Mixed Organic Matter Research Articles

The aftermath of the CPE and the Carnian–Norian transition in northwestern Sichuan Basin, South China

The northwestern Sichuan Basin (South China) was a portion of eastern Tethys where, during the Late Triassic, a sharp lithological transition from oolitic–bioclastic limestones and sponge reef mounds to dark grey terrigenous clays, siltstones and sandstones is visible in several localities. The timing and significance of this major facies transition is still unclear. Here we report new biostratigraphic and carbon stable isotope data from Hanwang and Jushui, northwestern Sichuan Basin. Sporomorphs, ammonoids, conodonts and halobiid bivalves show that the lithological change is Late Carnian to Early Norian in age. This amended age determination facilitates recalibration of the magnetostratigraphy in the area allowing correlation between the Late Triassic of the Sichuan Basin and the Astrochronostratigraphic Polarity Time Scale. A carbon stable isotopic perturbation across the Carnian–Norian Boundary (CNB) is missing in our sections, or it is concealed because of the mixed organic matter sources. Our findings pinpoint the position of the CNB to a short stratigraphic interval of c. 12 m thickness in the Sichuan Basin. The studied sections greatly extend the palaeogeographical documentation of the CNB and provide novel information on biostratigraphy and chemostratigraphy that should be considered in defining the best position of the Norian Global Stratotype Section and Point.

Organic source of crude oils and 1D basin modeling of upper Cretaceous rocks, Badr Concession, Abu Gharadig Basin, Western Desert, Egypt

The Badr Concession exists in Abu Gharadig basin, which is a great oil province in Western Desert, Egypt. This work concerned on studying the geochemical characteristics and organic source of crudes produced from Abu Roash “C” (AR/C) Member in BED15-1, BED15-3, and BED15-4 wells using gas chromatography (GC) analysis. Also, the BasinMod Software is used to construct models of burial history that detect thermal maturity and generation timing for Cretaceous sources based on modeled Vitrinite reflectance (%Ro). The oil samples are not biodegraded, due to the existence of an intact paraffin envelope in all three oils as revealed from low normal-alkane/isoprenoids and the distribution of different light hydrocarbons. These crudes have pristane/phytane (Pr/Ph) ratio that ranged from 1.03 to 1.08 indicating that those oils are generated from mixed organic matter such as algae and submerged macrophyts which are the main constituents which are deposited and preserved in lacustrine environment under reducing to suboxic condition. The Pr/nC17 and Ph/nC18 ratios indicate that these crudes are mature. Also, the models of burial history indicate that Abu Roash Formation reached mid maturation stage and these results are in agreement with GC results. Generally, the hydrocarbon generation began in Late Cretaceous and reached the peak during the Tertiary.

Geochemical characteristics and analysis of crude-oil source in the deep-water area of the Baiyun Sag, South China Sea

In the Baiyun Sag, the oil relationship with possible source rocks is complicated, and little research on oil sources in the area has been performed. In this paper, geochemical studies of carbon isotopes, biomarkers, paleoenvironmental deposition, and crude oil maturity, carried out with the use of oil samples from the Baiyun Sag, demonstrate that the organic matter in crude oil has an oxidizing depositional environment and primarily lacustrine facies conditions, with a significantly higher plant input. The oil samples used are mature to highly mature. Crude oil in the northern area of the Baiyun Sag is more mature than samples in the eastern part of the sag. Despite limited source rock data, we were able to conclude that the crude oil samples were derived mainly from the Enping Formation; other potential source rocks of the Wenchang and Zhuhai Formations may also have contributed to the reservoirs in different parts of the sag. Furthermore, the source of crude oil in each structure in the Baiyun Sag was analyzed; for example, crude oil in the LH19-5 structure was generated from the organic matter of the Enping Formation, and crude oil in the LW3-1 structure was derived from the mixed organic matter of the Enping, Wenchang, and Zhuhai Formations. © 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Effect of organic fertilizer application on growth characteristics and saponin content in Codonopsis lanceolata

