Recent Sabkha Research Articles

The significance of gypsum morphology in interpreting environmental changes caused by human construction, Red Sea coastal evaporation environment, Saudi Arabia

Field and petrographic descriptions of recent sabkha sediments at the eastern coast of Al-Kharrar lagoon, Red Sea coast of Saudi Arabia indicate the co-existence of gravel-sized, arrowhead, twinned gypsum crystals (< 23 cm long) and lenticular gypsum crystals (4–10 cm in size) of subaqueous and subaerial origin, respectively. Sand- and silt-sized, individual, lenticular and tabular gypsum crystals are widespread in the subsurface sediments of the sabkha. The twinned and lenticular gypsum crystals are highly enriched in sediment impurities, whereas tabular gypsum consists of clear crystals that are commonly associated with microbial lamination. The arrowhead, twinned gypsum crystals are formed subaqueously in a permanent supratidal pond that subsequently desiccated into a supratidal sabkha due to artificial construction of a barrier of concrete wall and gravelly dumps at the eastern margin of the lagoon. The lenticular and tabular gypsum crystals grow subaerially below the sediment surface of intertidal–supratidal sabkha by inclusive and displacive growth. The hindered supply of tidal floods to the former supratidal pond due to barrier construction leads to change in the depositional condition from upward, free growth of twinned gypsum crystals on the floor of the supratidal pond, to intrasediment growth of lenticular and tabular gypsum in a subaerial, supratidal sabkha setting. Deflation of fine sediments from the desiccated pond leads to exposure of a mixture of gravel-sized, arrowhead, twinned and lenticular gypsum crystals on the surface of the present day, supratidal sabkha setting. The results of this study indicate that the rapid change in the depositional condition due to human inference leads to desiccation of the supratidal pond, and changes in the morphology of the deposited gypsum from arrowhead, twinned crystals to lenticular crystals.

Middle Devonian (Givetian) supratidal sabkha anhydrites from the Moesian Platform (Northeastern Bulgaria)

The Middle Devonian (Givetian) anhydrites from deep wells in the Moesian Platform (Northeastern Bulgaria) are commonly distinguished into nodular and contorted structures. The latter includes a great variety of non-bedded (nodular, nodular-mosaic, mosaic and mosaic to massive), bedded (bedded nodular, bedded nodular-mosaic and bedded-mosaic to massive) and distorted (distorted nodular-mosaic, distorted mosaic, distorted bedded-mosaic, and “ropy bedded”) types. Microscopically, the anhydrite types are characterized by felted, subfelted and microcrystalline (aphanitic) microfabrics. The associated carbonate lithofacies and the synsedimentary/early diagenetic anhydrite features suggest that these sediments were formed in an arid peritidal setting with well distinguished subtidal (ostracod mudstones and wackestones, paleosiphonoclad wackestones and packstones and ostracod-peloidal packstones and grainstones), intertidal (microbial mats) and supratidal (sabkha anhydrites) zones. The described nodular and contorted anhydrites are interpreted as originated by similar mechanisms as those operating in recent sabkha settings in the Arabian Gulf. Most probably, they are the result of replacement/displacement intrasediment sulphate growth within the vadose and upper phreatic zones of the supratidal sabkha. The various nodular and contorted types are regarded as formed from incipient nodular structure and represent different stages of anhydrite nodule enlargement and growth deformation due to additional sulphate accumulation in the supratidal zone.

The Possible Origin of Hydrocarbon Generation Sourced From an Evaporative Environment: A Comparative Analog of Recent and Older Environments

This work focuses on recent coastal sabkha at Ras Shukeir with older analogs of Miocene age from Gulf of Suez and Mediterranean Sea coast of North Sinai. Their presence represents indicators of prolific biological activity and productivity. TOC content, Rock-Eval pyrolysis, infrared spectroscopy, and gas chromatography for kerogen of recent sabkha and core samples from both analogs justify the possibility of the evaporative environments as hydrocarbons generator. The evaporitic environments can produce organic matter leading to hydrocarbon potentialities upon reaching optimum maturation. The obtained results propose that recent sabkha can uphold enriched altitudes of TOC content. The older analog (e.g., Ras Gemsa, SE Zeit) is anticipated to yield fair to excellent content, containing kerogen of type I and II with intermittent type III. This indicates oil prone source rock derived mainly from algal and planktonic biomass together with bacterial residues accumulated under saline to hypersaline and moderately to moderately high reducing condition. This favors that the studied examples are analogs of possible generation of hydrocarbons sourced from evaporative environment.

