Point Bar Research Articles

Controlling Effect of Wave-Dominated Delta Sedimentary Facies on Unconventional Reservoirs: A Case Study of Pinghu Tectonic Belt in Xihu Sag, East China Sea Basin

In order to find the “sweet spots” of unconventional oil and gas from the Pinghu Formation in the Pinghu Tectonic Belt, we are committed to clarifying the development and distribution rules of coal-measure source rocks and tight reservoirs as well as the controlling factors. Using 3D seismic and logging data, combined with logging constraints of target lithology and pyrolysis experiments of source rock, "source and reservoir" research of uncoventional oil and gas was carried out in the Pinghu Tectonic Belt. The results show that two stages of regression and one stage of transgression occurred in the Pinghu Formation, resulting in river-controlled and wave-controlled delta-neritic facies dominated by sedimentary facies, source rocks developed in interdistributary bay and swamp microfacies, and tight sandstones in point bar and distributary channel microfacies are developed. The accumulation of coalbed methane and shale gas is controlled by the sedimentary facies and the degree of thermal evolution under the factors of burial depth. The accumulation of tight sandstone is closely related to the dominantly sedimentary facies and diagenetic modification of physical properties and faults. It is concluded that the structural type, type and distribution of faults, and depositional environment of the Pinghu Tectonic Belt in the Xihu Sag are the key factors controlling the development and accumulation of coal-measure source rocks and tight sandstone reservoirs. This understanding provides a clear direction for the deep exploration of unconventional oil and gas in the sag and provides a reference for finding reservoir “sweet spots.”

Natural levees increase in prevalence in the backwater zone: Coastal Trinity River, Texas, USA

Abstract Flood dynamics in low-relief landscapes control the lateral exchange of water and sediment between a river and its floodplain. Locations where these exchanges occur for any given river discharge depend on local bank elevations, which in turn depend on the type of landform present immediately adjacent to the river channel. Our analysis separated landforms bordering a river into six categories: levee, scroll bar, counter point bar, channel-bend cutoff, erosional surface, and inactive surface. Each landform is associated with a different range of elevations. Levees are the highest, and counter point bars and cutoffs are the lowest. Using a combination of lidar-derived measurements of topography and water-surface profiles derived from U.S. Geological Survey gauge data, we show that landforms at the margins of the river change with downstream position on the coastal reach of the Trinity River in the southern United States. The fractions of counter point bars and cutoffs decrease downstream, while the fraction and continuity of levees increase to nearly 100%. This spatial change correlates with downstream reductions in channel-bend migration and deformation, and the measured range in river stage. As a result, the greatest range in bank elevations occurs upstream where variation in river stage is also highest. Meanwhile, the smallest range in bank elevation and river stage exists in the coastal backwater zone. Our analysis indicates that essentially all levees within the backwater zone are overtopped by flow associated with a single river discharge. Moving upriver, the discharge associated with levee-overtopping flow systematically increases. This study highlights the morphodynamic control on coastal river flooding.

Willows on the Edge—Riparian Vegetation Growth and Planting on Anthropogenic Point Bars, Apalachicola River

Willows on the Edge—Riparian Vegetation Growth and Planting on Anthropogenic Point Bars, Apalachicola River

Reservoir Architecture in Tide-Dominated Estuary: A Case Study of McMurray Formation Oil Sand Reservoir in the Athabasca Block, Canada

