Thin Mud Layer Research Articles

Seismic airgun sound propagation in shallow water of the East Siberian shelf and its prediction with the measured source signature

Seismic airgun sound was measured with an autonomous passive acoustic recorder as a function of distance from 18.6 to 164.2 km in shallow water (<70 m) at the continental shelf of the East Siberian Sea in September 2019. The least-square regression curves were derived in the zero-to-peak sound pressure level, sound exposure level, and band level in a frequency range between 10 and 300 Hz using the initial amplitude scaled from the near-field hydrophone data. In addition, propagation modeling based on the parabolic equation with the measured source spectrum was performed for range-dependent bathymetry, and the results were compared with the band level of the measurements. The sediment structure of the measurement area was a thin layer of iceberg-scoured postglacial mud overlying a fast bottom with high density based on grounding events of past ice masses. The observed precursor arrivals, modal dispersion, and rapid decrease in spectrum level at low frequencies can be explained by the condition of the high-velocity sediment. Our results can be applied to studies on the inversion of ocean boundary conditions and measurement geometry and basic data for noise impact assessment.

Damping coefficient by long waves—viscoelastic mud–current interaction

In this work, we study the damping of long linear waves propagating on a thin mud layer, which obeys a viscoelastic behavior, in the presence of a marine current; two cases are considered: (1) a current traveling in an opposite way to the wave propagation and (2) in the same way to the wave propagation. We obtain an asymptotic solution to the dimensionless governing equations, which allows identifying the competition between the different mechanisms involved to gain insight into the physics by which coastal mud responds to water waves. To determine the shear stresses into the viscoelastic mud, we have used the well-known Maxwell rheological model. At the interface water–mud, we assume the presence of a small Stokes' layer, and this condition allows us to consider the continuity of shear stresses and velocities at the interface. The effects of the mud physical parameters as well as the hydrodynamics impact of the water waves on the damping coefficient, fluid velocities, and shear stresses and on the free surface elevation are analyzed. The results show that the maximum value of the damping coefficient occurs when the mud thickness is of the same order of magnitude as the Stokes' layer and for increments of the current magnitude traveling in an opposite way to the wave propagation. The asymptotic solution is compared with solutions reported in the specialized literature and the results adjust properly.

Possibly the oldest fish-made resting traces

The Silurian Sharawra Member (middle to late Llandoverian) in Saudi Arabia exhibits unique surface traces with exceptional preservation: Seven small, wing-shaped traces occur on a sandstone slab showing well-defined hummocky cross-stratification having a few decimeters wavelength being covered by a thin mud layer. These traces are preserved as concave epirelief along with elongated internal striae and surrounded by slightly elevated levees. Preservation of these delicate, 10–20 mm long and ∼10 mm wide traces suggests that they were formed after a storm event when mud had already settled to the sediment surface. The lack of wave-generated sedimentary structures implies deposition between fair-weather and storm-wave base probably preventing further rapid reworking by waves. Based on their geometry, internal pattern, and spatial distribution, these wing-shaped traces are interpreted to have been produced by relatively stationary bottom-feeding fish, morphologically similar to ancestors of Gobiidae, probably in the Actinopterygii class. The majority of fish-made trace fossils record feeding and locomotion behaviour, whereas the wing-shaped traces are interpreted to represent resting structures made by fish that pressed their fins downward on the muddy sediment surface and hence, represent undertracks. These traces are possibly the oldest fish-made structure documented thus far. These wing-shaped traces are described as Pisquiesichnus dashtgardi igen. et isp. nov. in this study.

Propagating characteristics of waves on a thin layer of mud

Propagating characteristics of waves on a thin layer of mud

Formation and evolution of roll waves in a shallow free surface flow of a power-law fluid down an inclined plane

A laminar flow of a thin layer of mud down an inclined plane under the action of gravity is considered. The instability of a film flow and the formation of finite amplitude waves are studied within the framework of both two-dimensional governing equations of a power-law fluid and its depth-averaged hyperbolic simplification. The conditions of the existence of roll waves for these models are formulated in terms of the Whitham criterion. A free surface evolution and the development of roll waves are numerically calculated. The amplitude of roll waves obtained by the 2D equations is slightly larger than that for the 1D model. Moreover, for certain flow parameters, the small perturbations of the basic solution grow for the 2D equations and decay for the depth-averaged model. A two-parameter class of exact piecewise-smooth solutions of the 1D model is obtained and a comparison with a numerical solution is made. In the region of these parameters, diagrams of the roll waves existence are constructed.

