Bol. Soc. Venezolana Espel. v.35 Boletín de La Sociedad Venezolana de Espeleología - LUMINESCENCE of CAVE MINERALS

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Boletn de la Sociedad Venezolana de Espeleologaversin impresaISSN 0583-7731

Bol. Soc. Venezolana Espe l. v.35 Caracas dic. 2001

LUMINESCENCE OF CAVE MINERALS

Yavor Y. Shopov

General Physics Department. Sofia University, Sofia.Bulgaria.

ABSTRACT

Some speleothems when exposed to energy sources (light,electrons, heat, etc.) may exhibit luminescence. The color ofluminescence may vary with changes of the excitationsources, because they may excite different luminescentcenters existing in the mineral. The study of the phenomenahas shown that organic matter impurities in the minerals of the speleothems are the maicause of the effect. Luminescence studies have been used -among others- in thassessment of: paleotemperature, paleo-solar activity, measurement of cosmic ray flutectonic history of an area, and annual growth rates also help speleothems dating. Sluminescence is useful to gather a wide variety of paleoenvironmental information, anmainly in the study of Quaternary climate.

Key words: cosmic rays, paleoclimatology, paleoenvironment, annual growth ringspeleothems, Quaternary.

RESUMEN

Algunas espeleotemas al ser expuestas a diferentes fuentes de energa, como luelectrones,calor, etc. emiten luminiscencia. El color de esta emisin puede cambiar seglas fuentes de excitacin y porque pueden excitar distintos centros luminiscentes dmineral. El estudio del fenmeno ha mostrado que las impurezas de materia orgnica elos minerales de las espeleotemas son la causa principal del efecto. Los estudios dluminiscencia entre otros han sido usados en la evaluacin de: paleotemperatura, paleflujo solar, mediciones del flujo de rayos csmicos, historia tectnica y, por medio de l

medicin de las bandas anuales de crecimiento ayudan en la datacin de espeleotemas.luminiscencia ha mostrado ser muy til para obtener una variedad de informacipaleoambiental, y muy especialmente en los estudios del clima del Cuaternario.

Palabras claves: rayos csmicos, paleoclimatologa, paleo-ambiente, bandas dcrecimiento anual, espeleotemas, Cuaternario.

Recibido en febrero de 2001

INTRODUCTION

Many speleothems exhibit luminescence (light emission) when exposed to ultraviolet (Ulight sources (strobe, photo flash, flash powder, "black light", etc.) or other high ener

beams (electrons, X- Rays, heat, etc.). Depending on the excitation source there aspecific kinds of luminescence: photoluminescence (excited by ultraviolet -UV- and othlight sources), X-ray luminescence (by X-Rays), cathodoluminescence (by electron beamthermoluminescence (by heat), candoluminescence (by flames) and triboluminescence (crushing). Different types of excitation may excite different luminescent centers- electrodefects of the crystal lattice; admixture ions substituting ions in the crystal lattice
http://www.addthis.com/bookmark.php?v=250&username=xa-4c347ee4422c56dfhttp://www2.scielo.org.ve/scielo.php?lng=eshttp://www2.scielo.org.ve/scielo.php?lng=eshttp://www2.scielo.org.ve/scielo.php?script=sci_issuetoc&pid=0583-773120010012&lng=es&nrm=iso...http://www2.scielo.org.ve/scielo.php?script=sci_arttext&pid=S0583-77312001001200003&lng=es&nrm=iso...http://www2.scielo.org.ve/scielo.php?script=sci_arttext&pid=S0583-77312001001200005&lng=es&nrm=iso...http://www2.scielo.org.ve/cgi-bin/wxis.exe/iah/?IsisScript=iah/iah.xis&base=article%5Edesp&index=AU&format=iso....pft&lang=e&limit=0583-7731http://www2.scielo.org.ve/cgi-bin/wxis.exe/iah/?IsisScript=iah/iah.xis&base=article%5Edesp&index=KW&format=iso....pft&lang=e&limit=0583-7731http://www2.scielo.org.ve/cgi-bin/wxis.exe/iah/?IsisScript=iah/iah.xis&base=article%5Edesp&format=iso....pft&lang=e&limit=0583-7731http://www2.scielo.org.ve/scielo.php?script=sci_serial&pid=0583-7731&lng=es&nrm=iso...http://www2.scielo.org.ve/scielo.php?script=sci_alphabetic&lng=es&nrm=iso...http://www2.scielo.org.ve/scielo.php?script=sci_alphabetic&lng=es&nrm=iso...http://www2.scielo.org.ve/scielo.php?script=sci_serial&pid=0583-7731&lng=es&nrm=iso...http://www2.scielo.org.ve/cgi-bin/wxis.exe/iah/?IsisScript=iah/iah.xis&base=article%5Edesp&format=iso....pft&lang=e&limit=0583-7731http://www2.scielo.org.ve/cgi-bin/wxis.exe/iah/?IsisScript=iah/iah.xis&base=article%5Edesp&index=KW&format=iso....pft&lang=e&limit=0583-7731http://www2.scielo.org.ve/cgi-bin/wxis.exe/iah/?IsisScript=iah/iah.xis&base=article%5Edesp&index=AU&format=iso....pft&lang=e&limit=0583-7731http://www2.scielo.org.ve/scielo.php?script=sci_arttext&pid=S0583-77312001001200005&lng=es&nrm=iso...http://www2.scielo.org.ve/scielo.php?script=sci_arttext&pid=S0583-77312001001200003&lng=es&nrm=iso...http://www2.scielo.org.ve/scielo.php?script=sci_issuetoc&pid=0583-773120010012&lng=es&nrm=iso...http://www2.scielo.org.ve/scielo.php?lng=eshttp://www.addthis.com/bookmark.php?v=250&username=xa-4c347ee4422c56dfhttp://www2.scielo.org.ve/scieloOrg/php/articleXML.php?pid=S0583-77312001001200004&lang=es


