Shoal Research Articles

CHARACTERIZING MODERN AND HOLOCENE BARRIER-ISLAND ENVIRONMENTS WITH FORAMINIFERAL ASSEMBLAGES: AN EXAMPLE FROM A WAVE-DOMINATED, MICROTIDAL BARRIER-ISLAND SYSTEM, NORTH CAROLINA, USA

Abstract Recent research has shown that sedimentological information in barrier-island settings may provide more detailed interpretations of some past coastal environments than interpretations based upon foraminifera. This research investigates whether targeted documentation of modern foraminifera in specific coastal environments can result in higher resolution micropaleontology-based paleoenvironmental reconstructions. Bear Island, North Carolina, characterized by little human disturbance, was chosen for detailed documentation of foraminifera in modern barrier-island-related environments. Modern sediments in all subenvironments were predominantly siliciclastic (< 30 % clastic carbonate debris) in composition: clastic carbonate allochems (e.g., mollusk shell fragments, echinoid spines) were admixed with fine- to medium-grained quartz sand. The hypothesis that modern foraminiferal assemblages of 26 modern coastal subenvironments can be distinguished based upon their foraminiferal assemblages was tested by discriminant analysis and resulted in the recognition of four environmental supergroups: shoreface, ebb-tidal delta, flood-tidal delta/inlet channel, and “barrier-combined” (foreshore, washover, dune, sandflat, spit, longshore bar, and trough). Holocene paleoenvironments represented by foraminiferal assemblages in 16 vibracores collected from the modern inner shelf, shoreface, ebb-tidal delta, and inlet environments of Bogue Banks, immediately adjacent to Bear Island, were interpreted, via discriminant analysis, based upon the modern dataset. Holocene and modern foraminiferal assemblages were similar but variations in species abundance and species diversity allowed for alternative paleoenvironmental classification of core samples at varying levels of probability. The methodology of this research is widely applicable to other coastal environments.

Diagenesis of continental tight sandstone and its control on reservoir quality: A case study of the Quan 3 member of the cretaceous Quantou Formation, Fuxin uplift, Songliao Basin

Research on the diagenesis of continental sandstone reservoirs can provide scientific guidance for the prediction of reservoir sweet spots. The low permeable-interbedded thin and thick sandstone reservoirs of the Cretaceous Quantou Formation's Quan 3 Member in the Fuxin Uplift, Songliao Basin, were used as an example in this work to investigate the diagenesis of continental tight sandstone and its influence on reservoir quality. A large number of thin section, scanning electron microscopy, granularity, X-ray diffraction, and petrophysical property measurements were used to study the petrological characteristics and diagenesis. The reservoir space evolution mode of continental sandstones in this area was constructed by combining diagenesis sequences and the evolution of petrophysical properties of the Quan 3 Member. The results show that the compositional maturity of the sandstone reservoirs of the Quan 3 Member is relatively low and their lithologies are mainly lithic feldspar sandstone and feldspar lithic sandstone, followed by lithic arkose sandstone, feldspathic litharenite and a small amount of lithic sandstone. The average particle size of the target sandstones is 0.11 mm, and the fine sandstone to coarse siltstone are favorable reservoirs. The studied sandstone reservoirs have undergone intense diagenetic transformations, including compaction (pressure solution), cementation, dissolution, and metasomatism. Moreover, the complex diagenetic environment changes in the Quan 3 Member include early alkaline-acidic→mid-alkaline→late acidic. The shallow sandstones are in the meso-diagenetic A1 stage; when the burial depth exceeds 800 m, they enter the meso-diagenetic A2 stage; and when the burial depth exceeds 1600 m, they enter the meso-diagenetic B stage. It was found that diagenesis has significant control over the quality of continental sandstone reservoirs. Compaction is the primary factor controlling the quality of the target reservoir. It controls the differences in the petrophysical properties of the reservoirs in the eastern and western regions; that is, the physical properties of the Quan 3 Member in the east are higher than those in the west. Cementation and dissolution are secondary controlling factors of reservoir quality that control the differences in reservoir petrophysical properties in the northern and southern regions; that is, the physical properties of the Quan 3 Member in the north are better than those in the south. The most favorable reservoirs of the Quan 3 Member are developed in the Fuyu Oilfield, which is distributed in the southeast region and develops fine sandstones of branch channels and meandering river point sand bars of delta plains that suffer the least compaction and the strongest dissolution. This study may provide crucial clues for predicting the sweet spot reservoirs of the Quan 3 Member in the study area. Furthermore, the study provides a reference for the different diagenesis controls on the pore space evolution of continental tight sandstone reservoirs.

