Tufa is a variety of limestone formed when carbonate mineralsprecipitate out of water in unheated rivers or lakes. Geothermally heated hot springs sometimes produce similar (but less porous) carbonate deposits, which are known as travertine. Tufa is sometimes referred to as (meteogene) travertine.[1] It should not be confused with hot spring (thermogene) travertine. Tufa, which is calcareous, should also not be confused with tuff, a porous volcanic rock with a similar etymology that is sometimes also called "tufa".
Modern and fossil tufa deposits abound with wetland plants;[2] as such, many tufa deposits are characterised by their large macrobiological component, and are highly porous. Tufa forms either in fluvial channels or in lacustrine environments. Ford and Pedley (1996)[3] provide a review of tufa systems worldwide.
Deposits can be classified by their depositional environment (or otherwise by vegetation or petrographically). Pedley (1990)[4] provides an extensive classification system, which includes the following classes of fluvial tufa:
Spring – Deposits form on emergence from a spring/seep. Morphology can vary from mineratrophic wetlands to spring aprons (see calcareous sinter)
Braided channel – Deposits form within a fluvial channel, dominated by oncoids (see oncolite)
Cascade – Deposits form at waterfalls, deposition is focused here due to accelerated flow (see Geochemistry)
Barrage – Deposits form as a series of phytoherm barrages across a channel, which may grow up to several metres in height. Barrages often contain a significant detrital component, composed of organic material (leaf litter, branches etc.).
Rubaksa tufa plug, after drying of the river, in Ethiopia
Lacustrine deposits
Lacustrine tufas are generally formed at the periphery of lakes and built-up phytoherms (freshwater reefs), and on stromatolites. Oncoids are also common in these environments.
Calcareous sinter
Although sometimes regarded as a distinct carbonate deposit, calcareous sinter formed from ambient temperature water can be considered a sub-type of tufa.
Calcareous speleothems may be regarded as a form of calcareous sinter. They lack any significant macrophyte component due to the absence of light, and for this reason they are often morphologically closer to travertine or calcareous sinter.
Tufa columns are an unusual form of tufa typically associated with saline lakes. They are distinct from most tufa deposits in that they lack any significant macrophyte component, due to the salinity excluding mesophilic organisms.[3] Some tufa columns may actually form from hot-springs, and may therefore constitute a form of travertine. It is generally thought that such features form from CaCO3 precipitated when carbonate rich source waters emerge into alkaline soda lakes. They have also been found in marine settings in the Ikka fjord of Greenland where the Ikaite columns can reach up to 18 m (59 ft) in height.[5]
Biology
Tufa deposits form an important habitat for a diverse flora. Bryophytes (mosses, liverworts etc.) and diatoms are well represented. The porosity of the deposits creates a wet habitat ideal for these plants.
The Pyramid and Domes tufa rock structures, Pyramid Lake, Nevada
Geochemistry
Modern tufa is formed from alkaline waters, supersaturated with calcite. On emergence, waters degas CO2 due to the lower atmospheric pCO2 (see partial pressure), resulting in an increase in pH. Since carbonate solubility decreases with increased pH,[6] precipitation is induced. Supersaturation may be enhanced by factors leading to a reduction in pCO2, for example increased air-water interactions at waterfalls may be important,[7] as may photosynthesis.[8]
Recently it has been demonstrated that microbially induced precipitation may be more important than physico-chemical precipitation. Pedley et al. (2009)[9] showed with flume experiments that precipitation does not occur unless a biofilm is present, despite supersaturation.
Tufa is occasionally shaped into a planter. Its porous consistency makes it ideal for alpine gardens. A concrete mixture called hypertufa is used for similar purposes.
^Koban, C.G.; Schweigert, G. (1993). "Microbial origin of travertine fabrics - two examples from Southern Germany (Pleistocene Stuttgart travertines and Miocene riedöschingen Travertine)". Facies. 29: 251–263. doi:10.1007/BF02536931. S2CID 129353316.
^ abFord, T.D.; Pedley, H.M. (1996). "A review of tufa and travertine deposits of the world". Earth-Science Reviews. 41 (3–4): 117–175. Bibcode:1996ESRv...41..117F. doi:10.1016/S0012-8252(96)00030-X.
^Pedley, H.M. (1990). "Classification and environmental models of cool freshwater tufas". Sedimentary Geology. 68 (1–2): 143–154. Bibcode:1990SedG...68..143P. doi:10.1016/0037-0738(90)90124-C.
^Buchardt, B.; Israelson, C.; Seaman, P.; Stockmann, G. (2001). "Ikaite tufa towers in ikka fjord, southwest Greenland: their formation by mixing of seawater and alkaline spring water". Journal of Sedimentary Research. 71 (1): 176–189. Bibcode:2001JSedR..71..176B. doi:10.1306/042800710176.
