Evaporite

Throughout geological time, evaporite sediments form by solar-driven concentration of a surface or nearsurface brine. Large, thick and extensive deposits dominated by rock-salt (mega-halite) or anhydrite (mega-sulfate) deposits tend to be marine evaporites and can be associated with extensive deposits of potash salts (mega-potash). Ancient marine evaporite deposition required particular climatic, eustatic or tectonic juxtapositions that have occurred a number of times in the past and will so again in the future. Ancient marine evaporites typically have poorly developed Quaternary counterparts in scale, thickness, tectonics and hydrology. When mega-evaporite settings were active within appropriate arid climatic and hydrological settings then huge volumes of seawater were drawn into the subsealevel evaporitic depressions. These systems were typical of regions where the evaporation rates of ocean waters were at their maximum, and so were centred on the past latitudinal equivalents of today's horse latitudes. But, like today's nonmarine evaporites, the location of marine Phanerozoic evaporites in zones of appropriate adiabatic aridity and continentality extended well into the equatorial belts. Exploited deposits of borate, sodium carbonate (soda-ash) and sodium sulfate (salt-cake) salts, along with evaporitic sediments hosting lithium-rich brines require continental-meteoric not marine-fed hydrologies. Plots of the world's Phanerozoic and Neoproterozoic evaporite deposits, using a GIS base, shows that Quaternary evaporite deposits are poor counterparts to the greater part of the world's Phanerozoic evaporite deposits. They are only directly relevant to same-scale continental hydrologies of the past and, as such, are used in this paper to better understand what is needed to create beds rich in salt-cake, soda-ash, borate and lithium salts. These deposits tend be Neogene and mostly occur in suprasealevel hydrographically-isolated (endorheic) continental intermontane and desert margin settings that are subject to the pluvial-interpluvial oscillations of Neogene ice-house climates. When compared to ancient marine evaporites, today's marine-fed subsealevel deposits tend to be small sea-edge deposits, their distribution and extent is limited by the current ice-house driven eustasy and a lack of appropriate hydrographically isolated subsealevel tectonic depressions. For the past forty years, Quaternary continental lacustrine deposit models have been applied to the interpretation of ancient marine evaporite basins without recognition of the time-limited nature of this type of comparison. Ancient mega-evaporite deposits (platform and/or basinwide deposits) require conditions of epeiric seaways (greenhouse climate) and/or continent-continent proximity. Basinwide evaporite deposition is facilitated by continent-continent proximity at the plate tectonic scale (Late stage E through stage B in the Wilson cycle). This creates an isostatic response where, in the appropriate arid climate belt, large portions of the collision suture belt or the incipient opening rift can be subsealevel, hydrographically isolated (a marine evaporite drawdown basin) and yet fed seawater by a combination of ongoing seepage and occasional marine overflow. Basinwide evaporite deposits can be classified by their tectonic setting into: convergent (collision basin), divergent (rift basin; prerift, synrift and postrift) and intracratonic settings. Ancient platform evaporites can be a subset of basinwide deposits, especially in intracratonic sag basins, or part of a widespread epeiric marine platform fill. In the latter case they tend to form mega-sulfate deposits and are associated with hydrographically isolated marine fed saltern and evaporitic mudflat systems in a greenhouse climatic setting. The lower amplitude 4 and 5th order marine eustatic cycles and the greater magnitude of marine freeboard during greenhouse climatic periods encourages deposition of marine platform mega-sulfates. Platform mega-evaporites in intracratonic settings are typically combinations of halite and sulfate beds.