Chironomid larvae destroy cultivated microbial mat in protected Adriatic salterns

Abstract The Sečovlje salterns on the Northern Adriatic coastline encompass both active and abandoned salt pans on the estuary of the Dragonja River. They are protected as a nature park by a governmental decree and by the Ramsar Convention on Wetlands of International Importance. In the Sečovlje salterns, salt is still gathered according to a traditional process originating from the 14th century. The high quality of the traditionally produced salt is attributed to a cultivated microbial mat (called ‘petola’) that covers the floor of the crystallization basins and provides a barrier from the anoxic mud. Every spring, in a process called ‘fertilization’, the microbial mat is covered by a layer of mud, a practice that is supposedly crucial for the maintenance of the petola, but its exact role and underlying mechanisms are not yet fully understood. In early spring 2018 the microbial mat, primarily composed of the filamentous cyanobacterium Coleofasciculus chthonoplastes, was infested by dipteran larvae, which occurred at densities of up to 20,000 m−2. Based on the morphological features of the larvae and imagos, and on DNA analysis of the mitochondrial cytochrome c oxidase subunit I (COI) gene, the newly identified pest was determined to be a chironomid. Under laboratory conditions, larvae fed upon the cyanobacterial mat and destroyed its structure. In the laboratory, the application of a thin layer of saltern mud in a manner typical for the salt production process prevented the development of chironomid larvae and maintained the structure of the microbial mat. In the salterns, omitting the fertilization step resulted in a considerable weakening of the petola layer. The results reveal the possible biological background for the fertilization process and thus provides important knowledge for the conservation of the traditional man‐made aquatic ecosystem of the Sečovlje salterns.

Multidisciplinary discovery of ancient restoration using a rare mud carapace on a mummified individual from late New Kingdom Egypt.

CT scans of an unnamed mummified adult from Egypt, now in the Chau Chak Wing Museum, University of Sydney (NMR.27.3), reveal it to be fully sheathed in a mud shell or carapace, exposing a mortuary treatment not previously documented in the Egyptian archaeological record. The carapace was placed between layers of linen wrappings thus it was not externally visible. Radiocarbon dating of textile samples provide a range of c.1370–1113 cal BC (95.4% probability), with a median date of 1207 cal BC. When assessed against mummification techniques of the era, the individual is placed in the late 19th–20th Dynasty, at the later end of this date range. Multi-proxy analysis including μ-XRF and Raman spectroscopy of carapace fragments from the head area revealed it to consist of three layers, comprising a thin base layer of mud, coated with a white calcite-based pigment and a red-painted surface of mixed composition. Whether the whole surface of the carapace was painted red is unknown. The carapace was a form of ancient conservation applied subsequent to post-mortem damage to the body, intended to reconfigure the body and enable continued existence of the deceased in the afterlife. The carapace can also be interpreted as a form of elite emulation imitating resin shells found within the wrappings of royal bodies from this period.

Effect of confined boundary and mud-layers on depressurization-based gas recovery and land subsidence in hydrate reservoirs

Hydrate reservoirs present numerous challenges due to their occurrence in ultra-deep regions, presence of mud-layers, unconfined boundaries, and complex morphological heterogeneities. Individual effect of some of these reservoir settings on overall production is known, however, a systematic assessment of their mutual impact on gas production and land subsidence is essential from production outcome point of view. In the present study, we address the mutual effect of confined boundaries and mud-layers, and their subsequent impact on depressurization induced gas recovery and land subsidence in hydrate reservoirs. Reservoir conditions are considered to be representative of Indian hydrate reservoirs. A numerical study is performed using a multiphase, multicomponent hydrate reservoir simulator externally coupled with a semianalytical subsidence model. Results indicate that the gas production vary by a large margin depending on whether the reservoir is confined or unconfined. Presence of mud-layers affects the overall gas production significantly, where, for an unconfined reservoir, hydrate dissociation is higher in reservoirs with thin mud-layers. Properly sealed reservoirs are more vulnerable to depressurization induced subsidence than poorly sealed reservoirs. Subsidence possibility for the reservoir with a higher number of mud-layers is lower and is the greatest for a reservoir with no mud-layers.

