Release of organic nitrogen compounds from Kerogen via catalytic hydropyrolysis

High hydrogen pressure pyrolysis (hydropyrolysis) was performed on samples of solvent extracted Kimmeridge Clay Formation source rock with a maturity equivalent to ca. 0.35% vitrinite reflectance. We describe the types and distributions of organic nitrogen compounds in the pyrolysis products (hydropyrolysates) using GC-MS. Compounds identified included alkyl-substituted indoles, carbazoles, benzocarbazoles, quinolines and benzoquinolines. The distributions of the isomers of methylcarbazoles, C₂-alkylcarbazoles and benzocarbazoles in the hydropyrolysates were compared to a typical North Sea oil. The hydropyrolysates compared to the North Sea oil, showed increased contributions from alkylcarbazole isomers where the nitrogen group is "exposed" (no alkyl substituents adjacent to the nitrogen functionality) and appreciable levels of benzo[b]carbazole relative to benzo[a]- and benzo[c]carbazoles. Hydropyrolysis is found to be an ideal technique for liberating appreciable quantities of heterocyclic organic nitrogen compounds from geomacromolecules. The products released from the immature Kimmeridge Clay are thought to represent a potential source of nitrogen compounds in the bound phase (kerogen) able to contribute to the free bitumen phase during catagenesis.     

Release of bound aromatic hydrocarbons from late Archean and Mesoproterozoic kerogens via hydropyrolysis

Hydrogen-lean kerogens (atomic H/C<0.4) isolated from the 2.5-billion-year-old (Ga) Mt. McRae Shale, Hamersley Group, at Tom Price, Western Australia, were studied via hydropyrolysis, a continuous-flow technique that degrades organic matter in a stream of high-pressure hydrogen assisted by a dispersed Mo catalyst. The hydropyrolysates yielded predominantly phenanthrene and pyrene, and higher polyaromatic hydrocarbons and alkylated homologues were generated in low relative concentrations. Saturated hydrocarbons were not detected. The molecular and carbon isotopic compositions of the hydropyrolysates are very similar to aromatic hydrocarbons obtained by solvent extraction of the host rocks. Because molecular structures covalently attached to kerogen are unaffected by contamination, this indicates that both the bound and extractable aromatic fractions are syngenetic with the host rocks. Therefore, the results of the hydropyrolysis experiments provide compelling evidence for preserved bitumen of Archean age. The very high proportion of nonalkylated polyaromatic hydrocarbons in the hydropyrolysates is consistent with hydrothermal dehydrogenation of the kerogen, and a marked concentration difference of pyrene in rock extracts and hydropyrolysates might be explained by hydrothermal redistribution of the bitumen. The kerogen and bitumen composition is therefore consistent with models suggesting a hydrothermal origin for the giant iron ore deposits at Mt. Tom Price. Comparison of the Archean samples with hydropyrolysates from immature Mesoproterozoic kerogens from the Roper Group, McArthur Basin, Northern Territory, and with pyrolysis experiments on Proterozoic kerogens in the literature suggests that Precambrian kerogens are frequently highly aromatic and lipid-poor regardless of their degree of thermal preservation.     

低熟油、烃源岩中含氮化合物分布规律及其地球化学意义

对八面河地区原油、油砂以及不同成熟度和岩性有异的烃源岩中吡咯类化俣物的分布特征及其潜在的地球化学意义进行了探讨。结果表明，随着成熟度的增加，八面河地区烃源岩中吡咯类化合物中屏蔽化程度高的异构体比屏蔽化程度低的异构体富集，咔唑及苯并咔唑系列中低相对分子质量的同系物比高相对分子质量的同系物富集，苯并[a]咔唑比苯并[c]咔唑富集。八面河地区原油中吡咯类化合物有较为明显的运移分馏效应，观察到高、低相对分子质量的同系物间的运移分馏效应比不同类型异构体间的分馏效应更为显著，而前者受成熟度的影响可能相对小于后者；发现吡咯类化合物的油气运移分馏效应不仅体现于不同氮官能团屏蔽、半屏蔽和暴露三类异构体间，同样体现于同一类型的同分导师构体之间，指示此类化合物有较强的活性。吡咯类化俣物与烃类化合物一样具有多方面潜在的地球化学意义。     

Hydrothermal petroleum of Lake Chapala,Citala Rift,western Mexico: Bitumen compositions from source sediments and application of hydrous pyrolysis

Hydrothermal simulation experiments were performed with contemporary sediments from Lake Chapala to assess the source of the lake tars. The precursor-product relationships of the organic compounds were determined for the source sediments and their hydrous pyrolysis products. The pyrolysis products contained major unresolved complex mixtures of branched and cyclic hydrocarbons, low amounts of n-alkanes, dinosterane, gammacerane, and immature and mature hopane biomarkers derived from lacustrine biomass sources. The results support the proposal that the tar manifestations in the lake are not biodegraded petroleum, but were hydrothermally generated from lacustrine organic matter at temperatures not exceeding about 250 °C over brief geological times.     

