Total Organic Carbon Profiles Research Articles

Diagenetic processes and nutrients diffusive fluxes at the sediment-water interface in the Bizerte Lagoon (North Tunisia)

Diagenetic reactions occurring in the sediments of Bizerte Lagoon along with their seasonal variation were assessed through examining the concentration profiles of nutrients and dissolved Fe and Mn in the supernatant water and pore waters, as well as the profiles of total organic carbon, carbonates, Fe and Mn contents in the particulate phase. The results indicate that these diagenetic reactions followed the classical sequence of oxidant reduction following the degradation of organic matter with a successive reduction of NO3−, MnO2, Fe (OH)3 and SO42−. In particular, a delay was observed in the winter sequence which occurred at greater depth due to higher Eh in surface layer. Generally, NO3−, NH4+ and PO43− seem to originate from sediments as reflected by their measured flux from sediments to the water column while the reverse was quoted for SO42− as reported from other Mediterranean environments. In addition, oxygenation of the water column reduces the diffusive fluxes of (NO3−, NH4+, PO43−) released into the pore water during mineralization of organic matter.

Total organic carbon (TOC) quantification using artificial neural networks: Improved prediction by leveraging XRF data

This study develops a new artificial neural network (ANN) model for predicting the total organic carbon (TOC) of an organic-rich carbonate mudstone formation using conventional well log data and X-ray fluorescence spectroscopy (XRF) analysis. The data used in the study include conventional well logs, redox-sensitive elements from XRF, and TOC values measured in lab for a total of 150 core samples obtained from five wells. Selected well logs including gamma ray (GR), bulk density (RHOB), uranium (URAN), and XRF-derived elements, including molybdenum (Mo), copper (Cu), and nickel (Ni), were used to train and develop the ANN model to predict and generate continuous high-resolution TOC log profiles for the five wells. TOC data were classified into two groups based on geological descriptions and well locations. Statistical analyses were performed to establish the range of data used for each group and to evaluate relationships among the TOC and input parameters. The developed ANN model showed a high performance in providing a continuous profile of TOC. The difference between absolute average is less than 0.50 and the correlation coefficient (R-value) is greater than 0.70. Empirical correlations were extracted from the best performing ANN model, which will allow easy and quick estimation for TOC values. The developed correlations outperform available methods for determining TOC and reduce the estimation error by 42 %.

Ensemble Learning for Predicting TOC from Well-Logs of the Unconventional Goldwyer Shale

Precise estimation of total organic carbon (TOC) is extremely important for the successful characterization of an unconventional shale reservoir. Indirect traditional continuous TOC prediction methods from well-logs fail to provide accurate TOC in complex and heterogeneous shale reservoirs. A workflow is proposed to predict a continuous TOC profile from well-logs through various ensemble learning regression models in the Goldwyer shale formation of the Canning Basin, WA. A total of 283 TOC data points from ten wells is available from the Rock-Eval analysis of the core specimen where each sample point contains three to five petrophysical logs. The core TOC varies largely, ranging from 0.16 wt % to 4.47 wt % with an average of 1.20 wt %. In addition to the conventional MLR method, four supervised machine learning methods, i.e., ANN, RF, SVM, and GB are trained, validated, and tested for continuous TOC prediction using the ensemble learning approach. To ensure robust TOC prediction, an aggregated model predictor is designed by combining the four ensemble-based models. The model achieved estimation accuracy with R2 value of 87%. Careful data preparation and feature selection, reconstruction of corrupted or missing logs, and the ensemble learning implementation and optimization have improved TOC prediction accuracy significantly compared to a single model approach.

