Muddy Sand Research Articles

ANALYSIS OF MANGROVE FOREST VEGETATION ON MOLAS BEACH, BUNAKEN DISTRICT, MANADO CITY

The lack of scientific information about the current condition of the mangrove ecosystem on the Molas beach in the Bunaken District of Manado City is an important reason to conduct a study related to the analysis of mangrove forest vegetation. The purpose of this research is to identify the types of mangroves and to find the Important Value Index (INP) of mangroves on the Molas beach in the Bunaken District of Manado City. Data collection was conducted using the line transect method with plots at only one observation station, which was then analyzed to determine the Importance Value Index (INP). Based on the observations, it was found that four types of mangroves were present at the research location. The dominant mangrove species are Bruguiera Cylindrica, Bruguiera gymnorrhiza, Aegiceras cosniculatum, and Ceriops tagal. The substrate condition, which is dominated by muddy sand, and the water quality parameters that affect mangrove growth generally still meet the standards for mangrove growth. The species Ceriops tagal has the highest values of Relative Density, Relative Frequency, and Relative Dominance, resulting in the highest INP. Meanwhile, the lowest INP was found in the species Bruguiera gymnorrhiza in the tree category

Temporal Analysis of Mangrove Canopy Cover of High Resolution Satellite Imagery on the West Coast of Bangkalan Regency, Madura East Java

Mangroves are plants that live in muddy substrates, muddy sand, sand to tidal areas. These plants have important roles for marine organisms, carbon sequestration, as shoreline protectors from waves or erosion and sediment filters before entering the sea. The influence of human activity in the form of conversion of mangrove land to other forms or caused by natural disasters is a dangerous threat to the mangrove ecosystem. The magnitude of mangrove cover change is an important component so information is needed on changes in the spatial and temporal distribution of mangrove cover. This study aims to temporally analyze mangrove cover using high-resolution satellite imagery on the West Coast of Bangkalan Regency. This research uses secondary data in the form of Planetscope high-resolution satellite images from 2018 - 2023. The data will be processed to determine changes in mangrove area using Fv (Fractional Vegetation Cover). Calculation of the Fv (Fractional Vegetation Cover) value is done from the results of the minimum and maximum values of NDVI (Normalized Difference Vegetation Index). The results showed that there was a change in mangrove cover which was initially included in the FVC (Full Vegetation Coverage) class in 2022 with an area of 41.12 Ha to the HVC (High Vegetation Coverage) class with an area of 84.82 Ha in 2020. At the Arosbaya location, the highest Fv value occurred in 2019 with an area of 206.48 Ha. Reduction of mangrove area occurred in Sepulu and Arosbaya sub-districts due to land use change and sedimentation.

Heavy metals in core sediments from the western Bay of Bengal: implications on historical pollution, eco-environmental risks, and potential sources

The western Bay of Bengal is particularly susceptible to the harmful impacts of increasing coastal pollution, as coastal population and urban development are occurring at unprecedented rates. The rapid urbanization and industrialization along the east coast of India coupled with the transfer of contaminants into the Bay of Bengal through riverine systems, causing a direct impact on marine ecosystems. In the present study, an attempt has been made to understand the heavy metal distribution on shelf sediments in the western part of the Bay of Bengal to infer their source, processes, and historical changes in marine pollution. Three short sediment core samples were collected and analysed for sediment texture, organic matter, and heavy metals. Cores 1 and 2 contain a high amount of sand content, representing shallow marine with moderate to high-energy conditions, and were deposited at a recent time. Core 3 was dominated by muddy sand to sandy mud, which denotes calm sedimentation without any turbulence, and these sediments were deposited under relatively low-energy conditions. The higher concentration of organic matter in the top layers of the core indicates both marine and terrestrial input. The heavy metal contents show quite heterogeneous and variable distributions from one element to another and from one core to another. The calculated pollution indices such as Contamination Factor (CF), and Geoaccumulation Index (Igeo) and Pollution Load Index (PLI) values indicate that all the core sub-samples are severely enriched and highly polluted by Cd and moderately polluted by Pb. The increased heavy metal concentration in the upper portion of the sediment cores and moderate to considerable ecological risks indicate that these metals have been deposited in the study area for the past few decades.

