High Corg Content Research Articles

Geochemical characterization of surface sediments from the Ridracoli reservoir area and surroundings, Italy. Details on bulk composition and grain size

Sediment characterization of Ridracoli reservoir, an artificial lake for water supply, and surroundings of the Fiumi Uniti catchment in the northern Apennines, Emilia-Romagna, Italy, is carried out to evaluate the overall status of the drainage basin encompassing the reservoir. The study area combines the reservoir catchment that is part of the Foreste Casentinesi-Monte Falterona-Campigna National Park, formed by the construction of a dam operating since 1982 for drinking water storage and electricity production, and the upstream side of Fiumi Uniti catchment that flows into the Adriatic Sea, including also nearby sub-catchments of Ridracoli reservoir, named Corniolo and Pietrapazza.We collected surface sediments within the area of the reservoir and riverbed sediments of surroundings catchments, analyzed grain size distribution and the chemical composition, including carbon and nitrogen. This work investigates the chemistry and distribution of elements within the study area, evaluates the dam's effect upstream and downstream, and studies the processes that happen in rivers and the reservoir. The bulk composition is mainly represented by SiO2, Al2O3, CaO, with high Corg content reflecting the Marnoso Arenacea Formation geology of the area. Statistical data analysis on the available parameters suggests the presence of two main types of sediment, namely clayey and carbonate-dominated sediments. On the reservoir area, the relationship between elements and clay matrix and organic matter, besides iron, points to a potential grain size influence, degradation of organic matter, and mineralization processes. The grain size analysis shows that silty and clayey sediments are in the bottom of the reservoir, and sand, is apparent in sediment samples from the tributaries, due to sorting effects and likely directly explained by metals concentrations. This reasoned investigation included further samples from the literature to consider the entire surrounding area and was supported by Principal Component Analysis and Cluster Analysis.

Field calibrations of a Diviner 2000 capacitive soil water content probe on a shallow groundwater site and the application in a weighable groundwater lysimeter

The determination of the volumetric soil water content θv by means of capacitive profile probes is often applied to investigate the soil water storage change ΔS that serves as basis for decisions in agricultural water management. The soil properties have a big effect on the accuracy of the θv measurements. The use of only one calibration function, often provided by the manufacturers of the probes, cannot fulfil the requirements of all site conditions. Therefore, many individual calibration functions have in the past been determined for different soils and sensors. A literature review of existing calibration functions of the capacitive profile probe Diviner 2000 shows the broad range of available functions. The review makes it clear that there is a lack of functions for organic soils. These soils are typical soils of wet sites with shallow groundwater tables. The soil moisture is of big importance for many ecological processes of these sites and therefore an exact determination of θv is important. A Diviner 2000 profile probe was calibrated on such a shallow groundwater site in a classic field calibration procedure and the determined functions were applied to the soil profile of a weighable groundwater lysimeter. The soil water storage change ΔS was estimated with the measured θv values and compared with the measured mass change Δm of the lysimeter. The mean error (bias) between ΔS with the field calibration function and Δm was 7.8 kg and the root mean squared error (RMSE) 19.9 kg. An iterative adaptation of the calibration functions to the measured Δm values of the lysimeter reduced the bias to 0.9 kg and the RMSE to 14.0 kg. The investigations illustrate the problems of a classic field calibration under the conditions of a shallow groundwater site with low θv changes in deeper soil horizons and soils with high Corg contents as well as the inaccuracy in the determination of ΔS based on θv measurements with capacitive profile probes.

Nomadic Transformation of Mountain-Meadow Brown Soils (Dystric Cambisols) of the Svydovets Array of the Ukrainian Carpathians

In the highlands of the Ukrainian Carpathians, brown soil formation process is supplemented by turf, which significantly affects the soil properties and composition formation – this way unique shallow, rubble, highly acidic, base unsaturated, mountain-meadow brown soils with high Corg content (Dystric Cambisols) are formed. Irrational and haphazard farming in the valleys leads to the soil degradation and formation of specific anthropogenically altered mountain-meadow brown soil. To study the features of mountain-meadow brown soil formation and to analyze changes in properties, as a result of economic activity, we conducted detailed soil-geographic research within the valleys of the Svydovets array. Research has established that anthropogenically altered mountain-meadow brown soils are characterized by lower Corg rates, higher acidic reaction of the soil solution, high hydrolytic acidity and the dominance of exchange calcium in the absorbing soil complex, different qualitative humus composition – humate-fulvate. As a result of anthropogenic soil transformation, composition indicators underwent distinct changes – soil of the genetic horizons with a decrease in the total porosity; structure of the humus-accumulative horizon of virgin soil has undergone transformation and is characterized as prismoidal.

