Sand Ridges Research Articles

How do morphological characteristics affect tidal asymmetry in the Radial Sand Ridges?

While it is widely recognized that the Radial Sand Ridges (RSR) in the South Yellow Sea are predominantly shaped by tidal forces, there remains a limited understanding of how this distinctive morphological configuration—characterized by an interlaced channel-ridge system—can subsequently influence local tidal dynamics. This study examines the effects of morphological features on tidal asymmetry, taking into account seabed slope, relative depths between ridges and channels, and channel convergence. Three principal indices—namely tidal-duration-asymmetry (TDA), peak-current-asymmetry (PCA), and slack-water-asymmetry (SWA)—are employed to quantify various dimensions of tidal asymmetry. The findings indicate that SWA serves as the most morphology-sensitive indicator, whereas TDA exhibits minimal sensitivity to morphological changes. Furthermore, seabed steepness emerges as a critical factor influencing tidal asymmetry within the RSR; steeper slopes enhance intrinsic energy conversion processes, thereby inducing tidal asymmetries. Additional analysis reveals that streamwise advection accounts for an average of 88 % of total advection scale while controlling for spatial heterogeneity. Specifically, the average integral sum of advection terms along submerged sand ridges is 2.53 times greater than that along the deepest section of the tidal channel line—a significant contributor to spatial variability in SWA. With a positive seabed slope, the apex of the RSR acts as a source for overtides which interact with incoming astronomical tides, consequently generating tidal asymmetries. Moreover, this study illustrates varying dependencies of tidal asymmetry on bottom stress across channels and ridges, contributing to spatial variability in arc direction among RSRs. Ultimately, this research elucidates complex interactions between tidal flow and morphological characteristics within RSRs and provides insights into tide evolution in analogous ebb-shoal systems.

Storm-Driven Tree Exposure and Geomorphic Change: Predicting the Distribution of Preserved Late Pleistocene Tree Stumps on the Outer Alabama Continental Shelf

The Alabama Underwater or Drowned Forest is a well-preserved Late Pleistocene (dated to 72–56 ± 8 ka, 2σ) terrestrial landform on the northern Gulf of Mexico continental shelf that provides geomorphic and ecosystem information rarely preserved during the glacial intervals. Stumps of bald cypress (Taxodium distichum (L.) Rich.) trees were exposed in ∼18 m of water following Hurricane Ivan in 2004. This research investigates geomorphic changes to the Mississippi-Alabama-Florida (MAFLA) sand sheet, which presents as shore-oblique Holocene sand ridges, and the exposure and burial of tree stumps following the passage of Hurricane Sally in 2020 using repeat sidescan and bathymetric surveys (2015–2016 and 2021). Using two newly identified tree exposure areas and their geological properties, this research also hypothesized a new location where tree stumps may be outcropping. The bathymetry indicates regions with up to ∼1 m of erosion and deposition over the five years between the two surveys. Similarly, the sidescan sonar indicates changes in the location and numbers of exposed tree stumps as well as between 47,000 and 62,500 tons of sediment erosion within the study area following Hurricane Sally. The 2015 and 2016 data found 25 tree contacts whereas the 2021 survey found 76 tree contacts and only 5 of them occurred in both surveys suggesting the tree exposures are dynamic and presumably changing with the passing of large tropical cyclones. Additionally, the hypothesized exposure location had 26 newly identified tree stump contacts within a mixed texture unit along the sand-mud boundary, confirming our understanding of the geomorphic characteristics leading to the exposure of the buried forest. This research will expand the potential areas for investigations into Late Pleistocene ecosystems and landforms and their associated climatic and ecologic conditions in the Gulf of Mexico as well as in other passive continental margins.