Unveiling Preliminary Study of the Holocene Sedimentary Environments and Biofacies in Western of Al-Hammar Marsh, Southern Part of Iraq

Biofacies and sedimentary environment analyses were conducted across three sites west of Al-Hammar Marsh. Excavations were undertaken at different depths for a comprehensive study. The initial site was probed at 9 m depth, followed by the second site at 5 m, and the third site at 9 m. Subsequent examination of these samples aimed to unveil insights into grain size, fossil contents, and their respective ecological settings. The grain size analysis revealed three distinct sediment types: silt, sandy silt, and muddy sand. Additionally, fossil assemblages hinted at three primary biofacies. The first facies represented a fresh marsh-fluvial environment identified across all three sites at different depths. Specifically, this biofacies manifested from the surface to about 200 cm in site one, 50-150 cm in site two, and 50-250 cm in site three. The second biofacies indicated a shallow marine environment at depths ranging from 250 to 550 cm in site one, 200-300 cm in site two, and 300-650 cm in site three. Lastly, the third biofacies denoted a lagoon or tidal flat environment observed at 600-900 cm depths in site one, 300-500 cm in site two, and 700-900 cm in site three. Notably, the third biofacies in site three exhibited signs of influence from alkaline freshwater, particularly in the third location at a depth of 700-800 cm. This influence was attributed to a mixture of marine and freshwater species, including; Quinqueloculina candeiana, Quinqueloculina angulta, Cubicula fluminalis, and Melanoides tuberculate. Abundant occurrences of these species were noted in the silty clay lithology of this layer.

Depositional model of the Holocene coquinas - Albardão platform, southern Brazil

For the past decade, giant deepwater oil discoveries in the pre-salt section of the Campos and Santos basins of Brazil, have brought significant attention to offshore exploration activities along the South Atlantic margins. The prolific Cretaceous coquina deposits in these basins are part of the pre-salt rock record and constitute an effective but complex and heterogeneous hydrocarbon reservoir difficult to predict and model. Parting from this context, an evaluation of the sedimentological, structural and taphonomic criteria for coquinas are essential to better understand and predict the facies distribution and depositional models of the pre-salt coquinas strata. Based on this premise, the present work aims to genetically interpret 133 mixed carbonate-siliciclastic bottom sediments of the Albardão shelf – a modern marine coquina analogue, using facies description, investigating the relationship with hydrodynamic forces, and accessing the influence of morphology and structural framework on their deposition. From these analyses, we recognized a hybrid facies, three modern carbonate facies in analogy to the carbonate rock classification and four siliciclastic facies. These eight facies were then grouped into three facies associations representing high, moderate, and low energy facies. The high energy facies association comprises rudstones (Rf) and grainstones (Gf) with highly fragmented bivalve shells and barnacles abundantly present in the beach system, above the fair-weather wave base limit (FWWB). These facies also occur offshore on bathymetric highs above the storm wave base limit (SWB) but display less reworking than the coastal high energy facies above the FWWB due to wave shoaling. The moderate energy facies association consists of hybrid sand (Hs), sand (S) and muddy sand (mS) occurring between the FWWB and SWB limits in the offshore transition zone with extensive winnowing action and low rate of reworking. The low energy facies association includes sandy mud (sM), mud (M) and micritic mud (Mc), characterized by the decantation of the fine sediments below the offshore SWB limit. The results confirm a bottom facies distribution controlled by depth, shelf profile morphology and energy from incident waves. The fragmented rudstone and fragmented grainstone facies are the best-recognized reservoirs with both having high porosity and high permeability.

Mapping benthic sediment types and composition in a turbid Jamaican bay using hydroacoustic data and different spatially explicit interpolation techniques

