Speleothems,( /ˈspiːliːəθɛm/; Ancient Greek) are mineral deposits that accumulate over time within caves. The term speleothem, coined by Moore (1952)[1], is derived from the Greek spēlaion "cave" + théma "deposit". Speleothems are most commonly composed of limestone, dolomite, and other calcium carbonate minerals. They can take a variety of forms, depending on their depositional history and environment. Due to their unique composition and gradual growth, they can be used as paleoclimate proxies.
More than 250 variations of cave mineral deposits have been identified.[2] The vast majority of speleothems are calcareous, composed of calcium carbonate (CaCO3) in the form of calcite or aragonite[3]. Less commonly, speleothems are composed of gypsum, mirabilite, or opal.
The coloring of speleothems depends on their composition. Speleothems of pure calcium carbonate and calcium sulfate are translucent and colorless[4]. The presence of iron oxide or copper provides a reddish brown color. The presence of manganese oxide can create darker colors such as black or dark brown. Speleothems can also be brown due to the presence of mud and silt.
Carbonate speleothems form via dissolution of limestone or dolomite during reactions with acidic groundwater, and reprecipitation of calcium carbonate minerals in cave formations. Rainwater reacts with carbon dioxide in soil to create slightly acidic water: [5]
As the low pH water travels down through calcium carbonate bedrock, it dissolves the carbonate bedrock via the reaction:
CaCO3 + H2CO3 → Ca2+ + 2 HCO3−
When the solution reaches the cave ceiling, the lower pCO2 in the cave drives precipitation of calcium carbonate minerals due to CO2degassing:
Ca2+ + 2 HCO3− → CaCO3 + H2O + CO2
Many factors impact the formation of speleothems, including the rate and direction of water seepage, the amount of acid in the water, the temperature and humidity content of a cave, air currents, the above ground climate, the amount of annual rainfall and the density of the plant cover.
Over time, the accumulation of these mineral precipitates form stalagmites, stalactites, and flowstones, which compose the major categories of speleothems.
* A Stalactite * B Soda straws * C Stalagmites * D Coned stalagmite * E Stalagnate or column * F Drapery * G Drapery * H Helictites * I Moonmilk * J Sinter pool, rimstone * K Calcite crystals * L Sinter terrace * M Karst * N Body of water * O Shield * P Cave clouds * Q Cave pearls * R Tower cones * S Shelfstones * T Baldacchino canopy * U Bottlebrush stalactite * V Conulite * W Flowstone * X Trays * Y Calcite rafts * Z Cave popcorn or coralloids * AA Frostworks * AB Flowstone * AC Splattermite * AD Speleoseismites * AE Boxworks * AF Oriented stalactite * AG collapsed rubble
Speleothems take various forms, depending on whether the water drips, seeps, condenses, flows, or ponds. Many speleothems are named for their resemblance to man-made or natural objects. Types of speleothems include:[6]
Dripstone is calcium carbonate in the form of stalactites or stalagmites
Stalactites are pointed pendants hanging from the cave ceiling, from which they grow
Soda straws are very thin but long stalactites with an elongated cylindrical shape rather than the usual more conical shape of stalactites
Helictites are stalactites that have a central canal with twig-like or spiral projections that appear to defy gravity
Include forms known as ribbon helictites, saws, rods, butterflies, hands, curly-fries, and "clumps of worms"
Chandeliers are complex clusters of ceiling decorations
Ribbon stalactites, or simply "ribbons", are shaped accordingly
Stalagmites are the "ground-up" counterparts of stalactites, often blunt mounds
Broomstick stalagmites are very tall and spindly
Totem pole stalagmites are also tall and shaped like their namesakes
Fried egg stalagmites are small, typically wider than they are tall
Columns result when stalactites and stalagmites meet or when stalactites reach the floor of the cave
An image of a flowstone formation.Flowstone is sheet like and found on cave floors and walls
Draperies or curtains are thin, wavy sheets of calcite hanging downward
Bacon is a drapery with variously colored bands within the sheet
Rimstone dams, or gours, occur at stream ripples and form barriers that may contain water
Stone waterfall formations simulate frozen cascades
Cave crystals
Dogtooth spar are large calcite crystals often found near seasonal pools
Frostwork is needle-like growths of calcite or aragonite
Cryogenic calcite crystals are loose grains of calcite found on the floors of caves, and are formed by segregation of solutes during the freezing of water.[7]
Speleogens (technically distinct from speleothems) are formations within caves that are created by the removal of bedrock, rather than as secondary deposits. These include:
Cave popcorn, also known as "coralloids" or "cave coral", are small, knobby clusters of calcite
Cave pearls are the result of water dripping from high above, causing small "seed" crystals to turn over so often that they form into near-perfect spheres of calcium carbonate
Snottites are colonies of predominantly sulfur oxidizing bacteria and have the consistency of "snot", or mucus
Calcite rafts are thin accumulations of calcite that appear on the surface of cave pools
Hells Bells, a particular speleothem found in the El Zapote cenote of Yucatan in the form of submerged, bell-like shapes
Lava tubes contain speleothems composed of sulfates, mirabilite or opal. When the lava cools, precipitation occurs.
