Dry Lake Research Articles

Isotopic and hydrochemical evidence for the source and mechanism of groundwater salinization in Kashan Plain aquifer in Iran.

Groundwater salinization and interaction between Playa Lake and regional groundwater were investigated using multi-chemo-isotopic evidences. Forty groundwater and 26 Kashan Playa Lake (KPL) water samples were collected and analyzed for their geochemical compositions. The evolution of hydrochemical facies in Kashan Plain Aquifer (KPA) to KPL is Ca-HCO3 (19%), Mix Ca-Cl (9%), Ca-Cl (17%), and Mix Na-Cl and Na-Cl (55%). Also, the Hydrochemical Facies Evolution Diagram (HFE-D) proposed cation exchange as the main process of salinization in KPA. Based on the binary hydrogeochemical diagrams of (Na+/Cl-)/Cl-, (Ca2+ + Mg2+)/HCO3- + SO42-, and Cl/Br, dissolution of halite and gypsum in the Miocene marlstone in the KPA is the main source of salinity. The δ18O of waterin aquifer and playa water samples varies from -10.03 to 7.03‰ (VSMOW) with an average of -6.95‰ and -60.73 to 25.08‰ with average of -45.82‰ for δ2H. Based on the results, the relation between δ18O and δ2H, and δ18O and Br, approves discharge of saline water from KPA to KPL. Likewise, the isotopic composition of δ34SO4, varies from 5.95 to 22.55‰ CDT in KPA, and 5.95 to 9.99 ‰ CDT in KPL. Also, the relations between δ18O-δ34SSO4 and Cl-δ34S were non-linear, indicating that sulfur concentration in KPA and KPL changed due to sulfide oxidation and sulfate reduction in the freshwater and deep brines in the aquifer and mixed during the over-pumping in the KPA. Oxidation of sulfide minerals in the mineralized region in the western part of the aquifer (recharge zone) may have been the source of sulfur leached by seasonal runoff. Water-rock interaction, ion exchange, and hydraulic gradient have been the dominating factors in changing the water chemistry between aquifer and playa leading to saline groundwater discharged to the playa.

High prevalence of urinary schistosomiasis in a desert population: results from an exploratory study around the Ounianga lakes in Chad

BackgroundResearching a water-borne disease in the middle of the Sahara desert might not seem the most relevant concern. However, nomadic Sahelian pastoralists health concerns regarding their livestock and anecdotal reports about trematode infections of Fasciola spp. and Schistosoma spp. in desert-raised animals justified an exploratory study focusing on the lakes of Ounianga in Northern Chad. The aim was to test whether trematode parasites such as Schistosoma spp. occur in human populations living around the Sahara desert lakes of Ounianga Kebir and Ounianga Serir in northern Chad.MethodsThe study was carried out in January 2019 and comprised of three components. First, a cross sectional survey based on a random sample drawn from the population to detect infections with S. haematobium and S. mansoni; second, focus group discussions exploring disease priorities, access to health and health seeking behaviour; and third, surveying water contact sites for intermediate host snails. Samples of trematode parasites and snails were confirmed on species level by molecular genetic methods. For parasitological and malacological surveys descriptive statistics were performed. Qualitative data analysis included the full review of all transcripts, followed by a descriptive and explorative thematic analysis.ResultsAmong 258 participants, the overall S. haematobium prevalence using urine filtration was 39.2% [95% confidence interval (CI): 33.5–45.1%], with 51.5% of the infected suffering from heavy infection. The intermediate host snail of S. haematobium (Bulinus truncatus) occurred at water contact sites near both study villages, revealing the potential for local transmission. Although a positive S. mansoni point-of-care circulating cathodic antigen (POC-CCA) test result was obtained from 8.6% (95% CI 5.7–12.8%) of the samples, no intermediate host snails of S. mansoni were found, and the relevance of S. mansoni remains uncertain. Qualitative findings underline the importance of morbidity caused by urinary schistosomiasis, and the lack of access to diagnostics and treatment as a major health concern.ConclusionsThis research revealed a high prevalence of urinary schistosomiasis in the population living around the lakes of Ounianga in the Sahara, a United Nations Educational, Scientific and Cultural Organization (UNESCO) world heritage site in Chad. Despite the high public health importance of the associated morbidity expressed by the population, there is no access to diagnostics and treatment. Further work is needed to develop and test a context-adapted intervention.Graphical

