree with the Tmax values. Anomalously low C29 20S/(20S + 20R) and C29 ββ/(ββ + αα) sterane ratios are present in all the samples, and are interpreted as due to the terrigenous organic matter input or the coal-related depositional environment. In addition, biomarkers and iron sulfide morphology indicate that the organic matter of the mudstones deposited in a proximal setting with shallow, brackish/fresh water bodies. With consideration of preservation of organic matter, the redox conditions are dysoxic. Redox oscillations resulted in the records of oxic conditions in some samples. Finally, the coals and the mudstones mainly generate gas and have poor oil generative potential.

Geochemical Studies of Cenozoic Shale Beds of the Western Cis-Caucasian Region

Geochemical parameters of the Cenozoic shale strata of the western Ciscaucasia have been analyzed. Oil source strata were identified in the study. The geochemical characteristics of organic matter (OM) of the Kumian rocks revealed high oil source potential of the rocks. The formation and emigration of hydrocarbons (HCs) were inferred from qualitative and quantitative changes. Sapropelic OM generated large amounts of hydrocarbons in the Kuma Sequence, with the value increasing from the top to the bottom of the profile. Para-autochthonous and migratory bitumoids were registered on the PC3 gradation and well-developed on the MK2 gradation (at a depth of 4.6–5.0 km). A comprehensive study of OM from Khadumian rocks by pyrolysis, bituminology, and chromatography showed that all kerogen types were developed in the rocks, but mixed OM with moderate oil source potential predominated. Maximal organic carbon (Corg) concentrations and genetic potential were observed within the Western Kuban trough, as well as in the strip of outcrops in the Adygei ledge area. The improvement in geochemical parameters in these areas is due to a decrease in the terrigenous component in the crude OM in the same direction.

Evaluation of alkane indexes for quantifying organic source from end member mixing experiments based on soil and algae

Abstract The identification for the sources of organic matters (OMs) is necessary to better understand biogeochemical cycling of carbon in aquatic environments. Hence, we intend to evaluate quantitative contributions of OM sources by using typical n -alkane indexes. In this regard, the end-member mixing experiment was designed as an example of theoretical system, which was physically mixed by two contrasting OM sources (e.g. soil and algae). Two sources showed distinct patterns with the long-chain alkanes (e.g., mainly C 25 , C 27, C 29, C 31 and C 33 ) for soil, but mid-chain alkanes (e.g., mainly C 19, C 21, C 23 and C 25 ) for algae. However, typical n -alkane indexes such as average chain length (ACL), carbon preference index (CPI), and aquatic plants % (P mar-aq ), except for terrestrial/aquatic ratio (TAR), were not well reflected for different proportions of mixed OM sources, indicating the overestimated contribution of soil sources. With respect to source tracking capability of n -alkane indexes, the calculated regression slope indicated non-linear relationships (R 2 = 0.52–0.67) in ACL, CPI, and P mar-aq , and linear relationships (R 2 = 0.86) in TAR, while the most precise capability was found for carbon isotopic compositions (δ 13 C) of C 25 alkane (linear relationships; R 2 = 0.97) calculated from the isotope mixing model. Thus, the present study suggests that a binary mixing model of C 25 alkanes concentrations combined with their isotopic values should be a promising tool for quantifying each contribution of autochthonous and/or allochthonous OM in natural aquatic environments.

Effect of Organic Characteristics on Sludge Settleability in an AAO System

The effects of different mixed organic matter ratios on sludge settleability were examined from the succession patterns of microbial community structure, and changes of microbial intracellular and extracellular polymers in the activated sludge. The experimental results showed that when organic matter was dissolved in the influent, the sludge settleability was optimal (SVI=70 mL·g-1), which was better than that for influent water with partially dissolved organic matter (SVI=120 mL·g-1) and particulate organic matter (SVI=280 mL·g-1). According to the analysis of microbial community structure, Thiothrix, Chryseolinea, and Trichococcus were important in influencing the sludge settleability. Of these, particulate organic matter promoted the growth of Trichococcus, and dissolved organic matter promoted the growth of Thiothrix and Chryseolinea. In addition, changes in the bacterial community also had an important influence on the changes of intracellular and extracellular polymers, which either enhanced or impeded settleability. The higher the content of dissolved organic matter in the influent, the higher the storage of intracellular polymeric substances and, therefore, the better the sludge settleability. The sludge settleability was significantly negatively correlated with polysaccharides, proteins, and the Zeta potential in the LB-EPS.

