Dolomitization,gypsum calcitization and silicification in carbonate–evaporite shallow lacustrine deposits          下载免费PDF全文

Mª Angeles Bustillo  Ildefonso Armenteros  Pedro Huerta 《Sedimentology》2017,64(4):1147-1172

This paper describes and interprets the mineral and facies assemblages that occur in carbonate–evaporite shallow lacustrine deposits, considering the importance of the processes pathway (i.e. dolomitization, gypsum calcitization and silicification). The Palaeogene deposits of the Deza Formation (Almazán Basin, central‐northern Spain) are selected as a case study to determine the variety of physicochemical processes taking place in carbonate–evaporite shallow lakes and their resulting diagenetic features. Dolostones are the predominant lithology and are composed mainly of dolomite with variable amounts of secondary calcite (5 to 50%), which mainly mimic lenticular gypsum (pseudomorphs). Five morphological types of dolomite crystal were identified as follows: dolomite tubes, dolomite cylinders, rhombohedral dolomite, spheroidal and quasi‐rhombohedral dolomite, and cocoon‐shaped dolomite. The dolomite cylinders and tubes are interpreted as the dolomitized cells of a widespread microbial community. The sequence of diagenetic processes started with growth of microlenticular interstitial gypsum in a calcareous mud deposited on the playa margin mudflats, and that sometimes included microbial sediments. Immediately following growth of gypsum, dolomite replaced the original calcite (or possibly aragonite) muds, the microbial community and the gypsum. Partial or total replacement of gypsum by dolomite was related mainly to the biomineralization of endolithic microbial communities on gypsum crystals. Later calcitization took place under vadose, subaerial exposure conditions. The development of calcrete in distal alluvial settings favoured the release of silica and subsequent silicification on the playa margin mudflats. Stable isotope compositions of calcite range from ?9·02 to ?5·83‰ δ¹³C_PDB and ?7·10 to 1·22‰ δ¹⁸O_PDB; for the dolomite, these values vary from ?8·93 to ?3·96‰ δ¹³C_PDB and ?5·53 to 2·4‰ δ¹⁸O_PDB. Quartz from the cherts has δ¹⁸O_SMOW values ranging from 27·1 to 31·1‰. Wide variation and relatively high δ¹⁸O_SMOW values for dolomite indicate evaporitic and closed hydrological conditions; increased influx of meteoric waters reigned during the formation of secondary calcite spar.  相似文献   

高盐度地下水~(14)C测年样品采集技术探讨   总被引：4，自引：0，他引：4  

焦鹏程  刘成林  齐继祥  王弭力  陈永志 《地学前缘》2003,10(2):309-312

高盐度地下水 (卤水 ) 14 C样品采集是同位素水文地质界的一个难题。罗布泊钾矿区卤水的化学组成特征是 :平均矿化度为 35 3.5 g/L ,SO2 -4的质量浓度 4 4 .0 3g/L ,HCO-3 的质量浓度为0 .2 71g/L。为此 ,文中借鉴一般地下水 (淡水或微咸水 ) 14 C样品的采集原理 ,设计出一套真空取样装置。其操作步骤是 ,首先通过调节卤水的 pH值 ,使得水中的无机碳以CO2 气体的形式溢出 ,然后 ,导入装有NaOH与BaCl2 混合溶液的样品瓶中 ,在野外获得高盐度卤水14 C测年样品。罗布泊卤水测试结果表明 ,这一流程有效地解决了硫酸盐干扰问题 ,卤水14 C样品质量可靠。该技术可为高盐度地下水测年提供有效手段 ,对低盐度地下水14 C取样也具有重要的推广使用价值。  相似文献   