Hydrochemical Approach to Groundwater in the Environment of the Public Discharge of Lake Mbeubeuss (Dakar, Senegal)

To determine the origin and the processes of groundwater mineralization in the Mbeubeuss lake area, the major ion concentrations of the groundwater were compared to those of the rainwaters which constitute the input function of the aquifer of the Quaternary sands in the area of lake Mbeubeuss. The physico-chemistry of groundwater near the public discharge and its surroundings, has shown that the true value of the electrical conductivity of waters are around 2000 µS/cm. Values of electrical conductivity greater than 2000 µS/cm would represent the particular mineralization of ground waters by the public discharge of lake Mbeubeuss. The chemical facies of ground waters are dominated by the sodium and potassium chloride and calcium chloride facies. The study of the relationship between the major chemical elements and the chloride ion and the representation in the modified Chadha diagram of the chemical analyzes of ground waters from the campaigns of July 1998, July 2002 and March 2003, made it possible to highlight the different sources and processes controlling the mineralization of ground waters in the Mbeubeuss Lake area. Despite the proximity to the sea which suggests a considerable contribution of salts by aerosols and sea spray, the mineralization of ground waters in the area of lake Mbeubeuss is largely due to leachate from household waste and the influence of old sediments of the dry lake Mbeubeuss. The main processes controlling the mineralization of ground waters are marine contributions (aerosols and sea spray), dissolution-precipitation of minerals from the aquifer matrix, atmospheric CO2 diffusion, base exchanges, dilution-concentration and anthropogenic pollution.

Wurst Storm Rising

Our subject is the legacy of Dada implicit to the Burning Man phenomenon. Animate in the provocative output of fin-de-siècle French Symbolist writer and puppeteer Alfred Jarry, and filtered through the antics of the San Francisco Cacophony Society, Dada is foundational to the cultural aesthetic of Burning Man, by which we mean the event in Nevada’s Black Rock Desert playa (Black Rock City) and a global network of “burn” events. We address the significance of the Cacophony Society expedition that inaugurated the desert phase of Burning Man in 1990, “Zone Trip # 4: Bad Day at Black Rock.” Integral to the surreal tourism ventured by Cacophonists prior to the inception of Burning Man, and pivotal to its desert phase, the Zone Trip kindled “Burner” culture on the Black Rock playa and abroad. Exploring the Dadaist impulse affecting Black Rock City and woven into a worldwide network, informed by interpretative and applied methods, the article addresses art projects (including those designed and implemented by Vitos) at three regional events—Israel’s Midburn and Germany’s Burning Bär and Kiez Burn—visited in 2018 and 2019 as part of a multisited ethnography of the Burning Man movement. As these projects illustrate, the ghost of Jarry haunts, as the spirit of Dada animates, the transnational “burnscape.”

Towards understanding desert shorelines - coastal landforms and dynamics around ephemeral Lake Eyre North, South Australia

ABSTRACT While shorelines around playa lakes have traditionally played a key role for reconstructing late Quaternary megalakes in drylands, little attention has been given to recent shorelines associated with episodic filling events of modern ephemeral playa lakes such as Kati Thanda-Lake Eyre in central Australia. We here present results from geomorphic mapping around the playa margin of Lake Eyre North and interpret these data regarding timescales and drivers of shoreline processes. The diversity and distribution of landforms point to lithology and variations in wave energies as major controls on large-scale shoreline geomorphology. Our results suggest that the presence or absence of shoreline features is an incomplete and inaccurate indicator of past lake levels. Instead, wave-built landforms in ephemeral playa lake settings need to be considered threshold-related phenomena, with differences in frequency, magnitude and rate of water level change leading to vertically differing potential for wave-driven geomorphic activity and thus topographic differences between landforms. While mainland barriers probably best represent rare peak lake levels, barrier spits or islands dominantly form at lower and intermediate levels through lower energy longshore drift, thus providing a more complete record of playa flood events. Additionally, the lowest magnitude events offer potential for frequent wetting and drying along playa margins that effectively drives salt-related production and aeolian sediment deflation. Therefore, in contrast to marine or perennial lake shorelines, the complete range of wind-driven sedimentary processes needs to be coupled with an accurate understanding of lake-specific flooding frequency and magnitude towards a comprehensive model of shoreline evolution around playa lakes.