Organic fertilizers were applied in four different forms: mixed organic matter, fermentation cake, bacterial culture, and rice husks, excluding conventional chemical fertilizer and non-treatment used as control. The results showed that soil pH was acidified after fermentation cake and chemical fertilizer treatment. Specifically, chemical fertilizer treatment showed higher phosphoric-acid content than other treatments, while total N content was higher in fermentation cake, mixed organic matter and chemical fertilizer. Growth of Codonopsis lanceolata showed superior tendency in the treatment of mixed organic matter and fermentation cake. Lancemacides, the major saponin of C. lanceolata, could be identified as foetidissimoside A, lancemaside A, lancemaside B, and lancemaside D. However, among them, quantitative analysis could not be conducted on foetidissimoside A due to its very low content, and lancemaside A was the most abundant saponin in the root from all the treatments. The content of lancemaisde A according to organic fertilizer application showed the highest value of 0.12 mg g−1 in the treatment of mixed organic matter, followed by the fermentation cake, bacterial culture, non-treatment, rice husks and chemical fertilizer, in that order. The content of lancemaside B and D was very low compared to lancemaside A, and there was no difference among treatments. Therefore, it was verified that the growth of C. lanceolata was superior in application of mixed organic matter and fermentation cake, and the major saponin, lancemaside A, was also increased.

Geochemical characteristics of light hydrocarbons and their influencing factors in natural gases of the Kuqa Depression, Tarim Basin, NW China

In order to determine the source of the light hydrocarbons in the Kuqa Depression of the Tarim Basin, Northwest China, their geochemical characteristics are documented, and possible influencing factors are discussed in a broad context on the basis of geochemical analyses of natural gas samples from 19 wells in combination with previously reported natural gas components and carbon isotope values from the same depression. The biomarker analytical results show that (a) methyl cyclohexane (37.5–60.3%) of natural gas predominates the C7 light hydrocarbon series (methyl cyclohexane, heptanes, and dimethyl cyclopentane), and (b) the heptane content (25.0–54.8%) is also relatively high. The C6–7 light hydrocarbon series (aromatics, normal alkanes, and cycloalkanes) have abnormally high aromatics (benzene and toluene) content (26.2–83.8%). Heptane value (13.31–37.77%) and isoheptane value (2.10–7.64%) indicate that the Kuqa natural gases are of high maturity and typical of coal‐derived gas (gas generated by sapropelic source rock). Their light hydrocarbons, however, appear to have some characteristics of mixed‐source organic matter. Specifically, the light hydrocarbons in the Dina 2 gas field show characteristics of the coal‐derived gas; those in the Dabei gas field show some features of the oil‐associated gas (gas generated by humic source rock), whereas those in the Kela 2 and Keshen 2 gas fields and Well Yangtake‐101 display characteristics of the mixed source organic matter. The abnormally high content of the aromatics in the Kuqa Depression may have resulted mainly from their high productivity during the thermal maturity of humic type organic matters and the gases accumulation of late stage. The different relative contents of the aromatics in various oil and gas fields may have been accounted by different organic matter types, maturity, and distribution patterns of source rocks.

Distribution of organic matter in Callovian-Lower Berriasian deposits of the western part of the Yenisei-Khatanga regional trough and adjacent areas of the West Siberian geosyneclise

This study presents the results of geochemical analysis of organic matter and paleogeographic reconstructions supplemented by data from well log interpretation and cyclostratigraphic analysis for the Vasyugan, Georgiev, and Bazhenov Horizons of the Callovian-Lower Berriasian section in the western part of Yenisei-Khatanga regional trough and adjacent areas of the West Siberian geosyneclise. It was found that each horizon contains zones dominated by terrigenous, mixed, and aquatic organic matter. The distribution of different types of organic matter over the area and throughout the section has been examined. It was shown that the accumulation of aquatic organic matter took place in the deepest parts of the trough during the Callovian-Oxfordian. The area of accumulation of aquatic organic matter expanded considerably and reached its maximum extent within the Bolshaya Kheta megasyneclise during the Kimmeridgian and Early Volgian and in the west Yenisei-Khatanga regional trough during the Volgian and Early Berriasian.

