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Calcite dendrite crystals are important but poorly understood components of calcite travertine that forms around many hot springs. The Lýsuhóll hot-spring deposits, located in western Iceland, are formed primarily of siliceous sinters that were precipitated around numerous springs that are now inactive. Calcite travertine formed around the vent and on the discharge apron of one of the springs at the northern edge of the area. The travertine is formed largely of two types (I and II) of complex calcite dendrite crystals, up to 1 cm high, that grew through the gradual addition of trilete sub-crystals. The morphology of the dendrite crystals was controlled by flow direction and the competition for growth space with neighbouring crystals. Densely crowded dendrites with limited branching characterize the rimstone dams whereas widely spaced dendrites with open branching are found in the pools. Many dendrite bushes in the pools nucleated around plant stems. Growth of the dendrite crystals was seasonal and incremental. Calcite precipitation was driven by rapid CO2 degassing of CO2-rich spring waters during the spring and summer. During winter, when snow covered the ground and temperatures were low, opal-A precipitated on the exposed surfaces of the dendrites. Segmentation of dendrite branches by discontinuities coated with opal-A and overgrowth development around sub-crystals resulted from this seasonal growth cycle. The calcite dendrite crystals in the Lýsuhóll travertine differ in morphology from those at other hot springs, such as those at Lake Bogoria, Kenya, and Waikite in New Zealand. Comparison with the calcite dendrite crystals found at those sites shows that dendrite morphology is site-specific and probably controlled by carbonate saturation levels that, in turn, are controlled by the rate of CO2 degassing and location in the spring outflow system. 相似文献
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英国约克郡( Yo rkshire Dale)国家公园钙华苔藓植物群落研究 总被引：8，自引：0，他引：8
报道英国约克郡国家公园5个钙华沉积地点苔藓植物群落调查结果。该区域钙华苔藓群落共13个,由12科15属18种组成。区系地理成分由北温带和世界广布两种成分组成;生活型以垫状矮丛集型和交织型占优势。根据钙华沉积环境特征,划分Cron钙华苔藓群落、洞穴钙华苔藓群落、瀑华苔藓群落、峭壁钙华苔藓群落和泉华苔藓群落等5种类型。调查结果表明,研究区现代苔藓植物群落钙华沉积作用十分显著。 相似文献
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Sedimentology of coexisting travertine and tufa deposits in a mounded geothermal spring carbonate system,Obruktepe, Turkey 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Benjamin Lopez Gilbert Camoin Mehmet Özkul Rudy Swennen Aurélien Virgone 《Sedimentology》2017,64(4):903-931
The recent discoveries of deeply buried Cretaceous reservoir bodies in the Atlantic Ocean revealed that relationships between the distribution of spring carbonate deposits and faults are poorly understood. The well‐exposed Quaternary deposits at Obruktepe (Denizli Basin, Turkey) provide an opportunity to reconstruct the three‐dimensional sedimentary architecture of such a system. Integration of sedimentological, lithofacies and geochemical analyses reveals complexity in the lateral relationships between sedimentary environments, faults and geothermal spring carbonates. Five environmental systems are distinguished based on the lithofacies analysis: (i) vent; (ii) smooth slope; (iii) travertine‐terrace; (iv) tufa‐barrage; and (v) flood systems. Encrusting, baffling and settling sedimentary processes are reflected in data acquired at several scales, from lithofacies observations to the morphology and arrangement of geobodies, together with microfabrics and stable carbon and oxygen isotope data. Mean values of +4·9‰ δ13C and −8·74‰ δ18O Vienna PeeDee Belemnite reflect geothermal circulation of springwaters. The environmental distribution and lithofacies indicate a lateral continuum between travertine and tufa deposits within this hot spring system. This finding supports two depositional models in which water flow variation is the main control on both CaCO3 precipitation and the resulting formation of travertine and tufa. The proposed models address the factors responsible for the development of these complex mound‐shaped carbonate spring deposits, and how they are related to fluid circulation at depth and in association with faults. 相似文献