Sedimentology and geomorphology of Lake Yamma Yamma - A long-lived structurally controlled playa lake of the Lake Eyre Basin, Australia

ABSTRACT Intraplate tectonism and continental climate change have important roles in the evolution of the arid Lake Eyre Basin, one of the world’s largest interior basins, and a place with economic, environmental, and cultural significance for many Australians. Just off one of the main rivers of the Basin, Cooper Creek, Lake Yamma Yamma – a 20 km by 40 km ephemeral feature – traps sediment ~750 km upstream and ~90 m higher than the ultimate base level of the Basin – Kati Thanda-Lake Eyre. This paper is the first to report on the sedimentology and geomorphic evolution of this modern ephemeral playa lake. Field-based sedimentology, laboratory-based grain size analysis, satellite image interpretation, inundation frequency maps, hydrological data, and digital elevation data, were used to interpret sedimentary processes and the evolution of the lake. Results suggest Lake Yamma Yamma is a long-lived feature. Evolution is primarily structurally controlled, with the main lake delta migrating north-west over time. Quaternary fluvial, lacustrine and aeolian deposition is likely controlled by intraplate tectonism, and palaeo-shorelines may be remnant features of a prior climate regime. Age dating of this sedimentary archive could provide important information on the history, palaeoclimate, and evolution of the Lake Eyre Basin, and the Australian continent.

Topographic insights in the Frome-Callabonna system and the elevation of a newly surveyed highstand shoreline

ABSTRACT Lakes Frome, Callabonna, Blanche and Gregory are playa lakes on the eastern and northern sides of the Flinders Ranges, South Australia. Between 2007 and 2019 we surveyed key topographic features of the lakes, including shorelines, lake floors and the alluvial sills that separate the lakes with differential GPS (DGPS). We combine these observations with the analysis of a hybrid DEM that blends data from multiple sources. The lowest elevation of the Frome-Callabonna system based on the hybrid DEM is −8.33 m Australian Height Datum (AHD) at Lake Callabonna but −5.42 m AHD based on DGPS field data. Both values are considerably lower than previous estimates based on spot heights and contours. The DGPS data for Lake Callabonna support the Shuttle Radar Terrestrial Mission (SRTM) estimates of lake-floor elevations but with a mean difference of 1.7 m in elevation. There are larger differences in elevation between the hybrid DEM and the DGPS data for the floor of Lake Frome (mean difference of 4.25 m). We also report on a newly topographically surveyed high shoreline at Lake Callabonna between 20.1 and 20.8 m AHD, the highest to date.

Greenhouse Gas Emission from Inland Open Water Bodies and Their Estimation Process—An Emerging Issue in the Era of Climate Change

The persistent rise in concentrations of greenhouse gases (GHGs) in the earth’s atmosphere is responsible for global warming and climate change. Besides the known source of GHGs emissions like energy, industry, and agriculture, intrinsic emissions from natural inland water bodies like wetland, rivers, reservoirs, estuaries, etc. have also been identified as other hotspots of GHGs emission and gaining the attention of the scientific communities in recent times. Inland fisheries in India are threatened by climate changes such as a change in temperature, precipitation, droughts, storm, sea-level rise, saltwater intrusion, floods that affect mostly the production, productivity and ultimately affect the fishers’ livelihood. There are, however, different mitigation and adaptation strategies to cope with the effects of climate change. Carbon sequestration and other related management interventions are one of the options available minimizing GHGs emissions from inland open waters, particularly the wetlands and coastal mangroves which are well known worldwide for their significant role in the storage of carbon. Assessment of C efflux from exposed sediments in dry streams, reservoirs, lakes, rivers, and ponds into the atmosphere can be considered imperative for a better understanding of their role as a C-sink or as a C-source to the atmosphere.