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incorporated in cavities of that lattice; inclusions of other minerals; or fluid inclusionmolecules, ions or radicals adsorbed inside of the lattice. Some or all of them may exist ia single speleothem.

Absorption of excitation energy by a mineral leads to increase of electrons from grounstate to an excited level. Sooner or later these electrons fall down to a lower level whilemitting light. If the emission proceeds only during the excitation (immediately after thrising) then it is called "fluorescence", if it proceeds later (usually seconds or minutes) theit is called "phosphorescence". In the later case, falling of electrons from the excited statproceeds through intermediate levels (thus taking more time), so the energy of the emitte

light is less than the energy of fluorescence (i.e. color of the emitted light is shifted tred). Some luminescent centers produce only fluorescence, but other both fluorescence anphosphorescence.

The color of luminescence is determined by the type of luminescing centers. Color may vawith changes of the excitation sources, because they may excite different luminescecenters existing in the mineral. Every luminescent center has its own excitation spectrtemperature dependence and conditions of excitation. One color of luminescencsometimes, can be produced by a single luminescent center or by combination of twoseveral centers. The decay rate of luminescence (time for visible disappearance of thluminescence afterglow after switching off the excitation source) may vary from virtual zefor fluorescence to minutes or hours for phosphorescence. It is also characteristic for eveluminescent center. Brilliance (brightness) of luminescence is a function of the numberluminescence centers. It is almost linearly proportional to concentration of luminescecenters in transparent or white calcite, but can be substantially decreased by ligabsorption in color centers of clay and others colored inclusions of color admixture ions iless-pure calcite.

The easiest and most efficient method of excitation is irradiation by UV light sourcproducing photoluminescence,

and when the term luminescence is used it refers to this kind of excitation. Every caver casee phosphorescence of speleothems in caves by irradiating of speleothems withphotographic flash with closed eyes, and with the rapid opening of the eyes after flashinThis simple technique is useful for the previous diagnostics of cave mineral and th

selection of samples for laboratory analysis. Such Visual Luminescent Analysis (VLA) hbeen widely used in caves (TARCUS-CSSR 1981), usually with the photographic flash balso with other simple devices such as portable UV lamps with short wave UV (SWUV) anlong wave UV (LWUV). Slacik (1976) used a simple apparatus which registered totemitted light by a galvanometer with a photo cell for the quantitative evaluation of thluminescence intensity. However, data obtained by the VLA method are subjective (nmeasured quantitatively) and the determination of luminescence activators is not possiblIn fact attempts to determine activators of the luminescence with VLA and chemicanalysis leads to incorrect results. Statements that Sr causes violet luminescencecarbonates (e.g. Kropachev et al.1971) and Cu- causes pale-green and blue luminescenof calcite and aragonite (e.g. Rogers and Williams 1982) are in error. Sr-ions do not havelectron transitions in the visible region of the spectra and cannot activate luminescence icarbonates, and Cu is known to cause reduction of luminescence induced by other catio