This paper presents a detailed description of the sedimentary characteristics and architecture model of the tidal-dominated estuary reservoir in the Lower Cretaceous McMurray formation. Based on a thorough study of the core data, 13 lithofacies were recognized. The lithofacies associations were divided into nine types of architecture elements, that is channel, salt marsh, fluvial point bar, tidal point bar, mud flat, mixed flat, sand flat, tidal bar and offshore. Through the combination of high resolution seismic data and well data, the architecture model was established. The boundary surfaces of each architecture elements are depicted and the logging characteristics is concluded. The cross-section is constructed to reveal the superimposition model of different architectural elements with the seismic profiles. The plane and vertical distribution of architectural elements are revealed and the sedimentary model is constructed. In the longitudinal section of estuary, the architecture elements is fluvial deposits (channel, fluvial point bar, and salt marsh), tidal flat (mud flat, mixed flat, and sand flat), tidal bar, tidal flat and offshore from land to sea. In the cross section, tidal bar, sand flat, mixed flat, mud flat, tidal point bar and salt marsh are distributed successively from the center to the sides. Tidal bars and sand flats are the best reservoirs in terms of physical properties. We focus on the analysis of their architecture and summarize their stacking patterns. We propose tidal bars as compounds are lateral accretion. Tidal bar has high-angle continued lateral accretion, with a dip angle of 6–12°. Sand flat also has lateral-migrated characteristics, but their dip angle is 2–6° which is smaller than tidal bars. As a result, the dimension and stack of a single tidal bar and sand flat are quantified. The tidal bar was lateral stacking or vertical stacking with lateral-migrated or forward-migrated sand flat and existed vertical and lateral erosion-filling phenomenon. Tidal bars have width of 100–550 m and length of 800–2,400 m, and sand flats are 300–2,500 m long. Tidal bars and sand flats made up the best reservoirs. The study provides some insights for future research of estuarine sedimentary patterns and reservoir architecture.

Morphological Changes of Sharp Bends in Response to Three Gorges Project Operation at Different Discharges

Dam construction often changes downstream fluvial processes by reducing sediment supply. Taking Tiaoguan reach and Laijiapu reach of the lower Jingjiang Reach downstream of the Three Gorges Project as examples, three-dimensional flow velocity, sediment, and bed elevation were observed in the two bends for investigating the impact of flow structure and sediment transport of different discharges on sharp bend morphology. Results indicated that the flow structure and sediment transport process in curved channels depended upon the flow stages, which affected the patterns of erosion and deposition along the point bars and concave banks. Flow separation and development of secondary flow were depended on the shapes of point bars and flow depths nearby, and the strength of secondary flow increased with flow discharge. The high flow discharges, which had high sediment carrying capacity and stream power, provided the main driving force for erosion on upstream point bar, thus the type and duration of floods were crucial factors in the morphological evolution of meandering bends. The reduction of sediment supply should be responsible for erosion on the point bars, causing the flow to migrate toward the convex banks. In meandering rivers with reduced sediment supply, retreats (push inward) of inner (convex) banks dominated advances (pull inward) of outer (concave) banks. In addition, the formation and development of concave-bank bars might relate particularly to meander curvature. This study is expected to constitute a reference for bank protection and river management in meandering bends downstream of reservoirs.

Geologic Modeling and Ensemble-Based History Matching for Evaluating CO2 Sequestration Potential in Point bar Reservoirs

The target reservoirs in many CO2 projects exhibit point bar geology characterized by the presence of shale drapes that act as barriers preventing the leakage of CO2. However, the extent of the flow barriers can also impede the displacement of CO2 in such reservoirs and restrict the storage volume. Therefore, developing a framework for modeling point bars and their associated heterogeneities is crucial. Yet, for the point bar model to be geologically realistic and reliable for evaluating CO2 sequestration potential, it should be calibrated to reflect historical data (e.g., CO2 injection data). This study is therefore in two parts. The first part focusses on the modeling of point bar heterogeneities (i.e., lateral accretions and inclined heterolithic stratifications). To ensure that the heterogeneities are preserved, we implemented a gridding scheme that generates curvilinear grids representative of the point bar curvilinear geometry. We subsequently incorporated a grid transformation scheme to facilitate geostatistical modeling of reservoir property distributions. The second part of this study is a model calibration step, where the point bar model is updated by assimilating CO2 injection data, in an ensemble framework. Ensemble-Kalman Filter was used first to update ensembles of point bar geometries, to select the geometry that yields the closest match to observed data. Within this geometry, indicator-based ensemble data assimilation was used to perform updates to the ensemble of point bar permeability models. The indicator approach overcomes the Gaussian limitation of the traditional ensemble Kalman filter. The workflow was run on the Cranfield, Mississippi CO2 injection dataset. It was observed, after model calibration, that the final updated ensemble of models yields a reasonable match with the historical data. The updated models were run in a forecast mode to predict the long-term CO2 sequestration potential of the Cranfield point bar reservoir. Results demonstrate that 1) preserving the heterogeneities in the point bar modeling process, and 2) constraining the point bar model to historical data (e.g., CO2 injection data) are essential for accurately evaluating the CO2 sequestration potential in point bar reservoirs.