Organic matter in modern saline systems tends to accumulate in bottom sediments beneath a density-stratified mass of saline water where layered hydrologies are subject to oscillations in salinity and brine level. Organic matter is not produced at a constant rate in such systems; rather, it is generated in pulses by a halotolerant community in response to relatively short times of less stressful conditions (brackish to mesohaline) that occur in the upper part of the layered hydrology. Accumulations of organic matter can occur in any layered brine lake or epeiric seaway when an upper less-saline water mass forms on top of nutrient-rich brines, or in wet mudflats wherever waters freshen in and above the uppermost few millimetres of a microbial mat. A flourishing community of halotolerant algae, bacteria and archaeal photosynthesizers drives the resulting biomass bloom. Brine freshening is a time of “feast” characterized by very high levels of organic productivity. In a stratified brine column (oligotrophic and meromictic) the typical producers are planktonic algal or cyanobacterial communities inhabiting the upper mesohaline portion of the stratified water mass. In mesohaline holomictic waters, where light penetrates to the water bottom, the organic-producing layer is typically the upper algal and bacterial portion of a benthic laminated microbialite characterized by elevated numbers of cyanobacteria.
Short pulses of extremely high productivity in the upper freshened part of a stratified brine column create a high volume of organic detritus settling through the column and/or the enhanced construction of benthic microbial mats in regions where freshened waters reach the hypersaline base of the column. With the end of the freshening event, ongoing intensely arid conditions mean that salinity, temperature and osmotic stress increase rapidly in the previously freshened water mass. This leads to a time of mass die-off of the once flourishing mesohaline community (“famine”). First, these increasingly salty waters no longer support haloxene forms. Then, halotolerant life dies back, and finally by the halite precipitation stage, only a few halophilic archaea and bacteria remain in the brine column (typically acting as heterotrophs and fermenters). Repeated pulses of organic matter, created during a feasting event followed by a famine event, create laminated organic-enriched sediment on an anoxic bottom.
There are three, possibly four, major mesohaline density-stratified settings where organic-rich laminites (petroleum source rocks) accumulated in ancient “famine or feast” saline settings: (1) basin-centre lows in marine-fed evaporitic drawdown basins, associated with basinwide evaporites; (2) mesohaline intra-shelf lows on epeiric platforms, associated with platform evaporites; (3) saline-bottomed lows in under-filled perennial saline lacustrine basins; (4) closed seafloor depressions in halokinetic deep-water marine slope and rise terrains. An inherently restrictive hydrology means that the same mesohaline settings show a propensity to evolve into regions characterized by the accumulation of widespread evaporite salts. If this happens soon after deposition of a layer of organic-rich sediment there is an increased likelihood of evaporite plugging in the source-rock layer, this in-turn decreases expulsion efficiency and downgrades the laminite bed’s ability to act as a prolific source rock.

The objective of this study is to understand and predict the alteration of porous rock by crystallization of salts. Samples of different rocks have been tested according to the EN 12370 standard test. Two parameters are proposed to evaluate the alteration of a rock during these tests. The alteration index AI represents the cycle in which the first damages occur. The alteration velocity AV represents the alteration rate at the end of the experiment, when the decay has become regular. These parameters can be estimated with the help of a microstructural study of the rocks. The most relevant intrinsic parameters of the stones for this estimation are capillary coefficient, evaporation coefficient, tensile strength and P-waves velocity. An evaluation of the alteration pattern is also proposed depending on the eventual heterogeneities and anisotropies of the rocks. The influence of the dimension and shape of the samples is also discussed.

Salt water intrusion is investigated in a coastal groundwater system in the northern part of the province Noord-Holland, The Netherlands. Density dependent groundwater flow is modeled in three-dimensions with MOCDENS3D. This computer code is a version of MOC3D (Konikow et al., 1996) that has been adapted to simulate transient density-driven groundwater flow. Results from the model suggests that in this Dutch hydrogeologic system a severe and irreversible salinisation is already occurring. Within a few tens to hundreds of years, the salinity of the shallow aquifer is estimated to increase substantially. This salinisation process is a result of human activities such as the reclamation of the low-lying areas during the past centuries. Without changing the present boundary conditions, seepage into the low-lying areas will decrease slightly because of predicted increases in groundwater salinity. However, the rate in salt load through the Holocene aquitard into the low-lying areas will increase significantly due to an increase in salinity in the shallow aquifer. In addition, a relative sea level rise of 0.5 m per century will intensify the salinisation process, causing an enormous increase in salt load in all low-lying areas in this part of The Netherlands.

We propose a method for estimating interval velocity using the kinematic information in defocused diffractions and reflections. We extract velocity information from defocused migrated events by analyzing their residual focusing in physical space (depth and midpoint) using prestack residual migration. The results of this residual-focusing analysis are fed to a linearized inversion procedure that produces interval velocity updates. Our inversion procedure uses a wavefield-continuation operator linking perturbations of interval velocities to perturbations of migrated images, based on the principles of wave-equation migration velocity analysis introduced in recent years. We measure the accuracy of the migration velocity using a diffraction-focusing criterion instead of the criterion of flatness of migrated common-image gathers that is commonly used in migration velocity analysis. This new criterion enables us to extract velocity information from events that would be challenging to use w...

