Evaporites and siliciclastics of the Permian Nippewalla Group of Kansas, USA: a case for non-marine deposition in saline lakes and saline pans

The mid‐Permian Nippewalla Group of Kansas consists of bedded evaporites, red‐bed siliciclastics and grey siliciclastics deposited in a non‐marine environment. Lithologies and sedimentary features indicate lacustrine and aeolian deposition, subaerial exposure and palaeosol formation. Grey siliciclastic mudstones characterized by planar and convolute laminations, ostracods, peloids and plant material represent a freshwater‐brackish perennial lake facies. Bedded anhydrites containing gypsum‐crystal pseudomorphs, clastic anhydrite grains and grey mud drapes and partings suggest deposition in saline lakes. Bedded halites consist of chevron and cumulate crystals, dissolution surfaces and pipes and mudcracked microcrystalline salt crusts, which were deposited in saline pans dominated by flooding, evaporative concentration and desiccation. Chaotic halite, composed of red‐bed mudstone and siltstone with displacive halite crystals, formed in saline mudflats. Red‐bed mudstone and siltstone with little or no displacive halite, but with abundant cracking, root and plant features, suggest deposition in a dry mudflat. Red‐bed sandstone, composed of well‐sorted, well‐rounded quartz grains cemented with halite, indicate aeolian and rare shallow‐water deposition. Most deposition took place in halite‐dominated ephemeral saline lakes surrounded by saline and dry mudflats, sandflats and sand dunes. Evaporation, desiccation, flooding and wind played significant roles in this environment. The Nippewalla Group siliciclastics and evaporites represent an evolution from a perennial lacustrine system to a non‐marine, acidic saline pan system in the mid‐continent of North America. The problem of distinguishing between ancient marine and non‐marine evaporites, as well as recognizing those evaporites deposited in acid settings, with detailed field, core and petrographical study of both evaporite deposits and associated sedimentary rocks has successfully been addressed. In addition, interpretations of mid‐Permian palaeoclimate data in the form of short‐term air temperature proxies within longer‐term wet–dry trends have been made. These data provide a new palaeogeographic and palaeoclimatic model for the mid‐Permian of western Pangaea.     

Halite saltern in the Canning Basin, Western Australia: a sedimentological analysis of drill core from the Ordovician-Silurian Mallowa Salt

The Late Ordovician-Early Silurian Mallowa Salt of the Carribuddy Group, Canning Basin, north-west Australia, is the largest halite deposit known in Australia, attaining thicknesses of 800 m or more within an area of approximately 200 000 km². Study of 675 m of drill core from BHP-Utah Minerals’ Brooke No. 1 well in the Willara Sub-basin indicates that the Mallowa Salt accumulated within a saltern (dominantly subaqueous evaporite water body) that was subject to recurrent freshening, desiccation and exposure. Textures and bromine signatures imply a shallow water to ephemeral hypersaline environment typified by increasing salinity and shallowing into evaporitic mudflat conditions toward the top of halite-mudstone cycles (Type 2) and the less common dolomite/anhydrite-halite-mudstone cycles (Type 1). The borate mineral priceite occurs in the capping mudstones of some cycles, reinforcing the idea of an increasing continental influence toward the top of mudstone-capped halite cycles. The rock salt in both Type 1 and Type 2 cycles typically comprises a mosaic of large, randomly orientated, interlocking halite crystals that formed during early diagenesis. It only partially preserves a primary sedimentary fabric of vertically elongate crystals, some with remnant aligned chevrons. Intraformational hiati, halite karst tubes and solution pits attest to episodic dissolution. Stacked Type 2 cycles dominate; occasional major recharges of less saline, perhaps marine, waters in the same area produced Type I cycles. The envisaged saltern conditions were comparable in many ways to those prevailing during the deposition of halite cycles of the Permian Salado Formation in New Mexico and the Permian San Andres Formation of the Palo Duro Basin area in Texas. However, in the Canning Basin the cycles are characterized by a much lower proportion of anhydrite, implying perhaps a greater degree of continental restriction to the basin. The moderately high level of bromine in the Mallowa Salt (156·5 ± 43·5 ppm Br for primary halite, 146·1 ± 54·7 ppm Br for secondary halite) accords with evolved continental brines, although highly evaporative minerals such as polyhalite and magnesite are absent. The bromine levels suggest little or no dissolution/reprecipitation of primary halite and yet, paradoxically, there is little preservation of the primary depositional fabric. The preservation of early halite cements and replacement textures supports the idea of an early shutdown of brine flow paths, probably at burial depths of no more than a few metres, and the resultant preservation of primary bromine values in the secondary halite.     