Bulk geochemical characteristics and carbon isotope composition of oils from the Sayhut sub-basin in the Gulf of Aden with emphasis on organic matter input, age and maturity

The Sayhut sub-basin is undergoing hydrocarbon exploration province in the Gulf of Aden, South Yemen. In this study, geochemical analyses were performed on three oil samples from two exploration wells in the Sayhut sub-basin. The results were used to describe the source organic matter input, age and maturity and to correlate between crude oils from different pay zones.The high saturated hydrocarbon values of more than 70% indicate that the analysed oils are normal crude oils and not degraded oils. This is supported by a complete suite of their normal alkanes and acyclic isoprenoids. The hydrocarbon distributions of normal alkane and isoprenoid with bulk carbon isotope data also suggest that the analysed oils are grouped into two genetic families and were generated from marine-source rock. The family A presents by one oil sample representing Harshiyat reservoir rock and characterized by relatively high Ph/Ph ratio>2 and δ13C values of their saturated and aromatic hydrocarbon fractions range from −26.1‰ to −24.8‰. This oil family was derived from mixed organic matter with high contribution of a terrigenous organic matter input. The family A was deposited under suboxic conditions during the Late Cretaceous age. The family B presents by two oil samples representing Ghaydah and Habshiyah reservoir rocks and characterized by relatively low Ph/Ph ratio<2 and carbon isotope less than −23 for their saturated and aromatic hydrocarbon fractions. These oils were generated from source rock containing high contributions of marine organic matter (e.g., algal and microbial) with minor amount of land plant source inputs that was deposited in more reducing conditions. The family B oils are consistent with those of the Paleogene Umm Er Radhuma source rock.The hydrocarbon distribution and oil composition data also indicate that the analysed oils were generated from mature source rocks with a peak oil-window maturity.

Geochemistry of Cretaceous rocks, Pakistan: II. Interpretation of source, depositional environment and lithology of organic matter

ABSTRACTThe sediment samples from Cretaceous sequences, Lower Indus Basin, were investigated using biomarkers approach to predict the source, depositional environment and lithology of organic matter. The Parh and Upper Goru Formations demonstrate the presence of algal organic matter deposited under anoxic and suboxic conditions. The interpretation was supported by relatively high distribution of C27 5α (H), 14α (H), 17α (H) 20R (ααα-20R) steranes. The samples of Lower Goru Formation reveal mixed organic matter, predominantly terrestrial and oxic, as apparent from biomarkers distribution. The Sembar Formation specifies mixed input of organic matter more terrigenous input at intervals, deposited under anoxic and suboxic conditions. Geochemical analyses performed on Cretaceous strata show that hydrocarbons were derived from organic matter of mixed origin, predominantly terrestrial, deposited under anoxic and oxic conditions.

The Fouling Characteristics of NOMs on the Microfiltration Ceramic Membrane

ABSTRACT Kim, K.-J. and Jang, A., 2017. The fouling characteristics of NOMs on the microfiltration ceramic membrane. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 60–64. Coconut Creek (Florida), ISSN 0749-0208. The filtration performance and fouling characteristics of mixed natural organic matters (NOMs) on monolith ceramic microfiltration (MF) membrane was investigated in a dead-end mode under constant transmembrane pressure (TMP) with periodic backwash. Humic acid (HA), bovine serum albumin (BSA), and sodium alginate (SA) were used for the investigation of the fouling potential. In a pilot-scale filtration test, the fouling characteristics of NOMs were evaluated by the various operation conditions, including solution pH, foulant mixture, and rate of flux recovery. The NOMs and mixed NOMs caused severe permeability reduction, and the fouling potential varied significantly with d...

Source rock characteristics, depositional setting and hydrocarbon generation potential of Cretaceous coals and organic rich mudstones from Gombe Formation, Gongola Sub-basin, Northern Benue Trough, NE Nigeria