Speleothems are studied as climate proxies because their location within cave environments and patterns of growth allow them to be used as archives for several climate variables.[8] By sampling along a dated transect of a speleothem, speleothems chemical composition and growth rates provide paleoclimate records similar to those from ice cores. Variations in precipitation alter the width of new ring formation, where closed ring formation shows little rainfall, and wider spacing shows heavier rainfall. Denser speleothems indicates higher moisture availability.
The principal proxies that are recorded in speleothems include stable isotopes of oxygen (δ18O) and carbon (δ13C), giving high-resolution data that can show annual variation in rainfall temperature and precipitation.[9][10] These indicators, alone and in conjunction with other climate proxy records, can provide clues to past precipitation, temperature, and vegetation changes over the last ~500,000 years.[11]
The geometrical way in which stalagmites grow, which varies based on the height the water is falling from and the rate of flow, is also used in paleoclimate applications. Weaker flows and short travel distances form narrower stalagmites, while heavier flow and a greater fall distance tend to form broader ones.[11] Additionally, drip rate counting and trace element analysis of the water drops themselves have been shown to record shorter-term variations in the climate at high resolution, such as drought conditions attributed to the El Niño–Southern Oscillation (ENSO) climate events.[12]
A particular strength of speleothems for paleoclimate proxies is their unique ability to be accurately and precisely dates over much of the late Quaternary by radiocarbon dating and uranium-thorium dating[13]. For accurate dating, the speleothem must have been in a closed system without recrystallization.
Calthemites: secondary deposits not formed in caves
Secondary deposits derived from concrete, lime, mortar, or calcareous material as found on man-made structures outside the cave environment or in artificial caves (e.g. mines and tunnels), can mimic the shapes and forms of speleothems,[6] but are classed as calthemites.[14] The occurrence of calthemites is often associated with concrete degradation,[15] but could also be linked to leaching of lime, mortar or other calcareous material (e.g. limestone and dolomite).[14] Despite similar appearances, "calthemites" (created outside the cave environment) are not considered to be "speleothems" (created inside the cave environment), and vice versa, as per their definitions.[1]
^Li, Zheng-Hua; Driese, Steven G.; Cheng, Hai (2014). "A multiple cave deposit assessment of suitability of speleothem isotopes for reconstructing palaeo-vegetation and palaeo-temperature". Sedimentology. 61 (3): 749–766. doi:10.1111/sed.12078. ISSN1365-3091.
^Richards, David A.; Dorale, Jeffrey A. (2003). "Uranium-series Chronology and Environmental Applications of Speleothems". Reviews in Mineralogy and Geochemistry. 52 (1): 407–460. Bibcode:2003RvMG...52..407R. doi:10.2113/0520407. ISSN1529-6466.
^ abSmith, G.K., (2016). "Calcite Straw Stalactites Growing From Concrete Structures", Cave and Karst Science, Vol. 43, No. 1, pp. 4–10, (April 2016), British Cave Research Association, ISSN1356-191X.
The article gives a general overview of speleothems. It does go into more detail regarding their composition, which is helpful. In the "Types and Categories" there is good information, but it could benefit from additional visual aids. There is good information about speleothems' chemistry and their use as climate proxies. In the section about absolute dating, there is a warning about possible original research, which is not the goal of a Wikipedia article. This section needs to be edited so as to not include original research. It spends a lot of time discussing possible original research, which was much longer than the more relevant topic of Chemistry. Because both are rather sparse, perhaps the Origins and Composition and the Chemistry section should be combined.
The tone is very informative and straightforward. This tone, however, does shift in the section "Absolute Dating." In this section, the author is more inquisitive and speaks in possibilities, using words such as "could." This section is slightly informal compared to the rest of the article, using words such as "tricky." Additionally, this section is not entirely neutral.
This article has a lot of sources, and most of them come from reputable scientific journals and reviews. However, some come from more questionable sources, and some are independent research. The largest issue with this articles sources is that they are not properly cited in-line. This creates possibilities for plagiarism. I checked several citations and the links worked. One of its sources, "Picture Climate: What Can We Learn From Caves? | NOAA Climate.gov". www.climate.gov. Retrieved 2017-04-29," only had one reviewer, which might be insufficient.
There have been conversations discussing the necessity and neutrality of the "Absolute Dating" section. There has also been discussions regarding some possible superfluous information about non-speleothems. There has been some talk of inaccessible links; although I have not found that to be the case. The article is rated a level 5 vital article, and it is part of four projects. The four projects are Wiki Project Environment, Climate Change, Geology, and Caves.
This is a user sandbox of Anonymoustrib. You can use it for testing or practicing edits. This is not the sandbox where you should draft your assigned article for a dashboard.wikiedu.org course. To find the right sandbox for your assignment, visit your Dashboard course page and follow the Sandbox Draft link for your assigned article in the My Articles section.
Various formations in the Hall of the Mountain Kings, Ogof Craig a Ffynnon, South Wales, Great Britain.
Stalactites and columns in Natural Bridge Caverns, Texas.
More formations in Natural Bridge Caverns, Texas.
California Caverns, Calaveras County, California; one of many caverns located in the Sierra Foothills of California.