^Bialkowski, S.E. 2004. . Archived from the original on 2009-02-28.
^Zhang, D.; Zhang, Y; Zhu, A.; Cheng, X (2001). "Physical mechanisms of river waterfall tufa (travertine) formation". Journal of Sedimentary Research. 71 (1): 205–216. Bibcode:2001JSedR..71..205Z. doi:10.1306/061600710205.
^Riding, R. (2000). "Microbial carbonates: the geological record of calcified bacterial-algal mats and biofilms". Sedimentology. 47: 179–214. doi:10.1046/j.1365-3091.2000.00003.x.
^Pedley, M.; Rogerson, M.; Middleton, R. (2009). "Freshwater calcite precipitates from in vitro mesocosm flume experiments: a case for biomediation of tufas". Sedimentology. 56 (2): 511–527. Bibcode:2009Sedim..56..511P. doi:10.1111/j.1365-3091.2008.00983.x.
^Forster, A.; Forster, S.C. (1996). "Troglodyte dwellings of the Loire Valley, France". Quarterly Journal of Engineering Geology and Hydrogeology. 29 (3): 193–197. doi:10.1144/GSL.QJEGH.1996.029.P3.01. S2CID 128896993.
^"Au Turonien". Une histoire de la Touraine à travers ses roches (in French). Retrieved 2010-10-01.
tufa, confused, with, tuff, porous, volcanic, rock, also, called, tufa, other, uses, disambiguation, variety, limestone, formed, when, carbonate, minerals, precipitate, water, unheated, rivers, lakes, geothermally, heated, springs, sometimes, produce, similar,. Not to be confused with tuff a porous volcanic rock also called tufa For other uses see Tufa disambiguation Tufa is a variety of limestone formed when carbonate minerals precipitate out of water in unheated rivers or lakes Geothermally heated hot springs sometimes produce similar but less porous carbonate deposits which are known as travertine Tufa is sometimes referred to as meteogene travertine 1 It should not be confused with hot spring thermogene travertine Tufa which is calcareous should also not be confused with tuff a porous volcanic rock with a similar etymology that is sometimes also called tufa Tufa columns at Mono Lake California Contents 1 Classification and features 1 1 Fluvial deposits 1 2 Lacustrine deposits 1 3 Calcareous sinter 1 4 Speleothems 1 5 Columns 2 Biology 3 Geochemistry 4 Occurrence 5 Uses 6 See also 7 References 8 External linksClassification and features EditModern and fossil tufa deposits abound with wetland plants 2 as such many tufa deposits are characterised by their large macrobiological component and are highly porous Tufa forms either in fluvial channels or in lacustrine environments Ford and Pedley 1996 3 provide a review of tufa systems worldwide Barrage Tufa at Cwm Nash South Wales Fluvial deposits Edit Deposits can be classified by their depositional environment or otherwise by vegetation or petrographically Pedley 1990 4 provides an extensive classification system which includes the following classes of fluvial tufa Spring Deposits form on emergence from a spring seep Morphology can vary from mineratrophic wetlands to spring aprons see calcareous sinter Braided channel Deposits form within a fluvial channel dominated by oncoids see oncolite Cascade Deposits form at waterfalls deposition is focused here due to accelerated flow see Geochemistry Barrage Deposits form as a series of phytoherm barrages across a channel which may grow up to several metres in height Barrages often contain a significant detrital component composed of organic material leaf litter branches etc Rubaksa tufa plug after drying of the river in Ethiopia Lacustrine deposits Edit Lacustrine tufas are generally formed at the periphery of lakes and built up phytoherms freshwater reefs and on stromatolites Oncoids are also common in these environments Calcareous sinter Edit Although sometimes regarded as a distinct carbonate deposit calcareous sinter formed from ambient temperature water can be considered a sub type of tufa Huanglong Sichuan China Speleothems Edit Calcareous speleothems may be regarded as a form of calcareous sinter They lack any significant macrophyte component due to the absence of light and for this reason they are often morphologically closer to travertine or calcareous sinter Tufa at Trona Pinnacles California Columns Edit Tufa columns are an unusual form of tufa typically associated with saline lakes They are distinct from most tufa deposits in that they lack any significant macrophyte component due to the salinity excluding mesophilic organisms 3 Some tufa columns may actually form from hot springs and may therefore constitute a form of travertine It is generally thought that such features form from CaCO3 precipitated when carbonate rich source waters emerge into alkaline soda lakes They have also been found in marine