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Bands of large (up to 4 cm long) three-dimensional crystallographic dendrites form the terrace fronts in an old travertine mound exposed near Clinton, British Columbia. The dendrites, with their long axes perpendicular to the terrace front, are characterized by numerous levels of branching. Each branch is formed of multitudes of skeletal rhombs, four- and six(?)-sided bipyramidal crystals, or prismatic hexagonal crystals that are precisely aligned along crystallographic precepts. Although individual branches are formed of one type of subcrystal, neighbouring branches may be formed of different subcrystal types.Highly supersaturated waters that were generated by rapid CO2 degassing of the spring water during its turbulent flow over the steep terrace fronts probably drove dendrite precipitation. The presence of growth lines indicates that growth was episodic. Type I growth lines probably formed annually in response to seasonal climate changes whereas Type II growth lines, which formed less frequently, may reflect changes in the flow velocity and/or flow patterns of the spring waters.Early diagenetic modification of the dendrites involved crystal face enlargement, cements formed of trigonal prisms or needle-fiber crystals, microbial infestation that mediated substrate dissolution, and/or deposition of detrital calcite crystals that formed in the water column. Much of the diagenetic modification may have taken place during the periods when the dendrites had temporarily stopped growing.The dendrites in the Clinton travertine are an excellent example of complex, episodic calcite crystal growth that was extensively modified by early diagenetic processes in a surface environment. The same spring waters from which the dendrites were precipitated mediated much of the early diagenesis. 相似文献
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The Urrea de Jalón tufa deposits constitute the 20‐ to 50‐m‐thick caprock (0·3 km2) of an isolated mesa. They disconformably overlie horizontal strata of the Tertiary Ebro Basin (NE Spain), which contains a thick succession of lacustrine gypsum and marls, followed by limestones, marls and, locally, fluvial sandstones and mudstones. The tufa deposits show a complex, large‐scale framework of basin‐like structures with centripetal dips that decrease progressively from the base to the top of the tufa succession, and beds that thicken towards the centre of the structure (cumulative wedge‐out systems). These geometries reveal that the tufa deposits were affected by differential synsedimentary subsidence. Distinct onlapping depressions reflect time migration of the subsiding areas. The studied carbonates are composed mostly of low‐Mg calcite, with minor quartz. Some samples have anomalously high contents of Fe, Mn and Ba that may exceed 1% (goethite, haematite and barite are present). Carbonate facies are: (a) macrophyte encrustation deposits; (b) bryophyte build‐ups; (c) oncolite and coated grain rudstones; (d) non‐concentric stromatolite‐like structures; (e) massive or bioturbated biomicrites; and (f) green and grey marls. Facies a and c show a great variety of microbial‐related forms. These facies can be arranged in dm‐ to 2‐m‐thick vertical associations representing: (i) fluvial–paludal sequences with bryophyte growths; (ii) pond‐influenced fluvial sequences; and (iii) lacustrine–palustrine sequences. The Urrea de Jalón tufa deposits formed in a fluvio‐lacustrine environment that received little alluvial sediment supply. Isotope compositions (δ13C and δ18O) reveal meteoric signatures and accord with such a hydrologically open system of fresh waters. The Fe, Mn and Ba contents suggest an additional supply of mineralized waters that could be related to springs. These would have been discharge points in the Ebro Depression of a regional aquifer of the Iberian Ranges. Rising groundwater caused the solution of the underlying evaporites and the synsedimentary subsidence of the tufa deposits. 相似文献