Organic carbon burial by river meandering partially offsets bank erosion carbon fluxes in a discontinuous permafrost floodplain

Abstract. Arctic river systems erode permafrost in their banks and mobilize particulate organic carbon (OC). Meandering rivers can entrain particulate OC from permafrost many meters below the depth of annual thaw, potentially enabling the production of greenhouse gases. However, the amount and fate of permafrost OC that is mobilized by river erosion is uncertain. To constrain OC fluxes due to riverbank erosion and deposition, we collected riverbank and floodplain sediment samples along the Koyukuk River, which meanders through discontinuous permafrost in the Yukon River watershed, Alaska, USA, with an average migration rate of 0.52 m yr−1. We measured sediment total OC (TOC) content, radiocarbon activity, water content, bulk density, grain size, and floodplain stratigraphy. Radiocarbon activity and TOC content were higher in samples dominated by silt as compared to sand, which we used to map OC content onto floodplain stratigraphy and estimate carbon fluxes due to river meandering. Results showed that the Koyukuk River erodes and re-deposits a substantial flux of OC each year due to its depth and high migration rate, generating a combined OC flux of a similar magnitude to the floodplain net ecological productivity. However, sediment being eroded from cutbanks and deposited as point bars had similar OC stocks (mean ± 1 SD of 125.3±13.1 kg OC m−2 in cutbanks versus 114.0±15.7 kg OC m−2 in point bars) whether or not the banks contained permafrost. We also observed radiocarbon-depleted biospheric OC in both cutbanks and permafrost-free point bars. These results indicate that a substantial fraction of aged biospheric OC that is liberated from floodplains by bank erosion is subsequently re-deposited in point bars rather than being oxidized. The process of aging, erosion, and re-deposition of floodplain organic material may be intrinsic to river–floodplain dynamics, regardless of permafrost content.

A hierarchical stochastic modeling approach for representing point bar geometries and petrophysical property variations

The flow of fluids in point bars is affected by the existence of heterogeneities like shale drapes that are found on the surfaces of inclined heterolithic stratifications. In fact, these shale drapes can act as fluid flow baffles; therefore, developing a framework for modeling point bars and their associated heterogeneities is vital. In this study, a stochastic process-based modeling approach is presented for capturing the main point bar heterogeneities: accretion surfaces (i.e., the aerial heterogeneity) and inclined heterolithic stratifications (i.e., the vertical heterogeneity). The former was modeled using a sine-generation function and the latter, with a sigmoidal function after which they were combined into a 3D point bar model. To ensure proper modeling of petrophysical properties, we developed a more representative gridding scheme which generates curvilinear grids representative of the point bar geometry. This grid was then transformed into a rectilinear grid to allow for geostatistical simulation after which all petrophysical properties were mapped back into the original curvilinear grid. An essential element of this modeling approach is the stochastic representation of shale drapes at the interface between successive accretion surfaces. The workflow was tested using a real field dataset for the Cranfield field, Mississippi. The constructed model was then subjected to a flow simulation study mimicking a CO2 storage scenario. Various sensitivities were simulated to evaluate the effect of heterogeneities on CO2 flow within the point-bar. Results demonstrate the importance of representing point-bar related heterogeneity and the spatial distribution of shale drapes on CO2 plume migration and storage.

