Distribution Of Carbonates Research Articles

A highly effective strain screened from soil and applied in cementing fine sand based on MICP-bonding technology

Soil cementation based on microbially induced calcite precipitation (MICP) technology is a new research hotspot in the field of biogeotechnical engineering. However, due to the presence of only calcium bonds among particles, MICP-cemented soil shows obvious brittleness, which is the bottleneck of the application of MICP technology in geotechnical engineering. MICP-bonding technology can improve the shortcoming of high brittleness of the calcium bond by increasing the plastic bond among matrix particles. Based on MICP-bonding technology, this study isolated a high-efficiency strain named XR1#, which has the ability to produce both urease and extracellular polysaccharide. Gene sequencing identified the strain as Bacillus oceanicus. The superiority of XR1# bacteria is its ability to induce mineralization and polysaccharide production at the same time. Through the combination of calcium carbonate crystal filling and extracellular polysaccharide bonding, the strength and ductility of the sand column were improved, and the brittle characteristics of traditional MICP technology were reduced. By studying the effect of nutrient elements of the culture medium on calcium precipitation and polysaccharide yield, the two metabolites of XR1# bacteria could be artificially regulated. In an experiment with microbial-cemented fine sand, compared with the traditional Sporosarcina pasteurii, XR1#-cemented sand columns had high production and uniform distribution of calcium carbonate, high strength, and good ductility, and showed obvious advantages. This study provides a new strain with high efficiency and multiple functions for MICP-bonding technology and a new research idea for reducing MICP brittleness.

Indian Ocean sedimentary calcium carbonate distribution and its implications for the glacial deep ocean circulation

The ocean plays a critical role in the global climate by modulating atmospheric CO2 via carbon exchange between the atmosphere and the ocean, a process tightly linked to ocean circulation changes. Ocean circulation transports atmospheric CO2 to the deep ocean via deep water formation and then transfers it with respired CO2, which regulate CaCO3 accumulation in marine sediments on seafloor. Compared to studies on the Atlantic and Pacific, much less has been done on past circulation changes in the Indian Ocean. This is partly due to the lack of systematic investigation on sub-basinal scales calcium carbonate (CaCO3) distributions and limited understanding of their controlling mechanisms in the Indian Ocean. Based on an extensive data compilation and a simple carbonate accumulation model, here we show that CaCO3 distributions in various basins of the Indian Ocean are mainly controlled by ocean circulation changes with productivity only playing a secondary role. Comparison of CaCO3 distributions between the Last Glacial Maximum (LGM) and the late Holocene suggests little change in deep water acidity between these times. If the source-water acidity remains unchanged through time, this finding suggests a vigorous ventilation of the deep Indian Ocean during the LGM. Given that the glacial oceans were likely more alkaline, the stability of deep Indian acidity must suggest greater storage of carbon (mainly as bicarbonate ion) during the LGM. Additionally, we find a very corrosive LGM deep water in the Southwest Indian Basin which may be attributed to intrusion of the Pacific Deep Water.

Variation of lacustrine carbonate deposition in the Eocene Dongying Depression and its comparison with Holocene environments

AbstractThe sedimentary characteristics and preservation potential of lacustrine carbonates provide fundamental information on climate change. The lacustrine carbonate deposition in the Eocene Dongying Depression was investigated using a combination of mineralogical, petrological and geochemical analyses. Micritic calcite/dolomite, granular calcite, columnar calcite, calcareous shell fragments and reworked detrital calcite were identified. Varying patterns of carbonates (VPC) including lithofacies, geochemical indicators and carbonate distribution were revealed in the Dongying Depression: (i) carbonates hardly precipitate in the nearshore area (average 12 wt %); (ii) carbonate content is high (average 53 wt %) in the shallow lake and (iii) gradually decreases to reach a minimum (average 24 wt %) in the deeper part of the lake. Comparison of VPC in four Holocene lakes (the Qinghai Lake and Barkol Lake in China, Oro Lake in Canada and Montcortès Lake in Spain) with the Dongying Depression suggests that four distinct lake stages were developed, namely the terrigenous clastic/gypsum-rich, carbonate-rich, carbonate-decreasing and carbonate-poor stages. A depositional model of lacustrine carbonates influenced by detrital influx, climate, palaeoproductivity and salinity is developed. This study contributes to the understanding of the genetic mechanisms of lacustrine carbonate deposition to reconstruct environmental changes.