Beach Placer Deposit Modelling using Geospatial Methods: A Case Study from Brahmagiri Mineral Sand Deposit, Puri District, Odisha

Abstract An integrated approach has been attempted for 3D representation of various geo-exploration data pertaining to Brahmagiri Mineral Sand Deposit (BMSD). GIS platforms are utilized to represent the prime depositional environments of sediments under which Total Heavy Minerals (THM) concentrated. In recent times, deeper exploration by sonic drilling has been carried out in the main sand bar of the deposit and retrieved huge lithological data. Different 3D visualization of exploration data using various geological Softwares (ArcGIS, Rockworks and Datamine) carried out.Understanding the morphology of the deposit is carried out using the topographic representation on GIS platform. Discontinuous linear dune ridges are present across the deposit. Sand column explored at an average depth of 40m represents the variety of depositional environment (lagoonal, barrier and beach) within basin. Lithological correlation for the entire (20km) stretch of BMSD carried out and major sand units have been summarized for the area. Heavy mineral (HM) concentrations in each sand column and their correlation using geospatial methods classify the trend and extent of mineralization into two potential zones (Zone 1 and Zone 2) depth wise. This study emphasizes the relationship between surface and subsurface manifestation of exploration data which reveals that BMSD could be part of Barrier bar system having different sub-depositional environments as back-barrier, barrier beach and inlet channel which are controlling the total heavy mineral concentration at various depths. Upper zone of ore body is confined to beach regime whereas lower zone is controlled by combination of beach, back-barrier and inlet channel sediments.

The controlling effect of chair-shaped slope break landforms on sedimentation in continental faulted basins: A case study in the Xilinhaolai area, Baiyinchagan depression, Erlian Basin, China

To reveal the geomorphic characteristics of the gentle slope zone in a continental faulted basin and its control on sedimentary systems, we have performed the geomorphic units division and comprehensive analysis of seismic facies, well-log facies, and core facies in the Xilinhaolai area in the western area of the Baiyinchagan depression, North China. The results find that the gentle slope in the Xilinhaolai area developed a chair-shaped slope break, which includes four geomorphic segments: steep slope of the depression margin (SSDM), shallow-water gentle slope (SWGS), deepwater steep slope (DWSS), and depression center. The chair-shaped slope break controlled the distribution of the sand body by controlling the water depth and hydrodynamic type of sedimentation. The SSDM was a favorable place for the deposition of beach bars. It has become a good oil reservoir not only because of its shallow burial and good physical properties but also because of the location configured with stepped faults. On the SWGS, the active river current and lake waves caused the deposition of large-scale braided river deltas and shoal bars, which are already the main oil and gas areas discovered in the Xilinhaolai area. On the DWSS, a large-scale slump turbidite fan developed and became a very favorable oil and gas reservoir near the oil and gas source rock. The slumped turbidite fans on the DWSS and the shoal bar on the SSDM are potentially favorable reservoirs for future oil exploration.

A Modeling Approach for Beach-Bar Sand Reservoirs Based on Depositional Mode and Sandbody Volume

Beach-bar sand in lacustrine facies represents one of the most significant reservoirs. Depending on the depositional characteristics, it can be further divided into two different sedimentary microfacies, beach sand and the bar sand. Favorable reservoirs are often developed in bar sand. The lower section of the upper part of the 4th member of the Shahejie Formation in the Gao89-1 block is a typical nearshore shallow water beach-bar deposit. Oil distribution is influenced by lithofacies and physical properties. In order to better characterize the heterogeneity within beach-bar sandbodies, a modeling method based on the depositional mode and sandbody volume is proposed. Firstly, a sandbody model is established. On this basis, an algorithm for distinguishing between beach and bar sand based on vertical thickness is proposed. The model is post processed based on the sandbody volume to remove unreasonable sandbodies. The method allows for a more realistic three-dimensional geological model of the beach-bar sands in the study area than the classical two-point geostatistical, object-based, and multi-point simulation method. A facies-controlled modeling approach is used to establish a petrophysical property model on this foundation; the result shows that the property models better reflect the characteristics of the petrophysical distribution in the Gao89-1 block.

