Low Sedimentation Rates Research Articles

Erosion-free rheumatoid arthritis: clinical and conceptional implications—a BARFOT study

BackgroundBone erosions may appear early or later during rheumatoid arthritis (RA), causing joint damage and functional impairment. However, in some patients erosions do not occur, even after several years of disease. This study evaluates the prevalence, clinical relevance and possible predictors of erosion-free RA.MethodsSix hundred and eight patients from an early RA cohort (BARFOT) having radiographs of hands and feet at inclusion and after 1, 2, 5 and 8 years were studied. Clinical and functional assessments were performed on all these time-points.ResultsIn all, 144 patients (24%) did not develop erosions up to 8 years follow-up (Never erosive group), while 464 patients (76%) had erosions on one or more assessments (Ever erosive group). At diagnosis, the patients in the Never erosive group were significantly younger, satisfied fewer ACR criteria, and were less frequently RF- and/or anti-CCP- positive compared with those in the Ever erosive group. The Never erosive patients had consistently more tender joints, lower erythrocyte sedimentation rate (ESR) and, from two years and onwards, fewer swollen joints. Absence of rheumatoid factor (RF) and/or anti-CCP were strong independent predictors for erosion-free disease. The erosion-free patients were less frequently treated with DMARDs and/or prednisolone.ConclusionsOne-quarter of the patients was erosion-free during eight years in this early RA cohort. Erosion-free patients had a less severe disease course as to disease activity and were more often seronegative compared with those with erosive disease. The results suggest that non-erosive RA represents a milder form of RA.

Analysis of the factors affecting mortality after non-traumatic major lower extremity amputations.

The aim of this study was to evaluate the prognostic factors affecting mortality after major lower extremity amputations in patients with diabetes mellitus and peripheral vascular disease. For this retrospective study, 484 patients (345 male, 139 female) who were previously diagnosed with diabetes mellitus and peripheral vascular disease and underwent first-time nontraumatic major lower extremity amputations between January 2008 and January 2021 were included. The mean age of the patients was 64.2 ± 13.8 (20-114). In 32.4% of patients, peripheral vascular disease was the underlying cause, whereas diabetes mellitus was responsible for the etiology in 67.6% of patients. About 68.8% of patients had below-knee amputations, whereas 2.9% had bilateral below-knee amputations, 27.1% had above-knee amputations, and 1.2% had hip disarticulation performed. Gender, age, amputation level, amputation etiologies, Charlson comorbidity index, need for blood transfusion, and laboratory findings such as hemoglobin, platelet, albumin, erythrocyte sedimentation rate, C-reactive protein, sodium, potassium, and neutrophil to lymphocyte ratio levels were recorded preoperatively and at the time of discharge. Patients were grouped as died ≤1 month, ≤3 months, ≤6 months, and ≤12 months or alive. Advanced age, female gender, high Charlson comorbidity index, blood transfusion requirement, proximal amputation level, preoperative low platelet, preoperative low albumin, and parameters such as low hemoglobin, low erythrocyte sedimentation rate, high sodium, low platelet, low albumin, high C-reactive protein, and high neutrophil to lymphocyte ratio at time of discharge were seen to have a statistically significant effect on mortality at 1 month, 3 months, 6 months, and 12 months postoperatively. Preoperative high C-reactive protein had a statistically significant effect on mortality at 1 and 3 months postoperatively, whereas low C-reactive protein had a statisti cally significant effect on mortality at 6 months postoperatively. High potassium at the time of discharge was associated with mortality at 6 and 12 months postoperatively. This study has shown us that mortality rates are affected by modifiable parameters at the time of discharge such as hemoglo bin, sodium, potassium, platelet, and albumin, and normalization of these parameters before discharge could reduce the rates of mortality in the postoperative period. Level IV, Prognostic Study.