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Mounds that have formed around spring vents occur in a variety of environmental settings, many at sites generally difficult or inaccessible for sampling. In contrast, over 500 tufa mounds occur in the dry bed of Searles Lake, California. The mounds range from minor features to 45 m in height; most are 5 to 12 m high. These mounds, composed of calcite and aragonite, formed associated with spring vents in the Pleistocene lake bottom. Thus, analyses of these mounds in Searles Lake provide a model with regard to the origin and architecture of tufa mounds. The mounds consist of four distinctive tufa facies. The initial deposits consist of porous tufa, including the innermost (porous 1) and the outermost (porous 2) deposits, followed by nodular tufa, then columnar tufa, and laminated crusts. There are two simple sequences of tufa deposition. The first sequence is from porous 1 to nodular to laminated crusts and, finally, to porous 2. A second sequence consists of: porous 1 to columnar to laminated crusts and, lastly, to porous 2. Facies changes are a response to changes in environmental conditions from deep water (porous 1 facies) to an essentially dry lake phase (during and after the formation of laminated crusts facies), to deep water (porous 2 facies) and, at the present time, totally dry. The primary constituents that comprise the tufa deposits include thin laminae, pisoids, spherulites, peloids and stromatolite‐like crusts. On the microscopic scale, these constituents dominantly make up nano‐spheres, micro‐rods and rod‐like crystals, as well as other calcified bodies. These constituents are interpreted to be the calcified remains of bacterial bodies. These findings suggest that microbial participation in the construct of other mounds should be a major concern of investigation, both for terrestrial and extraterrestrial spring‐fed mounds. 相似文献
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The Condat tufa is a localised deposit, reaching 8.2m in thickness, composed of freshwater carbonates deposited in a complex series of environments which include marsh, spring and stream facies. Five radiocarbon determinations had previously been obtained from different stratigraphic levels within the tufa and had given a consistent series, ranging from 12320 ± 175 BP to 31050 ± 1500BP. Although the youngest two dates, from near the surface of the tufa, had been rejected as being anomalously young, the older dates were regarded as indicating tufa formation during the last cold stage. Biostratigraphic analyses of the molluscan and ostracod faunas, presented here, demonstrate that the tufa formed under fully temperate conditions throughout. The occurrence of certain snails that are either locally extinct (e.g. Belgrandia marginata) or unknown living in western France (e.g. Daudebardia brevipes), together with the geomorphological setting, suggest that the tufa is of interglacial age. New radiocarbon determinations of the Condat tufa all proved to be >33 Ka BP and support this conclusion. 相似文献
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A relict mound of Holocene barite (BaSO4) tufa underlies the Flybye Springs, a small, barium‐rich, cold sulphur spring system in the Northwest Territories of Canada. The tufa is composed of relatively pure barite with ≤0·34 wt% Ca2+ and ≤0·77 wt% Sr2+. The mound is made up of coated bubble, raft, undulatory sheet, stromatolitic, coated grain and detrital conglomerate barite tufa. Although previously unreported in barite, these lithotypes are akin to facies found in many carbonate spring deposits. Raft and ooid‐coated grain tufa was formed via ‘inorganic’ barite precipitation in spring water ponds and tributaries where rapid oxidation of sulphide to sulphate established barite supersaturation. Undulatory sheet tufa may have formed by the reaction of dissolved barium with sulphate derived from the oxidation of extracellular polysaccharide‐rich colloidal sulphur films floating in oxygenated, barite‐saturated spring water ponds. Coated bubble, oncoid‐coated grain and stromatolitic tufa with filamentous microfossils was formed in close association with sulphur‐tolerant microbes inhabiting dysoxic and oxygenated spring water tributaries and ponds. Adsorption of dissolved barium to microbial extracellular polysaccharide probably facilitated the development of these ‘biogenic’ lithotypes. Detrital conglomerate tufa was formed by barite cementation of microdetrital tufa, allochthonous lithoclasts and organic detritus, including caribou hair. Biogenic textures, organic artefacts and microfossils in the Flybye barite tufa have survived diagenetic aggradational recrystallization and precipitation of secondary cements, indicating the potential for palaeoecological information to be preserved in barite in the geological record. Similarities between the Flybye barite tufa and carbonate spring deposits demonstrate that analogous textures can develop in chemical sedimentary systems with distinct mineralogy, biology and physiochemistry. 相似文献
