Pore Water Salinity Research Articles

Donnan-ion hydration model to estimate the electroosmotic permeability of clays

Electroosmotic permeability is a soil parameter that is fundamental for designing and implementing environmental remediation, dewatering, or soil stabilization processes. It presents a narrow range of variation compared to hydraulic permeability, so that in many occasions no experimental tests are carried out to determine it. Traditionally, the Helmholtz–Smoluchowski equation has been used to estimate electroosmotic permeability, despite having several drawbacks that make it difficult to apply, as it was deduced for large capillaries (unusual in clays) and its dependence on the zeta potential of the soil, difficult to measure and dependent on a wide variety of factors. The present work describes a semi-empirical formulation that allows the estimation of the electroosmotic permeability as a function of the specific surface area and the total void ratio and is based on the Donnan equilibrium and the ion hydration models. The parameters for modeling are calibrated and validated with experimental data, obtaining better results than those given by the Helmholtz–Smoluchowski model. In addition, the expected trends in the behavior of clays that can be found in the literature are obtained in a quantitative and consistent manner for different types of clays with variable water content and pore water salinity.

Relative importance of conceptual and computational errors when delineating saltwater intrusion from resistivity inverse models in heterogeneous coastal aquifers

In coastal areas, geological heterogeneity influences the geometry and characteristics of the freshwater-saltwater mixing zone. Geophysical electrical and electromagnetic methods are increasingly used to delineate the freshwater-saltwater mixing zone or for groundwater model calibration. However, in practical applications, it is common when assessing pore water salinity from resistivity models to disregard the spatial variability of the aquifer properties assuming pore salinity is the dominant control on bulk electrical conductivity. In this paper we use a coupled hydrogeophysical model to assess the discrepancies in recovered salinity caused by the geophysical inversion and the application of the chosen petrophysical model when heterogeneity is ignored. We find that errors made when neglecting heterogeneity during petrophysical transformation are equivalent or higher in magnitude than inversion errors, more so when an inappropriate petrophysical model is used, but exhibit different spatial distribution. The results show that their combined effect results in significant overestimation of the spreading of the mixing zone. The analysis provides new insights to the groundwater community to better evaluate the reliability of geophysically-derived information when delineating the freshwater-saltwater interface or when geophysics is used quantitatively as part of model scenario simulation, uncertainty analysis or optimisation strategies.

Effect of Salinity on Rheological Behavior of Cement-Treated Dredged Clays as Fills

AbstractThe rheological behavior of dredged clays at various pore water salinities treated with portland cement was investigated for beneficial use in structural fill applications. The focus was on...

Using an airborne electromagnetic method to map saltwater intrusion in the northern Salinas Valley, California

Saltwater intrusion can pose a serious threat to groundwater quality in coastal regions. Estimating the extent of saltwater intrusion is vital for groundwater managers to plan appropriate mitigation strategies. The airborne electromagnetic (AEM) method is commonly used to evaluate groundwater resources, but it is challenging to apply in coastal environments because the low resistivity of saltwater-saturated aquifers attenuates the electromagnetic signal quickly and the relationship between electrical resistivity and pore water salinity is complex. However, if successful, the AEM method can supply information to address questions of critical importance in coastal regions. We investigated the extent of, and controls on, saltwater intrusion using the AEM method in the northern Salinas Valley, CA, USA. We collected 635 line-km of AEM data in the study area, the inversion results of which produced estimates of the electrical resistivity of the subsurface, reaching depths of between 50 and approximately 200 m below the ground surface. We have developed a relationship between the AEM electrical resistivity model and groundwater salinity, calibrated from borehole geophysical and water quality measurements, which allowed us to generate images revealing the distribution of saltwater and fresher groundwater in the study area. This fresher groundwater (defined as “a source of drinking water”) was successfully mapped out in the unconfined aquifer (the Dune Sand Aquifer) and the uppermost confined aquifer (the 180-Foot Aquifer) in the study area, illustrating a groundwater recharge process that helps mitigate saltwater intrusion in the 180-Foot Aquifer. Deep, low-resistivity bodies also were mapped, indicating regions where saltwater likely is migrating vertically from the 180-Foot Aquifer into the lower confined aquifer (the 400-Foot Aquifer). The findings from this case study demonstrate the value of acquiring AEM data for investigating the distribution of salinity in coastal aquifers impacted by saltwater intrusion.