Shaking table test and numerical research on seismic response of a CFST arch bridge for different soil grounds

Severe damages or failures of arch bridges on different soil grounds have been reported during previous strong earthquakes. The influence of different soil grounds on the seismic response of arch bridges is unclear. In this study, three large-scale shaking table tests were conducted to investigate the seismic response of a model bridge abutment of a concrete-filled steel tubular (CFST) arch bridge, which was set inside a model soil box at a reduced scale of 1/90. Grounds with three types of soil were simulated: silty clay, clay-gravel layered, and bare gravel soil. The accelerations and displacements of the model soils and the sliding displacement and settlement of the model bridge abutment were evaluated through the tests. The test results showed that the soil types significantly affected the seismic response of the soil and bridge abutment system, and the spectral characteristics of input waves significantly affected the acceleration amplitude ratio (AAR) of the bridge abutment; however, the changing trend of the AAR was usually related to the corresponding soil types. The soil grounds exhibited a remarkable filtering effect along the soil heights under seismic excitations, and the filtrations of the frequency components of the input waves for different soil grounds shows significant difference. Furthermore, the dynamic shear stress–strain curves showed that the silty clay soil remained in the nonlinear behavior development stage under strong seismic excitations, while the bare gravel soil remained in the linear behavior development stage. The energy dissipation capacity of the bare gravel soil ground could not be utilized. The test results in this study can be used for seismic risk assessment of different soil grounds, to guide the optimal seismic design of arch bridges for different soil grounds.

Impacts of Fracture Roughness and Near-Wellbore Tortuosity on Proppant Transport within Hydraulic Fractures

For unconventional reservoir hydraulic fracturing design, a greater fracture length is a prime factor to optimize. However, the core observation results from the Hydraulic Fracturing Test Site (HFTS) show that the propped fractures are far less or shorter than expected, which suggests that the roughness and tortuosity of hydraulic fractures are crucial to sand transport. In this study, a transport model of sands is first built based on experimental measurements on the height and transport velocity of the sand bank in fractures with predetermined width and roughness. The fracture roughness is quantified by using the surface height integral. Then, three-dimensional simulations are conducted with this modified model to further investigate the impact of tortuous fractures on sand transport, from which a regression model is established to estimate the propped length of hydraulic fractures at a certain pumping condition. The experiment results show that the height of the sand bank in rough fractures is 20–50% higher than that in smooth fractures. The height of the sand bank decreases with the reduction in slurry velocity and increases with the increase in sand diameter. Sand sizes do little effect on the transport velocity of the sand bank, but the increase in slurry velocity and sand volume fraction can dramatically enhance the migration velocity of the sand bank. The appearance of tortuous fractures decreases the horizontal velocity of suspended particles and results in a higher sand bank compared with that in straight fractures. When the sand bank reaches equilibrium at the tortuous position, it is easy to produce vortices. So, there is a significant height of sand bank change at the tortuous position. Moreover, sand plugging can occur at the entrance of the fractures, making it difficult for the sand to transport deep into fractures. This study explains why the propped length of fractures in HFTS is short and provides a regression model that can be easily embedded in the fracturing simulation to quickly calculate dimensions of the propped fractures network to predict the length and height of propped fractures during fracturing.