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J. B. Murton A. Baker D. Q. Bowen C. J. Caseldine G. R. Coope A. P. Currant J. G. Evans M. H. Field C. P. Green J. Hatton M. Ito R. L. Jones D. H. Keen M. P. Kerney R. McEwan D. F. M. McGregor D. Parish J. E. Robinson D. C. Schreve P. L. Smart 《Quaternary Science Reviews》2001,20(18)
River-channel and colluvial deposits, near Marsworth, Buckinghamshire, record a temperate-periglacial-temperate sequence during the late Middle Pleistocene. The deposits of a lower channel contain tufa clasts bearing leaf impressions that include Acer sp., and Sorbus aucuparia and containing temperate arboreal pollen attributed to ash-dominated woodland. The tufa probably formed at the mouth of a limestone spring before being redeposited in a small river whose deposits contain plant remains, Mollusca, Coleoptera, Ostracoda and vertebrate bones of temperate affinities. The sediments, sedimentary structures and limited biological remains above the Lower Channel deposits indicate that fluvial deposition preceded climatic cooling into periglacial conditions. Fluvial deposition recurred during a later temperate episode, as shown by the mammalian bone assemblage in stratigraphically higher channel deposits. The Upper Channel deposits are confidently attributed to Oxygen Isotope Sub-Stage 5e (Ipswichian) on the basis of their vertebrate remains. However, the age of the Lower Channel deposits is less clear. The mammalian and coleopteran remains in the Lower Channel strongly suggest correlation with Oxygen Isotope Stage 7 on the basis of their similarities to other sites whose stratigraphy is better known and the clear difference of the Lower Channel assemblage from well-established faunas of Ipswichian or any other age. By contrast, U–Th dating of the tufa clasts suggests an age post 160 ka BP, while Aile/Ile ratios on Mollusca point to an Ipswichian age and younger. Four ways of interpreting this age discrepancy are considered, the preferred one correlating the Lower Channel deposits with Oxygen Isotope Stage 7. 相似文献
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尼雄地区早白垩世磁铁矿以成矿岩体及矿床研究偏多,忽略围岩时代及其成矿地质背景分析。尼雄早白垩世磁铁矿可分为矽卡岩型和热液脉型,而达及藏布地区热液脉型磁铁矿与基性岩脉密切相关,通过共生辉长岩岩脉锆石U-Pb年龄(120.1±1.7 Ma)限定热液脉型磁铁矿成矿时代约120 Ma,与已经确定成矿时代的矽卡岩型铁矿成矿时代一致,指示尼雄矿田两种类型磁铁矿受控于相同的地质背景。通过尼雄岩体碎屑岩围岩(原上二叠统敌布错组)碎屑锆石测年,获得其沉积时代介于130～120 Ma之间,故将上二叠统敌布错组重新厘定为下白垩统则弄群。结合区域地层及岩浆岩新资料,认为冈底斯中部则弄群火山岩与侵位于其中的岩体构成一个早白垩世火山-侵入杂岩体系,其与尼雄矿田早白垩世磁铁矿密切相关。该早白垩世火山-侵入杂岩地球化学特征及尼雄附近浅表层次构造共同指示冈底斯中部在早白垩世处于伸展构造背景。最后,依据伸展构造背景新认识建立了尼雄地区早白垩世磁铁矿成矿地质模型。 相似文献
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In the periods 1980–1986 and 1990–2007 many boreholes were sunk during hydrogeological investigations in the center of the
Karlovy Vary (Carlsbad) hot spring system. The extent and the depths reached were the greatest in the history of the geological
investigation of the discharge area of the thermal system. The results of the drilling program enabled a detailed study of
the rocks, groundwater and spring sedimentation in the area as well as the preparation of new proposals for changes in the
spring-protection zones. The spring sedimentation consists of world-renowned hot spring travertine, with a wide range of morphological
varieties of different origins and of different ages. The oldest U-series age data (230 ± 14 ka BP) have been obtained for
travertine relicts located 22 m above the present-day bottom of the narrow valley of the Teplá River. Five other travertine
deposits, partly overlapping in space and time were identified on the bottom and slopes of the valley. They were formed by
gradual growth, by river erosion and since the fourteenth century by human activities. 相似文献
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A preliminary analysis of the formation of travertine and travertine cones in the Jifei hot spring,Yunnan, China 总被引：3，自引：2，他引：1
Yaping Liu Xun Zhou Bin Fang Haiyan Zhou Tsutomu Yamanaka 《Environmental Earth Sciences》2012,66(7):1887-1896