Characterizing the diverse hydrogeology underlying rivers and estuaries using new floating transient electromagnetic methodology

The hydrogeology below large surface water features such as rivers and estuaries is universally under-informed at the long reach to basin scales (tens of km+). This challenge inhibits the accurate modeling of fresh/saline groundwater interfaces and groundwater/surface water exchange patterns at management-relevant spatial extents. Here we introduce a towed, floating transient electromagnetic (TEM) system (i.e. FloaTEM) for rapid (up to 15 km/h) high resolution electrical mapping of the subsurface below large water bodies to depths often a factor of 10 greater than other towed instruments. The novel FloaTEM system is demonstrated at a range of diverse 4th through 6th-order riverine settings across the United States including 1) the Farmington River, near Hartford, Connecticut; 2) the Upper Delaware River near Barryville, New York; 3) the Tallahatchie River near Shellmound, Mississippi; and, 4) the Eel River estuary, on Cape Cod, near Falmouth, Massachusetts. Airborne frequency-domain electromagnetic and land-based towed TEM data are also compared at the Tallahatchie River site, and streambed geologic scenarios are explored with forward modeling. A range of geologic structures and pore water salinity interfaces were identified. Process-based interpretation of the case study data indicated FloaTEM can resolve varied sediment-water interface materials, such as the accumulation of fines at the bottom of a reservoir and permeable sand/gravel riverbed sediments that focus groundwater discharge. Bedrock layers were mapped at several sites, and aquifer confining units were defined at comparable resolution to airborne methods. Terrestrial fresh groundwater discharge with flowpaths extending hundreds of meters from shore was also imaged below the Eel River estuary, improving on previous hydrogeological characterizations of that nutrient-rich coastal exchange zone. In summary, the novel FloaTEM system fills a critical gap in our ability to characterize the hydrogeology below surface water features and will support more accurate prediction of groundwater/surface water exchange dynamics and fresh-saline groundwater interfaces.

Complex conductivity of rammed earth

Searching for recyclable materials of construction, in the objective of building sobriety and resilience, is a major issue of our current societies. Mudbricks of compacted rammed earth represent an ancient construction material with many advantages associated with its availability, cost of production, potential reuse, and with a very low carbon footprint. Moisture content affects the mechanical resistance of such materials, which could become mechanically weak above a critical value. Therefore, non-intrusive characterization techniques able to image the water content distribution of these materials is highly in demand. We apply a recently developed theory of complex electrical conductivity (alias induced polarization) to characterize core samples of rammed earth materials in the laboratory. Complex conductivity describes both the ability of a porous material to conduct an electrical current (characterized by the in-phase conductivity) and its ability to store reversibly electrical charges (characterized by two interconnected properties namely the quadrature conductivity and the normalized chargeability). Samples of rammed earth and clayey soils with different pore water salinities, saturations, and compaction states are measured with the complex conductivity method in the frequency range 100 mHz–45 kHz. The in-phase and quadrature conductivities of the complex conductivity of rammed earth are connected to the water content offering therefore a new non-intrusive tomographic technique to study the water content distribution in walls made of rammed earth. The data are all consistent with the so-called dynamic Stern layer model of complex conductivity for clayey materials. This new approach provides a general method to image the change in the water content of walls made of rammed earth, a task that electrical conductivity imaging cannot perform as a stand-alone technique.

Greenhouse Gas Fluxes of Mangrove Soils and Adjacent Coastal Waters in an Urban, Subtropical Estuary.

Mangroves are known to sequester carbon at rates exceeding even those of other tropical forests; however, to understand carbon cycling in these systems, soil-atmosphere fluxes and gas exchanges in mangrove-adjacent shallow waters need to be quantified. Further, despite the ever-increasing impact of development on mangrove systems, there is even less data on how subtropical, greenhouse gas (GHG) fluxes are affected by urbanization. We quantified carbon dioxide (CO2) and methane (CH4) fluxes from mangrove soils and adjacent, coastal waters along a gradient of urbanization in the densely-populated, subtropical San Juan Bay Estuary (PR). Edaphic (salinity, pH, surface temperature) factors among sites significantly covaried with GHG fluxes. We found that mangrove systems in more highly-urbanized reaches of the estuary were characterized by relatively lower porewater salinities and substantially larger GHG emissions, particularly CH4, which has a high global warming potential. The magnitude of the CO2 emissions was similar in the mangrove soils and adjacent waters, but the CH4 emissions in the adjacent waters were an order of magnitude higher than in the soils and showed a marked response to urbanization. This study underscores the importance of considering GHG emissions of adjacent waters in carbon cycling dynamics in urbanized, tropical mangrove systems.