PLAYA DYNAMICS AND SALINITY: A STUDY OF YELLOW LAKE ON THE HIGH PLAINS OF TEXAS

Saline playas on the Southern High Plains are almost always located on large cattle ranches but they are of limited value to the herds of cattle grazing around their outer margins. Saline playas are often without water for extended periods and, after inundation, they experience considerable evaporative loss leading to hypersaline conditions. The primary goal of this study was to develop a quantitative method that combines the transitory nature of playa lakes and the variability of salinity into a set of parameters that can be used to compare playas or other surface water sources. Regarding water quality, a variable was developed that describes the fraction of observations with salinity levels below the salt tolerance threshold for cattle. With regard to water availability, water depth measurements were used to compute the fraction of time that a playa contains water. These two variables are combined to form a new variable that represents the fraction of time that water is both available and of acceptable quality. To demonstrate the utility of this method, data was collected at Yellow Lake, a large saline playa located on the Yellow House Ranch northwest of Lubbock, Texas. Results suggest that the playa contained water 50.8% of the time over a five-year period but the fraction of water samples with acceptable salinity was only 6.5%. The resulting fraction of time that water was both available and of acceptable quality was only 3.3%. This technique could be used to compare other ephemeral surface water sources in the region.

Effects of simulated rainfall enhancement on sediment CO2 flux in dry lakebed of Barkol Lake, China

Understanding the responses of lake sediment carbon process to climate change is an important part of a comprehensive understanding of lake carbon budget. To explore the effects of future rainfall increase on sediment carbon flux, undisturbed sediment samples were collected from the bottom of dry lake Barikun in Hami, Xinjiang for the incubation experiment. Based on the increase rate of precipitation (4 mm·10 a-1) and the distribution characteristics of rainfall in the plant growing season in Hami, Xinjiang since 1960, five rainfall treatments were set (86 mm, T0; 94 mm, T1; 102 mm, T2; 110 mm, T3; 126 mm, T4) based on the rainfall in growing season of 2016 (86 mm). We analyzed the effects of rainfall increase on sediment CO2 flux. Results showed that compared with that before rainfall, the sediment CO2 flux increased after 1 day of rainfall in the study area. Compared with that during May to July, the CO2 flux of sediments in August to October decreased. There was no variation of CO2 accumulative emission among the T0-T3 treatments from May to October. However, the average CO2 emission rate under the T3 treatment (0.22 μmol·m-2·s-1) was significantly higher than that under the T4 treatment (0.14 μmol·m-2·s-1). All treatments showed CO2 sink at the first day of rainfall (1 d), with T4 treatment (-0.13 μmol·m-2·s-1) having the highest "carbon sink" capacity. After 1 day, the CO2 sink converted to CO2 source under the five rainfall treatments, with the CO2 emission rate under T3 treatment (0.34 μmol·m-2·s-1) being significantly higher than those under other treatments. Compared with May, the CO2 emission fluxes of T2-T4 treatments were significantly higher than those at the time from August to October. Under the condition with relatively stable temperature, the CO2 flux of sediments was significantly correlated with the sediment moisture and air humidity. In the next 60 years, the continuous increase of future rainfall may be an important factor promoting CO2 emission from lake sediment in arid regions, and thus affecting global warming.

Designing a Surveillance System to Monitor the Adverse Health Effect of Environmental Disasters: A Case Study of Drying Lake Urmia-Iran

BackgroundThrough designing a surveillance system, steps to policy making and designing measures needed to reduce the potential risks of environmental disasters on human health could be taken. Therefore, this study aimed to develop a model for Environmental Disasters Diseases Surveillance System (EDDS) to monitor Adverse Health Effects (AHEs) of Environmental Disasters (AHEEDs).MethodsAs the first step, the literature review was conducted to identify the AHEEDs. Then, using the results of the first step and analyzing the existing documents, the AHEEDs were identified, and, based on the experts’ opinions, high-priority effects were included in the EDDS. Then, using semi-structured interviews, 20 experts’ views on the appropriate model of EDDS were investigated. To design the initial model, a panel of experts was formed with six participants. Finally, the Delphi technique was used for expert opinion and model finalization.ResultsAs a result of the literature review and document analysis, 41 hazards/diseases were identified. Finally, ten diseases were suggested to enter the EDDS. In the experts’ view, it is better that communicable diseases be reported actively and urgently and Non-Communicable Diseases (NCD) actively and non-urgently. From the participants’ point of view, the most significant achievements of the EDDS can be organizational and managerial, health promotion, and economic achievements.ConclusionDeveloping a dedicated EDDS for AHEEDs can be very helpful for better management of these effects. To this end, the model proposed in this study can serve as a guide for national and local policymakers to implement surveillance systems for AHEEDs.