Morphological discrimination of fouling Ulva and Blidingia species on Pyropia rafts in Rudong, China: an in-field protocol for early monitoring of algae forming the Yellow Sea green tide

Abstract Fouling seaweeds on nori cultivation rafts in Subei radial sand ridges (Jiangsu, China) are believed to be the source of the Yellow Sea green tide (YSGT). Although major species are consistent across years, their biomass and proportions undergo significant annual changes, which was speculated to be related to the size of YSGT. Therefore, early detection and biomass assessment of the bloom-forming algae are crucial, increasing the need to develop a morphological identification method suitable for large sample sizes in the field. In this study, fouling seaweeds were collected from this area in spring 2017. Five major species, Ulva aragoënsis, Ulva compressa, Ulva linza, Ulva prolifera, and Blidingia sp. were molecularly identified, and confirmed as the predominant fouling seaweeds on nori rafts over the past decade. In this unique ecological niche, the morphological features of species changed significantly yet stably. Based on morphological observations, an identification key for these five species was established. Furthermore, a simplified version containing only two indices was developed for practical field use, with an average accuracy of 81 % (δ 2 = 0.003) in empirical accuracy assessments. This method can be used to monitor the community structure and succession of fouling seaweeds at the geographical source of YSGT.

Geomorphology and sediment mobility on sand banks: A study of Dogfish Bank, Hecate Strait, Northeast Pacific Ocean

AbstractMovement of sediment along shallow continental shelves is a natural process with wide‐ranging environmental and economic implications, making it of high importance to marine spatial planning efforts in the offshore. Development of marine renewable energy, for instance, requires detailed understanding of the morphodynamics of mobile bedforms to select foundation types and ensure safe installation of infrastructure in shallow shelf environments. This study evaluates geomorphology and sediment mobility of Dogfish Bank (< 20 mbsl) in the Hecate Strait offshore British Columbia, Canada, using hydroacoustic and airborne bathymetric data combined with seismic profiles and grain‐size information. These data reveal current‐swept features ranging from sediment‐depleted lag to sediment‐abundant sand ridges and dunes, with sand ribbons and furrows in‐between. Seismic reflection data show up to 15 m of surficial sand concentrated beneath north‐aligned sand ridges that dominate the bathymetry of northwest Hecate Strait. Sand ribbons (typically understood sediment‐limited features in shallow marine environments) are notably maintained over seabed with comparable sand thickness to adjacent dunes (i.e. sediment‐abundant features), suggesting local spatial variability in hydrodynamics and sediment characteristics (principally grain size) influence expression of mobile bedforms. Repeat mapping between 2008 and 2019 shows dunes and ribbons both migrate northwards, with largest seafloor changes along northeast‐facing lee sides of dunes, matching closely with published models of sediment mobility which suggest northward bedform migration is largely driven by storms. Median total migration distance is 164 m (northward) for dunes (time‐averaged rate of 14.9 m/year). Sand ribbons show less migration (median northward distance of 73 m) and migrate in a depth‐dependent manner. Because sand ribbons are typically flow‐parallel features, their lateral migration likely results from varying current directions and flow acceleration over shallower seabed. Sand ribbon migration should therefore a consideration in studies examining seabed change, particularly when they are formed over unconsolidated sediment.

Between-year weather differences and long-term environmental trends both contribute to observed vegetation changes in a plot resurvey study.

Repeated surveys of vegetation plots offer a viable tool to detect fine-scale responses of vegetation to environmental changes. In this study, our aim was to explore how the species composition and species richness of dry grasslands changed over a period of 17 years, how these changes relate to environmental changes and how the presence of spring ephemerals, which may react to short-term weather fluctuations rather than long-term climatic trends, may influence the results. A total of 95 plots was surveyed in 2005 and resurveyed in 2022 in dry grasslands of the Kiskunság Sand Ridge (Hungary, Eastern Central Europe), where there has been a significant increase in mean annual temperature during the last decades, while no trends in precipitation can be identified. Db-RDA was performed to reveal compositional changes. The changes in environmental conditions and naturalness state were assessed using ecological and naturalness indicator values. We also compared per-plot richness of all species, native species and non-native species of the old and the new relevés. All analyses were repeated after removing all spring ephemerals. We found clear temporal changes in species composition. Mean temperature indicator values increased, while mean soil moisture indicator values decreased during the 17 years. Also, decreasing per-plot richness was detected both for all species and for native species, while mean naturalness increased. After the removal of spring ephemerals, the compositional changes were less obvious although still significant. The increase in the temperature indicator values remained significant even without the spring ephemerals. However, the decrease in the moisture indicator values, the decrease in the number of all species and native species, as well as the increase in naturalness indicator values disappeared when spring ephemerals were excluded from the analyses. Our study demonstrates that between-year weather differences and long-term environmental trends both contribute to observed vegetation changes.