Glauberite–halite association of the Zaragoza Gypsum Formation (Lower Miocene, Ebro Basin, NE Spain)

Glauberite is the most common mineral in the ancient sodium sulphate deposits in the Mediterranean region, although its origin, primary or diagenetic, continues to be a matter of debate. A number of glauberite deposits of Oligocene–Miocene age in Spain display facies characteristics of sedimentologic significance, in particular those in which a glauberite–halite association is predominant. In this context, a log study of four boreholes in the Zaragoza Gypsum Formation (Lower Miocene, Ebro Basin, NE Spain) was carried out. Two glauberite–halite lithofacies associations, A and B, are distinguished: association (A) is composed of bedded cloudy halite and minor amounts of massive and clastic glauberite; association (B) is made up of laminated to thin‐bedded, clear macrocrystalline, massive, clastic and contorted lithofacies of glauberite, and small amounts of bedded cloudy halite. Transparent glauberite cemented by clear halite as well as normal‐graded and reverse‐graded glauberite textures are common. This type of transparent glauberite is interpreted as a primary, subaqueous precipitate. Gypsum, thenardite or mirabilite are absent in the two associations. The depositional environment is interpreted as a shallow perennial saline lake system, in which chloride brines (association A) and sulphate–(chloride) brines (association B) are developed. The geochemical study of halite crystals (bromine contents and fluid inclusion compositions) demonstrates that conditions for co‐precipitation of halite and glauberite, or for precipitation of Na‐sulphates (mirabilite, thenardite) were never fulfilled in the saline lake system.     

Criteria for the recognition of salt-pan evaporites

Layered evaporites can accumulate in: (1) ephemeral saline pans, (2) shallow perennial lagoons or lakes, and (3) deep perennial basins. Criteria for recognizing evaporites deposited in these settings have yet to be explicitly formulated. The characteristics of the ephemeral saline pan setting have been determined by examining eight. Holocene halite-dominated pans (salt pans) and their deposits (marine and non-marine) from the U.S., Mexico, Egypt and Bolivia. These salt pans are typified by alternating periods of flooding, resulting in a temporary brackish lake, evaporative concentration, when the lake becomes saline, and desiccation, which produces a dry pan fed only by groundwater. The resulting deposits consist of alternating layers (millimetres to decimetres) of halite and mud. The layers of halite are characterized by: (1) vertical and horizontal cavities, rounded crystal edges and horizontal truncation surfaces, due to dissolution during flooding; (2) vertical ‘chevrons’ and ‘cornets’ grown syntaxially on the bottom during the saline lake stage; (3) halite cements (overgrowths and euhedral cavity linings) and disruption of layering into metre-scale polygons, produced during the desiccation stage. The muddy interbeds are characterized by displacive growth of halite during the desiccation stage. Immediately below the surface of the pan the halite layers are ‘matured’ by repeated episodes of dissolution and diagenetic crystal growth. This results in porous crusts with patches of ‘chevron’ and ‘cornet’ crystals truncated by dissolution, clear diagenetic halite cement, and internal sediment. These layers of ‘mature’ halite closely resemble the patchy cloudy and clear textures of ancient halite deposits. Holocene salt-pans are known to cover thousands of square kilometres and cap halite deposits hundreds of metres thick, so they are realistic models for ancient evaporites in scale, e.g. Permian Salado Formation of New Mexico-Texas, which preserves many primary salt-pan features.     

