Column Conditions Research Articles

Collision damage quantification of RC pier columns coupling axial, flexural and shear effects

Reinforcement concrete (RC) pier columns are the main supporting elements of many highway bridges and city viaducts, therefore the health state of a pier column is critical to the safe operation of bridges. Vehicle-pier collision accidents, which occur increasingly frequently, often induce unexpected damage to an impacted pier column, threatening the safety of bridges. It is important to define appropriate damage indices that can be used to effectively assess the conditions of a pier column damaged by a vehicle collision in a quantitative manner. Previous researchers have proposed many types of damage indices to quantify the degree of damage to an RC column. However, the existing damage indices often suffer from limitations such as undefined upper- and lower-bound rules, ignorance of shear deformation, etc. This paper proposes a plasticity-based damage index, which uses the accumulation of plastic deformation to reflect the damage state of an impacted RC pier column. The proposed damage index ranges between 0.0 and 1.0 which can effectively couple axial, flexural and shear deformation of RC sections during vehicle collisions with detailed model validations using experimental data. A detailed parametric study is then conducted which shows that the damage index can very effectively trace the time-history and spatial distribution of damage on an RC pier column during vehicle collisions.

Infaunal invertebrate community relationships to water column and sediment abiotic conditions

Infaunal invertebrates are affected by the overlying water and the sediment in which they live. Therefore, understanding how these environmental conditions impact infauna is critical for evaluating how they may respond to future changes in these conditions due to climate change. Here, we considered which abiotic variables, for example, salinity, sediment characteristics (i.e. mean grain size, sorting), and water column and sediment carbonate chemistry, influence infaunal invertebrate communities and juvenile bivalve abundance at intertidal sites. We used data from sites in two regions in New Brunswick, Canada with contrasting tidal regimes and oceanographic conditions, the Bay of Fundy and the Southern Gulf of St. Lawrence. We were particularly interested in bivalve recruitment due to the importance of bivalves in ecosystem services and predicted sensitivity to climate change impacts. Using data collected in 2020 and 2021, statistical modeling was done to determine which abiotic variables were potential drivers of multivariate community composition as well as species richness, total abundance, and juvenile bivalve abundance. We found that carbonate chemistry variables, both sediment and water, explained a large amount of variation (~ 7–44%) in infaunal invertebrate communities in the two regions in both our multivariate and univariate analyses. Sediment pH explained the most variation (16.9%) in the multivariate analyses for the Bay of Fundy sites. However, in the Southern Gulf of St. Lawrence, salinity explained the most variation (9.8%) in the multivariate community composition. In the univariate modeling, alkalinity, either water column or sediment, was included in all top models for all four dependent variables, suggesting the importance of this carbonate chemistry variable for bivalves and infaunal communities. Climate change is expected to have large impacts on carbonate chemistry conditions in the oceans, specifically pH, carbonate availability, and alkalinity. The influence of carbonate chemistry parameters on infaunal invertebrate communities in these regions shows the potential sensitivity these animals have to future oceanic conditions.

Organic matter enrichment in shale deposited proximal to paleo-uplifts and its impact on shale gas exploration

Much of the global exploration and development of shale gas is focused on organic-rich shale deposited in basin or slope/basin margin settings. There is a clear need to assess the degree to which organic-rich shale deposited in other settings, notably proximal to paleo-uplifts, are promising shale gas prospects. Organic-rich sediments that accumulated proximal to paleo-uplifts are recognized globally and include the Cambrian Niutitang Formation, Ordovician-Silurian transition “hot shales”, and modern sediments of the Black Sea. Though the subject of recent research efforts, much remains to be learned of the mechanisms of organic matter enrichment of fine-grained sediment deposited adjacent to paleo-uplifts. Our study focuses on the Ordovician Wufeng Formation that accumulated proximal to uplifted areas of the Upper Yangtze platform. Though the TOC content of the analyzed Wufeng Formation samples recovered from near the paleo-uplifts is less than that of Wufeng samples collected from basin or slope/basin margin settings, average TOC value of the former can still reach more than 2%. Wufeng Formation shale deposited proximal to paleo-uplifts accumulated under conditions of medium to high paleoproductivity, elevated terrigenous clastic input and sedimentation rate, and oxic-suboxic water column conditions. Principal component analysis suggests that the factor most critical to organic matter enrichment of Wufeng deposits proximal paleo-uplifts was paleo-redox conditions. The TOC abundance in Wufeng Formation shale deposited during late Katian stage is higher than that of shale deposited during Hirnantian stage. It was at the Hirnantian stage that the paleo-uplifts became most active in association with the Kwangsian Orogeny resulting in diminished paleoproductivity and preservation conditions as reflected in the reduced organic matter abundance of associated shale. Uplift of the paleo-uplift of the Yangtze Platform, a manifestation of the Kwangsian Orogeny during the Ordovician-Silurian transition, appears to have been largely responsible for spatial and temporal distribution differentiation of organic matter abundance of the Wufeng Formation of the Upper Yangtze Platform. Results of the present study contribute supplementary information regarding the mechanism of organic matter enrichment in shale and can provide guidance for shale gas exploration and development in geologically similar regions.