Seasonal variations in surface processes and hydroclimate on an alpine lake, NE Tibetan Plateau

Koucha Lake, located in Qinghai Province, north-eastern Tibetan Plateau (NETP) at an elevation of 4530 m a.s.l. Occupies an ideal position to investigate the seasonal hydroclimatic variations and related surface processes during the Holocene. We re-investigated the lake and analysed a new sediment core from the deepest part of the lake. Grain size measurements and related endmember modelling analyses (EMMA) in combination with ostracod associations together with geochemical parameters and mineral compositions from core sediments were used as relevant proxies for hydro-climatic reconstruction.A comparison of δ18O/δD from various waters on the NETP indicates a clear depleted isotopic signature of non-monsoon moisture supply in comparison to summer rainfalls, highlighting the summer evaporation for δ18O enrichment, as a reference for interpreting δ18O values from lake sediments for various situations of hydrological balance. Based on the individual core chronology the multi-proxy data indicate a very low sedimentation rate over the entire period in accordance with the catchment topography and the absence of well-developed and constant river systems, limiting the flux of sediment supply to the lake. Thus, Koucha Lake remains almost a closed system since the Lateglacial, except for the early mid-Holocene part of the sequence. The coarser particle components and their representative endmembers for spring flood and permafrost thaw between 11.9 and 10.1 cal Ka BP and from 4.5 to ca. 1.0 cal Ka BP point to lower lake levels, influenced by long winter duration with dry summer interruptions, and lighter oxygen isotopes were preserved at low evaporations. Fine-grained sediments supplied by permafrost thaw associated with activating summer surface erosion led to lake level rise between 10.1 and 4.5 cal Ka BP and during the last 1000 years, with a maximum during 7.6–7.1 cal Ka BP. Their enriched δ18O values indicate extended summer duration and concomitant evaporation enhancement, albeit a positive hydrological balance. We suggest that the interannual latitudinal shifts of the intertropical convergence zone (ITCZ) and westerly Jet and attendant varying monsoon rain belt locations are responsible tracers for the variation of the hydrological budget of the lake and the variable spatio-temporal precipitation patterns in humid and (semi) arid regions in China.

The Holocene environmental changes revealed from the sediments of the Yarkov sub-basin of Lake Chany, south-western Siberia

Lake Chany is the largest endorheic lake in Siberia whose catchment is entirely on the territory of Russia. Its geographical location on the climate-sensitive boundary of wet and dry landscapes provides an opportunity to gain more knowledge about environmental changes in the West Siberian interior during the Holocene and about the evolution of the lake itself. Sediment cores obtained from the Yarkov sub-basin of the lake in 2008 have been comprehensively studied by a number of approaches including sedimentology and AMS dating, pollen, diatom and chironomid analyses (with statistical interpretation of the results), mineralogy of authigenic minerals and geochemistry of plant lipids (biomarker analysis.). Synthesis of new results presented here and published data provides a good justification for our hypothesis that Lake Chany is very young, no older than 3.6 ka BP. Before that, between 9 and 3.6 ka BP, the Chany basin was a swampy landscape with a very low sedimentation rate; it could not be identified as a water body. In the early lake phase, between 3.6 and 1.5 ka BP, the lake was shallow, 1.2–3.5 m in depth, and it rose to its modern size, up to 6.5 m in depth, during the last millennium. Our data reveal important changes in the understanding of the history of this large endorheic lake, as before it was envisioned as a large lake with significant changes in water level since ca. 14 ka BP. In addition to hydrology, our proxies provide updates and details of the regional vegetation and climate change since ca. 4 ka BP in the West-Siberian forest-steppe and steppe. As evolution of the Chany basin is dependent on hydroclimatic changes in a large region of southern West Siberia, we compare lake-level change and climate-change proxies from the other recently and most comprehensively studied lakes of the region.

Onychocellidae (Bryozoa) from the Maastrichtian Kallankurichchi Formation, Ariyalur Group, southern India

Onychocellidae (Bryozoa, Cheilostomatida) are one of the dominant components of the cheilostomatid bryozoan fossil assemblage in the Kallankurichchi Formation of the Ariyalur Group, Cauvery Basin, South India. The present study describes and illustrates eleven species of Onychocellidae from the sedimentary deposits of this formation. Among these, ten species are already known from these deposits, while one species is left in open nomenclature. Bryozoan fauna thrived during transgressional period indicating shallow marine environment and low sedimentation rate.

