Sedimentation Rates Research Articles

The potential influence of drains on the recent sediment characteristics and sedimentation rates of Lake Qarun, Western Desert, Egypt

The potential influence of drains on the recent sediment characteristics and sedimentation rates of Lake Qarun, Western Desert, Egypt

The evolution of the Maya coastal landscape in the Mexican Caribbean during the last 6200 years

The modern configuration of tropical coastlines is a result of changes in sea level and regional hydroclimates during the Holocene. In some regions, such as the Yucatan Peninsula, human occupation has also played an important role in defining coastal dynamics. We use a multiproxy analysis of a 6200-year-long sedimentary record from La Encantada lagoon, located near the Bay of Chetumal, Mexican Caribbean, to reconstruct local and regional environmental dynamics. By characterizing the record in terms of pollen and charcoal content, and geochemical composition, we aim to determine the relative importance of sea level rise, long term trends of moisture availability, and anthropic influences in the evolution of the Mayan coastal landscape. Our findings indicate a dominance of marine influences between ∼6200 and 5000 cal yr. BP, probably resulting from the rapidly rising sea level. During this time, whereas the water column was brackish, fluvial dynamics seem characterized by high erosion and the development of riparian mangroves. The geochemical record indicates a millennial-scale trend towards drier conditions, likely associated with the southward migration of the Intertropical Convergence Zone through the Holocene. This trend is also reflected in a progressive increase in the abundance of deciduous taxa in the vegetation. Centennial-scale climatic dynamics, on the other hand, seem associated with variability of the North Atlantic Subtropical High. Anthropogenic influence is evident around ∼5000 cal yr. BP, when local fires became more frequent and riparian mangroves were depleted. Taxa associated with human influence substantially increased at ∼3600 cal yr. BP, coinciding with an erosion increase indicated by the geochemical record. At ∼2200 cal yr. BP, anthropic disturbance indicators decrease, suggesting a potential role of modified agricultural practices to control soil erosion. The last ∼1000 years have been characterized by a decline of agricultural activity and a recovery of the riparian mangroves, suggesting modern vegetation is a result of forest recovery during the last millennium. Overall, our results show that sea level rise and changes in the regional hydroclimate modulate the evolution of the regional landscape, particularly through influences on the sedimentation rates. However, human occupation represents an overpowering influence that can modulate processes associated with natural forcings.

Maximum respiration rates in hyporheic zone sediments are primarily constrained by organic carbon concentration and secondarily by organic matter chemistry

Abstract. River corridors are fundamental components of the Earth system, and their biogeochemistry can be heavily influenced by processes in subsurface zones immediately below the riverbed, referred to as the hyporheic zone. Within the hyporheic zone, organic matter (OM) fuels microbial respiration, and OM chemistry heavily influences aerobic and anaerobic biogeochemical processes. The link between OM chemistry and respiration has been hypothesized to be mediated by OM molecular diversity, whereby respiration is predicted to decrease with increasing diversity. Here we test the specific prediction that aerobic respiration rates will decrease with increases in the number of unique organic molecules (i.e., OM molecular richness, as a measure of diversity). We use publicly available data across the United States from crowdsourced samples taken by the Worldwide Hydrobiogeochemical Observation Network for Dynamic River Systems (WHONDRS) consortium. Our continental-scale analyses rejected the hypothesis of a direct limitation of respiration by OM molecular richness. In turn, we found that organic carbon (OC) concentration imposes a primary constraint over hyporheic zone respiration, with additional potential influences of OM richness. We specifically observed respiration rates to decrease nonlinearly with the ratio of OM richness to OC concentration. This relationship took the form of a constraint space with respiration rates in most systems falling below the constraint boundary. A similar, but slightly weaker, constraint boundary was observed when relating respiration rate to the inverse of OC concentration. These results indicate that maximum respiration rates may be governed primarily by OC concentration, with secondary influences from OM richness. Our results also show that other variables often suppress respiration rates below the maximum associated with the richness-to-concentration ratio. An important focus of future research will identify physical (e.g., sediment grain size), chemical (e.g., nutrient concentrations), and/or biological (e.g., microbial biomass) factors that suppress hyporheic zone respiration below the constraint boundaries observed here.