High-resolution climatic (monsoonal) variability reconstructed from a continuous ~2700-year sediment record from Northwest Himalaya (Ladakh)

A chronologically well-constrained sedimentary archive from Upshi (Ladakh) was studied using a multi-proxy approach namely palynology, environmental magnetism, total organic carbon (TOC), total nitrogen (TN), stable isotopes of carbon and nitrogen providing a continuous vegetation, and paleoenvironmental history spanning the last ~2700 years with a temporal resolution of ~43 years. Pollen assemblage shows non-arboreal pollen (NAP) and non-pollen palynomorph (NPP) were dominant around the Upshi from ~2646 to 2431 cal. yr BP, indicating warmer conditions. Arboreal pollen (AP) and NAP gradually increased from 2431 to 1860 cal. yr BP in the study area, under warm and wet conditions, corresponding to the Roman Warm Period (RWP). This phase also witnessed enhanced sediment δ15N and χlf values. From ~1860 to ~1154 cal. yr BP increased Chenopodiaceae/Amaranthaceae and substantial spread of NPP suggest decreased temperature and prevalence of cold-dry climate. This period also records declining trends of χlf, δ15N, δ13Corg, TOC, and TN contents. From ~1154 to 293 cal. yr BP, the vegetation type reversed to mixed conifer and broad-leaved forest with significant increase in herbaceous taxa, rising δ15N, δ13Corg, TOC, and TN suggesting warm and wet conditions in the study area. This period broadly corresponds to the ‘Medieval Warm Period’ (MWP). Among all the proxies employed, depth profiles of TOC and TN (wt%) appear to respond best against external climate forcing showing remarkable correlation(s) with residual Δ14C in atmosphere, indicating dominance of intrinsic solar variability on regional climate/environment. The reconstructed recorded is well connected with established historical events and cultural activities of the Eurasian region.

Synchronous response of sedimentary organic carbon accumulation on the inner shelf of the East China Sea to the water impoundment of Three Gorges and Gezhouba Dams

Coastal seas, located between continents and the open ocean, are an important active carbon pool. The sedimentary total organic carbon (TOC) in these areas is a mixture of terrestrial and marine sources, and can be a powerful proxy for tracing natural processes and human activities. In this study, one fine-grained sediment core (DH5-1) from the inner shelf of the East China Sea was systematically analyzed for TOC and black carbon (BC) contents and TOC stable carbon isotope ratios (δ13C). By combining these data with 210Pb dating, an improved carbon correction model and a two end-member mixing model, we reconstructed century-scale high-resolution sequences of corrected TOC, terrestrial TOC and marine TOC contents and identified two carbon depletion events in the DH5-1 record. The two events, shown as two minima in the TOC profiles, correspond temporally to 1985-1987 AD and 2003-2006 AD, which exactly matches the water impoundment of the Gezhouba Dam and Three Gorges Dam, respectively. In addition, the variations in TOC contents and δ13C values before, during or after the minima demonstrate a relationship between the depletion events and water impoundment of the dams on the Changjiang River. The TOC reductions may represent synchronous responses of sedimentary TOC and resultant ecological effects on the inner shelf of the East China Sea to the water impoundment of the dams. These new TOC records reflect the interaction between natural and anthropogenic processes and, accordingly, provide a deep insight and important references for assessing marine ecological effects resulting from water impoundment of largescale dams.

Effects of intensification of the Indian Summer Monsoon on northern Andaman Sea sediments during the past 700 years

Recent studies have revealed an intensification of the Indian Summer Monsoon (ISM) over the past 700 years, but its influence on the sediments in the northern Andaman Sea is unclear. To examine this influence, we used radiocarbon-dated sediment core StMY6, acquired 100 km offshore in the northern Andaman Sea from the Ayeyarwady River mouth, and obtained a 700-year-long record of the grain-size distribution and geochemistry of the sedimentary sequence. The ISM influences precipitation surrounding the Ayeyarwady River, and thus the river water and sediment discharges to the northern Andaman Sea near the river mouth in the Ayeyarwady River and the weathering intensity in the river catchment. Based on the system, we propose that higher sedimentation rates and larger modal grain size (the most abundant size in the grain-size distribution of sediments) and lower carbonate concentrations after about AD 1600 can be attributed to higher ISM intensity. Profiles of total organic carbon (TOC) content and carbon/nitrogen (C/N) ratios, however, did not show any trends after about AD 1600, which suggests that the ISM has had little influence on these proxies at this site.