Challenging Radiocarbon Chronostratigraphies in Central Arctic Ocean Sediment

AbstractBased on the analysis of fish otolith assemblages from surface sediments of the Lomonosov Ridge (Arctic Ocean), we demonstrate that the very low Holocene sedimentation rates and winnowing of fine sediments result in the mixing of the whole Holocene populations at the sediment surface. Specimens from the Marine Isotope Stage (MIS) 3 or older could even be recovered in the surface due to a sedimentary hiatus at some locations in the central Arctic during the last glacial maximum. Two examples illustrate that 14C‐stratigraphies from planktic foraminifers in underlying cored sediments reflect the mixing between Holocene and MIS 3 or older populations, thus invalidating continuous age‐depth inferences based on 14C ages. Hence, much caution is required when attempting to set paleoceanographic reconstructions based on 14C chronologies in a low sediment accumulation rate environment such as the central Arctic Ocean. Already published paleoceanographic reconstructions from this area might thus require some revisions.

Paleoenvironmental conditions over the Caribbean Large Igneous Province during the Late Cretaceous in NW of South American Margin: A sedimentological and ichnological approach

The Late Cretaceous in northwest South America was a period marked by synchronous regional geological processes (e.g., accretion of oceanic terranes, arc magmatism, sea-level fluctuations, oceanographic dynamics), related to the interaction of the Caribbean Large Igneous Province (CLIP) with the NW margin of South America. This synchroneity makes it difficult to reconstruct the complex geological evolution of this region. In Colombia, Upper Cretaceous marine sedimentary and low-grade metamorphic rocks are commonly exposed in both the Western Cordillera and the Sinú-San Jacinto Basin in the Pacific and Caribbean regions respectively. Significant deformation and structural complexity are the main limiting factors for sedimentological and paleontological studies of these deposits.Detailed sedimentological and ichnological analyses were carried out in eight sections, two in the Caribbean region and six in the Pacific region. The Caribbean sections are composed of limestones, mudrocks, siliceous and calcareous mudrocks, and cherts, associated with pelagic and hemipelagic deposits (E2.2 and G2.1 facies). The Pacific sections are characterized by two facies associations, one composed of mudrocks, limestones, as well as chert associated with pelagic and hemipelagic deposits (E2.2 and G2.1 facies) and the other of interlayered siliceous mudrocks and sandstones associated with turbiditic systems (C2 facies). Upper Cretaceous deposits in both regions are characterized by relatively low to moderate abundant and diverse trace fossils assemblages, consisting of Chondrites, Planolites, and Zoophycos in the Caribbean region and Chondrites, ?Nereites, Phycodes, Phycosiphon, Planolites, Thalassinoides, and Zoophycos in the Pacific region, assigned to the Zoophycos ichnofacies. Sedimentological and ichnological features suggest deposition in deep-marine environments characterized by pelagic, hemipelagic, and turbiditic sedimentation. Integrated with the biostratigraphical framework, this allows us to establish a regional correlation between both regions. High nutrient supply, poor oxygenation, and low hydrodynamic energy and sedimentation rates interrupted by episodic increases associated with turbiditic deposits are main paleoenvironmental factors controlling the sedimentation over the CLIP during Late Cretaceous.

Caracterización geoquímica y geomecánica de la Formación Mungaroo, offshore del noroeste de Australia

The geochemical characterization of the Mungaroo Formation rocks shows the presence of kerogen type II/III and III which characterizes the Exmouth Plateau sub-basin as a gas prone basin. Using 13 burial histories constructed from well data, we identified three tendencies: One with high sedimentation rates between the Middle Triassic and Upper Triassic (69.3-95.3 m/Ma), another one with high sedimentation rates between the Lower and Upper Cretaceous (67-158 m/Ma), and the last one with low sedimentation rates (18-40 m/Ma) during the Upper Cretaceous until present time. All these trends defined active generation zones (or gas kitchens) between 2,000 and 4,400 km2. High sedimentation rates during the Cretaceous and Triassic times were key to the burial history of the Mungaroo Formation because they allowed these rocks to reach the required depths to transform its organic matter. In contrast, in the area with low sedimentation rates, radiogenic heat flow was the trigger for the transformation of the organic matter. The generation/expulsion of hydrocarbons from these shales occurs since 100 My, consequently explaining the large gas accumulation found in the sub-basin. Currently, the Mungaroo formation is in the gas generation window at depths of 4,500 to 5,500 m below sea level. The shales of this formation show TOC% values higher than 2% reaching the gas generation zone (Ro% >1.3) and suggesting its potential as an unconventional gas reservoir. However, geomechanical features such as low fragility, under pressure, and thickness, condemns its unconventional potential.