Determination of tetrabromobisphenol A and its brominated derivatives in water, sediment and soil by high performance liquid chromatography-tandem mass spectrometry.

Tetrabromobisphenol A (TBBPA) was typical brominated flame retardant and potential environmental endocrine disruptor, and it had persistence, bioaccumulation and chronic toxicity. Simultaneous determination of ultra-trace TBBPA, tribromobiphenol A (tri-BBPA), dibromobiphenol A (di-BBPA), monobromobisphenol A (mono-BBPA) and bisphenol A (BPA) was developed by high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS), the parent ion charge ratios (m/z) had been optimized. The linear range was wider and the limit of detection was (LOD) 0.09 ~ 0.21ngmL-1, which could detect trace pollutants. The extraction efficiency was improved by optimizing the parameters, HLB cartridge was used in the water sample by solid phase extraction (SPE), the recovery rates in water samples were over 80.28% with three concentration levels, the relative standard deviations (RSD) were less than 7.12%, and the minimum detection limit of the method was 0.90 ~ 2.10 × 10-3ngmL-1. Soil and sediment samples were extracted by accelerated solvent extraction (ASE), the recovery rates in soil and sediment were over 79.40% and 75.65%, the minimum detection limit was 0.0225 ~ 0.0525ngg-1, RSD was less than 7.19%. The proffered method was successfully utilized to detect actual samples, the residue of di-BBPA and mono-BBPA are detected in Naihe River and Shuxi River in Tai'an City, residue of di-BBPA and mono-BBPA was detected in the soil, and there was low residual amount of di-BBPA, mono-BBPA and BPA in the sediment of Shuxi River.

Outsized Turbidity Currents as a Primary Mechanism for Neoproterozoic Organic Carbon Delivery to the Deep Sea

Levees in modern deep-marine systems have been shown to sequester significant amounts of organic carbon due largely to their expanse and high rates of sedimentation. However, relatively few studies have examined organic carbon sequestration in ancient deep-marine leveed slope channel systems. Physical and geochemical analyses of well-exposed levee deposits in the Neoproterozoic Windermere Supergroup in B.C., Canada have shown that intervals of organic-rich (up to 4% TOC) strata correlate with conditions of elevated sea level and primary productivity on the shelf. Organic matter (OM) occurs primarily as micro- to nano-scale carbon adsorbed onto the surface of clay grains and notably occurs mostly in anomalously thick, mud-rich sandstone beds that are interspersed within successions of thin-bedded, comparatively organic-poor turbidites. The concentration of organic carbon in thick beds suggests that even when primary productivity is high it only becomes mobilized in significant quantities into the deep sea by uncommon, outsized turbidity currents. Although markedly more common in organic-rich intervals, thick, organic-rich beds occur also in organic-poor levee deposits, suggesting that the occurrence and frequency of outsized flows may be linked to primary productivity on the shelf. High rates of OM production and fallout would result in rapid accumulation of OM on the seafloor that then binds and provides mechanical strength to the accumulating sediment. Later this overthickened, organic-rich sediment pile becomes gravitationally unstable and ultimately remobilized downslope. These failure events create large, surge-like flows that are considerably thicker than the depth of the slope channels through which they travel. Accordingly, continuous overspill over the channel margins results in the deposition of an anomalously thick, sand- and organic-rich bed. These episodic events not only deplete the outer continental shelf of OM, but apparently also reduces the gradient slope of the local seabed, which then results in the more typical smaller, channel-confined organic-poor turbidity currents. Additionally, the abrupt and single-bed occurrence of OM-rich strata suggests that the buildup of organic-rich strata and seafloor stabilization was rapid but only of limited duration. Significantly, this study suggests that outsized turbidity currents that originate on the outer continental shelf are the primary mechanism for organic matter delivery to the deep sea, at least in pre-vegetation times, and that flow size and frequency, in addition to primary productivity, exerts an important control on the distribution of organic carbon in deep-sea sediments.