内陆湖盆"深水成盐"形成条件和识别标志:以东濮凹陷与现代盐湖为例

位于我国东部的许多新生代盆地,在地质历史时期发育了巨厚的岩盐沉积。尽管这些盆地的成盐模式研究已经历了40多年,但由于缺乏“深水成盐”的现代沉积模式,到底是“深盆-深水”还是“深盆-浅水”成盐,一直难以定论。为了理解“深水成盐”的控制因素,很多现代盐湖开展了水文学和水化学调查,然而这些湖盆的矿物组合各不相同,“深水成盐”的形成条件和控制因素尚不清楚。本文对死海、佛瑞湖等“深水成盐”的现代盐湖以及我国东濮凹陷沙三段的成盐特征进行了解剖,从盐度、水深、湖平面波动以及卤水分层等角度探讨了“深水成盐”的形成条件,对比分析了“深水成盐”的相对位置以及沉积物特征,总结了“深水成盐”的识别标志。研究表明,盐岩层系在岩心和测井资料上显示出多尺度的旋回性。“深水成盐”为水深较大的洼陷中心成盐,与盆缘的“浅水成盐”同盆共存。沉积相对岩盐层系的结构和组成有明显的控制作用,其中洼陷带的“深水成盐”,主要在洼陷带的卤水-湖底沉积物界面附近,析出和增生粗晶的盐类矿物,常与富含有机质和黄铁矿的暗色泥岩共存;而湖滨附近的“浅水成盐”,单层厚度薄,结晶粒度细小,通常含有较多的陆源碎屑。死海为代表的现代盐湖以及东濮凹陷等古代成盐盆地的沉积特征表明,“深水成盐”发生于湖平面的下降期,而且卤水剖面的厚度对蒸发岩的形成分布有明显的控制作用,同时具有“深水”和“深盆”特征的内陆盐湖更容易形成单层厚度大、横向稳定的岩盐沉积。本研究有助于改变人们以往对内陆湖盆成盐机理的认知,尤其是现代盐湖的卤水分层析盐特征,对解读地质历史中的其他成盐事件具有重要启示。基于现代沉积实例的“深水成盐”识别标志,可以为古代岩盐沉积模式的建立提供限定条件。     

Origin and evolution of major salts in the Darling pans,Western Cape,South Africa

Sediment and water samples from 12 saline pans on the semi-arid west coast of South Africa were analysed to determine the origin of salts and geochemical evolution of water in the pans. Pans in the area can be subdivided into large, gypsiferous coastal pans with 79–150 g/kg total dissolved salt (TDS), small inland brackish to saline (2–64 g/kg TDS) pans and small inland brine (168-531 g/kg TDS) pans that have a layer of black sulphidic mud below a halite crust. The salinity of coastal pan waters varies with the seasonal influx of dilute runoff and dissolution of relict Pleistocene marine evaporite deposits. In contrast, inland pans are local topographic depressions, bordered on the north by downslope lunette dunes, where solutes are concentrated by evaporation of runoff, throughflow and groundwater seepage. The composition of runoff and seepage inflow waters is determined by modification of coastal rainfall by weathering, calcite precipitation and ion exchange reactions in the predominantly granitic catchment soils. Evaporation of pan waters leads to precipitation of calcite, Mg–calcite, dolomite, gypsum and halite in a distinct stratigraphic succession in pan sediments. Bicarbonate limits carbonate precipitation, Ca limits gypsum precipitation and Na limits halite precipitation. Dolomitisation of calcite is enhanced by the high Mg/Ca ratio of brine pan waters. Brine pan waters evolve seasonally from Na–Cl dominated brines in the wet winter months to Mg–Cl dominated brines in the dry summer months, when 5–20 cm thick halite crusts cover pan surfaces. Pan formation was probably initiated during a drier climate period in the early Holocene. More recent replacement of natural vegetation by cultivated land may have accelerated salt accumulation in the pans.     