(Tarashtan 1978). Cu (2+) can excite only infrared luminescence of some sulfides, butmay just increase the concentration of electron defects by distortion of the crystal latticAlso, interpretations of the visible luminescence of calcite as Pb-activated (Slacik 1976) anot correct, because Pb in calcite emits only UV light (Tarashtan 1978, Shopov et a1988b).

It is known that almost 50 cave minerals have the capacity of exhibiting luminescen(Table 1), but only 17 had actually observed to be luminescent in speleothems so far. Sthe participation of cavers from all countries of the world will help to obtain a bettpicture of luminescence of cave minerals, aiding in future research endeavorInvestigations of the spectra of luminescence reveal new possibilities for luminesceresearch in mineralogy; for example, the determination of luminescent centers, thcharacter of isomorphic substitution, structural characteristics of the admixtures and defecenters and typomorphycal peculiarities of minerals.

Luminiscencecenter

Excitation Colorphosphor

Calcite


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1. Organics Hg-lamp, blue longinfiltration

2. Organics N -Laser, blue longinfiltration

3. Organics SWUV, blue-green longinfiltration

4. Organics N -Laser,Xe,

blue-green longinfiltration

5. Organics N-Laser, yellow-greenlong infiltration

6. Organics LWUV (Hg) yellow longinfiltration

7. Organics Ar-Laser,Xe,

yellow longinfiltration

8. Organics SWUV,LWUV

yellow-orangelong infiltration

9. CO N -Laser blue infiltration

10. UO SWUV greeninfiltration

12. UO N -Laser, Hg green (photo 9)infiltration

13. UO(magursilite?)

green-yellowinfiltration

14. Organics Hg, Xe bluish


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(LWUV) hydrothermal

50. Fe Xe-lamp(SWUV)

dark redhydrothermal

Hydrozincite

51. Organics N -Laser yellow-green,ore-weathering

52. Organics N -Laser yellow ore-weathering

53. Mn electronbeam

pink ?

54. CO electronbeam

blue infiltration

halite

55. Cl defect,electronbeam

violetinfiltration

darapskite

56. ? electronbeam

violetinfiltration

Candoluminescence ofgypsum

57. Mn hydrogenflame

green

58. ? hydrogenflame

lemon yellowinfiltration

Calcite thermoluminescence

59. ? UV+warming glow at 105 K

infiltration

60. ? Xe+heating glow at 350,500 K ?

X-Ray luminescence of calcite

61. CO X-rays blue infiltration

Table 1. Photoluminescence of Cave Minerals. Comments: 16- hydrocarbonspresent only in fluid inclusions in calcite, formed 1 km below the surface bywaters heated by earth thermal gradient (epithermal solutions) in a cave inCarlsbad Caverns region, Guadeloupe Mts., New Mexico, USA. 13- Spectra of thisluminescence is attributed by Tarashtan (1978) to luminescence of clusters of

mineral Magursilite sorbated in calcite; 25-30- Organic origin of luminescence ofthese minerals is under question, because molecules of sorbated water maycause similar luminescence (Tarashtan 1978) in aggregates like studied samples(moonmilk); Shopov also observed same cathodoluminescence in severalinfiltration calcites, but only in detrital filling layers, not in bulk clearspeleothems so its origin is not completely clear.

MEASUREMENT AND PHOTOGRAPHY OF LUMINESCENCE

Conventional Luminescent Spectral Analysis (LSA) of minerals requires expensive ancomplicated apparatus and highly qualified spectroscopist. Luminescence spectra of cavminerals have been measured by means of exciting them with nitrogen lasers (UgumoriIkeya 1980, Shopov 1988, 1989 a,b), Xe(2) and Hg-lamp (Shopov et al. 1988b, White

Brennan 1989), by Argon lasers (Shopov 1989b, White & Brennan 1989) and by He(2)Ne(2) lasers. A disadvantage of this method is that it is destructive and gives total spectof luminescence of the entire sample and is inapplicable for research of fine mixeaggregates such as moonmilk.