Patterns and cyclicity of Quaternary sedimentation above a subducting seamount at Rock Garden (Central Hikurangi margin, New Zealand)

Rock Garden (RG), located east off the North Island of New Zealand, is part of an accretionary ridge that is influenced by seamount subduction. Two ∼37 m long sediment cores, drilled with the seafloor drill rig (MeBo200) from RG, provide a continuous sedimentary record of the period between 1.95 and 0.4 Ma. This period, the Early-Middle Pleistocene transition (EMPT), was marked by a progressive increase in the amplitude of climate oscillations, and a shift of Milanković cycles from 41 ka towards a quasi-100 ka frequency in the absence of any significant change in orbital forcing. From the recovered core material of cores GeoB 20824–4 and GeoB 20846–1, we determined sediment physical properties, oxygen isotope (δ18O) values, and element concentration based on X-ray fluorescence (XRF) measurements. The element ratios were used as proxies for sediment composition and as paleo-environmental indices. In sediment physical properties, δ18O values, and geochemical properties, evidence for glacial and interglacial cycles and spectral periods of 405, 100, 41 ka were found. A shift of the spectral period from 41 to 100 ka took place in sediment cores during (1.4 to 0.4 Ma). Numerical ages obtained from tephra layers included in the sedimentary record enabled to estimate sedimentation rates from both cores. Although both drill sites are only 1800 m away from each other, sedimentation rates of 2.15 to 2.96 cm ka−1 (GeoB 20824–4) and 5.49 to 6.77 cm ka−1 (GeoB 20846–1), respectively, differ by a factor of two. This may be the reason why two facies-units were identified in core GeoB 20824–4, whereas sediments of core GeoB 20846–1 all belong to the same facies. A change of lithofacies in core GeoB 20824–4 between Unit I and Unit II in ∼20 mbsf at 1.5 to 1.4 Ma marks the initiation of the EMPT.

Pb-210 Dating of Ice Scour in the Kara Sea

Ice scours are formed when the keels of floating icebergs or sea ice hummocks penetrate unlithified seabed sediments. Until now, ice scours have been divided into “relict” and “modern” according to the water depth that corresponds with the possible maximum vertical dimensions of the keels of modern floating icebergs. However, this approach does not consider climatic changes at the present sea level, which affect the maximum depth of ice keels. We present an application of 210Pb dating of the largest ice scour in the Baydaratskaya Bay area (Kara Sea), located at depths of about 28–32 m. Two sediment cores were studied; these were taken on 2 November 2021 from the R/V Akademik Nikolay Strakhov directly in the ice scour and on the “background” seabed surface, not processed via ice scouring. According to the results of 210Pb dating, the studied ice scour was formed no later than the end of the Little Ice Age. Based on the extrapolation of possible sedimentation rates prior to 1917 (0.22–0.38 cm/year), the age of the ice scour is estimated to be 1810 ± 30 AD. The mean rate of ice scour filling with 70 cm thick sediments from the moment of its formation is around 0.33 cm/year.

Sediment dynamics and geomorphology of a submarine carbonate platform canyon system situated in an arid climate setting