Hydroacoustic sensors are better suited for mapping shallow turbid coastal waters, but surveys must take place along transects, necessitating the interpolation of processed, large, spatially dependent hydroacoustic datasets to produce continuous maps. The aim of this study was to evaluate the performance of interpolation techniques that can handle data obtained from a hydroacoustic survey (covering 23 km2) conducted in 2016 in a shallow bay in southwestern Jamaica. Independent data or a 5-fold cross validation were used to compare the accuracies of continuous maps of benthic sediment percentage composition and submerged aquatic vegetation cover (SAV), interpolated from the survey data using random forest (RF) regression (RFr), RFr kriging (RFrk) and Ensemble Machine Learning (EML) with rotated/oblique coordinates. Categorical/thematic maps of sediment types interpolated using RF (RFc) and EML classifiers and a spatial Markov chain model with indicator kriging predictor/simulation (Mc-IK) were also compared. RFr, RFc, RFrk and EML covariates included coordinates and auxiliary data. The following maps were more accurate than corresponding interpolated maps: EML - mud, sand, silt, clay and SAV; RFr - loss on ignition [LOI]; RFrk - calcium carbonate; Mc-IK – sediment types with 3 and 4 classes. The Mc-IK maps were also the most suitable maps for assessing spatial and quantitative changes. The predominant substrate type in the bay was muddy sand covering 15.7 km2. The highest percentage composition of mud, silt, clay, and organic matter [LOI] was found close to the mouth of the Black River where sandy mud was found, indicating a high input of terrigenous sediment. Calcium carbonate composition showed an opposite spatial trend and was positively associated with higher SAV percentage cover. The bay is now part of a protected area, as such, these maps will be used as a baseline to gauge the impact of increased protection/management on benthic dynamics.

Assessment of Some Clay Deposits from the Gercus Formation (Middle Eocene) for Brick Manufacturing in the Dokan Area, NE Iraq

The objective of this research is to evaluate the suitability of some clay deposits from the Gercus Formation (Middle Eocene) in the Dokan area, Northeastern Iraq for brick manufacturing. Physical properties of the raw material including grain size analysis and Atterberg limits showed that composed mostly of sand and silt with a minor proportion of clay and classified as muddy sand. According to the plasticity chart, the studied sample plotted on the field of silt and organic clay with low plasticity. The geochemical analysis by X-ray fluorescence revealed that composed of a low percentage of silica and alumina and a high percentage of calcium oxide and magnesium oxide. The mineralogical analysis by X-ray diffraction showed that the studied samples were composed of non-clay minerals (dolomite, quartz, hematite, albite, anatase, and orthoclase) and clay mineral (montmorillonite, kaolinite, and illite). Twelve ceramic briquettes were prepared from the clay sample by semi-dry pressing method and pressed by 200 kg/cm² pressure with 14 – 15 % moisture content and fired at 880, 900, and 920 °C for evaluation tests of linear firing shrinkage, apparent porosity, water absorption, bulk density, efflorescence, and compressive strength. Results of physical and mechanical properties of the studied ceramic briquettes compared with the specification of Iraqi standard (1993) for clay brick manufacture, according to this specification the studied sample was not suitable for brick manufacturing due to a high percentage of water absorption and low compressive strength.

Net Transport Patterns of Surficial Marine Sediments in the North Aegean Sea, Greece

The spatial distribution of sediments on the seafloor reflects the various dynamic processes involved in the marine realm. To analyze sediment transport patterns in the North Aegean Sea, 323 surficial samples were obtained and studied. The granulometry data revealed a diverse range of grain sizes of surficial sediments, ranging from purely sandy to clay. The predominant size classes were silt and muddy sand, followed by sandy silt and mud. However, there were very few samples that fell within the clay classes. The sorting coefficient ranged from 0.21 to 5.48, while skewness ranged from −1.09 to 1.29. The sediment transport patterns were analyzed based on the grain-size parameters (mean, sorting, and skewness). The results showed the variability of flow parameters involved in sediment distribution. River influx and longshore drift near the shoreline are the most significant factors affecting sediment transport. At the open sea, sediment distribution is mainly controlled by general water circulation patterns, especially by the outflow of low-salinity waters from the Black Sea through the Dardanelles and the Marmara Sea. The heterogeneity of sediment textural parameters across the study area suggests that seafloor sediments are further reworked in areas where water masses are highly energetic. It can be concluded that open sea water circulation controls sediment distribution patterns at the open shelf, while close to the coast, river discharge plays a key role.

Particle aggregation induced by microorganisms is a key mechanism for the biostabilization of coastal sediment