The conventional method for photography of fluorescence (PF) is not adaptable for cav


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photography, because it needs long exposition times (30-60 min) and a permanent electrsource. This method [using long UV- lamp with UV- passing filter (filter of wood) and a Uabsorption (cut) filter on the camera] always distorts the color of luminescence, becauseis impossible to choose a pair of filters which can absorb whole emission of the UV-lamwithout absorbing a part of the luminescence of the sample. If an UV-absorption filter inot used to absorb lamp emission, UV photos will be obtained instead of photosfluorescence.

The simplest method for luminescent research (Table 2), which can be used by every cavis Impulse Photography of Phosphorescence (IPP) (Shopov & Grinberg 1985, Shopov 1989a

The equipment used for this method consists of a photo camera with a shutter delayewhich opens the shutter several thousands of a second after flash emission ends. It usordinary photo flash to excite speleothem luminescence. Addittion of an impulse UV-sour(flash with a UV-passing filter) (IPFP) can give both photos of fluorescence anphosphorescence together or separately. Photographic slides obtained using this methocan be developed by Color Slide Spectrophotomerty (CSS) for the preparation of spectradiffuse reflectance and phosphorescence of fluorescence (Shopov & Georgiev 1987, 1989It is intended for research of wideline spectra, such as luminescence of most speleotheformed at normal cave conditions (at temperature below 40C) (Shopov et al. 1989a).allows an easy non-destructive determination of objective information of minercomposition and speleothem luminescence, easy collection of information for CM anconditions of their formation in caves, and it represents an information source f

speleologists who do not have access to expensive and complicated analytical equipment.

METHOD OBTAINABLE INFORMATION

I. Impulsephotography ofluminescence (IPL)

1. Photography of &phosphorescence(IPP)

2. Photography offluorescence &phosphorescence(IPFP).

Diagnostics of minerals, registration of color &zonality of fluorescence and phosphorescence itsspectra; UV photography, extraction of singlemineral samples, chemical changes of themineral-forming solution, climate and solaractivity variations during the Quaternary.

II. Laserluminescentmicrozonalityanalysis

Microzonality of luminescence, changes of themineral forming conditions (LLMZA), climate &solar activity variations during Quaternary (withresolution up to 0.4 days), speleothem dating(with accuracy 1 year), interruptions of thespeleothem growth, annual rainfall in the past,

estimation of past cosmic rays (CR) and galacticCR

III. Color slidespectrophotometry(CSS)

Wideband spectra of phosphorescencefluorescence and diffuse reflectance of minerals,spectra of quick processes.

IV. Autocalibrationdating (ACD)

High precision speleothem dating of speleothemsof any age, climatic and solar activity cycles,variations of the speleothem growth rate.

V. Time resolvedphotography ofphosphorescence(TRPP)

Determination of the lifetime of the luminescentcenter. Estimation of the temperature of thedeposition, plus all information obtainable by IPP


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Table 2. Methods in speleothem luminescence research.

Minerals are not pure chemical substances and contain many admixtures. Usually severcenters activate luminescence of the sample and the measured spectrum is a sum of thspectra of two or more of them. Monochromatic excitation light is necessary to determinspectra of luminescence of each ion. Determination of luminescence activators ispeleothems is a very difficult task and has been solved only by two large labs of SofiUniversity (Bulgaria) and PennState University (USA) (Shopov et al. 1988, White & Brenna1989). Lasers and Raman spectrometers used for measurements of luminescent spectallow also the determination of the luminescent mineral in the speleothem, because th

narrow Raman lines appearing in luminescence spectra at high resolution scanning acharacteristic for different minerals (Fig. 1).