ABSTRACTChanges in neritic carbonate production and sediment transport off platforms are related to climate variations, sea‐level fluctuations and tectonic processes. Canyon systems marking the platform slopes represent critical source‐to‐sink pathways transporting shallow‐water sediments basinward. However, these export systems and related processes are primarily studied on platform slopes in humid to tropical climate settings. A newly discovered canyon system on the leeward margin of the Al Wajh platform (north‐east Red Sea) represents the ideal laboratory to investigate source‐to‐sink pathway dynamics in an arid climate that prevailed since the Late Pleistocene. A high‐resolution bathymetry map was established to characterize the slope morphology. The system displays a U‐shaped, 10 km long main channel dominantly sourced by the north‐west/south‐east running outer channel and two smaller 2 to 3 km long canyons. The latter are positioned perpendicular to the main canyon. A 4 km wide head scarp at the reef edge and dozens of amphitheatre‐shaped scarps along the mid to lower slope suggest significant slope failures over time. The analysis of four sediment cores collected on a profile down the canyon revealed sedimentation rates of 26 cm/ka at the mid‐slope to 9.4 cm/ka in the basin. Three main sediment‐export processes were identified: (i) sandy and neritic component‐poor turbidites; (ii) winnowing of strontium‐rich carbonate fines through surface currents; and (iii) remobilized carbonate fines on the upper slope. As of the Last Glacial, turbidites are predominantly deposited during times of significant sea‐level instability, both rises and falls, whereas their flat‐topped‐tropical counterparts show a higher turbidite frequency during highstands. Strontium‐rich carbonate fines are exported similarly through time in both climate settings. Overall, sediment export is controlled by: (i) the platform morphology (flat‐topped versus rimmed lagoon); (ii) variations in sediment production; (iii) sea‐level variations (exposure or flooding of sediment production areas); and (iv) the interaction between the sedimentary system and atmospheric changes (sediment production and delivery).

Clinical characteristics, diagnosis and management of Sweet syndrome induced by azathioprine.

Sweet syndrome is a rare complication of azathioprine treatment with unelucidated clinical features. The purpose of this study was to investigate the clinical characteristics of azathioprine-induced Sweet syndrome (AISS) and provide a reference for diagnosis, treatment and prognosis. We collected relevant case reports of AISS by searching Chinese and English databases from 1960 to December 31, 2022, extracted the data and carried out a retrospective analysis. The median age of the 44 patients was 50 (range 9-89) years, and they included 32 males (72.7%). Fever (86.4%) and arthralgia (31.8%) were the most common clinical symptoms. The skin lesions were mainly pustules (54.5%), papules (40.9%), plaques (40.9%) and nodules (31.8%), which were mainly distributed on the extremities (54.5%), face (38.6%) and hands (36.4%). Laboratory examination revealed neutropenia (65.9%) as well as elevated C-reactive protein (63.6%) and erythrocyte sedimentation (40.9%) rates. Histopathology of the lesioned skin showed neutrophil infiltration (93.2%) and dermal edema (38.6%). Symptom relief was achieved at a median time of 7days (range 2-28days) after azathioprine discontinuation in all patients. Nine patients (20.5%) had skin lesions that recurred within 24h after taking azathioprine again. Clinicians and pharmacists should grasp the regularity and characteristics of AISS and should not recommend the readministration of azathioprine, to avoid the recurrence of Sweet syndrome.

Removal of Water Turbidity by Different Coagulants

During the last decade, there has been a concern about the relation between aluminum residuals in treated water and Alzheimer disease, and more interest has been considered on the development of natural coagulants. The present study aimed to investigate the efficiency of alum as a primary coagulant in conjunction with mallow, Arabic gum and okra as coagulant aids for the treatment of water samples containing synthetic turbidity of kaolin. Jar test experiments were carried out for initial raw water turbidities 100, 200 and 500 (NTU). The optimum doses of alum, mallow, Arabic gum and okra were 20, 2, 1 and 1 mg/L for100 NTU turbidity level, 35, 4, 2 and 3 mg/L , for 200NTU turbidity level and 50, 8, 10 and 8 mg/L for 500 NTU turbidity level, respectively. The optimum pH was 7 for alum, and 7.5 for mallow, Arabic gum and okra. The residual turbidity was 3.34 to 6.81 NTU by using alum as a primary coagulant with mallow, Arabic gum and okra, and pH values of the treated water by the natural coagulants were 6.1 to 7.01. The optimum dose of thenatural coagulants in the present study has higher efficiency in removing high turbidity in comparison with low turbidity.Natural coagulant showed many advantages in coagulation/flocculation process. By using natural coagulants, considerable decreasing in Al2(SO4)3 consumption, and Increasing in the rate of sedimentation can be achieved.