Prediction of radiographic progression pattern in patients with ankylosing spondylitis using group-based trajectory modeling and decision trees.

This study aimed to identify trajectories of radiographic progression of the spine over time and use them, along with associated clinical factors, to develop a prediction model for patients with ankylosing spondylitis (AS). Data from the medical records of patients diagnosed with AS in a single center were extracted between 2001 and 2018. Modified Stoke Ankylosing Spondylitis Spinal Scores (mSASSS) were estimated from cervical and lumbar radiographs. Group-based trajectory modeling classified patients into trajectory subgroups using longitudinal mSASSS data. In multivariate analysis, significant clinical factors associated with trajectories were selected and used to develop a decision tree for prediction of radiographic progression. The most appropriate group for each patient was then predicted using decision tree analysis. We identified three trajectory classes: class 1 had a uniformly increasing slope of mSASSS, class 2 showed sustained low mSASSS, and class 3 showed little change in the slope of mSASSS but highest mSASSS from time of diagnosis to after progression. In multivariate analysis for predictive factors, female sex, younger age at diagnosis, lack of eye involvement, presence of peripheral joint involvement, and low baseline erythrocyte sedimentation rate (log) were significantly associated with class 2. Class 3 was significantly associated with male sex, older age at diagnosis, presence of ocular involvement, and lack of peripheral joint involvement when compared with class 1. Six clinical factors from multivariate analysis were used for the decision tree for classifying patients into three trajectories of radiographic progression. We identified three patterns of radiographic progression over time and developed a decision tree based on clinical factors to classify patients according to their trajectories of radiographic progression. Clinically, this model holds promise for predicting prognosis in patients with AS.

Circadian as a prognostic factor for radiation responses in patients with cervical cancer: A nested case‑control study.

The radiation response of cervical cancer is thought to be enhanced by the levels of melatonin due to its roles in the circadian cycle and cancer growth. In the present study, the roles of circadian rhythms and melatonin levels as prognostic factors for predicting the radiation response in patients with cervical cancer were examined. In this nested case‑control study, patients with good and poor responses to radiotherapy were assessed in terms of the time‑of‑day radiation treatment was administered and further influencing factors. The radiation time was determined, as the subjects were either irradiated in the morning (06.00‑10.00am) or afternoon (04.00‑06.00pm). Data on tumour size and other biological parameters were collected and analysed by binary logistic regression. Among the 56patients examined, most subjects had good radiation responses. Most patients were <50years old with an initial body weight of >50kg, no pain prior to radiation, low erythrocyte sedimentation rates, normal intravenous urography results, moderate or good differentiation on pathology and histo‑pathologically non‑keratinised cells. According to the multivariate analysis, the irradiation time as a surrogate of the circadian cycle (morning vs. afternoon), the initial haemoglobin(Hb) level and the clinical tumour size were significant predictors of the radiation response. The circadian cycle, tumour size and Hb levels may affect the radiation response in patients with cervical cancer. In addition, the morning group had better 5‑year overall survival, but it was not significant, possibly due to the small cohort size. Further research is required to identify more relevant prognostic factors using different radiotherapy techniques [National Clinical Trial (NCT) no.NCT05511740, registration date, 08/20/2022].