塔西南坳陷中新生代蒸发岩沉积初探

通过资料搜集、蒸发岩野外露头地质调查、石盐岩沉积特征分析及盐类矿物学研究,对塔里木盆地塔西南坳陷中新生代蒸发岩的分布、层位、盐类矿物组合、成因进行了初步探讨。塔西南坳陷石盐岩沉积呈透镜体状,主要沿西昆仑山前分布,常含有褐红色、灰绿色泥砾,泥砾岩性与吐依洛克组下段岩性一致,推测应为吐依洛克组沉积晚期海退期成盐,其层位应归属于吐依洛克组上段。石盐岩透镜体在横向分布上不连续,反映了当时塔西南坳陷内部可能存在多个古盐湖次级凹地,其在干旱气候条件下经浓缩蒸发成盐。蒸发岩矿物除石盐、石膏外,还见有杂卤石、钙芒硝等,其中杂卤石可能为后期富钾卤水交代原生石膏的产物,而乌泊1井石盐表面大量的次生钙芒硝可能为盐湖后期石盐析出阶段含钙地下水缓慢持续补给盐湖的产物。     

Modern halite sedimentation processes and depositional environments,Hutt Lagoon,Western Australia

Abstract

Contemporary layered halite in the Hutt Lagoon, Western Australia, forms distinct precipitational and clastic fades, which are ascribed to seasonal ponding and playa development in the lagoon respectively. Field and laboratory documentation of the halite types and monitoring of surface water chemistry for several annual hydrologic cycles indicate that following evaporative concentration of ponded seawater halite layers, characterized by zoned and clear halite crystal varieties, are developed. During early stages of annual playa development, vadose solution and precipitation appear to be most active within and above the capillary fringe zone, causing diagenetic modification of the halite textures, fabrics and structures. Ultimately, clastic halite facies are produced by wind reworking of the earlier deposits, in response to progressive evaporative drawdown of the brine level in the main depression area of the lagoon.

The co-existence of the halite precipitates and clastites is related to a dynamic equilibrium in the water budget of the Hutt Lagoon. This equilibrium is best exemplified by limitation of brine level fluctuations to a narrow repetitive zone. Identification of similar early diagenetic features, such as vadose solution, precipitation, overgrowth, replacement and mechanical reworking of surface halite sediments, in ancient evaporite deposits may aid in a better understanding of the role of brine level fluctuation on genesis and diagenesis of subaqueous/subaerial halite.     

Neogene evaporites in desert volcanic environments: Atacama Desert, northern Chile

The Upper Miocene and Pliocene evaporite deposits of the Atacama Desert of northern Chile (Hilaricos and Soledad Formations) are among the few non‐marine evaporites in which aridity not only formed the deposits, but has also preserved them almost unaltered under near‐surface conditions. These deposits are largely composed of displacive Ca sulphate and halite together with minor amounts of glauberite, thenardite and polyhalite. However, at the base and top of these deposits, there are also beds of gypsum crystal pseudomorphs that originally formed as free‐growth forms within shallow brine bodies, rather than as displacive sediments. The halite is present as interstitial cement, displacive cubes and shallow‐water, bottom‐growth chevron crusts. Most of the calcium sulphate is presently anhydrite, pseudomorphous after gypsum, that was the primary depositional sulphate mineral. The secondary anhydrite formed under early diagenetic conditions after slight burial (some metres) resulting from the effect of strongly evolved pore brines. The anhydrite has been preserved without rehydration during late diagenetic and exhumation stages on account of the arid environment of the Atacama Desert. Both the Hilaricos and the Soledad Formations contain geochemical markers indicating that these Neogene evaporites had a largely non‐marine origin. Bromine content in the halite is very low (few p.p.m.), indicating neither a sedimentological relation with sea water nor the likelihood of direct recycling of prior marine halites. Moreover, the δ³⁴S of sulphates (+4·5‰ to +9‰) also reflects a non‐marine origin, with a strong volcanic influence, although some recycling of Mesozoic marine sulphates cannot be ruled out. δ³⁴S of dissolved sulphate from hot springs and streams in the area commonly displays positive values (+2‰ to +10‰). Leaching of oxidized sulphur and chlorine compounds from volcanoes and epithermal ore bodies, very common in the associated drainage areas, have been the main contribution to the accumulation of evaporites. The sedimentary and diagenetic evolution of the Hilaricos and Soledad evaporites (based on lithofacies analysis) provides information about the palaeohydrological conditions in the Central Depression of northern Chile during the Neogene. In addition, the diagenesis and exhumation history of these evaporites confirms the persistence of strongly arid conditions from Late Miocene until the present. A final phase of tectonism took place permitting the internal drainage to change and open to the sea, resulting in dissolution and removal of a significant portion of these deposits. Despite the extensive dissolution, the remaining evaporites have undergone little late exhumational hydration.     