Sequence Stratigraphy and Implications for Shale Gas Exploration in the Southern Sichuan Basin, South China

In contrast to the widely used sequence stratigraphic models for passive continental margins, the stacking patterns of strata within epeiric seas, which are influenced by regional tectonic activity, may display opposing characteristics during the same geological period. These variations serve as a record of basin evolution and also affect the accumulation of hydrocarbons within the strata. Our study investigated the development potential of the deep Longmaxi Shale in the southern Sichuan Basin by examining the sequence stratigraphy and sedimentary fill patterns. Using a combination of core observation, well-logging data analysis, and 3D seismic profile interpretation, we aimed to gain an understanding of the sedimentary fill history of the Longmaxi Shale during the Early Silurian. Our analysis revealed that deglaciation and regional tectonic events affected the sequence stratigraphy, resulting in unconformities that were identifiable using seismic data and wireline logs. Through an analysis of thirty wireline logs and two seismic profiles, we identified two third-order sequences suggested in the Lower Longmaxi Formation. Within the two third-order sequences were five systems tracts, with the first exhibiting a complete cycle of sea-level change and the second cycle being incomplete due to regional tectonic events. The graptolite succession on the upper Yangtze Platform provided a temporal view of the sequence stratigraphy and sedimentation rates of the Longmaxi Shale. The thickness trends of the systems tracts reflected the interplay of short-term eustasy fluctuations, subsidence, and uplift. Our analysis suggests that regional subsidence played a significant role in the deposition of the second transgressive systems tract (TST) in the Weiyuan and Luzhou areas, which represents a promising target for shale gas exploration, in addition to the first TST. However, the Changning area experienced a relative sea-level decrease due to the intense uplift of the Qianzhogn Paleo-uplift and the increased supply of sediment and is interpreted as a highstand systems tract (HST); it is not considered to have shale gas exploration potential.

Estimation of Sediment Concentration Using Sediment Rating Curve Approach in Isser Watershed (North-West of Algeria)

Estimation of Sediment Concentration Using Sediment Rating Curve Approach in Isser Watershed (North-West of Algeria)

In situ Strontium isotope stratigraphy of fish teeth in deep-sea sediments from the western Clarion-Clipperton Fracture Zone, eastern Pacific Ocean

The geochronology of deep-sea sediments beneath the carbonate compensation depth (CCD) presents a challenge due to the calcareous microfossils dissolution, low sedimentation rates, sedimentary hiatus, and redeposition. Fish teeth, commonly found in deep-sea sediments, have been utilized for Sr isotope stratigraphic dating. However, continuous Sr isotope exchange with pore water limits the utility of fish teeth in this context.In this study, we employed laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS), scanning electron microscopy (SEM), and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) to obtain accurate stratigraphic chronology results from rare earth element and yttrium (REY)-rich sediments in the Clarion-Clipperton Fracture Zone (CCFZ) of the Pacific Ocean.Our analysis indicated that a fish tooth characterized by a dense structure and low La content exhibited a relatively initial 87Sr/86Sr ratio. Additionally, La contents at the same depth displayed a strong positive correlation with 87Sr/86Sr ratios, suggesting that Sr isotopes exchange with pore water during early diagenesis when La and other elements entered the fish teeth. However, certain fish teeth were able to resist early diagenesis alteration due to their dense structure.Based on in situ Sr-isotope stratigraphy results, we estimated the REY-rich layer age in core GC1901 to be 24–32 Ma, consistent with the REY-rich layers of DSDP/ODP in the CCFZ. Our study thus provides a new method for in situ Sr isotope analysis of fish teeth, which improves the accuracy of Sr isotope stratigraphy of pelagic sediments and could be widely used in deep-sea exploration.