Biofilm surrounding sediment particles can significantly enhance the stability of coastal sediment. This phenomenon is known as biostabilization. Biofilm mainly consists of extracellular polymeric substances (EPS) and microorganisms. While the role of EPS in biostabilization is well-established, microbial contribution requires further exploration. Herein, an experiment was conducted to compare the stability and morphological characteristics of sediment under the effects of biofilm (with microorganisms) and pure EPS extracted from the biofilm (without microorganisms). The microorganisms used for biofilm culture are composed of diatoms and chlorella. The sediment used is a mixture of well-sorted muddy sand (D50 = 77 μm). Erosion tests showed that in the early stage of biofilm culture (within 17 days), biofilm and pure EPS had a similar ability to stabilize sediment, suggesting that in this stage, biofilm stabilized sediment relying on EPS. However, after 17 days of culture, biofilm showed a stronger ability to stabilize sediment than pure EPS, implying that in this stage, biofilm stabilized sediment by both EPS and microorganisms. These results indicate that microorganisms can also contribute to biostabilization, but during the early stage of culture, microorganisms in biofilm cannot make such contributions. Optical observations found that when the sediment-stabilizing ability of biofilm and pure EPS was comparable, the morphological characteristics of sediment particles under the effects of them were similar, both appearing as scattered single particles. However, when biofilm exhibited a stronger sediment-stabilizing ability, sediment particles with biofilm connected into large-size aggregates, whereas sediment particles with pure EPS remained single and scattered. These results suggest that in the later stage of biofilm culture, microorganisms play a role in the aggregation of sediment particles and hence contribute to biostabilization. Based on these findings, a conceptual framework has been proposed for predicting sediment stability under the effects of biofilm.

Variable downcanyon morphology controlling the recent activity of shelf-incised submarine canyons (Alboran Sea, western Mediterranean)

This research aims to distinguish genetic sedimentary processes building canyon geomorphological patterns and the factors driving different sedimentary activities in two nearby Mediterranean shelf-incised submarine canyons (Carchuna and Motril) that exhibit different degrees of incision on the narrow margin of the northern Alboran Sea.The straight Carchuna Canyon incises the shelf up to 200 m off the coastline and exhibit steep canyon walls featuring narrow terraces, muddy sands with high contents of organic matter along the thalweg, and transported shelf benthic foraminifera in distal settings. The Motril Canyon head is wider and incises the shelf edge, ca. 2 km off the coastline. It exhibits a sinuous morphology and less steep walls, wider terraces, and higher sedimentation rates with muddy sediments along the thalweg. In both canyons, cross-section relief, width, incision, and area decrease downslope, although these parameters increase locally.The downslope variations of geomorphological parameters are attributed to enhanced erosional/depositional processes promoted by tectonically controlled abrupt changes of the axial channel orientation. The degree of shelf incision, the location of the canyon heads in relation with the local sediment sources, and the seasonally variable hydrodynamic regimes determine the different degrees of recent canyon activity. The Motril Canyon is interpreted as a mature system that reflects episodic activity, collecting fine-grained sediments from the nearby Guadalfeo River. The Carchuna Canyon exhibits a youthful developmental stage whose activity is more continuous and involves sediment trapping of littoral cells and continuous downslope sand transport.

Initial observations of the impacts of infauna on portable free fall penetrometer measurements in sandy parts of Mobile Bay

The seabed surface provides habitat for abundant and diverse fauna, whose burrowing activities have been shown to modify geotechnical properties of surface sediments. Whether these impacts affect geotechnical properties on larger scales of traditional measurements has not been well studied. This study represents an initial attempt to assess whether infaunal activity affects seabed properties on a scale relevant for, and therefore, detectable in portable free fall penetrometer measurements. Specifically, we examine sediment strength profiles of the upper 10–70 cm of sandy (poorly graded sand and muddy sand) seabed sediments in Mobile Bay, Alabama, USA, hypothesizing that infauna create heterogeneity in sediment structure that would lead to variability in PFFP vertical profiles as well as among replicate measurements at a site. Sediments were composed predominantly of sands, with only 17% of the sites featuring sand contents < 97% and median grain sizes ranging from 0.0987 to 0.3457 mm. Sediment strength generally decreased with a decreasing sand content, but variability was not explained by sand content alone. PFFP impacts in sandier sites (> 97% sand) were limited to the surface few cm, but considerable vertical and spatial variability in muddy sands and lower strength at sites with abundant burrowing infauna suggest that infaunal activities may affect PFFP measurements in these sediments.