Partial canopy loss of mangrove trees: Mitigating water scarcity by physical adaptation and feedback on porewater salinity

Trees species in the mangrove genus Avicennia can shed canopy parts when exposed to adverse environmental conditions, such as increases in porewater salinity. The individual-based model BETTINA enables the quantification of the tree's water use depending on its allometric characteristics. It thus provides a tool to model the equilibrium between plant size and density in a mangrove stand and porewater salinity. When the model is coupled with a simple water balance approach, the water use of trees corresponds to water uptake from the soil and, in combination with water fluxes, an increase of salinity in the root zone. Annual variations of the sea level, the tidal regime, groundwater inflow, and precipitation have an impact on the equilibrium of the combined system. Higher salinities lead to lower potential gradients and reduced water uptake of the plant. With a combined modelling approach (single tree model BETTINA with a simple water balance approach), we examined the dampening effects of consecutive partial canopy loss for the survival of the tree. We found that (i) the tree is able to decrease water demand and uptake and thus may reduce the tree's effect on soil water salinity, (ii) the reduced branch length leads to a reduced xylem flow resistance, and (iii) the reduction in height has a small positive effect on the water potential gradient between leaves and soil. Individual-based models can enhance our understanding of the regulating impact of the partial canopy loss on water balance in the combined plant-soil system.

Geological investigation of the settlement behaviour of two highways in Lianyungang region

In the past 20 years, more than ten highways are built in the Lianyungang region, Jiangsu province, China. Among them, two highways (Coastal Highway A, close to the coastline, and Lianyan Highway B, approximately 25 km from the coastline) are crucial to the local highway network. However, the settlements of these two highways are significantly different, despite the same building method and location in a region with similar sediment provenance and sedimentary environment. A higher settlement rate was observed for the highway constructed far from the coastline. To clarify the mechanism, a series of field and laboratory tests based on regional geological survey were conducted in this study. Test results showed that the sensitivity difference of the soil induced by the pore water salinity leaching is the main reason for those observations. With pore water salinity leaching, the water content and plastic limit of Lianyungang marine soft clays remained almost unchanged, whereas the liquid limit and plasticity index of the soft clay near highway B gradually decreased with an increase in the liquidity index. The increase in the liquidity index subsequently decreased the remoulded strength of the soils far from the coastline. Simultaneously, the natural strength remained approximately the same due to leaching, and this led to an increase in the sensitivity, suggesting a strong structure. During the filling construction, the construction load and deviatoric stress under the embankment may have destroyed the clay structure. Therefore, a large settlement and high settlement rate resulted for the highway constructed far from the coastline.

Mangrove leaf species-specific isotopic signatures along a salinity and phosphorus soil fertility gradients in a subtropical estuary

Mangrove ecotypes are distinct monospecific or mix-species assemblages and used as classification criteria to evaluate coastal biogeochemical cycles at the local, regional, and global scales. However, it is not clear how plant nitrogen and carbon content, including bulk δ13C and δ15N and n-alkane δ13C values, vary across species and within species when plants are exposed to the interaction between nutrient (nitrogen-N, phosphorus-P) availability and stressors (i.e., salinity). Here we present significant differences in green leaves wax n-alkane δ13C (δ13Cn-alkane) values and brown-senescent leaves C:N atomic ratios and total phosphorus (TP) concentrations of three mangrove species (Rhizophora mangle, Laguncularia racemosa, and Avicennia germinans) that reflect ecophysiological adaptations to nutrient availability and salinity along the Shark River estuary (SRE), South Florida, USA. Linear models between leaf wax δ13Cn-alkane values and species location along TP fertility and salinity gradients showed distinct differences, particularly between the species A. germinans and R. mangle. Our analyses showed that leaf wax δ13Cn-alkane properly represented major differences in ecophysiological responses by each mangrove species. We also found that both R. mangle and L. racemosa showed different isotopic footprints among the SRE upper, middle and lower estuarine salinity regions. Further, the green leaves bulk δ13C values in R. mangle (−32.3‰ to −27.6‰) were positively correlated with distance from the mouth of the estuary. In contrast, L. racemosa showed a negative relationship with distance and a narrower bulk δ13C range (−29.8‰ to −28.1‰) in comparison to the other two species. A. germinans, a species found only in the brackish (salinity: 18.8 ± 1.2) and saline (30.3 ± 0.53) estuarine regions, also showed a positive bulk δ13C relationship with distance. Because of the well-defined species-specific leaf wax n-alkane δ13C values along both water column/soil pore water salinity and TP gradients, we propose these values as a potential salinity proxy for paleoclimate reconstruction.