Highlighting relationships between sand thicknesses, reservoir-seal pairs and paleobathymetry from a sequence stratigraphic perspective: An example from Tortonian Serravallian deposits, onshore Niger Delta Basin

The utilization of sequence stratigraphic concepts in identifying sands and their spatial continuity in distinct gross depositional settings is key, especially in frontier settings where data paucity is a common challenge. In the Baka field, onshore Niger Delta, detailed reservoir correlation guided by sequence stratigraphic framework analysis showed the distribution of sand and shale units constituting reservoir-seal pairs (RSP) correlatable across the field. Within the 3rd-order packages, it is observed that the lowstand systems tract (LST) and highstand systems tract (HST) contain more RSPs and thicker 4th- and 5th-order sands than the transgressive systems tract (TST). In terms of bathymetry, it is noted that irrespective of systems tracts, the RSP Index (RI) decreases from the proximal shallow/inner shelf settings to the more distal outer shelf areas. Amongst all three systems tracts, intervals interpreted as lowstand prograding complexes contain the best developed sands and highest RSP. Sand development within the LSTs has been controlled by a pronounced growth fault regime accompanied by high subsidence and sedimentation rates. This is linked to the basinward migration of the sands during prolonged sea-level fall, creating significant accommodation space for sand deposition. On the other hand, the TSTs known to mark periods of progressive sea-level rise and landward migration of sandy facies, show thinner sands enclosed in much thicker, laterally extensive, and better-preserved deeper marine shales. Interpreted seismic sections indicate intense growth faulting and channelization that influenced the syn- and post-depositional development of the sand packages across the field. The initial timing of deformation of sub-regional faults in this area coincides with periods of abrupt falls in sea level. This approach could be useful for predicting sand-prone areas in frontier fields as well as possible reservoir-seal parameters required for some aspects of petroleum system analysis and quick-look volume estimation.

An improved method for paleoflood reconstruction from core sediments in the upper Yellow River

Fluvial deposits represent a sedimentary archive of paleohydrological information, which can be utilized to reconstruct unrecorded floods. A multi-index (grain size, end-member model, and geochemistry elements) approach of core sediments from the upper Yellow River was used to reconstruct its flood history. A high-resolution geochemical profile of the 20.71-m-deep core was obtained by an XRF core scanner. A comparison of sediment grain size with geochemical element ratios indicated that ln(Zr/Ti) can be used as a grain size proxy for the core sediment. Combined with the end-member modeling analysis, the flood energy index (FEI) was constructed to highlight the flood signals and their similar trends with sediment ln(Zr/Ti). Coarsened grain size and increased ln(Zr/Ti) suggested that a high-frequency flood phase appeared to occur in the early Holocene (11–6.5 ka) and late Holocene (3.5–0 ka), while low-frequency floods occurred in the middle Holocene (6.5–3.5 ka). An extreme hydrological phase occurred during 5.8 ka–5.9 ka, which coincided with a sharp increase in sedimentation rates from 0.14 mm/yr to 0.48 mm/yr. The flood activities at the upper reach of the Yellow River are considered to respond to climate variability with the monsoonal shift.

Clinical, laboratory and radiological evaluation of intensive care patients who developed COVID-19-associated pneumomediastinum

Objective: This study aims to identify possible risk factors and clinical, laboratory, or radiological predictors for COVID-19 associated pneumomediastinum. Methods: Patients who developed pneumomediastinum under mechanical ventilation (MV) due to COVID-19 pneumonia during intensive care unit (ICU) (Group1), and patients who died without developing pneumomediastinum during ICU (Group2) were compared statistically in terms of age, laboratory parameters, medical treatments, mechanical ventilator parameters, and radiological findings. Results: Group1 patients were significantly younger than Group2 patients (p<0.05). There was no significant difference between groups in terms of laboratory parameters except N/L ratios and sedimentation rates(p>0.05).There was no significant difference between the groups in terms of dominant infiltration pattern, pleural and pericardial effusion (p>0.05). The incidence of organizing pneumonia pattern, and infiltration of more than 75% of the total lung parenchyma were significantly higher in Group 1 (p<0.01). The rates of favipiravir treatment, immunomodulatory therapy and prone positioning were significantly lower in Group1 than Group2 (p<0.01). There was no significant difference between groups in terms of the duration of ICU hospitalization and MV,PEEPmax, PIPmax and PaO2/FiO2 (p>0.05). Conclusion: Care should be taken in terms of pneumomediastinum in patients who show diffuse organized pneumonia patterns affecting more than 75% of the parenchyma area.