Nitrogen loading resulting from major floods and sediment resuspension to a large coastal embayment

Major floods pose a severe threat to coastal receiving environments, negatively impacting environmental health and ecosystem services through direct smothering with sediment and nutrient loading. This study examined the short and long-term impacts of the February 2022 major flood event on mud extent and sediment nitrogen flux in Moreton Bay (the Bay), a large, sub-tropical embayment in Southeast Queensland, Australia. Short-term impacts were assessed three days after the flood peak by sampling surface water at 47 sites in the direction of the predominant circulation pattern. Longer-term impacts were assessed by undertaking an intensive sediment survey of 223 sites and a nutrient flux experiment using sediment core incubations to simulate calm and resuspension conditions for the four key sediment classes. Short-term impacts revealed elevated turbidity levels extended across the Bay but were highest at the Brisbane River mouth, ammonium concentrations varied inversely with surface turbidity, whereas nitrate concentrates closely tracked surface turbidity. The sediment survey confirmed fine sediment deposition across 98 % of the Bay. Porewater within the upper 10 cm contained a standing pool of 280 t of ammonium, with concentrations more than three orders of magnitude higher than overlying surface waters. The nutrient flux experiment revealed an order of magnitude higher sediment ammonium flux rate in the sandy mud sediment class compared to the other sediment classes; and for simulated resuspension conditions compared to calm conditions for sand, muddy sand, and mud sediment classes. Scaling across the whole Bay, we estimated a mean annual sediment flux of 17,700 t/year ammonium, with a range of 13,500 to 21,900 t/year. Delivery of fine sediments by major floods over the last 50 years now impact >98 % of the benthic zone and provide a major loading pathway of available nitrogen to surface waters of Moreton Bay; representing a significant threat to ecosystem health.

FLUVIAL SEDIMENTOLOGY OF THE RIVER ETHIOPE SEDIMENTS, NIGER DELTA, SOUTHERN NIGERIA

Despite modern advances in the study of rivers globally, there remains a plethora of work to be done especially in the area of fluvial sedimentology of some present-day river systems. Previous studies on fluvial sedimentology of the sediments of the river Ethiope (in southern Nigeria) are meagre. Grain size analytical methods are indispensable to infer siliciclastic sediments' hydrodynamic conditions, transportation mode(s), and sedimentary environments. Twenty-eight samples (n=28) of the river Ethiope sediments were selected and studied using granulometric analyses (mechanical sieving and pebble morphometric methods). The granulometric analyses results revealed that the obtained sediments were comprised of 82.75% sand, 9.33% gravel, and 7.92% mud. A ternary diagram of sand-gravel-mud shows the sediments are mainly gravelly sand, with few indicating slightly gravelly sand, gravelly muddy sand, muddy sand, and sandy gravel. The grain size statistical analysis shows that the river Ethiope sediments consist of medium to coarse, poorly-sorted to moderately well-sorted, strongly coarse skewed to strongly fine skewed, and very platykurtic to extremely leptokurtic sands. The pebble morphometric analysis revealed that the pebbles range in shape from bladed (B) 22%, compact-bladed (CB) 17%, compact (C) 16%, compact-platy (CP) 16%, compact-elongated (CE) 12%, platy (P) 5%, to elongated (E) 5%. The integration of bivariate plots, ternary diagrams, and C-M patterns plotted for the sediments of the river Ethiope indicated a fluvial environment with sediments characterised by low to moderately high energy that transport sediments of different sizes and grades through saltation, traction, and suspension modes. This study also confirms that sediment transport modes such as saltation, traction, and suspension typify river environments. In general, the existing sedimentologic models derived from grain size analysis of sediments and pebble morphometric methods obtained from modern-day rivers can be applied to better understand transport modes, sedimentary processes, and palaeoenvironments of their ancient counterparts.

Characteristics of minerals and oxide compounds in sediment collected from blood cockle culture areas at Bandon Bay, Thailand.

Bandon Bay is a very fertile bay for coastal aquaculture, especially for blood cockles (Anadara granosa). Its structural pattern supports the flow of nutrients which directly sent from many rivers resulted the high production capacity of blood cockle at the top level in the country. Besides organic compounds present in sediment, inorganic substances are essential for growth, survival and shell development of blood cockles. A comparative study of minerals and oxide compounds which accumulated in the sediments at eight stations around the cockle culture area was conducted. These stations are located along the estuaries at Tha Thong, Tha Chang, Phum Riang, and Tapi. The proportion of oxide compounds were determinedusing X-Ray Fluorescence (XRF) technique and minerals were analyzed by Atomic Absorption Spectroscopy (AAS). Results showed that sediment characteristics, oxide composition and the amount of minerals among the stations are different from each other. The sediments of the eastern and the western coasts were characterized as crumble clay and muddy sand, respectively. Twelve types of oxide compounds, namely SiO2, Al2O3, Fe2O3, K2O, Cl, MgO, Na2O, SO3, CaO, TiO2, MnO, P2O5 were found in various quantities, with SiO2, Al2O3, and Fe2O3 were the fundamental minerals ranging from 85.64-90.82%. Tha Thong estuary in the east coast showed highly significant quantities (P<0.05) of potassium, calcium and manganese compared to the other estuaries.

