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1.
U-Series Chronology of Lacustrine Deposits in Death Valley, California   总被引：1，自引：0，他引：1  
Uranium-series dating on a 186-m core (DV93-1) drilled from Badwater Basin in Death Valley, California, and on calcareous tufas from nearby strandlines shows that Lake Manly, the lake that periodically flooded Death Valley during the late Pleistocene, experienced large fluctuations in depth and chemistry over the last 200,000 yr. Death Valley has been occupied by a long-standing deep lake, perennial shallow saline lakes, and a desiccated salt pan similar to the modern valley floor. The average sedimentation rate of about 1 mm/yr for core DV93-1 was punctuated by episodes of more-rapid accumulation of halite. Arid conditions similar to the modern conditions prevailed during the entire Holocene and between 120,000 and 60,000 yr B.P. From 35,000 yr B.P. to the beginning of the Holocene, a perennial saline lake existed, over 70 m at its deepest. A much deeper and longer lasting perennial Lake Manly existed from about 185,000 to 128,000 yr B.P., with water depths reaching about 175 m, if not 330 m. This lake had two significant “dry” excursions of 102–103yr duration about 166,000 and 146,000 yr B.P., and it began to shrink to the point of halite precipitation between 128,000 and 120,000 yr B.P. The two perennial lake periods correspond to marine oxygen isotopic stages (OIS) 2 and 6. Based on the shoreline tufa ages, we do not rule out the possible existence 200,000 yr ago of yet a third perennial lake comparable in size to the OIS 6 lake. The234U/238U data suggest that U in tufa owes its origin mainly to Ca-rich springs fed by groundwater that emanated along lake shorelines in southern Death Valley, and that an increase of this spring-water input relative to the river-water input apparently occurred during OIS 6.  相似文献   

2.
Geochemical Evolution of Great Salt Lake, Utah, USA   总被引：1，自引：0，他引：1  
The Great Salt Lake (GSL) of Utah, USA, is the largest saline lake in North America, and its brines are some of the most concentrated anywhere in the world. The lake occupies a closed basin system whose chemistry reflects solute inputs from the weathering of a diverse suite of rocks in its drainage basin. GSL is the remnant of a much larger lacustrine body, Lake Bonneville, and it has a long history of carbonate deposition. Inflow to the lake is from three major rivers that drain mountain ranges to the east and empty into the southern arm of the lake, from precipitation directly on the lake, and from minor groundwater inflow. Outflow is by evaporation. The greatest solute inputs are from calcium bicarbonate river waters mixed with sodium chloride-type springs and groundwaters. Prior to 1930 the lake concentration inversely tracked lake volume, which reflected climatic variation in the drainage, but since then salt precipitation and re-solution, primarily halite and mirabilite, have periodically modified lake-brine chemistry through density stratification and compositional differentiation. In addition, construction of a railway causeway has restricted circulation, nearly isolating the northern from the southern part of the lake, leading to halite precipitation in the north. These and other conditions have created brine differentiation, mixing, and fractional precipitation of salts as major factors in solute evolution. Pore fluids and diagenetic reactions have been identified as important sources and especially sinks for CaCO3, Mg, and K in the lake, depending on the concentration gradient and clays.  相似文献   

3.
本文是在建立了盐酸胍法制备样品用于氧同位素分析方法研究的基础上,测定了察尔汗湖区各类天然水及ZK88-01占孔岩心的原生石盐流质包裹体氢氧稳定同位素组成。该方法适用于高盐度卤水微量δ18O分析,具有成本低、操作简便和定量转化的优点,值得在国内推广。 根据原生石盐包体水δD、δ18O的分布特征,论述了察尔汗盐湖距今5万年来湖水的演化历程。划分出三种不同成盐环境下的演化期,各期中古湖水体具有波动的继承性,各期间可能存在成盐环境的突变.根据天然水δD、δ18O关系初步获得该区蒸发线为:δD=2.5δ18O-45.3;证实了剖面上部淤泥水与达布逊湖水下渗有关;下部明显地有侧向水补给.  相似文献   