Characteristics of sedimentary organic matter and vascular plants in tropical brackish Bolgoda Lake, Sri Lanka: Implications for paleoecology and chemotaxonomy

Tropical brackish ecosystems are characterized by mangrove-dominant communities which are well-adapted to extreme and unique environmental conditions. Organic matter (OM) derived from adjacent vegetation contributes to the chemical composition of sediments. Sedimentary OM can thus be used for paleoecological studies. Surface and core sediments of Bolgoda Lake were analyzed to identify sources of OMs using C, N, S elemental analysis and gas chromatography-mass spectrometry. C/N ratios of raw sediments and protokerogen derivatives illustrate the preferential degradation of mixed OM in surface sediments and mangrove muds. The n-alkanes distributions show that vascular plants are predominantly preserved in sediments due to resistance to microbial decomposition and available biomass in the watershed. Taraxerone provides the most important chemotaxonomical information to identify mangrove-dominant sediments. Ternary n- C27, n- C29 and n- C31 alkanes relationships show that mangrove-dominant sediments are enriched in n-C31along with significant amounts of n-C29. Mangrove and herbaceous plants (grasses and/or floating plants) can be preferentially dispersed in tropical brackish sediments. The relative proportions of n-C27, n- C29 and n- C31n-alkanes can be applied to identify different growth habitats of a particular landmass. The mangrove biomarker (pentacyclic taraxerone) and visualized long-chain n-alkanes proportions (i.e., n-C27, n- C29 and n-C31) can thus be used as chemotaxonomical indicators to reconstruct the paleoecological characteristics of tropical brackish vegetation.

Early Cretaceous ferruginous and its control on the lacustrine organic matter accumulation: Constrained by multiple proxies from the Bayingebi Formation in the Bayingebi Basin, inner Mongolia, NW China

The greenhouse climate in the Cretaceous period promoted widespread organic-rich marine/lacustrine black shales or mudrocks. Organic matter (OM) accumulation is generally affected by preservation conditions and surface water primary productivity. The detail of organic-rich mudrock formation in lacustrine system still remains enigmatic. The widespread OM-rich mudrocks in the Cretaceous period as petroleum source rocks in many large terrestrial petroliferous basins in China offer an opportunity to explore the mechanism of lacustrine OM accumulation. Fe speciation, CSFe system, pyrite morphology, pyrite-sulfur isotopic composition, elements, and biomarkers in the Bayingebi Formation from a drill core in the Bayingebi Basin, Inner Mongolia, NW China are used to constrain redox conditions, OM source and primary productivity in a lacustrine system. Our results show that the dark-gray mudrocks in the Bayingebi Formation were deposited in ferruginous and stratified water-column in the Bayingebi Basin. The biomarkers suggest a mixed organic matter source of algae, bacteria and high plant with a low algal contribution. The surface-water primary productivity during the deposition of the Bayingebi Formation was low and shows a weak correlation with total organic carbon (TOC) content. The OM accumulation in early Cretaceous lacustrine system was mainly controlled by redox conditions. Ferruginous anoxic conditions in lacustrine system may have high potential for hydrocarbon source rocks owing to the reduction of oxygen decomposition.

GEOCHEMISTRY OF SEEP AND PRODUCED OIL SAMPLES FROM SOUTHERN CAMEROON

Crude oil samples from surface seeps in the Douala Basin (southern Cameroon) and from producing fields in the nearby Rio del Rey and Kribi‐Campo sub‐basins were analysed for bulk and molecular geochemical parameters by inductively coupled plasma – mass spectrometry (ICP‐MS), gas chromatography – mass spectrometry (GC‐MS) and isotope ratio mass spectrometry (IRMS). The aims of the study were to assess the composition of the oils, to evaluate the relationship between the seep oils and the oils from producing fields, and to highlight the significance of the data for oil exploration in the region. Chromatograms of the saturate fractions of the oils exhibit biodegradation ranging from very light (PM1 on the scale of Peters and Moldowan, 1993) in oil from the offshore Lokele field in the Rio del Rey sub‐basin, to severe (PM 6+) for seep oils from the Douala Basin. A plot of Pr/n‐C17 (1.3– 5.0) versus Ph/n‐C18 (0.8–2.6) for the samples further supports mild biodegradation in some samples (Lokele, Kole, Ebome), and demonstrates that the oils from the Lokele and Kole fields (Rio Del Rey sub‐basin) and from Ebome field (Kribi‐Campo sub‐basin) originated from mixed organic matter with a dominant marine contribution. The Pr/Ph ratio (1.8–2.3) for the Lokele, Kole and Ebome oil samples, and the V/(V+Ni) ratios (&lt; 0.5) for the seep oils (Douala Basin) and the oils from the Lokele, Kole and Ebome fields, indicate derivation from source rocks deposited in oxic – dysoxic environments. The CPI (1.0–1.1) demonstrates that the Lokele and Ebome oils originated from mature source rocks, with the ratios of C31 22S/(S+R) (0.57 to 0.63) and C30‐βαH/C30‐αβH (0.18–0.23) for the Lokele, Kole and Moudi samples indicating early oil window maturity. Both V/(V+Ni) ratios (0.06–0.22) and δ13C (‐26.96 to ‐24.89 ‰) were used for correlation of the oils, with the seep oils from the Douala Basin showing the closest relationship to the oil from the Lokele field. The presence of mature Type II / III source rocks in different basins in southern Cameroon suggests significant potential for oil exploration in the region.