Mid-latitude alluvial and hydroclimatic changes during the Paleocene–Eocene Thermal Maximum as recorded in the Tremp-Graus Basin, Spain

A short episode (~170 kyr) of extremely high global temperatures that occurred ~56 Ma, known as the Paleocene–Eocene Thermal Maximum, is widely considered an ancient analogue of the ongoing anthropogenic warming. This ancient hyperthermal event consisted of three phases, onset, core and recovery, which are respectively represented in the mid-latitude south Pyrenean Tremp-Graus Basin by three successive terrestrial units, the Claret Conglomerate, the Yellowish Soils and the Gypsum-rich Unit, each of them recording a different sedimentary response to evolving climatic and hydrological regimes. The Claret Conglomerate is mainly made up of calcareous conglomerates and is acknowledged to record an abrupt hydrological change during the onset phase. This unit most likely formed in an alluvial megafan, an interpretation here reinforced with new architectural information and by comparison with naturally occurring small-scale fan-like accumulations. Assuming the similarity between the onset of the Paleocene–Eocene Thermal Maximum and the anthropogenic warming, recent hydrological and meteorological data from mid-latitude Spain were compiled for comparison purposes. This comparison concurs with published modelling results about hydroclimate changes in the Pyrenees during the hyperthermal event, postulating an enhancement of seasonal contrast with augmented frequency and intensity of floods but no significant change in total rain. Furthermore, the comparison suggests that the Claret Conglomerate accumulated during extreme rainfall episodes that mainly occurred in autumn. The Yellowish Soils are mostly composed of silty marls with ubiquitous small-sized carbonate nodules and intercalated calcarenites. The marls were deposited in floodplains and the calcarenites in point bars and crevasse splays of meandering rivers. The scarcity of conglomerates entails a near absence of strong currents, and the carbonate nodules perennial or seasonal arid conditions. These nodules occur within cumulate palaeosols, the development of which required regular sedimentary increments during inundations on the floodplains. Sedimentation rates of siliciclastic material on the floodplains increased significantly during the core of the hyperthermal event, as well as at river outlets in coastal settings, which shows that erosion was accelerated and rules out the occurrence of protective, dense vegetation. Combined, these characteristics suggest persistent very dry summers, but a smooth wet season without intense precipitation events. Lastly, the profusion of gypsum in the youngest unit is clear proof of an arid climate during the recovery of the hyperthermal event. In essence, the studied deposits provide a unique window into the sequence of hydroclimatic change during the rise, peak and decline of an ancient global warming event in a mid-latitude terrestrial setting, against which ongoing climate-change data and future projections can be compared.

Insights into the geomorphology of the Ceará Basin, Brazil, by combining seismic attributes, machine learning, and rock-physics analyses

Abstract We utilize 3D seismic data and robust rock-physics models, combined with a well dataset, to investigate the subsurface of the Mundaú sub-basin, Brazil. Seismic attributes analysis and unsupervised machine-learning approaches were able to produce high-resolution images to allow the mapping of the 3D geometry of ancient geomorphological features across stratigraphic levels, from the Albian to the Turonian interval. Significant deep-water elements were identified using seismic attributes and machine-learning techniques (i.e. channel complex, point bars, feeder channels, faults, depocentres, dendritic lobes, smaller channels and distributaries). In addition, the petrophysical analysis enhanced the subsurface characterization by employing a deep convolutional network that allowed S-wave modelling and synthetic seismic generation. The well-log data analysis validated interpretation of sand-prone deposits; in addition, the rock-physics modelling provided insight into the deposited lithologies. After the petrophysical analysis, seismic facies classification was performed using machine-learning techniques, including self-organizing maps and independent component analysis, which provided valuable insights into the geomorphology of this under-researched basin. The enhancement of seismic and petrophysical data with machine learning proves to be a useful technique for better characterizing this basin. This approach may be used on similar frontier hydrocarbon basins to help de-risk petroleum exploration.