The Jifei hot spring emerges in the form of a spring group in the Tibet–Yunnan geothermal zone, southwest of Yunnan Province, China. The temperatures of spring waters range from 35 to 81°C and are mainly of HCO3–Na·Ca type. The total discharge of the hot spring is about 10 L/s. The spring is characterized by its huge travertine terrace with an area of about 4,000 m2 and as many as 18 travertine cones of different sizes. The tallest travertine cone is as high as 7.1 m. The travertine formation and evolution can be divided into three periods: travertine terrace deposition period, travertine cone formation period and death period. The hydrochemical characteristics of the Jifei hot spring was analyzed and compared with a local non-travertine hot spring and six other famous travertine springs. The results indicate that the necessary hydrochemical conditions of travertine and travertine cones deposition in the Jifei area are (1) high concentration of HCO3 − and CO2; (2) about 52.9% deep source CO2 with significantly high value; (3) very high milliequivalent percentage of HCO3 − (97.4%) with not very high milliequivalent percentage of Ca2+ (24.4%); and (4) a large saturation index of calcite and aragonite of the hot water. 相似文献
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Travertine formation in Plitvice National Park, Yugoslavia: chemical versus biological control 总被引：5，自引：1，他引：5
Hydrochemical studies of the Plitvice Lakes and their tributaries (Croatia/Yugoslavia) were coupled with micromorphological investigations on carbonate lake sediments and recent travertines. Karst springs discharge water from aquifers in Triassic and Jurassic dolomites and limestones and collect in lakes, which are ponded behind accreting travertine dams. Waters at springs have a high CO2 partial-pressure (greater than 7000 ppm) and are slightly undersaturated with respect to calcite (saturation index less than —0·03). CO2 partial pressure is quickly reduced in swift running streams, leading to very high supersaturation with carbonate minerals (saturation indices between 0·74 and 0·53). Calcite deposition, however, is restricted to the lake bottoms (formation of lake marl) and to the tufa dams. The annual carbonate precipitating capacity of the system based on water balance and downstream loss of dissolved ions is estimated to be on the order of 10 000 t CaCO3 as cascade deposits (tufa dams) or as micrite in lakes behind the travertine dams. The initial stages of travertine formation as a result of morphological, biological, and chemical factors are (i) moss settling on small ridges in the creek courses, (ii) epiphytes (diatoms and cyanobacteria) settling on the moss surface, (iii) micrite particles resuspending from lake bottoms and being trapped on mucous excretions from bacteria and diatoms, and (iv) inorganic calcite precipitating as sparite at nucleation sites provided by these crystal seeds. Geochemical studies of the lake marl and tufa dams show that amino acids are dominated by aspartic acid. Carbohydrates come from structural polysaccharides of diatoms. The sticky excretions, rich in aspartic acid, are necessary for the initiation of calcite precipitation. They may be a response of algal and bacterial metabolism to environmental stress by either nutrient depletion or high calcium concentrations in ambient waters. The formation of tufa and micrite (lake marl) appears to be initiated by localized biological factors and is not governed by mere calcite supersaturation of the water. Oligotrophy may be an essential precondition for the formation of fresh water carbonate deposits. 相似文献
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A sedimentary facies model for stepped,fluvial tufa systems in the Iberian Range (Spain): the Quaternary Piedra and Mesa valleys 总被引：1，自引：0，他引：1
Stratigraphic and sedimentological analyses of the Quaternary tufa and associated deposits in the Piedra and Mesa river valleys allowed a number of stages of their sedimentary evolution to be characterized, and a depositional sedimentary model for this north‐central sector of the Iberian Range (Spain) to be established. The proposed sedimentary facies model may explain tufa arrangements in other medium to high gradient, stepped, fluvial tufa systems with narrow transverse profiles occurring in temperate, semi‐arid areas, in both recent and past scenarios. There are several tufa deposits within the Piedra and Mesa river valleys that, over a maximum thickness of about 90 m, record one or more stages of tufa deposition produced following the fluvial incision of the bedrock or previous tufa deposits. Each depositional stage begins with coarse detrital sedimentation. Six fundamental, vertical sequences of tufa facies with small amounts of detrital material