东营凹陷沙四段盐湖的深水成因模式

东营凹陷下第三系沙四段广泛发育的蒸发岩类与暗色泥、页岩和深水浊积砂体呈现明显韵律层,为厚度达千米的盐湖沉积。通过分析了该地区蒸发岩地层的沉积特征和沉积条件,认为东营凹陷沙四段蒸发岩类的物质基础是深层卤水 深部古老地层中的盐类物质是其盐源 凹陷中北部的同沉积深大断裂是沟通凹陷与地壳深部盐类物质的通道。在此基础上提出东营凹陷沙四段盐湖的深水成因模式,可与东非裂谷基伍湖和东濮凹陷下第三系深水成因盐湖对比。     

Origin and geochemistry of Miocene marine evaporites associated with red beds: Great Kavir Basin,Central Iran

During the Cenozoic numerous shallow epicontinental evaporite basins formed due to tectonic movements in the Northern Province of the Central Iran Tectonic Zone (the Great Kavir Basin). During the Miocene, due to sea‐level fluctuations, thick sequences of evaporites and carbonates accumulated in these basins that subsequently were overlain by continental red beds. Development of halite evaporites with substantial thickness in this area implies inflow of seawater along the narrow continental rift axis. The early ocean basin development was initiated in Early Eocene time and continued up to the Middle Miocene in the isolated failed rift arms. Competition between marine and non‐marine environments, at the edge of the encroaching sea, produced several sequences of both abrupt and gradual transition from continental wadi sediments to marginal marine evaporites in the studied area. These evaporites show well‐preserved textures indicative of relatively shallow‐brine pools. The high Br content of these evaporites indicates marine‐derived parent brines that were under the sporadic influence of freshening by meteoric water or replenishing seawater. However, the association of hopper and cornet textures denotes stratified brine that filled a relatively large pool and prevented rapid variations in the Br profile. Unstable basin conditions that triggered modification of parent brine chemistry prevailed in this basin and caused variable distribution patterns for different elements in the chloride units. The presence of sylvite and the absence of Mg‐sulphate/chlorides in the paragenetic sequence indicate SO₄−depleted parent brine in the studied sequence. Petrographic examinations along with geochemical analyses on these potash‐bearing halites reveal parental brines which were a mixture of seawater and CaCl₂‐rich brines. The source of CaCl₂‐rich brines is ascribed to the presence of local rift systems in the Great Kavir Basin up to the end of the Early Miocene. Copyright © 2007 John Wiley & Sons, Ltd.     

Geochemical and isotopic constraints on the interaction between saline lakes and groundwater in southeast Australia

Major ion and stable isotope geochemistry allow groundwater/surface-water interaction associated with saline to hypersaline lakes from the Willaura region of Australia to be understood. Ephemeral lakes lie above the water table and locally contain saline water (total dissolved solids, TDS, contents up to 119,000 mg/L). Saline lakes that lack halite crusts and which have Cl/Br ratios similar to local surface water and groundwater are throughflow lakes with high relative rates of groundwater outflows. Permanent hypersaline lakes contain brines with TDS contents of up to 280,000 mg/L and low Cl/Br ratios due to the formation of halite in evaporite crusts. These lakes are throughflow lakes with relatively low throughflow rates relative to evaporation or terminal discharge lakes. Variations in stable isotope and major ion geochemistry show that the hypersaline lakes undergo seasonal cycles of mineral dissolution and precipitation driven by the influx of surface water and evaporation. Despite the generation of highly saline brines in these lakes, leakage from the adjacent ephemeral lakes or saline throughflow lakes that lack evaporite crusts is mainly responsible for the high salinity of shallow groundwater in this region.     