OSL and radiocarbon dating of core TBF-1 on the outer shelf of the East China Sea and implications for late Quaternary stratigraphic correlation

It is crucial to establish a robust chronology for understanding late Quaternary sedimentation processes and environment changes in response to sea-level fluctuation on shelves. The shelf of the East China Sea (ECS) is featured by huge terrigenous sediment input and striking land -sea interaction during the late Quaternary. However, there remains controversy in chronostratigraphic rebuilding of transgression and regression deposits during eustatic-glacial cycles, mainly due to a lack of reliable dating data. In this study, an extensive comparison of 17 optically stimulated luminescence (OSL) and 15 AMS 14C ages from core TBF-1 (upper 40 m) provides a constraint in chronostratigraphic reconstruction since Marine Isotope Stage (MIS) 5. OSL ages range from 9.5 ± 0.7 to 67.3 ± 4.8 ka at depths from 2.00 to 28.00 m, while 14C ages range from 6645 to 41435 cal a BP at depths from 0.02 to 17.52 m. Regression analysis demonstrates a high level of agreement between OSL and 14C ages, with r2 values of 0.91 and 0.90, respectively. For Holocene sediments (U1), both OSL and 14C methods are applicable in tidal sand ridges, however, it should be noted that 14C ages may exhibit a young bias of up to 3 ka. For pre-Holocene sediments (U6-U2), OSL ages are robust within saturation limitation of OSL signal (De up to ca. 166 Gy), cross-checked by feldspar post-IR IRSL (pIRIR) dating protocol. Nevertheless, the shell 14C ages (11620 and 10390 cal a BP at depths of 13.95–14.56 m) in Last Glacial Maximum (LGM) fluvial sediments of U2 are significantly underestimated, because of their susceptibility to recrystallization and overgrowth, resulting in carbon exchange with environment. While the peaty layer's14C age in deltaic deposition (17.50 m, U5) was determined to be 36420 cal a BP, coincided with OSL age of 39.6 ± 3.9 ka. The chronostratigraphy since MIS 5 for core TBF-1 exhibits a significant correlation with previously published cores SFK-1, DZQ4, and DH02, on the ECS outer shelf. Through the evaluation of those underestimated 14C ages and saturated OSL ages, we re-elucidated the primary sedimentary facies and their respective formation periods. This sedimentary stratigraphic illustration exhibits significant consistency with eustatic-glacial cycles. The renewed chronological framework for ECS shelf allows better correlation between the late Quaternary sedimentary evolution and the land-sea interaction on open shelves dominated by siliciclastic sedimentation.

The regressive surface of marine erosion generated by tides: A case study from a Pleistocene tidal sand ridge sequence, Calabria, Southern Italy