reveal the sedimentary processes that occurred in different fluvial environments: channel areas with: (i) free‐flowing water; (ii) barrages and/or cascades; and (iii) dammed water and palustrine floodplains. The proposed sedimentary model involves narrow, stepped, fluvial valleys in which tufa cascades were common. Alternating intervals of bryophyte and stromatolite facies commonly formed at some cascades. Many of these represented barrage‐cascade structures that consisted of phytoclast rudstones, thick phytoherms of mosses and associated stromatolites, and curtain‐shaped phytoherms of stems. Upstream of these structures, dammed areas with bioclastic sands and silts developed and palustrine vegetation grew. The channel stretches between barrages and/or cascades were loci for extensive stromatolite growth in fast flowing water. The palustrine floodplain was home to pools and drainage channels. The model also explains the growth of some barrages in the River Piedra that surpassed the height of the divide, with the diffluence of the main channel into a secondary course forming other tufa deposits in the area. The distribution and abundance of certain types of tufa facies in fluvial basins may be an indicator of differences in their gradients. The facies studied in this work suggest that the gradient of the ancient River Piedra was steeper than that of the ancient River Mesa. Assuming similar scenarios for climate and hydrology, the depositional settings mentioned above and their dimensions would have been determined mainly by the gradient and width of the associated river valleys. This sedimentary model may also be useful for inferring variations in other river basin slopes, as well as accounting for the presence of tufas in areas that normally have no permanent water input. 相似文献
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Influence of microbial photosynthesis on tufa stromatolite formation and ambient water chemistry, SW Japan 总被引：1，自引：0，他引：1
Photosynthetic influences on tufa stromatolite formation and ambient water chemistry were investigated at two well-studied streams depositing tufa in Southwestern Japan (Shirokawa and Shimokuraida). The tufa stromatolites in both streams are composed of fine-grained calcite crystals showing annual lamination, and colonized by a number of filamentous cyanobacteria as well as non-phototrophic bacteria. Microelectrode measurements of pH, O2, and Ca2+ near the stromatolite surface (the diffusive boundary layer; DBL) revealed that the investigated tufa stromatolites are formed by photosynthesis-induced CaCO3 precipitation (PCP): cyanobacterial photosynthesis induces calcite precipitation under light conditions, while respiration of cyanobacteria and non-phototrophic bacteria inhibits precipitation in the dark. The bulk water chemistry at the lower sites of the investigated streams showed the daytime decreases of Ca2+ concentration and alkalinity that was expected for significant influence of PCP, while the other expected change, increased pH, was not observed. In order to examine this discrepancy, a novel approach using semi-in situ microelectrode measurements was applied to perform precise quantitative calculations. The calculation results demonstrated that the observed Ca2+ concentration and alkalinity decreases were caused by PCP, and that the concomitant pH increase was expected to be under the detection level of a conventional pH meter. Although the amount of PCP is supposed to be significantly affected by light intensity, observations in Shimokuraida revealed that the amount of PCP on cloudy day nonetheless accounted for about 80% of that on sunny day. Despite the significant role of PCP for tufa stromatolite formation, PCP accounted for only about 10% of the precipitated calcite in the investigated streams, which indicates that tufa stromatolites, the characteristic deposits in the streams, are responsible for only a small portion of calcite precipitation, and the rest is considered to precipitate inorganically at biofilm-free substrates. 相似文献
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塔里木盆地苏盖特布拉克地区下寒武统肖尔布拉克组发育3种类型碳酸盐岩微生物（蓝细菌）建造,即下部微生物丘状和层状建造、中上部微生物礁和顶部叠层石建造。微生物丘状和层状建造的特点是似层状孔洞和纹层结构发育,形成于潮下高能带,与微生物席粘结有关,分布相对稳定。微生物礁是由枝状或丛状微生物骨架生长和微生物席粘结两种方式形成,分布较广,可分为两大期：第1大期发育在海退背景下,呈宏观块状建造特征;第2大期则发育在较大的海侵背景下,呈现两期点礁特征。叠层石建造发育在更大范围的海侵背景下,超覆于点状建造之上,要求的水动力条件相对较强,由微生物粘结作用形成,其中叠层石和核形石是其重要标志,仅分布在研究区北部的苏Ⅱ、苏Ⅲ和苏Ⅳ剖面近顶部。 相似文献