Optimizations of the EA-IRMS system for δ15N analysis of trace nitrogen

The elemental analyzer-isotope ratio mass spectrometer (EA-IRMS) technique is widely utilized to measure the nitrogen isotope ratio (δ15N) in various environmental samples. However, this method has limitations when analyzing samples with low nitrogen content (e.g., soils, rocks and atmospheric deposition) due to significant sample dilution (>99%) before entering the ion source. To reduce sample size requirement and increase sensitivity, modifications can be made to the elemental analyzer and analytical conditions to transfer more sample gas to the ion source. In this study, we presented four modifications to the EA-IRMS instrument, including the reaction tube, water trap, gas chromatography (GC) column, and inlet splitter connected to ConFlo, along with the analytical conditions of the GC column, carrier gas flow rate, and split ratio for improving sensitivity. The results show that reducing the carrier gas flow rate from 80 to 30 mL/min increased the sensitivity of the EA-IRMS system by twofold. By increasing the split ratio from 3:2 to 3:1, the sensitivity increased from 2.32 Vs/μg N to 3.93 Vs/μg N. The optimized EA-IRMS has a sample size requirement of at least 12 μg N and a standard deviation of <0.2‰ for δ15N analysis. We found that the modifications of the GC column and water trap had a negligible influence on sample peak and measurement and thus were deemed unnecessary. The effective modifications in the study were reducing the carrier gas flow rate and increasing split ratio, which increased the concentration of the analyte gas per unit volume and more efficient sample transfer to the ion source. This upgraded method can provide crucial technical support for environmental samples with low nitrogen content.

Stress-strain behavior of columns confined with bamboo reinforced concrete jacket

ABSTRACT The need for retrofitting of building structures is generally caused by two cases: to repair damaged structures or to improve the structural performance of weak structures. The concrete jacket method is widely chosen to solve the problem due to the more economical and simple procedure compared to other methods. In this study, retrofitting using bamboo-reinforced concrete jacket (BRCJ) was applied on reinforced concrete columns. Bamboo was used to replace steel as the longitudinal and transverse reinforcements of the concrete jacket with the aim of finding an alternative for an environmentally friendly green material and a lower-cost manufacturing process compared to steel. The performance of the jacket was studied by investigating the confinement effectiveness that is influenced by initial column conditions, spacing of bamboo stirrups, and the slenderness of longitudinal reinforcement. The outcomes showed that the bamboo-reinforced concrete jackets were able to strengthen the columns up to 170% and 140% of the initial strength of the undamaged and damaged columns, respectively. The BRCJ is more effective on columns that are still at the pre-peak-strength stage. The confinement effectiveness is also largely affected by the bamboo stirrups spacing. By reducing the spacing of bamboo stirrups to about half that of steel stirrups, the ductility ratio of retrofitted columns increased up to 90% higher than the original columns. Further, the confinement effect of BRCJ can also be increased by increasing the slenderness ratio of bamboo longitudinal reinforcement. Finally, the stress–strain relationship for concrete columns retrofitted with bamboo-reinforced concrete jackets has been proposed which shows great agreement with the experimental data. Overall, BRCJ has shown promising results to be used to strengthen damaged or weak structures.