NATURAL FEATURES AND HYPOTHESES OF ORIGIN NEASHORE BARS IN THE COASTAL ZONE OF NON-TIDAL SEAS

Problems of the research. The article considers the origin, morphology and dynamics of unique forms of coastal-marine relief in the coastal zone of non-tidal seas, under the influence of the hydrogen factor, an exceptionally strong potential of mechanical energy, sufficiently large reserves of sand deposits (fractions of 0.05–1.00 mm), active influence of wave impulses and wave currents in the zone of energy dissipation, active nanoexchange between the shore and the underwater slope. It is shown that this issue has a long history of scientific research in different countries due to its important practical significance. Long years we researching the alongshore sand drifting between C. Bol. Fontain in North to Jebriyan Bay in South as a experimental natural object of the North-Western part of the Black Sea. Theoretical elaborations and methods. Among the natural features of the named landforms, the researchers distinguish 8 leading ones, which are manifested only in the environment of the coastal zone. Therefore, the purpose of the article is to consider the genetic hypotheses of the formation of underwater sand bars in the coastal zone of the seas over the past 100 years, and on this basis – to outline, evaluate, analyze several hypotheses about the formation of bars, show their positives and disadvantages, name the genetic features for the physical geographical. coastal environments As part of the eight most important and most common features, we have identified the following: distribution of wind wave sizes and wave current velocities; the value of the steepness of the underwater slope covered with sediments; value of sediment sizes and hydraulic value of coastal zone sediments; some processes of wave transformation and dispersion of wave energy; certain individual processes of sediment movement of different hydraulic magnitudes in a cell of a sandy coastal zone; steepness of wind waves during storms in the spray source; active action of sand drifts by movement along the coastline and under the influence of the regime of transverse sediments; the nature of underwater swells is different, because one of them moves from the underwater slope to the shore, another – from the shore towards the sea, and the third is dynamically stable. Main results and conclusions. As can be seen, the main hypotheses and the corresponding features of the formation of underwater swells act on their own, separately from the general process of development of the coastal zone of the seas. Such a principle does not meet the elementary requirements for the definition and evaluation of complex geographic natural systems. This is especially true for the coastal zone of the seas, where all the genetic components of the continental, oceanic, and coastal-marine types interact closely in a complex. They act unanimously. It is from such positions, according to this principle, that underwater sand bars and other coastal-marine landforms should be investigated. In other elements of the exogenous part of the geographic envelope, they are not found anywhere and determine the uniqueness of the coastal zone of the seas. The authors of these variants build their hypotheses on separate parts of natural coastal phenomena. Until now, researchers have avoided complex, systematic approaches to this topic. Therefore, the article provides recommendations for improving the theory of the genesis and development of underwater swells within different sites of alongshore sand drifting.

Characteristics of water alternating CO2 injection in low-permeability beach-bar sand reservoirs

Water flooding can be ineffective in highly heterogeneous low-permeability beach-bar sand reservoirs. The introduction of CO2 flooding helps boost the oil production of the reservoirs but only in an early stage. During the late stage of flooding, gas channeling would occur. Water alternating gas (CO2) (WAG) process can be used to delay gas channeling and improve the effect of CO2 injection, though its adaptability to beach-bar sand reservoirs remains unclear. In order to clarify CO2 injection characteristics in these reservoirs, experiments were carried out in high-temperature high-pressure NMR on-line displacement experiment apparatus to simulate different flooding modes on synthetic cores that can reflect the vertical heterogeneity of beach-bar reservoirs. Different CO2 injection modes were implemented on these cores and the displacement characteristics and residual oil distribution features during both WAG injection and continuous CO2 injection were analyzed quantitatively and qualitatively. The results show that the scheme of WAG injection after continuous CO2 injection can obtain better oil displacement efficiency than that of the scheme of continuous CO2 injection after WAG injection, but there is no significant difference in respect of oil displacement efficiency of WAG flooding between the mode of bar-injection – beach-production (injection into bar sand – production from beach sand) and the mode of beach-injection – beach-production (injection into and production from beach sand), with the former mode having a higher oil recovery rate. The wider pore-size distribution range of microscopic residual oil after WAG injection shows great potential of enhancing oil recovery from subsequent continuous gas injection. When WAG injection is implemented prior to continuous CO2 injection, the displacement effect of the latter is more significant. This research may provide a theoretical basis for CO2 EOR in this type of reservoirs.