Microfacies analysis and diagenetic fabric of the Lockhart Limestone exposed near Taxila,Margalla Hill Range,Punjab, Pakistan

The microfacies analysis and diagenetic fabric of the Lockhart Limestone are studied in an outcrop section exposed in the Margalla Hill ranges. The Lockhart Limestone is predominantly composed of medium to thick bedded, nodular and occasionally brecciated, highly fossiliferous limestone with thin interbeds of marl and shale. On the basis of detailed petrographic investigations, four microfacies have been identified including bioclastic packstone, wackestone (siliciclastic bioclastic rich sub-microfacies), wackestone-packstone, and mud-wackestone. Based on the microfacies analysis, the Lockhart Limestone is interpreted to have been deposited in the fore-shoal mid-ramp, mid-ramp, and outer ramp depositional environments. The Paleocene age has been assigned to the Lockhart Limestone based on age diagnostic foraminifera, i.e., Miscellanea, Lockhartia, and Ranikothalia. The diagenetic fabric of the Lockhart Limestone is characterized by several diagenetic features such as micritization, neomorphism (aragonite to calcite transformation and development of microspar), compaction, pressure dissolution (microstylolites), and cementation (calcite-filled microfractures). Such diagenetic features are developed in marine, meteoric, and burial diagenetic settings. The Paleocene Lockhart Limestone of Pakistan shows analogous features to that of the Paleocene Zongpu Formation (Member-3) of the Gamba-Tingri Basin of southern Tibet based on the outcrop features, microscopic fabric, and depositional environment.     

辽河盆地大民屯凹陷沈95区块砂岩储层中钙质夹层研究

钙质夹层是控制剩余油形成与分布的主要因素之一.辽河盆地大民屯凹陷沈95区块钙质夹层十分发育,利用丰富的岩心、测井资料,识别并探讨了钙质夹层的分布规律及成因.研究表明:本区钙质夹层是早期无铁碳酸盐与晚期含铁碳酸盐胶结形成的两期夹层;早期钙质夹层主要分布于泛滥平原亚相、三角洲平原亚相;晚期钙质夹层主要发育于三角洲前缘亚相,且一般位于砂泥岩接触带,厚层砂岩顶底部碳酸盐胶结物较中部高.早期钙质夹层是沉积期、成岩早期,蒸发作用使富钙孔隙水中的钙质沉淀形成的;晚期钙质夹层是在有机酸作用下,Ca2+、Mg2+在烃源岩(泥岩)中溶解,再于储集岩(砂岩)中沉淀形成的.根据夹层的分布规律可以更有效地挖掘剩余油.     

Diagenetic origin of Basal Anhydrite in the Cretaceous Maha Sarakham salt: Khorat Plateau, NE Thailand

Development of a diagenetic anhydrite bed at the base of the Cretaceous Maha Sarakham Saline Formation (the `Basal Anhydrite' member) of the Khorat Plateau in north-eastern Thailand took place due to leaching and/or pressure dissolution of salt at the contact between an underlying active sandstone aquifer system and an overlying massive halite-dominated evaporite sequence. Basal evaporites composed of halite with intercalated anhydrite of the latter sequence are undergoing dissolution as a result of subsurface flushing, with anhydrite produced as the insoluble residue. The result is a 1·1 m thick interval of nodular anhydrite displaying unique, basin-wide continuity. Observed textures, petrographic features and chemical data from the anhydrite and associated authigenic minerals support the origin of the Basal Anhydrite Member as an accumulation residue from the dissolution of the Maha Sarakham salts. Petrographically, the anhydrite in this unit is made up of crystals that are blocky and recrystallized, sheared, generally elongated and broken, and is bounded at the bottom by organic-rich stylolite surfaces. Authigenic and euhedral dolomite and calcite crystals are associated with the anhydrite. Traces of pyrite, galena and chalcopyrite are present along the stylolite surfaces suggesting supply of fresh water from the underlying sandstone at highly reducing conditions of burial. The δ<sup>34</sup>S of sulphate in the Basal Anhydrite averages 15 ‰ (CDT) and falls within the isotopic composition of the anhydrite in the Cretaceous Maha Sarakham Formation proper and the Cretaceous values of marine evaporites. Measured δ<sup>18</sup>O in dolomite range from ?4·37 to ?14·26‰ (PDB) suggesting a re-equilibration of dolomite with basinal water depleted in <sup>18</sup>O and possible recrystallization of dolomite under relatively elevated temperatures. The δ<sup>13</sup>C, however, varies from +1·57 to ?2·53‰ (PDB) suggesting a contribution of carbon from oxidation of organic matter. This basal anhydrite bed, similar to basinwide beds found at the bottom of many giant evaporite sequences, has always been considered to be depositional. Here, at the base of the Maha Sarakham Formation, we demonstrate that the anhydrite is diagenetic in origin and was formed by accumulation of original anhydrite by dissolution of interbedded halite from waters circulating though the underlying aquifer: it represents an `upside-down' caprock.     