LUMINESCENCE OF HYDROTHERMAL MINERALS

Luminescence of the high temperature hydrothermal minerals is mainly due to catiobecause molecular ions and molecules destruct are destructed at high temperatureTherefore, the luminescence of cations can be used to indicate the hydrothermal conditiounder which the cave minerals are formed (Fig. 2, shown in inside back cover). Mineraldeposited by low-temperature hydrothermal solutions have short-life fluorescence due tcations and long phosphorescence due to molecular ions. For example, the orange-reluminescence of Mn(2+) in calcite sensitized by Pb(2+) can be observed only ihydrothermal calcite, because Mn(2+) has no strong bands of excitation and can lumines

only in the presence of Pb(2+) in Ca(2+) sites which absorbs UV light and transmexcitation energy to Mn(2+) which luminesce. But Pb(2+) have very big ion radius and casubstitute Ca (2+) only at high temperatures. Therefore, if calcite has only orange-red anshort-time phosphorescence, it is sure to have formed in high hydrothermal temperaturhydrothermal solutions (>300C). But if it has long-time phosphorescence in addition tred-orange one, then it is a low-temperature hydrothermal calcite (Shopov 1989a,bMinimal temperatures for the appearance of this orange- red luminescence was estimateby Y. Dublyansky (pers. comm.) by fluid inclusion analysis in hydrothermal cave calcites tbe about 40C, but our direct measurements of luminescence of calcites in hot sprinshows that even at 46C such luminescence did not appear, and it probably does nappear at < 60C. Luminescence of hydrothermal calcite formed at lower temperaturlooks similar to usual speleothem luminescence (Fig. 2).

Fig. 1.Luminescence spectra of organic material in a calcite speleothem(broad line) and Raman lines for aragonite; excitation frequency = 488nm, blue line of Ar-laser.
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Fig. 2. Characteristic red luminescence of hydrothermal calcitedue to Mn-Pb couple incorporated in the crystal lattice. Theinternal red part of this calcite from Carlsbad cave has beenformed at epithermal conditions, 1 km below Earth's surface.When rapid uplift of the region happened infiltration watersfrom the surface start to deliver organics. They have greenphosphorescence, which together with Mn-Pb couple produceorange luminescence in the outer part of the crystal. Thisluminescence layer allows dating of the cave uplift.

PALEOENVIRONMENTAL APPLICATIONS OF SPELEOTHEM LUMINESCENCE

Luminescence is a property of cave minerals most sensitive to depositional conditio(Tarashtan 1978). Therefore, it can be used for determining these conditionLuminescence of minerals formed at normal cave temperatures (0-40C) is due mainly tmolecular ions and sorbated organic molecules (Fig. 3). Luminescence of uranil-ion (Fig.is also very common in such speleothems. Before using a speleothem for apaleoenvironmental work it is necessary to determine that all luminescence of the samplis due to organics. This requires the use of an expensive Raman or luminescenspectrometer, plus an Electron Spin Resonance (ESR) spectrometer or chromatograp(Shopov 1989ab).

Fig. 3. Luminescence of organic materials in infiltration cave calcite. Variations ofthe color of luminescence of organics are due to variations of the plantscommunity growing over the cave during transitions from glacial to interstadialclimate.

Fig. 4.Annual banding of luminescence of uranil- ion in a calcite flowstone due to


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variations in pH of the water.

Luminescence, Paleotemperature and Paleo-Solar Activity

Calcite speleothems usually display luminescence produced by calcium salts of humic anfulvic acids derived from soils above the cave (Shopov 1989 a,b, White & Brennan 1989These acids are released by the roots of living plants, and by the decomposition of deavegetative matter. Root release is modulated by visible solar radiation via photosynthesiwhile rates of decomposition depend exponentially upon soil temperature. The sotemperature depends mainly on solar infrared and visible radiation in case that the cave i

covered only by grass or upon air temperatures in case that cave is covered by forestbush (Shopov et al.1994). In the first case, microzonality of luminescence of speleothecan be used as an indirect Solar Activity (SA) index (Shopov et al.1990), but in the seconcase it can be used as a paleotemperature proxy. So, depending on the cave site, we mspeak about "solar sensitive" and "temperature sensitive" luminescent speleothem recorsimilar to tree-ring records, but in our case the record may depend only on temperatureon solar irradiation (Shopov et al.1996a).

