Modern Sediments Research Articles

Sediment routing in an incised valley during Hurricane Harvey (2017) in Houston, Texas, USA: Implications for modern sedimentation

Abstract Southeastern Texas (United States) recorded one of the largest flooding events in U.S. history during Hurricane Harvey (25–31 August 2017), mobilizing millions of cubic meters of sediment in Houston fluvial-estuarine systems. We conducted an integrated quantitative analysis to determine the net minimum volume of sediment transported during the storm using subaerial elevation change, satellite and ground-based images, and sediment dredging reports along major waterways. The 12 fluvial-estuarine streams and two controlled reservoir drainages in the Houston area transported a minimum of ~2.723 × 107 m3 of sediment. This volume is ~6–51 times larger than the average annual volume of sediment delivered to Galveston Bay in modern times (in the past 200 yr), and ~30–118 times larger when compared to Holocene rates. Nearly ~26% of the measured volume was deposited in Addicks and Barker reservoirs, decreasing holding capacities by ~1.2% and ~1.6%, respectively. In the stream drainages, sediment was mobilized from west-northwest of Houston and pulsed toward Galveston Bay, highlighting the extreme short-term variability in sediment delivery. Sediment flux through the Houston region during Harvey is an example of sediment storage followed by a pulsed delivery of high sediment volume rather than continuous delivery of sediment. Comparison of sediment volumes transported through natural and modified drainages through Houston demonstrates that channel modification resulted in significant bypass of sediment downstream. Urban watershed management is more effective when continual updates are implemented based on regional circumstances rather than based on historical fluxes.

Relict and Modern Sediments on the Continental Shelf of the Northern South China Sea: A Reconsideration

AbstractUnderstanding the temporal‐spatial patterns of modern and relict sediments is of importance for assessing changes in the Quaternary environment and sea‐level. Sedimentological and geochemical data is presented, along with in situ shell‐based accelerator mass spectrometry 14C ages of 30 samples from the surface sediments on the northern shelf of the South China Sea (NSSCS). The authors’ data show that the NSSCS surface sediments exhibit considerable diversity in composition. Modern sediments are primarily constrained to the NW inner shelf, which is fed by fluvial sands sourced from Coastal South China river systems and dominated by the Pearl River Estuary delivery. The transport and discharge of the terrestrial sediments to the NSSCS is highly influenced by the Guangdong Longshore Current and its secondary cyclonic eddies. Relict sediments dominated by well‐sorted, medium‐ and coarse‐grained sands were identified in the NW Shenhu and NW Dongsha areas of the outer NSSCS. The sedimentology and geochemistry of the relict sediments imply that they were deposited in a dry and cold environment either during the low sea levels of the late Pleistocene (∼40 ka) or the early Holocene (∼10 ka). To the east, the Taiwan Shoal and vicinity are dominated by a sand mixture, at which the relict sediments were reworked by terrigenous supply and modern hydrodynamic environment due to the compound action of the Guangdong Longshore Current, seasonal cyclones, and Kuroshio Intrusion. The present isobaths of ∼−90 m in the NSSCS might be the reflective of the early Holocene coastal delta or the last glacial maximum shoreline.

Sediment transport trend and its influencing factors in coastal bedrock island sea areas-a case study of Chudao island, China

Coastal bedrock islands sea areas have a unique natural environment, frequent human activities, and complex sedimentary dynamic processes. In this paper, we select the Chudao Island sea area off the coast of Shandong Peninsula, China, as a typical research area to investigate the sediment transport trends and influencing factors by means of high-precision bathymetric survey, high-density sediment sampling, grain-size trend analysis and hydrodynamic numerical modeling. Results and analysis indicate that the grain size parameters including mean grain-size, sorting coefficient and skewness are zonal distributed, roughly parallel to the isobaths. While the overall sediment transport trend is from island shore to sea, with several convergence centers near the loop centers of bottom flow and at the edge of the agriculture area. The near-bottom flow velocity is primary factor that controlling the significance of sediment transport trend, while the flow decides the general patterns of sediment transport trend and sediment distribution. Submarine topography can either directly transport sediments down its slope, or indirectly affect the direction of sediment transport by constraining the near-bottom flow from shallow to deep waters. Besides the natural factors of bottom flow and submarine topography, human activities represented by aquaculture also affect the sediment transport trend in coastal bedrock island sea areas. First, the increased sedimentation rate caused by organic matters and the diffusion of scallop fragments may cause sediment coarsening. Second, the artificial aquaculture facilities can reduce flow velocity and therefore hinder the initiation, suspension and transport of sediment near the aquaculture areas. Our methods and findings provide high-resolution details to insight into the sediment transport trends to improve the understanding of the modern sediment dynamics in small-scale coastal bedrock island sea areas and provide reference for corresponding engineering and agriculture activities.

