Lacustrine carbonate tufa facies of Winnemucca Dry Lake Basin, Nevada, U.S.A.

ABSTRACT Lacustrine carbonate tufa deposits are common in present-day lakes and dry pans of the western United States, and large-scale deposits (> 100 m high) are found throughout the subbasins of Pleistocene Lake Lahontan. This study presents a depositional model for very well exposed tufa in Winnemucca Dry Lake, a subbasin of Lake Lahontan, that incorporates new observations of tufa growth over length scales of 10–4–102 m. Tufa depositional facies are defined on the basis of outcrop morphology and texture. Deposits were mapped using satellite imagery and field observations. Tufa facies and volumes were quantified for seven tufa exposures across the basin using digital outcrop and elevation models from aerial images acquired from a small uncrewed aerial system (sUAS). Tufa thin sections were examined using transmitted-light petrography and scanning electron microscopy and combined with measurements of porosity and permeability to define small-scale facies characteristics. Both porosity and permeability are highly variable across textures; average values for both (ϕ = 29%, k = 5.5 D) indicate that all tufa types may exhibit excellent reservoir properties. The age and distribution of these facies across the basin are directly linked to hydroclimate and variations in lake level. The most important controls on tufa distribution at the basin scale are basin hydrology and pathways of groundwater inflow. Groundwater flow into the basin is largely concentrated along the western flexural margin along the contact between volcanic and volcaniclastic bedrock and alluvial sediments, rather than concentrated along the border fault margin, in contrast to other models which predict strong fault control of tufa occurrence. Microbially influenced tufa textures and morphologies are the most volumetrically significant tufas in the basin, composing between 77% and 100% of tufa volume at individual exposures; these are inferred to form during times when lake waters were warmer and levels higher, while physico-chemical processes dominate during early tufa formation, and generally in colder waters and under conditions of lower lake level. Deposition of tufas is a result of combined physical, chemical, and biological factors that are directly related to the basin geology and hydroclimate; however, the importance of each controlling factor is highly variable both spatially and temporally, complicating the development of effective and predictive depositional models. This case study describes tufa deposition intrinsically linked to basinal hydroclimatic histories, and understanding these relationships may assist in predicting volumes, physical properties, and stacking patterns of petroleum reservoir facies in lacustrine basins.

Distribution of Viable Bacteria in the Dust-Generating Natural Source Area of the Gobi Region, Mongolia

The Gobi Desert is a major source of dust events, whose frequency of occurrence and damage caused have recently significantly increased. In the present study, we investigated the types of live bacteria present in the surface soil of the Gobi Desert in Mongolia, and determined their genetic identification as well as their geographical distribution. During the survey, four different topographies (dry lake bed, wadi, well, and desert steppe) were selected, and land characteristics were monitored for moisture and temperature. The surface soil was aerobically cultured to isolate bacterial colonies, and their 16s rDNA regions were sequenced. The sequence data were identified through NCBI-BLAST analysis and generated phylogenetic trees. The results revealed two phyla and seven families of isolates from the sample points. Each isolate was characterized by their corresponding sample site. The characteristics of land use and soil surface bacteria were compared. Most of the bacteria originated from the soil, however, animal-derived bacteria were also confirmed in areas used by animals. Our findings confirmed the existence of live bacteria in the dust-generating area, suggesting that their presence could affect animal and human health. Therefore, it is necessary to further investigate dust microbes based on the One Health concept.

Simultaneous Middle Pleistocene eruption of three widespread tholeiitic basalts in northern California (USA): Insights into crustal magma transport in an actively extending back arc

Mapping and chronology are central to understanding spatiotemporal volcanic trends in diverse tectonic settings. The Cascades back arc in northern California (USA) hosts abundant lava flows and normal faults, but tholeiitic basalts older than 200 ka are difficult to discriminate by classic mapping methods. Paleomagnetism and chemistry offer independent means of correlating basalts, including the Tennant, Dry Lake, and Hammond Crossing basalt fields. Paleomagnetic analysis of these chemically similar basalts yield notable overlap, with statistical analysis yielding 7 chances in 1,000,000 that their similar mean remanent directions are random. These basalts also have overlapping 40Ar/39Ar ages of 272.5 ± 30.6 ka (Tennant), 305.8 ± 23.9 ka (Dry Lake), and 300.4 ± 15.2 and 322.6 ± 17.4 ka (Hammond Crossing). Chemical and paleomagnetic analyses indicate that these spatially distributed basalts represent simultaneous (<100 yr uncertainty) eruptions, and thus we use 305.5 ± 9.8 ka (weighted mean) as the eruption age. Their vents align on a N25°W trend over a distance of 39 km. Tennant erupted the largest volume (3.55 ± 0.75 km3) at the highest elevation; both factors decay to the south-southeast at Dry Lake (0.75 ± 0.15 km3) and Hammond Crossing (0.15 ± 0.05 km3). We propose vertical magma ascent beneath the Tennant vent area, where the most evolved, high-SiO2 magma erupted, with lateral dike propagation in the brittle crust. Propagation was near orthogonal to east-west extension (0.3–0.6 mm/yr) along north-northwest–trending normal faults.