The ongoing exploration activities at the Maiganga coal mine uncover some missing gaps in the stratigraphy of the Late Cretaceous Gombe Formation. Therefore, there is a need to further investigate this sequence, including the organic facies variations and distributions of the coals, mudstones and sandy-shaly sediments in the Gombe Sandstone (Formation), Gongola Sub-basin, Northern Benue Trough of Northeastern Nigeria. Geochemical and petrographic methods were used to assess the organic matter source input, paleodepositional conditions, thermal maturity and hydrocarbon generation potential of the analysed Maiganga and Yaya-Ngari samples. Field observations showed four coal seams interbedded with mudstones and shales deposited in coarsening upward sequence of a deltaic environment. Evaluation based on the source rock analyses (SRA) reveals that Maiganga sedimentary facies is dominated by terrestrial source input of Type III kerogen. This is supported by the biomarker study suggesting land plant origin for the organic matter with minor lacustrine and marine influences, in Maiganga, that grades into predominantly mixed organic matter input of a transitional (terrestrial to marine) environment in the Yaya-Ngari area. This shows a progressive movement towards marine source input. Paleodepositional conditions of organic matters were sub-oxic to oxic in Maiganga, while the mixed organic matters in Yaya-Ngari were deposited in sub-oxic conditions. Based on organic petrology and bitumen extraction data, the Maiganga coal was distinctly observed to be immature of pre-oil generation window, while the Yaya-Ngari is in early oil generation window. These analysed sediments are mainly gas prone based on the dominance of Type III kerogen, although the presence of Type II/III kerogen supported by relatively higher HI may indicate gas/oil potential for the Maiganga coal. On the other hand, Type IV kerogen dominated the Yaya-Ngari samples. This suggests that these shales are gas prone or do not possess any hydrocarbon generation potential as indicated by the very low HI values.

Organic geochemistry investigations of crude oils from Bayoot oilfield in the Masila Basin, east Yemen and their implication for origin of organic matter and source-related type

Thirteen crude oil samples from fractured basement reservoir rocks in the Bayoot oilfield, Masila Basin were studied to describe oil characteristics and to provide information on the source of organic matter input and the genetic link between oils and their potential source rock in the basin. The bulk geochemical results of whole oil and gasoline hydrocarbons indicate that the Bayoot oils are normal crude oil, with high hydrocarbons of more than 60%. The hydrocarbons are dominated by normal, branched and cyclic alkanes a substantial of the light aromatic compounds, suggesting aliphatic oil-prone kerogen. The high abundant of normal, branched and cyclic alkanes also indicate that the Bayoot oils are not biodegradation oils.The biomarker distributions of isoprenoid, hopane, aromatic and sterane and their cross and triangular plots suggest that the Bayoot oils are grouped into one genetic family and were generated from marine clay-rich source rock that received mixed organic matter and deposited under suboxic conditions. The biomarker distributions of the Bayoot oils are consistent with those of the Late Jurassic Madbi source rock in the basin. Biomarker maturity and oil compositions data also indicate that the Bayoot oils were generated from mature source rock with peak oil-window maturity.

Organofacies and paleoenvironment of lower Carboniferous mudstones (Dishuiquan Formation) in Eastern Junggar, NW China

The sedimentary rocks of the Dishuiquan Formation represent an important potential source for volcanic rock reservoirs and record the transition of the depositional environment from marine to terrestrial during paleo-Junggar oceanic subduction. The source rock potential and paleoenvironment of mudstones from Dishuiquan Formation in Eastern Junggar, were determined by organic petrography, Rock-Eval, molecular and stable carbon (δ13C) analyses. TOC, S2, and hydrogen index (HI) values suggest a fair to good organic richness in mudstone samples from the C-2 well. Moreover, an early mature to mature state for all the samples is inferred based on the Rock-Eval and biomarker parameters. The maceral composition, molecular geochemistry and carbon isotopic results for kerogen reveal that all the mudstone samples are characterized by a mixed organic matter assemblage (Types II–III) with relatively high percentages of terrigenous organic matter. The low to intermediate values of Pr/Ph and the high abundances of β-carotene and gammacerane indicate the presence of a dysoxic, reducing, high-salinity sedimentary environment during the deposition of the Dishuiquan Formation. Numerous parameters derived from the organic geochemical analyses indicate that the terrigenous organic matter increased with decreasing salinity and oxidation in the sedimentary environment. This study concludes that a warm, wet climate provided a continuous fluvial input of terrigenous plant debris and fresh water. The organic geochemical data, combined with the tectonic setting, reveal a restricted, semi-closed marine depositional environment during the deposition of the Dishuiquan Formation in the early Carboniferous.