An Analytical Study on Wave-Current-Mud Interaction

This study aims at providing analytical investigations to the first and second-order on the wave–current–mud interaction problem by applying a perturbation method. Direct formulations of the wave–current–mud interaction could not be found in the literature. Explicit formulations for the particle velocity, dissipation rates, and phase shift in the first order and the mass transport in the second-order have been obtained. The findings of the current study confirmed that by an increase in the current velocity (e.g., moving from negative to positive values of current velocity), the dissipation rates and mud (instantaneous and mean) velocity decrease. The proposed assumption of a thin mud layer (boundary layer assumption) matches with the laboratory data in the mud viscosity of the orders of (0.01 N/m2) in both wave dissipation and mud mass transport leading to small ranges of discrepancies. The results from the newly proposed model were compared with the measurements and the results of an existing model in the literature. The proposed model showed better agreements in simulating the mud (instantaneous and mean) velocity compared to the existing one.

Small amplitude water wave propagation through mangrove forests having thin viscoelastic mud layer

The effect of a thin viscoelastic mud layer on the wave propagation through mangrove forests has been analyzed within the framework of linear theory. The trunks of mangrove trees are assumed to be in the upper water layer and roots are assumed to be in the lower thin mud layer. The dispersion relation has been obtained and the attenuation rate has been computed. The effects of the physical parameters like viscosity and shear modulus of elasticity of the mud, density of the forest, depth of the mud has been analyzed in the context of attenuation and propagation of waves. The present model will be a realistic and significant approach to understand water wave propagation through mangrove forests.

Manchuriophycus-like elliptical cracks in thin mudstones intercalated with lacustrine sandstone: Intrastratal crack formation in water-saturated sediments

Manchuriophycus-like elliptical cracks are found in thin mudstone layers and lenses intercalated with wave-rippled lacustrine sandstone beds of the Lower Cretaceous Jinju Formation, South Korea. The cracks are interpreted as intrastratal shrinkage cracks formed by liquidization and injection of sand, hydroplastic deformation of mud, and concomitant dewatering of the sediments in water-saturated conditions. The cracks are considered to have been formed by earthquake and/or wave-induced loading and initiated where smectite was presumed to be locally concentrated in the mud. It is hypothesized that the cracks were developed into the elliptical outline, reflecting that of an interference ripple trough, due to permeability differences between two thin mud layers deposited over the rippled sand layer.

Sediment Transport near Ship Shoal for Coastal Restoration in the Louisiana Shelf: A Model Estimate of the Year 2017–2018

Ship Shoal has been a high-priority target sand resource for dredging activities to restore the eroding barrier islands in LA, USA. The Caminada and Raccoon Island pits were dredged on and near Ship Shoal, which resulted in a mixed texture environment with the redistribution of cohesive mud and noncohesive sand. However, there is very limited knowledge about the source and transport process of suspended muddy sediments near Ship Shoal. The objective of this study is to apply the Regional Ocean Modeling System (ROMS) model to quantify the sediment sources and relative contribution of fluvial sediments with the estuary and shelf sediments delivered to Ship Shoal. The model results showed that suspended mud from the Atchafalaya River can transport and bypass Ship Shoal. Only a minimal amount of suspended mud from the Atchafalaya River can be delivered to Ship Shoal in a one-year time scale. Additionally, suspended mud from the inner shelf could be transported cross Ship Shoal and generate a thin mud layer, which is also considered as the primary sediment source infilling the dredge pits near Ship Shoal. Two hurricanes and one tropical storm during the year 2017–2018 changed the direction of the sediment transport flux near Ship Shoal and contributed to the pit infilling (less than 10% for this specific period). Our model also captured that the bottom sediment concentration in the Raccoon Island pit was relatively higher than the one in Caminada in the same period. Suspended mud sediment from the river, inner shelf, and bay can bypass or transport and deposit in the Caminada pit and Raccoon Island pit, which showed that the Caminada pit and Raccoon Island pits would not be considered as a renewable borrow area for future sand dredging activities for coastal restoration.