POLARIMETRIC CALIBRATION OF L-BAND AIRBORNE SAR DATA

The PolSAR calibration ensures that the relationship between the SAR observations and the target characteristics on the ground are consistent and resembles the theoretical estimation which in turn improves the overall data quality. Essentially, calibration prevents the propagation of uncertainty into further analysis to characterise the target. In this study, the UAVSAR L-Band data of Rosamond dry lake bed has been calibrated. The calibration of amplitude and phase are carried out with the help of the corner reflector array present in the Rosamond site. The dataset is further calibrated for the crosstalk and channel imbalance using the Quegan’s distortion model. Since the crosstalk distortion model requires an accurate estimation of the covariance matrix, the optimal kernel size for the its computation is selected based on the distortion model behaviour with varying window sizes. Furthermore, the effectiveness of the calibration process has been studied using polarimetric signatures and other statistical measures.

Origin of aeolian dust emitted from the Tarim Basin based on the ESR signal intensity and crystallinity index of quartz: the recycling system of fine detrital material within the basin

The Tarim Basin is the major source of aeolian dust in the northern hemisphere. Glacial activity in the mountains, transportation by rivers and homogenization by wind are believed to be responsible for dust production within the basin. However, the major source(s) and homogenization process(es) are not clear. Moreover, provenance studies on fine fractions have never been conducted. Here, we measured electron spin resonance (ESR) signal intensity and the crystallinity index of quartz in fine (< 16 μm) and coarse (> 64 μm) fractions of river sediments, dry lake sediments and mountain loess to examine the process(es) that produce aeolian dust. The result suggests that the coarse fraction of the river sediment was derived from the bedrock in the drainage area. The ESR signal intensity and crystallinity index of the fine fraction of river sediments from the Tian Shan Mountains and mountainous rivers in the westernmost Kunlun and Pamir mountains are also similar to the coarse fraction, suggesting the same sources. However, the ESR signal intensity and crystallinity index of the fine fraction of river sediments from the Kunlun Mountains are different from the coarse fraction and converge towards values close to the average for the fine fraction of river sediments and mountain loess. Convergence of the ESR and crystallinity index values for the fine fraction of river sediments from the Kunlun Mountains can be explained by contamination of the river sediments by aeolian dust. The convergent values resulted from the homogenization of fine detrital material by repeated recycling within the basin.

Water- and land-borne geophysical measurements before and after the sudden drainage of large karst lakes in southern Mexico

&lt;p&gt;The karst lakes of the sparsely-populated Lacandon Forest in Chiapas, southern Mexico, and their associated sediment infill are attracting increasing attention as high-resolution and continuous environmental and climate archives. To evaluate the information stored in the sediments, paleolimnologists retrieve sediment cores and analyze multiple biological and non-biological indicators. Our geophysical measurements presented here were motivated by the need to determine coring locations providing continuous sediments records from a total of four lakes of the Lacandon Forest. Therefore, we mapped the sediment thickness on the lake floor by applying seismic, electrical, and electromagnetic methods. The measurements were carried out with floating devices &amp;#8211; and, after the sudden drainage of two of the studied lakes, complemented by measurements on the exposed lake floor.&lt;/p&gt;&lt;p&gt;During a first campaign in March 2018 when lakes were filled, we collected seismic data with a sub-bottom profiler (SBP). Furthermore, we collected transient electromagnetic (TEM) data with a floating measuring device to investigate the potential of the method for the determination of sediment thicknesses as an alternative to seismic methods. After the lake-level maximum that coincided with the first campaign, the water levels of two of the studied lakes dropped dramatically by July 2019, leaving lake Metzabok (maximum depth ~15 m) dry and lake Tziban&amp;#225; (~70 m) with a water level decreased by approx. 30 m. In October 2019, when lake levels were still low, we conducted a second survey covering the dry lake floor of lake Metzabok and some dry parts of lake Tziban&amp;#225;. During this second campaign, we collected electrical resistivity tomography (ERT), induced polarization (IP), and seismic refraction tomography (SRT) data along selected lines of the 2018 survey.&lt;/p&gt;&lt;p&gt;Our 2018 results from the water-borne survey show that sediment thickness estimates from seismic (SBP) and electrical (TEM) data agree well for water depths up to 20 m and sediment thicknesses ranging from 2 m to 10 m. The 2019 data collected on the dry lake floor confirms the findings of the first campaign and &amp;#8211; due to the smaller distance between measuring devices and target &amp;#8211; results in a more detailed picture of sediments and the underlying limestone bedrock.&lt;/p&gt;

Li and Ca Enrichment in the Bristol Dry Lake Brine Compared to Brines from Cadiz and Danby Dry Lakes, Barstow-Bristol Trough, California, USA