Discrete Element Simulation on Sand-Bed Collision Considering Surface Moisture Content

The process of aeolian sand transport is an important mechanism leading to the formation and evolution of local landforms in coastal areas and desert lakes. For a long time, the role of surface moisture in incipient motion of sand grains by wind stress has been extensively studied but, in fact, sand-bed collision is the main mechanism in steady aeolian sand flow. At present, the lack of understanding of surface moisture content on sand-bed collision limits the application of aeolian sand transport models in wet coastal areas. In this paper, we adopt numerical simulations to discuss and analyze the effect of cohesive forces formed by surface moisture content on the sand-bed collision process based on discrete element method. High density contact forces appear with the surface moisture increasing, and form a closed structure around the edge of crater to resist the avulsion in horizontal direction. Under high moisture condition, even though the ejected sand grains saltate away from the surface, the tension forces will prevent from leaving. The ejected number trend with incident velocity shows some nonlinear characteristics due to the unequally distributed force chains and liquid bridges in the unsaturated sand bed surface.

Three‐Dimensional Electrical Resistivity Characterization of Mountain Pass, California and Surrounding Region

AbstractThe Sulphide Queen carbonatite deposit at Mountain Pass in southeast California is a world class rare earth element (REE) resource. This study images electrical resistivity structure of the REE deposit and surrounding area to characterize resources under cover. An east‐west elongated grid (35 × 15 km) of 65 wideband magnetotelluric stations spanning from eastern Shadow Valley to eastern Ivanpah Valley were collected and modeled in three‐dimensions (3‐D). Gravity, aeromagnetic, and geologic data are used to inform interpretation of structures in the resistivity model, including the following observations. Shadow Valley is filled with conductive sediment that locally dips southward to a depth of 1 km. The Kingston Range‐Halloran Hills detachment fault dips westward at ∼15 degrees. The REE deposit is a moderate low resistivity zone dipping southwest to a possible depth of ∼1 km, and is bounded by the North and South faults and bisected by the Middle fault. Ivanpah Dry Lake is underlain by a north striking southward dipping sedimentary basin. Two possible zones of mineralization are observed in Ivanpah Valley, one along the western edge of Ivanpah Dry Lake and one on the western edge of valley along a new inferred fault. The brittle‐ductile transition is imaged at ∼10 km below mean sea level. No deep electrically conductive structures are imaged to be related to the REE deposit likely due to the complex geologic history of the Mojave terrane. Future studies should regional target Proterozoic rocks and search within for geophysical signatures similar to Mountain Pass.

Stratigraphic relationship between Rimrock Lake and Hay Lake playa sediments, Harney Basin, eastern Oregon, USA

Stratigraphic relationship between Rimrock Lake and Hay Lake playa sediments, Harney Basin, eastern Oregon, USA

Etudes géochimiques et geomorphologie lacustre du bassin du lac Yakhi en Mongolie orientale

This study presents the landscape evolution of Lake Yakhi basin in eastern Mongolia where the lake plays an important role in the surface water resources. The multiple paleoshoreline features indicate wave-cut terraces, whereas the modern-day shorelines show that Lake Yakhi is at rapid northward regression. The paleo- and modern-day shorelines imply that the paleo-Lake Yakhi may have covered an extensive area with different hydrological conditions in the past. Lake Yakhi shows a decreasing trend in an area with a loss of ~62.2 km2 or 63.9% of the total area during the past five decades. The hydrological dynamics of Lake Yakhi during the last 50 years show its shift into a playa lake coinciding with the local climate changes in warming since 1987 and drying since 1992. In the lake's margin, mafic igneous provenance indicates a derivation from weathered granite and gneiss terrains on the oceanic island arc. However, in the lake's center, felsic igneous and quartzose sedimentary provenances show a derivation from the pre-existing sedimentary terrain on the active continental margin. Lake Yakhi sediments show the granite (felsic) and granite basalt (felsic to mafic) source rocks with mostly shale and arkose. The A-CN-K ternary plot shows that granites, granodiorites, and tonalities dominated in the lake sediments may have been transported from the source rocks enriched in plagioclase and feldspars. The weathering trend in the source area shows a low degree of chemical weathering and the chemical maturity shows a climatic shift from semiarid to arid climatic conditions in the Lake Yakhi basin.