Manganese and iron reduction dominate organic carbon oxidation in surface sediments of the deep Ulleung Basin, East Sea

Abstract. Rates and pathways of benthic organic carbon (Corg) oxidation were investigated in surface sediments of the Ulleung Basin (UB) characterized by high Corg contents ( > 2.5 %, dry wt.) and very high contents of Mn oxides ( > 200 µmol cm−3) and Fe oxides (up to 100 µmol cm−3). The combination of geochemical analyses and independently executed metabolic rate measurements revealed that Mn and Fe reduction were the dominant Corg oxidation pathways in the center of the UB, comprising 45 and 20 % of total Corg oxidation, respectively. By contrast, sulfate reduction was the dominant Corg oxidation pathway, accounting for 50 % of total Corg mineralization in sediments of the continental slope. The relative significance of each Corg oxidation pathway matched the depth distribution of the respective electron acceptors. The relative importance of Mn reduction for Corg oxidation displays saturation kinetics with respect to Mn oxide content with a low half-saturation value of 8.6 µmol cm−3, which further implies that Mn reduction can be a dominant Corg oxidation process even in sediments with lower MnO2 content as known from several other locations. This is the first report of a high contribution of manganese reduction to Corg oxidation in offshore sediments on the Asian margin. The high manganese oxide content in the surface sediment in the central UB was maintained by an extreme degree of recycling, with each Mn atom on average being reoxidized ∼ 3800 times before permanent burial. This is the highest degree of recycling so far reported for Mn-rich sediments, and it appears linked to the high benthic mineralization rates resulting from the high Corg content that indicate the UB as a biogeochemical hotspot for turnover of organic matter and nutrient regeneration.

Geochemical and micropaleontological character of Deep-Sea sediments from the Northwestern Pacific near the Kuril–Kamchatka Trench

Sediments from the abyssal plain adjacent to the Kuril–Kamchatka Trench were collected during the German–Russian cruise for the Kuril Kamchatka Biodiversity Study, and the chemical composition, quantitative content, and species composition of collected diatoms were studied. The collected sediments are silt and clayey silt, the SiO2am and Corg contents range 7.58–19.38% and 0.44–1.55%, respectively. The enrichment of silts by amorphous silica indicates the presence of a significant number of organisms (predominantly diatoms) with an opal skeleton. High Corg content in sediments reflects biological productivity, which is controlled by factors such as water circulation and the distribution of nutrients. Interrelation trends among chemical constituents is investigated via multi-component statistics. Diatom assemblages reflect present-day water masses characterized by high nutrient content, surface water circulation, and sedimentation conditions for different parts of the study area. Analysis of this new data also highlights changes in the response of diatom flora due to abiotic factors.

Oil source rocks at mesozoic and cenozoic continental margins: Communication 2. Oil source rocks at continental margins in the second half of the cretaceous and in the Cenozoic

Oil source rocks represent sequences with the Corg content ranging from 3–5 to 15–20%. Sedimentary sections of large petroliferous basins usually include one or two such sequences, which generated liquid and gaseous hydrocarbons (HCs) during their long-term subsidence to the elevated temperature zone. The middle episode of the Late Cretaceous was marked by the accumulation of sediments with a high Corg content in different areas of the World Ocean. However, truly unique settings favorable for accumulation of the sapropelic organic matter (OM) appeared at continental margins that primarily faced the Tethys Ocean. The La Luna Formation is one of the best known source rock sequences responsible for the generation of liquid HCs in basins of the Caribbean region. In the Persian Gulf, the Kazhdumi Formation composed of marls and clayey limestones is considered the main oil-generating sequence. In the Paleogene after closure of the Tethys, the Pacific continental margins became the main domains that accumulated source rocks. The maximal deposition of sapropelic OM in this region corresponded to the early-middle Eocene. In the Neogene, the accumulation of source sediments was associated with deltas and submarine fans of large rivers and with upwelling zones. In basins of the Californian borderland, the main oil-generating sequences are represented by siliceous rocks of the Monterey Formation. They were deposited in a regional upwelling zone related to the cold California Current.