Relatively few discharging playas in western United States extensional basins have high concentrations of lithium (Li) and calcium (Ca) in the basin-center brines. However, the source of both these ions is not well understood, and it is not clear why basins in close proximity within the same extensional trough have notably different concentrations of Li and Ca. In the Barstow-Bristol Trough, California, USA, three playas in separate topographically closed basins vary in Li and Ca concentrations from northwest to southeast: 71–110 mg/L Li and 17–65 g/L Ca at Bristol Dry Lake, 20–80 mg/L Li and 7.5–40 g/L Ca at Cadiz Dry Lake, and <5 mg/L Li and <0.5 g/L Ca at Danby Dry Lake. Using new and historic data from recently drilled wells (2017–2018), it has been determined that there is minimal variation of temperature, Li, and major ion concentrations with depth (down to 500 m), suggesting that the brines are well mixed and likely to circulate slowly due to density driven flow. Although it has been postulated that geothermal fluids supply the Li and Ca to Bristol and Cadiz closed basins, there is little to no surface evidence for geothermal fluids, except for a young (80,000-year-old) volcanic crater in Bristol Dry Lake. However, major-ion chemistry of fluid inclusions in bedded halite deposits show no change in brine chemistry over the last 3 million years in Bristol Dry Lake indicating that the source of lithium is not related to these recent basaltic eruptions. Mg–Li geothermometry of basin-center brines indicates that Bristol and Cadiz brines have possibly been heated to near 160 °C at some time and Danby brine water has been heated to less than 100 °C, although Cadiz and Danby lakes have no known surface geothermal features. The difference in Li concentrations between the different basins is likely caused by variable sources of both ions and the hydrology of the playas, including differences in how open or closed the basins are, recharge rates, evaporative concentration, permeability of basin-center sediments, and the possible amount of geothermal heating. The differences in Ca concentrations are more difficult to determine. However, historic groundwater data in the basins indicate that less saline groundwater on the north side of the basins has molar Ca:HCO3 and Ca:SO4 ratios greater than one, which indicates a non-saline groundwater source for at least some of the Ca. The similar Li and Ca concentrations in Bristol and Cadiz lakes may be because they are separated only by a low topographic divide and may have been connected at times in the past three million years. All three basins are at least Miocene in age, as all three basins have been interpreted to contain Bouse Formation sediments at various depths or in outcrop. The age of the basins indicates that there is ample time for concentration of Li and Ca in the basins even at low evaporation rates or low geothermal inputs. The source of Li for brines in Bristol and Cadiz basins is postulated to be from ancient geothermal fluids that no longer exist in the basin. The source of Li to the sediment may be either geothermal fluids or dissolution and concentration of Li from tephra layers and detrital micas or clays that are present in the sediments, or a combination of both. The source of Ca must at least partially come from groundwater in the alluvial fans, as some wells have Ca:HCO3 ratios that are greater than one. The source of Ca could be from the dissolution of Ca-bearing igneous rocks in the surrounding catchments with limited HCO3 contribution, or dilute geothermal water migrating up through faults in the basin margin. The relatively low concentration of Li and Ca in Danby playa is likely caused by a lack of sources in the basin and because the basin was (or is) partially hydrologically open to the south, reducing the effectiveness of evaporative concentration of solutes. Bristol Dry Lake is likely the only hydrologically closed basin of the three because although Cadiz has a similar brine chemistry and salinity, there is almost no halite deposition in the basin. It is only Bristol Dry Lake that contains 40% halite in its basin center.

Drying Lakes: A Review on the Applied Restoration Strategies and Health Conditions in Contiguous Areas

Decrease of saline lakes, which comprise 44% of all available lake water, is a major concern. It additionally accelerates the desertification process of the region. Thus, various countries have taken different actions in protecting their lake water levels. The aim of this paper is to assess different strategies directed to tackle the decreased lake water levels in Lake Urmia and the Aral Sea, which split into the North Aral Sea and South Aral Sea. These are among the world’s largest and fastest drying saline lakes observed in the past 50 years and have both reduced to 10% of their original size. The paper presents a thorough review of academic reports, official documents, and databases. Although the dry-up of a lake is a natural process, it has been sped up by human interventions in the hydrological cycle. Dust storms (strong winds) cause problems in the surroundings. In the case of the Aral Sea, they transmit the pollutants from the dry lake bed causing severe health issues. Various strategies were implemented to manage the socio-economic conditions caused due to the drying of lakes. The strategy implemented for the North Aral Sea was to restore the lake by reducing the water withdrawals from the Syr Darya river, which lead to increased water inflow to the sea. The suggested strategy for Lake Urmia was to restore the lake by water transfer activities from various water sources. These projects have not yet been realized. The strategy implemented for the South Aral Sea was to use a dry lake bed to diversify the economy by oil and mineral extraction along with developing a tourist industry based on the considerable interest to come and observe an ecological disaster of such monumental proportions. These findings show that there is no common best solution for this type of problem. The best fit depends on the local context and it is strongly path-dependent.