Characteristics of Seepage Barriers in Fluvial Reservoirs of Meandering Rivers and Their Impacts on Water Injection Development: A Case Study of Neogene Guantao Formation in Block M, Gudao Oilfield

To deepen our understanding of reservoir heterogeneity, seepage barriers in the study area were divided into interlayer, intralayer, and planar levels based on their spatial distribution characteristics and then investigated by taking the third member of the Neogene Guantao Formation in the block M of the Gudao oilfield as an example. Based on their genesis characteristics, the interlayer seepage barriers were divided into the overbank sand-overbank sand type, overbank sand-channel type, isolated channel superposition type, and channel shallow-cut type. The planar seepage barriers were categorized into the channel boundary type, abandoned channel type, channel-overbank sand type, and floodplain mudstone type. The intralayer seepage barriers were classified into the mudstone type and physical property type. Classifying multiple levels of different types of seepage barriers led to the refinement of their spatial characteristics. The strength of seepage barriers was characterized using the “seepage barrier coefficient” and “reservoir quality coefficient,” and the small-valued coefficients of the interlayer and intralayer seepage barriers indicated that these seepage barriers are characterized by large thickness, high mudstone content, poor physical properties, and weak seepage ability. The strength of the planar seepage barriers was dependent on the sedimentary facies types and channel stages, and the difference between planar seepage barriers was characterized using the reservoir quality coefficient. The seepage barriers were described based on the multilevel classification of seepage barrier categories, the intralayer seepage barriers with a lateral accretion pattern in the meandering river point bars were identified and described, and the distribution characteristics of seepage barriers were summarized at multiple levels. The method of “hierarchical analysis, skeleton construction, and category fitting” was used to establish 3D models of different levels of seepage barriers, and a modeling method based on the characteristics of intralayer seepage barriers under the constraint of architecture pattern was used to model intralayer seepage barriers with a lateral accretion pattern. In the monitoring of water injection profiles, it was found that the extent of blockage achieved by seepage barriers affects the water injection volume and thus controls the fluid transport pattern. Due to the development characteristics of the seepage barrier in the formation, there are some differences in injection production efficiency under different well pattern matching modes. The research on the distribution characteristics of different levels of seepage barrier categories provides a reliable geological basis for improving the injection-production relationship.

Cretaceous (Maastrichtian) chelonian burrows preserved in floodplain deposits in the Bauru Basin of Brazil: Evidence for the fossorial origin of turtle shells

Burrowing behavior is an important adaptation of animals that live in arid and semi-arid conditions. In this paper, we describe examples of vertebrate burrows from the Upper Cretaceous (Maastrichtian) Adamantina Formation of the Bauru Basin, Brazil, most likely produced by turtles. The Adamantina Formation preserves abundant and diverse turtle body fossils such as Bauruemys elegans (Testudines: Pleurodira); however turtle burrows have not been previously documented. The newly reported burrows are preserved in fluvial sandstone facies and exposed in sections that partially preserve their three-dimensional geometry. Burrows are simple J-shaped tunnels with a cross-sectional shape that is semicircular (half-dome) with a flattened floor. Such burrows show a partially preserved entrance with an inclined ramp angle (22°), and grooves and ridges up to 1 cm in width preserved along the burrows walls and floor. The architecture and sedimentary facies of the host sandstone body, together with the occurrence of Taenidium barretti and the absence of rhizoliths, suggest that the burrow was excavated by scratch digging into an exposed point bar of a meandering river channel. Based on burrow morphology, dimensions, as well as ridges,and grooves in the walls and floor, we propose that burrows were formed by a chelonian (such as a freshwater turtle) during aestivation. We highlight that these are first examples of turtle burrows reported from the Cretaceous, and their occurrence reinforces the hypothesis that the original function of turtle shells was as an adaptation to fossorial behavior.