Petrological and geochemical investigations of potential source rocks of the central Congo Basin, Democratic Republic of Congo

Paleozoic and Mesozoic outcrop and core samples (REMINA Dekese and REMINA Samba wells) covering various stratigraphic intervals from the central Congo Basin were analyzed for total organic carbon (Corg), total inorganic carbon (Cinorg), and total sulfur content. Rock-Eval analysis and vitrinite reflectance (Ro) measurements were performed on the basis of the Corg content. Fifteen samples were chosen for molecular organic geochemistry. Nonaromatic hydrocarbons (HCs) were analyzed by gas chromatography (GC)–flame ionization detection and GC–mass spectrometry. Samples of the Alolo shales from the Aruwimi Group (Lindi Supergroup, late Neoproterozoic to early Paleozoic) are in general very poor in Corg (most samples 0.5%) and contain a high amount of degraded organic matter (OM). All samples of this group revealed a type III to IV kerogen and cannot be considered as a potential source rock. Permian–Carboniferous sediments from the Lukuga Group (Dekese well and outcrop samples) contain moderate contents of organic carbon (2%). The Tmax values (heating temperature at which the top peak of S2 occurs) indicate early mature OM, partly also a higher level of maturity because of Ro (0.6–0.7%) and production index values (S1/S1 + S2 0.2). All samples contain hydrogen-poor type III to IV kerogen with low HC generation potential, only having a very minor gas generation potential. The kinds of OM, as well as the biological markers, indicate a terrestrial-dominated depositional environment. Organic geochemical investigations on Upper Jurassic (Stanleyville Group) to Lower Cretaceous (Loia Group) samples from the Samba well and outcrops in the northeastern part of the Congo Basin reveal moderate to high contents of organic carbon (as much as 25%). The kerogen has very high hydrogen index (HI) values reflecting type I kerogen of excellent quality in the Stanleyville Group (as much as 900 mg HC/g Corg) and type I to II kerogen in the overlying Loia Group (as much as 900 mg HC/g Corg). Outcrop samples from the Stanleyville Group have variable partly high Corg contents and are also characterized by very high HI values (as much as 900 mg HC/g Corg). The samples studied are too immature for petroleum generation. Based on biomarker analysis, an aquatic anoxic depositional environment can be assumed for the Stanleyville Group, whereas a lacustrine deposition is likely for the samples of the Loia Group. Based on the geologic knowledge of the area, deposition under lacustrine conditions is most likely also for the Stanleyville Group. Both the Stanleyville and Loia groups can be regarded as excellent petroleum source rocks and could be part of a petroleum system if sufficient burial and maturation have occurred. The presence of resedimented vitrinite particles in the Lukuga Group of the Dekese well with a slightly higher maturation rank than the autochthonous vitrinites suggests that 3000–4000 m (9840–13,120 ft) of Carboniferous to Devonian sediment has been eroded from the eastern margin of the Congo Basin. Finally, Ro data were used to create one-dimensional models for the Dekese and Samba wells, giving an overview of the burial, thermal, and maturity histories of the area.

Oxygen minimum seafloor ecological (mal) functioning

Although organic matter (OM) settling on the seafloor is generally rapidly recycled, a key ecological process, large scale burial events manifest itself in the marine sedimentary record as organic carbon (Corg)-rich layers. Presently, this prevails under certain oceanic settings such as the oxygen minimum zones (OMZ) where OM accumulates in underlying sediments. A basic question that remains is as to what extent this Corg accumulation reflects ecological “malfunctioning” or a shunting of ecological processes? Experimenting with eastern Arabian Sea OMZ sediment we found no evidence that Corg accumulation here is not due to trophic satiation or to low tolerance of biota to severe oxygen depletion. However, we found direct evidence that suggests that the OMZ sediment Corg has very low bioavailability that probably impairs biological transformation.In the first set of experiments, the impact of oxygenation on the benthic ecological functioning was examined by following the fate of fresh, highly degradable OM (13C-labelled diatoms) in intact sediment cores incubated for 7days under normoxic versus suboxic bottom water conditions. Tracer organic matter assimilation (by bacteria and fauna) and respiration was evident and similar under both treatments and demonstrates that the benthic response was not hindered by severe oxygen depletion. Furthermore, relatively low biomass standing stock of fauna and bacteria, in spite of sediment high Corg content, together with this clear uptake of fresh tracer OM suggest that the benthic community was not food saturated.In a second set of experiments, the bioavailability of in situ OMZ organic matter was determined directly through CO2 production rate measurements in bottle sediment–water slurry incubations. In sharp contrast to fresh tracer algal carbon which had a half-life 0.07years, the OMZ surficial sediment OM half-life was ~67years already in very early diagenesis. Clearly, a distinct difference in functioning and indicates that a large fraction of OMZ sediment organic matter is evidently excluded from immediate first-hand biotic transformation but on its own represents a link between the “fast (biological)” and the “slow (geological)” carbon cycle along the continuum of OM recycling. Furthermore, while this rapid shift out of the “fast” biological cycle may be common or characteristic of large scale OM accumulation events, a comparison with an ancient Corg-deposit suggest that the trigger mechanisms may not be uniform.