Influence of the Hanjiang River’s Inlet Sediment Decrease on Modern Sedimentation in the Underwater Delta

The Hanjiang River is the second-largest river in Guangdong Province, China. The modern sedimentation pattern of the Hanjiang subaqueous delta has been significantly affected by changes in the sediment delivered by the Hanjiang River. Based on multiperiod charts and columnar samples from the Hanjiang subaqueous delta, the influence of a sharp decrease in the sediment flux from the Hanjiang River on the deposition of the Hanjiang subaqueous delta in the past 60 years was studied through a combination of chart-based analysis of the evolution of erosion and deposition and the analysis of sediment samples. The results showed that the significant reductions in sediment fluxes from the Hanjiang River and Rongjiang River had obviously spatially differentiated effects on the deposition pattern of the Hanjiang subaqueous delta. The significant decreases in sediment fluxes from the Hanjiang River and the Rongjiang River caused the sediment grain size of the columnar samples in the near-estuary area of the Hanjiang River subaqueous delta to coarsen upward, the deposition rate to decrease, and the depositional state to change to an erosional state. Since the sediments discharged into the ocean after reservoir impoundment are mainly fine-grained suspended sediments, the supply of coarse-grained sediments in the Hanjiang subaqueous delta decreased, resulting in the upward fining of the columnar samples. The spatial response pattern of the Hanjiang subaqueous delta to the sharp decrease in sediment flux into the sea differed significantly from those of the Yangtze and Yellow subaqueous deltas.

Metals and metalloids in high-altitude Pyrenean lakes: sources and distribution in pre-industrial and modern sediments.

High-altitude Pyrenean lakes are ecosystems far from local pollution sources, and thus they are particularly sensitive to the atmospheric deposition of metals and metalloids. This study aims to quantify the effect of human activity in 18 lakes located in both side of the France-Spain frontier. Sediment cores were collected in summer 2013, sampled at a 1cm resolution and the concentration of 24 elements was measured by ICP-MS. Statistic and chemometric analysis of the results highlights the influence of the geographical position and lithogenic features of each lake basin on trapping pollutants. More than the 80% of the lakes showed values of enrichment factor (EF) above 2 for at least one of the elements investigated in at least one core interval, which corroborates the existence of historical anthropogenic inputs of elements in the studied area. The results demonstrate the natural origin of As and Ti in Pyrenees, together with the significant anthropogenic inputs of Cd, Pb, Sb and Sn from ancient times. The data set points mining activities as the main historical source of pollution and illustrate the large impact of the industrial revolution. The regional variability could reflect also differential long-range transport, followed by dry or wet deposition.

Geochemical Assessment of the Modern Sediments of a Lake in the North of Russia

Core sediment (sapropel) samples were collected from Lake Okunozero, the Republic of Karelia, Russia, to assess the distribution of heavy metals and their main fractions, probable sources of pollution, and potential ecological and toxicological risks for the water body. Heavy metal concentrations were measured by the mass spectrometry method using an XSeries-2 ICP-MS. The sequential extraction of heavy metals from sapropel samples was performed using the scheme of Tessier. According to the Russian Interstate Standard (GOST), the sapropel of Lake Okunozero is suitable for use in agriculture. The exceedances of the regional background levels were detected only for Pb and Cd. In accordance with Pollution Load Index (PLI) and Potential Ecological Risk (RI), no ecotoxicological risk in researched sediments was found. A significant correlation between some investigated heavy metals was established. Most heavy metals were in the insoluble mineral phase (Mn et al.) or were associated with organic matter (Cu, Zn, Mo, Ni). Only Mn, Zn, Cd, and Pb were found in the available fraction from 13 to 24% of the total metal content in the sediments. Other metals were less associated with the available fraction.

