Saline Mud Research Articles

Virgibacillus kekensis sp. nov., a moderately halophilic bacterium isolated from a salt lake in China

A Gram-positive, moderately halophilic, motile, strictly aerobic, endospore-forming, oxidase- and catalase-positive, rod-shaped bacterium, strain YIM kkny16(T), was isolated from a saline mud sample collected from the Keke salt lake in the Qaidam Basin, north-west China. This isolate grew in the presence of 0-25 % (w/v) NaCl and at pH 6.0-10.0 and 10-50 degrees C; optimum growth was observed with 10 % (w/v) NaCl and at pH 7.0 and 37 degrees C. Strain YIM kkny16(T) had meso-diaminopimelic acid as the diagnostic diamino acid, MK-7 as the predominant respiratory quinone, with a significant amount of MK-6, and anteiso-C(15 : 0), iso-C(14 : 0) and C(16 : 1)omega7c alcohol as major fatty acids. Major polar lipids were diphosphatidylglycerol and phosphatidylglycerol. The DNA G+C content was 41.8 mol%. Phylogenetic analysis based on 16S rRNA gene sequences confirmed that strain YIM kkny16(T) was a member of the genus Virgibacillus, exhibiting sequence similarities of 94.9-97.3 % to the type strains of recognized Virgibacillus species. Strain YIM kkny16(T) could be differentiated from recognized Virgibacillus species based on phenotypic characteristics, chemotaxonomic differences, phylogenetic analysis and DNA-DNA hybridization data. On the basis of evidence from this polyphasic study, strain YIM kkny16(T) is considered to represent a novel species of the genus Virgibacillus, for which the name Virgibacillus kekensis sp. nov. is proposed. The type strain is YIM kkny16(T) (=DSM 17056(T)=CGMCC 1.6298(T)).

Sedimentology and stratigraphic sequence of the Gavkhoni playa lake, SE Esfahan, Iran

The Gavkhoni playa lake is surrounded by alluvial fan deposits to the north, south and east and the Varzaneh aeolian sand field to the west. Four major sub-environments including: sand flat/saline sand flat, sand beach, mud flat/saline mud flat and salt pan and seven major facies can be recognized in this playa lake. Sand flat results from transportation of sand by wind from the adjacent sand dunes. The mud flat reflects rapid deposition on a lower flood plain during wet, shortly after sheet floods. The saline mud flat and salt pan is as a result of three stages: flooding, evaporation and desiccation. After flooding, when the shallow ephemeral lake becomes concentrated by evaporation, saline mud flat is formed and finally the formation of salt pan starts.

Lithostratigraphy and chemostratigraphy of the Mesoproterozoic Sibley Group, northwestern Ontario, Canada

The 950 m thick Sibley Group is a relatively flat-lying assemblage of siliciclastic and chemical sedimentary rocks exposed from the northwest shore of Lake Superior to the Lake Nipigon region of Ontario. Remnants of the Sibley Group occur in an ovoid area that sagged at ~1.5 Ga, creating accommodation space for braided fluvial sediments, derived as either first or multicycle detritus from the Trans-Hudson Orogen. This was followed by a transgressive episode and deposition of lacustrine siliciclastics and evaporites. An influx of sediment from the south occurred immediately prior to final contraction of the lacustrine system and deposition of strandline, stromatolite-bearing carbonates. The change in paleoslope was accompanied by development of a north–south-oriented half-graben. Overlying subaerial deposits represent deposition on a sabkha or saline mud flat. This assemblage is abruptly succeeded upward by flooding of the basin and major deltaic progradation and capped by a delta-top fluvial system with extensive preservation of floodplain deposits. The majority of the deltaic sediment was derived from Proterozoic sources to the south. An unconformity separates this assemblage from a thick succession of sandstone deposited as an aeolian dune field, with detritus probably coming from as far as the New Quebec Orogen to Baltica region. The geochemistry of medium-grained sandstone denotes that sediment became more mature and quartz-rich upsection and that the source areas evolved to more felsic and less alkalic compositions. Paleomagnetically correlated units in the Belt Supergroup, Apache Group, and Troy Quartzite in western North America indicate that the broad climatic fluctuations recorded in the Sibley Group may represent continent-wide events.