Last glacial cycle hydrological change at Lake Tyrrell, southeast Australia     

Tim Stone 《Quaternary Research》2006,66(1):176-181

Lake Tyrrell is the largest playa in the Murray Basin of southeast Australia. Optical dating of transverse dune (lunette) sediments extends the lake's radiocarbon chronology to the last interglacial period. The highest lake level was attained 131,000 ± 10,000 yr ago, forming Lake Chillingollah, a megalake that persisted until around 77,000 ± 4000 yr ago. Pedogenesis of its sandy lunette continued until buried by a silty clay lunette deflated from the lake floor 27,000 ± 2000 yr ago. The dated soil-stratigraphic units correlate with the upper Tyrrell Beds and contain evidence that humans visited the lakeshore before 27,000 yr ago. The Lake Chillingollah megalake was synchronous with very high lake levels in monsoon-dominated Australia, yet it was not influenced by tropical monsoon systems. It was filled instead by increased winter rainfall from westerly low-pressure fronts. Greater effective precipitation across Australia is evident, the result of a weakened subtropical high-pressure zone.  相似文献   

Deformation structures and an alteration zone linked to deposition of volcanogenic sulphate in an ancient playa (Oligocene of Nebraska, USA)     

DAVID B. LOOPE  JOSEPH A. MASON†  HUIMING BAO‡  RICHARD M. KETTLER  C. WILLIAM ZANNER¶ 《Sedimentology》2005,52(1):123-139

Historic, sulphur-rich volcanic eruptions have altered global climate for as much as five years, and much larger events are known from the geologic record. At Scotts Bluff, Nebraska, Early Oligocene strata of the lower Arikaree Group contain a tephra bed with abundant calcite pseudomorphs after gypsum. Previous work has shown sulphate from the pseudomorphs in this tephra bears a high ¹⁷O anomaly indicative of oxidation of sulphur gases by ozone or hydrogen peroxide in the atmosphere. Possible sources of the tephra were caldera eruptions at about 28 Ma in the San Juan volcanic field of south-western Colorado (∼500 km SW of the study site) and the eastern Great Basin (∼1000 km WSW). The present sedimentological study shows that tephra and volcanogenic sulphate were deposited and preserved within a small, surface-discharging playa that developed on the irregular upper surface of aeolian siltstones of the subjacent White River Group. Sulphate solutions (including perhaps sulphuric acid) percolated downward within the vadose zone, dissolving early formed smectite cement within underlying volcaniclastic sandstones, reddening these rocks along an irregular alteration front. Preserved fine-scale stratification within the sandstones precludes the possibility that reddening took place during pedogenesis. Displacive growth of gypsum at the playa centre folded tephra beds and forced tephra into underlying sandstones, forming elongate cones. The large mass fraction of gypsum (now replaced by calcite) in the playa sediments suggests a huge, long-distance delivery of sulphate aerosols. Some of the sulphate and tephra may have come from the same eruption, or the fine-grained tephra may simply have aided preservation of dry-fog sulphate derived from an unrelated, effusive eruption of lava.  相似文献   

Sympatric distribution of an Australian salt lake wolf spider and scorpion     

Peter Hudson 《International Journal of Salt Lake Research》1997,6(1):1-3

The South Australian distributions of three species of arachnidendemic to salt lakes is documented. The spiders Lycosa alteripa and L.eyrei have allopatric distributions and L. eyrei and the scorpionAustralobuthus xerolimniorum are sympatrically distributed.  相似文献   

