Halite Crust Research Articles

A Siliciclastic Coastal Sabkha, Red Sea Coast, Saudi Arabia

A modern, siliciclastic sabkha occupies the widespread, low lying and almost flat area to the east of AI-Kharrar lagoon on the west of Saudi Arabia. Four sedimentary facies were recognized in shallow cores: (1) surface sand layer associated with halite crust; (2) light brown clayeysandy unit displaying interstitialevaporatic minerals; (3) grey calcareous sandy unit which represents sediments accumulated during marine transgression; and (4) basal poorly sorted gravely-clayey sands of continental origin (Pre-Holocene alluvial deposits). The thickness of the sabkha and marine-lagoonal facies ~facies 1, 2, 3) in general decreases towards the south and east. There are two evaporative assemblages in the studied sabkha. The first assemblage occurs in the southern part and includes gypsum, high Mg-calcite and dolomite. It has formed through reworking of the sediments by flood water from the lagoon and subsequent rapid evaporation. The absence of aragonite in the surface sediments and its presence in those of the subsurface indicate that not only penecontempor3cneous alteration of aragonite to dolomite but also later diagenetic processes have been active. The second assemblage in the central and northern parts of the sa,kha is dominated by gypsum and high Mg-calcite in the surface sediments. Aragonite occurs only in subsurface sediments. Mg concentrations did not reach a level to initiate diagenetic dolomitization. The observed mineralogical distribution is typical for coastal-marine evaporative system. هناك سبخة شاطئية سليسية حديثة في منطقة منخفضة نسبيا ومسطحة تقريبا تقع شرق لا جون الخرار على الساحل السعودي للبحر الأحمر . ولقد أوضحت دراسة هذه السبخة أنها تحتوي على أربع سحن رسوبية هي كالآتي:

Holocene carbonate facies model, Ras Shukhier hypersaline pool and its surrounding sabkha, west Gulf of Suez, Egypt

The Holocene Ras Shukhier pool is an active carbonate depositional subenvironment surrounded by an evaporitic supratidal sabkha. Field and petrographic studies of the carbonate constituents of the pool lead to the recognition of seven sedimentary facies. These are: (1) carbonate lithoclast-pellet-aggregate sand facies, (2) algal (cyanophyt) stromatolites comprising stratiform cryptalgal laminites and laterally close-linked hemispheroids (LLH-C), (3) pellet-lime mud with dolomitized bioclastic floatstone/packstone crusts, (4) pellet-lime mud facies, (5) gastropod ( Cerithium) pellet-lime muddy sand facies, (6) puffy gypsum crust, and (7) tufa limestone patches. The lateral distribution of the carbonate facies in the pool is dependent on the orientation of the pool with respect to the prevailing northwest winds and on the direction of water seepage. The evaporitic sabkha is classified here into: (a) a seasonally water-covered rim where the carbonates and evaporites formed seasonally by direct precipitation from the surface water, and (b) a subaerially exposed sabkha with lithified halite crust exhibiting tepee structures. The occurrence of carbonates, followed by sulphates and halites, within the sabkha siliciclasts, have been developed by sedimentation from brines migrating upward.

Diagenesis of Saline Pan Halite: Comparison of Petrographic Features of Modern, Quaternary and Permian Halites

ABSTRACT Petrographic studies of modern saline pan halites (Saline Valley, CA; Salina Omotepec, Baja California, Mexico) and Quaternary shallow-buried (0-200 m) halites (Saline Valley, CA; Bristol Dry Lake, CA; Searles Lake, CA; Qarhan saline pan, Qaidam Basin, China; Lake Uyuni, Bolivia) show that the diagenetic modification of halite begins contemporaneously with deposition, is most intense within the upper few meters of burial, and is essentially complete within the first 45 m of burial. Halite crusts from modern saline pans that have undergone repeated episodes of flooding, evaporative concentration, and desiccation contain abundant syndepositional diagenetic features. These mature modern halites are dominated by dissolution textures and fabrics (formed during flood stages) and cementati n textures (formed during desiccation stages). Interlayered mud beds contain varying amounts of displacive halite crystals. At shallow burial depths, halites retain many textural features of mature modern saline pan halite. Halites below the first few meters are no longer susceptible to dissolution from floodwaters but continue to be cemented by clear halite. Within the first 10 m of burial, cementation reduces the porosity of halite crusts to less than 10%. The remaining pore spaces are completely filled by burial depths of approximately 45 m. Displacive growth of halite in muds continues at shallow-burial depths and is probably limited to the first few tens of meters of burial depth. The mechanisms for cementation and displacive growth of halite at shallow-burial depths probably include (1) evaporative concentration of groundwater brines and (2) cooling of surface brines when they sink below the sedime t surface. Undeformed halites from the Permian Salado and Rustler Formations of New Mexico contain delicate syndepositional textures and abundant clear halite cements that are comparable to those observed in modern saline pan halites and shallow-buried halites. The Permian halites are interpreted to have undergone a depositional and early diagenetic history similar to the modern and Quaternary analogs. Complete cementation of saline pan halites at shallow burial depths has important implications for the origin of saline formation waters in sedimentary basins. Parent evaporite brines may not be stored in the pores of halite rocks and later expelled during burial compaction if the rocks are cemented early, and tightly crystallized halite rocks may also impede the downward migration of dense syndepositional brines.