Wind erodibility of Arenosols and its driving factors during sand dune fixation: A wind tunnel experiment

Determining the wind erodibility (WE) of Arenosols (sandy soils) and its driving factors is imperative for evaluating wind erosion in desert ecosystems. Here, we performed a wind tunnel experiment to determine the WE of mobile sand dunes (MSDs), semifixed sand dunes (SSDs), and fixed sand dunes (FSDs) in the Ulan Buh Desert, and revealed its relationships with soil properties, such as soil organic matter (SOM), calcium carbonate (CaCO3), and particle size distribution (PSD). Moreover, we investigated the variation in WE subject to wetting-drying processes with diverse soil moisture gradients. We suggested taking the derivative of the wind erosion content of wind speed (K) to indicate WE, which offered a fresh approach to infer WE from observations in wind tunnel experiments. The results indicated that: compared with the MSDs and SSDs, the FSDs performed better in terms of vegetation cover and soil properties, but the variation in WE was not statistically significant among different sand dunes. WE correlated positively with SOM and CaCO3 and correlated negatively with coarse soil particles. In addition, WE was substantially affected by the wetting process. The critical relative moisture content needed to hamper wind erosion ranged from 3.4 to 3.7% (gravimetric) in the Ulan Buh Desert. However, the variation in WE was not statistically significant between before and after the wetting-drying process. The results of our study are expected to provide new insights into the wind erosion of Arenosols.

Comparison of different treatment methods on macro-micro characteristics of Yellow River silt solidified by MICP technology

The cementation of Yellow River silt into green and sustainable building materials through microbial induced calcium carbonate precipitation (MICP) is a novel technology with a wide range of applications. The MICP treatment of abandoned Yellow River silt was carried out by multiple-phase injection method and pre-mixing method in this paper. The effects of cementation solution concentration and treatment times on the chemical conversion efficiency were investigated, and the effectiveness of the two treatment methods in improving the mechanical properties of Yellow River silt was evaluated. The results showed that the chemical conversion efficiency of the pre-mixing method was about 5% higher than that of the multiple-phase injection method. With the increase of the cementation solution concentration and the treatment times, the unconfined compressive strength (UCS) of the samples treated by the pre-mixing method increased faster and the distribution of calcium carbonate (CaCO3) was more uniform. After ten treatments, the UCS of the samples treated by pre-mixing method exceeds 5 MPa with a relatively uniform CaCO3 content of 25%.

Effects of Land Use on Riverine Dissolved Inorganic Carbon (DIC) and δ13CDIC in a Karst River Basin, Southwestern China