罗布泊盐湖富钾卤水成因再探讨——碎屑层卤水蒸发实验分析   总被引：1，自引：0，他引：1  

孙小虹  刘成林  焦鹏程  颜辉  陈永志  马黎春  张永明  王春连  李文学 《矿床地质》2016,35(6):1190-1204

罗布泊盐湖钙芒硝岩孔隙中蕴藏有超大型规模的卤水钾矿,富钾卤水成因一直备受关注。罗北凹地从统一的罗布泊大湖区中分隔出来后,成盐过程中其湖水仍以南部大湖的补给为主,罗北凹地卤水化学演化与"大耳朵"湖水密切相关。"大耳朵"湖区含石膏碎屑层普遍储藏有卤水,应该是罗北凹地盐湖的"源卤水",钾离子(ρ(K~+)为3.12 g/L左右)已初步富集,平均矿化度为198.83 g/L。为了查明该卤水的化学演化趋势及析盐序列,笔者于2009年、2010年两次采集了大量卤水样品,分别进行室内等温蒸发和自然蒸发实验。蒸发实验结果表明:随着卤水浓缩首先析出(硬)石膏,随后析出大量石盐,最后出现少量钾石盐和光卤石,与EQL/EVP卤水蒸发模型模拟结果相似。将碎屑层卤水蒸发过程中化学组成变化与罗北凹地卤水进行对比,结果显示罗布泊古湖水蒸发至石膏沉积之后,在罗北凹地水化学组成明显发生变化,没有大量石盐沉积,而以钙芒硝沉积为主。推测应是受到深部"富钙水"的持续补给,而"大耳朵"湖起到"预备盆地"的作用,罗布泊古湖水经"大耳朵"湖蒸发浓缩后,钾离子得到初步富集,在流入罗北凹地后与深部"富钙"水混合,强烈蒸发浓缩,大量钙芒硝矿物析出,最后形成富钾卤水。  相似文献   

The macrobenthic fauna of a former perennial and now episodically filled mexican saline lake     

Javier Alcocer  Alfonso Lugo  Elva Escobar  Malinali Sánchez 《International Journal of Salt Lake Research》1996,5(3):261-274

Totolcingo (El Carmen), a large and now episodically filled playa lake in the east-ernmost portion of the Mexican Plateau, filled with water in 1993. Water persisted for just one month (May). Alkaline (pH 10), saline (K₂₅ up to 30,000S/cm) waters, dominated by NaHCO₃ and Na₂CO₃, characterized the lake. The fauna was depauperate. The components of the fauna wereEphydra (Hydropyrus)hians Say (ephydrid),Limnodrilus hoffmeisteri Claparède (tubificid), andBerosus sp. (Coleoptera). The species in the lake were widely dispersed and typical inhabitants of saline lakes. Possible reasons for the depauperate fauna include (a) overall physical and chemical conditions, (b) unpredictable hydrology, and (c) the short (one month) inundation period prevented colonization.  相似文献   

Dryland continental mudstones: Deciphering environmental changes in problematic mudstones from the Upper Triassic (Carnian to Norian) Mercia Mudstone Group,south‐west Britain     

Paul Milroy  V. Paul Wright  Michael J. Simms 《Sedimentology》2019,66(7):2557-2589

The sedimentology, petrography and mineralogy of the seemingly monotonous Late Triassic Mercia Mudstone Group across the Severn Basin and Bristol Channel region reveals a bipartite division of mudrock facies above and below the Arden Sandstone Formation. Frequently cryptic sedimentary and pedogenic features reveal diverse alluvial, aeolian, playa‐lacustrine and pedogenic processes operating at different times, locations and scales probably in response to climate change. The current study found no evidence of significant marine influence in either of the two mudrock facies associations that are described here. Blocky claystones dominate the lower Mercia Mudstone Group (Sidmouth Mudstone Formation), with pedogenic features such as slickensides, mottling, tubules and carbonate/sulphate nodules common and widespread. The claystones are of alluvial/lacustrine origin with subordinate sheet sandstones, themselves overprinted by pedogenic features, reflecting occasional high intensity rainfall events. These facies reflect a seasonal (wet/dry) semi‐arid climate favouring development of transformed/neoformed (smectite‐rich) clay minerals of intrabasinal origin. Massive to weakly stratified silty mudstones dominate the upper Mercia Mudstone Group (Branscombe Mudstone Formation). Commonly conchoidally weathered, locally gypsiferous, but with distinct sedimentary structures scarce, they alternate with subordinate blue‐grey laminated silty mudstones. Together they reflect fluctuating hydrological conditions within extensive saline mudflats and ephemeral playa lakes, with laminated facies deposited under subaqueous conditions during more humid phases whereas massive mudstones reflect modification through interstitial growth/dissolution of sulphates and deflation of surface sediments during drier episodes. These facies reflect increased aridity during deposition of the upper Mercia Mudstone Group compared with the lower Mercia Mudstone Group, favouring development of detrital/transformed (illite–chlorite) clay minerals of extrabasinal origin. The described facies associations and the sedimentary fabrics and structures that characterize them, occur widely in the Mercia Mudstone Group across the United Kingdom and comparable facies associations may be anticipated in other fine‐grained red bed successions. Recognition of these facies may aid palaeoenvironmental interpretation of such sequences on Earth and, potentially, on Mars also.  相似文献   