Two new “flagship” ciliates (Protozoa, Ciliophora) from Venezuela: Sleighophrys pustulata and Luporinophrys micelae

Sleighophrys pustulata nov. gen., nov. spec. and Luporinophrys micelae nov. gen., nov. spec. were discovered in a slightly saline mud and soil sample from some flat, dry puddles in the Maracay National Park on the north coast of Venezuela. Their morphology was studied in vivo, in protargol preparations, and in the scanning electron microscope. The new genera are monotypic and belong to the trachelophyllid haptorids. They are characterized by the unique shape of the epicortical scales (lepidosomes). Sleighophrys pustulata, which has a size of about 180×23 μm, possesses type I and unique type V lepidosomes which are hat-shaped and about 7×7 μm in size. Luporinophrys micelae, which has a size of about 200×35 μm, possesses types I, II, and unique type VI lepidosomes which are narrow, about 10 μm high cones composed of fibrous stripes connected by polygonal meshes. The conspicuous body size and the richly structured, comparatively large lepidosomes make S. pustulata and L. micelae biogeographic flagships which may help to cast some light on the pending question whether or not microorganisms have biogeographies. The available data suggest that both species have a restricted geographic distribution, not only because they were not described previously, but mainly because they were absent in about 2000 freshwater samples from central Europe and in about 1000 soil samples collected globally.

Affinities of some common estuarine macroinvertebrates to salinity and sediment type: empirical data from Eastern Cape estuaries, South Africa

Fourteen species of subtidal macrobenthos present in thirteen Eastern Cape estuaries, South Africa, were compared with regard to correlations with two important environmental variables (salinity and sediment mud content). Species were divided into five different faunal components based on their affinity with one of the two variables, namely marine species, oligohaline species, estuarine sand species, estuarine mud species, and species whose distribution seemed independent of either environmental variable. Although most species exhibited wide tolerance ranges to both environmental variables, preference ranges could be identified in many cases. Among the fourteen species studied, three were found mostly at high salinities, two were confined to sandy substratum, and four showed a clear preference for muddy sediment. The crab Paratylodiplax algoense was identified as a euryhaline marine species and the larvae of chironomid midges, previously believed to be oligohaline species, were found to be tolerant to near seawater salinities.

Sedimentology of the Miocene evaporitic succession in the north of Çankiri-Çorum basin, central Anatolia, Turkey

The upper Miocene non-marine sediments of the Cankiri-Corum basin in central Anatolia, have both evaporitic and non-evaporitic successions. These sediments were deposited in an evaporitic lake which had temporary episodes of palustrine conditions in response to seasonal or climatic changes. The successions show different facies such as sulfates, carbonates and siliciclastics. The sulfates comprise primary, reworked and diagenetic gypsum. The primary deposits are predominantly laminated gypsum, bedded gypsum and selenite. The reworked (detrital) gypsum comprises gypsite, gypsarenite, gypsrudite and breccias. The diagenetic type comprises micro- and macrogypsum nodules. The carbonates mainly include clayey limestone, oolitic limestone and dolomite. The siliciclastics comprise red beds and both channel and non-channel, conglomerates and mudstones. Laminated gypsum, composed of alternating gypsum and dolomite, was a result of environmental schizohalinity. Bedded gypsum was precipitated in the deeper part of the lake during high evaporation periods. Chevron-type selenite crystals formed on saline mud flats during the times of aridity, whereas the discoidal-type seen in the organic-rich mudstones occurred in the gypsiferous marshes during the times of humidity. Reworked (detrital) gypsum dominates the lake margin. These formed during periodic wet episodes that caused reworking of primary gypsum. Gypsum nodules occurred as both early and late diagenetic products. Carbonates and siliciclastics were deposited during the freshening periods of the lake. Climatic or seasonal changes were the main causes of the depositional styles of the upper Miocene evaporitic and non-evaporitic lacustrine deposits in Cankiri-Corum basin. Additionally, the transition upward from alluvial to lake environment implies an important change in drainage patterns that likely occurred as a result of marginal fault activity.

Microbial community of a saline mud volcano at San Biagio-Belpasso, Mt. Etna (Italy).