Biogene,klastische und evaporitische Sedimentation in einem mesothermen monomiktischen ufernahen See (Golf von Aqaba)

The genesis and development of a monomictic, mesothermal lake and its sediments is demonstrated by the analysis of sediment cores from different parts of the lake and from different stages of development. The compounds which build up the sediments, consist of irregular large particles from the surrounding crystalline rocks, of fine grained silt sediments from catastrophic flud deposits, of evaporitic series, and algae mats. The thickness of the different layers and their distribution in various parts of the lake; the different compounds, absolute age determinations, the carbonate layers and algae mats allow the definition of different stages of development of the lake. Causes and influences of an unusual type of monomixis with summer turnover are discussed and related to the sedimentary environment. Annual fluctuations in physical and biological limnology lead to the development of annual cycles in mat development and evaporites, which are reflected in the varved sediments. Inorganic sedimentation of terrestrial sediments, evaporites and organic matter accumulation are in shifting equilibrium which can be analysed by changes in the sediment types. Within the zone of biologic decay of algae via photosynthetic and other sulfur bacteria and heterotrophic bacteria, biogenic aragonite, Mg-Calcite and sulfides are precipitated. The autigenic dolomite occuring within the algae mats could not be attributed to biological precipitation so far. The lake started out as a lagoon approximately 4500 years B.P. Algae mat development was initiated after the lagoon was separated from the open sea (2400 B.P.). The central parts of the lake subsided at a time between 1900 and 1600 B.P. At this time the algae mat deposition, which until then took place in the whole lake, was restricted to the remaining shallow parts. Years of extremely high precipitation and catastrophic floods are represented by silt layers in the western parts of the lake, while coarser terrestrial sediments are intercalated in the algae mats of the eastern parts. Oöids, carbonate laminae, oncoliths and other types of carbonate particles within the algae mats are defined as biogenic by SEM analyses and laboratory experiments.     

Carbazoles and benzocarbazoles confirm migration of leaked petroleum through caprocks and overlaying formations of Valhall Well 2/8-8 in the North Sea

A wildcat may not result in a petroleum prospect; however, it may indicate potential need for frontier exploration, since petroleum could leak into economic accumulations. Carbazoles and benzocarbazoles are nitrogen compounds in petroleum and can be employed to explicitly explain migration direction and distance of leaking petroleum. The hypothesis of this study is that the mechanism of the reaction involving the attraction of carbazoles to clay minerals on the matrix of the walls along their migration pathways determines the isomer that is preferentially attached to the mineral matrix. The objectives of this study are (a) to produce a profile for carbazoles and benzocarbazoles ratios in the cap rock overlying the reservoir, (b) to compare carbazole and benzocarbazole ratios to 20S/(20S + 20R) αααC₂₉ Sterane maturity ratios (c) to infer migration direction from the carbazoles and benzocarbazoles ratio. Samples used were side wall cores and drill cuttings of water-based mud drilling. The EOM (extractable organic matter) from various formations overlying the reservoir was obtained using Soxtherm Automatic Equipment. The TPH (total petroleum hydrocarbon) was obtained from the EOM by using a precleaned isolute C₁₈ 500 mg / 3 mL column, eluted with hexane, while the polars were eluted with dichloromethane. Fractionation into saturates and aromatics was done using a silver nitrate–silica gel column. The profiles of 1,8/1,3 and 1,8/2,4 dimethyl carbazoles and the benzocarbazoles ratios show a vertical gradient of decreasing ratio with increasing vertical distance from the reservoir. This corroborates the %VRo equivalent of 20S/(20S + 20R) αααC₂₉ Sterane and the carbazole ratios infer vertical migration of leaked petroleum.     