Climate–surface–pore‐water interactions on a salt crusted playa: implications for crust pattern and surface roughness development measured using terrestrial laser scanning          下载免费PDF全文

Joanna M. Nield  Giles F. S. Wiggs  James King  Robert G. Bryant  Frank D. Eckardt  David S. G. Thomas  Richard Washington 《地球表面变化过程与地形》2016,41(6):738-753

Sodium accumulating playas (also termed sodic or natric playas) are typically covered by polygonal crusts with different pattern characteristics, but little is known about the short‐term (hours) dynamics of these patterns or how pore water may respond to or drive changing salt crust patterning and surface roughness. It is important to understand these interactions because playa‐crust surface pore‐water and roughness both influence wind erosion and dust emission through controlling erodibility and erosivity. Here we present the first high resolution (10^?3 m; hours) co‐located measurements of changing moisture and salt crust topography using terrestrial laser scanning (TLS) and infra‐red imagery for Sua Pan, Botswana. Maximum nocturnal moisture pattern change was found on the crests of ridged surfaces during periods of low temperature and high relative humidity. These peaks experienced non‐elastic expansion overnight, of up to 30 mm and up to an average of 1.5 mm/night during the 39 day measurement period. Continuous crusts however showed little nocturnal change in moisture or elevation. The dynamic nature of salt crusts and the complex feedback patterns identified emphasize how processes both above and below the surface may govern the response of playa surfaces to microclimate diurnal cycles. © 2015 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

1976-2015年柴达木盆地湖泊演变及其对气候变化和人类活动的响应   总被引：3，自引：0，他引：3  

段水强 《湖泊科学》2018,30(1):256-265

柴达木盆地众多的湖泊不仅对维持当地脆弱的生态环境具有极其重要的作用,而且中心盐湖也是重要的矿产资源.进入21世纪以来,受气候变化和人类活动的共同影响,盆地湖泊发生了一系列重大变化.为科学认识这一问题,选取了1976-2015年6期Landsat系列卫星影像,解译了该区域1 km²以上的湖泊水面,并分析了湖泊变化对气候和人类活动的响应.结果表明：柴达木盆地湖泊面积总体上存在扩张（1976-1990年）萎缩（1990-2000年）扩张（2000-2010年）萎缩（2010-2015年）4个阶段的变化过程,2010年湖泊面积最大,2015年湖泊又明显萎缩.就气候水文因素而言,湖泊面积变化主要受山区降水径流的影响.湖面变化与前3 a的降水径流关系最为密切.进入21世纪以来,气候变化与上游社会经济耗水、盐湖周边人为阻隔河湖连通、开采卤水、修建人工盐田、排放老卤等人类活动,对盆地中心湖泊的空间格局、面积都产生了显著影响,苦水沟、达布逊湖南部形成了新湖泊,鸦湖、团结湖面积显著扩大,东、西台吉乃尔湖逐渐萎缩、干涸,一里平湖由以前的干盐湖在2010年一跃成为盆地最大的湖泊.针对盐湖大规模开发产生的负面影响,提出了合理开发盐湖资源的建议.  相似文献