Pore Water Characterization of the Tight Rocks of Bazhenov Formation Using the Water and Salt Extracts

The paper presents the results of the pore water composition investigation of tight shales of the Bazhenov Formation rocks of Western Siberia, obtained by integrated interpretation of the experimental data of the water and salt extracts. The two methods of cation exchange capacity (CEC) measurement were applied – Pfeffer and Hexaamminecobalt trichloride method. Both of them showed similar results. CEC varies from 3.45 to 4.53 meq/100 g by Pfeffer method and from 3.51 to 4.35 meq/100 g by Hexaamminecobalt trichloride method. Ca, Na, Mg, K form exchange complex of all studied core samples. According to interrelation (rNa+rK)>rCa the exchange complex type is marine and was inherited from the composition of the paleobasin seawater. It was found that water extract composition depends on the core mineral content, except chlorine, which originates from the pore water. Using the thermodynamic modelling in PHREEQC program, next ratio of exchange cations was found - Na (up to 91%), Mg (up to 5.6%), Ca (up to 2 .6 %) and K (up to 0.8%). According to the calculation using the water extracts results, the pore water salinity changes from 1.23 to 21.96 g/L.

Pore-water chemistry and its influence on rock mechanical properties and hydrogeophysical processes in a mudstone slope in the southwestern Taiwan badlands

Bedrock characteristics and its influence on hydrogeophysical processes in a Plio-Pleistocene mudstone slope were examined in southwestern Taiwan. Previous works carried out in this area indicated seasonal patterns of the bedrock physical properties and deterioration of the mechanical strength during weathering to generate extremely high rates of erosion during heavy rainfall, thereby forming badland topography. This area has a humid subtropical climate that is characterised by distinct dry and rainy seasons. During the rainy season, high rates of erosion of the weathered mudstone occur during rainfall events. To investigate impact of characteristics of bedrock physical properties on hillslope weathering and erosion processes in this area, we analysed the pore-water chemistry, specific surface area, and swelling of the mudstone of the studied slope and performed in situ monitoring of water content and pore-water electrical conductivity at 2.5–40 cm depths near the slope surface. The results indicate that the mudstone contains saline pore water, is categorized as dispersive, and has a dense fabric, thereby favouring the occurrence of rock mechanical breakdown due to chemical osmosis. The influence of rock mechanical properties and bedrock behaviour on the hydrogeophysical processes near the slope surface varies with the season. During the dry season, the water content of the mudstone near the slope surface decreases, causing desiccation cracks to form and concentrating salt on rock surfaces. Water contents at 40 cm depths increased within 1 h after rainfalls during the monitoring intervals of the dry season, suggesting that surface water infiltrates rapidly by gravity into networks of cracks during infrequent rain events. During the following rainy season, intense rainfall events moisten the slope surface layer and increase the volume of the mudstone by swelling caused by chemical osmosis. The swelling is associated with an enlargement of the pore size of the mudstone during the dilution of saline water by fresh rainwater, with the greatest amount of swelling occurring at or near the surface where salt is most concentrated. Water contents at 40 cm depths scarcely responded to rainfalls during the monitoring intervals of the rainy season, suggested that this swelling closes desiccation cracks and prevents surface water from migrating downwards into the slope. The resulting seasonal erosion occurs by slope surface wash caused by intense rain during the late rainy season. The newly exposed mudstone on the slope starts to become desiccated during the subsequent dry season, and a new cycle of weathering commences.