Sedimentology,mineralogy, and geochemistry of the Late Quaternary Meyghan Playa sediments,NE Arak,Iran: palaeoclimate implications

Playas are shallow ephemeral lakes that form in arid and semi-arid regions. Iran has a large number of playas such as Meyghan Playa, which is located in the northeast of Arak city that borders the central Iran and Sanandaj-Sirjan zones. This study aims to investigate the mineralogical, sedimentological, and geochemical characteristics of the playa sediments. In order to determine the palaeoenvironment, we carried out X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) studies. Meyghan Playa sediments consist of very fine-grained sediments and contain both evaporite and clastic minerals. The evaporite minerals include calcite, gypsum, halite, glauberite, and thenardite, whereas clastic minerals are quartz and clay. The calcite abundance decreases from the margin to the central portion of the playa but gypsum and halite abundances show an increasing trend from the margin to the center. This observation is consistent with the general zonation of other playas. Variations of calcite and gypsum concentration profiles present increasing and decreasing trends with depth, which could be ascribed to the changes in climatic factors. These factors include brine chemical modifications owing to changes in evaporation and precipitation rates and variations in relative abundance of anions-cations or in the rate of clastic and evaporite minerals due to variations in the freshwater influx (climatic changes) with time. A decrease in calcite and increase in sulfate minerals (especially gypsum) with depth is probably due to the higher water level and rainfall, a more humid climate, and salinity variations.     

Origin of halite brine in the Onondaga Trough near Syracuse,New York State,USA: modeling geochemistry and variable-density flow

Halite brine (saturation ranging from 45 to 80%) lies within glacial sediments that fill the Onondaga Trough, a bedrock valley deepened by Pleistocene glaciation near Syracuse, New York State, USA. The most concentrated brine occupies the northern end of the trough, about 10 km downgradient of the northern limit of halite beds in the Silurian Salina Group, the assumed source of salt. The chemical composition of the brine and its radiocarbon age suggest that the brine originally formed about 16,700  years ago through dissolution of halite by glacial melt water and later mixed with saline bedrock water. Two hypotheses regarding the formation of the brine pool were tested through variable-density flow simulations using SEAWAT. Simulation results supported the first hypothesis that the brine pool was derived from a source in the glacial sediments and then migrated to its current position, where it has persisted for over 16,000  years. A second hypothesis that the brine pool formed through steady accumulation of brine from upward flow of a source in the underlying bedrock was not supported by simulation results, because the simulated age distribution was much younger than the age estimated from geochemical modeling.     

Stable chlorine isotope evidence for non-marine chloride in Badenian evaporites, Carpathian mountain region

Routine trace-element geochemistry suggests that components in putative marine halite evaporites may be partly of nonmarine origin, but such interpretations are commonly ambiguous. Stable chlorine isotopes may provide a less-ambiguous marker of chloride origin where δ³⁷Cl departs from the range predicted for evaporite formation from seawater. Bedded halite with primary sedimentary textures preserves original δ³⁷Cl values. Measurable change in δ³⁷Cl can be generated by incongruent dissolution of halite, but only if less than half the original halite remains. Badenian (middle Miocene) halite from the Forecarpathian and from the East Slovakian and Transcarpathian basins has a δ³⁷Cl range of – 0.2 to 0.8‰. Two phenomena cannot be explained by simple evaporation of 0.0‰ seawater. At Wieliczka, the Shaft Salt has distinctive δ³⁷Cl values (– 0.2 to 0.0‰) relative to neighbouring salt beds (0.2 to  0.6‰), requiring a large, abrupt input of brine with negative δ³⁷Cl. Halite with high (0.6 – 0.8‰) δ³⁷Cl near the base of the East Slovakian and Transcarpathian evaporites requires a large input of chloride with positive δ³⁷Cl into the basins. Expulsion of basin brine with non-0‰δ³⁷Cl into the evaporite basins may account for the nonmarine chloride sources.     