Dark fermentation effectiveness as a key step for waste biomass refineries: influence of organic matter macromolecular composition and bioavailability

In next generation bio-based refineries, hydrolysis and primary (or extractive) fermentations by undefined microbial cultures (UMC) are precursors of secondary bio-transformations, in which H2, CO2 and mixed carboxylates are used as substrate for achieving added-value target products (e.g. bio-based chemicals, bio-plastics and pigments). Dark fermentation (DF) is the most simple UMC-driven hydrolysis and primary fermentations to extract gaseous and soluble mixtures of compounds from raw biomass. Which solid fractions (types of macro-molecules) of mixed raw organic matter (OM) are efficiently hydrolyzed + fermented during DF is an aspect that was rarely considered in depth. Here, a first attempt was made to propose a new approach for understanding the effects of DF on different fractions of biomass. A set of seven different biomasses underwent optimized DF tests and, for simplicity, only the gaseous main product, i.e. bio-hydrogen potential (BHP) production, was used as parameter to assess DF efficacy. BHP was studied in relation with OM characteristics: on one side, chemical composition (macro-molecular fractions) and, on the other side, bioavailability to UMC attack (using two different biological assays). BHP was found significantly correlated (Pearson's test for p < 0.05, n = 7) only to acid detergent lignin (negatively), soluble sugars and sugars + starch (positively). Bioavailability was negatively correlated with fibrous fractions and to fat-like fractions, but correlations with BHP were poorer (p > 0.05, n = 7). A statistical model (partial least square regression) was proposed for predicting BHP from OM characteristics, with interesting predictability. In the next future, the proposed approach should be widened to better understand the DF effectiveness not only referred to its gaseous products, but especially focusing on the wide range of soluble products (carboxylates), thought as substrates for secondary biorefinery. Copyright © 2015 John Wiley & Sons, Ltd.

Indication origin and type of organic matter and its relation to depositional conditions using molecular composition and geochemical elements: the Jurassic Amran sediments from Samae area in the Taiz Governorate, Southwestern Yemen

This study is the first attempt which provides information regarding the biomarker characteristics and geochemical elements of the Jurassic Amran sediments from Samae area in the Taiz Governorate, Southern Yemen. The geochemical results helped us to investigate the origin and type of organic matter and its relation to environment conditions during deposition of the sediments. The Amran sediments have the highest concentration of terrestrial detritus elements (e.g., SiO2, Al2O3) with relatively high carbonate element (CaO), indicating that these sediments are limestones with argillaceous and clastic contents that are deposited in a shallow marine environment. This is supported by low total sulfur (TS) contents and Sr/Ba ratios and biomarker environment indicators. Their biomarkers provide also evidence for a mixed organic matter by aquatic and terrigenous organic matter contributions. This is confirmed by bimodal distribution of normal alkanes, relation of acyclic isoprenoids to normal alkanes, relatively high tricyclic terpanes compared to tetracyclic terpanes, and high proportion of C27 (36.1–44.4 %) and C29 (33.4–41.1 %) compared to C28 (21.9–23.8 %) regular steranes. Moreover, the suboxic bottom water conditions are evidenced in the Jurassic Amran argillaceous limestone sediments, as identified from V/Ni, and pristane/phytane (Pr/Ph) ratios in the range of 1.53–2.54 and 1.09–1.38, respectively. Therefore, suboxic conditions contribute to organic matter (OM) preservation during deposition of the Amran sediments.

Evidences for a Paleocene marine incursion in southern Amazonia (Madre de Dios Sub-Andean Zone, Peru)

This article presents new biostratigraphic dating, facies analysis, organic geochemical data and Nd–Sr isotopic provenance from five outcrops of southern Amazonia (MD-85, MD-177 MD-184, MD-255 and MD-256) to document for the first time the presence of a shallow marine ingression in the Paleocene of southern Amazonia basin. The co-occurrence of a selachian assemblage encompassing Potobatis sp., Ouledia sp., and Pristidae indet. with the ostracod Protobuntonia sp. and the charophytes Peckichara cf. varians meridionalis, Platychara perlata, and Feistiella cf. gildemeisteri suggests a Paleocene age for the studied deposits (most likely Thanetian but potentially Danian). Fifteen facies have been recognized and have been grouped into three facies assemblages. Facies association A corresponds to the sedimentary filling of a tide-influenced meandering channel formed in the fluvial–tidal transition zone. Facies association B is related to more distal tidal-flats, little channelized tidal inlets and saltmarsh deposits. Facies association C corresponds to a stressed shallow marine environment such as a bay or a lagoon. The δ13CTOC value (−23.4‰) of MD-184 is enriched in 13C compared to the other samples suggesting the presence of substantial amounts of marine organic matter in MD-184. The δ13CTOC values of samples from other outcrops (−27.3 to −29.8‰) indicate a mixed organic matter origin, from terrestrial to brackish environments. The analyzed sediments have similar Nd–Sr isotopic compositions as those of the Cenozoic sediments of the Altiplano (εNd(0) values from −6.2 to −10.7 and 87Sr/86Sr compositions from 0.712024 to 0.719026) indicating a similar volcanic source. This multidisciplinary dataset documents the presence of a tide-dominated estuary sourced by the proto-Western Cordillera debouching into a shallow marine bay during Paleocene times. This transgression might be explained by subsidence created in response to the proto-Western Cordillera loading. Similar to Miocene marine incursions affecting the Pebas megawetland, Paleogene marine incursions in the Amazonian foreland basin associated with Andean uplift may have played a role in the Neotropical biodiversity dynamics in favoring biogeographical isolation and promoting allopatric speciation for terrestrial organisms.