Determination of oxylipins and their precursors in breast milk by solid phase extraction-ultra high performance liquid chromatography-triple quadrupole tandem mass spectrometry

Oxylipins and their precursors (long-chain polyunsaturated fatty acids, LCPUFAs) are key intercellular signaling molecules influencing the inflammatory response. Each oxylipin has pro- and/or anti-inflammatory effects, and the relative abundance of different oxylipins can alter the inflammatory balance, making it important to clarify the oxylipin profile of breast milk for optimal infant health. The extraction, identification, and simultaneous quantification of oxylipins in breast milk are challenging due to the structural similarity, limited stability, and the low endogenous concentration of oxylipins and the complex matrix of breast milk. This study aimed to develop a solid phase extraction-ultra high performance liquid chromatography-triple quadrupole tandem mass spectrometry (SPE-UPLC-MS/MS) method for the comprehensive and specific quantification of oxylipins and their precursors in breast milk. The LC conditions (including column, mobile phase, and gradient conditions) and SPE procedure (including SPE cartridges, elution solvent, and elution volume) were optimized to achieve accurate quantification and better analyte recovery. A single 18-minute chromatographic run allows for the quantification of 20 oxylipins and 5 PUFAs. The results showed good linearity (R2 > 0.99) over the concentration range of 2 to 100 ng/mL, with the instrument detection limits ranging from 0.01 to 0.90 ng/mL for oxylipins and 0.02 to 0.59 ng/mL for PUFAs. The method is rapid, sensitive, and reproducible (RSD ≤ 10%) and is suitable for the quantitative analysis of oxylipins and their precursors in infant formula samples.

Acoustic ducting by shelf water streamers at the New England shelfbreak.

Greater sound speed variability has been observed at the New England shelfbreak due to a greater influence from the Gulf Stream with increased meander amplitudes and frequency of Warm Core Ring (WCR) generation. Consequently, underwater sound propagation in the area also becomes more variable. This paper presents field observations of an acoustic near-surface ducting condition induced by shelf water streamers that are related to WCRs. The field observations also reveal the subsequent disappearance of the streamer duct due to the passage of a WCR filament. These two water column conditions are investigated with sound propagation measurements and numerical simulations.

Magnetic saturation enhancement of gold-capped nickel nanorods

Nickel nanorods (NRs) capped with gold (Au/Ni) were grown into porous anodic aluminum oxide templates and subsequently transferred onto Au/Si (100) substrates. A high dense 2D array of Ni and Au/Ni nanorods was analyzed by vibrating sample magnetometry; it was found that an increase in 14.8% of the magnetic moment following the deposition of Au caps. In order to further investigate this phenomenon, the magnetic distribution of Au/Ni nanorods was studied by off-axis electron holography. The magnetization and induction strengths were evaluated to be 4.7 × 105 A/m and 0.62 T, respectively, which is equivalent to magnetometry measurements of the Ni NR arrays. Remarkably, a vortex state configuration was imaged in the Au segment by the retrieved magnetic phase of the electron holograms under free lens conditions of the transmission electron microscope column. It was concluded that the magnetic distribution in the Au segment is associated with a ferromagnetic coupling with Ni and correlated with the magnetometry measurements.

Novel intensified process for di-isopropyl ether production from isopropanol etherification using reactive distillation technology

The preparation of di-isopropyl ether (DIPE), as an important chemical solvent, by isopropanol (IPA) etherification is limited by chemical equilibrium and azeotropic formation in its production processes. A novel sustainable etherification process based on reactive distillation (RD) coupled with extractive distillation is proposed. The reaction of IPA etherification was carried out by cation exchange resin NKC-9 in a 250 mL autoclave and fitted by a pseudo-homogeneous model. According to the reaction kinetic, the IPA etherification RD model was established. To confirm the viability of RD and the accuracy of the model, pilot-scale RD experiments for generating DIPE were investigated. Based on the established model matching the pilot scale experiments, the operating conditions of the etherification RD column were optimized by sensitivity analysis. The simulation results show that the conversion of IPA in the RD column can be increased from 18.2 % to 77.9 % compared with autoclave and the yield of DIPE in the whole process flowsheet can reach 99.9 %, which demonstrates that combining reactive distillation with extractive distillation technology is a feasible and advantageous solution for DIPE production.