AbstractThe regressive surface of marine erosion is a key stratigraphic discontinuity used to identify episodes of forced regression in marine strata. Typically, it marks the base of shallow‐marine (e.g. shoreface and deltaic) deposits eroding over relatively deeper‐water (e.g. shelf and prodelta) lithofacies. While well‐documented in marginal‐marine areas, its occurrence in offshore or strait settings dominated by tidal currents is less understood. This study investigates lower Pleistocene outcrops in the Plio‐Quaternary Siderno Basin, Calabria, southern Italy, where tidal sand ridges developed in a Mediterranean strait. High‐resolution drone images reveal a basinward‐dipping basal surface marking the onset of tidally dominated sedimentation. This discontinuity separates underlying shelf fines from overlying cross‐stratified, tidal bioclastic/siliciclastic arenites, indicating a prolonged period of marine regression in a strait setting. The stratal architecture of the ridges shows cross‐strata aggradation in up‐dip sections, transitioning down‐dip into balanced aggrading/prograding strata, and further basinward into markedly prograding deposits. These features are interpreted to reflect an initial phase of normal regression, evolving into forced regression. This latter stage is characterised by a progressive deepening of the basal discontinuity, causing more erosional effects on the underlying beds, with a vertical basinward fall of about 60 m over 2 km. Internal foreset geometry (two‐dimensional vs. three‐dimensional cross strata) and their vertical and lateral repetition indicate stages of equilibrium and disequilibrium for tidal bedforms, reflecting varying current speeds and water depth changes. The regressive surface of marine erosion here is formed by tidal currents, rather than waves, suggesting a new type of sequence stratigraphic discontinuity associated with tide‐dominated settings.

Siliciclastic Reservoir Geo-modeling using TGS-SIS hybrid algorithm of the Upper Cibulakan Formation, Offshore Northwest Java Basin

Abstract The Upper Cibulakan is the primary hydrocarbon-producing formation in the Offshore Northwest Jawa area, operated by PHE ONWJ (Pertamina Hulu Energy Offshore Northwest Jawa). The productive interval in this formation comprises alternating sandstone and shale up to 45 feet of thick. Geologically, this interval is a shallow marine deposit with strong influence of tidal in the Ardjuna Sub-Basin, offshore part of Northwest Jawa Basin. The good quality reservoir layer is associated with Tidal Sand Ridges (TSR) facies characterized by lenticular sedimentary structures and the occurrence of shale intercalation in sandstone. The occurrence of shale, regarding its facies association package, varies greatly and significantly determines the quality of the reservoir. The geometry and quantity of facies distribution and association will significantly affect the calculation of hydrocarbon reserves during the modelling processes. Considering this, the selection of modeling methods and algorithms must be carried out appropriately. The use of the SIS (Sequential Indicator Simulation) algorithm in describing the TSR facies distribution still has shortcomings in randomness. Correspondingly, it requires to be combined with the TGS (Truncated Gaussian Simulation) method as it plays a great impact in calculating the distribution of sandstone and reservoir geometry. Meanwhile, SIS defines shale intercalation within TSR facies. Combining these two methods produces a more precise model of TSR facies associations. Besides, the concept of reservoir deposition is easier to explain based on the outcome result from the combined methods.

Extracting waterline and inverting tidal flats topography based on Sentinel-2 remote sensing images: A case study of the northern part of the North Jiangsu radial sand ridges

Muddy tidal flats with landforms vary widely over space and time. The evolution of tidal flats topography has had a significant impact on the region. Therefore, there is a need to develop methods for rapidly and accurately characterizing tidal flats topography. This study applied thresholding segmentation (TS), machine learning, and two image classification methods to Sentinel-2 remote sensing images to extract the instantaneous waterline of the northern part of the North Jiangsu Radial sand Ridges (NJRSR). Tidal level data at specific time intervals were obtained using the Delft3D and TPXO9 models, after which tidal flats topography inversion was conducted. As a result, varied among the different classification methods, with the K-Nearest Neighbors (KNN) algorithm producing the optimal waterline extraction. Furthermore, the accuracy of tidal level simulation was improved by employing Delft3D software and constructing a scaled-down model of the study area. Comparisons with Delft3D model simulations of tidal levels with observations at three tide gauge stations yielded accuracies of 17.5 cm, 18.5 cm and 17.9 cm, this result showed that the establishment of the tidal level model can enhance the accuracy of tidal flats Digital Elevation Model (DEM) inversion. In fact, the combined application of the KNN algorithm and Delft3D model within retrieval of tidal level provided the most accurate topographic inversion, with an average error of 0.297 m, which was reduced to 0.292 m after median filtering, and the results indicated a trend of southward erosion in the tidal flats in the study area, with a turning point roughly located in the southern part of Doulong Port. The results of this study can help improve the future monitoring of dynamic changes in intertidal wetland topography and the conservation and development of tidal flats areas.

