Enclosed Extent of the Saline Water and its Constraints on the Sedimentary and Salt Forming Characteristics:A Case Study of the Paleogene Playas in Hoh Xil Basin

1 Introduction There is a long period of hot,arid climates in the Jurassic-Neogene,in the eastern of the Neo-Tethys where is been called Western Yunnan—Qiangtang tectonic belt(Zheng et al.,2010).Especially in the Paleogene,under the control of the planetary winds and the north subtropical high pressure belts,a ribbon arid,semi-arid

Exploration of playa surface crusts in Qehan Lake, China through field investigation and wind tunnel experiments

Globally,many lakes are drying up,leaving exposed lakebeds where wind erosion releases dust and sand rich in salt and harmful heavy metals into the atmosphere.Therefore,understanding the characteristics and spatial distribution of playa surface crusts is important to recognize the manifestation of salt dust storms.The objective of this study was to explore the playa surface crust types as well as their spatial distribution and evolution of Qehan Lake in Inner Mongolia Autonomous Region,China to understand the salt dust release potential of different types of playa surface crusts.Various crust characteristics were investigated by field sampling in Qehan Lake,and playa surface crusts were further divided into five types:vegetated areas,salt crusts,clay flats,curly crusts,and margins.It should be noted that curly crusts were distributed in clay flats and covered only a small area in Qehan Lake.The spatial distribution characteristics of playa surface crust types were obtained by supervised classification of remote sensing images,and the salt dust release potential of crusts was explored by the wind tunnel experiments.The field investigation of Qehan Lake revealed that playa surface crust types had a circum-lake band distribution from the inside to the outside of this lake,which were successively vegetated areas,clay flats,salt crusts,and margins.The spatial distribution patterns of playa surface crust types were mainly controlled by the hydrodynamics of the playa,soil texture,and groundwater.There was a significant negative correlation between crust thickness and electrical conductivity.The results of the wind tunnel experiments showed that the initial threshold of friction wind velocity for the salt dust release was higher in clay flats(0.7–0.8 m/s)than in salt crusts(0.5–0.6 m/s).Moreover,the particle leap impact processes occurring under natural conditions may reduce this threshold value.Salinity was the main factor controlling the difference in the initial threshold of friction wind velocity for the salt dust release of clay flats and salt crusts.This study provides a scientific reference for understanding how salt dust is released from a lakebed,which may be used for ecological restoration of dry salt lakes.

Origin of Some Transversal Linear Features of NE-SW Trend in Iraq, and Their Geological Characters

Iraq is located at the extreme northeastern part of the Arabian Plate, which is in collision with the Eurasian Plate. This collision is still onward, and has caused alignment of the evolved structures in NW-SE trend, mainly, especially in the northern, northeastern and eastern sides of Iraq. However, many transversal linear features of NE-SW trend, represented by rivers, streams, valleys, playas, anticlines and offsets are developed, in parallel trend to the main compressional forces created by the aforementioned collision. Many examples from different parts of Iraq confirm the mechanism of their formation through the geological, geomorphological, tectonics and structural aspects. Although the existing linear features are tens of kilometers in length, but almost no surface displacements were reported, except very few, in some parts of Iraq. The given examples are selected to be the most obvious, when geophysical data are available, the surface and subsurface geology of the involved area is correlated to deduce whether the surface expression coincides with the subsurface or otherwise. A brief tectonic history is also given.

Saline dust storms and their ecological impacts in arid regions

In many arid and semiarid regions,saline playas represent a significant source of unconsoli-dated sediments available for aeolian transport,and severe saline dust storms occur frequently due to human disturbance.In this study,saline dust storms are reviewed systematically from the aspects of con-cept,general characteristics,conditions of occurrence,distribution and ecological impact.Our researches showed that saline dust storms are a kind of chemical dust storm originating in dry lake beds in arid and semiarid regions;large areas of unconsolidated saline playa sediments and frequent strong winds are the basic factors to saline dust storm occurrence;there are differentiation characteristics in deposition flux and chemical composition with wind-blown distance during saline dust storm diffusion;and saline dust storm diffusion to some extent increases glacier melt and results in soil salinization in arid regions.An under-standing of saline dust storms is important to guide disaster prevention and ecological rehabilitation.