Distribution of meiobenthos in the Nazaré canyon and adjacent slope (western Iberian Margin) in relation to sedimentary composition

Abundance of metazoan meiofauna and foraminifera, and biomass and community structure of nematodes, were investigated in the benthic zone along the Nazare Canyon and adjacent continental slope in relation to concentration of organic matter and its suitability as a food source for the meiobenthos. The Nazare canyon sediments were richer in organic carbon (Corg), total nitrogen, and phytopigments than the adjacent open slope. In addition, phytodetritus was fresher in the canyon sediment than on the slope (higher chlorophyll a: phaeopigments). Nevertheless, the abundance of polychaetes, copepods, bivalves, nematodes, total metazoans, and nematode biomass were not always higher in the canyon than on the adjacent open slope. Lower densities occurred in the upper and middle canyon, and living benthic foraminifers were significantly more abundant on the adjacent slope. The stations in the upper and middle canyon contained infinitesimal numbers of foraminifers. Reduced diversity and evenness and high K-dominance of the nematode assemblages in the upper part of the canyon indicated environmental stress, perhaps related to high Corg content and sedi- ment disturbance. Non-selective deposit-feeders dominated the nematode assemblages of the upper and middle parts of the canyon, whereas a more diverse trophic structure was found in the deeper parts and the open slope. Conditions in the upper and middle areas of the Nazare canyon are harsh, and only opportunistic organisms can survive there.

A geochemical application of the ITRAX scanner to a sediment core containing eastern Mediterranean sapropel units

Abstract The ITRAX micro-X-ray fluoresence (XRF) core scanner has been applied in a sediment geochemistry investigation. The core sections selected contain examples of the organic-rich sedimentary units (sapropels) that form periodically in the eastern Mediterranean basin. Sapropels are visually obvious from their dark coloration, but the ITRAX X-radiograph also reveals physical property changes that result mainly from the high pore-water content of sapropels. A consideration of wavelength-dispersive XRF data from discrete samples of the most recent sapropel (S1) was made along with the set of elements reported by the ITRAX instrument’s energy-dispersive XRF system over core sections containing S1. This allowed selection of a suite of eight inter-element ratios or element integrals through which characteristic features of sapropel development and geochemistry were revealed. While recognizing that the measured XRF element integrals from the ITRAX do not have an exact constant relationship with element concentration over changing sediment types, this combination of ratios provides significant information for geochemical interpretation. These include evidence for: (i) the presence of high C org contents in the visual sapropel from Ba/Ti and Br/Cl ratios; (ii) a thinning of the original sapropel thickness by post-depositional oxidation from Mn/Ti and Cu/Ti ratios; (iii) pyrite authigenesis in the residual visual sapropel from Fe/Ti and S/Cl ratios and the As integral; and (iv) aragonite formation in and around the sapropel from the Sr/Ca ratio. These same ratios were then used to interpret ITRAX data from a deeper section of the same core containing the older sapropel S3, where the same characteristics, including the relict post-depositional oxidative thinning of the original unit, could be identified with only minor differences of detail. Directions of supply of Fe, As and Cu into the sapropels could be inferred from profile shapes.

Is Glassiness a Common Characteristic of Soil Organic Matter?