The fate of three typical persistent organic pollutants in bioretention columns as revealed by stable carbon isotopes

There is a lack of simple and effective methods to quantify the fate processes of persistent organic pollutants (POPs) in bioretention systems. In this study, the fate and elimination processes of three typical 13C-labeled POPs in regularly added bioretention columns were quantified using stable carbon isotope analysis techniques. The results showed that the modified media bioretention column removed more than 90% of Pyrene, PCB169 and p,p'-DDT. Media adsorption was the dominant removal mechanism for the reduction of the three exogenous organic compounds (59.1–71.8% of the input) although plant uptake (5.9–18.0%) was also important. Mineralization was effective in degrading pyrene (13.1%) but had a very limited effect on p,p'-DDT and PCB169 removal (<2.0%), the reason for which may be related to the aerobic conditions of the filter column. Volatilization was relatively weak and negligible (<1.5%). The presence of heavy metals inhibited the removal of POPs to some extent: media adsorption, mineralization and plant uptake were reduced by 4.3–6.4%, 1.8–8.3% and 1.5–3.6% respectively. This study suggests that bioretention systems are an effective measure for the sustainable removal of POPs from stormwater and that heavy metals can inhibit the overall performance of the system. Stable carbon isotope analysis techniques can help to investigate the migration and transformation of POPs in bioretention systems.

Evolutions of sedimentary facies and palaeoenvironment and their controls on the development of source rocks in continental margin basins: A case study from the Qiongdongnan Basin, South China Sea

Hydrocarbon resources in the Qiongdongnan Basin have become an important exploration target in China. However, the development of high-quality source rocks in this basin, especially in its deep-water areas, are still not fully understood. In this study, evolutions of sedimentary facies and palaeoenvironment and their influences on the development of source rocks in diverse tectonic regions of the Qiongdongnan Basin were investigated. The results show that during the Oligocene and to Miocene periods, the sedimentary environment of this basin progressively varied from a semi-closed gulf to an open marine environment, which resulted in significant differences in palaeoenvironmental conditions of the water column for various tectonic regions of the basin. In shallow-water areas, the palaeoproductivity and reducibility successively decrease, and the hydrodynamic intensity gradually increases for the water columns of the Yacheng, Lingshui, and Sanya-Meishan strata. In deep-water areas, the water column of the Yacheng and Lingshui strata has a higher palaeoproductivity and a weaker hydrodynamic intensity than that of the Sanya-Meishan strata, while the reducibility gradually increases for the water columns of the Yacheng, Lingshui, and Sanya-Meishan strata. In general, the palaeoenvironmental conditions of the water column are the most favorable to the development of the Yacheng organic-rich source rocks. Meanwhile, the Miocene marine source rocks in the deep-water areas of the Qiongdongnan Basin may also have a certain hydrocarbon potential. The differences in the development models of source rocks in various tectonic regions of continental margin basins should be fully evaluated in the exploration and development of hydrocarbons.

Biome responses to a hydroclimatic crisis in an Early Cretaceous (Barremian–Aptian) subtropical inland lake ecosystem, Northwest China

The Early Cretaceous palaeoclimate was characterized by arid–humid alternation and accompanied by a series of short-term extreme environmental events, resulting in significant disturbances to the terrestrial ecosystem. However, the discontinuity of terrestrial geological records leads to a lack of detailed research on the coevolution mechanism of organisms and the environment. This study aims to investigate the response of the late Barremian–early Aptian subtropical lake biome structure to the hydroclimate crisis in the Yin'e Basin based on palynology, macropalaeontology, and geochemistry (i.e., major and trace elements, organic carbon isotopes, and biomarkers). The warm and semihumid climate promoted an increase in the abundance and degree of divergence in the vegetation, and the brackish–oxic conditions of the water column were conducive to the prosperity of aquatic organisms. The early aridification of the climate led to a decline in the lake level and a salinity crisis. The saline–suboxic conditions of the water column triggered the first aquatic crisis, while bacterial populations increased gradually. Cooling and continuous aridification led to a significant reduction in the types and amount of vegetation. The insufficient supply of nutrients and the continuous shrinking of the lake caused a second aquatic crisis, and several macroscopic organisms disappeared. The multivariate correlation analysis based on geochemical parameters showed that the palaeoclimate was the key driving factor for the evolution of palaeolakes and their conditions in the water column, and there was a close relationship among the ecological environmental indicators. The petrological and geochemical parameters suggest the existence of lacustrine hydrothermal activity, which could also have a direct impact on the ecological environment of the lake. This study of the Bayingebi Formation palaeolake in the Yin'e Basin provides a strong example of the close coupling changes in the palaeoclimate and lake ecosystem to understand the continental sedimentary response to Early Cretaceous palaeoclimate warming events.