A study on the effect of compaction on transport properties of soil gas and water. II: Soil pore structure indices

Experimental data on the effects of compaction and applied organic matter (OM) on macropore structure indices, more particularly on pore continuity, have yet rarely been documented. In this study, static compaction was simulated in the laboratory at 150, 225, and 300kPa upon rice husk, rice straw, compost, sawdust, and wood bark-mixed soils and control. Measurements of relative gas diffusivity (Dp/D0)100 and air permeability (ka100) were conducted at −100cm H2O soil matric suction after measurement of saturated hydraulic conductivity (ks). Corresponding dry bulk density (ρd), total porosity (f), and air content (ɛ100) values were also determined. Volume of macropores (ϕ≥30μm) and micropores (ϕ<30μm) were expressed as volume of air and water at −100cm H2O soil matric suction, respectively, relative to the volume of soil solid. Specific gas diffusivity (SD100) and specific air permeability (Ska100) were calculated as (Dp/D0)100/ɛ100 and ka100/ɛ100, respectively. Analogous to the SD100 and Ska100, specific hydraulic conductivity (Sks) was defined as ks/ɛ100. The results showed that compaction significantly increased ρd, which was followed by a reduction in f, and the mixed OM resulted in a significantly lower ρd and higher f than the control. The volume of macropores was reduced by compaction whereas the volume of micropores remained unaffected, for which the mixed OM tended to result in a higher volume of macropores than the control. Compaction resulted in more tortuous macropores for gas diffusion (lower SD100) and less continuous macropores for gas convection (lower Ska100) for which a significant difference was more pronounced between the 300 and 150kPa compactions. Compaction also resulted in fewer continuous macropores for water movement as indicated by lower Sks. The mixed OM was likely to result in a lower SD100, but except for rice straw tended to result in a higher Ska100 than the control. In addition, the mixed OM also seemed to result in a higher Sks than the control. Of the OM-mixed soils, the decrease in (Dp/D0)100 and ka100 was more sensitive to compaction (i.e., decrease in ɛ100) than that of the control whereas the decrease in ks acted conversely. Discussion of the measured (Dp/D0)100, ka100, and ks is presented in the companion paper.

Simulation of the impacts of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe(II)-oxidizing biofilm

The microaerobic iron-oxidizing bacteria in circumneutral environment produce extracellular polymeric substances (EPS) with unique morphologic features, such as stalks or sheaths, which can be regarded as geobiological signatures. The Archean and early Palaeoproterozoic oceans were anoxic with high soluble Fe(II) that were suggested to have been oxidized through the metabolism of Fe(II)-oxidizing bacteria. The precursor of the ultrafine hematite in banded iron formation (BIF), e.g., ferrihydrite, was suggested to be the mineral record of microbial Fe(II)-oxidation at that time. However, both the biological materials and primary iron minerals were prone to being altered by diagenetic or low-grade metamorphic processes. This makes it difficult to interpret the genesis of Precambrian BIFs. Here, we report experimental simulation on the effects of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe(II)-oxidizing bacteria and their biomass. Stalks, sheaths, and iron oxide spheroidal aggregates are partially preserved after the 100 MPa/300°C treatments, which indicates the mixed organic matters and iron oxides could survive the diagenetic or low-grade metamorphic processes. Some organic-mineral mixing structures carry information on microbial processes, though they appear similar to pseudomorphs of fossilized bacteria.