Palaearctic Osmia bees of the subgenera Hemiosmia, Tergosmia and Erythrosmia (Megachilidae, Osmiini): biology, taxonomy and key to species

Osmia (Hemiosmia), O. (Tergosmia) and O. (Erythrosmia) are three related Palaearctic osmiine bee subgenera (Megachilidae, Megachilinae, Osmiini) comprising eight, seven and four species, respectively. Analysis of female pollen loads and field observations revealed that the species of both O. (Hemiosmia) and O. (Tergosmia) have a distinct or even exclusive preference for Fabaceae as pollen hosts. Species of O. (Erythrosmia) also collect pollen on Fabaceae, but additionally frequently visit nototribic flowers of Lamiaceae and Antirrhineae (Plantaginaceae), which they exploit by rubbing a specialized facial pilosity over the raised anthers. The representatives of O. (Hemiosmia) and the basal members of O. (Tergosmia) build their brood cells in self-excavated burrows in the ground, whereas the more derived O. (Tergosmia) species as well as the O. (Erythrosmia) species place them in preexisting cavities above-ground, which are empty snail shells hidden under prominences of rocks or under stones in the latter subgenus. In O. (Hemiosmia) and O. (Tergosmia), the brood cells are entirely constructed from foreign material and either consist of chewed leaves ("leaf pulp") in the former subgenus or are distinctly three-layered with a thin layer of mud sandwiched between two layers of large pieces of petals in the latter subgenus. In O. (Erythrosmia), the brood cells within the shell whorls are delimited by one-layered partitions of leaf pulp and the nests are closed by a barricade of densely packed small particles followed by a double wall of leaf pulp at the shell opening. The taxonomic revision of the three subgenera revealed the existence of an undescribed species, O. (Hemiosmia) spinicoxa spec. nov., which occurs in southwestern Morocco. The subgenus O. (Ozbekosmia) Zanden, 1994 syn. nov. is newly put into synonymy with O. (Tergosmia) Warncke, 1988. Osmia (Tergosmia) rhodoensis arquata Warncke, 1988 syn. nov. and O. (Tergosmia) tergestensis ononidis Ferton, 1897 syn. nov. are no longer accepted as valid subspecies of O. (Tergosmia) rhodoensis (Zanden, 1983) and O. (Tergosmia) tergestensis Ducke, 1897, respectively. Identification keys for all species of the three subgenera are given.

Nesting biology and distribution of Stenancistrocerus (Paratropancistrocerus) obstrictus (Morawitz, 1895) (Hymenoptera: Vespidae: Eumeninae).

Nesting of Stenancistrocerus obstrictus was studied in the Republic of Dagestan, Russia. Ten nests were observed, six of them were dissected and their structure was studied. The nests were located in preexisting holes in a clayey cliff. Females searched for a place for the nest during more than a day. The holes with nests were 2.5-10.5 cm in length and 3-4 mm in diameter. Nest entrances were surmounted by laced earthen turrets curved downwards. The maximum length of a turret was 2 cm; the turrets had more laced structure at their distal ends while they became more solid towards the base. Nests consisted of a row of 3-10 cells separated by thin mud partitions. The cells were 5-9 mm in length. All lateral walls of the cells, as well as the vestibular cell were lined with a thin layer of mud. Females collected the building material outside the nests; they mixed clayey earth with regurgitated liquid and formed mud pellets used for the nest construction. Complete nests were sealed by final plugs; their turrets were dismantled by the females. The provision was tiny larvae of an unidentified curculionid beetle; several dozens of them were stored per cell. No parasites and associates were found in the nests. Reproductive success amounted to 92%. Adult feeding was recorded on flowers of Tamarix hohenackeri. The species is univoltine; hibernation occurs at the prepupa stage. Adult wasps are active from the end of May to the end of July. Nesting biology of the genus Stenancistrocerus and its phylogenetic position are discussed. Such a type of the nesting could be regarded as intermediate between nesting in various preexisting cavities and the excavation of burrows in an earthen substrate. The distribution of S. obstrictus is summarized; it includes Russia (Astrakhan Prov., Kalmykia, Stavropol Terr., Dagestan), Armenia, and Azerbaijan; the presence of the species in Eastern Europe is confirmed. The lectotype of Odynerus obstrictus Morawitz, 1895 is designated.