Maturation stages of glauconites: A combined electron microprobe, Raman, and thermogravimetric study

Glauconite mineral is one of the most sensitive indicators of low sedimentation rate in the marine environment. The time of residence of glauconites at the sea bottom before burial is reflected by their so-called maturity that is differentiated based on their K2O content.The present work aims to investigate the evolution of glauconites during the transition toward the highly evolved level. Complementary electron microprobe, Raman, and Thermogravimetric analysis were performed on glauconitic grains from the Belluno basin (N Italy) with different K2O content in order to verify whether the level of glauconites evolution affects the results of these surveys.The obtained results show that Raman spectra are sensitive to the grade of glauconite maturations. First, spectra of mature glauconites are more structured, due to the lower degree of Al substitution in the octahedral sites.Moreover, the position of the strongest Raman peak (Si–Ob–Si mode) at ∼700 cm−1 shows two contrasting behaviors in the early (K2O <8%) and late (K2O> 8%) stages of glauconites maturation, respectively. TGA measurements reveals that the presence of interlayer water is also related to the state of glauconites maturations. The obtained results were explained in the light of different isomorphic substitutions occurring at octahedral level in the mature and non-mature glauconites, thus allowing to obtain a deeper insight onto the mechanism of glauconites evolution.

Trends in organic matter deposition in the Cretaceous of the eastern Mediterranean: Revisiting and updating the chronology and facies of the Eratosthenes Seamount deposits

In this study we revisited the Cretaceous of the Eratosthenes Seamount (ESM) from IODP LEG 160 Hole 967E, updating the chronology, depositional environment, and paleobathymetry of the ESM. Our goal was also to address the spatio-temporal distribution of organic matter and, by comparison with the eastern margins of the Levant Basin, discuss basin-wide controls on its deposition and preservation.The investigated core has a relatively continuous Cretaceous succession from the Aptian to the Danian. By identifying the Pα Zone we conclude that the base of the Paleocene is included in the 967E section. A total of 17 ages were identified, with low sedimentation rates of 0.04–2.37 cm/kyr. Petrographic analysis revealed pronounced differences, from micritic pellets, benthic foraminifera, algae, and mollusks in the bottom part of the core, to deep water facies in the uppermost Cretaceous. Paleobathymetry ranged between 0.5 and 5 m in the Aptian to 300–600 m in the Maastrichtian.Both high productivity and OMZ conditions prevailed during the Cenomanian–Turonian, as well as elsewhere in the eastern Mediterranean. While the low core recovery might affect reliable interpretation, we present two alternative explanations for the high vs. low organic content of the Campanian–Maastrichtian in the eastern Levant Basin vs. the ESM: (1) Location relative to upwelling cells; (2) Relative bathymetry, with the ESM representing a paleohigh for much of the Cretaceous, similar to the organic-poor anticline deposits in the eastern Levant, where the massive intervals of organic-rich carbonates accumulated only in the synclines of the Syrian Arc deformational belt.

Enrichment and sources of REY in phosphate fractions: Constraints from the leaching of REY-rich deep-sea sediments

Rare earth elements and yttrium (REY)-rich deep-sea sediments, regarded as a potential resource, have triggered extensive investigations over the last decade. The conclusion that the REY enrichment is closely related to the phosphate components contradicts the low REY content (ΣREY) of marine phosphorites, leading to questions about the control of deep-sea phosphate on the enrichment and cycling of REY. Herein, we performed a series of chemical leaching experiments on a group of REY-rich samples (up to 5983 ppm) from two sediment cores obtained from the Pigafetta Basin in the western Pacific to investigate the phosphate and non-phosphate fractions. We found that phosphate components in deep-sea sediments, termed REY-rich phosphates, contain a mean ΣREY of 27,635 ppm and ΣREY/P2O5 of >0.75, which are 1–2 orders of magnitude higher than that of marine phosphorites. The 87Sr/86Sr (0.7083–0.7092) and εNd (–6.41 to –5.15) of the phosphate fractions exhibited strong terrigenous attributes and fell within the range of that of bottom water since 25 Ma. Notably, the non-phosphate components, primarily phillipsite and clay, exhibited stronger terrigenous attributes, confirming extremely low sedimentation rate in the study area. The development and accumulation of REY-rich phosphate, as a consequence of low sedimentation rate in deep water together with erosion and sorting by bottom current, control the content and patterns of REY in deep-sea sediments. Fe-Mn oxides that migrated to the seafloor from the water column were limited and consumed less REY, although their strong Ce enrichment led to the loss of Ce in seawater. The phosphate components in sediments inherited the primary REY pattern of seawater and became the major REY budget on the seabed. In this study, we propose that the mineralization during the sinking of biological particles not only controls the REY distribution in the water column but also becomes an important REY source migration to the seabed and rapidly releases at the sediment–water interface. Consequently, REY can be effectively concentrated by the phosphate components under low sedimentation rates, yielding weak fractionated seawater REY patterns with lower Y/Ho ratios.