Geomorphological processes following the construction of an offshore artificial island in the radial sand ridges of the South Yellow Sea

Offshore artificial islands represent a novel way to develop and utilize marine space resources. Previous research has focused on predicting erosion and deposition distributions following the islands construction, utilizing laboratory experiments and numerical simulations. However, the absence of long-term continuous monitoring has hindered systematic studies on the geomorphological processes of these islands. A 20-years of underwater terrain monitoring scheme was conducted before and after construction of the Rudong Artificial Island in Jiangsu Province, China. The results were combined with on-site observations of tidal currents, suspended sediment concentrations, and surficial sediment to investigate the evolution of the water channel–sand ridge system and the development process of local scour around the artificial island. The results indicated that after the construction of the artificial island, its surrounding water channels showed an overall evolution trend of the north channel shifting towards the north, the middle channel widening and moving south, and the south channel extending westward and southward. Scour has been observed at the four corners of the artificial island, with the peak depths of 7.3 m, 5.6 m, 13.7 m, and 12.2 m at the southwest, northwest, northeast, and southeast corners respectively. The scour in the southwest and northwest corners reached an equilibrium within five years. However, in the southeast corner, continuous erosion of the shoal on the southeast side of the artificial island enhanced the local hydrodynamic force, leading to further scour development. The large-scale scour in the northeast corner was mainly caused by changes in the local flow field following the construction of water intake pipelines and their protection projects. These geomorphological changes are the joint results of the natural evolution of the radial sand ridges and local erosion and deposition from engineering construction. Currently, the sandbanks surrounding the island are still undergoing dynamic evolution following engineering construction, and local scour around the island has not yet reached equilibrium.

The morphology and formation of a binary sand ridge in the Beibu Gulf, northwestern South China Sea

The overall morphological characteristics and shallow architecture of a tidal sand ridge were examined for the first time in the Beibu Gulf, northwestern South China Sea. The linear sand ridge is characterized by a unique binary feature in terms of its shape, constituents, architecture, and behavior. In the northern part, the crestline has rotated anticlockwise to the principal tidal currents, the sediment is coarse, and large active sand waves occur on the surface. In the southern part, the crestline is parallel to the principal tidal currents, the sediment is fine, and no large bedforms have developed on the crest. The sand ridge has shrunk in the northern part and elongated at its southern end in recent decades, leading to a southward or southeasterly movement. The upper strata of the northern part mainly comprise inclined bedding, whereas parallel bedding prevails in the southern part. The bedding implies historically dominant transport directions in different sand ridge parts and suggests that flow modification occurred during ridge evolution. The inclined bedding in the lower strata of the northern part dips to the south or southeast, indicating the existence of unidirectionally moving sand waves. This is unusual for a growing sand ridge where convergent sand transport should have already occurred. The present sand ridge is interpreted as a source from the joining of a sand wave assemblage and an adjoining nascent sand ridge, which has experienced stages of connection, accretion, and migration. The transformation of a sand wave assemblage to the northern part is attributed to the hydraulic change from a unidirectional residual flow regime over sand waves to a bidirectional residual flow regime. This flow regime change was not related to sea level changes but benefited from a new sand body that was produced by sand waves merging into the original nascent ridge.

Geomorphological features along the shelf of the southern Brazilian margin: Implications for shallow-water sediment transport induced by ocean currents