Geochemistry and organic petrology study of Kimmeridgian organic-rich shales in the Marib-Shabowah Basin, Yemen: Origin and implication for depositional environments and oil-generation potential

Kimmeridgian organic-rich shales of the Madbi Formation from the Marib-Shabowah Basin in western Yemen were analysed to evaluate the type of organic matter, origin and depositional environments as well as their oil-generation potential. Results of the current study establishes the organic geochemical characteristics of the Kimmeridgian organic-rich shales and identifies the kerogen type based on their organic petrographic characteristics as observed under reflected white light and blue light excitation. Kerogen microscopy shows that the Kimmeridgian organic-rich shales contain a large amount of organic matter, consisting predominantly of yellow fluorescing alginite and amorphous organic matter with marine-microfossils (e.g., dinoflagellate cysts and micro-foraminiferal linings). Terrigenous organic matters (e.g., vitrinite, spores and pollen) are also present in low quantities. The high contributions of marine organic matter with minor terrigenous organic matter are also confirmed by carbon isotopic values. The organic richness of the Kimmeridgian shales is mainly due to good preservation under suboxic to relatively anoxic conditions, as indicated by the percent of numerous pyritized fragments associated with the organic matter. The biomarker parameters obtained from mass spectrometer data on m/z 191 and m/z 217 also indicate that these organic-rich shales contain mixed organic matter that were deposited in a marine environment and preserved under suboxic to relatively anoxic conditions.The Kimmeridgian organic-rich shales thus have high oil and low gas-generation potential due to oil window maturities and the nature of the organic matter, with high content of hydrogen-rich Type II and mixed Type II-III kerogens with minor contributions of Type III kerogen.

Characterization of Physicochemically Abnormal Coals in the Matarere Formation (Cerro Saroche National Park, Venezuela)

Proximate and ultimate analyses, % Rm , vitrinite anisotropy, Rock-Eval T max, and biomarkers have been studied on several coal samples collected at two outcrops in the Cerro Saroche National Park (Venezuela) in order to determine their geochemical characteristics. The results indicate that these coals were deposited in a transitional paleoenvironment under weakly reducing conditions (Palaeogene Matatere Formation), and were derived from mixed organic matter input. Carbon content and other data (%Rm and anisotropy) suggest high levels of maturity (matagenesis to metamorphism) of these coals. However, this does not correspond to the low-volatile bituminous stage (late catagenesis) according to the ASTM classification by rank. These coals might have reached overmaturity as a result of heating by Neogene igneous events.

A multiproxy study between the Río de la Plata and the adjacent South-western Atlantic inner shelf to assess the sediment footprint of river vs. marineinfluence

Proxies of terrigenous versus marine input (Al and Ti, Fe/Ca and Ti/Ca ratios), origin of organic matter (δ13C, δ15N and C/N ratio), productivity (Corg; Nt; CaCO3, P, Ca, and Ba content; and Ba/Al and Ba/Ti ratios), hydrodynamics (grain size, mean diameter and sorting) and biological records of the main features of the environment (benthic foraminifera assemblage distribution) were used to assess the sediment footprint of river vs. marine influence along the salinity gradient between the Rio de la Plata (RdlP) estuary and the adjacent South Western Atlantic Shelf. These criteria permitted characterisation and interpretation of the sedimentary processes influencing transition between three known environments: tidal river, estuarine and marine zones. Increases in sand and clay content at the transition between tidal river and proper estuarine zones indicate resuspension/deposition processes associated with the maximum turbidity zone (MTZ). The MTZ was also characterised by an increase in mixed organic matter content indicated by stable carbon and nitrogen isotope values, an increment in productivity proxies (Corg, Nt and CaCO3) and the substitution of the Miliammina fusca assemblage (brackish environments) for the Ammonia tepida assemblage (estuarine environments). The transition between estuarine and marine environments was characterised by a sharp (up to 99%) increase in sand content, reflecting the progradation of modern RdlP sediments toward relict continental shelf sediment. C/N values typical of the marine environment, decreased trace element concentrations and the distribution of the Buliminella elegantissima assemblage (a more marine assemblage) also highlight the marine environment. This paper is particularly important as a tool both to better understand sedimentological dynamics in salinity fronts (along the shelf sediment of large estuaries) and to elaborate more precise palaeoenvironmental and palaeoceanographic reconstructions.