In San Biagio of Belpasso, approximately 20 km south of Mt. Etna, in the area of contact between volcanic and sedimentary formations, a number of small (3- 60 cm in diameter) active mud eruptions discharge CO2-rich gases, mud and NaCl brines. They can be described as mini-volcanoes owing to their typical conic shapes and continuously bubbling peak craters. Samples were collected from the active peak craters at a depth of 20 cm and DNA was immediately extracted and amplified with universal 16S rRNA gene-specific primers, followed by cloning procedure. A total of 140 bacterial clones obtained were screened and clustered by restriction fragment length polymorphism (RFLP) analysis. The pool of 16S rRNA sequences representing each RFLP cluster was subjected to phylogenetic analysis. All of the 33 sequences analysed were affiliated with the kingdom of Eubacteria; 28 sequences (77% of all clones) affiliated with the Proteobacteria, two sequences (19% of all clones) were affiliated with Actinobacteria and three sequences (4% of all clones) were affiliated with the Flexibacter-Cytophaga-Bacteroides division. The data obtained suggest that the microorganisms phylogenetically affiliated to autotrophic methane oxidizers and heterotrophic hydrocarbon degraders belonging to the gamma-subclass of Proteobacteria are major constituents of the microbial communities of the saline volcanic muds. Overall, the composition of the microbial community of the San Biagio mud volcano resembles the compositions of marine microbial communities, which might indicate that wind-blown seawater vapour acted as an inoculum for microbial community described in present work.

Apofrontonia lametschwandtneri nov. gen., nov. spec., a new peniculine ciliate (Protozoa, Ciliophora) from Venezuela

Apofrontonia lametschwandtneri was discovered in a highly saline mud and soil sample from a flooded area on the north coast of Venezuela (Maracay National Park). Its morphology was studied in vivo and in silver preparations, as well as in the scanning electron microscope. The new genus Apofrontonia belongs to the family Frontoniidae and is characterized by a combination of three features, viz., a pyriform vestibular opening occupying more than half of the body length; a bowl-shaped vestibulum that posteriorly gradually merges into the cell surface, completely exposing three similarly-structured peniculi; many (>6) vestibular kineties covering the sigmoidal right vestibular wall and not extending beyond the oral cavity. Apofrontonia lametschwandtneri nov. spec. differs from a European congener, A. obtusa (Song and Wilbert 1989) nov. comb. (basionym: Frontonia obtusa Song and Wilbert 1989), by body size (180 m vs. 80 m), number of somatic (155 vs. 90) and vestibular kineties (13 vs. 9), and the number (25 vs. 4–5) and location (scattered vs. lateral) of contractile vacuoles. Considering that A. lametschwandtneri has not been found in Europe, although it is a very large, conspicuous ciliate, it might be endemic to South America.

Cuticular disruption and mortality of Caenorhabditis elegans exposed to culture filtrate of Byssochlamys nivea Westling

AbstractA strain of a Byssochlamys nivea, isolated from saline mud in Western Australia as a part of statewide survey of soil fungi for nematophagous activity, was evaluated for its effect on nematodes. Culture filtrate of the fungus grown on potato dextrose broth for 7 days caused structural changes in the cuticle, aggregation of individuals, and mortality of Caenorhabditis elegans. In addition, the culture filtrate completely inhibited hatching of C. elegans eggs. Exudates from agar colonies also caused cuticular disruption and mortality of C. elegans. The cuticular disruption observed, not reported in nematodes before, was initiated in the labial region and spread towards the posterior region of the nematode within 10 min of application. This reaction occurred only in live nematodes. Cuticular disruption and mortality caused by the culture filtrate varied according to growth conditions. The active compound(s) in the culture filtrate were thermostable (100°C for 1 h); however freezing the culture filtrate (-20°C for 2 days) eliminated the activities, as did dialysis (<14 000 molecular weight). Cuticular disruption and mortality were also observed when the nematode was exposed to culture filtrates of two other strains of B. nivea supplied by CBS, The Netherlands. The culture filtrate also inhibited in vitro growth of the plant-pathogenic fungi Fusarium oxysporum, Gaeumannomyces graminis var. tritici, Phytophthora cinnamomi, Pythium irregulare and Rhizoctonia solani.