Maturity studies and source-rock potential in the southern Sverdrup Basin, Arctic Canada

The purpose of the study is to better understand the relationship between organic matter optical properties and the presence of potentially large oil and gas accumulations in Arctic Canada. The type and thermal maturity of the dispersed organic matter of the Mesozoic formations in the southern Sverdrup Basin, Melville Island, have been studied using organic petrology and Rock-Eval pyrolysis.All types of organic matter are present in the strata of Mesozoic age. Hydrogen-rich liptinite is dominated by alginite (Botryococcus and Tasmanites), dinoflagellate cysts and amorphous fluorescing matrix. Sporinite, cutinite, resinite and liptodetrinite made up the lesser hydrogen-rich exinite. Vitrinite reflectance in Cretaceous sediments ranges from 0.36 to 0.65% R_o; in Jurassic sediments it ranges from 0.40 to 1.0% R_o and in the Triassic from 0.45 to 1.30% R_o, showing an overall increase with depth of burial.Cretaceous sediments of the Deer Bay Formation are thermally immature and contain organic matter of terrestrial origin. The Upper Jurassic shales of the Ringnes Formation contain predominantly organic matter of liptinitic and exinitic origin with a considerable vitrinitic input. At optimum maturation levels, potential source beds of this formation would have a good hydrocarbon-generating potential. The hydrocarbon potential, however, would be limited to the generation of gases due to the leanness of the source rocks. Parts of the Lower Jurassic Jameson Bay Formation are organic-rich and contain a mixed exinitic/vitrinitic organic matter, Botryococcus colonial algae but visible organic matter is dominated by high plant remains (mainly spores). The Schei Point Group shales and siltstones contain organic matter of almost purely marine origin, whereas the predominantly higher plant-derived organic matter found in the Deer Bay, Jameson Bay and partly in the Ringnes formations have higher TOC. Among the Schei Point Group samples, the Cape Richards and Eden Bay members of the Hoyle Bay Formation are richer in TOC (>2.0%) than the Murray Harbour Formation (Cape Caledonia Member). This may reflect differences in the level of maturity or in the depositional environment (more anoxic conditions for the former).Regional variations in the level of thermal maturity of Mesozoic sediments in Sverdrup Basin appear to be a function of burial depth. The Mesozoic formations thicken towards the basin centre (NNE direction), reflecting the general pattern of increasing thermal maturity north of Sabine Peninsula. However, the regional thermal-maturation pattern of the Mesozoic is not solely a reflection of the present-day geothermal gradient, which indicates that anomalous zones of high geothermal gradient may have existed in the past, at least since when the Mesozoic sediments attained maximum burial depth. The contour pattern of the regional variation of maturity at the base of numerous Triassic formations is similar to that of the structural contours of the Sverdrup Basin, indicating that present-day maturation levels are largely controlled by basin subsidence.     

Petroleum degradation and associated microbial signatures at the Chapopote asphalt volcano, Southern Gulf of Mexico

At the Chapopote Knoll in the Southern Gulf of Mexico, deposits of asphalt provide the substrate for a prolific cold seep ecosystem extensively colonized by chemosynthetic communities. This study investigates microbial life and associated biological processes within the asphalts and surrounding oil-impregnated sediments by analysis of intact polar membrane lipids (IPLs), petroleum hydrocarbons and stable carbon isotopic compositions (δ¹³C) of hydrocarbon gases. Asphalt samples are lightly to heavily biodegraded suggesting that petroleum-derived hydrocarbons serve as substrates for the chemosynthetic communities. Accordingly, detection of bacterial diester and diether phospholipids in asphalt samples containing finely dispersed gas hydrate suggests the presence of hydrocarbon-degrading bacteria. Biological methanogenesis contributes a substantial fraction to the methane captured as hydrate in the shallow asphalt deposits evidenced by significant depletion in ¹³C relative to background thermogenic methane. In sediments, petroleum migrating from the subsurface stimulates both methanogenesis and methanotrophy at a sulfate-methane transition zone 6-7 m below the seafloor. In this zone, microbial IPLs are dominated by archaeal phosphohydroxyarchaeols and archaeal diglycosidic diethers and tetraethers. Bacterial IPLs dominate surface sediments that are impregnated by severely biodegraded oil. In the sulfate-reduction zone, diagnostic IPLs indicate that sulfate-reducing bacteria (SRB) play an important role in petroleum degradation. A diverse mixture of phosphohydroxyarchaeols and mixed phospho- and diglycosidic archaeal tetraethers in shallow oil-impregnated sediments point to the presence of anaerobic methane-oxidizing ANME-2 and ANME-1 archaea, respectively, or methanogens. Archaeal IPLs increase in relative abundance with increasing sediment depth and decreasing sulfate concentrations, accompanied by a shift of archaeol-based to tetraether-based archaeal IPLs. The latter shift is suggested to be indicative of a community shift from ANME-2 and/or methanogenic archaea in shallower sediments to ANME-1/methanogenic archaea and possibly benthic archaea in deeper sediments.     