Such records allow for the reconstruction of past solar activity. In case of Coldwater cavIowa, US, we have obtained a high correlation between the luminescent record (Fig. 5and the Solar Luminosity Sunspot index, and have reconstructed sunspot numbers sin1000 AD (Shopov et. al. 1996a) with precision of 10 sunspot numbers (which is within thframe of experimental error of the measurements). In the case of Rats Nest cave, Albert

Canada, we have obtained a good correlation between luminescent intensity and atemperatures recorded for the last 100 years and have reconstructed annual atemperatures for last 1500 years at the cave site with precision of 0.35C (Shopov et a1996a). However, the intensity of luminescence was not found to be dependent on actuprecipitation and sunspot numbers. As a result of such studies, NASA used a recordflowstone luminescence from Duhlata cave, Bulgaria (Shopov et al. 1990) to obtainstandard record of variations of Solar Irradiance (the "Solar constant") for the last 1000years by calibration of the luminescence record with satellite measurements (D. Hoyt, percomm.).

Fig. 5.Sunspot cycles: (a) a luminescent record with step of 3.78 a/pxwith a maxima and minima "tuned" (upper inset = original, untuned,luminescent record). (b) inverted residuals d 14C record derived fromthe composite calibration record from tree rings (Stuiver & Kra 1986)(lower inset = annual sunspot numbers smoothed by a 20 yr filter,


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measure after 1700 AD and estimated from aurora frequency before1700 DC; Shove 1983). Reproduced from Shopov et al. (1994).

Luminescence and Cosmic Rays Flux

A time series of a Solar Activity (SA) index "Microzonality of Luminescence of Speleothemcan be obtained by Laser Luminescence Microzonal analysis (LLMZA) of cave flowstonesdescribed by Shopov (1987). This technique uses a relatively simple device, but the qualiof results is as good as high is the experience of the researcher, because every samplrequires a different approach. Many restrictions for samples for LLMZA apply (Shopov 1987

LLMZA allows for the measurement of luminescent time series with duration of hundredsthousands of years, but time steps for short time series can be as small as 6 hou(Shopov et al.1994) allowing resolution of 3 days (Shopov et al.1988a).

A striking correlation has been achieved between the inverted Cosmic Rays proradiocarbon record and a LLMZA speleothem record (Fig. 5b) (Shopov et al. 1994). Thradiocarbon record represents the Cosmic Ray Flux (CRF) and its modulation by the solwind (which represents solar activity). Cosmic rays produce cosmogenic radiocarbon in thupper atmosphere by nuclear reactions. To reconstruct the past CRF the luminescent recoshould be inverted (Shopov et al.1993). This was obtained by reconstruction of the solmodulation of the CRF during the last 50,000 years with a resolution of 28 years (Shopet al. 1995). This record was also correlated with an independent record of thGeomagnetic Dipole intensity (Shopov et al. 1996e), since solar wind modulates thgeomagnetic dipole as well. Galactic CRF selfvariations in the last 6,500 years wereconstructed (Shopov et al. 1996b) with a 20 year resolution by subtracting of the solmodulation (represented by a speleothem luminescence record) from the CRF (representeby a record of production of cosmogenic radiocarbon). These last results represent GalactCRF variations beyond the Solar System (due to supernova explosions), where there is nsolar modulation.

Luminescence and Paleosoils

Luminescence organics were first detected in speleothems by Gilson & Macarthney (1954and are humic and fulvic acids according to White & Brennan (1989). More precisely, thcan be divided in 4 types:- (1) calcium salts of Fulvic acids, (2) calcium salts of humacids, (3) calcium salts of huminomelanic acids, and (4) organic esters (M. Williams, percomm.). All of them are usually present in a single speleothem with hundreds of chemiccompounds with similar chemical behavior, but of different molecular weightSuperposition of luminescence bands of all this compounds gives the broadline spectraspeleothem luminescence. Concentration distribution of these compounds (and theluminescence spectra) depends on the type of soils and plants over the cave, so the stuof luminescent spectra of these organic compounds can give information about paleosoiland plants in the past (White & Brennan 1989). Changes in visible color of luminescencespeleothems suggest major changes of plants communities growing hundreds of thousanof years through glacial and interglacial periods (Fig. 3, shown in inside back cover).