A logging calculation method for shale adsorbed gas content and its application

A large part of shale gas occurs in organic matter and clay mineral surfaces in an adsorption state (20–85%). In a shale reservoir, the pore surfaces of organic matter and clay minerals are the main locations for shale gas adsorption. However, calculating the adsorption gas content is a difficult problem in logging. In order to build a calculation model for adsorption gas, a series of experiments was conducted to understand the relationship between adsorption gas content, mineral type, and content in the Zhaotong Longmaxi formation. These experiments show that organic matter has the most specific surface area and is the most important adsorption matter in the reservoir, especially under low pressure. Clay minerals become more important as the pressure increases. The KIM formula, which is widely used in coalbed methane, was introduced in this work. At a certain temperature and pressure in a reservoir, the gas adsorption specific surface can be simplified as a function of total organic carbon and clay mineral content. The calculated results from the Zhaotong A well are in good agreement with the experiments. The well logging information is used to further calculate the clay minerals of the Zhaotong A well profile, the total organic carbon profile, and the adsorption volume profile. The adsorption gas and total gas of the Zhaotong A well Longmaxi group in a lower place had similar reductions, which is consistent with the field desorption experiment.

Influence of the natural organic matter in the removal of caffeine from water by fixed-bed column adsorption

The removal of caffeine from tap water by F-400 granular activated carbon in fixed-bed adsorption experiments was carried out. Textural and chemical characterization of the adsorbent through N2 adsorption–desorption isotherms, Fourier transform infrared spectrometry, isoelectric point determination and scanning electron microscopy studies was developed in studies previously reported. Caffeine breakthrough curves and total organic carbon profiles at different operation conditions (inlet concentration, volumetric flow rate and mass of adsorbent) were obtained. These experimental results showed a displacement of the natural organic matter from the active sites exerted by caffeine molecules due to their higher affinity to the surface carbon. This behavior led to an overshooting, a local outlet natural organic matter concentration higher than the feed quantity. A competitive effect seems to be observed in the removal of the target compound, decreasing the efficiency of the process. Axial dispersion coefficients and dimensionless numbers were estimated for the caffeine removal onto F-400 activated carbon. Therefore, the regeneration of the adsorbent by adsorption–desorption cycles was studied.

Total and permanganate-oxidizable organic carbon in the corn rooting zone of US Coastal Plain soils as affected by forage radish cover crops and N fertilizer

Forage radish (Raphanus sativus L. var. longipinnatus) is a relatively new winter cover crop becoming widely grown in humid temperate North America. Little is known about how the use of this fall/winter cover crop may influence carbon sequestration and distribution in the soil profile in corn silage production system. The objectives of this study were to determine quantities and distribution in the soil profile of total organic carbon (TOC) and permanganate oxidizable carbon (POXC) as affected by forage radish cover crops and to examine the relationship between TOC and POXC in the profile. While there was no significant difference in TOC between radish (RAD) and no cover crop (NC) treatments for each depth interval at each site, the TOC in RAD (10.3gC/kg) was higher compared with NC (9.3gC/kg) in surface soil depth (0–30cm) when analyzed across all site years. Forage radish impacts on POXC were observed not only for surface horizons (0–15cm), but also for deep horizons (90–105cm). Banded nitrogen fertilizer affected the soil C:N ratio deep in the soil profile at both sites (at 90–105cm in RAD and at 60–75cm in NC). Where N fertilizer was applied, soil POXC in 0–30cm was significantly greater following radish (535.7mg POXC/kg) than following no cover crop (418.2mg POXC/kg). Additionally, strong positive linear relationships between POXC and TOC were observed (P<0.05), with a much steeper regression slope (higher POXC/TOC ratio) in the 60–105cm layer (POXC/TOC ratio=0.22) was much steeper than for the surface soil (0–30cm) with POXC/TOC ratio=0.05. We speculate that the higher POXC levels may have resulted from increased rooting and exudation by both corn and radish where nitrogen fertilizer was placed. Using forage radish cover crops show potential for mitigating against soil C depletion.