The characteristics of the biomarkers and δ13C of n-alkanes released from thermally altered solid bitumens at various maturities by catalytic hydropyrolysis

Solid bitumen occurs extensively in the paleo-reservoirs of marine sequences in southern China. The fluids in these paleo-reservoirs have usually experienced severe secondary alteration such as biodegradation and/or thermal maturation. The concentrations of extractable organic matter (EOM) in the resulting solid bitumens are too low to satisfy the amount required for instrumental analysis such as GC–MS and GC–IRMS. It is also difficult to get enough biomarkers and n-alkanes by dry pyrolysis or hydrous pyrolysis directly because such solid bitumens are hydrogen poor due to high maturities. Catalytic hydropyrolysis (HyPy) can release much more EOM from solid bitumen at mature to highly over-mature stages than Soxhlet extraction, dry pyrolysis and hydrous pyrolysis. However, whether the biomarkers in hydropyrolysates can be used for bitumen-source or bitumen–bitumen correlations has been questionable. In this study, a soft biodegraded solid bitumen sample of low maturity was thermally altered to various maturities in a closed system. HyPy was then employed to release bound biomarkers and n-alkanes. Our results show that the geochemical parameters for source and maturity based on biomarkers released from these thermally altered bitumen residues by HyPy are insensitive to the degree of thermal alteration. Furthermore, the maturity parameters are indicative of lower maturity than bitumen maturation products at a corresponding temperature. This suggests that biomarker source and maturity parameters, based on the products of HyPy, remain valid for bitumens which have suffered both biodegradation and severe thermal maturation. The distributions of δ¹³C of n-alkanes in hydropyrolysates are also insensitive to the temperature used for bitumen artificial maturation. Hence, the δ¹³C values of n-alkanes in hydropyrolysates may also provide useful information in bitumen–bitumen correlation for paleo-reservoir solid bitumens.     

南海北部油气缓释环境沉积物脂类化合物组成特征

认识沉积环境有机碳留存状况是阐述油气形成过程中有机碳早期成岩的关键内容。以南海珠江口盆地及其邻近海域为背景,通过研究表层沉积物中脂类化合物的形态组成,认识脂类有机碳的来源和留存状态,阐述特征脂类分子的早期成岩特征。结果表明,研究区域表层沉积物有机碳含量为0.22%～0.66%,有机碳稳定同位素分布在-20.88‰～-22.93‰之间,表现为显著的海源特征。沉积物中共检测出21种脂肪酸、6种脂肪醇、8种甾醇和植醇;总脂肪酸、脂肪醇、甾醇和植醇含量分别为12.57～40.27μg/g、5.35～8.98μg/g、0.15～3.75μg/g和0.01～3.99μg/g干重,总体表现为靠近珠江口和台湾海峡略高。脂类化合物的存在形态以游离态(FR)和碱性水解态(BH)为主,酸性水解态(AH)贡献较低;其中植醇和甾醇呈现显著的BH优势,植醇中未检出AH组分的贡献。脂类化合物主要来自于海洋现场生产,海洋微藻和细菌的相对贡献率分别为21.18%～33.78%和11.02%～15.64%,陆源高等植物贡献低于5%。来源于硫酸盐还原菌的支链脂肪酸在靠近珠江口海域高达1.79～2.62μg/g,占总脂肪酸的5.14%～6.50%,并与硫酸盐还原过程相关的古菌分布相一致。     

Highly isotopically depleted isoprenoids: molecular markers for ancient methane venting