Simulated Dynamic Evaporation of Yiliping Salt Lake Brine

1 Introduction There are numerous salt lakes in western China(Zheng Mianping,et al.,2011).Yiliping playa on the western Qaidam Basin is a magnesium sulfate subtype dry salt lake with high concentrations of potassium,boron and lithium.

THE EVOLUTION OF SMALL LAKE BASINS IN THE GOBI DESERT IN MONGOLIA

In order to investigate pluvial lakes in the Gobi two places were selected for field studies: Khongoryn Els inSouth- and Mongol Els in West-Mongolia. In the eastern and central parts of Khongoryn Els two small endorheic basins,Bayan Tukhem and Khongoryn Gol depressions were studied. Pluvial lake deposits and beach ridges both supposedly mid-Holocenein age give evidence of a 9m and a 15m deep freshwater lake,respectively. Today both depressions are nearlydried out and exposed to wind deflation. A different situation was found at Uujin Sair river valley which cuts through thedune field at its lowest and narrowest (3 km) part. Here, a 22.5 m thick fossil accumulation of at least 20 layers of fine sand(dune sand)alternating with silt(fluvial playa sediment)was exposed and OSL dated. 12 dates ranging between 14ka and17ka reveal the accumulation as Late Glacial which correlates well with the aridity at that time reported for Central Asia byseveral authors. Interpreting the dates it seems obvious that the whole sediment was quickly deposited in a period of about16ka,and shortly after dissected by the Uujin Sair during a similar short time due to increasing humidity of the climate.Another situation was found at the eastern rim of Mongol Els. Two rivers,Shurgiyn Gol and Zavran Gol are impinging hereon the high dunes which have damed both rivers in the past. A younger, shallow lake existed during mid-Holocene( ^(14)C-dated to some 5.5ka)and a large, 17m deep lake( ^(14)C -- dated to some 39ka) probably during stage 4. Expected OSLdates will hopefully support this hypothesis. Anyhow, the palaeogeography of the dune field was different from today; itmoved eastward daming the large river Shurgiyn Gol.

Measuring the Condition of Saline Wetlands Threatened by Agricultural Intensification

The saline wetlands,or'saladas',of Monegros Desert,NE Spain,contain biodiversity that depends on the estab- lishment of a prognostic monitoring system that can warn of approaching irreversible damage.In the context of a lack of existing biodiversity inventories for the saladas,we determined their state of conservation and vulnerability using seven physical indicators:escarpment continuity,cropping,stone dumping,size,water occurrence,distance to roads,and proximity to irrigated areas.These features were combined into three meaningful indexes,i.e.,conservation,current vulnerability,and future vulnerability,thus creating an assessment of the preservation or degradation of saladas in the context of encroaching agricultural irrigation projects.The proposed indexes produced consistent results and showed that a great number of the Monegros wetlands were threatened,regardless of their size or frequency of water occurrence.Only 20% of the saladas studied were classified as being in a good or very good conservation,whereas 50% were in bad or very bad shape.A high current vulnerability was found for 60% of the saladas.For saladas located in land to be irrigated, we predicted that 73% would have a high or very high future vulnerability.Currently,58% of the saladas were in bad or very bad condition and fully 65% of the saladas,variable in size,presented a bad or very bad prognosis.Our approach provides a monitoring strategy for the conservation of saline wetlands threatened by agricultural intensification,especially irrigation.