Seismic diagenetic facies prediction of tight sandstone in the offshore sparse well area: An example from the Xihu Depression of the East China Sea Basin

The purpose of this study is to forecast the spatial distribution of diagenetic facies (DF) of tight sandstone in the offshore sparse wells area. Analytical test data, rock physics experiment data and prestack seismic data were used to study the spatial distribution of seismic diagenetic facies (SEISDF) of tight sandstone of the second (H4b) submember of the fourth (H4) member of the Huagang (E3h) Formation in the N gas-field, Xihu Depression, East China Sea Basin. Based on diagenesis and diagenetic minerals, core-based DF of the H4b sandstone were divided into chlorite-coated facies (CHF), calcite-cemented facies (CAF), dissolution facies (DIF), tightly compacted facies (TIF), and quartz-cemented facies (QUF). Various seismic elastic parameters were obtained by prestack elastic parameter inversion method, and sensitive seismic elastic parameters were selected according to the seismic identification principle of DF. In order to predict the spatial distribution of DF, four DF and sensitive seismic elastic parameters were integrated to establish a SEISDF prediction model based on supervised learning, and obtain a diagenetic facies comprehensive index (DFCI) that can distinguish four DF. Then, the 90° phase conversion technique of seismic lithology was used to realize the consistency of the DFCI between isochronous stratigraphic interfaces with core-based DF. The stratal slicing technique of seismic geomorphology was used to make stratal slices of the DFCI between isochronous stratigraphic interfaces. Representative stratal slices were singled out, and the spatial distribution of the SEISDF was interpreted. This study shows that the H4b1 sublayer primarily develops the TIF, while the H4b2 and H4b3 sublayers chiefly develop the QUF, CHF, and DIF. Compared with the H4b2 and H4b3 sublayers, the areas of the QUF and DIF in the H4b4, H4b5, and H4b6 sublayers slightly increase. The QUF are mainly distributed in the subaqueous distributary channel and a small number of sheet sand and channel bar depositional facies in the form of continuous sheets. The CHF are primarily developed in lenticular shape in the channel bar and a small amount of sheet sand and subaqueous distributary channel depositional facies. The most favorable DIF are chiefly developed in the subaqueous distributary channel, channel bar, and sheet sand depositional facies near the fault, which are distributed in strips. This study proposes a very valuable method for the SEISDF prediction of tight sandstone, which can provide a reference for the study of DF of similar strata in other sedimentary basins.

Developing and monitoring an innovative NNBF to nourish a bay bar: An example from the southeast shore of Lake Ontario

This project tests a cost-effective, innovative dredged sediment placement technique targeted to nourish an eroded barrier bar. The dredged sediment was placed in the nearshore in a Cobble Bell, a form designed to allow for efficient dispersal and migration of sediment by natural processes in this location (such as predominant waves and longshore transport) in a desired direction along the bar. We describe the regional and site assessment undertaken, and explain the way design parameters including technical feasibility, assumptions about wave climate, and constructability were accounted for. A monitoring protocol was designed and implemented to measure the vertical and horizontal accretion on the barrier bar. This included survey transects using RTK equipment and surface analysis of beach volume and morphology change via drone images and photogrammetry. Field measurements of the bar indicated that within the first few days, the piled material eroded rapidly, and over the next few months, migrated downshore, widening the previously breached area. This suggests that the cobble bell nature-based feature has the potential to both accelerate and slow down natural processes in ways that enhance the performance and attractiveness of the beach while minimizing costs. In addition to the monitoring results, we describe a monitoring protocol that is both simple and effective which can be adapted by local entities interested in the management of their coastal landscapes.