Numerical modeling for drilling fluid invasion into hydrate-bearing sediments and effects of permeability

Drilling fluid invasion into hydrate-bearing sediments could induce hydrate dissociation and complicate heat and mass transfer around wellbore, and further affect mechanical strength of hydrate-bearing sediments and accurateness of wellbore logging interpretations. In this study, a cylindrical numerical model was established to study the characteristics of drilling fluid invasion into hydrate-bearing sediments and the effects of permeability on this process. The distributions of temperature, pressure, saturation, and salinity of pore water around wellbore at different time were obtained. The pressure and temperature around wellbore gradually increase, and the hydrate around wellbore dissociates with the high-temperature drilling fluid invasion. Meantime, water and gas generated from hydrate dissociation gradually migrate outward and then form ‘secondary hydrate’ in some areas outside wellbore. Dissociation and formation of hydrate can sharply change the salinity of pore water around wellbore. The drilling fluid invasion and hydrate dissociation ranges become larger when the intrinsic permeability is higher. The salinity in sediments decreases sharply while the dilution range is narrow when drilling fluid invasion into hydrate-bearing sediments with low permeability. In addition, the permeability decline exponent of the Masuda model has a significant influence on drilling fluid invasion. However, the Corey exponents of the relative permeability model only have a limited influence on drilling fluid invasion into hydrate-bearing sediments with low intrinsic permeability (e.g., 5.5 mD), while they have a noticeable influence on hydrate-bearing sediments with high intrinsic permeability (e.g., 75 mD).

Characterisation of submarine depression trails driven by upslope migrating cyclic steps: Insights from the Ceará Basin (Brazil)

Abstract Circular to elliptical topographic depressions, isolated or organized in trails, have been observed on the modern seabed in different contexts and water depths. Such features have been alternatively interpreted as pockmarks generated by fluid flow, as sediment waves generated by turbidity currents, or as a combination of both processes. In the latter case, the dip of the slope has been hypothesized to control the formation of trails of downslope migrating pockmarks. In this study, we use high-quality 3D seismic data from the offshore Ceara Basin (Equatorial Brazil) to examine vertically stacked and upslope-migrating trails of depressions visible at the seabed and in the subsurface. Seismic reflection terminations and stratal architecture indicate that these features are formed by cyclic steps generated by turbidity currents, while internal amplitude anomalies point to the presence of fluid migration. Amplitude Versus Offset analysis (AVO) performed on partial stacks shows that the investigated anomalies do not represent hydrocarbon indicators. Previous studies have suggested that the accumulation of permeable and porous sediments in the troughs of vertically stacked cyclic steps may create vertical pathways for fluid migration, and we propose that this may have facilitated the upward migration of saline pore water due to fluid buoyancy. The results of this study highlight the importance of gravity-driven processes in shaping the morphology of the Ceara Basin slope and show how non-hydrocarbon fluids may interact with vertically stacked cyclic steps.

Numerical modeling of methane hydrate accumulation with mixed sources in marine sediments: Case study of Shenhu Area, South China Sea

The natural gas hydrates detected in Shenhu Area, South China Sea are considered to have great potential for exploitation and to become a research hotspot. However, details of the dynamic accumulation and evolution processes of gas hydrate over a long time in this area remain unclear. In this study, we developed a numerical model to predict the accumulation of gas hydrates in the marine sediments by introducing the biogenic methanogenesis module to the framework of the existing simulator TOUGH+HYDRATE. A one-dimensional dynamic model was applied to reproduce the formation of gas hydrate at site SH2 in Shenhu Area. The burial of sediments and associated phenomena (e.g., evolution of temperature, sediment compaction and consequent reduction in sediment porosity and permeability, fluid expulsion) are taken into account. Modeling results indicate that with the conventional conversion coefficient (CC) of organic carbon to methane of 0.15, the amount of in-situ biogenic methane is not sufficient to form the highly saturated hydrate detected at this location and the remaining methane (91.4%) is supplied by the upward flow of fluids. The tectonic movement that took place about 1.5 Ma created pathways for the fluids to migrate vertically. The pore water and methane gas fluxes in the upward fluids were determined as 2 × 10−10 kg/s·m2 and 1 × 10−11 kg/s·m2, respectively, using the proved hydrate saturation profile and measured pore water chlorinity from recovered core samples. The distribution of hydrate in the sediments is significantly influenced by pore water salinity. The inhibitory effect of salt on hydrate formation, which shifts the pressure of three-phase (i.e., solid hydrate, methane gas and pore water) equilibrium to actual pore water pressure, could be the major reason for the appearance of a three-phase co-existence zone in the hydrate concentrated zone. Additionally, the water flux and diffusivity of salt have a profound effect on the formation of gas hydrate by affecting the salinity of pore water in the gas hydrate concentrated zone. The results of this study are of great significance for guiding marine gas hydrate exploration and resource evaluation.