A siliciclastic coastal Sabkha, capricorn coast, Queensland, Australia

A small (3 km 2), modern, siliciclastic sabkha occurs landward of Kemp Beach on the Capricorn Coast of central Queensland, Australia. Five sedimentary facies were recognized in shallow cores: (1) surface sand layer and associated halite crust; (2) a mottled clayey peat unit displaying interstitial gypsum (this layer has formed by vertical accretion of algal mats); (3) a unit of mangrove peat and clay with abundant jarosite corresponding to the locations of previous mangrove-lined tidal channels; (4) a carbonaceous sandy unit which represents the sediment that accumulated in a lake bordered by mangroves; and (5) a basal, well-sorted sand unit. Evaporative pumping during dry winter months is the dominant hydrologic process in this sabkha. Water lost from subsurface brines is replenished by subsurface flow of sea water via a pre-existing tidal channel now covered by the prograding sequence. The main aquifer below the sabkha surface is the carbonaceous sandy unit. The construction of a weir across the tidal channel maintains a relatively uniform water level below the sabkha surface during the wet summer period. However, during dry winter months, the piezometric gradient is such that the water flow is primarily unidirectional from the ocean inlet, through the mangrove-lined channel, to the subsurface aquifer below the sabkha. Analyses of subsurface waters revealed a gradient from almost normal marine salinity in the lake to a four-fold increase in subsurface brines. Correspondingly, there is a linear increase in major cation concentrations, with the exception of Ca 2+ which becomes depleted due to precipitation of gypsum. During dry winter months a halite crust forms at the surface. In contrast to most previously described sabkha environments, aragonite does not occur. Its absence may be explained by the large organic matter content of the sediments within the aquifer, inhibiting calcium-carbonate precipitation.

Peuplements benthiques à Cyanophycées des marais salants de Salin-de-Giraud (Sud de la France)

In Salin-de-Giraud solar salt work pools, Cyanophyceae are dominant in benthic populations. Two main types of communities can be recognized : 1) Laminated mats in weak salinity areas (<150 g/1) with Microcoleus chthonoplastes frequently exclusive (but which may be covered by a Lyngbya aestuarii layer), being the result of superposition in time of two competitive phenomena : Cyanophycean growth and sedimentary contribution either of detrital or chemical origin. As the gypsum precipitation occurs, Microcoleus mats disappear. 2) Communities associated with gypsum and halite crusts. In gypsum pools, they may be composed of several layers : a) a lower purple layer of ph.otosynthetic bacteria ; b) a mid dark-green layer of filamentous Cyanophyceae (Phormidium and Spirulina species) mixed with some coccoids (Aphanothece div. sp. essentially) ; c) an upper orange-colored layer of coccoids (with an Aphanothece sp. as major component) may grow during summer, but disappears during winter when pools are emptied, which is the rule in Salin-de-Giraud. The basal level of halite crust is colonized by a filamentous form Phormidium sp. For these communities, stratification of species is associated to physiological properties of organisms, and sedimentary deposits only act as a support in such pools.

SOME HOLOCENE GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL OBSERVATIONS FROM OMAN AND THEIR PALAEOGEOLOGICAL IMPLICATIONS

Observed exhumed Pleistocene river channel conglomerates now standing as ridges, and inland sabkha sedimentological structural phenomena from Oman, are discussed. Their significance as tools in the interpretation of similar palaeogeological environments is considered. Correlation with similar channel fills elsewhere in Arabia and Iran indicates aggradation as having occurred between 35,000–7,000 yrs BP and suggests that this was principally by sustained flow during pluvial phases accompanying the last global glaciation, (at least in this part of the Middle East). Elevations of the now inverted channels above their deflated desert surroundings are used for calculating deflation rates, and reservoir porosity‐permeability characteristics of similar ancient deposits are considered. Additional and new data on halite crust structures from the Umm‐as‐Samim inland sabkha are presented mainly in photographs backed by factual data which are commented upon; sabkha formation probably commenced about 4,500 yrs BP. The preservation of similar origin halite deposits in the stratigraphic record is briefly discussed.This note is intended to augment data on desert environments that appear to have either had passing mention, or simply recording without assessment of their significance as tools or indicators in the interpretation of similar palaeogeological environments. It is the hope that the observations recorded here will stimulate further work on these and other Holocene phenomena in the region concerned and also elsewhere, together with dissemination of results, so that implications to various aspects of applied geology can be better evaluated and understood.