Reconstruction of the conditions for the formation of red-colored sandstones of the Tersky coast based on a comparative analysis of the structure of ancient and modern deposits (Kola Peninsula)

The paper presents the results of studying the Riphean red-colored sandstones of the Tersky coast of the White Sea. 21 structural elements characterizing the conditions of rock formation have been considered, including 15 ancient and 6 modern deposits. Observations were carried out for 10 years in two areas of the White Sea coast. The purpose of the research is to establish the reasons for the absence of organic matter, the origin of the hematite admixture in the Riphean sandstones, and to assess the climatic conditions during their formation. These issues are key to identifying the Proterozoic red formation. The data have shown that some rock structures are similar in ancient and modern deposits. Such structures include, for example, wave ripples repeating in detail the dimension, shape, and orientation in both epochs, and therefore can be used to assess ancient marine sedimentation conditions. However, most of the structures testify to fundamental differences in the conditions of rock formation. It has been established that takyrs were systematically formed in ancient rocks and hematite was deposited, which indicates the arid climate in the Riphean and the specific composition of sea water. The most important difference between ancient deposits is the absence of fauna and flora in them.

Control of diatom and chrysophyte cyst dynamics by a meteorologically driven mixing regime in eutrophic Lake Żabińskie, northern Poland

Abstract Ongoing climate warming has strong moderating control over aquatic processes, such as ice cover duration, length of the growing season, vertical mixing patterns, thermal stratification, and the availability of light and nutrients. These fundamental mechanisms in turn influence the population dynamics of aquatic organisms such as diatoms and chrysophytes. In our study, over 3.5 years with contrasting meteorological conditions, we investigated eutrophic Lake Żabińskie located in northeast Poland. By combining observational data of meteorological conditions, physicochemical variables measured in the water column, and modern sedimentation, we sought to explain the relationships between changes in meteorological conditions, dynamics of total fluxes and the taxonomic composition of diatoms and chrysophyte cysts. Our results show the direct influence of meteorological conditions on physicochemical conditions and their indirect influence on total diatom and chrysophyte cyst fluxes and taxonomic succession. The former refers to the importance of air temperature and wind speed in shaping the mixing regime of Lake Żabińskie, while the latter refers to the nutrient cycling driven by changes in the mixing regime, which in turn influences the formation of biotic signals in the sediment. Our study also revealed that the biotic response to unusual meteorological conditions that occurred in 2020 (i.e., warm winter without ice cover) differed from typical years in terms of the phenology of diatom and chrysophyte cyst blooms. However, this response was not as pronounced as in lakes with lower productivity and can be attributed to the already turbid conditions and high nutrient concentrations, which alter the threshold for noticeable changes to occur. The taxonomic composition of diatoms and chrysophyte cysts also changed in response to changes in meteorological conditions. Complex interactions between physical and chemical conditions masked the direct influences of meteorological conditions on lake biota under eutrophic conditions. Nevertheless, high‐resolution monitoring enabled indirect links to be recognised. Both phenology and turnover in community composition responded to changes in meteorological conditions. These results show how ongoing climate change might affect biota in eutrophic lakes in the future.

Anthropogenic and natural contribution of potentially toxic elements in southwestern Ganges–Brahmaputra–Meghna delta, Bangladesh

Elemental composition, multivariate statistical analyses with the absolute principal component score-multiple linear regression (APCS–MLR) model, and different pollution indices in Upper and Lower Southwestern Ganges–Brahmaputra–Meghna (GBM) delta sediments were studied to characterize pollution, ecological risk and quantify potential toxic element sources of the area. Toxic metals concentrations were higher in Lower Delta and individual pollution indices showed Upper Delta was moderately polluted by arsenic, chromium, cobalt, copper and lead, and Lower Delta was moderately–strongly polluted by the same metals. Synergistic indices include Potential Ecological, Toxic, Nemerow, and Pollution Risk indices in Upper and Lower Delta sediment ranged from 47.17–128.07, 2.03–12.19, 29.92–65.42, 0.28–1.62, and 69.17–246.90, 8.00–13.47, 20.53–152.92, 1.18–1.58, indicated low and moderate risk pollution, respectively. Statistical models represent the metals dominantly originated from nature for Upper Delta, and both natural and anthropogenic activities contributed to Lower Delta sediment. The study found that the modern deposit in Lower Delta became more contaminated and thus enhanced ecological risk.