Carbon Sequestration and Sedimentation in Mangrove Swamps Influenced by Hydrogeomorphic Conditions and Urbanization in Southwest Florida

This study compares carbon sequestration rates along two independent tidal mangrove creeks near Naples Bay in Southwest Florida, USA. One tidal creek is hydrologically disturbed due to upstream land use changes; the other is an undisturbed reference creek. Soil cores were collected in basin, fringe, and riverine hydrogeomorphic settings along each of the two tidal creeks and analyzed for bulk density, total organic carbon profiles, and sediment accretion. Radionuclides 137Cs and 210Pb were used to estimate recent sediment accretion and carbon sequestration rates. Carbon sequestration rates (mean ± standard error) for seven sites in the two tidal creeks on the Naples Bay (98 ± 12 g-C m−2·year−1 (n = 18)) are lower than published global means for mangrove wetlands, but consistent with other estimates from the same region. Mean carbon sequestration rates in the reference riverine setting were highest (162 ± 5 g-C m−2·year−1), followed by rates in the reference fringe and disturbed riverine settings (127 ± 6 and 125 ± 5 g-C m−2·year−1, respectively). The disturbed fringe sequestered 73 ± 10 g-C m−2·year−1, while rates within the basin settings were 50 ± 4 g-C m−2·year−1 and 47 ± 4 g-C m−2·year−1 for the reference and disturbed creeks, respectively. These data support our hypothesis that mangroves along a hydrologically disturbed tidal creek sequestered less carbon than did mangroves along an adjacent undisturbed reference creek.

Environmental change in Yellow Sea during the last deglaciation to the early Holocene (15,000–8,000 BP)

This study is the first reconstruction of the paleoenvironment and paleovegetation during the Holocene (interglacial) and last deglaciation periods of the Yellow Sea. Carbon isotope and biomarker (n-alkane and alkenone) compositions of organic carbon matter (OM) from core 11 YS PCL14 collected from the central Yellow Sea recorded past changes in East Asian Monsoon (EAM) climates. The result shows the variability of the EAM affected the sedimentary profile of total organic carbon (TOC), the stable isotopes of bulk organic carbon (δ13Corg), the atomic ratio of carbon and nitrogen (C/N ratio), and biomarker content. The oscillations of TOC along the sediment core might be associated with the paleoceanographic conditions (changes in the sea level) related to the contribution of the autochthonous and allochthonous OM input. Two climatic conditions were distinguished (warm/humid and cold/dry) based on the n-alkane proxy, and the observed changes in δ13C of individual n-alkane (δ13CALK) between the Holocene and last deglaciation were attributed to changes in plant distribution/type. A shift in vegetation type between climatic periods occurred as a result of different photosynthetic response to CO2 and temperature among C3 and C4 plants. The most interesting new finding of this work is the fact that alkenone derived temperature changed independently with global climate change, which might be related to the influence of the Kuroshio current in the Yellow Sea. The variations in the intensity of the EAM could be the main mechanism accounting for the paleoenvironmental and paleoceanographic variation observed in the central Yellow Sea.

Modeling of biomass fractionation in a lab-scale biorefinery: Solubilization of hemicellulose and cellulose from holm oak wood using subcritical water

Lignocellulose fractionation is a key biorefinery process that need to be understood. In this work, a comprehensive study on hydrothermal-fractionation of holm oak in a semi-continuous system was conducted. The aim was to develop a physicochemical model in order to reproduce the role of temperature and water flow over the products composition. The experiments involved two sets: at constant flow (6mL/min) and two different ranges of temperature (140–180 and 240–280°C) and at a constant temperature range (180–260°C) and different flows: 11.0, 15.0 and 27.9mL/min. From the results, temperature has main influence and flow effect was observed only if soluble compounds were produced. The kinetic model was validated against experimental data, reproducing the total organic carbon profile (e.g. deviation of 33%) and the physicochemical phenomena observed in the process. In the model, it was also considered the variations of molecular weight of each biopolymer, successfully reproducing the biomass cleaving.