settings in the Ikka fjord of Greenland where the Ikaite columns can reach up to 18 m 59 ft in height 5 Biology EditTufa deposits form an important habitat for a diverse flora Bryophytes mosses liverworts etc and diatoms are well represented The porosity of the deposits creates a wet habitat ideal for these plants The Pyramid and Domes tufa rock structures Pyramid Lake NevadaGeochemistry EditModern tufa is formed from alkaline waters supersaturated with calcite On emergence waters degas CO2 due to the lower atmospheric p CO2 see partial pressure resulting in an increase in pH Since carbonate solubility decreases with increased pH 6 precipitation is induced Supersaturation may be enhanced by factors leading to a reduction in p CO2 for example increased air water interactions at waterfalls may be important 7 as may photosynthesis 8 Recently it has been demonstrated that microbially induced precipitation may be more important than physico chemical precipitation Pedley et al 2009 9 showed with flume experiments that precipitation does not occur unless a biofilm is present despite supersaturation Calcite is the dominant mineral precipitate followed by the polymorph aragonite citation needed Tufa dam in Chelekwot EthiopiaOccurrence EditTufa is common in many parts of the world including Pyramid Lake Nevada US tufa formations Big Soda Lake Nevada US tufa formations only a century old Mono Lake California US tufa columns Trona Pinnacles California US tufa columns Matlock Bath Derbyshire United Kingdom North Dock Tufa United Kingdom Plitvice Lakes National Park Croatia Basturs Lakes Pallars Jussa Catalonia tufa mounds Various parts of Armenia such as Artik The southwestern coastline of Western Australia Near Groot Marico in the North West Province South Africa The Kadishi Tufa Blyde River Canyon Mpumalanga Province South AfricaSome sources suggest that tufa was used as the primary building material for most of the chateaux of the Loire Valley France This results from a mis translation of the terms tuffeau jaune and tuffeau blanc which are porous varieties of the Late Cretaceous marine limestone known as chalk 10 need quotation to verify 11 failed verification Uses EditTufa is occasionally shaped into a planter Its porous consistency makes it ideal for alpine gardens A concrete mixture called hypertufa is used for similar purposes See also EditList of types of limestone Limestone deposits listed by locationReferences Edit Pentecost A 2005 Travertine Dordrecht Netherlands Kluwer Academic Publishers Group ISBN 1 4020 3523 3 Koban C G Schweigert G 1993 Microbial origin of travertine fabrics two examples from Southern Germany Pleistocene Stuttgart travertines and Miocene riedoschingen Travertine Facies 29 251 263 doi 10 1007 BF02536931 S2CID 129353316 a b Ford T D Pedley H M 1996 A review of tufa and travertine deposits of the world Earth Science Reviews 41 3 4 117 175 Bibcode 1996ESRv 41 117F doi 10 1016 S0012 8252 96 00030 X Pedley H M 1990 Classification and environmental models of cool freshwater tufas Sedimentary Geology 68 1 2 143 154 Bibcode 1990SedG 68 143P doi 10 1016 0037 0738 90 90124 C Buchardt B Israelson C Seaman P Stockmann G 2001 Ikaite tufa towers in ikka fjord southwest Greenland their formation by mixing of seawater and alkaline spring water Journal of Sedimentary Research 71 1 176 189 Bibcode 2001JSedR 71 176B doi 10 1306 042800710176 Bialkowski S E 2004 Use of Acid Distributions in Solubility Problems Archived from the original on 2009 02 28 Zhang D Zhang Y Zhu A Cheng X 2001 Physical mechanisms of river waterfall tufa travertine formation Journal of Sedimentary Research 71 1 205 216 Bibcode 2001JSedR 71 205Z doi 10 1306 061600710205 Riding R 2000 Microbial carbonates the geological record of calcified bacterial algal mats and biofilms Sedimentology 47 179 214 doi 10 1046 j 1365 3091 2000 00003 x Pedley M Rogerson M Middleton R 2009 Freshwater calcite precipitates from in vitro mesocosm flume experiments a case for biomediation of tufas Sedimentology 56 2 511 527 Bibcode 2009Sedim 56 511P doi 10 1111 j 1365 3091 2008 00983 x Forster A Forster S C 1996 Troglodyte dwellings of the Loire Valley France Quarterly Journal of Engineering Geology and Hydrogeology 29 3 193 197 doi 10 1144 GSL QJEGH 1996 029 P3 01 S2CID 128896993 Au Turonien Une histoire de la Touraine a travers ses roches in French Retrieved 2010 10 01 External links Edit Wikimedia Commons has media related to Tufa category Mono Lake Committee Tufa Retrieved from https en wikipedia org w index php title Tufa amp oldid 1117145761, wikipedia, wiki, book, books, library,