Determining source-specific terrigenous organic carbon contributions in sediments from the Yellow River estuary, Northeast China: A test of source apportionment models

Molecular organic geochemistry has been used effectively to determine terrigenous organic carbon (OC) contributions from different sources in modern sediments. However, mathematic modelling using source-specific parameters could be a potentially simple-effective approach to identify the terrigenous OC signals. In this study, the Yellow River estuary was chosen to probe whether source apportionment models can determine source-specific OC contributions. The end-member mixing model suggests that terrigenous OC contributed 57.0% ± 10.2% to the sedimentary OC. n-Alkane distributions were used to perform Unmix and positive matrix factorization (PMF) to separate terrigenous and autochthonous OC into more specific sources. PMF modelling delineates the contributions of high terrigenous plants, fossil OC, macrophyte-sourced OC, and bacterial and algal-sourced OC as 22.9% ± 14.3%, 26.2% ± 19.4%, 26.5% ± 19.3%, and 24.4% ± 17.1%, respectively. In assessing terrigenous contributions, PMF results (48.7% ± 13.5%) almost agrees with the end-member mixing model (57.0% ± 10.2%), consistent and comparable with previously published data (~ 50%), while Unmix (73.9% ± 18.7%) is significantly overestimated. Interestingly, macrophyte-sourced OC from coastal wetland identified by PMF was less investigated previously and should call attention in the future study. Consequently, modelling results match well with previously published data, suggesting that mathematic modelling can be an effective approach to quantitatively evaluate source-specific terrigenous OC contributions to estuary sediments and other complex aqua-land systems. However, caution must be taken in respect to the modelling uncertainty, which could be mainly induced by sample number, diversity, and robust interpretation on chemical parameters.

RESULTS OF STUDYING THE PLEISTOCENE IN THE VILGORT SECTION (CHERDYN DISTRICT, PERM TERRITORY)

Link for citation: Plyusnin A.V., Sulima A.I., Marinov V.A., Vdovichenko S.I., SamodurovS.A. Results of studying the Pleistocene in the Vilgort section (Cherdyn district, Perm territory). Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 5, рр.148-158.In Rus. The relevance. The study of glacial deposits, which is one of the main components of most continental sedimentary formations of all ages, makes it possible to identify the features of its structure and formation, as well as to establish the facies-genetic confinement. This is especially true for Quaternary geology, since makes it possible to carry out stratigraphic comparisons and identify paleogeographic settings for the formation of deposits. This paper presents the results of a comprehensive lithological and biostratigraphic study of the Vilgort section of the Kolva river valley, Cherdyn district of the Perm Territory. The main aim of the research is to study the geological section and substantiation of the age of the Mesozoic deposits according to the fauna complex. Objects: continental deposits of the Middle Pleistocene, exposed in the right side of the river Kolva. The deposits of this region are poorly studied. References are sown in the literature about the Mesozoic fauna found in the Vilgort section. Methods: geomapping, layered lithological description, layer-by-layer sampling, biostratigraphic studies. Results. These studies made it possible to carry out a detailed layer-by-layer description and stratigraphic subdivision of the Vilgort section. The Permian carbonate deposits are overlain by eluvial-deluvial deposits of the Likhvin horizon, they are overlain first by lacustrine-glacial, and then by glacial deposits of the Dnieper horizon of the middle Pleistocene with erratic blocks of Mesozoic repeatedly redeposited terrigenous rocks. Due to the neotectonic activity of the right-bank block part of the Vilgort area, which underwent uplift in the Late Pleistocene, most of the Upper Pleistocene deposits were eroded, which explains the stratigraphic unconformity, when modern deposits lie on glacial deposits of the Middle Pleistocene. According to the results of micropaleontological studies, foraminifers were identified from samples taken in the fifth layer: the Middle Volgian substage of the Volgian stage (sample 1); distributed in the interval of the Ryazanian Stage of the Lower Cretaceous (sample 3) and the middle and upper substages of the Volgian Stage (sample 4).