Luminescence and tectonic

The tectonic uplift of an area (i.e.,uplift of bedrock) can be deduced by luminescence icombination with the absolute dating methods. For example, some speleothems froCarlsbad Cavern, New Mexico, exhibit luminescence due to epithermal mineralizatioforming solutions in the older part of the speleothem, but the mixing of these waters witsurface waters containing organic compounds appear in younger parts of the speleothemthus suggesting a time of uplift during the speleothem deposition (Shopov et al.1996d).

Luminescence and annual growth rates of speleothems

Speleothem growth rate may vary significantly within a single speleothem, resulting in nolinear time scale of obtained paleoclimatic records (Shopov et al. 1992, 1994). Thesvariations represent rainfall variations in the case there are no growth interruptio(hiatuses) in studied part of the speleothem. Luminescence techniques are able t

visualize annual microbanding in speleothem which are not visible in normal light (Fig. 6If this banding is visible in normal light or luminescent curves have sharp profiles or jumlike in Baker et al.(1993), then it suggests that speleothem growth stopped for a certaiperiod during the year (or years) and such time series are not useful for obtainingrainfall proxy records.


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In the case of Rats Nest cave, Alberta, Canada, we obtained a good correlation betweespeleothem annual growth rates derived by measuring the distance between broad maximof annual structures of luminescence and the actual annual precipitation in Banff, Albertfor the last 100 years. We have reconstructed annual precipitation records for last 28years at the cave site with precision of 80 mm/year (Shopov et al.1996c). By comparinluminescent speleothem records with other solar proxy records, we have also obtainereconstructions of growth rates and precipitations in Bosnek karst region near Duhlatcave, Bulgaria for the last 50,000 years, and for Coldwater cave, Iowa, USA, in the la6,500 years (Shopov et al.1996c).

Finally, it must be pointed out that speleothem's luminescence may be used to determinthe absolute age of speleothem itself (Ugumori & Ikeya 1980, Shopov et al.1991). Fordiscussion of this connection refer to Ford (1997).

Fig. 6. Annual banding of luminescence of organics in a flowstonecrossection. Microscopic magnification x30 (for 24 x 36 mm size of thepicture). Dark parts are clay inclusions. Fluid inclusions are visible asbubbles and some crystal surfaces are also visible.

CONCLUSIONS

Speleothem luminescence of organics compounds can be used for obtaining a broad rangof paleoenvironmental information. Some speleothems can be used as natural climatstations to obtain proxy records of Quaternary climate with annual resolution.

REFERENCES

1. Baker A., P. L. Smart, R. L. Edwards & D. A. Richards. 1993. Annual growth bandings incave stalagmite. Nature, 364: 518-520. [ Links]

2. Ford D. 1997. Dating and paleo-environment studies of speleothems. In: C. Hill & P.Forti. Cave minerals of the word. Nat. Speleol. Soc. Ed., 2nd. ed., p. 271-283. [ Links

3. Gilson J. R. & E. Macarthney. 1954. Luminescence of speleothems from Devon, U. K.:The presence of organic activators.Ashford Speleological Soc. Jour.,6: 8-11. [ Links

4. Kropachev A. M., K. A. Gorbunova & V. Y. Tzikin. 1971. Metachromatism andluminescence of the carbonate speleothems from the caves of Bashkiriya of KrasnoyarskRegion. Peshchery, 10-11: 74-80. [ Links]

5. Shopov Y. Y. 1988. Methodics of Laser Luminescent Spectral Analysis of Powders andMinerals. In: "Spectral Methods of solving of the problems of the Solid State Physics",Scientific Commission on "Atomic and Molecular Spectroscopy" of A.S. USSR, Acad. Sci.Press, Moskow, p. 185-190. (in Russ.) [ Links]

6. -----. 1987. Laser luminescent microzonal analysisA new method for investigation ofthe alterations of the climate and solar activity during Quaternary. In:T. Kiknadze (Ed.),Problems of Karst Study of Mountainous Countries,Proc. International Symp. of SpeleologMeisniereba (Tbilisi). Exped. Annual Sofia Univ.,3-4, p. 104-108. [ Links]

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Bol. Soc. Venezolana Espel. v.35 Boletín de La Sociedad Venezolana de Espeleología - LUMINESCENCE of CAVE MINERALS