4.
The Emet basin is one of the Neogene basins in western Turkey containing significant amounts of borate minerals, mainly colemanite. The petrologic study of core samples from two exploratory wells in the Do?anlar sector, under optic and electron microscopy, reveals a complex mineral association in which probertite, glauberite, and halite constitute the major primary phases (without mineral precursors) precipitated in a saline lake placed in a volcano-sedimentary context. Other sulfates (anhydrite, gypsum, thenardite, celestite and kalistrontite), borates (colemanite, ulexite, hydroboracite, tunellite, kaliborite and aristarainite), and sulfides (arsenopyrite, realgar and orpiment) are attributed to early diagenesis. So far, the Do?anlar deposit is the most important deposit of probertite known up to now.Chemical changes in the groundwater inflow led to the precipitation of Ca-bearing borates (colemanite) in the tuff-flat environment surrounding the lake, while Na–Ca sulfates and borates (glauberite and probertite) precipitated in the center of the lake. Fluid inclusion compositions in halite indicate that the advanced brines correspond to the Na-K-Cl-SO4 type. During restricted stages of the saline lake, the residual brines seeped through the tuff-flat sediments, leading to transformations of previous precipitates that resulted in the formation of K-bearing minerals.The abundance of coccoid-like biogenic dolomite, colloidal arsenopyrite and the isotopic composition of sulfates are indicative of bacterial sulfate reduction. In contrast, arsenic sulfides are attributed to acidophilic micro-organisms in oxidizing conditions. Fluctuations of redox conditions in both free and interstitial brines control the biological influence in some diagenetic transformations.  相似文献   

5.
末次间冰期以来新疆巴里坤湖蒸发盐的沉积环境记录   总被引：25，自引：9，他引：16       下载免费PDF全文
沉积物岩芯的碳酸盐、石膏等蒸发盐含量和矿物组成的证据显示了新疆巴里坤湖末次间冰期以来一直是一个水位变化频繁的浅水盐湖,有时甚至为间歇式的湖泊,约在34000aB.P.前后巴里坤湖沉积相发生了显著的变化,34000aB.P.之前为泥坪-湖滨相沉积,34000aB．P．之后为成湖相沉积。尽管我们对巴里坤湖34000aB．P．前后的沉积相变难以理解,但是长期处于浅水状态的巴里坤湖沉积物中蒸发盐的含量和矿物组成仍然与气候变化密切相关。在泥坪-湖滨相形成的碳酸盐中白云石相对的增加是地表强烈蒸发的结果。以石膏为主的蒸发盐含量增加是温度和降水增加所致,而其含量减少则是冰川前进致使补给水矿化度降低造成的。这使我们获得了该区古气候变化并不服从于冰期与雨期同步模式的信息。  相似文献   

6.
Salt mounds are commonly distributed along playa margins and typically comprise alternating layers of loose fine sand and slightly hard halite-rich sediments as a result of long-term underground spring activity. A model of salt mound development was constructed for this study. It suggests that wind-blown sand supply and upward recharge of underground springs are two important factors in salt mound construction. Furthermore, it proposes that salt mound height is mainly controlled by the vertical transport range of underground springs and the thickness of the capillary fringe. A 1.5 m representative profile dug from the center of salt mound LP1 in the Lop Nor playa revealed a fairly complicated mineral assemblage including halite, gypsum, anhydrite, glauberite, epsomite, anhydrite, calcite, bischofite, polyhalite, schoenite, kieserite and carnallite. This matches closely with the assemblage predicted by the EQL/EVP model. The groundwater in the area is highly concentrated brine rich in Cl− and Na+ and poor in Ca2+, displaying low alkalinity, and containing considerable amounts of SO42−, Mg2+ and K+. Chemical analysis of groundwater revealed considerable variation in the salinity and chemical composition of groundwater over time. The Cs-137 technique was used to measure the accumulated ages of the salt mounds. This method may prove useful in the research of relatively young playa environments where carbon dating techniques are unworkable because of an absence of carbon-rich materials in recent saline sediments.  相似文献   