Until now, glass transitions were detected in isolated humic and fulvic acids as well as in distinct soil samples with usually high Corg contents. The results of this study indicate that glassiness has to be considered a common characteristic of soil organic matter (SOM). However, two types of glassiness were observed in various soil types. Additionally to a typical glass transition with low intensity, a slowly reversing glasstransition-like step transition with significantly higher intensity was detected in 52 out of 102 tested soil samples. The intensity of this transition type is correlated to the organic matter content of the samples. The transition behavior additionally depends on characteristics of the locations and changes within soil profiles. Relations to particulate organic matter (POM), mineral-associated organic matter (MOM), and the thermostable fraction of the soil samples were not significant. A surprising result of the study is that the step transition temperatures of all analyzed air-dried soil samples range between 51 and 67 degrees C in closed systems, pointing to a superordinate mechanism which controls the matrix rigidity of the organic molecules. This may be represented by the formation of hydrogen bond based cross-links between water molecules and SOM suggested in a previous study. Thus, glassiness in SOM may be caused by physical and physicochemical mechanisms.

Distribution of selected elements and PAH in freshly deposited sediments of waste water streams from Lubin district, Southwest Poland

Nine selected elements (Cu, Pb, As, Zn, Co, Ni, Cr, Cd and Fe) were determined by inductively coupled plasma atomic emission spectroscopy in 15 samples from the tailings pond (Zelazny Most) and waste water streams (Moskorzynke and Rudna) in the Kupferschiefer mining district in Southwest Poland. Waste water from mining and industry enter the Zelazny Most pond. The water then flows through Moskorzynke and Rudna streams, and discharges into the River Odra. The analytic results indicate that the contamination with Cu, Pb, Zn, As, Co, Cd and Fe extend about 6 km along the streams in contrast to the non‐polluted samples close the River Odra. Their concentrations reach a level, which could be toxic for plants, animals and humans. The contamination with Ni and Cr continued at least 20 km along Rudna stream. Besides mechanical transport, redox conditions and Corg contents also played an important role for trace element and Fe contamination in Rudna stream. The samples with high Corg contents have also high contents of trace metals. In Moskorzynke stream the element contamination was mainly caused by mechanical transport of particles. Polyaromatic hydrocarbon (PAH), which is abundant in Kupferschiefer, is toxic for animals and humans. The PAH concentration in the stream sediments was determined by GC and GC/MS. The results indicate that the contamination of PAH reaches 6 and 17 mg kg−1 in samples TP1 and RS6, respectively. In the other samples, the PAH contents are lower than 3 mg kg−1. Some PAH could be solved by waste water in the tailings pond and migrated to the stream sediments. Some PAH might be contained in particles which were transported mechanically from the tailings pond into stream sediments.

Integrated Geochemical and Paleoecological Approach to Petroleum Source Rock Evaluation, Cretaceous Niobrara Formation, Lyons, Colorado: ABSTRACT

Studies of the upper Turonian to upper Coniacian or lower part of Niobrara Formation (in ascending order, the Fort Hays Limestone Member and the marlstone, shale, and limestone of the lower part of the Smoky Hill Shale Member) reveal a significant relationship between petroleum source rock potential and paleoclimate. Trends in bioturbation, ^dgrO18 (oxygen isotopic ratio), and Corg (organic carbon content) during lower Niobrara deposition suggest that paleoclimatic factors limited bioturbation of the sediment, favored high Corg contents, and resulted in excellent source rock potential in the shale unit of the lower Smoky Hill Member. From the Fort Hays through the overlying marlstone unit, ^dgrO18 in inoceramid shells shows a gr dual shift from nearly normal marine values (-2 to -4%) to lighter values (-4 to -6%); over the same interval, Corg changes from relatively low values (0.1-1.4%) to moderate values (0.5-2.5%). Bioturbation throughout these units is high. A marked shift toward heavier ^dgrO18 (-6.0 to -9.1%) occurs upward into the shale unit and coincides with increase in Corg (2.3-4.9%) and an absence of bioturbation. In the limestone unit, ^dgrO18 shifts to less negative values (-6.2 to -6.5%), Corg decreases (average 1.5%), and bioturbation returns. The trend toward more negative ^dgrO18 and higher Corg values in the shale unit is inferred to reflect a lowering of surface-water salinity in the Western Interior seaway due to cl matic warming and increased freshwater imput. Resultant salinity stratification of the water column apparently inhibited vertical mixing and oxgenation of the bottom waters, resulting in limited benthic activity and enhanced preservation of organic matter. End_of_Article - Last_Page 842------------