Modeling Soil Porewater Salinity Response to Drought in Tidal Freshwater Forested Wetlands

AbstractThere is a growing concern about the adverse effects of saltwater intrusion via tidal rivers, streams, and creeks into tidal freshwater forested wetlands (TFFW) due to sea level rise (SLR) and intense and extended drought events. However, the magnitude and duration of porewater salinity in exceedance of plant salinity stress threshold (2 practical salinity units, psu) and the controlling factors remain unclear. In this study, we developed a TFFW soil porewater salinity model, in which the feedback mechanisms between soil salinity and evapotranspiration and hydraulic conductivity were incorporated. We selected sites (upper, middle, lower tidal freshwater forest sites, and oligohaline marsh site) along the coastal floodplains of two rivers, the Waccamaw River (SC, USA) and the Savannah River (GA and SC, USA), that represent landscape salinity gradients from tidal influence of the Atlantic Ocean. The model results agreed well with field measurements and revealed that with drought‐induced saltwater intrusion, the mean annual soil porewater salinity and duration of elevated soil porewater salinity (>2 psu) increased significantly compared to the normal (nondrought) condition, posing a threat to the health and ecosystem services of TFFW even in the absence of SLR. Model results also showed more severe salinity stress under drought for the lower forest sites along the two rivers, where soil salinity values have already been at or in exceedance of the 2 psu threshold.

Three-dimensional voxel geological model of a riparian lowland and surrounding catchment using a multi-geophysical approach

The distribution and volume of organic sediments as well as the flow pathways in riparian lowlands are important parameters when determining the potential denitrification capacities of a catchment. A headwater catchment in Denmark was investigated with a range of geoelectrical and electromagnetic geophysics as well as shallow boreholes to create a geological model of a riparian lowland. The organic sediments showed a high resistivity variation when measured resistivities were compared with borehole lithology. Chemical analyses of soil and groundwater samples were used to explain the resistivity variation. Resistivity was observed to correlate well with pore water salinity entailing that ionic input into the riparian aquifer was of considerable importance to the resistivity of peat sediments as well as the interpretation of geological boundaries. Based on the analyses of resistivity variations a set of geological surfaces were interpreted on 86 sections. The surfaces were interpolated using ordinary kriging and compiled into a structured three-dimensional grid with uniformly sized voxels measuring 10 × 6 × 0.5 m (x, y, z directions). The resulting model may be used for evaluating the volume and distribution of peat and as a geological basis for hydrobiogeochemical modelling.

Application of spectral induced polarization for characterizing surfactant-enhanced DNAPL remediation in laboratory column experiments

The widespread presence of entrapped dense non-aqueous phase liquid (DNAPL) in the subsurface poses a continuing challenge to groundwater remediation. Cost-effective and high-resolution subsurface characterization is a critical issue for further DNAPL recovery due to the complexity of DNAPL source zone architecture (SZA). Geophysical techniques provide a noninvasive, spatially continuous and cost-effective way for monitoring the DNAPL remediation process. In particular, the spectral induced polarization (SIP) method has shown great potential in environmental problems. In this study, we performed real-time SIP measurements on DNAPL contaminated soil in columns to quantitatively assess the ability of SIP method for monitoring surfactant-enhanced DNAPL remediation process. Chemical data was simultaneously collected during the remediation process to verify the results obtained by SIP method. Taking account into the variations of subsurface environment, we conducted a series of column flushing experiments under different flow rate, surfactant concentrations and fluid salinities. The results highlight that SIP method is able to effectively monitor the DNAPL remediation process, as well as to evaluate the remediation efficiency under different conditions. The variations in the flow rate, the concentration of surfactant and the salinity of pore water not only affect remediation effectiveness, but also have an impact on the SIP signatures. This study shows that SIP performs better for monitoring DNAPL remediation at a relatively low flow rate of ~ 0.4 m/d, low surfactant concentration of 5000 mg/L and high salinity of 1.0 S/m, with an error of saturation estimation (RMSES) <0.1.