Seasonal Upwelling Conditions Modulate the Calcification Response of a Tropical Scleractinian Coral

Natural processes such as upwelling of deeper-water masses change the physical-chemical conditions of the water column creating localized ocean acidification events that can have an impact on the natural communities. This study was performed in a coral reef system of an archetypical bay within the Tayrona National Natural Park (PNNT) (Colombia), and aimed to quantify net calcification rates of a foundational coral species within a temporal context (6 months) taking into account the dynamics of seasonal upwelling that influence the study area. Net calcification rates of coral fragments were obtained in situ by the alkalinity anomaly technique in short-term incubations (~2.5 h). We found a significant effect of the upwelling on net calcification rates (Gnet) (p &lt; 0.05) with an 42% increase in CaCO3 accretion compared to non-upwelling season. We found an increase in total alkalinity (AT) and dissolved inorganic carbon (DIC) with decreased aragonite saturation (Ωara) for the upwelling months, indicating an influence of the Subtropical Under Water mass (SAW) in the PNNT coral community. Significant negative correlations between net calcification with temperature and Ωara, which indicates a positive response of M. auretenra with the upwelling conditions, thus, acting as “enhancer” of resilience for coral calcification.

Preventing Mislabeling: A Comparative Chromatographic Analysis for Classifying Medical and Industrial Cannabis.

Gas chromatography (GC) techniques for analyzing and determining the cannabinoid profile in cannabis (Cannabis sativa L.) are widely used in standard laboratories; however, these methods may mislabel the profile when used under rapid conditions. Our study aimed to highlight this problem and optimize GC column conditions and mass spectrometry (MS) parameters to accurately identify cannabinoids in both standards and forensic samples. The method was validated for linearity, selectivity, and precision. It was observed that when tetrahydrocannabinol (Δ9-THC) and cannabidiolic acid (CBD-A) were examined using rapid GC conditions, the resulting derivatives generated identical retention times. Wider chromatographic conditions were applied. The linear range for each compound ranged from 0.02 μg/mL to 37.50 μg/mL. The R2 values ranged from 0.996 to 0.999. The LOQ values ranged from 0.33 μg/mL to 5.83 μg/mL, and the LOD values ranged from 0.11 μg/mL to 1.92 μg/mL. The precision values ranged from 0.20% to 8.10% RSD. In addition, forensic samples were analyzed using liquid chromatography (HPLC-DAD) in an interlaboratory comparison test, with higher CBD and THC content than GC-MS determination (p < 0.05) in samples. Overall, this study highlights the importance of optimizing GC techniques to avoid mislabeling cannabinoids in cannabis samples.

Phytoplankton pigment dynamics in marine lake fluctuating between stratified and holomictic euxinic conditions

Biomass dynamics in the marine lake are strongly dependent on seasonal variability in vertical stratification, indicating rapid adaptation of phytoplankton to short-term changes in the water column. A small marine lake (Rogoznica Lake, Croatia), which fluctuates between stably stratified and holomictic euxinic conditions, was used as a model to study the phytoplankton responses to environmental perturbations, in particular the anoxic stress, caused by periodic holomixia. The epilimnion showed significant temporal and vertical variability with a chlorophyll a subsurface maximum with the highest biomass near the chemocline. Fucoxanthin-containing biomass (diatoms) dominated in the epilimnion in colder seasons and was first to recover after holomictic euxinic events. The shift towards the smaller groups prevailed during highly stratified water column conditions in warmer seasons. Results for the hypolimnion were more enigmatic, with high concentrations of alloxanthin, zeaxanthin, and violaxanthin indicating the presence of a viable small-size mixotrophic community under extreme conditions.