7.
In many arid and semiarid areas, dry lake beds (saline playa) represent a tremendous source of unconsolidated salt-rich sediments that are available for aeolian transport. Severe salt-dust storms caused by the erosion of such landforms have become very harmful natural phenomena. In this study, sample analysis and field erosion monitoring of Ebinur Lake was conducted to investigate the salt content, chemical composition, and wind erosion intensity of surface salt-rich sediments. The effects of salt-dust rising from the playa on the growth and physiological health of plants were also evaluated in this study through a leaf dustfall test. The results indicate that water-soluble salts assemble densely on the dry lake bed surface. At a depth of 0–2 cm, the highest salt contents can exceed 40%, with sulfate and chloride being the main anions present and Na+, Ca2+, and Mg2+ being the primary cations. The annual wind erosion rate ranged from 0.48 to 5.6 cm in the northwest portion of the lake and from 0.24 to 0.96 cm in the southeast portion. Salt-dust storms caused by wind erosion of saline playa sediments seriously influenced the normal absorption of minerals by plant leaves. Under the influence of salt-dust storms, plant leaves absorb more Na+, but far less K+.  相似文献   

8.
Criteria for the recognition of salt-pan evaporites   总被引：6，自引：0，他引：6  
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.  相似文献   

9.
The discovery of layered, SO4-rich sediments on the Meridiani Planum on Mars has focused attention on understanding the formation of acid–saline lakes. Many salt lakes have formed in southern Australia where regional groundwaters are characterized by acidity and high salinity and show features that might be expected in the Meridiani sediments. Many (but not all) of the acid–saline Australian groundwaters are found where underlying Tertiary sediments are sulfide-rich. When waters from the formations come to the surface or interact with oxidised meteoric water, acid groundwaters result. In this paper examples of such waters around Lake Tyrrell, Victoria, and Lake Dey-Dey, South Australia, are reviewed. The acid–saline groundwaters typically have dissolved solids of 30–60 g/L and pH commonly <4.5. Many contain high concentrations of Fe and other metals, leached from local sediments. The combination of acidity and salinity also releases Ra. Around salt-lakes, these acidic waters often emerge at the surface in marginal spring zones where the low density (ρ ∼ 1.04) regional water flows out over the denser (ρ ∼ 1.16) lake brines. In the spring zones examined, large amounts of Fe are commonly precipitated. In a few places minerals of the alunite-jarosite family are formed which can trap many other metals, including Ra. The studied groundwater systems were discovered by U exploration programs following up radiometric anomalies related to this Ra. Evaporation concentrates the lesser soluble salts (gypsum and some halite) on the surface of the lakes. The lake brines contain most of the more soluble salts and form a column within the porous sediments which is held in place by hydrostatic forces around the salt-lake. These brines are near-neutral in pH.  相似文献   

10.
在盐湖沉积演化过程中,钾盐矿物在盐类沉积的中晚期阶段才开始析出。因此,研究含盐系盐类的沉积地球化学特征,不仅可以从侧面获取岩盐的沉积物源和成盐古卤水蒸发浓缩程度等地球化学信息,而且更能揭示古盐湖钾盐富集趋势。文章通过对库车盆地钾盐科探1井钻取的岩芯样品进行高精度采样测试,得出岩盐中Mg×103/Cl、K×103/Cl、Li×103/Cl与K+、Mg2+、Li+、Ca2+、Cl-含量的垂向变化规律。并与库车盆地其他钻孔中的岩盐含钾性进行对比,同时,依据钻井剖面岩性特征,与潜江凹陷和大汶口凹陷含盐系剖面进行对比,论述研究区成盐的地球化学特征,对其钾盐成矿前景进行分析和评价。  相似文献   