Influence of Sand Supply and Grain Size on Equilibrium Upper Regime Bedforms

AbstractNotwithstanding the large number of studies on bedforms such as dunes and antidunes, predicting equilibrium bedform type and geometry for a given flow regime, sediment supply and caliber remains an open problem. Here, we present results from laboratory experiments specifically designed to study how upper regime bedform type and geometry vary with sediment supply and caliber. Experiments were performed in a sediment feed flume with flow rates varying between 5 and 30 l/s and sand supply rates varying between 0.6 and 20 kg/min. We used both uniform and non‐uniform sands with geometric mean diameters varying between 0.22 and 0.87 mm. Analysis of our data and data available in the literature reveals that the ratio of total (bedload plus suspension) volume transport rate of sediment to water discharge Qs/Qw plays a prime control on upper regime equilibrium beds. Equilibrium bedforms transition from washed out dunes (lower regime) to downstream migrating antidunes (upper regime) for Qs/Qw between 0.0003 and 0.0007. For values of Qs/Qw greater than 0.0015, the bedform length increases with Qs/Qw. At these high values of Qs/Qw, equilibrium in fine sand is characterized by upstream migrating antidunes, cyclic steps, and significant suspended load. In experiments with coarse sand, equilibrium is characterized by plane bed with bedload transport in sheet flow mode. Standing waves form at the transition between downstream migrating antidunes and upstream migrating bedforms.

USING RADIOISOTOPE METHODS TO DATE Cs INFLOW TO BOTTOM SEDIMENTS OF THE YENISEI RIVER

The long-term study of samples of bottom sediments (BS) of the Yenisei River revealed the presence of a unique set of artificial radionuclides (Co, Cs, Eu, Eu), which made it possible to combine different methods for calculating sedimentation rates for a retrospective assessment of river BS. Studies have been carried out to determine the sedimentation rates by various methods, using natural non-equilibrium Pb, the ratios of artificial isotopes Cs/Co and Eu/Eu, and marker Co, in several sections of the Yenisei River - downstream of the radioactive discharges of the Mining and Chemical Combine (MCC) of Rosatom near the villages of B. Balchug and Atamanovo, as well as upstream of the MCC discharges in the reference areas near the villages of Esaulovo and Shivera. Estimation of sedimentation rates using non-equilibrium Pb, Cs/Co and Eu/Eu isotope ratios, and marker Co for reference areas and the areas near villages located downstream of the MCC showed that their values lay in the range of 0.5-1.3 cm/year. A chronology of Cs influx into BS was constructed using different radioisotope methods, which demonstrated that the maximum Cs influx into BS in the reference regions of the villages of Esaulovo and Shivera and in areas of the village of B. Balchug was noted during the extreme flood of 1966. Cs maxima were also found in the BS layers whose dating coincided with the floods of 1988 and 1995-1997.