We propose that organic compounds found in a Miocene limestone from Marmorito (Northern Italy) are source markers for organic matter present in ancient methane vent systems (cold seeps). The limestone contains high concentrations of the tail-to-tail linked, acyclic C₂₀ isoprenoid 2,6,11,15-tetramethylhexadecane (crocetane), a C₂₅ homolog 2,6,10,15,19-pentamethylicosane (PME), and a distinctive glycerol ether lipid containing 3,7,11,15-tetramethylhexadecyl (phytanyl-) moieties. The chemical structures of these biomarkers indicate a common origin from archaea. Their extremely ¹³C-depleted isotope compositions (δ¹³C ≈ −108 to −115.6‰ PDB) suggest that the respective archaea have directly or indirectly introduced isotopically depleted, methane-derived carbon into their biomass. We postulate that a second major cluster of biomarkers showing heavier isotope values (δ¹³C ≈ −88‰) is derived from sulfate-reducing bacteria (SRB). The observed biomarkers sustain the idea that methanogenic bacteria, in a syntrophic community with SRB, are responsible for the anaerobic oxidation of methane in marine sediments. Marmorito may thus represent a conceivable ancient scenario for methane consumption performed by a defined, two-membered bacterial consortium: (1) archaea that perform reversed methanogenesis by oxidizing methane and producing CO₂ and H₂; and (2) SRB that consume the resulting H₂. Furthermore, the respective organic molecules are, unlike other compounds, tightly bound to the crystalline carbonate phase. The Marmorito carbonates can thus be regarded as “cold seep microbialites” rather than mere “authigenic” carbonates.     

甘肃省阳山超大型金矿床的有机地球化学特征研究

甘肃省文县阳山金矿是我国地质勘查储量最大的卡林-类卡林型金矿床,赋矿地层为泥盆系一套碳-硅-泥质地层.矿区发育了大量碳质千枚岩,富含有机碳.本文研究了矿石和围岩可溶有机质的生物标志物、有机质的来源和成熟度、干酪根的碳同位素等,论述了阳山金矿床的有机地球化学特征及有机质与成矿的关系,查明了参与成矿的有机质主要是菌藻类等低等生物.生物标志化合物参数和干酪根的H/C-O/C原子比值指示阳山金矿有机质成熟度较高,达到了无烟煤的演化阶段.在热演化的过程中,有机质裂解产生的CH_4和C-2H_6等进入成矿流体中,参与了成矿过程.阳山金矿赋矿地层中含有生物成因的草莓状黄铁矿,显示生物-有机质参与了地层的预富集作用.有机碳含量、有机质的类型和金的丰度之间相关性不明显,说明在阳山金矿的成矿过程中有机质对金的沉淀贡献不大,但是有机质可能参与了金的预富集和运移.     

准噶尔盆地北三台地区湖相原油咔唑类化合物的地球化学特征

准噶尔盆地北三台地区北 82井、北 83井和沙 10 8井湖相原油咔唑类化合物的分布特征表明,油气运移作用是影响该区原油中咔唑类化合物分布的重要因素。沿油气运移方面,咔唑类化合物具有明显的分馏效应。总的趋势是原油中咔唑类化合物、高分子量的烷基咔唑化合物和苯并咔唑化合物的含量逐渐减少,低分子量咔唑和甲基咔唑,以及具屏蔽效应的二甲基咔唑和苯并 [a]咔唑异构体的相对含量则逐渐增加。利用咔唑类化合物的分馏效应,可有效地指示油气运移方向。     

Pollen distribution in large freshwater lake of arid region: a case study on the surface sediments from Bosten Lake,Xinjiang, China

The interpretation of the pollen records from lake sediments is always hampered by a lack of information relating to different pollen production, transportation, deposition, and preservation. It is important to understand the modern process of pollen sedimentation and its climatic implications. This paper presents results from a palynological study on 61 surface sediments samples from Bosten Lake, the largest inland freshwater lake in China. Our results suggest that Chenopodiaceae and Artemisia dominate the modern pollen assemblages and have stable percentages at most sites of the lake basin except for the estuary area. Pollen Artemisia/Chenopodiaceae ratio is about 0.5, indicating the dry climate of the region. Principle Components Analysis (PCA) of pollen data can identify the pollen samples as several ecological groups from different parts of the lake. Pollen transportation dynamics and the mixing effect of lake currents and waves on pollen deposition have affected the pollen assemblages. The distribution of Typha pollen seems to be affected by the location where the parent plants grow. Picea pollen has higher percentages at estuary area, suggesting fluvial transport. Pollen concentration has high values at the central part of the lake basin due to the sedimentation focusing process effect. Our results suggest that the pollen assemblages of the sediment core from the central part of the lake can potentially record the regional vegetation history.     