11.
Hydrogeochemical data from lake, sediment pore, and well waters were used to quantify groundwater seepage and the associated transport of phosphorus to Lake Persimmon, Florida, USA. The data show that lake chloride concentrations vary as a function of lake elevations that are controlled by groundwater inflow. A whole-lake average seepage rate, estimated using a simple one dimensional advection-diffusion model fitted to the lake chloride profile, currently averages 2.3 ± 0.3 cm yr-1 and is in reasonable agreement with the rate of advective flow obtained from the pore water chloride profile. The ratios of nutrient regeneration versus sulfate consumption indicate that the phosphorus enrichment in deeper portions of sediment pore water is most likely a result of groundwater phosphorus transport through sediment. Thus, the net inputs of groundwater phosphorus to the lake, calculated using the deep pore water phosphorus concentration, are about 7.4 ± 4.3 mg P m-2 yr-1 and comparable with recent in situ estimates from seepage meters. This study provides a simple hydrogeochemical method for estimating hydrologic and phosphorus inputs via groundwater to the lake, thereby supporting current efforts for lake management.  相似文献   

12.
As one of the lakes on the Yunnan-Guizhou plateau, Lake Chenghai, which is a typical closed lake with the precipitation accounting for one-third or more of the annual water input, has a high total salinity (almost like a saline lake). The inorganic C, O isotopic composition of lake sediments bears much sensitive information about environmental change in the catchment, while their correlations revealed the hydrological conditions under which the lake was closed. Their compositional variations are controlled by temperature, precipitation, photosynthesis, dissolving equilibrium of the carbonate system and hydrological condition. According to our research on inorganic C, O isotopic composition of Lake Chenghai sediments, we investigated the environmental change of this catchment several decades ago. The results showed that Lake Chenghai has kept good hydrological closing conditions in the past several decades, as indicated by the good correlation of inorganic C, O isotopic composition of sediments; and that the environmental change in this catchment shows a tendency of periodical evolution on a 10−11-years scale, although the signal noise is relatively high at the bottom of the sediment core. And we also can extend C, O isotopes, a sensitive environmental indicator, to nearly saline lake environments with a high degree of mineralization.  相似文献   

13.
The central trough of the Bolivian Altiplano is occupied by two wide salt crusts: the salar of Uyuni, which is probably the largest salt pan in the world (10,000 km2) and the salar of Coipasa (2,500 km2). Both crusts are essentially made of porous halite filled with an interstitial brine very rich in Li, K, Mg, B (up to 4.7 g/l Li, 4.3 g/l B, 30 g/l K and 75 g/l Mg). Lithium reserves are the highest known in the world, around 9 × 106 tons. Potassium, magnesium and boron reserves in brines are also important (around 194 × 106 tons K, 8 × 106 tons B and 211 × 106 tons Mg).

The crusts are the remnant of saline Lake Tauca (13,000–10,000 yr BP). Its salinity was estimated approximately at 80 g/l. Its paleochemistry was derived in two ways: (1) by dissolving the present amounts of all chemical components in the former lake volume, and (2) by simulating the evaporation of the major inflows to the basin. The resulting chemical compositions are quite different. The dissolution-derived one is 5 to 50 times less concentrated in Li, K, Mg, B than the evaporation-simulated ones. However all compositions present the same Na and Cl contents. This suggests either a removal of bittern salts or an enrichment of the former lake water in Na and Cl.

The most probable interpretation is that Lake Tauca redissolved a salt crust akin to that existing today. Several older lakes have been detected on the Altiplano. Nevertheless, such an explanation only pushes the problem back. It is likely that the anomaly was transferred from one lake to an other. Three hypotheses may be put forward: (1) bittern seepage through bottom sediments, (2) uptake of the missing components by minerals, and (3) leaching of ancient evaporites from the catchment area at the beginning of the lacustrine history of the basin. The excess halite could have been recycled from lake to lake. This latter process seems to be the most effective to explain the large excess of Na and Cl over the bittern solutes — Li, K, Mg and B. The occurrence of almost pure Na/1bCl saline springs flowing out from a gypsum diapir in the northern Altiplano gives substantial support to this hypothesis.  相似文献   


14.
张幼勋 《矿床地质》1983,2(3):69-71
吴城碱矿是世界罕见的古代天然碱矿床之一,属于典型的陆相碳酸盐型盐湖沉积。矿床赋存于一个早第三纪断陷盆地中,该盆地发育了厚约2400余米的陆相碎屑—蒸发岩。天然碱距地表650—900余米,呈多层状产出,下部为天然碱矿层,上部则为含岩盐天然碱层。矿床盐类矿物组合以天然碱为主,次为石盐、重碳酸钠盐。共生矿物有磷钠钙石、氯碳钠镁石,未见通常在碳酸盐湖中出现的硫酸盐矿物——芒硝。  相似文献   