Vascular plant biomarker distributions and stable carbon isotopic signatures from the Middle and Upper Jurassic (Callovian–Kimmeridgian) strata of Staffin Bay, Isle of Skye, northwest Scotland

The molecular and stable carbon isotopic composition of higher plant biomarkers was investigated in Middle to Upper Jurassic strata of the Isle of Skye, northwest Scotland. Aromatic hydrocarbons diagnostic of vascular plants were detected in each of nineteen sedimentary rock samples from the Early Callovian to Early Kimmeridgian interval, a succession rich in fossil fauna including ammonites that define its constituent chronozones. The higher plant parameter (HPP) and higher plant fingerprint (HPF) calculated from the relative abundance of retene, cadalene and 6-isopropyl-1-isohexyl-2-methylnaphthalene (ip-iHMN) exhibit several large fluctuations throughout the Skye succession studied. These molecular profiles contrast with both (1) the more uniform profiles previously observed in Jurassic successions, putatively of the same age, from other palaeogeographical settings, including the Carnarvon Basin, Western Australia and (2) the steady rise in global sea level during this interval. This suggests that the HPF profiles of Jurassic marine successions may not be reliable indicators of global climate change. Our results indicate that other factors such as local tectonism, resulting in changes to the relief and landscape of the hinterland, likely influenced the palaeoflora and the mode of transport of its detritus into adjacent marine depocentres. However, the Skye succession showed similar δ13C profiles of total organic carbon (TOC; comprising mainly fossil wood), the vascular plant biomarker retene and a predominant phytoplanktonic biomarker (phytane). The apparent isotopic relationship between terrigenous and marine-derived biomarkers supports a strong coupling of the atmosphere and ocean. The maximum isotopic excursion occurs in the Cardioceras cordatum ammonite biozone of the Early to Middle Oxfordian, which may be indicative of changes in atmospheric and oceanic levels of CO2.

C:N:P Molar Ratios, Sources and 14C Dating of Surficial Sediments from the NW Slope of Cuba.

The surficial sediments recovered from 12 sites located near the channel axis of the Florida Straits and the lower slope off NW Cuba were analyzed for total organic carbon (TOC), nitrogen (TN), phosphorus (TP), elemental C:N:P ratios, C and N isotopic values, and 14C dating. The depth profiles of TOC, TN, and TP (0-18 cm) displayed a downcore trend and a significant variation. The TOC values were low (0.15 to 0.62%; 66 to 516 µmol g-1). Sites near the island’s lower slope had lower TOC average concentrations (158-333 µmol g-1) than those closer to the channel axis (averaging 341-516 µmol g-1; p <0.05). The TN concentrations near the lower slope attained 0.11% (80 µmol g-1), whereas, towards the channel axis, they decreased to 0.07% (55 µmol g-1; p<0.05). The C:N ratios ranged from 1.9 to 10.2. The mean molar C:N ratio (5.4) indicated a marine hemipelagic deposition. The TP was lower at sites near the lower slope (38.4 to 50.0 µmol g-1; 0.12% to 0.16%) than those near the channel axis (50.0 to 66 µmol g-1; 0.15 to 0.21%). C:P fluctuated from 7.7 to 14.1 in the surficial sediment layer. The bulk organic δ13Corg and δ15N values confirmed pelagic organic sources, and the 14C dating revealed that the sediments were deposited during the Holocene (1000-5000 yr BP). We suggest that the hydrodynamic conditions in the Straits influence vertical and advective fluxes of particulate organic material trapped in the mixed-layer, which reduces the particulate matter flux to the seabed.