Geotop of Lut Playa： Quaternary Geomorphologic Evidence and Civilization

The cultural and geomorphological heritages in Playas as a key address to find out past fluctuations called geotop. Iran is strategically located on an important trade route （Silk Road） between four cradles of civilization namely, Babylon, Mesopotamia, Indus and Yangtze （Chinese）. Iran is grafting point of four human civilizations which creates Persian civilization about 4,000 years ago. The Lut Desert and Dasht-e Kavir located the central and eastern Iran have been focal points for human settlements since 7,000 years ago. The geoarcheological findings on the Siyalk hills of Kashan located in the Dasht-e Kavir and Jiroft region located in the Lut desert are confirmations for human settlement since more than 7,000 years ago. Shorehzar that is a Persian equivalent word for Arabic word of Sabkha is considered as a Playa geomorphic type which involves precious evidences of quaternary fluctuations. In this article, geomorphological and paleoenvironmental investigations are integrated to provide a framework of environmental change for the late Pleistocene and early-mid Holocene periods in the main deserts of Iran, Lut. In this article based on main geotops of Lut, the quaternary evolutions have been discussed. The investigations are showing that Playas were bed of civilization in Iran Deserts.

An Attempt to Date the Salt-mounds in the Lop Nor Playa

1 Introduction The Lop Nor playa,located in the eastern end of the Tarim Basin,capped with a thick salt crust covering an area of approximately 5,500 km2(Ma 2007)that closely resembles a"Great Ear"in satellite images.Understanding the formation of the salt crust can provide important

Wind erosion from crusted playa surfaces by no saltation and with saltation:A comparison through laboratory wind tunnel experiments

Playas are common in many arid regions and recognized as a major source of hypersaline particles.A better understanding of wind erosion on crusted playas has significant implications for land management and pollution control practices.We hypothesized that wind erosion rates of crusted playas were complicated and controlled by the interactions between playa crust and wind-induced saltation conditions.However,comparisons regarding the effects of different playa crusts on wind erosion under no saltation(NS)and with saltation(WS)conditions were lacking.In this study,laboratory wind tunnel experiments were carried out to simulate both NS and WS conditions,to investigate the erosion rates of different crust types(Salt,Takyr,and Puffic crust)at different wind speeds.Results showed that:1)Salt crust had greater crust strengths than did Takyr crust and Puffic crust;2)wind erosion rates under the WS condition were up to 60 times greater than those under the NS condition,suggesting that sand bombardment was the dominant mechanism responsible for removal of fine material from crusted playa surfaces;3)both sand bombardment rate and wind erosion rate of the playa crusts increased with increasing wind speed under the WS conditions;4)Puffic crust exhibited a greater rate of wind erosion compared to both the Takyr and Salt crusts under the Ns condition,yet tended to have a lower rate of wind erosion compared to both the Takyr and Salt crusts under the WS condition.This difference can be attributed to the fact that soft Puffic crusts are pliable and can dissipate the force of impacting grains under the Ws conditions.Our results indicated that wind erosion processes on crusted playas are complicated and are affected by wind-induced saltation and crust type,specifically crust strength and elasticityofthesurface.

Geomorphologic Characteristics of Polygonal Features on Chloride-Bearing Deposits on Mars: Implications for Martian Hydrology and Astrobiology

Over 600 chloride-bearing deposits(chlorides) have been identified on the southern highlands of Mars. These chlorides have critical implications for hydrology and astrobiology: they are indicators of an evaporating super saturated solution, and they could have provided habitat environments for halophilic microorganisms and preserved organic matter. One of the prominent geomorphology characteristics of these chloridebearing regions is the polygonal features within them. The origin of these polygonal features is still in debate. In this study, we have surveyed 153 locations of chlorides using 441 high resolution imaging science experiment(Hi RISE) images to characterize the geomorphology of polygonal features. We identified 3 types of polygonal features of distinct geomorphologic characteristics: fractures, raised ridges, and transitional polygons between fractures and raised ridges. We evaluate previously proposed hypotheses of the formation of the polygonal features, and suggest that the 3 types of polygonal features are indicators of different stages of salt crust formation. Salt crust is usually formed through multiple groundwater activities, and it often occurs in playa environment on Earth. The unique hydrological and astrobiological implications of the chlorides with polygonal features make these deposits of high priority for future landed on and/or sample return exploration missions of Mars.