15.
The Wucheng trona deposit, one of the rare ancient trona deposits in the world, is genetically of typical terrestrial facies carbonate sediments of brine lake. Contained in an Eogene block basin composed of terrigenous clastic-evaporite rocks some 2400 m in thickness, it occurs 650 to over 900 m beneath the earth's surface in the form of multilayers, the lower part being pure trona beds while the upper part consisting of trona beds interbedded with halite streaks. Saline minerals are trona and to a much less amount, halite and nahcalite, associated with such minerals as shortite and northupite. Mirabilite, a rather common mineral in the carbonate salt lake, has not yet been found here. The unusually developed sedimentary cyclothem of the host rock, predo-minantly argillaceous dolomite- kuchersite- (halite-bearing) trona, makes up a most striking feature of this deposit, and the trona bed lies invariably on the kuchersite-dolomite facies. Although belonging to one of the minerogenetic series of saline deposit, the trona deposit, instead of being simply a product of the evaporation of brine, has its specific mineral-forming conditions and sedimentation mechanism. Trona is a typical product of the terrestrial facies carbonate lake. lts formation, therefore, requires the persistent supply of large quantities of Na-rich carbonate type water which, being actually surface water or ground water circulating through the metamorphic and igneous rocks at the periphery of the basin, constitutes an indispensable factor in the sedimentation of trona by its concentration and evaporation. Besides, the coicentration of CO8<.sub>-2 and HCO8- in the solution is related to the partial pressure of CO2. Only when sufficient CO2 is unceasingly supplied can nahcalite and trona be precipitated. CO2, in turn, depends on the presence of large amounts of organism for its formation. These factors are prerequisites for the precipitation of the trona deposit, making it distinctly different from other saline deposits. Other formation conditions of the Wucheng trona deposit, such as the existence of a closed basin controlled by tectonics, the alternate arid and semiarid climates, are quite analogous to those of other saline deposits. Some controversial problems concerning this kind of deposit are also put for ward in this paper for further investigation, including the feasibility of taking the abundance of sulfate minerals as a criterion of distinguishing ancient tronas from recent ones, the influence of material resources and climate conditions upon the variation of ore types, and the origin of the highly-concentrated sodium brine in areas adjacent to the Wucheng deposit.  相似文献   

16.
R. W. RENAUT 《Sedimentology》1993,40(2):271-301
Late Quaternary fluviolacustrine siltstones, mudstones and claystones (Loboi Silts) on the northern margins of the saline, alkaline Lake Bogoria in the Kenya Rift Valley contain up to c. 40% authigenic analcime and minor natrolite. The zeolitic sediments are reddish brown and up to 1 m thick. The amount of analcime increases upward in the profile, but decreases with distance from the lake. The altered sediments show many pedogenic features including zeolitic root mats, rootmarks, concretions and carbonate rhizoliths. Residual patches of calcrete locally cap the zeolitic rocks. The profile is interpreted as an exhumed palaeosol and land surface on the former margins of the lake. The analcime occurs as submicroscopic (0–5–2–5 μ.m) subhedral and euhedral crystals, which have an average Si/A 1 ratio of 2–33 (as determined by X-ray microanalysis) or 2–18 (d-value of 639 analcime peak). The analcime formed in lake marginal sediments (soils) by reaction of silicate detritus with Na2CO3 rich pore waters concentrated close to the land surface by evaporative pumping and evapotranspiration. Poorly ordered clay minerals were probably the main reactants. Authigenic illite may have been a by-product of the reactions. Chemical analyses suggest that pore waters supplied some of Na+, and possibly K+ and SiO2. The associated calcrete and rhizoliths were formed during or shortly after the main period of zeolitic alteration. The Ca2+ may have originated from infiltrating dilute runoff and groundwater. Authigenic smectite was precipitated in open porosity following analcime formation. The zeolitic alteration at Lake Bogoria provides a relatively recent analogue for lake marginal zeolites found in many ancient saline, alkaline lake sediments.  相似文献   

