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Neogene plains around the Mediterranean basin are characterized by considerable groundwater salinization. Some studies have misidentified seawater intrusion as the main source of salinity. Across northern Morocco, we gathered δ18OSO4 and δ34SSO4 data from coastal and inland aquifers, Messinian marls, and volcanic products. Differences in the isotopic composition between Messinian marls and some groundwater in all aquifer samples indicate that salinization in groundwater is a consequence of dissolution of Messinian evaporite deposits; nevertheless, modern agriculture and wastewater strongly influence depletion in levels of δ34SSO4. Our novel approach enables effective investigation of processes governing salinity in Neogene basins to support more informed water resource management and governance. [ABSTRACT FROM AUTHOR]

Point bars formed by meandering river systems are an important class of sedimentary deposit and are of significant economic interest as hydrocarbon reservoirs. Standard point‐bar models of how the internal sedimentology varies are based on the structure of small‐scale systems with little information about the largest complexes and how these might differ. Here a very large point bar (>25·0 m thick and 7·5 × 13·0 km across) on the Mississippi River (USA) was examined. The lithology and grain‐size characteristics at different parts of the point bar were determined by using a combination of coring and electrical conductivity logging. The data confirm that there is a general fining up‐section along most parts of the point bar, with a well‐defined transition from massive medium‐grained sands below about 9 to 11 m depth up into interbedded silts and fine–medium sand sediment (inclined heterolithic strata). There is also a poorly defined increase in sorting quality at the transition level. Massive medium sands are especially common in the region of the channel bend apex and regions upstream of that point. Downstream of the meander apex, there is much less evidence for fining up‐section. Finer sediment accumulated more readily after the establishment of a compound bar in the later stages of construction, at the terminal apex and in the bar tail. This work implies that the best reservoir sands are likely to be located in the centre of the point bar, deposited in a simple bar system. Reservoir quality decreases towards the bar edge. The early‐stage channel plug is largely composed of coarsening‐upward cycles of silt to clay and is dominated by clay and clayey silt material with poor reservoir characteristics. [ABSTRACT FROM AUTHOR]

A publicly available seismic dataset from a lab experiment shows the dependence of quality factor (Q) simultaneously on water saturation and stress in unconsolidated sand. Large Q gradients (e.g., > 10 m−1) necessitate a spectral ratio method modified to assume that Q changes with each ray path, thereby eliminating false Q values (e.g., < 0). Interval Q values (Qint) increase the most with depth (dQ/dz=43m−1) and stress (dQ/da=0.0025/Pa) in dry sand and the least in partially saturated sand (dQ/dz=10m−1 and dQ/da=0.0013/Pa) where attenuation created by local fluid flow reaches a maximum. Expected Qint values can be extrapolated from dQ/da and are bounded by Qint of the dry (Qdry) and partially saturated (Qwet) media (e.g., Qdry≥Qint≥Qwet). Qint deviations outside this range may be explained by changes in effective stress, attenuation mechanism, or sediment composition. Field estimation of seismic attenuation in natural settings may be helped by these constraints, although attenuation remains subject to careful consideration of other factors, e.g., grain size, sorting, and shape. [ABSTRACT FROM AUTHOR]

Soil density, porosity, elastic moduli, and the soil-water characteristic curve (SWCC) are important properties for soil characterization. However, geotechnical and laboratory tests for soil properties are costly and limited to point sampling sites. Seismic surveys can provide laterally continuous, seismic soil property values that may complement geotechnical borehole tests with less cost. We have developed a workflow to invert for soil properties and the SWCC from seismic P- and S-wave velocity-versus-depth profiles interpreted from shallow (<25 m depth) unconsolidated sediments under conditions of near-full saturation (>99%). The inversion is performed by using the covariance matrix adaptation evolution strategy to search automatically for optimal input soil property values by minimizing the misfit between field-based velocity profiles and predicted velocity profiles based on the Hertz-Mindlin and Biot-Gassmann theories. The results from seismic soil property inversion are validated by comparison with geotechnical as well as laboratory results conducted independently in the same area as the seismic survey. For each seismically recognizable layer, soil types are interpreted from the inverted soil density and elasticity, aided by the SWCC to help detect thin units that are below the original seismic resolution of the field data. There is flexibility to apply our suggested workflow in future studies. For a known geologic setting, empirical relationships and other velocity prediction models could also be incorporated into the suggested workflow to improve inversion results and extract additional information in soils. [ABSTRACT FROM AUTHOR]