As an important part of the riverine carbon cycle, dissolved inorganic carbon (DIC) has attracted continuous attention. The stable carbon isotope (δ13CDIC) of DIC can reflect its sources and transformations. However, the effects of land use on DIC and δ13CDIC are rarely investigated. To study the influencing factors of DIC and δ13CDIC, river water samples were collected and analyzed from the Chishui River basin, a typical karst river basin in southwestern China. The upper reaches of the Chishui River basin were predominantly underlain by carbonate sedimentary rocks, whereas the lower reaches contained mostly siliciclastic sedimentary rocks, and the forest coverage in the lower reaches was relatively high. The elemental compositions of the river water revealed that the hydrochemistry of rivers in the upper reaches of the basin was mainly controlled by carbonate weathering, whereas the hydrochemistry of some tributaries in the lower reaches was mainly affected by silicate weathering. During the wet season, the average values of c (DIC) and the δ13CDIC value were (1940±493) μmol·L-1 and (-9±1) ‰, respectively, whereas the c (DIC) was relatively high, and the δ13CDIC value was more positive in the dry season, with the average values of (2334±626) μmol·L-1 and (-7.3±1) ‰, respectively. The DIC of most samples was mainly controlled by carbonate weathering under an open system and was derived from carbonate minerals and atmospheric and soil CO2. The seasonal variations in the c (DIC) and δ13CDIC values suggested that c (DIC) was regulated by climate, hydrology, and biology. The increasing contribution of biological carbon to DIC in summer was the main cause of the more negative δ13CDIC value in the wet season, whereas the dilution effect of higher discharge was the main cause of the low c (DIC) in the wet season. The samples from three tributaries in the lower reaches with the highest proportion of silicate and forest distribution had the highest dissolved organic carbon concentration[c (DOC)], the lowest c (DIC), and the most negative δ13CDIC value in the wet season. The proportion of carbonate distribution had positive correlations with c (DIC) in the wet and dry seasons, indicating that lithology was the main controlling factor of c (DIC). The rivers draining the carbonate areas had a lower c (DIC) and a more negative δ13CDIC value in the wet season than those in the dry season, whereas for the rivers draining non-carbonate areas with high forest coverage, the c (DIC) was higher and the δ13CDIC value was significantly more negative in the wet season than those in the dry season. This implies that c (DIC) and δ13CDIC are significantly affected by land use when they are less affected by lithology.

Effects of microbial strains on the mechanical and durability properties of lightweight concrete reinforced with polypropylene fiber

This research investigated the impact of calcium carbonate precipitation induced by the activity of four microbial strains known as Sporosarcina pasteurii, Bacillus megaterium, Sporosarcina ureae, and Bacillus licheniformis at cell concentrations of 107 cells/ml on lightweight fiber concrete (LWFC). Three mixed designs with different fiber percentages (0%, 0.5%, and 1%) were considered for evaluation of the effects of these bacteria and polypropylene fiber on the mechanical properties and durability of LWC, which contained Leca aggregate. The experimental results indicated that the simultaneous addition of bacteria and fiber was effective and improved compressive, tensile, and flexural strength. It also reduced concrete water absorption and permeability in the specimens. In specimens with B. licheniformis and 1% fiber, a maximum increase of approximately 32.65% was observed in tensile strength and a 28.39% decrease was observed in water absorption with respect to the control specimens. A comparison of the bacterial specimens revealed that B. licheniformis and B. megateterium performed better in the induction of calcium carbonate precipitation and distribution of fiber in the concrete matrix than S. pasteurii and S. ureae to reduce the balling phenomenon. In addition, SEM-EDX and XRD analyses were conducted to verify the formation of calcium carbonate in the concrete matrix and characterize the crystalline phases of the calcite.

Lake Chukhlomskoe in the Late Pleistocene and Holocene (Kostroma region, Russia)

Abstract. The article discusses the first results of geomorphological and paleolimnological study of Lake Chukhlomskoe (Kostroma region). We analyzed the topography of the lake bottom using new bathymetric data from 2021 fieldwork. The structure of the lake basin slopes was studied using hand drilling. Analytical characteristics of the bottom sediments core (grain size distribution, loss on ignition, magnetic susceptibility, AMS-dating and palynological data) are presented. The distribution of organic matter, carbonates and particle size by depth allow us to correlate the bottom sediments of Lake Chukhlomskoe with the sediments of other well-studied large lakes (Belaya Struga, Galichskoe and Seliger).

Facile Aluminum Porphyrin Complexes Enable Flexible Terminal Epoxides to Boost Properties of CO2‐Polycarbonate

AbstractIncorporation of flexible monomer is regarded as a valid way to the chemical modification of the highly brittle poly(cyclohexene carbonate) (PCHC), which derived from the copolymerization of CO2 and cyclohexene oxide (CHO). However, toxic metal catalyst such as cobalt dominates these terpolymerizations which against the green development philosophy. Here, a series of environmentally benign aluminum porphyrin catalysts with different steric and electronic effects for the terpolymerization of CO2, CHO, and terminal epoxides with various flexible pendant alkyl groups to adjust the properties of PCHC is reported. The resulting terpolymers display a random distribution of cyclohexene carbonate along the backbone with a regulated terminal epoxide insertion from 30% to 70%. Moreover, the mechanical properties can be well regulated in a wide range indicating the feasibility of the present approach. The present study provides a green way to chemical modification of rigid PCHC.