풋거름작물 재배 후 추비처리가 더덕의 생육 및 사포닌 함량에 미치는 영향

Background: This study was conducted to investigate the effects of fertilization with the application of mixed organic matter after cultivating green manure crops on the growth and saponin content of Codonopsis lanceolata Trautv.<BR> Methods and Results: Five type of cultivation of green manure crops were done: hairy vetch as a single seedling crop (HV), hairy vetch and rye as a mixture of seedling (HV/R), additional fertilization with mixed organic matter after cultivation of a seedling mixture (HV/R/MO), chemical fertilizer (CF), and a non-treated control (NT). The total nitrogen content was the highest in the HV/R/MO treatment, followed by the HV, CF, HV/R and NT treatments, respectively. Nitrogen fixation was higher in the single seedling treatment with hairy vetch (HV) than in the treatment with a mixture of hairy vetch and rye seedling (HV/R). Moreover, the growth of C. lanceolata was greatly increased by the application of additional fertilizer after treatment with the mixture of hairy vetch and rye seedlings. The HV/R/MO treatment produced the highest total lancemaside content among the treatments, followed by HV, HV/R, CF, and NT, respectively.<BR> Conclusions: It was verified that C. lanceolata experienced superior growth with the application of mixed organic matter as additional fertilizer after the cultivation of green manure crops, and the content of its major saponins, lancemasides were also increased by this treatment.

Physical and geochemical properties of crude oils in relation to their source rocks, Alif field, Marib Sub-basin, Yemen

Physical and geochemical properties were performed on three crude oils from Alif-01 well in the Marib sub-basin. The analyzed samples comprise medium specific gravity (37° API), reflecting mature source rocks. The thermal maturity of the analyzed oils is also indicated from the high content of aliphatic hydrocarbons (HC). The compositions of HC further suggest that analyzed oils belong to paraffinic oils. The n-alkane and isoprenoid distributions reveal that the analyzed oils are derived from marine source rock, containing mixed organic matter, with some terrestrial input and deposited under relatively reducing conditions. The features of the analyzed oils are consistent with the Madbi source rock characteristics in the basin.

Development background of Mesozoic high-quality source rocks: Evidence from microfossils in North Carnarvon Basin, Australia

Based on numerous microfossils in Mesozoic of North Carnarvon Basin in Australia, the Mesozoic paleoclimate and paleoenvironment were analyzed, the paleogeographic background and development model of Mesozoic high-quality source rocks were investigated and discussed. Variation of microfossil species and their relative contents in Mesozoic different intervals indicates changes of paleoclimate and paleoenvironment. The paleoclimate shows a cycle variation of arid–humid–arid–humid, the regression occurred in the Early Triassic–Late Triassic and the transgression occurred in the Late Triassic–Late Cretaceous. Four sedimentary facieses including delta facies, littoral facies, restricted sea facies and open sea facies were developed in the Mesozoic. The open sea was mainly developed in the Early Triassic, the delta was distributed in the Middle–Late Triassic, the restricted sea was especially well developed in the Jurassic, and the restricted sea and open sea were mainly distributed in the Cretaceous. Characteristics of microfossil assemblage in these four sedimentary facies are dramatically different. From the delta facies, littoral facies, restricted sea facies to open sea facies, content of pollen gradually decreases, but content of the dinoflagellate + acritarch gradually increases. The delta facies and littoral facies are dominated by the pollen. In the restricted sea facies, content of the pollen is equivalent to that of the dinoflagellate + acritarch. The open sea facies is dominated by the dinoflagellate and acritarch. Supply of sediment and formation of organic matter are influenced by the paleoclimate and paleoenvironment, and type of organic matter is controlled by the microfossil assemblage. Based on the palaeogeographic background, paleoclimatic condition and microfossil assemblage, two developmental models of the Mesozoic source rocks such as the development model of terrestrial organic matter under the background of large delta and the development model of mixed organic matter under the background of the restricted sea, were proposed.