Organic matter enrichment of the Late Triassic Bagong Formation (Qiangtang Basin, Tibet) driven by paleoenvironment: Insights from elemental geochemistry and mineralogy

The Upper Triassic dark mudstones in the Qiangtang Basin are key source rocks for petroleum exploration. However, the factors controlling organic matter enrichment in these dark mudstones remain unclear, especially for pro-deltaic core mudstones, which inhibit source rock distribution predictions. Well QZ-7 contains several Upper Triassic dark mudstone intervals (marked by A to G) with total organic carbon (TOC) contents of 0.57–2.73% (avg. of 1.13%). The TOC contents in intervals A, C, E, and G are generally higher than those in intervals B, D, and F. Here, detailed mineralogical and geochemical analyses of these dark mudstones are analyzed to address the organic matter enrichment mechanism. Paleosalinity, redox, detrital influx, sedimentation rate, and productivity proxies suggest that these dark mudstones were deposited in a brackish-salt and anoxic-dysoxic water environment with low detrital influx, sedimentation rate, and primary productivity. Organic-rich intervals of A, C, E, and G generally show higher salinity, lower oxygen levels, detrital influx, and sedimentation rates than the organic-poor intervals of B, D, and F. The significant positive correlations of TOC with paleosalinity proxies and redox indices indicate that anoxic and stratified high-salinity water columns primarily controlled organic matter preservation. The significant negative correlations between TOC and detrital influx proxies and moderate negative correlation between TOC and (La/Yb)N suggest that increasing detrital influxes diluted organic matter, while a low sedimentation rate promoted organic matter preservation. The effect of primary productivity on organic matter enrichment was limited, as evidenced by the weak correlation between TOC and P/Ti.

Clinical Profile and Short-Term Outcome of Cerebral Venous Thrombosis in a Nepalese Population: A Retrospective Study

Introduction: Cerebral venous thrombosis (CVT) is a rare cause of stroke. The increased awareness among the physicians and the suspiciousness of the myriad of its clinical presentation with increased availability of investigation modules and therapeutic options has led to a decrement of mortality and morbidity. The study intends to assess the clinical etiological profile of patients of CVT and also to assess short-term outcomes and if any factors are associated with it. Methods: It was a hospital-based retrospective, observational cross-sectional study at a tertiary care center in Kathmandu among adult CVT patients from August 2019 to August 2021. Clinical, etiological, and radiological data, the outcome at discharge, and any factors influencing this were assessed where possible. Data were analyzed using SPSS 25 software. Analysis of the descriptive data was performed and independent factors influencing short-term outcome (admission date &lt; 7 days) were analyzed. Results: There were a total of 15 cases included in the study. The study showed female predominance (66.7%. The mean age of the patients was 48.87 years. Four (26.7%) patients had hypertension. The history of oral contraceptive pill (OCP) use was among five (33.33%) females. A significant association was present with direct signs in CT scan (p=0.02), and low erythrocyte sedimentation rate (ESR), p= (0.02). Conclusions: OCP and hypertension are increasingly recognized as independent risk factors for CVT. The presence of direct signs in the CT head and the presence of high ESR have independent predictive value in assessing short-term outcomes.

Effect of survey parameters on unmanned aerial vehicles-derived topography for coastal dune monitoring