RELATIONSHIP BETWEEN OVIPOSITION OF Podocnemis unifilis AND WATER LEVEL IN PERUVIAN AMAZONIAN FLOODPLAINS

In the Amazon floodplains, hydrological variability plays a crucial role by shaping the habitat, offering shelter and feeding or breeding areas. During the dry season, some fresh water turtles such as the yellow-spotted turtle (Podocnemis unifilis Troschel, 1848) use the sand banks at point bar areas as breeding sites, which must be available in time for the start of oviposition. In this study, we used altimetry-derived water level data from radar satellites combined with in-situ hydrological measurements to evaluate water level variations and relate them to oviposition starting dates (2003-2012) from Pacaya-Samiria National Reserve, Peru. Synchronous hydrological behavior was found between the major river stems (Ucayali and Marañon) and the inner rivers (Pacaya and Samiria), thus enabling the utilization of water level in the main river stem to correlate with oviposition in the inner rivers. Mean oviposition date was July 23nd with selection of a narrow water level range (92 masl ± 0.9 SD). Consistent shifts towards early/late oviposition were found for years with early/late dry season onset. Extreme biological shifts in terms of oviposition date onset, were identified for specific years (2004, 2010 and 2011) mainly for the extreme dry year of 2010.

Drivers of functional diversity in the hyporheic zone of a large river

The effects of regional (hydrogeology and geomorphology) and local (sediment and hydrology) characteristics on hyporheic assemblages were studied along a 40-km reach of a large gravel-bed river. Hyporheic water and fauna were sampled at the upstream and downstream positions of 15 large gravel bars. The resulting 30 stations varied in their sediment grain size, stability and direction of river-aquifer exchanges. The study concludes that at the 40-km (sector) scale, the longitudinal distribution of hyporheic fauna was controlled by 1) the hydrogeology of the valley (i.e. gaining vs loosing sectors) that modifies abundance and taxonomic richness of stygobites 2) current channel morphometry of the river (i.e. shape and location of meanders), and 3) historical changes (i.e. river incision) which modify abundance and richness of assemblages. At the local scale, we found that surface grain size and stability of the sediment evaluated by visual observation were poor predictors of hyporheos composition. In contrast, the local hydrology (i.e. downwellings, upwellings, low vertical exchanges) explained a large part of the abundance, taxonomic richness and composition of the hyporheic assemblages. Stations with low vertical exchanges were found poorly colonized, while the upwelling zones were rich in stygobites and downwelling areas harbor abundant and species-rich temporary hyporheos. It was also observed that functional diversity was controlled by the same parameters, with high relative abundances of stygobites in upwelling zones and POM feeders in downwelling zones. The heterogeneity of hydrological patterns, with alternation of upwellings and downwellings may represent the optimal spatial structure for hyporheic biodiversity conservation and resilience in rivers.

Three-Dimensional Hole Size (3DHS) Approach for Water Flow Turbulence Analysis over Emerging Sand Bars: Flume-Scale Experiments

The many hydrodynamic implications associated with the geomorphological evolution of braided rivers are still not profoundly examined in both experimental and numerical analyses, due to the generation of three-dimensional turbulence structures around sediment bars. In this experimental research, the 3D velocity fields were measured through an acoustic Doppler velocimeter during flume-scale laboratory experimental runs over an emerging sand bar model, to reproduce the hydrodynamic conditions of real braided rivers, and the 3D Turbulent Kinetic Energy (TKE) components were analyzed and discussed here in detail. Given the three-dimensionality of the examined water flow in the proximity of the experimental bar, the statistical analysis of the octagonal bursting events was applied to analyze and discuss the different flume-scale 3D turbulence structures. The main novelty of this study is the proposal of the 3D Hole Size (3DHS) analysis, used for separating the extreme events observed in the experimental runs from the low-intensity events.

Subaerial and upper-shoreface morphodynamics of a highly-dynamic enclosed beach in NW Baja California