Pressure coring a Gulf of Mexico deep-water turbidite gas hydrate reservoir: Initial results from The University of Texas–Gulf of Mexico 2-1 (UT-GOM2-1) Hydrate Pressure Coring Expedition

The University of Texas Hydrate Pressure Coring Expedition (UT-GOM2-1) recovered cores at near in situ formation pressures from a gas hydrate reservoir composed of sandy silt and clayey silt beds in Green Canyon Block 955 in the deep-water Gulf of Mexico. The expedition results are synthesized and linked to other detailed analyses presented in this volume. Millimeter- to meter-scale beds of sandy silt and clayey silt are interbedded on the levee of a turbidite channel. The hydrate saturation (the volume fraction of the pore space occupied by hydrate) in the sandy silts ranges from 79% to 93%, and there is little to no hydrate in the clayey silt. Gas from the hydrates is composed of nearly pure methane (99.99%) with less than 400 ppm of ethane or heavier hydrocarbons. The δ13C values from the methane are depleted (−60‰ to −65‰ Vienna Peedee belemnite), and it is interpreted that the gases were largely generated by primary microbial methanogenesis but that low concentrations of propane or heavier hydrocarbons record at least trace thermogenic components. The in situ pore-water salinity is very close to that of seawater. This suggests that the excess salinity generated during hydrate formation diffused away because the hydrate formed slowly or because it formed long ago. Because the sandy silt deposits have high hydrate concentration and high intrinsic permeability, they may represent a class of reservoir that can be economically developed. Results from this expedition will inform a new generation of reservoir simulation models that will illuminate how these reservoirs might be best produced.

TRANSFORMATION OF THE NEOEUXINIAN LAKE INTO THE BLACK SEA AT THE NEOPLEISTOCENE - HOLOCENE BOUNDARY ON PALEONTOLOGICAL DATA

Problem Statement and Purpose. The transformation of the Neoeuxinian Lake into the Black Sea at the Neopleistocene-Holocene boundary represents a considerable interest for Quaternary geology. The age of the boundary, the character of the transformation (gradual, gradual but with oscillations, prominent, or catastrophic), and changes in salinity are highly controversial. The main goal of the paper is to contribute to the controversial subjects using the high-resolution paleontological (foraminifera. ostracoda. and mollusks) data supplemented by palynological data and radiocarbon datings.Data &amp; Methods. The study area is located within the northwestern (Ukrainian) and western (Bulgarian) shelf of the Black Sea. The material for micropaleontological study was obtained by the coring using the Ukrainian research vessel “Vladimir Parshin” and the Bulgarian research vessel “Academician L. Orbeli" in 2008 and 1976. respectively. All cores are located outside the isobath 100 m. The results of previous micropaleontological investigations are used for comparison. Microfauna was investigated according to the method of V. V. Yanko. Radiocarbon dating was performed by AMS (Core 38) or conventional - P-counting (Core 2345) methods on Mytilus and Dreissena shells.Results. Foraminifera are not adapted to freshwater environment. As a rule, the border between brackish and freshwater environment can be traced by their disappearance, with the exception of Allogromiida species with organic tests, which were not found in the studied material. For this reason, the presence of relatively diverse calcareous foraminifera suggests that the Neoeuxinan lake was brackish. Geochemical (salinity of pore water) and micropaleontological data are in full agreement.If there would not be inflow from the Mediterranean Sea until 7.2 ka BP or 8.4 ka BP according to the first and second catastrophic flooding scenarios of Ryan et al., no Mediterranean immigrants would be present in sediments older than 8.4 ka BP.However, they are present in sediment columns as can be seen from our and other researchers investigations. If the colonization of the Neoeuxinan lake by Mediterranean immigrants would be prominent or catastrophic, there would be a sharp increase in the species diversity and quantity of forammifera. ostracods and mollusks. However, these parameters increase gradually. The boundary between the Upper Neopleistocene and Holocene lies within 9 and 10 thousand years ago. The transformation of Neoeuxinan lake into the Black Sea was gradual: from brackish to a semi-marine, and then to a marine water body in course of the Mediterranean transgression during Holocene. The increase in salinity- occurred gradually over 3600 years, while the rate of penetration of sea water was about 0.05-1.7 cm a-1. The Holocene marine transgression was progressive in nature, intensifying with the transition from the early to late Holocene. The high-resolution micropaleontological study of Core 38 provides new data on the last pages of the development of the brackish Neoeuxinan lake that are mostly absent in other cores. Changes in the foraminiferal assemblages on the Pleistocene - Holocene boundary depend on the facies. They are more pronounced in marine facies compared to shallow ones, especially in areas affected by paleorivers. Palynological data provide evidence for cold climate at the end of the Neoeuxinian time.