Coastal dunes are fragile ecosystems emerging at the interface between marine and continental environments. They provide multiple services, among which are the protection against the impact of storms and the hosting of diverse and unique species of fauna and flora. However, changes in the topography or biological component of these systems may endanger the perpetuation of service provision. Topographic changes within dunes can significantly differ in magnitude depending on the type of process (i.e., marine or aeolian) and the temporal scale of analysis (event to annual scale), making their monitoring a challenging task. In recent years, unmanned aerial vehicles (UAVs) have been increasingly used to monitor coastal dunes, proving to be a cost-efficient methodology for the collection of topographic data. Yet, the application of UAVs in combination with the structure from motion approach to obtain digital surface models (DSMs) presents some limitations related to the level of accuracy provided for the evaluation of topographical changes in dunes with low sedimentation rates. This work explores different survey configurations using UAVs flying at low altitudes with the aim of obtaining high-quality DSMs with vertical accuracies preferably around or lower than 0.04 m. Several tests were performed to evaluate the influence of different parameters on the accuracy of the DSM, including flight altitude and orientation, density and spatial distribution of ground control points (GCPs), terrain slope, vegetation cover, and sun-related parameters. The results indicate that the intended accuracies can be obtained by combining overlapped perpendicular flights, GCPs distributed regularly following a diamond grid, with densities of at least 6 GCPs per hectare, sun altitudes between 30 and 40 deg, and a total solar radiation per hour between 1750 and 2250 KJ / m2. In addition, better results were obtained across gentle slope areas, suggesting the eventual need to adapt to the particularities of each site to ensure the accuracy.

Palaeosedimentary Environment and Formation Mechanism of High-Quality Xujiahe Source Rocks, Sichuan Basin, South China

AbstractTriassic Xujiahe source rocks, the main gas source of shallow tight gas, are the most typical continental coal-bearing source rocks in the Sichuan Basin, South China. However, the organic matter enrichment section cannot be identified easily, leading to limited progress in the exploration of coal-bearing tight gas. This paper reveals the main controlling factors of the organic matter enrichment, reconstructs the evolution process of the Xujiahe palaeosedimentary environment, proposes a dynamic enrichment mechanism of the organic matter, and determines the organic matter enrichment section of the high-quality coal-bearing source rocks by geochemical characteristics of the source rocks, major elements, and trace elements. The results show that the Xujiahe sedimentary environment can be divided into a fluctuating stage of transitional sedimentation, stable stage of transitional sedimentation, fluctuating stage of continental sedimentation, and stable stage of continental sedimentation. The Xujiahe source rocks were featured with high-quality coal-bearing source rocks with high total organic carbon and maturity and good parent material in the stable stage of transitional sedimentation and fluctuating stage of continental sedimentation, in which the water was connected with the Palaeo-Tethys Ocean with abundant terrestrial organisms. The water was shallow in the fluctuating stage of transitional sedimentation with a low sedimentation rate, leading to poor organic matter enrichment. The Palaeo-Tethys Ocean withdrew westward from the Yangtze plate in the late period of the fluctuating stage of continental sedimentation, leading to the absence of algae and dinosteranes and a decrease in biological productivity in the stable stage of continental sedimentation. Therefore, high terrestrial inputs and biological productivity and high sedimentation rate were conducive to the organic matter preservation in the coal-bearing source rocks.

Bioturbation supplying young carbon into West Antarctic continental margin sediment

Accelerator Mass Spectrometry (AMS) 14C dating is a widely applied method for establishing high-precision chronologies used to underpin late Quaternary paleoclimatic studies. Feedbacks associated with Antarctic Ice Sheets (AIS) and Southern Ocean variance are thought to have played a critical role in regulating past global climate changes since the Last Glacial Maximum. However, determining the exact role of the AIS and Southern Ocean in these changes has proven difficult because of the sparse occurrence of biogenic carbonate suitable for AMS 14C dating in Antarctica. Consequently, AMS 14C dating is often measured on acid insoluble organic matter (AIOM) from bulk sediment samples, which are often biased towards ages that are older than the depositional age, due to pervasive reworking of old carbon. In this scenario, ages can still potentially provide maximum deposition ages, but such interpretations need to be assessed carefully. Here, we document AIOM and foraminifer AMS 14C dates at the same depth intervals from Antarctic continental margin cores, and we find AIOM AMS 14C dates can range between 2000 and 16,000 years younger than those of foraminifera samples. The younger AIOM 14C dates were found in bioturbated sedimentary facies, which often have extremely low sedimentation rates in Antarctica. In cores with low sedimentation rates, the down sediment contribution of organic carbon from macro-benthos can be quite significant in the sediment column with low organic carbon concentration. After considering possibilities of contamination, foraminifer reworking, and remineralization of secondary carbonate to explain this offset, we conclude that bioturbation plays an important role in the Antarctic carbon cycle as a young carbon supplier to depth into the sediment column. This has clear implications for using condensed sedimentary sections to date post-LGM records in Antarctica. These bioturbation processes also have implications for novel radiocarbon dating methods that have recently been developed to overcome sediment reworking processes and more accurately constrain timing of past AIS retreat, including ramped pyrolysis and compound specific isotopes methods.