Quaternary palaeohydrological evolution of a playa lake: Salada Mediana, central Ebro Basin, Spain

Sedimentary features, mineralogy, bulk geochemical composition, stable isotope analyses and pollen data from sediment cores were used to reconstruct the Late Quaternary depositional evolution of the Salada Mediana playa lake (central Ebro Basin, northeastern Spain). The 150‐cm‐long sediment core sequence is composed of gypsum‐ and dolomite‐rich muds (Lower and Middle sections) and black, laminated, calcite‐bearing sediments (Upper section). The Salada Mediana formed as a karstic depression in the Miocene gypsum substratum during the Late Pleistocene. The Lower section was deposited in a sulphate–carbonate saline lake that ended with a period of desiccation and basin floor deflation. Subsequent deposition (Middle section) took place in a playa‐lake system. Two cycles of lower water table and expanded saline mud flats occurred. The Holocene sequence is missing, probably as a result of aeolian erosion. Sedimentation resumed only a few centuries ago, and saline pan environments dominated until modern times. The Salada Mediana facies succession was mainly governed by fluctuations in the hydrological balance, brine composition, and salinity; however, aeolian processes (detrital input and deflation) and recycling of previously precipitated salts also played a significant role.

New water-soluble ampholytic polysaccharides for oilfield drilling treatment: a preliminary study

New water-soluble ampholytic polysaccharides with carboxybetaine groups, which were prepared by grafting the zwitterionic monomer 2-(2-methacryloethyldimethylammonio)ethanoate onto hydroxyethyl cellulose, have been tested for their properties as a multifunctional drilling-mud additive regarding clay hydration inhibition and mud rheological control. For the ampholytic polysaccharides investigated, an increase in carboxybetaine groups results in an enhanced inhibitive ability and the pH of the medium has an effect on the inhibition. A strong viscosifying efficiency for low-solid muds, especially for saline mud, has been observed.

Latest Oligocene–Late Miocene lacustrine systems of the north-central part of the Ebro Basin (Spain): sedimentary facies model and palaeogeographic synthesis

In the central part of the Ebro Basin (Spain), north of the Ebro River, three allostratigraphic or tectosedimentary units differentiated within the latest Oligocene–Late Miocene (upper Agenian–Vallesian) interval are sedimentologically characterized. These deposits represent carbonate and sulphate lacustrine environments fed by Pyrenean alluvial systems (Luna system and Huesca system). In each unit, several facies associations or lithofacies were mapped. These interfinger through time: gypsum lithofacies occupy the southernmost part of the study area and are surrounded by carbonate and/or detrital lithofacies to the north. Each lithofacies consists of different carbonate, sulphate and/or detrital facies, arranged in simple sequences, decimetres to metres thick. The four types of sequences characterized reflect a complex shallowing evolution involving carbonate or sulphate contexts. Thus, each lithofacies represents the sedimentation in a particular lacustrine or alluvial subenvironment. A single lacustrine system is proposed for the central part of the basin. Its evolution followed cycles of water level variations, which caused kilometre-scale migrations of the lake shoreline. In this model, two distinct situations or lakes alternated through time. (a) One represents high levels associated with a single body of dilute carbonate water, where massive carbonate facies formed influenced by organism proliferation. These lakes had wide palustrine vegetated margins, in which bioturbated facies developed. (b) The other represents low levels that correspond to a playa-lake model. Laminated sulphate deposits formed in the lake waters, while nodular gypsum originated in the surrounding saline mud flats and within the exposed, previously deposited carbonate sediments. Transitions from one situation to the other, including minor water level fluctuations within carbonate sedimentation conditions, were marked by the development of laminated and stromatolitic facies. Lake level variations were caused by climatic cycles and gave rise to the simple sequences and to the lithofacies lateral relationships recognized in this study. Correlation among tectosedimentary units in the studied Pyrenean domain and in the Iberian domain of the Ebro Basin shows that for units N1 and N2 the facies that resulted from dilute carbonate waters are rare in the lacustrine areas of the Iberian margin. This indicates that a strong hydrological contrast existed between both regions. On this basis, a theoretical asymmetrical facies model is proposed for the single lacustrine basin that extended over these regions.