From electromagnetic to sediment textural maps: an integrated approach to unravel the intra-point-bar variability of sediment properties

Sedimentary sand bodies that originated by the evolution of meandering channels such as point bars, host surficial aquifers, providing preferential pathways for groundwater flow in mud-dominated floodplains. These aquifers are a major source of freshwater, yet they can suffer from different environmental issues such as pollution and salt-water intrusion, which can critically damage agriculture and socio-economical activities. Understanding the internal architecture of point-bar bodies is essential to plan proper aquifer management and address environmental issues in coastal plains. To provide a spatially extensive, cost-effective characterization of point-bar body architecture, this work proposes a multidisciplinary approach to investigate geophysical and sedimentological data through statistical analyses, with an application to two palaeo-meanders in the Venetian Plain, Italy. In this setting, point-bar deposits mainly consist of fine to coarse sand and display lower electromagnetic conductivity values compared to the surrounding muddy overbank deposits. Statistical multivariate analyses on sedimentological and geophysical properties overcome the qualitative direct dependence of electromagnetic conductivity on sediment grain size alone, highlighting a stronger relationship with sediment sorting. By calibrating this relationship on a reasonable number of samples representative of the different depositional bodies, this methodology finally provides maps of sediment textural properties at the meander scale.

Outer-shelf conduit within growth-fault compartment Pliocene Orinoco Delta

Prominent outcrops of the Pliocene Orinoco Delta along the southeast coast of Trinidad Island display a well-known, very thick Icehouse succession of storm-wave dominated delta lobes, as part of a 10–12 km thick Neogene continental-margin prism. There is a previously discovered, steep incision or conduit (400 m wide) with south and north-bounding erosion surfaces, cutting deeply into the Mayaro Formation shelf-edge delta deposits. The ca. 100 m-thick infill of the conduit shows an initial muddy succession passing upwards to very coarse-grained debrites, rotated and slumped blocks, and structureless sandstones that pass upward to a stacked series of sandy to muddy channel fills. The channels show spectacular tidal rhythmites, probably developed on the point bars of subaqueous tidal channels. As one piece of the topset of the shelf-edge delta clinoform, this conduit displays features of the linkage hub between the landward on-shelf delta systems and the basinward slope deposits.New fieldwork and a re-examination of the incision-infill reveal new details and suggest three possible origins of the conduit: ① the first is a no river feeder, shelf-edge collapse scar, extending onto the upper slope and infilled by deeper to shallower deposits. This shelf-edge cutting canyon interpretation is supported by the presence of hardground ichnology on the steep walls of the incision and the abundance of chaotic blocks and debrites in the lower two-thirds of the incision infill. ② The second is a shelf channel or valley linking fluvial channels to on-shelf and outer shelf deltas. This river-connected, subaqueous shelf valley origin, is supported by the upward-coarsening nature of the infill succession and especially the occurrence of shallow-water tidal channels in the upper third of the infill. ③ The third is a canyon developed mainly during transgression or highstand with a collapsed canyon-head infill and an overlying muddy tidal-channel system that had only limited sediment bypass to the deepwater slope and basin floor. This case represents both the shallow-water and the deeper water features of the infill succession, and is supported by similar large shelf-edge collapse features seen elsewhere in the Cruse and Moruga Formations of the paleo-Orinoco margin. This case, unrelated to river supply, also benefits from slight rotational shelf-edge uplift to trigger collapse.The known Cedar Grove growth fault was active and located some 4 km to the west from the present coast on the southeast corner of Trinidad Island. The growth-fault trapped thickened outer shelf to shelf-edge delta-front and delta-plain sediments within the hanging-wall compartment as the fault stretched about 20 km along strike. All the shelf-edge aggradation and its partial collapse were likely triggered by growth-faulting. After some muddy backfilling and coarse-grained block collapse into the invaginated shelf-edge, this scalloped area attracted a belt of subaqueous tidal channels, thus healing the eroded topography.