Increases in groundwater salinity down gradient are a common occurrence in catchments throughout Australia, exacerbating the effects of dryland salinisation in discharge areas. Groundwater hydrochemical and isotopic data from the Willaura catchment in south-eastern Australia, which is affected by both primary (natural) and secondary (human-induced) salinity, allowed the factors that cause the down gradient trend in salinisation within this catchment to be determined. The overall salinity of the groundwater (0.8–70 mS/cm) is controlled by evapotranspiration, which concentrates cyclic salts in the unsaturated zone, greatly increasing the salinity of the soil–water to 3700–6400 mg/L Cl−. The progressive addition of this saline soil–water to fresher groundwaters recharged on the catchment margins causes a gradual increase in salinity down gradient. The groundwater stable isotope compositions show that most recharge occurs in winter and spring. Groundwater salinities increase around the saline lakes of the discharge zone, due to direct evaporation from shallow watertables and minor dissolution of halite (as indicated by Cl−/Br− ratios). Mineral–water interactions within the aquifers cause a slight overall reduction in salinity; conversion of kaolinite to smectite and illite, and cation exchange of Na+ for Ca2+ on smectites, cause Na+/Cl−, Mg2+/Cl−, K+/Cl−, Si/Cl− and HCO3−/Cl− ratios to progressively decline and pH to gradually increase down gradient. Oxidation of organic matter causes a strong decrease in the redox potential of the groundwaters down gradient. The groundwater ages increase from modern (containing tritium) on the catchment margins to ∼8000 years (based on 14C dating) at the end of the ∼25 km flow path. The older groundwaters are isotopically heavier than the younger waters, probably due to recharge during a wetter climate in the early Holocene. The groundwater ages show clearly that the progressive addition of saline soil–water, causing groundwaters to become more saline down gradient, has occurred throughout the Holocene and may explain the occurrence of primary salinisation within many Australian catchments.

Gas and minor oil production from the northwestern Uralsk basin is associated with TTGF, Çaganskaya and Darinskaya fields located along a NE–SW aligning chain of barrier reefs. Most important reservoir rocks of the basin are associated with shelf, reef, pinnacle reef, atoll and bar facies of the carbonate complex, deltaic or tidal facies of the platform deposits and clastic basinal

This study reports a multi-parameter geochemical investigation in water and sediments of a shallow hyper-eutrophic urban freshwater coastal lake, Zeekoevlei, in South Africa. Zeekoevlei receives a greater fraction of dissolved major
and trace elements from natural sources (e.g., chemical weathering and sea salt). Fertilizers, agricultural wastes, raw sewage effluents and road runoff in contrast, constitute the predominant anthropogenic sources, which supply As, Cd, Cu, Pb and Zn in this lake. The overall low dissolved metal load results from negligible industrial pollution, high pH and elevated metal uptake by phytoplankton. However, the surface sediments are highly polluted with Pb, Cd and Zn. Wind-induced sediment resuspension results in increased particulate and dissolved element concentrations in bottom waters. Low C/N ratio (10) indicates primarily an algal source for the sedimentary organic matter. Variation in sedimentary organic C content with depth indicates a change in primary productivity in response to historical events (e.g., seepage from wastewater treatment plant, dredging and urbanization). Primary productivity controls the enrichment of most of the metals in sediments, and elevated productivity with higher accumulation of planktonic debris (and siltation) results in increased element concentration in surface and deeper sediments. Aluminium, Fe and/or Mn oxy-hydroxides, clay minerals and calcareous sediments also play an important role in adsorbing metals in Zeekoevlei sediments.

In high-salinity and water-scarce environments, such as in hot and dry deserts, species develop adaptive strategies that are necessary for living in such harsh conditions. Continental ephemeral salt lakes (sabkhas) with periodic flooding from subsurface groundwater followed by high salt concentrations, such as the ones of the northern Africa Chotts, rank among the geological settings wherein the combined effect of salt concentration and fluctuation of water availability make the environment unstable and can thereafter lead to extreme changes. The present study investigates the continental sabkha environments of southern Tunisia, in which ecological niches (i.e. water and salt precipitates, including halite, gypsum, and dolomite) host microbial life. Halophilic microorganisms can be trapped in the extensive saline crusts of halite and gypsum, which can be regarded as the first step of their delivery to the fossil record. The study of halophiles can provide clues for the understanding of life strategies in extreme terrestrial environments, such as sabkhas, which are potential good terrestrial analogs for evaporite-bearing Martian deposits.