Terrestrial Snails and Slugs of Nevada, USA: An Overview of Taxa, Biogeography, and Habitat Affinities

The biogeography and habitat affinities of the Recent taxa of terrestrial mollusks of Nevada, western USA, are discussed herein. A total of 52 land snails and slug species were found in Nevada, of which 21 are newly reported records. Two native land snails found previously were not found by this author, and 6 additional species are possible for the state. Of the 47 species of land snail found in the state, 42 are considered native, while 5 are introduced. Only one slug, Deroceras laeve, is considered native, while 4 others are introduced. Land mollusks in eastern and central Nevada are derived from the Rocky Mountain Molluscan Province, such as Pupilla hebes, Microphysula ingersolli, and Oreohelix strigosa depressa (9 species, 18%), while southern Nevada supports species derived from the Southwestern Province, such as Gastrocopta spp., Striatura meridionalis, and Eremarionta rowelli (8 species, 16%). A Californian and Oregonian influence includes Pristiloma chersinella and Punctum californicum. Introduced land snails and slugs such as Deroceras reticulatum, Lehmannia valentiana, Cepaea nemoralis, and Rumina decollata are found in the gardens and parks of urban areas in Nevada. The present native land snail distributions in Nevada result from Miocene and Pliocene dispersal and establishment in the mountains of the Great Basin followed by Pleistocene and Holocene fragmentation and isolation. Xeric habitats such as sagebrush steppe, Pygmy conifer woodlands, and dry alkaline lake beds dominate much of the state and support very few or no land mollusks. Nine habitats are identified as being used by terrestrial mollusks in Nevada. Mountain woodlands, springs, and chaparral support 71% of the total fauna, which includes 36 land snail species and the slug Deroceras laeve where water, coniferous and deciduous vegetation, and moist litter are available between 1400 and 2800 m elevation. The more xeric Mojave Desert in the south (165–1100 m) and sagebrush steppe of the Great Basin (800–2000 m) support 3 and 4 species, respectively. The Pygmy coniferous woodlands occasionally support 2 species, except when the woodlands are associated with limestone cliffs and shrubs, where 5 species may be present (1600–2200 m). River valleys, perennial streams, and meadows (800–2000 m) make up only 1% of the state's land area but support 19 species of land mollusks. Subalpine and alpine habitats in the high mountains (2800–3400 m) support 13 species of land snails. Urban areas with greenhouses, parks, and casino gardens support 9 species of introduced land snails and slugs.

Uneven surface moisture as a driver of dune formation on ephemeral lake beds under conditions similar to the present day: A model‐based assessment from the Makgadikgadi Basin, northern Botswana

AbstractAn association between salt pans or dry lake beds and distinctive crescentic lake‐floor sand mounds (1–10 m high, tens to hundreds of metres wide) is commonplace in desert systems. In the Makgadikgadi Basin of northern Botswana, a debate about the formative processes of these landforms has persisted despite numerous morphometric, sedimentary and geochronological analyses, with mound landforms variously inferred to be aeolian dunes, subaqueous dunes, spring mounds or shoreline remnants. We propose a new formative mechanism which draws on the interaction between uneven moisture distribution on the pan surface and mobile aeolian sediments. We use a numerical model (ViSTA), which couples vegetation and aeolian sand transport dynamics, together with optically stimulated luminescence (OSL) dating of a mound in the Makgadikgadi Basin to investigate the feasibility of this ‘sticky mound hypothesis’. We find that under a range of modelled environmental conditions, uneven moisture distribution on the pan surface can lead to the development and stabilization of crescentic aeolian dunes, with these dunes growing upwind from the point of initial deposition, corresponding with the chronological data gained from OSL dating of a mound feature. On removal of this moisture, the modelled dunes erode and dissipate. These findings suggest that the formative mechanism of the mounds could be dependent on the interaction between differential drying of the pan surface and the competence of the aeolian sediment transport system across the pan floor.