Sedimentological characteristics and morphology of the aeolian sand dunes in the eastern part of the UAE, a case study from Ar Rub' Al Khali

The Umm Az Zimul–Al Wijan area is located in the southeastern part of the UAE and covers about 1600 km 2. It is bounded to the east by the Oman Mountains and to the south and west by the extensive dune area of Ar Rub' Al Khali. Field investigation revealed the common occurrence of parallel to sub-parallel sand ridges with a general east–west orientation. Also present, but less frequent, are barchan, barchanoid and star dunes. Interdune areas are classified into four types that include: dolomite, mixed ancient sabkha and ophiolitic rock fragments, mixed sand sheet and ophiolitic rock fragments, and recent sabkha. The textural characteristics of the sand forming the dunes are unimodal with a modal class in fine sand size, moderately to very well sorted, positively skewed and mesokurtic. Quartz grains are mainly subrounded to subangular. The similarity in roundness properties in different dune types in the eastern province of the UAE seems not to be influenced by dune form. Based on the heavy mineral suites and the angularity of quartz grains, it is believed that the sand sediments are mostly derived from the ultrabasic rocks forming the ophiolitic sequence of the Oman Mountains, acidic rocks of Iran and from the coastal area.

Miocene evaporitic sequence of the southern Mesopotamian Basin

Lithological analysis of the Lower Fars Formation in southern Iraq was carried out through the study of cuttings and cores, where available, and electric logs of 26 selected boreholes. The formation exhibits a complex repetition of various lithofacies, namely, limestone, dolomite, anhydrite/gypsum, halite, marl and siliciclastics. Four depositional cycles, with different thicknesses, were identified in the study area. The depositional environment of the formation is reconstructed as being a semi-closed marginal basin dominated by saline tidal flats receiving siliciclastic sediments. More than one Recent sabkha type could be the analogue of the studied sequence.

Genetic Characterization of Recent and Ancient Sabkha Systems: ABSTRACT

Ever since modern sabkhas were introduced to the geologic community and perceived as a concept applicable to ancient facies analysis, the literature has abounded with reports of inferred sabkha facies, many of which were compared with the modern Trucial Coast model of sabkha sedimentation. However, this well-described model probably has been overworked and stretched too far to be directly applicable to many ancient shallow-water to supratidal evaporite sequences. This predicament has risen partly because there is relatively little detailed information available on other modern sabkhas, despite the fact that there are other sabkhas around the world, few if any exhibiting the same characteristics as those of the Trucial Coast. Because all major depositional systems, such as marine deltas, for example (Galloway, 1975), exhibit a continuous spectrum of morphologic types, it must be recognized too that not all sabkhas are the same. They show significant variations in terms of physical processes that govern their development, and of the sedimentary responses to those processes. Thus, sabkhas should be distinguished or characterized on a genetic basis to prevent oversimplification and overuse of any one model. On the basis of dominant physical processes, three end members are recognized: (1) marine-, (2) fluvial-lacustrine-, and (3) eolian-dominated systems. Collectively, they may be displayed in a triangle diagram, upon which the positions of Recent sabkha systems can be superimposed. In general, playas fall into the fluvial-lacustrine-dominated field, interdune sabkhas are eolian-dominated, and coastal sabkhas are normally dominated by marine processes. Marine processes are mainly storm-, spring-, and wind-tidal flooding, and discharge of marine-derived brines at the sabkha surface. Playas, as well as some coastal sabkhas, are dominated by fluvial-lacustrine processes. Alluvial fans, flanking the landward side of coastal sabkhas and surrounding playa basins, contribute most of the sediment and consist of aquifers through which continental ground water flows, dissolves minerals, and discharges at the sabkha surface as saline brines. Wind, the third major process, is a factor in any sabkha, but is especially prevalent in interdune deflation depressions in both continental and coastal settings. It removes sediment above the ground-water table and enhances evaporation, resulting in precipitation of evaporites in interdune sediment. Sediment composition is the other significant factor in characterizing sabkha types. Carbonate-sulfate minerals (gypsum-anhydrite), soluble salts (halite, sylvite, polyhalite, etc), and terrigenous clastics are the dominant sedimentary components of sabkhas, but most are either dominated or distinguished by one or a mixture of those sediment types. By treating each of the three major sediment types as an end member, sediment variation between sabkhas can be displayed. A genetic examination of sabkha systems clearly reveals that the Trucial Coast is only one end member to a spectrum of sabkha types, both in terms of physical processes and sediment composition. Thus, care must be taken when comparing modern and ancient sabkha systems to correctly characterize the processes responsible for deposition of the strata in question and the dominant sediment composition. End_of_Article - Last_Page 1685------------