Carbonate bedrock control of soil Cd background in Southwestern China: Its extent and influencing factors based on spatial analysis

Previous studies have found that Cadmium (Cd) may be condensed during the processes of the weathering and soil formation over carbonate bedrock, which is a typical phenomenon in the southwest region of China. However, the extent of the high value background and the geographical factors influencing its spatial distribution are still unknown. This study collected data from the Multi-Purpose Regional Geochemical Survey (MPRGS) and the Regional Geochemistry-National Reconnaissance Program (RGNR) to investigate the extent and its controlling factors based on spatial analysis. It was found that the RGNR is an ideal data source for regional Cd background studies. Spatially, the high Cd area (Cd > 1.5 m/kg with reference of the GB15618-2018 soil environmental quality in China, 68.9 × 103 km2) coincide well with the carbonate distribution. In the total area (68.9 × 103 km2) with high Cd concentration, 89.8% is related to carbonates. The composition of parent rock, climate conditions, and landuse are controlling factors of the enrichment. The high Cd background effect of limestone is higher than that of dolomite and their effects decease with increasing detritus component they contain. Warm and humid climate in forest land helps to enrich Cd during weathering. Soil Cd concentration related to carbonate background can be predicted by major element concentrations, which is useful for differentiating Cd background from human pollution in the future soil pollution monitoring. Modelling by artificial neural network (ANN) is recommended rather than tradition multiple linear methods (LM) as the latter may have the effect of collinearity.

Distribution and depositional model of microbial carbonates in the Ordovician middle assemblage, Ordos Basin, NW China

Based on outcrop profiles, drilling cores, cast thin sections etc., the types, microfacies combinations and distribution pattern of microbial carbonates in the Ordovician middle assemblage of the mid-eastern Ordos Basin have been systematically analyzed. The middle assemblage of Ordovician in the mid-eastern Ordos Basin has microbial carbonates formed by the calcification of cyanobacteria, including microbial biostromes and microbial mounds made of stromatolites, thrombolites, and oncolites. The distribution of the carbonates shows obvious “stratum-control” and “regional” characteristics. The microbial biostromes 2–3 m thick each are controlled by sequence cycles and sedimentary facies changes, and were mainly formed in the tidal flat environment during the depositional stages of the Ma56 and Ma55 sub-members. The microbial biostrome in the Ma55 sub-member occurring near the carbonate-evaporite transition interface in the early stage of the transgression is distributed mainly in the Mizhi subsag in the eastern part of the basin; the microbial biostrome in the Ma56 sub-member turns up near the carbonate-evoporite transition zone in ring shape in the east of the central uplift. The ancient landform had noticeable control on the distribution of microbial mounds. The microbial mounds or mound-shoal complexes developing mainly during the depositional stages of Ma57_Ma510 sub-members are about 15–25 m thick in single layer and distributed largely in the Wushenqi-Jingbian paleouplift. The development model of the microbial carbonate rocks shows that the carbonate-evaporite lithologic transition zone and the Wushenqi-Jingbian paleouplift are favorable exploration zones of microbial carbonates in the Ordovician middle assemblages.