17.
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.  相似文献   

18.
柴达木盆地西部尕斯库勒盐湖280 ka以来沉积特征   总被引：2，自引：0，他引：2  
以柴达木盆地西部尕斯库勒盐湖干盐滩6个钻孔岩芯为研究对象,从岩性特征、成盐期、沉积类型、沉积结构、沉积幅度等方面探讨尕斯库勒盐湖沉积特征。研究表明,自280 ka以来尕斯库勒盐湖经历相对湿润-干旱的气候波动和气候演化,在距今43.6 ka左右进入最干旱时期,可能属于柴达木盆地第二次成盐期;沉积结构层分异现象不明显;各成盐期平均沉积速率变化不大,平均沉积速率比新疆和内蒙古地区高; 该湖沉积中心在盐湖的西北部。  相似文献   

19.
Lithium-rich brine within the sub-surface of the Salar del Hombre Muerto (SHM) salt pan in the Andes of northwestern Argentina has a chemical and isotopic composition which is consistent with Li derived from several sources: the modern halite saturated lagoon, Li-rich salts and brines formed recently, and dissolution of halite which precipitated from ancient saline lakes. SHM lies in the closed basin that includes part of the massive Cerro Galán caldera which is drained by the Río los Patos, which is responsible for 90% of surface runoff into the salar. The low Li isotope composition, +3.4‰, of this river is consistent with significant contributions of geothermal spring water. As water drains through the volcaniclastic deposits which cover a large proportion of the basin, Li removal, as indicated by decreasing Li/Na, occurs but without significant isotope fractionation. This indicates a mechanism of surface sorption onto smectite or ferrihydrite rather than Li incorporation into octahedral structural sites of clays. These observations suggest that conditions in this high altitude desert have limited the dilution of hydrothermal spring water as well as the formation of clay minerals, which jointly have allowed the Li resource to accumulate rapidly. Changes in climate on a multi-millennial time scale, specifically in the hydrologic budget, have resulted in solute accumulation rates that have been variable through time, and decoupled Li and Na fluxes. Inflow to the salar under modern conditions has high Li/Na (7.9 × 10−3 by wt) with δ7Li indistinguishable from basement rocks (−0.3‰ to +6.4‰), while under pluvial climate conditions the Li/Na of the saline lake was 40 times lower than the modern lagoon (0.1–0.3 × 10−3 compared to 10.6–13.4 × 10−3) with slightly higher δ7Li, +6.9‰ to +12.3‰, reflecting the uptake of 6Li into secondary minerals which formed under a wetter climate.  相似文献   

20.
The age framework of Qarhan Salt Lake in arid western China is still controversial due in part to (1) age discrepancy between conventional 14C and 230Th dating results, and (2) no AMS 14C ages of organic carbon from drilling cores in Qarhan Salt Lake were reported until now. In order to discuss these chronological problems, upper 54.50 m lacustrine sediments from a drilling core (ISL1A) recovered from Qarhan Salt Lake were dated based on 230Th and AMS 14C dating techniques. Results show that (1) AMS 14C ages of total organic carbon (TOC) from 4.65 to 30.29 m are almost in stratigraphic order and consistent with 230Th ages of halite in the corresponding layers; (2) AMS 14C ages of TOC from 30.29 to 54.50 m are younger with increasing depth. This phenomenon was also found in Shell Bar in the study area, suggesting that AMS 14C ages from upper 30.29 m are more reliable while those from lower 24.21 m in ISL1A may be underestimated; (3) 230Th ages of halite from lower 24 m lacustrine sediments are obviously older than AMS 14C ages of TOC in the corresponding layers, which results into different age framework of salt lake sediments in Qarhan Salt Lake; (4) if extrapolating these reliable AMS 14C ages in ISL1A, similar age framework with 230Th ages in this core confirms that 230Th ages are much close to the true ages of these sediments, which suggests that the forming timing of the bottom salt layer is ~50 ka.  相似文献   

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