Tsunami history over the past 2000 years on the Sanriku coast, Japan, determined using gravel deposits to estimate tsunami inundation behavior

At Numanohama Marsh on the rocky Sanriku coast in northeast Japan, we identified 17 sand layers with sedimentary structures characteristic of event deposits (i.e., a sharp erosional contact with the underlying unit, a normal and/or inverse grading structure, parallel/cross lamination, mud clasts, and/or a thin mud layer). Abundant marine nannofossils, coccoliths, and the small catchment area in the narrow valley suggest that these event layers were likely formed by inundations during tsunamis or storms. Among the 17 sand layers, nine contained gravels derived from the beach, riverbed, or slope areas. Six event layers contained all three of these gravels, suggesting a strong inflow current that transported round pebbles from the beach, erosion of wall rock in the valley during the inflow and outflow phases, and a backwash current that caused sub-angular riverbed gravel to accumulate in lowland areas. These six layers were traced up to 490 m inland from the coastline (present elevation: 7 m above mean sea level) and were several cm thick at almost every survey point. We concluded that these six event layers are tsunami deposits, and dating results revealed that they correlate with the 2011 Tohoku-oki earthquake; the 1933 and 1896 Sanriku-oki earthquakes; any of the 1763 Aomori-oki, 1793 Miyagi-oki, and 1856 Aomori-oki earthquakes; the 1611 Tohoku-oki earthquake; and the 869 Tohoku-oki (Jogan) earthquake. In addition, changes in the sedimentary environment inferred from diatom assemblages were well correlated with the deposition of three of the event layers. Two historical earthquakes — the 1454 and 1611 Tohoku-oki earthquakes — have been previously suggested as being the immediate predecessors of the 2011 Tohoku-oki earthquake, and our dating results favor the 1611 earthquake. Although the source region of the 869 Tohoku-oki (Jogan) earthquake has been estimated to have been off the Fukushima and Miyagi prefectures, our results suggest that the source region extended further north along the Japan Trench.

Numerical simulations of sand migration during gas production in hydrate-bearing sands interbedded with thin mud layers at site NGHP-02-16

The geomechanical behavior of gas hydrate-bearing sands during gas production is complex, involving changes in hydrate-dependent mechanical characteristics and also redistribution of stresses carried by the hydrate. When an interbedded mud layer is present, the complex response of the hydrate-bearing sediments is more pronounced because hydrate dissociation tends to occur preferentially in the sands adjacent to the hydrate-free mud layer, which can act as a heat source. This leads to non-uniform sediment deformation and potentially to shearing deformation along the sand/mud layers. In addition, since the hydrate-bearing sand permeability becomes far greater than the mud permeability with hydrate dissociation, a greater hydraulic gradient may exist along the interface between the sand/mud layers. These two behaviors may contribute to sand migration and thus a thorough study on the effect of a thin interbedded mud layer on the extent of sand migration is necessary. This paper presents numerical sand migration modeling of sand/mud interbedded hydrate-bearing sediments found at Site NGHP-02-16, one of 25 sites drilled as a part of National Gas Hydrate Program Expedition 02 (NGHP-02) in the offshore of India, subjected to depressurization. For a comparison and better understanding, simulation of homogeneous hydrate-bearing sediments is also conducted. It is found that greater sand migration occurs when the interbedded mud layer is present because of greater shearing deformation and greater pressure gradients at sand-mud interface. • This is the first work to analyze in detail the effect of presence of interbeds on sand migration. • Sediment deformation is mostly volumetric when homogeneous but becomes more deviatoric when interbedded. • Interbedded mud layers induce non-uniform hydrate dissociation, leading to greater sand migration in magnitude and duration.