Organic Geochemistry of Carbonate Rocks, Silicites and Black Shales of the Vendian (Ediacaran) Khatyspyt Formation, Northeastern Siberia

Abstract —The paper presents the results of the study of organic geochemistry of carbonate rocks, silicites, and calcareous mudstones of the Vendian (Ediacaran) Khatyspyt Formation in the northeast of the Siberian Platform. The distribution of dispersed organic matter (OM) is shown to be uneven. The formation comprises carbonate-dominated intervals depleted in OM, with total organic carbon content (TOC) &amp;lt; 0.1%, or weakly enriched in OM (TOC up to 0.4%), interstratified with carbonate-shale, carbonate-shale-siliceous, carbonate-siliceous and siliceous intervals enriched in OM (TOC up to 1–4%). There is also a thin-layered calcareous mudstones anomalously enriched in OM (black shales with TOC at 10%) cropping out in the Khorbusuonka River valley (unit thickness 10 cm). The redox conditions in the water column varied during deposition of the Khatyspyt Formation. Certain intervals characterize a stratified water column and euxinic bottom water conditions. During the study, the assessment was conducted of the OM catagenesis and the generative potential of the Khatyspyt Formation. Based on the results of geochemical study and the synthesis of information on the geological structure of sedimentary succession in the northeastern Siberian Platform, the Khatyspyt Formation has been evaluated as one of the hydrocarbon sources for the territory.

A Methodological Proposal for the Management of Submerged Cultural Heritage: Study Cases from Cartagena de Indias, Colombia

This paper proposes a comprehensive methodology for the management of submerged cultural heritage sites despite their worldwide location. The methodology is applied to four colonial shipwrecks located in Cartagena de Indias Bay (Colombia), two of them in the Inner Bay and two in the Bocachica sector. Five criteria are used and scored from 1 (indicating a low risk for the wreck) to 5 (high risk). The sum of the scores obtained at each criterion ranges from 5 to 25, and when the value obtained is higher than 15, management action is required. Five criteria were analyzed; (i) The historical criterion is based on the antiquity of the wreck. The ones investigated in this paper are associated with the Battle of Cartagena de Indias (A.D. 1741), having been submerged for ~280 years (all wrecks obtained a score of 3); (ii) The geographical criterion concerns the depth at which the wreck is located, which determines its accessibility. In Cartagena Bay, wrecks are situated at a water depth between 15.6 and 29.7 m (all wrecks were scored 4); (iii) The shipwreck condition criterion indicates the level of preservation, including organic and inorganic material, distinguishing among wooden hulls, ballast stones, and cannons. Obtained scores were 4 and 3 for the wrecks, respectively, located in the Inner Bay and in the Bocachica sector. (iv) The oceanographic criterion, linked to chemical and biological conditions of the water column, influences wreck conservation. All wrecks investigated scored 5. (v) The socioeconomic criterion indicates the multiple maritime and cultural activities presently taking place that might affect the wreck. In Cartagena Bay, all wrecks were scored 4. According to the total score obtained (20—Inner Bay and 19—Bocachica sector), guidelines for shipwreck conservation of cultural heritage in Cartagena Bay are proposed.

Conceptual design and process construction of [formula omitted]-propyl propionate production by reactive distillation

The purpose of this work is to perform the conceptual design and process construction of n-propyl propionate synthesis by reactive distillation. Firstly, the reaction kinetic and thermodynamic models were summarized. The isobaric vapor-liquid equilibrium data of the binary systems 1-propanol (1) + n-propyl propionate (2) and propionic acid (1) + n-propyl propionate (2) were measured. The UNIQUAC model was used to describe the thermodynamic behavior of this system. Secondly, non-reactive residue curve maps and reactive residue curve maps analyses were used for conceptual design to obtain the preliminary configuration and operating conditions of the reactive distillation column. Finally, the sensitivity analysis was used to evaluate the preliminary process configuration and identify key operational variables.