Modeling of subsurface sedimentary facies using Self-Attention Generative Adversarial Networks (SAGANs)

Understanding subsurface distribution features is crucial for reliable sedimentary facies modeling. Obtaining the distribution feature of complex subsurface sedimentary facies is challenging, especially non-stationary sedimentary facies which are location-specific, well-ordered, facies sequence (e.g., deltas). The application of machine learning algorithms has potential to assist with this imaging problem, particularly using the Generative Adversarial Networks (GANs) method. Recently, GANs have proven to be outstanding for unsupervised learning on complex distributions of training images. However, in most GAN-based model convolution processes, the information in a local area is computationally invalid for reproducing the global features of training images. To remedy this, we introduce an advanced Self-Attention Generative Adversarial Network (SAGAN) for subsurface geological facies modeling. Compared with the basic GANs, SAGANs introduce a self-attention mechanism to attain details from a long distance in the image, reproducing global features of training images. SAGAN case studies involve stationary channels and non-stationary delta facies. We use probability maps, variograms, connectivity functions, and visualization results to evaluate and compare our simulation realizations. For channel cases, SAGANs’ realizations can reproduce different distributions of channels and point bars in different river systems. For the delta case, the SAGAN method shows a better ability to reproduce delta non-stationary characteristics than the MPS and basic GAN methods. All results are of high quality and diversity, reproduced the known geological sedimentary patterns, and compared with the basic GANs, SAGANs can better reproduce the global features of non-stationary training images. It is demonstrated that our first proposed SAGANs for geological facies modeling represent a powerful method for reproducing depositional facies distribution pattern.

Geomorphological evolution of the Group I fluvial system, AX field, Malay Basin

The AX Field is located 167km off NNE Kerteh, Terengganu of Peninsular Malaysia, southwest of Malay Basin. This study is focused on the 3D seismic analysis of the Lower Miocene fluvio-deltaic Group I. The objective of the study is to evaluate the geomorphological evolution of fluvial succession and interpret the possible intra-basinal and extra-basinal controls on the fluvial evolution. One hundred strata slices were generated in order to evaluate the evolution of the fluvial systems within the Group I interval. Seismic attributes such as Root Mean Square (RMS), sweetness and spectral decomposition were computed to map channel geomorphology. Different fluvial styles were identified in the different parts of the study area. Variation of fluvial style were identified within the Group I interval including the low sinuosity system with tributary channels, high sinuosity system with broad meander belt and braided system. Fluvial channel imaged within the studied interval can be divided into six (6) stages based on the channel morphology. Stage 1 (1875 – 1810 ms), the oldest stage, displays high sinuosity channels. Braided system associated with coal deposition were imaged in Stage 2 (1810 – 1765 ms). During stage 3 (1765 – 1710 ms), the fluvial system is characterized by low to moderate sinuosity channel features that varies in scale and geometry. Stage 4 (1710 – 1675 ms) display fluvial style characterized by low sinuosity-to-straight system with tributary channels. Stage 5 (1675 – 1615 ms) is represented by high sinuosity fluvial system with broad meander belt and point bar. During Stage 6 (1615-1536 ms) the fluvial system displays moderate-to-high sinuosity. The high sinuosity system in period 6 exhibit well-defined meander scroll bar morphology that reveals the extension and translation course of the fluvial system.

Ártéri üledékek mikroműanyag tartalma az Alsó-Tisza egy kanyarulata mentén

Plastics get into the environment legally or illegally, and their amount is increasing continuously because their usage is constantly increasing. Microplastics (< 5 mm) have several morphological types: fragments can be formed by physical weathering of larger plastic objects; fibres usually originate from washing synthetic clothes; while pearls used in cosmetics get into the environment by means of communal waste. Our aim is to analyse the sedimentation pattern of microplastics on various floodplain forms along a natural meander of the Lower Tisza River, Hungary. The uppermost sediment layer (0–5 cm) of the floodplain forms contains 0–1800 microplastics/kg. The sediments of the swales (458–1300 particles/kg) and the point bar sediments (220–1600 particles/kg) are the most polluted, but the samples from the low-lying clay pits are also highly contaminated (818–880 particles/kg). The active point bar and the natural levee have lower levels of microplastic contamination (100–620 particles/kg). In the natural levee along the channel, microplastics are present to a depth of 50 cm (1753–4800 particles/kg), while in the distal parts of the floodplain only the upper 0–10 cm sediment layer is polluted. Plastic fibres are the most common plastic types in the samples, clearly indicating that they originate from treated or untreated wastewater.