14C GEOCHRONOLOGY AND RADIOCARBON RESERVOIR EFFECT OF REVIEWED LAKES STUDY IN CHINA

ABSTRACTLacustrine sediments are important archives for paleoclimate research, but there are evident carbon reservoir effects. Radiocarbon (14C) ages of lake sediments must be corrected for these effects before applying them to paleoclimate research. The authors review the lacustrine research from the last 20 years from different climatic regions in China, and systematically investigate the 14C age and correction methods used in the studies of 81 lakes. It is found that the climate-vegetation cover and distribution of carbonate around lakes are dominant factor controlling radiocarbon reservoir effects. In eastern China, the average 14C reservoir age is about 500 14C years and is associated with relatively dense vegetation. However, in northwest China and Qinghai-Tibet Plateau, widespread carbonate bedrock may markedly increase the radiocarbon reservoir age which frequently is about 1500 and 2500 14C years. A piecewise linear regression model provides more reliable 14C reservoir age correction that accounts for sedimentary facies and sedimentation rate changes. It is worth mentioning that when analyzing 14C ages deviated greatly from time sequence, the age anomalies may indicate important effects relevant to the study of climate and environmental changes.

Integration of a calcium carbonate crystallization process and membrane contactor–based CO2 capture

This research work presents the integration of polypropylene hollow fiber membrane contactor–based CO2 absorption unit using aqueous sodium hydroxide (NaOH) as the absorbent solution, and precipitation of high-quality calcium carbonate by addition of calcium chloride. The integrated crystallization process bypasses the need for cost-intensive energy regeneration of the absorbent solution. Given the lifetime of high added value precipitated calcium carbonate, the proposed approach for integrating solid particle formation and a carbon dioxide mitigation technique can be considered as a potential post-combustion technology for carbon capture, utilization and sequestration (CCUS). The overall CO2 mass transfer coefficient in the membrane contactor and subsequent crystallization process was investigated by conducting the experiments at different operating conditions. For a maximum hydroxide concentration of 5.01molL-1, an overall mass transfer coefficient of 2.25·10-4ms-1 and CO2 flux of 2.45·10-4molm-2s-1 were obtained for a 0.5Lmin-1 of gas flow rate. The proposed liquid–liquid crystallization process produces a narrow size distribution of micron-sized calcium carbonate with a mean diameter of 3–8 µm that can be used in the paper, coatings, food and biomedical industries.

(Invited) Model-based Analysis of Carbonation Effects in Anion Exchange Membrane Fuel Cells

Anion exchange membrane fuel cell (AEMFC) is a promising next generation (Pt-free) fuel cell technology. However, AEMFC do not yet demonstrate high performance when running on ambient air: CO2 in air results in a carbonation reaction that impacts membrane conductivity and electrode performance. This contribution analyses and quantifies the effect of CO2 from ambient air on the concentration profiles in the membrane and the anode and assesses the CO2 impact on fuel cell performance via modeling.[1] The physico-chemical model contains chemical and electrochemical reactions, liquid-gas phase equilibria as well as the transport processes in the cell. Results imply that a significant part of the CO2 that enters the cell is absorbed in the cathode and is transported as carbonate ions to the anode. Concentration profiles in the membrane reveal an enrichment zone of CO2 in the membrane close to the anode, negligible hydrogencarbonate and a wide distribution of carbonate across the membrane. The carbonate distribution affects overall anion exchange membrane conductivity. For practically relevant current densities of i > 500 mA cm-2 and typical excess ratios of 1.5 for the hydrogen feed, less than 10% of the anions in the membrane are carbonates. We show that while increasing cell temperature has an ambiguous effect on the carbonation process and on the total effect of CO2 on the cell, current density has a significant effect. The impact of CO2 on AEMFC performance can be significantly decreased when operating the cell at high current densities. A closer look at the transport processes in the membrane reveals that carbonate ions are purged out of the membrane when increasing current density. However, this process is unexpectedly slow. In the talk we will compare simulated and experimental temporal evolution of concentration profiles and conductivity. For validation, data obtained during decarbonation experiments in a setup to determine the true hydroxide conductivity of AEM [2] is used. Ion concentration profiles in the membrane are described quantitatively and it is shown how the differences in ion mobility delay the complete decarbonation process. The model-based insights of the talk aid experimentalists to build and operate well-performing air-fed AEMFCs. [1] U. Krewer, C. Weinzierl, N. Ziv, D. Dekel, Electrochimica Acta 263 (2018) 433-446 [2] A. Zhegur-Khais, F. Kubannek, U. Krewer, D.R. Dekel, J. Memb. Sci. 612, (2020) 118461

Mechanism of Sand Cementation with an Efficient Method of Microbial-Induced Calcite Precipitation.