Geochemistry and mineralogy of a recent sabkha along the coast of Sinai, Gulf of Suez

Most efforts in the study of sea-marginal sabkhas have concentrated on the Persian Gulf, but little is known about the sediments and mineralogy of sabkhas marginal to other seas. The purpose of this paper was to present some geochemical and mineralogical observations in a recent sabkha on the coast of Sinai along the Gulf of Suez. The sabkha is composed of coarse clastic sediments with marine-derived groundwater at depth of about 1 m. The general morphology, climate and water salinity of the Gulf of Suez resemble those of the Persian Gulf, despite the fact that the content of authigenic evaporites in this sabkha is more sparse. The evaporite minerals accumulated only in the upper 30–40 cm of the sabkha, below that and down to the groundwater table, there is no accumulation of evaporites. Laterally, the salinity of the groundwater in the sabkha and the concentration of evaporites in the sediments above it increase constantly with distance from the shore. In contrast to the Persian Gulf where anhydrite is a major evaporite mineral, in Belayim gypsum is the only calcium sulphate mineral in the recent sabkha. Anhydrite is found only in an old elevated sabkha where it recrystallized from gypsum. The gypsum occurs as interstitial crystal concentrations or lithified horizons almost exclusively at the depth of 20–40 cm below the sabkha surface. Above that, in the uppermost horizons, there is in situ accumulation of interstitial halite crystals. The total concentrations of gypsum and halite are almost equal in this sabkha. The sea water recharge in El Belayim is almost exclusively by seepage through the sabkha sediments and not by flooding. The groundwater under this sabkha is only slightly more saline than the Gulf water, thus, not heavy enough for extensive downward refluxing. The major hydrodynamic process must be upward migration of the brines from the groundwater, precipitating on the way gypsum and later halite with some magnesite. Since the sediments of the sabkha are too coarse to support extensive capillary movement, the brines must, therefore, migrate upwards due to ‘evaporative pumping’.

ANHYDRITE DIAGENESIS, CALCITIZATION, AND ORGANIC LAMINITES, WINNIPEGOSIS FORMATION, MIDDLE DEVONIAN, SASKATCHEWAN

ABSTRACT A laminite deposit consisting of calcareous, dolomitic, and anhydritic layers interleaved with black organic material floors interior parts of the Middle Devonian Winnipegosis salt basin of western Canada. Before compaction had affected it, part of the anhydritic laminite was diagenetically altered to coarsely crystalline calcite that enclosed the anhydrite and organic matter. This calcitized rock preserves features of the original sediment, and reveals that the laminar anhydrite had originally grown as anhydrite nodules in an organic substrate. In all essential respects, the crystal fabrics of the calcitized anhydrite nodules resemble those of Recent sabkha anhydrites, and the mode of growth was apparently identical. Enterolithic structure resulted from buckling of sheets of coalesced nodules, and was caused by continued growth of the nodules within confining laminae. Observed varieties of anhydrite fabric can be explained as products of compaction. The agency of pore-water pressure is important to the generation of flow fabrics. The range of anhydrite compaction-fabrics in general can be related to two matrix properties: compressibility and drainage. The original sediment, before invasion by anhydrite or calcitization, resembled blue-green algal mat. Volumetrically, the organic material comprised a large fraction of the sediment even after anhydrite-nodule growth, though later compaction reduced it to black partings where it was not calcitized. Stratigraphically, the presence of algal mat and nodular anhydrite on the basin floor implies nearly complete loss of water from the basin after Winnipegosis reef formation, and before halite accumulation supervened.