Cruziana and Helminthopsis in fluvial deposits of the uppermost Stockton Formation (Late Triassic), west-central New Jersey

Fluvial deposits of the uppermost Stockton Formation (Late Triassic), west-central New Jersey have yielded the trace fossils Cruziana tenella and Helminthopsis isp. The ichnotaxa belong to the Scoyenia ichnofacies. On the basis of stratification and primary sedimentary structures, the beds are interpreted as deposits in a meandering stream environment. Worm-like forms, nematodes, notostracans, myriapods, and arthropods are probably responsible for most of the animal traces in moist or wet channel and point bar sediments subject to aerial exposure.

Characterizing the subsea Pleistocene fluvial system of the Sunda shelf, offshore Malaysia, using multiattribute corendering and self-organizing maps

The advancement of multiattribute analysis techniques has significantly improved the ability to capture subtle geologic information that is not easily detected on the original seismic. The use of corendering and automated facies clustering/classification techniques with an appropriate set of seismic attributes increases the reliability and accelerates the interpretation process. We have proved the effectiveness of multiattribute corendering and self-organizing maps (SOMs) in characterizing the late Pleistocene fluvial system of the Sunda shelf that was previously studied using the original seismic only. The work aims to document the attribute expression and capture subtle depositional patterns of the fluvial system. We find that amplitude, texture, and spectral attributes delineate the lithology contrast among different depositional features, whereas geometric attributes reveal channel morphology. The red-green-blue and alpha blends significantly increased the data interpretability by manipulating up to four attributes in the same display. In addition, the SOM clustering aids in distinguishing among different sand-prone depositional elements and muddy facies. We use the cross-cutting relation and superposition rules to understand the stratigraphic evolution of the interval. We observe several fluvial depositional elements through a closely spaced time slicing, including straight channel, meander channel, point bar, crevasse splay, and levee. We recognize that the straight and low-sinuosity channels were developed along preexisting faults and find a deeper incision and thicker sediment fill than the other channel types. The widely variable fluvial style in the middle of the interval is attributed to a rapid change in the accommodation space and climate conditions. The small meanders that find a prominent dendritic pattern indicate a marine influence on the less channelized uppermost part of the interval. The well-imaged and documented shallow fluvial system in the area represents an excellent analogous that helps to understand and accurately predict the reservoir distribution in the deeper productive stratigraphic units.

Sedimentology and reservoir characteristics of delta plain reservoirs: An example from Messinian Abu Madi Formation, Nile Delta

Delta plain sandstones represent one of the major deltaic hydrocarbon reservoir compartments. The present research provides integrated sedimentological, petrophysical, and petrographical analyses of delta plain reservoirs using an example from the gas-bearing Messinian Abu Madi in the central part of the Nile Delta. The Abu Madi reservoir is interpreted as a tidally-influenced, fluvial-dominated delta plain, and it is subdivided into four sedimentological architectural elements: distributary channel, crevasse channel (straight and meandering), crevasse splays, and interdistributary bay fill. Although the distributary channel has the best reservoir quality (HFU 4 and HFU 5), it is characterized by a high degree of heterogeneity due to the complex interaction between fluvial discharge and tidal currents; straight crevasse channels (HFU 3 and HFU 4) are similar to the distributary channel but have relatively fine grain size and small sand body volume. The meandering crevasse channels are of low reservoir quality (HFUs 1 and 2) due to the formation of point bar muddy inclined heterolithics. According to the results, the delta plain reservoirs are microscopically dominated by quartzose, and litho- and feldspathic quartzose microfacies. The common mud-matrix and poorly sorted fabric due to rapid deposition as well as reworking by tidal/wave currents, that represent the main depositional controls on reservoir quality. Meanwhile, dissolution, anhydrite, quartz, and calcite as well as authigenic kaolinite and chlorite clays are the main diagenetic control factors on reservoir quality.