MORPHOLOGICAL IDENTIFICATION OF SEA CUCUMBER AND PROXIMATE ANALYSIS OF THE HABITAT SUBSTRATE OF MUDY SEA CUCUMBER ON MOLOSING ISLAND AND BIAU BEACH BOLAANG MONGONDOW REGENCY

Sea Cucumbers belong to the phylum Echinodermata, class Holothuroidea. These creatures are commonly found in areas near coral reefs, sandy waters, seaweed, seagrass beds, and muddy sands. This research aims to identify the various species of Sea Cucumbers in the waters around Molosing Island and Biau Beach, Bolaang Mongondow Regency. Furthermore, the research seeks to determine the nutritional content of the muddy substrate where Sea Cucumbers reside. The study involves observing the form, colour, and patterns (morphology) of Sea Cucumbers and testing the nutritional content of their muddy habitat substrate using proximate analysis with the SNI by difference method. The identification results of the form, colour, and patterns of Sea Cucumbers at Molosing Island and Biau Beach, Bolaang Mongondow Regency, reveal three species of Sea Cucumbers from different genera: Holothuturia and Stichopus. One species on Molosing Island is Holothuria leucospilota, while two on Biau Beach are Stichopus horrens and Stichopus vastus. Proximate analysis of the muddy habitat substrate of Sea Cucumbers includes the following parameters: ash content, protein content, crude fiber content, and fat content.

BLUE SWIMMING CRAB ENLARGEMENT TECHNIQUE: INSIGHT FROM SMALL-SCALE FISHERY IN THE SOUTH COAST OF PAMEKASAN, MADURA ISLAND

Pagagan Village, Pademawu District, and especially members of the "Berkah Capit Biru" fishermen, had the potential to carry out the sustainability of blue swimming crab because of the abundant crab fisheries. The purpose of this research was to encourage fishermen to not always carry out crab fishing activities in nature so nature remained sustainable and to increase the potential of natural and human resources who were enthusiastic about crab enlargement in Pagagan village. This research was conducted from January to May 2022. The crab breeding location measured 8x10 meters, had a substrate of muddy sand, and was in a coastal area bordering a mangrove ecosystem. Wooden stakes woven with bamboo with a netting around them were set higher than the wave. This enlargement technique did not use aeration in the form of wheels but only utilized tidal conditions so that periodic water changes occurred at the site. The stages in the crab enlargement technique are 1) site selection, 2) construction, 3) spreading seeds, 4) feeding, 5) controlling, and 6) harvesting. This enlargement technique is a solution for crab fishermen to meet market stocks. &#x0D; Keywords: blue swimming crab, enlargement technique, small-scale fishery

Sedimentary record of bottom currents and internal tides in a modern highstand submarine canyon head

ABSTRACTThe evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides, can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub‐bottom profiles, high‐resolution sediment core analyses (X‐ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine‐grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro‐scale and micro‐scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross‐laminations and fining‐upward successions, which are attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross‐cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re‐establishment of benthos and associated biogenic structures, supporting the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record.

Sedimentological and ichnological variations in fluvio‐tidal translating point bars, McMurray Formation, Alberta, Canada