Dedolomitization and other early diagenetic processes in Miocene lacustrine deposits, Ebro Basin (Spain)

Abstract A variety of meteoric diagenetic features reveal the development of a syngenetic karst on lacustrine deposits of the Ebro Basin. Diagenetic processes that operated on lacustrine laminated and stromatolitic carbonates include the following. (1) A first syndepositional stage with processes such as dolomitization, desiccation and related breccia formation and sulphate precipitation, either as lenticular gypsum crystals or nodules. This stage took place under progressive evaporation due to lake level fall, when the previous carbonate deposits became exposed as a supra-littoral fringe surrounding saline mud flats of adjacent sulphate depositional environments. (2) A second early diagenetic stage in which processes such as sulphate dissolution and collapse brecciation, dedolomitization, calcite spar cementation and silicification occurred as a result of meteoric water input that caused a progressive rise in lake level. Light isotopic compositions (δ 13 C and δ 18 O) of diagenetic calcites, versus heavier compositions in primary laminated and stromatolitic limestones, confirm a meteoric influence. The syngenetic karst is best developed at the boundary between two allostratigraphic units and coincided with one of the extensive stages of sulphate deposition at the end of the Early Miocene. The karst facies occurred in an area that was a low-relief barrier that separated two sites of sulphate deposition during low lake levels. This indicates that the karst development was controlled by topographic changes within the basin and record a shift from arid to wetter climatic conditions, as suggested by the overlying freshwater carbonate deposits. The presence of diagenetic features such as those described in the central Ebro Basin affecting saline lacustrine carbonates is relevant because they can be used as indicators of subaerial exposure periods in terrestrial environments and they also reveal important palaeogeographic and palaeoclimatic events of basinal extent.

Pedogenic and groundwater processes in a closed Miocene basin (northern Spain)

The Sepúlveda-Ayllón Basin (SAB) was an episodically closed Miocene basin adjacent to the Tertiary Duero Basin (northern Spain). The sediments studied here represent a depositional system developed from the margin to the centre of the basin by alluvial fan, mud flat and saline mud flat/ ephemeral lacustrine environments. An assemblage of authigenic lithotypes was formed in the basin, their distribution being influenced by that of the depositional environments within the basin. Authigenesis took place mainly before sedimentation of the next set of beds. In the distal alluuial fan, authigenesis of smectite (outer part), palygorskite (inner part) and calcrete predominates, and the original muddy deposits are still recognizable. In the mud flat, a more intense transformation of the sediments took place, with predominant formation of palygorskite (outer part), interstitial gypsum, calcrete (outer part), dolocrete (inner part) and brown silcrete. In the saline mud flat /ephemeral lake, original sediment was extensively disturbed and replaced by magnesian clays (sepiolite and magnesian smectite), interstitial gypsum, dolocrete and cream and white silcrete. Authigenic alteration within each cycle varied in time and place, and was both pedogenic and groundwater-related. The authigenic assemblages point to a closed basin under evaporation in a seasonally dry climate. At the end of this period the SAB became connected with the Duero Basin to the northeast, thus losing the endoreic regime. Consequently, the authigenic evaporitic assemblages were then unstable and were partially replaced by a late sparry calcrete.

Interfingering of evaporites and red beds: An example from the Queen/Grayburg formation, Texas

Interbedded red sandstone, siltstone, mudstone, anhydrite and halite comprise the Queen/Grayburg formation (Guadalupian) of the Palo Duro Basin. These deposits accumulated in a 28,000 km 2 epicontinental basin that was characterized by regional aridity and episodic, nearly basinwide influx of marine-derived hypersaline waters. In each of several recurrent progradational cycles a variety of environments developed in this basin including eolian dunes, interdune areas, sand sheets, saline mud flats, and broad, shallow expanses of marine-derived brine (salinas). Siliciclastic sources were in the west and northwest whereas brines were derived from the south and southwest. Eolian dune deposits are represented by medium- to high-angle (15–35°) cross-stratified, fine-grained sandstone. Interdune areas accumulated flat- to low-angle bedded, wind-rippled strata, which are moderately to well sorted, fine-grained sand with frosted grains and illuviation structures. Sand sheets are characterized by deposits of horizontally bedded, rippled to massive, well-sorted, very fine-grained sandstone with illuviation structures. Sheetwash deposition on sand sheets and mud flats produced sandstones and siltstones with graded bedding, ripples with mud drapes, and intraclasts, and also flaser-bedded siltstones and mudstones deformed internally probably by haloturbation. Saline mud flats produced admixtures of mud and coarsely crystalline halite (chaotic halite-mudstone) and were located on the margins of regionally extensive hypersaline environments (salinas) in which bedded anhydrite and halite were precipitated subaqueously. Queen/Grayburg facies are cyclic and occur in characteristic vertical sequences that comprise, from base to top, bedded anhydrite, bedded halite, chaotic halite-mudstone, fine-grained clastics with displacive halite, siltstone and mudstone with deformed ripples, and eolian clastics. The sharp contacts between these shallowing-upward sequences suggest that transgressions were rapid.