CONCEPT ABOUT ABIIOGENIC THEORY OF OIL GENESIS

The article considers alternative arguments, that contradict the accepted the organic hypothesis of oil origin, which must be taken into account at carrying out of oil and gas prospecting works. These conclusions must be used in the exploratory oil and gas well engineering in nonconventional reservoir types. The substantiation of the inorganic genesis of oil and gas, the assumption about the current age of hydrocarbon formation is proposed. The oil of many modern deposits undergoes dynamic processes, exchanges matter, information, while in the reservoir. This is proven by the chemistry of hydrocarbon molecules, characteristic only of oil, and their increased content in the surround-ing geological environment. A brief strategy of prospecting and exploration of commercial hydrocarbon reserves is outlined. The basic geological conditions for the potential belonging of the structure to the oil trap have been established. The well-known drilling data of an oil field dedicated to the Krasnoleninsky arch of the West Siberian oil and gas province are presented. The prospecting and exploration of oil reservoir is considered as the removal of two uncertainties: dynamic and static. The prospecting for oil involves the removal of dynamic uncertainty, which is a derivative of oil discrete reproduction and the formation of an accumulation. Its result is difficult to reliably identify. Geo chemical characteristics and prerequisites are no less important markers for prospecting and exploration.

Detrital zircon U–Pb ages and Hf isotope analyses of modern and Quaternary sediments in China: A new dataset with preliminary analysis

AbstractDevelopments of detrital zircon geochronology have resulted in an explosion of publications that report or discuss detrital zircon data. Combined detrital zircon U–Pb ages with Hf isotope analyses from modern and Quaternary sediments have been widely carried out with the aim of characterizing continental crustal evolution and tracing sediment provenance. Although several detrital zircon databases have compiled U–Pb and Hf data on global scale, the dataset of detrital zircon with a special focus on modern sediment has rarely been compiled. Here, we publish a new detrital zircon dataset of modern and Quaternary sediments in China with 59,535 U–Pb ages and 4,971 Hf isotope data, with detailed information of isotope ratios, ages, Th/U, etc. Four types of sediments have been classified according to sedimentary environments, including fluvial, marine, aeolian and alluvial sediments. Preliminary analysis is carried out on these compiled data to provide new insights into sedimentary provenance and crustal evolution in China. Eight age populations are identified corresponding to tectonic–thermal or magmatic events, including 2,300–2,700 Ma, 1,800–2,000 Ma, 700–1,000 Ma, 400–500 Ma, 200–300 Ma, 120–200 Ma, 80–120 Ma and < 60 Ma. Accompanying with quantitative comparison between sediments from various sedimentary environments, these U–Pb age distributions reveal the provenance link between “source” and “sink” in both exorheic and endorheic drainages. The compiled εHf(t) data reflect that the crustal history of China is apparently episodic, whose pattern is similar to that of global record. Further work will be implemented for database construction, including the integration of latest literatures, AI‐based data extraction and data aggregation.

The Chronology of Modern Sedimentation in the Storefjorden Strait (Svalbard Archipelago)

Periods of formation of different sedimentary lithotypes were determined using the results of the study of modern sedimentation processes in the Storefjorden Strait (West Spitsbergen). The chronology of sedimentation was established from variations in specific activity of 210Pb and 226Ra and verified by 137Cs data. Sedimentation rates have varied considerably over the last century in different parts of the sedimentation basin, ranging from 0.04 to 0.3 cm/yr. Sedimentation in the Storefjorden Strait was closely related to changing climatic conditions. Climatic factors (air temperature, atmospheric precipitation) have a different effect in morphologically different sections of the sedimentation basin. In the south of the strait, lithotypes are determined by an oceanological factor (bottom current). Despite the changes in sedimentation rate, the lithotype in the south of Storefjorden has remained stable for more than 100 years. In the north and in the central part of the strait, cooling in the period from 1970 to 1995 caused a change in the bottom sediment structure.

101 contact twins in gypsum experimentally obtained from calcium carbonate enriched solutions: mineralogical implications for natural gypsum deposits.

Gypsum twins are frequently observed in nature, triggered by a wide array of impurities that are present in their depositional environments and that may exert a critical role in the selection of different twin laws. Identifying the impurities able to promote the selection of specific twin laws has relevance for geological studies aimed at interpreting the gypsum depositional environments in ancient and modern deposits. Here, the effect of calcium carbonate (CaCO3) on gypsum (CaSO4·2H2O) growth morphology has been investigated by performing temperature-controlled laboratory experiments with and without the addition of carbonate ions. The precipitation of twinned gypsum crystals has been achieved experimentally (101 contact twin law) by adding carbonate to the solution, and the involvement of rapidcreekite (Ca2SO4CO3·4H2O) in selecting the 101 gypsum contact twin law was supported, suggesting an epitaxial mechanism. Moreover, the occurrence of 101 gypsum contact twins in nature has been suggested by comparing the natural gypsum twin morphologies observed in evaporitic environments with those obtained in experiments. Finally, both orientations of the primary fluid inclusions (of the negative crystal shape) with respect to the twin plane and the main elongation of sub-crystals that form the twin are proposed as a fast and useful method (especially in geological samples) to distinguish between the 100 and 101 twin laws. The results of this study provide new insights into the mineralogical implications of twinned gypsum crystals and their potential as a tool to better understand natural gypsum deposits.