TOC and satellite-sensed chlorophyll and primary production at the Arctic Front in the Nordic Seas

In the Arctic Front region south of Jan Mayen, vertical profiles of Total Organic Carbon (TOC) and hydrographic variables were measured during 3weeks in June 2007. From time series of satellite-sensed chlorophyll, it was determined that the field studies took place in the aftermath of the culmination of the spring bloom, both on the Arctic (Icelandic Sea) and Atlantic (Norwegian Sea) sides of the Arctic Front. TOC in the upper 50m was on average 60.9±7.6μM C on the Arctic side and 62.3±6.8μM C on the Atlantic side. Average in situ fluorescence was higher on the Atlantic side. Annual primary production calculated from satellite imagery showed no enhancement at the Front. To place the Frontal measurements in a larger perspective, satellite imagery over the entire Nordic (Greenland–Icelandic–Norwegian) Seas between 1998 and 2012 were studied. They showed that north of Jan Mayen the spring blooms normally last longer and culminate later with a higher concentration of chlorophyll at the peak in the colder water on the west side of the Front than in the Norwegian Sea. In the year of our expedition, the maximal concentration of satellite-sensed chlorophyll at spring bloom was three times higher in the central Greenland Sea than in the Norwegian Sea. Along the Arctic Front the maximal concentration of satellite sensed chlorophyll was always lower than in the central basins both west and east of the Front. The ordinal date of maximal spring bloom concentration of chlorophyll was negatively correlated with the maximal spring bloom chlorophyll concentration in the Norwegian and Icelandic Seas, but uncorrelated in the Greenland Sea. Interannual variation of primary production and maximal chlorophyll concentration was larger in the Greenland Sea then in the Icelandic and Norwegian Seas and we hypothesize that some of this variation is influenced by difference in energy efficiency between phototrophs and heterotrophs at low temperatures.

Quantitative application of post-stack inversion of organic-rich shale based on rock physics linear relationship and 3D seismic data, Perth Basin, Western Australia

Unconventional resources such as shale gas have been an extremely important exploration and production target. To understand the seismic responses of the shale gas plays, the use of rock physical relationship is important, which is constrained with geology and formation-evaluation analysis. Since organic-rich shale seismic properties remains poorly understood, seismic inversion can be used to identify the organic-rich shale from barren shale. This approach helps identify and map spatial distributions and of the organic rich shales. This study shows the acoustic impedance (AI), which is the product of compressional velocity and density, decreases nonlinearly with increasing total organic carbon (TOC) content. TOC is obtained using Roc-Eval pyrolysis for more than 120 core shale samples for the Perth Basin. By converting the AI data to TOC precent on the seismic data, we therefore can map lateral distribution, thickness, and variation in TOC profile. This extended abstract presents a case study of the northern Perth Basin 3D seismic with application of different approaches of seismic inversion and multi-attribute analysis with the rock physical relationships.

Solar photocatalytic mineralization of 2,4-dichlorophenol and mixtures of pesticides: Kinetic model of mineralization

Phytosanitary run off from agricultural fields represents highly disseminated local sources of pollution and corresponds to relatively small volumes which need to be treated (around 5m3 for a farm of a few tens of hectares). The simplicity, the robustness and the low energy consumption of the solar heterogeneous photocatalytic process make it well adapted to this application. Mineralization of phytosanitary effluent with this solar eco-technology was tested with a solar laboratory set up for a few tens of litres. Feasibility was explored step by step with preliminary solar experiments performed on 2,4-dichlorophenol (DCP) followed by solar mineralization carried out on two representative commercial pesticides and three real phytosanitary waste products which were directly collected from a vineyard area. The total organic carbon profiles showed advanced mineralization but the presence of a threshold must be underlined at about 70% of mineralization yield in the case of the two pesticides as well as for the phytosanitary wastewater. A complementary eco-toxicity measurement demonstrated that this threshold is not penalizing regarding the detoxification performance. The kinetic law of mineralization, taking into account the discontinuous solar UV irradiation developed and validated for DCP, was applied with success to the commercial solutions and the wastewater from agricultural activities. Scaling up of the process based on the validated kinetics associated with solar data leads to an annual treatment capacity of 3.5m3 for a reactor surface of 1m2.