Vegetation pattern and environmental correlates in coastal forests of the Australian monsoon tropics

A transect study of coastal forest vegetation on a lateritic peninsula in the Northern Territory revealed four distinct communities; eucalypt forest, mixed eucalypt forest-monsoon thicket, pure monsoon thicket and fringing coastal mangrove forest. The mangrove forest occurred in saline mud, the mixed and pure thicket on red earths and the eucalypt forest on both red and yellow earths. The eucalypt forest had less moisture in the surface soil than the other communities on the gentle slope above the mangroves. Evidence of past fire occurs in all the terrestrial communities, but the pure thicket is associated with a topographic position better protected from fire down-slope from the mixed community. Eucalypt regeneration in the mixed forest may be maintained by fires that have penetrated it from the frequently burnt eucalypt forest. It is possible that the mixed community is a fire sere occupying a site otherwise capable of supporting a pure thicket. However the pattern of vegetation has changed little in the recent past.

Anatomy of a Modern Marine Sabkha in a Rift Valley Setting, Northwest Gulf of California, Baja California, Mexico: ABSTRACT

An extensive sabkha, 100 by 20 km (62 by 12 mi), caps Holocene siliciclastic tidal flats along the coast of Baja California in the northwest Gulf of California structural trough. This sabkha, bounded on the west by alluvial fans, is a complex of sand flat, saline mud flat, gypsum-halite pan, and supratidal mud flat subenvironments. The sand flat, transitional between the fans and the sabkha, consists of horizontally to wavy laminated sand washed onto the flats by sheetfloods from the fans under upper-flow-regime conditions. The sand flat passes into saline mud flats characterized by massive mud crowded with discoidal gypsum crystals grown within the sediment, destroying the layering. This intrasediment growth of gypsum is driven by evaporative pumping of brine from a shal ow subsurface brine body. A gypsum pan occupies a wide, shallow depression within the saline mud flat. After storm flooding (either marine or meteoric) the pan becomes a temporary saline lake with an algal mat overgrowing a siliciclastic storm layer. Precipitation of gypsum needles from the open lake brine and bottom growth of gypsum prisms produce a gypsum layer that mimics the algal mat topography. Evaporation of the lake leads to (1) vadose diagenetic growth of gypsum that distorts and polygonally disrupts the gypsum layers (2) deposition of a surface halite layer in the center of the pan. These layered pan deposits are the evaporites of the sabkha. Seaward of the saline mud flats are supratidal mud flats underlain by millimeter-thick laminites with deep prism cracks, sheet cracks, an scattered gypsum discoid crystals. Pervasive mud cracking during long periods of nondeposition completely disrupts layering, creating a massive arid soil. A beach ridge separates this sabkha complex from the burrowed and ripple cross-laminated intertidal sediments. End_of_Article - Last_Page 460------------

Sedimentology and evaporite genesis in a Holocene continental‐sabkha playa basin—Bristol Dry Lake, California

ABSTRACTBristol Dry Lake, a 155 km2 continental‐sabkha playa basin in the Mojave Desert of south eastern California, is filled with at least 300 m of interbedded terrigenous clastics, gypsum, anhydrite, and halite. Evaporite facies conform approximately to a bull's eye pattern with gypsum and anhydrite surrounding a basin centre accumulation of halite. Transects through Bristol Dry Lake, from the alluvial fan to the centre of the playa, reveal: (1) crudely‐bedded, alluvial fan clastics interfingering with (2) playa‐margin sand flat and wadi sand and silt, followed by (3) gypsum, anhydrite, chaotic mud halite, and clay of the saline mud flat, and (4) salt‐pan halite beds.Terrigenous clastics were deposited in Bristol Dry Lake by sheetflow and by suspension settling from ponded floodwater. Some sediment has been reworked by aeolian processes to form barchan dunes around the playa margin. Thin nodular‐like beds of anhydrite and several types of gypsum occur across most of the playa. Giant hopper‐shaped halite cubes are suspended in saline mud flat facies, suggesting that they grew displacively in brine soaked sediment just below the surface. Thick beds (4 m) of halite, in the playa centre, may have formed through a complex alternating history of subaqueous and intrasedimentary precipitation under the influence of periodic floods, intense evaporation and brine‐level lowering, and capillary discharge of brines.The stratigraphy in the playa centre is cyclic. An ideal cycle consists of: (1) chaotic mud halite at the base overlain by (2) green to red clay with abundant, giant hoppers, and at the top (3) red clay, gypsum, and anhydrite with flaser‐ to wavy‐bedded sand and silt. This type of cycle probably records a gradual progradation of mud‐flat facies over salt pans.Bristol Dry Lake sediments are nearly identical to some of the Permian evaporites of the Permian Basin region, U.S.A. and they can serve as modern analogues for ancient‐sabkha facies analysis.