Devonian to Carboniferous continental-scale carbonate turnover in Western Laurentia (North America): upwelling or climate cooling?

The Devonian to Carboniferous (DC) transition coincided with a green-to-ice house climatic shift, anoxia, disappearance of lower latitude carbonate banks, and turnover from warm-to-cool water carbonate factories. In western Laurentia, the switch to carbonate factories dominated by cool-water biota was contemporaneous with a tectonically driven palaeogeographic change. To investigate this depositional shift and infer the relative impact of climate vs tectonics, a continental-scale sedimentological and geochemical study was conducted on twelve stratigraphic sections of DC strata from western Canada to southern Nevada (USA). The spatial–temporal distribution of microfacies records the turnover from [i] a Famennian lime mud-rich, shallow warm-water carbonate ramp with low sedimentation rates, mesotrophic conditions and tabular geometry to [ii] Tournaisian to Viséan lime mud-depleted and grainstone dominated cool-water carbonate ramp with anomalous high sedimentation rates, oligotrophic conditions and a pronounced slope. Positive excursions of δ18Ocarb (+ 2‰ V-PDB) and δ13Ccarb (+ 4‰ V-PDB) of Lower Mississippian carbonates likely correspond to the first cooling peak of the Carboniferous-Permian icehouse climate, following carbon withdrawal during black shale deposition during the late Famennian and early Tournaisian. However, late Tournaisian return of photozoan elements and their persistence throughout the Viséan suggests that warmer surface water existed, revealing a decoupling of the lower latitude ocean and the atmosphere. Shoaling of the thermocline was likely a result of cold-water upwelling along an open coast, as the Antler orogen no longer provided an oceanic obstruction to the west. This study shows that carbonate platforms are more susceptible to regional changes than global shifts.

Coleolus carbonarius Demanet, 1938 (incertae sedis) from the late Bashkirian (Carboniferous) of the Donets Basin

Problematic fossils Coleolus carbonarius Demanet, 1938 were described from seven localities of the Mospyne Formation (late Bashkirian, Carboniferous) of the central Donets Basin. Many authors attributed these conoidal fossils to various groups of animals, including worms, conulariids, pteropods, hyoliths, tentaculitids, gastropods, scaphopods, and other molluscs without specifying the class, as well as phyllocarids. Representatives of the genus Coleolus cannot belong to the scaphopods because the apex of their tube is closed. The aperture of the tube in living Coleolus is directed upwards, while in scaphopods it is directed downwards. The belonging of Coleolus to pteropods was challenged by previous authors. The assignment of Coleolus to Coniconchia is also incorrect, because the shells of Coniconchia have chambers, which are absent in Coleolidae. The ecological and some morphological characteristics of Coleolus indicate their proximity to sedentary polychaete annelids (Sedentaria) or phoronids (Phoronida). Almost all Coleolus remains come from sediments that formed in a shallow marine environment with a low sedimentation rate and contamination of the bottom silt and, possibly, the bottom layer of the water column with hydrogen sulphide. Coleolus carbonarius, according to all of the obtained data, was a semi-infaunal animal. The apical end of the tube was deeply immersed into the semi-liquid clayey silt. Only a small part of the tube protruded above the surface. The characteristic transverse ornament of the tube surface, possibly, increased the contact area of the unstable semi-liquid clayey silt and the tube and further stabilized the vertical position of the animal in the bottom sediment. The sedentary lifestyle of Coleolus apparently suggests that these animals fed on planktonic organisms and organic detritus suspended in the water column. This type of feeding is possible only in the presence of a developed hunting apparatus. The morphology of the tubes of Coleolus carbonarius Demanet, 1938 is described in the article, including the structure of their apical end and aperture. Traces of damage caused during the lifetime of animals on the apical part of their tube are also studied.