ABSTRACTSedimentological and ichnological descriptions of fluvio‐tidal translating point bars are rare, and complex physico‐chemical processes make highly detailed but concise facies descriptions challenging. Herein, mesofacies are defined to describe and interpret three ancient translating point bars from the Lower Cretaceous McMurray Formation, Alberta, Canada. Twenty‐three mesofacies are defined, based on their recurring sedimentological and ichnological characteristics. These mesofacies form the building blocks of beds and bedsets that make up three depositional facies. Facies 1 reflects sand dune migration at the channel base, which grades into inclined heterolithic stratification of Facies 2 and 3. Facies 2 occurs in the centre and seaward portions of the translating point bars and records tide‐dominated deposition of sand and muddy sand during periods of reduced river discharge. Ichnological suites and bioturbation intensities in these beds reflect persistent but variable brackish‐water conditions, fluctuating deposition rates and the deposition of mud. Mud beds are derived from flows with high suspended‐sediment concentrations. Tidally derived mud beds are typically bioturbated with trace fossil suites indicative of slow deposition rates and brackish‐water conditions. Mud deposited during elevated river discharge is burrowed after the dewatering of the bed. Facies 3 occurs at the landward apex of the translating point bar and is marked by sand‐rich and mud‐rich dune deposits with abundant soft‐sediment deformation, indicative of elevated flow velocities and deposition rates. Bioturbation is rare and sporadically distributed owing to unstable substrates. The distribution of the facies reflect the hydrodynamic variations that occurred vertically and laterally across the bar in response to temporal variations in fluvial and tidal flow interaction, as recorded by their mesofacies. The detailed facies analysis strongly suggests that deposition of the three McMurray Formation translating point bars occurred in proximity to the turbidity maximum zone of a fluvio‐tidal channel system.

Polychaetes (Annelida: Polychaeta) off Kyky (Black Sea, Trkiye) with descriptions of three new species.

The examination of benthic materials collected in September 2022 at six stations off Kyky (south-west coast of the Black Sea, Trkiye) both on hard (three stations) and soft substrata (three stations) at depths ranging from 8 and 27 m revealed a total of 57 polychaete species belonging to 22 families. Among the species, the polynoid Malmgrenia polypapillata is a new record for the Black Sea fauna, and three species belonging to the Syllidae (Erinaceusyllis defneae n. sp.) and Terebellidae (Polycirrus karadenizicus n. sp. and P. rhombolabiatus n. sp.) are new to science. Algae dominated (Cystoseira cinita, Cladophora sp. and Phyllophora crispa) rocky substrata had 30 polychaete species and a maximum polychaete density of 7325 individuals/m2, while soft bottom substrata (fine sand and muddy sand with shell fragments) possessed 38 species and a maximum polychaete density of 3520 individuals/m2. The family Nereididae (3176% of the total number of individuals), and the species Platynereis dumerilii and Polyphthalmus pictus dominated hard bottom stations, whereas the families Nephtyidae, Spionidae and Dorvilleidae, and the species Micronephthys longicornis, Protodorvillea kefersteini and Prionospio maciolekae were represented by high number of individuals at soft-bottom stations.

Seasonal iron fluxes and iron cycling in sandy bioirrigated sediments

Permeable sediments, which represent more than 50% of the continental shelves, have been largely neglected as a potential source of Fe in current global estimates of benthic dissolved iron (Fed) fluxes. There are open questions regarding the effects of a range of factors on Fed fluxes from these deposits, including seasonal dynamics and the role of bioirrigation. To address these gaps, we performed laboratory-based sediment incubation experiments with muddy sands during summer (21 °C) and winter (7 °C). We used bioirrigation mimics to inject overlying water into the permeable sediment with patterns resembling the bioirrigation activity of the prolific bioturbating polychaete, Clymenella torquata. Newly developed in-line Fe accumulators were used to estimate Fe fluxes with a recirculating set-up. We found high Fed fluxes from sandy sediments, especially in benthic chambers with simulated bioirrigation. In the winter fluxes reached &amp;gt;200 µmol Fed m-2 d-1 at the onset of irrigation and then decreased over the course of a 13-day experiment while in the summer fluxes from irrigated sediments reached &amp;gt;100 µmol Fed m-2 d-1 and remained high throughout a 7-day experiment. Despite different geochemical expressions of Fe-S cycling and resulting porewater Fed concentrations in winter and summer, large Fed fluxes were sustained during both seasons. Solid-phase and porewater concentration profiles showed that maximum concentrations of key constituents, including total solid-phase reactive Fe, and porewater Fed and ammonium, were located closer to the sediment water interface (SWI) in irrigated cores than in non-irrigated cores due to the upward advective transport of dissolved porewater constituents. This upward transport also facilitated Fed fluxes out of the sediments, especially during times of active pumping. Our study demonstrates the potential for large Fed fluxes from sandy sediments in both summer and winter, despite relatively low standing stocks of labile organic matter and porewater Fed. The primary driver of these high fluxes was advective porewater transport, in our study induced by the activity of infaunal organisms. These results suggest that permeable sediments, which dominate shelf regions, must be explicitly considered in global estimates of benthic Fed fluxes, and cannot be simply extrapolated from estimates based on muddy sediments.