Coupled vanadium and thallium isotope constraints on Mesoproterozoic ocean oxygenation around 1.38-1.39 Ga

The oxygenation state of the Mid-Proterozoic (1.8 – 0.8 Ga) ocean and atmosphere is heavily debated and has implications for the relationship between environmental O2 and the emergence of complex life. While recent geochemical proxy studies of Mesoproterozoic marine sedimentary rocks inform a picture of deep water redox dominated by widespread ferruginous (iron-rich and anoxic) conditions, a growing number of datasets indicate that short-lived ocean oxygenation events were recurrent features of this time interval. The spatial extent of previously reported Mesoproterozoic oxygen pulses is often unclear as they are predominantly observed via localized environmental proxies. In this study, we use the vanadium (V) and thallium (Tl) isotope paleoredox proxies to provide a global marine redox perspective during a short interval of the Mesoproterozoic. We reconstructed seawater V (δ51VSW) and Tl (ε205TlSW) isotopic compositions from shales from Unit 2 of the 1.38-1.39 Ga Xiamaling Formation (North China craton) that show an up-section shift in average δ51VSW values from 0.02‰ to 0.15‰ and a short-lived perturbation in ε205TlSW from −2.5 to −4.2. Mass-balance models for both isotopic systems are consistent with these isotopic shifts representing an expansion of oxic water column and porewater conditions from a more anoxic (ferruginous) baseline ocean state. The short-lived nature of the ε205TlSW perturbation versus the shift in δ51VSW suggests that environments sufficiently oxygenated to support widespread Mn oxide burial were only established for a fraction of this overall oxic expansion. The ocean residence time of V and Tl requires that this oxygenation event was global in extent and may reflect either a purely oceanic phenomenon such as global deepening of the oxycline, or alternatively, global ocean-atmosphere equilibration during a short-lived episode of elevated atmospheric oxygenation.

Geochemistry and petrology of petroleum source rocks in the Upper Cretaceous Qingshankou Formation, Songliao Basin, NE China

The Upper Cretaceous Qingshankou Formation in the Songliao Basin, NE China is known to contain excellent petroleum source rocks. In addition, it serves as a valuable record to study depositional conditions within the water column and climatic change. In this study, a large set of organic petrography, major and trace element geochemistry, as well as bulk and molecular organic geochemistry data obtained on 38 core samples of the first Member of the Qingshankou Formation (K2qn1) in the south central depression is reported. All rocks are thermally oil-mature, reaching the early to peak oil generation stage, indicated by the vitrinite reflectance (VRr) of approximately 0.8%. Two different types of lacustrine source rocks (units I and II) and two OM-rich layers within unit I are identified in the studied well. Basically, there is a lower unit 1, characterized by lower total organic carbon (TOC) content and an upper unit 2 characterized by higher TOC content. Furthermore, within unit 1, thin marine transgressive layers of approximately 1–2 m were identified. Generally, unit 1 is characterized by the lowest TOC and sulfur contents with average values of 1.31 wt% and 0.56 wt%, respectively. By contrast, unit 2 samples have significantly higher TOC (avg. 2.39 wt%) and sulfur contents (avg. 1.24 wt%). Samples, which represent the postulated marine transgressive events show the highest TOC (avg. 2.82 wt%) and sulfur contents (avg. 2.01 wt%). Unit 1 was mainly deposited in oxic-dysoxic and freshwater-brackish water column conditions based on multiple organic and inorganic geochemical proxies. By contrast, unit 2 and marine transgressive layers were deposited in less oxygenated and more saline environments. Source rocks from the K2qn1 generally show only minor terrestrial organic matter input. However, unit 1, containing type II-III kerogen, shows indications for a slightly more pronounced contribution from terrigenous higher plants than unit 2 and the marine transgressive layers, where the kerogen is almost exclusively derived from planktonic/algal and microbial organic matter. The low TOC content in unit 1 is attributed to multiple adverse factors for organic matter accumulation, including a relatively shallow, oxic-dysoxic, and weakly stratified water column and high dilution by terrigenous mineral matter. By contrast, more favorable conditions persisted during the deposition of marine transgressive layers and unit 2, e.g., a more reducing and stratified water column and lower dilution by terrigenous mineral matter.