Molecular and carbon isotopic analysis of individual biological markers: evidence for sources of organic matter and paleoenvironmental conditions in the Upper Ordovician Maquoketa Group, Illinois Basin, U.S.A.

Variations in the carbon isotopic composition (δ¹³C) of pristane, phytane, n-heptadecane (n-C₁₇), C₂₉ ααα 20R sterane, and aryl isoprenoids provide evidence for a diverse community of algal and bacterial organisms in organic matter of the Upper Ordovician Maquoketa Group of the Illinois Basin. Carbon isotopic compositions of pristane and phytane from the Maquoketa are positively covariant (r = 0.964), suggesting that these compounds were derived from a common source inferred to be primary producers (algae) from the oxygenated photic zone. A variation of 3‰ in δ¹³C values (−31 to −34‰) for pristane and phytane indicates that primary producers utilized variable sources of inorganic carbon. Average isotopic compositions of n-C₁₇ (−32‰) and C₂₉ ααα 20R sterane (−31‰) are enriched in ¹³C relative to pristane and phytane (−33‰) suggesting that these compounds were derived from a subordinate group of primary producers, most likely eukaryotic algae. In addition, a substantial enrichment of ¹³C in aryl isoprenoids (−14 to −18‰) and the identification of tetramethylbenzene in pyrolytic products of Maquoketa kerogen indicate a contribution from photosynthetic green sulfur bacteria to the organic matter. The presence of anaerobic, photosynthetic green sulfur bacteria in organic matter of the Maquoketa indicates that anoxic conditions extended into the photic zone.The δ¹³C of n-alkanes and the identification of an unusual suite of straight-chain n-alkylarenes in the m/z 133 fragmentograms of Ordovician rocks rich in Gloeocapsomorpha prisca (G. prisca) indicate that G. prisca did not contribute to the organic matter of the Maquoketa Group.     

Potential source rocks, organic geochemistry and thermal maturation in the southern depocenter (Kipourio–Grevena) of the Mesohellenic Basin, central Greece

The study area is the southern depocenter (depth > 4200 m) of the Mesohellenic Basin which extends between Kipourio and Grevena, central Greece. The Mesohellenic Basin is a Middle-Tertiary intramontane basin developed within the Hellenide orogen. Previous studies have focused on the depositional environments, configuration and hydrocarbon potential of the basin. In this paper we present additional geochemical and petrographic data from outcrop samples of the basin's southern depocenter, which is considered the most promising area, in terms of hydrocarbon prospectivity. A total number of thirty six samples were analysed: Rock-Eval pyrolysis, maceral analysis, vitrinite reflectance and thermal alteration index, bitumens extraction, liquid chromatography, and GC-MS. The samples were collected from deltaic deposits and submarine fan sediments of Late Eocene to Late Oligocene age. The TOC values of the analysed samples range between rich and very rich and the organic matter consists mainly of type III kerogen and the organic matter consider to be predominately gas prone. The thermal maturity assessed from T_max and vitrinite reflectance shows an immature stage of the organic matter along with the presence of layers having reached the very early mature stage. Vitrinite reflectance measurements and maturity calculations (applying the Lopatin modeling), reveal that the lower part of the depocenter sediments falls within the ‘oil window’. The extractable organic matter (EOM) (mg bitumens/g TOC) indicate the existence of samples (from deltaic deposits) with high ratio of transformation (EOM) (> 100 mg bitumen/g TOC). The GC and GC-MS analyses of the biomarkers indicate mainly the occurrence of terrestrial organic matter reflecting oxidizing conditions and both immature and very early mature stages. The results of the Rock-Eval pyrolysis and the distribution of the isoprenoids support the assumption of the input of an organic matter mixture.     