Chirp profiles collected on the southern Brazilian shelf were combined with sedimentological and hydrodynamic data to characterize shelf geomorphology, focusing on the development of outer shelf bedforms and their genetic links with major oceanic currents. Outer shelf sediment accumulations are interpreted as two scales of bedforms, such as dunes and sand ridges. In the São Paulo Bight, cuspate bedforms are bounded landward by a geomorphological scarp. The sector between Florianopolis and Mostardas also exhibits frequent asymmetric bedforms, whereas the inner- middle shelf is covered by semitransparent sheets. The southern Rio Grande Cone is characterized by stratified deposits covering vast outer shelf areas. Surficial sediment samples reveal a dominantly muddy composition and relatively high carbonate contents. Hydrodynamic data indicate a major influence of the Brazil Current over the São Paulo Bight. The prolific bedform outer-shelf environment is assumed to be mostly relict formed in a transgressive shallow-water setting. The sand ridges are believed to have evolved from a moribund stage characterized by morphological degradation to a relict stage, with preservation enhanced by fine-grained winnowing, coarse sediment armoring, and early cementation. Bedform migration seems to be occurring on the São Paulo Bight due to the presence of a nearly permanent meander of the Brazil Current. Over most of the inner shelf, the northward advection of sediments mainly led by the Brazilian Coastal Current has formed extensive fine-grained deposits. The occurrence of a relict shelf scarp may have conditioned the formation of the outer-shelf bedform environment. The vast spatial distribution of bedforms over most of the outer shelf seems comparable with other shelf areas, such as the south African shelf, dominated by the influence of unidirectional oceanic currents. Dune dimensions are lower on the Brazilian shelf, due to their relict character, the geomorphological configuration of the margin, and the scarcity of sand sources.

Coastal Evolution of Satingpra Peninsula, Songkhla Province: Implications for Understanding Songkla Lagoon Formation

Songkhla Lagoon has been studied for decades, but there is no clear evidence of its origin. As a barrier to the lagoon, the Satingpra Peninsula plays a crucial role in understanding its formation. Eleven sediment samples from sand ridges and tidal flats on the Satingpra Peninsular were collected and analysed for granulometry and geochronology. Both coarse-grained and fine-grained quartz-rich fractions were utilised to prepare samples of aliquots. The optically stimulated luminescence (OSL) dating was performed using the single-aliquot regenerative dose method for a determined (deposited) age. In addition, previous research, geological surveys and geochronological data were combined to explain their formation in this region. The OSL ages in the present study indicated that the late Holocene regression occurred between 0.36 and 3.27 ka (ka stands for 1,000 years). Integrated with previous studies, recorded ages dating back to the mid-Holocene sea level rise (ca. 6.5 ka) and the subsequent late-Holocene decline, indicate that both the old lagoon and middle beach ridge exhibit a sand ridge formation that runs parallel to the shoreline, extending from the south to the north. The middle sand, in this study, formed from about 3.02 to 1.5 ka ago resulting in the lagoon being isolated from the sea during that time. The lagoonal tide led the deposition as the present tidal flat from 3.3 to 1.7 ka. About 2.19 ka ago, the inner and middle ridges formed due to wind-driven processes influenced by a dry climate. This was followed by a continued sea level regression, leading to the formation of the outer ridge around 1.5 ka ago when the sea level was 1.4 m below the present sea level. However, it’s essential to consider this sea level data in relation to the tectonic and human-induced land motions in the surrounding area. HIGHLIGHTS OSL ages, based on average dose model at the Northern Satingpra Peninsula were 1.04 - 3.27 ka. The old sand ridges of the Satingpra Peninsula prograde northward after mid Holocene sea level highstand. Paleo sea level based on wind-wave sediments contact was 1.4 m lower than present day at 1.46 ka. GRAPHICAL ABSTRACT