Resuspension and transport of fine sediments by waves over a thin layer of viscoelastic mud with erosion

A mathematical model for the one-dimensional mass transport describing the concentration evolution of suspended sediments over a viscoelastic mud layer in the presence of erosion is presented. Using a perturbation method, the problem is set in terms of the concentration of particles at the water–mud interface. Numerical results show considerable difference from the cases of rigid and non-erodible interfaces. A singular behaviour of the particles concentration is observed when the mud depth approaches a resonant value, associated with negative convection velocity.

Dinosaur footprint assemblage from the Lower Cretaceous Khok Kruat Formation, Khorat Group, northeastern Thailand

The Khok Kruat Formation is the upper part of the Khorat Group, which consists of upper Lower Cretaceous non-marine sedimentary rocks in northeastern Thailand. Many dinosaur footprints have been known from the upper Lower Cretaceous (Aptian–Albian) Khok Kruat Formation at the Huai Dam Chum (Tha Uthen) site, northeastern Thailand. Approximately 600 tracks occur in thin mudstone layer of the northern part of the outcrop at the Huai Dam Chum track site. Two types of footprints, small-sized theropod and crocodylomorph are imprinted with mud cracks and ripple marks on the thin mud layer. Most of footprints are referred to cf. Asianopodus, and are imprinted by small-sized theropoda, probably ornithomimosauria. Theropod tracks are mainly separated into two groups, Group A and Group B. From ichnological viewpoints, the small-sized theropod track assemblage indicates the herd behaviour and its idiosyncratic group composition. In particular, the histogram of size-frequency measurements of Group A shows the anomalous bimodal distribution. We consider that there are two hypotheses; the first one is due to the male-female difference, and the second is a result of the different growing stage.

Mass transport in a thin layer of power-law mud under surface waves

The mass transport velocity in a two-layer system is studied theoretically. The wave motion is driven by a periodic pressure load on the free water surface, and mud in the lower layer is described by a power-law rheological model. Perturbation analysis is performed to the second order to find the mean Eulerian velocity. A numerical iteration method is employed to solve the non-linear governing equation at the leading order. The influence of rheological properties on fluid motion characteristics including the flow field, the surface displacement, the mass transport velocity, and the net discharge rates are investigated based on theoretical results. Theoretical analysis shows that under the action of interfacial shearing, a recirculation structure may appear near the interface in the upper water layer. A higher mass transport velocity at the interface does not necessarily mean a higher discharge rate for a pseudo-plastic fluid mud.

Acoustic response of targets in a shallow water, layered, environment: Experimental observations and simple ray model results

Synthetic aperture sonar (SAS) data were collected throughout May of 2014 during an experiment in St. Andrew's Bay, Panama City, FL. A brief overview is given of the SAS rail system and procedure used during the “BAYEX14” experiment. BAYEX14 was carried out in a shallow water, layered, environment, where water depth was approximately 8 m with a thin layer of mud (i.e., 0.15-0.30 m thickness) covering a sandy bottom. All targets settled into the mud and came to rest on the mud-sand interface. Scattering data from an aluminum finite cylinder, an aluminum pipe, and solid replicas of an 100-mm unexploded ordnance will be presented and compared to data taken previously in a sand-only environment and to model results. To model the scattered pressure, the ray paths are assumed to experience negligible refraction in passing through the mud layer to the mud-sand interface. However, the much higher attenuation in mud relative to water must be considered along the portion of the ray path in mud. For targets at long horizontal ranges, ray paths that interact with the water-air interface must be included to model an observed modulation of the target strength. [Research sponsored by ONR and SERDP.]