Provenance and transport mechanism of gravity core sediments in the deep-water area of the Qiongdongnan Basin, northern South China Sea

Reconstructing the role of provenance and transport mechanism of sediments deposited in deep-water environments is often complex because of myriad of factors such as variability in sediment sources, tectonics, bottom morphology, climatic changes and sea level fluctuations as well as current regime. The South China Sea (SCS) is situated at the tectonic intersection of the Pacific, Eurasian, and Indo-Australian plates, and provides an excellent natural laboratory for understanding source-to-sink transport processes of fluvial sediments. The Qiongdongnan Basin (QDNB) is located in the northern part of the SCS, and the deep-water area (>300 m) of the QDNB has a good hydrocarbon source and hydrocarbon accumulation conditions with a tremendous thickness since the late Miocene-Quaternary. However, the complex sources and transport mechanisms of sediments in the QDNB are undefined. In previous study QDNB may have a major provenance or a mixture of sources. In this paper, the sediments of two cores from the deep-water area of QDNB have been analyzed using several sedimentological and geochemical approaches, including measurements of grain size distribution(433 samples), the occurrence of minerals, and trace element geochemistry(37 samples)as well as strontium and neodymium isotopes(20 samples).The granularity analysis results first show that the 19S37 core can be divided into three stages while the 19S40 core is divided into two stages by clear vertical variations in grain size characteristics. Chlorite (62.0%) and Muscovite (33.6%) appear to be the predominant minerals in the 19S37 core, while the mineral assemblage of sediments from 19S40 mainly consists of kaolinite (37.4%), muscovite (29.2%) and chlorite (27.1%). The primitive mantle standardization curves and chondrite standardized distribution patterns of 19S37 and 19S40 are consistent and display enrichments in Th, U, Pb, and Nd and depletions in Ba, Nb, Sr, and Eu. In addition, the content of Sr fluctuates greatly with depth, which should reflect the influences of sea level changes and the relative proportion of various provenance components. The 143Nd/144Nd ratios and εNd values of the sediments from 19S37 are higher than those of the sediments from 19S40, and all the εNd values show narrow variations and range from −10.085 to −11.080. We conclude that the sediments of the deep-water area in the upper Pleistocene-Holocene were mainly from the sources of the Red River, Taiwan, Pearl River, Hainan Island, and Vietnam. The transport mechanism of the sediments from Hainan Island can be explained by the short distance between the source region and the sedimentary site, while the large amounts of terrigenous sediment inputs derived from the Red River and advantageous morphology make the Red River the largest sediment source to cores 19S37 and 19S40. The transport distance and amount of Deep Water Current could be even more powerful to make Taiwan be the second largest source of modern sediments in QDNB.

Quantitative Prediction of Braided Sandbodies Based on Probability Fusion and Multi-Point Geostatistics

Predicting the spatial distribution of braided fluvial facies reservoirs is of paramount significance for oil and gas exploration and development. Given that seismic materials enjoy an advantage in dense spatial sampling, many methods have been proposed to predict the reservoir distribution based on different seismic attributes. Nevertheless, different seismic attributes have different sensitivities to the reservoirs, and informational redundancy between them makes it difficult to combine them effectively. Regarding reservoir modeling, multi-point geostatistics represents the distribution characteristics of the braided fluvial facies reservoirs effectively. Despite this, it is very difficult to build high-quality training images. Hence, this paper proposes a three-step method of predicting braided fluvial facies reservoirs based on probability fusion and multi-point geostatistics. Firstly, similar statistical data of modern sedimentation and field paleo-outcrops were processed under the guidance of the sedimentation pattern to construct reservoir training images suitable for the target stratum in the research area. Secondly, each linear combination of selected seismic attributes was demarcated to calculate the principal component value and work out the elementary conditional probability. Lastly, the PR probability integration approach was employed to combine all conditional probabilities and calculate the joint probability. Then the joint probability was combined with training images to build a reservoir distribution model through multi-point geostatistics. We illustrated the detailed workflow of our new method by applying it to a braided fluvial reservoir modeling case in the Bohai Bay Basin, East China. The new method reduced the error of prediction results by 32% and 46% respectively, and the error of water content by 36.5% and 60.3%. This method is a potentially effective technique to predict and characterize the reservoir spatial distribution and modeling in other oil fields with the same geological background.