Estimating sediment budget is a challenge that requires understanding the morphological relationship between the subaerial beach and the upper and lower shoreface. Based on a unique dataset of monthly measured topographic and bathymetric measurements, this study describes the morphodynamics of the subaerial and subtidal sections of a highly-dynamic beach over a 5-year period (2015–2020). Typically, the beach presents a longshore bar trough (LBT) state at the end of the winter, driven by net offshore sediment transport. The nearshore morphology evolves into more reflective states (rhythmic bar beach, RBB; transverse bar rip, TBR; and low tide terrace, LTT) driven by onshore sediment transport when the incident wave-energy decreases over the spring and summer. Seasonal variations of the incident wave-energy resulted in large subaerial-subtidal exchanges of sediment (200–300 m3 m−1), but these exchanges were an order of magnitude smaller in yearly scales. Subaerial and upper-shoreface morphological changes varied alongshore. Larger variations existed in the south, influenced by persistent rip channels. Instead, alongshore processes resulting from changes in wave direction may control the morphodynamics in the center and north. The subtidal section in north and center gained significant amount of sand (300 m3 m−1) during high-energy conditions, which contributed to a net annual gain of 60 m3 m−1. The origin of that sediment is currently unknown, it could have bypassed from an adjacent beach, shifted alongshore or inputted from the lower shoreface deeper than the depth of closure. This research shows the presence of very large monthly-to-seasonal total volume fluctuations relative to net annual or multi-annual changes, and highlights that comparatively small additions to the annual sediment budget could potentially contribute to the long-term stability of the beach.

‘The wait for the Flood is also the wait for Fish!’: Water Commons among the Mishing on Majuli Island (Assam), India

Abstract Flood is often perceived as a destructive force in state and other hegemonic discourses on Majuli Island, India. However, for the indigenous Mishing who live near river banks or on chapories (sand bars), flood is not perceived as an abnormal external force, but as deeply intertwined with their daily living, culture and economy. More importantly, for the Mishing, flood represents the continuous annual creation of water commons. This paper examines the water commons formed by the annual deluge and describes the fishing culture of the Mishing in these commons. Contrary to privatised fishing grounds and private fisheries, where public access is limited, water commons are open to everyone and all villagers have equal access to this “common pool of resources.” Further, the paper examines the different aspects of Mishing subsistence fishing culture on the commons: community fishing; gender; fishing as subsistence and livelihood. This article is based on an ethnographic study of a Mishing village on Majuli Island. Participant observation and interviews were the main tools of data collection for this research. The paper concludes that Mishing subsistence fishing is economically and socio-culturally significant for the community, and Mishing fishing culture on the commons highlights their everyday life with the river on Majuli Island. Keywords: Chapori, commons, flood, Majuli Island, Mishing

Survival of the Strong and Dense: Field Evidence for Rapid, Transport‐Dependent Bed Material Abrasion of Heterogeneous Source Lithology

AbstractBed material abrasion is a major control on the partitioning of basin‐scale sediment fluxes between coarse and fine material. While abrasion is traditionally treated as an exponential function of transport distance and a lithology‐specific abrasion coefficient, experimental studies have demonstrated greater complexity in the abrasion process: the rate of abrasion varies with clast angularity, transport rate, and grain size. Yet, few studies have attempted to assess the importance of these complexities in a field setting. Here, we develop a new method for rapidly quantifying baseline abrasion rate in the field via Schmidt Hammer Rock Strength. We use this method, along with measurements of gravel bar lithology, to quantify abrasion in the Suiattle River, a basin in the North Cascades of Washington State in which sediment supply to the channel is dominated by recurrent debris flows from a tributary draining Glacier Peak stratovolcano. Rapid downstream strengthening of river bar sediment and a preferential loss of weak, low‐density vesicular volcanic clasts relative to non‐vesicular ones suggest that abrasion is extremely effective in this system. The standard exponential model for downstream abrasion, using single‐lithology abrasion rates fails to reproduce observed downstream patterns in lithology and clast strength. Incorporating heterogeneity in source material strength as well as transport rate‐dependent abrasion largely resolves this failure. Further work is needed to develop a comprehensive quantitative framework for the dependence of bed material abrasion on grain size and transport rate.