This paper presents an efficient method of microbial-induced calcite precipitation (MICP) for cementation of sand particles. First, the influence of initial pH value of the culture medium on the growth of bacteria was discussed. Then, the compressive strength and calcium carbonate content of cemented sand columns with different sand particle sizes were measured to indicate the cementation effectiveness. The microstructure of cemented sand columns as well as the mineral composition and distribution of calcium carbonate were characterised by means of scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) and X-ray diffraction (XRD). The results showed that the urease-producing bacteria S. pasteurii can be cultured at the initial pH values of 7–10, while a higher pH (e.g., 11) would hinder its growth and decrease its urease activity. The injection method of MICP with high standing time can cement sand columns effectively. Small average sand particle size of sand columns and high injection cycles can facilitate the gain of compressive strength, while calcium carbonate content of sand column higher than 8% can promote the increase of compressive strength. XRD results indicate that the fine grains generated on the surface of sand particles are calcite. The distribution of calcite on sand particles’ surface is broad and uniform. First, calcite was precipitated on the surface of sand particles, and then a precipitation layer was formed, which would connect sand particles through its high enough thickness and contribute to the development of compressive strength of the whole sand column.

Investigating Carbonate Distribution in Particle Size Components of Some Soils of Khuzestan Province

Investigating Carbonate Distribution in Particle Size Components of Some Soils of Khuzestan Province

Delineating reclamation zones for site-specific reclamation of saline-sodic soils in Dushak, Turkmenistan.

Soil salinization is the widespread problem seriously affecting the agricultural sustainability and causing income losses in arid regions. The major objective of the study was to quantify and map the spatial variability of soil salinity and sodicity. Determining salinity and sodicity variability in different soil layers was the second objective. Finally, proposing an approach for delineating different salinity and sodicity zones was the third objective. The study was carried out in 871.1 ha farmland in Southeast of Dushak town of Ahal Province, Turkmenistan. Soil properties, including electrical conductivity (EC), soil reaction (pH), sodium adsorption ratio (SAR), calcium carbonate and particle size distribution (clay, silt and sand fractions) in 0–30, 30–60, 60–90 and 90–120 cm soil layers were recorded. The EC values in different soil layers indicated serious soil salinization problem in the study area. The mean EC values in 0–90 cm depth were high (8 dS m-1), classifying the soils as moderate to strongly saline. Spatial dependence calculated by the nugget to sill ratio indicated a strong spatial autocorrelation. The elevation was the primary factor affecting spatial variation of soil salinity in the study area. The reclamation of the field can be planned based on three distinct areas, i.e., high (≥12 dS m-1), moderate (12–8 dS m-1) and low (<8 dS m-1) EC values. The spatial trend analyses of SAR values revealed similar patterns for EC and pH; both of which gradually decreased from north to the south-west. The amount of water needed to leach down the salts from 60 cm of soil profile is between 56.4–150.0 ton ha-1 and the average leaching water was 89.8 tons ha-1. The application of leaching water based on the amount of average leaching water will result in higher or lower leaching water application to most locations and the efficiency of the reclamation efforts will be low. Similar results were recorded for sulfur, sulfuric acid and gypsum requirements to remediate sodicity. The results concluded that the best management strategy in planning land development and reclamation schemes for saline and sodic soils require accurate information about the spatial distribution of salinity and sodicity across the target area.