Первые радиометрические датировки тонштейнов из угленосных отложений Кузнецкого бассейна: U-Pb-геохронология тайлуганской свиты

Tonsteins, predominantly solid kaolinite clay interbeds, are widespread in the coals of the Kuznetsk Basin and usually contain idiomorphic zircon grains of magmatic origin in quantities suitable for uranium-lead (U-Pb) radiometric dating. For the first time, tonstein zircons from coal seam 78 of the Tailugan Formation (Fm) are dated by two methods: Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Chemical Abrasion Isotope-Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS). The CA-ID-TIMS datings of 257.0 ± 1.3 Ma and 256.6 ± 0.4 Ma determine the age of the lower boundary of the Tailugan Fm and the Tailuganian Regional Stage at 257.0 Ma. We estimate the duration of the Tailuganian to be around 4.22 million years. The dating results make it possible to directly correlate the Tailuganian of the Kuzbass with the upper half of the Wuchiapingian and with most of the Changhsingian of the International Chronostratigraphic Scale. The accumulation rate of total sediments of the Tailugan Fm, calculated without considering the compaction index, is approximately 0.13–0.18 mm/year, and the rate of coal accumulation is 0.024 mm/year. Such values are comparable to the accumulation rates of the Late Paleozoic coal-bearing strata of the Donetsk Basin and Western Australia. The rate of peat accumulation during the Tailuganian, calculated at a compaction index of 10:1, has been estimated at 0.24 mm/year. This value is comparable to the rates of peat accumulation in the Holocene bogs of the Kuznetsk Alatau in Siberia and the European part of Russia. The presence of tonsteins in the coal seams of the Tailugan Fm suggests that the upper surface of the peat at the time of its accumulation was below the water level, serving as a protective screen for the thin volcanic deposits and preventing its erosion. The assemblages of macroflora, ostracods, conchostracans and bivalves considerably vary through the section of the Tailugan Fm. This variation makes it possible to identify in Kuzbass the stratigraphic level that corresponds to the boundary between the Wuchiapingian and Changhsingian stages in the future.

A new deglacial climate and sea-level record from 20 to 8 ka from IODP381 site M0080, Alkyonides Gulf, eastern Mediterranean

Records of relative sea-level rise for the last deglaciation are mostly limited to coral reef records and geophysical model estimates, but observational data from regions with temperate climates is sparse. We present a new relative climatic and regional sea-level rise record for glacial Termination 1 (Marine Isotope Stages [MIS] 2–1) based on ostracode paleoecology from the upper 8 m of the International Ocean Discovery Program (IODP) Site M0080 collected on Expedition 381, in the Gulf of Alkyonides, eastern Corinth basin of the Mediterranean Sea. Results show a series of major faunal transitions from lacustrine (Ponto-Caspian, Lake Corinth) glacial-age assemblages to fully marine (Mediterranean) interglacial assemblages between 20 and 8 ka. During glacial and early deglacial intervals, the Gulf of Alkyonides was characterized by non-marine lacustrine conditions with episodic sediment input from coastal, saline lake environments. Relatively stable lake shoreline conditions marked by the distinctive Tuberoloxoconcha sp. Existed from ∼17.5 to 15 ka. During the peak deglacial interval, the BØlling-AllerØd (B-A, ∼15–13.5 ka), rapid sea-level rise is indicated by a fully marine ostracode fauna colonization, which persisted from 13.5 to 7.5 ka (Late Pleistocene-Early to Middle Holocene).The transition from lacustrine to marine environments confirms that during the last glacial maximum (LGM) low sea level (130 - 125 m below present day), the Corinth-Alkyonides depocentres were lacustrine. Marine water breached the shallow Rion and Acheloos-Cape Pappas sills, which today are ∼50–60 m deep, separating the Mediterranean and Corinth-Alkyonides system beginning about 15 ka. Based on Alkyonides sedimentation rates, mean rates of sea-level rise during the B-A flooding of the Corinth-Alkyonides system are comparable to those obtained from coral reef sea level (SL) records, at least 10–20 mm yr−1. Changes in sedimentation and sill depths in this tectonically active region may have played a role in reconnection of the Mediterranean and Corinth/Alkyonides system over a prolonged period. However, the ages and scale of the faunal changes and their clear correspondence with previously published global sea-level curves and the regional sea-level curve based on deglacial land elevation changes predicted by the ICE-7G model suggests the M0080A deglacial is dominated by the glacio-eustatic sea-level rise and records details of global climate changes during Termination 1.