Hydrological Evolution of a Lake Recharged by Groundwater in the Badain Jaran Desert Over the Past 140 years

Understanding the evolution of lakes in arid areas is very important for water resource management. Previous studies have mainly focused on lakes with runoff recharge, while the evolution of groundwater recharge lakes in hyper-arid areas is still less known. In this study, an 86 cm-long sediment core was extracted from Sayinwusu Lake, one of groundwater-recharge lakes in the southeastern Badain Jaran Desert, Northwest China. 210Pb and 137Cs dating, total organic carbon (TOC) and total nitrogen (TN) contents, and mineral content analysis were used to reconstruct the lake evolution over the past 140 years. The evolution of Sayinwusu Lake since 1880 can be divided into two periods. In the first period from 1880 to 1950, the TOC and TN contents were low, and the minerals consisted of all detrital minerals, which indicate that the lake’s primary productivity and salinity were low. During the second period from 1950 to 2018, the contents of TOC, TN, and carbonate minerals increased rapidly at the beginning of the 1950s, indicating that the lake’s primary productivity and salinity increased. Comprehensive analysis of regional climate data suggests that the increase in evaporation caused by rising temperature is an important factor affecting lake evolution in the desert. Although precipitation has increased in the arid region of Northwest China in recent decades with increasing temperature, the enhancement of the evaporation effect is much greater. As a record from groundwater recharge lakes in deserts, our study provides new insight into projecting future lake changes in hyper-arid areas.

Facies analysis, petrography, and palynology of the Pirara Formation (Upper Jurassic-Lower Cretaceous) - Tacutu Basin (Roraima, Brazil)

The Tacutu Basin formed from the rifts system that occurred in the Caribbean region during the Mesozoic and culminated with in the opening of the North Atlantic Ocean. It evolved as a half-graben inserted in the Guiana Shield north of the Amazonian Craton. The Pirara Formation corresponds to the rift phase of the evolution of this basin, however the studies characterizing this unit are very scarce and little accurate due to the absence of outcrops. Therefore, there is much debate about the origin and depositional environment of the Pirara Formation, as some authors argue that the basin was episodically connected to the sea during the rifting, whereas others claim that was a continental-lacustrine environment, under arid to semi-arid climatic conditions. This work was based on investigations carried out on recently drilled rock cores of the Pirara Formation, which provides substantial new information regarding lithological and sedimentological data. The main objective was to characterize the lithofacies petrography palynofacies and constrains the paleoenvironmental interpretation of this unit. Three main lithofacies were identified: marlstone, siltstone, and black shale, with the latter yielding TOC content between 5% and 13.7% and organic matter consisting of phytoclasts, palynomorphs, and amorphous particles. Highly hypersaline conditions are indicated by the presence of pseudomorphs of evaporitic minerals, occurring in the marlstone and siltstone facies. Conversely no marine components take place in the palynological assemblages. The results demonstrate that the Pirara Formation represents a playa lake environment that evolved in the Southern Caribbean region in the Late Jurassic-Early Cretaceous during the opening of the Central Atlantic Ocean.

Stromatolites and calcitized evaporite in a hypersaline playa lake: Rossport Formation (Mesoproterozoic, Ontario)

ABSTRACT The Mesoproterozoic Rossport Formation of Ontario, Canada is generally interpreted as having been deposited in an intracratonic basin, most probably a rift‐related lake. While the Rossport, overall, is dominated by sandstone and shale, the Middlebrun Bay Member, in the middle of the formation, is a carbonate unit. The Middlebrun Bay Member, in exposures on the Channel Islands and along the north Shore of Lake Superior, consists most commonly of cherty, dolomitic microbial laminites and low‐relief columnar to conical forms. In contrast to typical outcrops, the Middlebrun Bay Member on Copper Island expresses as a massive, coarsely crystalline limestone unit, devoid of stromatolites or microbial laminae. Several features suggest dissolution and replacement of a primary, soluble phase such as an evaporite mineral. The top of the unit is marked by evidence of dissolution and collapse, including large sandstone clasts let down from the overlying bed. At petrographic scale, the Copper Island Carbonate comprises millimetre‐scale anhedral spar with abundant stylolites and concentration of insoluble material at grain boundaries, indicating recrystallization from a previous phase. Geochemical data from Copper Island and from correlative stromatolitic carbonate on Channel Island and mainland Ontario are consistent with hypersaline conditions, with elevated concentrations of carbonate‐associated sulphate, V and Ba. Based on these data, the massive carbonate exposed on Copper Island is interpreted as a calcitized evaporite, probably deposited originally as gypsum, and replaced by calcite during diagenesis. These data support previous work suggesting that the Middlebrun Bay interval was deposited during a period of increased aridity and low clastic influx, and further suggest that this restricted, hypersaline lake precipitated both carbonate and gypsum, comparable to modern arid playa lakes.