Facies analysis of the Semanggol Formation,South Kedah,Malaysia: A possible Permian–Triassic boundary section

Although the Permian–Triassic Semanggol Formation is widely distributed in northwestern Peninsula Malaysia and is made of various lithofacies, its sedimentology and possible relation with the Permian–Triassic boundary (PTB) were not considered before. In this study, detailed facies analysis was conducted for two sections of the Semanggol Formation at the Bukit Kukus and Baling areas, South Kedah to clarify its sedimentology and relation to the PTB. Four facies from the Permian part of the Semanggol Formation that were identified at the Bukit Kukus section include laminated black mudstone, interbedded mudstone and sandstone, volcanogenic sediments, and bedded chert. In Baling area, the Triassic part of the formation is classified into three members. The lower member comprises of claystone and bedded chert facies, while the middle member is composed of sandstone and claystone interbeds (rhythmite). On the other hand, the upper member is grouped into two main units. The lower unit is mainly claystone and includes two facies: the varve-like laminated silt and clay and massive black claystone. The upper unit is composed of various sandstone lithofacies ranging from hummocky cross stratified (HCS) sandstone to thinly laminated sandstone to burrowed sandstone facies. The HCS sandstones occur as two units of fine-grained poorly sorted sandstone with clay lenses as flaser structure and are separated by a hard iron crust. They also show coarse grains of lag deposits at their bases. The laminated black mudstone at the lowermost part of the Semanggol Formation represents a reducing and quite conditions, which is most probably below the fairweather wave base in offshore environment that changed upwards into a fining upward sequence of tide environment. Abundance of chert beds in the volcanogenic sediments suggests the deposition of tuffs and volcanic ashes in deep marine setting which continues to form the Permian pelagic bedded chert and claystone. The bedded chert in the lower member of the Triassic section suggests its formation in deep marine conditions. The rhythmic sandstone and claystone interbeds of the middle member are suggestive for its formation as a distal fan of a turbidite sequence. Lithology and primary sedimentary structure of the upper member suggest its deposition in environments range from deep marine represented by the varve-like laminated silt and clay to subtidal environment corresponds to the massive black claystone to coastal environment represented by the hummocky sandstone units and reaches the maximum regression at the hiatus surface. Another cycle of transgression can be indicated from the second hummocky unit with transgressive lag deposits that develops to relatively deeper conditions as indicated from the formation of relatively thick laminated sandstone and bioturbated massive sandstone facies that represent tidal and subtidal environment, respectively. Late Permian lithological variation from the radiolarian chert into early Triassic claystone probably resulted from a decrease in productivity of radiolarians and might represent a PTB in the Semanggol Formation. Volcanogenic sediments in the studied section can be used as an evidence for volcanic activities at the end of the Permian, which is probably connected to the nearby volcanic ash layers in the eastern China, the ultimate cause of the PTB in this area. Black mudstone in the Permian part of the studied section may be interrelated to the Latest Permian Anoxia that started to build in the deep ocean well before the event on shallow shelves.     

Sedimentological characteristics and facies of the evaporite-bearing Kirmir Formation (Neogene), Beypazari Basin, central Anatolia, Turkey

A thick sedimentary sequence comprising fluvial, lacustrine and volcano-sedimentary rocks is present in the Neogene Beypazari Basin, central Anatolia. These units display considerable lateral facies variation and interfinger with alkaline volcanic rocks along the north-eastern margin of the basin. The uppermost Miocene Kirmir Formation contains numerous evaporite horizons. The evaporite sequence is up to 250 m thick and may be divided into four lithofacies. In ascending stratigraphical order these are: (1) gypsiferous claystone facies, (2) thenardite-glauberite facies, (3) laminar gypsum facies and (4) crystalline gypsum facies. These facies interfinger with one another laterally along a section from the margins to central parts of the basin. The lithological and sedimentological features of the Kirmir Formation indicate fluvial, saline playa mudflat, hypersaline ephemeral playa lake and very shallow subaqueous playa lake depositional environments, which probably were influenced by alternating semi-arid and evaporative conditions.