Mangrove development on a remote volcanic island in the South Atlantic

Sueste Bay, in the Fernando de Noronha archipelago (FNA), contains the only mangrove area among the oceanic islands of the South Atlantic. This work aims to reconstruct this mangrove's evolution during the Holocene based on a morphostratigraphic study integrated with palynological and multi-elemental geochemical data, temporally calibrated with radiocarbon dating. The data obtained indicated that, around 8000 to 7000 cal yr BP, well-developed Rhizophora and Laguncularia mangroves established over altered rocks of the Quixaba (phonolites, lamprophyres, basanites, trachyandesites and basalts) and Remédios (basanites, melilite and melanophelinites) Formation, under rising relative sea level, about 2 to 3 m below present. This period was the last record of Rhizophora in the FNA. From 6000 to 3600 cal yr BP, the lagoon system was eroded and significantly retrograded, under rising RSL during at least part of time, leaving clay pebbles scattered in the lower/upper shoreface deposit as the only record of its reworking. This process limited mud/mixed flats near the mouth of the Maceió River. Under a relative stability of RSL from 3600 cal yr BP to the present, a progradation of coastal facies, including beach/foredunes ridges, occurred and allowed the development of the modern lagoon system over swales between aeolian sand ridges. Mangroves were only observed during modern times but in environmental conditions very different from those of the previous occurrence. Indeed, Laguncularia coexists with several invasive plants within the narrow mixed flats associated with a small and almost filled tidal creek, whose siltation may be a product of the artificial damming of the Maceió River to supply public water to the archipelago. This study highlights the complex interactions between natural processes, sea-level changes, and human activities in shaping the coastal evolution of the Fernando de Noronha archipelago over the Holocene.

Sedimentary evolution of the Nakdong River deposits on the Korea Strait shelf since the Last Glacial Maximum

We investigated the development of depositional systems and the evolution of the depositional sequence in the Korea Strait shelf deposits since the Last Glacial Maximum (LGM), integrating a dense grid of seismic data and multiple long-core datasets from the delta plain to offshore. This depositional sequence includes the lowstand systems tract (LST), transgressive systems tract (TST), and highstand systems tract (HST) over an incised valley sequence boundary. These tracts developed discrete depositional environments in both the bay and the open shelf area demarcated by the island arc. The evolution of these tracts can be delineated into five distinct phases based on the sea-level curve for the Korea Strait since the LGM. First, in the LST (the LGM lowstand; 25–17 kyr BP), fluvial deposits with upward-fining characteristics were observed in bedrock-incised valleys within the bay, while amalgamated fluvial deposits were identified in unconfined incised valleys over Pleistocene sequences on the open shelf. A shelf-margin delta was also detected along the continental shelf break. The TST is composed of three subunits: the lower, middle, and upper TSTs. In the lower TST (the post-LGM transgression; 17–13 kyr BP), estuarine deposits were occupied in the bay, while a broad sand sheet with a few moribund sand ridges was present on the open shelf. In the middle TST (the Younger Dryas (YD) event; 13–12 kyr BP), bay barrier islands were observed growing along the island arc, but a mid-shelf delta and a sand ridge developed on the open shelf. In the upper TST (the Early to Mid-Holocene transgression; 12–6 kyr BP), the fining-upward retrogradational bayhead delta–estuarine complex within a bay encircled by barrier islands developed toward the head of the estuary. Finally, in the HST (the Late Holocene highstand; 6–0 kyr BP), the coarsening-upward delta was prograding seaward, with its prodelta initially distributed off the river mouth and later as a mud belt along the eastern coast. The TST deposits, encompassing diverse sedimentary systems that make up a substantial portion of the depositional sequence on the shelf, were significantly influenced by a combination of topographical characteristics limiting the discharge of sediment from the river into the open shelf and the displacement of accommodation space with stepwise sea-level rise.

ЗООКОМПОНЕНТ ОБЪЁМНЫХ ФРАГМЕНТОВ БИОГЕОЦЕНОЗОВ В ЭКСПОЗИЦИИ МУЗЕЯ ЗЕМЛЕВЕДЕНИЯ МГУ

The exposition of the department "Natural Zones" in the Earth Science Museum of Moscow State University (25th floor, halls Nos 18-20) presents 15 full-scale exhibits of dry 3D fragments of biogeocenoses, namely: spotted tundra; forest tundra; swamps: flat-hummocky tundra, oligotrophic upland and mesotrophic lowland sedge; sprucegreen grass; grass-grass and tipchak-grass steppes; subtropical mountain forest; alpine meadows; semi-deserts; deserts - clay, wormwood-solyanka and ilak belosaksaulnik on ridge sands; and savannas. These exhibits demonstrate the interaction of the main natural components characteristic of the respective climatic conditions (soils, flora, and fauna). The article gives a description of the animal species represented in the exposition based on a visual examination of zoological exhibits and a study of their nomenclature and taxonomic changes.