A 100-year sedimentary record of natural and anthropogenic impacts on a shallow eutrophic lake, Lake Chaohu, China

In this study, the sediment profiles of total organic carbon, total nitrogen, C/N ratios, total phosphorus, N/P ratios, C/P ratios, particle sizes, and stable carbon and nitrogen isotopes (δ(13)C and δ(15)N) were used to investigate natural and anthropogenic impacts on Lake Chaohu over the past 100 years. Before 1960, Lake Chaohu experienced low productivity and a relatively steady and low nutrient input. The increasing concentration and fluxes of total organic carbon, total nitrogen, total phosphorus, together with changes in the δ(13)C and δ(15)N of organic material in the sediment cores, suggested that the anthropogenic effects on trophic status first started because of an increase in nutrient input caused by a population increase in the drainage area. With the construction of the Chaohu Dam, an increase in the utilization of fertilizer and the population growth which occurred since 1960, stable depositional conditions and increasing nutrient input resulted in a dominantly algae-derived organic matter source and high productivity. Nutrient input increased most significantly around 1980 following the rapidly growing population, with concomitant urbanization, industrial and agricultural development. This study also revealed that the concentration and distribution of nutrients varied between different areas of sediment within Lake Chaohu because of the influence of different drainage basins and pollution sources.

Can hydrocarbon source rocks be identified on seismic data?

Hydrocarbon source rocks contain significant volumes of organic matter, are capable of expelling petroleum when heated, and have produced most of the world's known oil volumes. Recently, source rocks have also become recognized as unconventional economic reservoirs. Here we present a new way of identifying, characterizing, and mapping spatial distributions and variations of thick source rocks (>20 m) that is based on seismic data only. This has a significant impact on the prospect risk assessment of petroleum plays. Rock property studies of organic-rich claystones show that the acoustic impedance (AI), which is the product of compressional velocity and density, decreases nonlinearly with increasing total organic carbon (TOC) percent. Claystones mixed with low-density organic matter (TOC > 3%–4%) have significant lower AI and higher intrinsic anisotropy than otherwise similar nonorganic claystones. This gives the top and base source rock reflections characteristic negative and positive high amplitudes, respectively, which dim with increasing reflection angle. In addition, the TOC profile, which is a smoothed TOC percent curve, influences the top and base amplitude responses. An upward-increasing TOC profile has the highest amplitude at the top, while the opposite asymmetry is observed for downward-increasing TOC profiles. By using seismic data, we therefore can map lateral distribution, thickness, variation in TOC profiles, and, with local well calibration, convert AI data to TOC percent. This approach to mapping source rocks may change the way petroleum systems are evaluated.

Contrasting temporal trends and relationships of total organic carbon, black carbon, and polycyclic aromatic hydrocarbons in rural low-altitude and remote high-altitude lakes

Historical records of total organic carbon (TOC), black carbon (BC), and polycyclic aromatic hydrocarbons (PAHs) were reconstructed in dated sediment cores from four nearby lakes in central Switzerland. In the sub-Alpine Lake Thun, located at 558 m a.s.l., the proximity to anthropogenic emission sources is reflected in higher input of BC and PAHs into sediments with fluxes only slightly decreasing during the last decades. PAH/BC ratios are relatively high and correlation between levels of total PAHs and BC is almost inexistent in Lake Thun, probably due to the presence of less condensed forms of the BC spectrum (char BC) that is underestimated with the chemothermal oxidation method applied in this study. The sediment profiles of TOC, BC, and PAHs are noticeably different in the mountain lakes located around 2000 m a.s.l. In Lake Engstlen, the PAH/BC ratios, as well as the correlation between PAHs and BC, point towards appreciable amounts of predominantly light soot particles. Light soot particles have higher mobility and can, therefore, be efficiently transported to this remote site. The proglacial Lake Oberaar is shown to be a receptor of BC and PAHs released by the fast melting adjacent glacier acting as a secondary source for these conservative species temporarily stored in the glacier ice. Finally, Lake Stein is in strong contrast to all other lakes. High flux of BC into Lake Stein, combined with constant temporal evolutions of BC and PAHs, and in particular BC/TOC ratios approaching 100% are all strong indications for a geogenic presence of graphite in its catchment area.