Influence of the Grouting Parameters on Microbially Induced Carbonate Precipitation for Soil Stabilization

As a novel, nature-like biomineralization process, microbially induced carbonate precipitation (MICP) has been successfully applied in soil stabilization. This study investigated the influence of biomass injected on the geotechnical performance of MICP treated sand. Grouting rate and particle sizes were also taken into account. The results showed that the injection of 1.0 or 1.2 PV biological solution achieved the most effective and uniform reinforcement of soil, depending on the grouting rate. Excessive biomass (1.5 PV biological solution) failed to promote the further improvement of the engineering performance of MICP reinforced sand. The relationship between strength and calcium carbonate content and SEM results indicated that for the small CaCO3 content, the improvement of soil strength is mainly controlled by the content of calcium carbonate rather than its distribution. When the amount of carbonate precipitation is sufficient to form bonding between soil particles, the distribution of calcium carbonate has a greater influence on mechanical properties. The strength of biocemented soil measured by layering indicated that the insufficient amount of biological solution (such as 0.5 PV biological solution) greatly weakened the reinforcement effect of soil away from the grouting port, and thus led to larger strength variability. Increasing the grouting rate of biological solution improved the uniformity of reinforcement, especially for medium grain sand. The results of this study provide a guide to facilitate the application of microorganisms in the engineering application practice of MICP.

Progradational slope architecture and sediment distribution in outcrops of the mixed carbonate-siliciclastic Bone Spring Formation, Permian Basin, west Texas

AbstractSediment transport and distribution are the keys to understanding slope-building processes in mixed carbonate-siliciclastic sediment routing systems. The Permian Bone Spring Formation, Delaware Basin, west Texas, is such a mixed system and has been extensively studied in its distal (basinal) extent but is poorly constrained in its proximal upper-slope segment. Here, we define the stratigraphic architecture of proximal outcrops in Guadalupe Mountains National Park in order to delineate the shelf-slope dynamics of carbonate and siliciclastic sediment distribution and delivery to the basin. Upper-slope deposits are predominantly fine-grained carbonate lithologies, interbedded at various scales with terrigenous (i.e., siliciclastic and clay) hemipelagic and gravity-flow deposits. We identify ten slope-building clinothems varying from terrigenous-rich to carbonate-rich and truncated by slope detachment surfaces that record large-scale mass wasting of the shelf margin. X-ray fluorescence (XRF) data indicate that slope detachment surfaces contain elevated proportions of terrigenous sediment, suggesting that failure is triggered by changes in accommodation or sediment supply at the shelf margin. A well-exposed terrigenous-rich clinothem, identified here as the 1st Bone Spring Sand, provides evidence that carbonate and terrigenous sediments were deposited contemporaneously, suggesting that both autogenic and allogenic processes influenced sediment accumulation. The mixing of lithologies at multiple scales and the prevalence of mass wasting acted as primary controls on the stacking patterns of terrigenous and carbonate lithologies of the Bone Spring Formation, not only on the shelf margin and upper slope, but also in the distal, basinal deposits of the Delaware Basin.

From seep carbonates down to petroleum systems: An outcrop study from the southeastern France Basin

Despite the obvious link between hydrocarbon seepage at the surface and the activity of petroleum systems at depth, the majority of studies on seep carbonates concentrate on shallow aspects, whereas they are rarely oriented toward a source-to-sink perspective. Here, seep carbonates are conceptualized as a key element for analyzing petroleum systems at basin scale. Mapping of a 150-m-thick, 200-m-wide outcrop of the Lower Cretaceous slope wedge of the southeastern France Basin reveals two distribution patterns of seep carbonate concretions: (1) aligned in a continuous bed secant to the stratigraphy and (2) clustered in patches vertically stacked over 35 m. The δ13C signatures of the seep carbonates as light as −40‰ Peedee belemnite point toward a biogenic methane–dominated seepage. A set of turbidite channels pinching out right below the seep carbonates is seen as a potential gas trap, whereas biostratigraphic analysis indicates that the channels are coeval with a prominent black shale in the center of the basin. Any biogenic methane generated by the black shale could have used the channels as drains up to their pinch-out. The switch from a continuous seep carbonate level to stacked patches suggests initial widespread capillary leakage, followed by the opening of a preferential migration pathway. The distribution of seep carbonates thus appears dominated by breaching mechanisms of reservoir–cap-rock seals. This case study illustrates how seep carbonate mapping, in combination with the tectono-sedimentary context of each basin, may be a valuable tool for petroleum geologists.