Shift of the Yenisei and Abakan Beds as Reasons for Constructing the Second Abakan Fort in 1707

The study explores the reasons behind the relocation of the construction site for Fort Abakan from the mouth of the Abakan River, as initially planned, to the right bank of the Yenisei River, between two mountains, Unyuk and Turan. The shift of sand ridges, damming these rivers and changing their beds, is examined, and the locations of the projected forts are described. Written sources suggest that the Abakan and Yenisei beds as related systems changed their positions simultaneously, likely between 1691 and 1697 and definitely no earlier than 700–400 BC. Modern hydrological data suggest that processes that occurred in the region in the Early Modern Age were essentially like those that occurred in the Early Iron Age. The earlier date of the Abakan bed’s change is evidenced by the destruction of the 1st millennium BC Tagar sites near Sartykov village on the Abakan. At present, the Yenisei makes an abrupt eastward turn in that place, following the general direction of rivers in the region. D.A. Klements’s idea that after leaving the Western Sayan canyon, the Yenisei had flowed westwards is rejected. The change of location for the prospective fort was caused by the evolution of riverine systems of Western Siberia, specifically by the shift in the Abakan bed.

People beyond the border in the sandbars of Damodar River: understanding the people’s management in a changing landscape, India

ABSTRACT Sandbars are narrow ridges of sand formed by the river system in Bengal delta in eastern India. Some charlands or riverbeds of the Damodar River are situated along both its banks as well as in its central channel, offering habitats for both human populations and wildlife. Throughout its history, the river has been known as ‘Sorrow of Bengal’ owing to its frequent inundations and devastating impact. Since the partition of India in 1947, numerous sandbars have been colonized at various stages. Before partition, the area consisted of vast fields covered with bushes. This paper elaborates on the living conditions of marginalized people of Bangladesh and the local settlers who have inhabited the sandbars. They face a multitude of challenges, including safety concerns during storms, a lack of access to essential amenities like water, electricity, healthcare, education, and employment opportunities, as well as transportation difficulties. Sandbars are susceptible to flooding, necessitating frequent evacuations for the residents when massive floods occur. Additionally, these riverbeds are often geographically isolated from neighbouring landmasses. Despite these challenges, both refugees and local settlers have managed to adapt to life on these transient sandbars. The research also elucidates how communities often develop unique techniques and technologies to mitigate the challenges posed by the river. Finally, this study demonstrates that assessments of vulnerability and insecurity are arbitrary and insignificant; however, immediate survival is crucial.

Delays in Territorial Development – Case Study of the Hungarian Sand Ridge Region

There are regions in Europe that are particularly vulnerable both environmentally and socially. Hungary's Sand Ridge in the Danube–Tisza Interfluve (Homokhátság in Hungarian) is considered such a region. The water balance of these lowland landscapes has been negative for decades, and complex ecological and social problems have escalated in parallel with aridification. Therefore, this region deserves special attention from the territorial development perspective. Over the last two decades, our successive studies have revealed that development policies in the region have been unsuccessful on multiple occasions, unable to alter the core negative trends significantly. We also noticed the mistakes and inertness of spatial planning when we worked on our current applied research: the Sand Ridge Regional Development Concept and Program. This study aims to explore deficiencies and shortcomings of the spatial policy and identify the factors that have slowed territorial development. Insights from interviews with experts and surveys conducted with local municipalities highlight that access to European Union funds has not alleviated long-standing conflicts. Resource-driven and uniform planning has become one of the main hindering factors. According to the experts, the necessary complex programs have not been implemented, and many initiatives have stalled. They also expressed concerns that Sand Ridge's natural and social endangerment will continue to increase.

A Novel Method to Detect Short-Term Erosion and Deposition Within the Intertidal Zones and its Application to the Large Radial Sand Ridges in China

A Novel Method to Detect Short-Term Erosion and Deposition Within the Intertidal Zones and its Application to the Large Radial Sand Ridges in China