Harmonic Extrapolation of Seismic Reflectivity Spectrum for Resolution Enhancement: An Insight from Inas Field, Offshore Malay Basin

For decades, how to improve the resolution limit of seismic data has been a concern for seismologists. For this reason, several geoscientists have proposed various methods of improving the bandwidth of the data. Discovering an easy and scientifically reliable means of improving seismic data resolution would undoubtedly help geophysicists interpret more complex details of the subsurface geology. In this study, we transformed the bandlimited time-domain seismic data to the frequency domain using the Fourier analysis method, and a basis pursuit atomic algorithm was applied to decompose the real and imaginary parts of the spectrum into summations of cosines and sines. The resultant reflectivity spectrum (in the frequency domain) was deconvolved by a pre-estimated wavelet spectrum to obtain the true earth’s reflectivity data spectrum and was subsequently extrapolated to beyond the original band limit. The result shows an extended bandwidth from 68 Hz to 161 Hz and 80 Hz to 170 Hz for both synthetic trace model and the main seismic data, respectively. Consequently, this improved vertical resolution of sub-seismic geologic features, such as crevasse splay, levee, barrier bar complex, lagoon inlet channels, alluvial fans, and fluvial channels, and shows subtle facies variations in Inas field.

Monitoring 23-year of shoreline changes of the Zengwun Estuary in Southern Taiwan using time-series Landsat data and edge detection techniques

More than 80% of sandy beaches in Taiwan have been experiencing a severe recession, although the sediment discharge of rivers in Taiwan is significantly higher than the world average producing almost 2% of global fluvial sediment discharge. This contradiction is primarily due to the widespread constructions of reservoirs and intensive anthropogenic activities in coastal regions. In addition, coasts are particularly vulnerable to hazards due to climate change, such as sea-level rise, as they are located at the transition zone of terrestrial and marine environments. Along with the fact that Taiwan is an island and is one of the most climate-vulnerable regions globally, coastal management and sustainability are nationally critical topics, especially considering the ongoing reformation and legislation of Taiwan's coastal conservation laws.As stated in the Sustainable Development Goals (SDGs) goal 14, accurate and continuous shoreline positions information is essential for coastal conservation. However, by reviewing previous global studies and projects commissioned by the Taiwanese government aiming at monitoring shoreline changes, they usually exhibit several limitations, such as limited band selections or conservative band ratio-derived water indices, relying on either manual digitization or simple thresholding methods, focusing on either artificial or smoothly shaped coasts, and using images acquired at considerably different tidal height levels.Therefore, in the present study, a subpixel shoreline extraction approach based on a sustainable cross-generation dataset and a robust edge detection algorithm is proposed. This approach is exemplified by the Zengwun River Estuary located in southwestern Taiwan—Taiwan's most critical coastal preservation region. By quantitatively analyzing the resultant time-series shoreline positions from 1999 to 2021, several hotspots of shoreline recession have been identified: an extreme erosional rate up to −69.4 m year−1 is revealed in the northern sand bank; while the offshore sand bar demonstrates an overall landward retreat rate of −35.4 ± 1.24 m year−1.

Microfacies and Reservoir Connectivity of Shore Sandbar, Southern Indus Basin, Pakistan

Shore sand bar reservoirs have attracted much attention as one of the target intervals with the greatest potential for petroleum exploration and development in marine sedimentary basins. Nevertheless, due to lack of effective research methods, it is difficult to analyze the rapid lateral change and heterogeneity in a sand bar reservoir, which has a major impact on the efficient petroleum development that seriously restricts the rolling evaluation and efficient development of sand-bar reservoirs. In this study, based on integrated analysis of cores, thin sections, logging, 3D seismic data, production test and dynamic data, through a combination analysis of drilling and seismic interpretation data—the petromineral composition, microfacies and reservoir connectivity of the shore sand bar in the southern Indus basin are investigated, which is used for the fine description of the sandbar reservoir. The results show that the shore sand bar is located in a relatively high-energy shore sedimentary environment, which is conducive to forming a favorable lithologic reservoir. Four sedimentary microfacies types are identified, including center bar, bar edge, inter bar and local mudstone interbeds. The sandbar microfacies are changed rapidly, and different microfacies types overlap each other, especially the inter bar and local mudstone interbeds that overlap and intersect in the center bar and bar edge, which significantly reduces the internal reservoir connectivity as well as intensifying the heterogeneity of the sandbar reservoir. The sandbar reservoir is not connected transversely, the physical properties are changing rapidly, and the sandbar reservoir is cut into several relatively independent oil reservoirs.