Contemporary Sedimentation in Lake Onego: Geochemical Features of Water, Suspended Matter, and Accumulation Rate

The spatio-temporal variability of the modern sedimentation process in Lake Onego, the second largest lake in Europe, was evaluated. The chemical composition of the lake water was studied. Sedimentation takes place in the oxidation conditions of low TDS water of the calcium bicarbonate type, where the ratio between terrigenous clastic material and lacustrine biochemical suspended matter in the material deposited to the bottom is close to one. We demonstrate that the sedimentation process in the lake is non-uniform. Sedimentation rates in different regions of the lake were estimated (0.1 to 2 kg per sq. m of bottom surface per year) through in situ surveys with sediment traps. Annual sediment input was estimated on the basis of the lake’s chemical balance. Analysis of the qualitative characteristics of the material deposited to the bottom shows its composition corresponds to the humus-Fe-Si type of sedimentation. The uniform texture and mineral composition and the similar multielement spectra of the sediments suggest that active water dynamics cause fine-grained suspended load to remain in the water column for prolonged time periods. Variations in the sediment chemical composition across the lake are due to natural causesand to unevenly distributed anthropogenic pressure.

The Content and Speciation of Radionuclides in Water and Bottom Sediments of the Laptev Sea

In the presented work, the features of the distribution of Cs-137 and plutonium isotopes in modern sediments of various parts of the Laptev Sea, selected during the expedition studies on the RV “Academician Mstislav Keldysh” in 2017 and 2019, were studied. It was found that the activity of Cs-137 in water and sediments is within the global level, which is typical for the seas of the Arctic region. In all the collected samples the specific content of Pu-239,240 isotopes is below the level of the minimum detectable activity. According to the results of isotope analysis of Pb-210, the sedimentation rates in two columns collected in the Laptev Sea are 0.18 and 0.23 cm/year. The study by several methods of the speciation forms of Pu-239, introduced into the samples of bottom sediments under laboratory conditions, showed that the main content of Pu-239 is associated with difficult-to-dissolve organo-mineral components. 30-39% Pu-239 was found in the composition of organic easily soluble acids and humic substances, which include fulvic and humic acids of bottom sediments.

Rotation of a Ferromanganese Nodule in the Penrhyn Basin, South Pacific, Tracked by the Earth's Magnetic Field

AbstractFerromanganese nodules are cm‐sized, authigenic, abyssal manganese‐iron‐hydroxide concretions. They grow very slowly at rates of a few mm per million years. Although their ages are older than millions of years, they are often found half buried on the modern sediment surface. The mechanisms for the nodules' persistence at the surface without complete burial could be linked to their occasional motion or agitation. Here, we report evidence for the rotation of a nodule from the Penrhyn Basin, South Pacific detected by paleomagnetism. The paleomagnetic inclinations of specimens from the nodules' surface are consistent with the recent geomagnetic fields. The paleomagnetic directions from the surface to the core show successive changes and form a great circle with a pole at (azimuth = 53.9°, dip = 32.1°). This suggests that the nodule rotated along its pole while successively recording magnetizations. As the nodule was found on a gentle slope at the foot of an abyssal hill, it may have moved downslope due to bottom current underwashing. Rock magnetic analyses of the nodule suggest the presence of magnetite in single domain and vortex states. Low temperature magnetometry revealed that magnetite grains were heavily oxidized to maghemite, especially close to the core of the nodule. The rotation may have exposed the rising part of the nodule to oxidative pore water. Oxygenated Antarctic Bottom Water might have caused remagnetization due to low temperature oxidation of magnetite. The rotation would also facilitate the omnidirectional growth of the nodules' mixed layer of diagenetic buserite and hydrogenetic vernadite.