Environmental evolution recorded by multi-proxy evidence in Lake Chenghai sediments, Yunnan Province during recent 100 years

Lacustrine sediments can provide potential information about environmental changes in the past. On the basis of high-resolution multi-proxy analysis including carbon and nitrogen contents of organic matter, C/N ratios, inorganic carbon contents, and carbon and oxygen isotopic composition of carbonate, together with precise 137Cs dating, the environmental evolution of Lake Chenghai, Yunnan Province, during the past 100 years has been investigated. It is shown that the carbonate in Lake Chenghai is authigenic, and the organic matter is mainly derived from aquatic plants and algae, instead of terrestrial-source materials. The environmental evolution of Lake Chenghai can be diverged into three periods with the contrasting characteristics during the past 100 years. Before 1940, the stable carbon and oxygen isotope values, the poor correlation between them and the lower carbon and nitrogen contents of organic matter suggested that Lake Chenghai was open, and the lake water was oligotrophic during that period. During 1940-1993, the negative δ13C values and the gradual increase of carbon and nitrogen contents of organic matter and C/N ratios indicated that the eutrophication was aggravated. The closeness of Lake Chenghai and human activities may be responsible for this eutrophication. After 1993, notable increases in carbon and oxygen isotopic values of carbonate, carbon and nitrogen contents of organic matter, C/N ratios and inorganic carbon contents demonstrated that the increase of lacustrine productivity and the serious eutrophication were resulted from strong human activities. Therefore, the multi-proxy in Lake Chenghai sediments has reliably recorded the natural environmental evolution and the impacts from human activities.     

Organofacies and paleoenvironment of the Oligocene Maikop series of Angeharan (eastern Azerbaijan)

The Maikop Formation, deposited in eastern Azerbaijan during Oligocene and Early Miocene times, contains prolific source rocks with primarily Type II organic matter. Paleontological analyses of dinoflagellate cysts revealed a Lower to Upper Oligocene age for the investigated succession near Angeharan. A major contribution of aquatic organisms (diatoms, green algae, dinoflagellates, chrysophyte algae) and minor inputs from macrophytes and land plants to organic matter accumulation is indicated by n-alkane distribution patterns, composition of steroids and δ¹³C of hydrocarbon biomarkers. Microbial communities included heterotrophic bacteria, cyanobacteria, chemoautotrophic bacteria, as well as green sulfur bacteria. Higher inputs of terrigenous organic matter occurred during deposition of the Upper Oligocene units of the Maikop Formation from Angeharan mountains. The terpenoid hydrocarbon composition argues for angiosperm dominated vegetation in the Shamakhy–Gobustan area.High primary bioproductivity resulted in a stratified water column and the accumulation of organic matter rich sediments in the Lower Oligocene units of the Maikop Formation. Organic carbon accumulation during this period occurred in a permanently (salinity-) stratified, mesohaline environment with free H₂S in the water column. This is indicated by low pristane/phytane ratios of all sediments (varying from 0.37–0.69), lower methylated-(trimethyltridecyl)chromans ratio in the lower units and their higher contents of aryl isoprenoids and highly branched isoprenoid thiophenes. Subsequently, the depositional environment changed to normal marine conditions with oxygen deficient bottom water. The retreat of the chemocline towards the sediment–water interface and enhanced oxic respiration of OM during deposition of the Upper Oligocene Maikop sediments is proposed.Parallel depth trends in δ¹³C of total OM, n-alkanes, isoprenoids and steranes argue for changes in the regional carbon cycle, associated with the changing environmental conditions. Increased remineralisation of OM in a more oxygenated water column is suggested to result in low TOC and hydrocarbon contents, as well as ¹⁵N enriched total nitrogen of the Upper Oligocene units.     

Characterization of organic matter in surface sediments of the Mackenzie River Basin, Canada

The particulate organic matter in < 63 µm surface sediments from the Mackenzie River and its main tributaries was studied using Rock-Eval pyrolysis and organic petrology. The organic matter in the sediments is dominated by refractory residual organic carbon (RC) of mainly terrigenous nature, as indicated by abundant inertinite, vitrinite, and type III kerogen. Sediments from the tributaries contained significantly more algal-derived organic matter than from the main channel of the river, highlighting the importance of low-energy system dynamics in the tributaries, which allows modest algal production, more accumulation, and better preservation of autochthonous organic matter. This is particularly true for tributaries fed by lacustrine systems, which showed the highest S1 and S2 fractions, and consequently higher total particulate organic carbon (POC) in the basin. Organic petrology of the sediment samples confirms abundant liptinitic materials (i.e., fat-rich structured algae, spores and pollen, cuticles, and resins). Forest fire and coal deposits are also confirmed to contribute to the basin. Assuming that suspended and fine surfacial sediments have a similar OC composition, the Mackenzie River is estimated to deliver a total POC flux of 1.1 Mt C/yr to its delta, of which 85% is residual carbon with liptinitic OC (S1 + S2) and S3 accounting for another 9% and 6%, respectively.