Evaporitic Lacustrine Environments of Canadian Plains: ABSTRACT

The plains of western Canada contain dozens of saline and hypersaline lakes which range in size from small ( 300 sq km) bodies of water. The shallowest lakes exhibit playa characteristics, flooding with water during the wet season but drying up during the summer and fall. The sediments of these lakes are composed of a mixed suite of siliclastics, carbonates, and evaporitic minerals. The major detrital minerals are quartz, dolomite, feldspars, and clay minerals. The authigenic carbonate minerals are aragonite, normal calcite, and high-Mg calcite. Evaporitic minerals include mirabilite, thernardite, gypsum, and bloedite. Spatially, the modern subenvironments in these basins usually exhibit a roughly concentric distribution, with a saline mud flat/sand flat occurring nearest the shore, followed by an ephemeral lake zone, and possibly a perennial lake. Although differing in scale and stage of development from basin to basin, all of the lakes have roughly similar near-surface stratigraphic profiles and facies distribution. The upper 25 to 50 cm consist of a thin (1 to 5 cm) crystalline crust overlying a thicker (5 to 50 cm) layer of mirabilite-thernardite-bloedite mush. Salt crust development, growth of large, euhedral mirabilite crystals, surface desiccation, and mineral dissolution all operate to create an extremely dynamic near-surface environment on a diurnal and seasonal basis. Underlying these uppe units is a zone of relatively dense salt crystal with minor mud interbeds. This unit can range in thickness from 40 m. Finally, underlying this dense crystal layer is a black, highly reducing, organic-rich, muddy clastic unit with variable salt crystal content. End_of_Article - Last_Page 592------------

Coastal Sabkha and Salt Pan Deposition of the Lower Clear Fork Formation (Permian), Texas

ABSTRACT Middle Permian (Leonard Series) evaporites, carbonates, and red beds of the lower Clear Fork Formation in the Texas Panhandle display many features common to modern coastal and continental sabkha facies. Similarities among lithofacies patterns and sequences, sedimentary structures, and anhydrite-halite textures and fabrics of both the lower Clear Fork Formation and modern sabkha facies permit construction of a model of halite deposition in coastal-sabkha salt pan environments which may be generally applicable to other ancient sabkha facies in intracratonic basins and around stable or rifted continental margins. Inferred coastal sabkha and marine inner-shelf environments and lithofacies recognized in the lower Clear Fork Formation are largely based upon analogous modern depositional se tings and include the following: 1) red siltstone to mudstone deposited in a wadi or desert alluvial-eolian plain and inner-sabkha mud flats, both passing basinward into 2) chaotic mudstone-halite of an inner-sabkha saline mud flat, which flanked 3) inner-sabkha salt pans bearing banded to massive halite and laminated anhydrite, and 4) nodular, nodular-mosaic, and massive anhydrite and dolomite deposited in marginal sabkha and inner shelf environments. Salt pans may have formed in the inner sabkha as a result of displacive gypsum-anhydrite growth and jacking up of the marginal sabkha surface, which impeded seaward drainage of floodwater off the sabkha. Modern process-sediment analogs include alluvial fans, saline mud flats, and salt pans of the coastal sabkhas in Baja, Mexico, the Trucial Coast, and Kutch, India. Evaporites and terrigenous clastics in Bristol Dry Lake, California, exhibit many features analogous with the Permian, suggesting that this setting, though strictly continental, serves as a process analog. Bromide values in lower Clear Fork halite average 40 ppm, which is less than an unaltered marine halite but still within the range of marine halite that has undergone diagenesis. Upward decreasing values in the lower Clear Fork upper-cycle may indicate a decrease in salinity during deposition or that the younger halite beds suffered more diagenesis than the underlying halite.