COBISS: 1.01 EVOLUTION AND AGE RELATIONS OF KARST LANDSCAPES RAZVOJ IN STAROSTNI ODNOSI KRAŠKIH POKRAJIN william B. wHITE1 Abstract UDC 551.44 William B. White: Evolution and age relations of karst landscapes Any karst landscape is a work in progress. Te observed evolution of the landscape is dictated by competing rate processes of surface denudation, stream downcutting, cave development, and tectonic uplif. quantitative data on these processes, applied to two physiographic provinces of the Appalachian Mountains of eastern United States gives ages and time scales that are in agreement with previous geomorphic interpretation. Te results are anchored, very loosely, by the few dates that have been established for cave sediments. Unfortunately, the measured rates vary over an order of magnitude as a result of local circumstances making regional interpretation a rough approximation at best. Key words: fuviokarst, karst denudation, landscape evolution. Izvleček UDK 551.44 William B. White: Razvoj in starostni odnosi kraških pokrajin Vsaka kraška pokrajina je delo, ki napreduje. Razvoj pokrajine, ki ga je mogoče opazovati, je odvisen od medsebojno tekmujočih procesov površinske denudacije, vrezovanja površinskih tokov, razvoja jam in tektonskega dvigovanja. Številčni podatki o teh procesih, zbrani za dve fziografski enoti v gorovju Apalači na vzhodu ZDA kažejo, da se starost in časovna skala ujemata s prejšnjimi geomorfnimi razlagami. Izsledke bolj ohlapno potrjuje nekaj podatkov, dobljenih za jamske sedimente. Žal pa so spremembe razmerja hitrosti zaradi lokalnih posebnosti v velikosti cele magnitude in je torej regionalna interpretacija v najboljšem primeru le grob približek. Ključne besede: kraška denudacija, razvoj pokrajine. INTRODUCTION: wHAT DO wE MEAN By THE “AGE” OF A KARST LANDSCAPE? By “landscape”, we usually mean some defned area of the earth’s surface as it exists at a single moment of time. Although most of the landforms remain constant on a human time scale, they are actually in the process of con-tinuous evolution. In at least a microscopic way, today’s landscape is not quite the same as yesterday’s landscape. If the time scale is extended to thousands or millions of years, very large changes will have occurred to the landscape. Caves will have come and gone. A karst landscape, such as a doline plain, might superfcially look the same but they wouldn’t be the same dolines. Te land surface is continuously lowered by dissolution. Old dolines disap-pear and new dolines are formed. Tus when we speak of the “age” of a karst landscape we must carefully specify both spatial scales and time scales. At the largest scales we can talk about global chemical erosion over geologic time (Gibbs et al., 1999). we can talk about the general lowering of a karst landscape, the phenomenon generally called “karst denudation”. we can talk about the diferential dissolution that produces surface karst landforms. we can talk about subsurface dissolution that produces caves. we can talk about the relative rates of landscape evolution on karstic and non-karstic rocks. we can talk about rates of tectonic uplif that provide the gravitational gradients that drive all of the processes. Te observed landscape in any geo- 1 Materials Research Institute and Department of Geosciences,Te Pennsylvania State University,University Park, PA 16802 USA; e-mail: wbw2@psu.edu Received/Prejeto: 20.12.2006 TIME in KARST, POSTOJNA 2007, 45–52 wILLIAM B. wHITE soil logic setting is the result of the interaction of all of thaensde competing rate processes. As a result, “age” becomes a very slippery concept. Te objective of the present paper is to determbiyn ea what constraints on the time evolution of karst lacnodn-scapes can be extracted from known rates of the lagnidv-e scape processes. Te discussion will be limited to fuvio-karst. Tis means that consideration much be given to mass transport by surface streams on both carbonate and non-carbonate rocks as well as subsurface mass transport exposed rock surfaces using embedded reference pins and a precision micro and Hanna, 1970). The micrometer works best on bare rock surfaces. Mos dissolution takes place under a soil mantle. A technique to measure dissolu by d thissol ution. Illustrat ive exam ples are taken from the Appalachian Mountains of eastern United States. In the Appalachians ar e di splayr e e d twa o in geologic se, t t itin i g s s: (1) i T ble limestl o ane v c a a llleys of the fs o ilde d h A e p v p o a lulachi ans w w a h ter e the k rarst s urf f daci e s is exposea d rb across wide van ll e e dy i f noors so that th e disolutional dissection of the karst is primarily vertical and distributed across the surface. (2) Te Appalachian Plateaus where the carbonate rocks are protected by clastic caprock and whe( r t e ) the diss o lutional attack i s primarily by valley incision around the perimeter. UNIFORM LANDSCAPE Setting aside the necessity for also residue, the evolution of a carbonate rock landscape be considered to be a purely chemical process. Te rBocekca mass is taken into solution and carried away by the choanr-d tinuous fux of water that moves through the system. Any measure of the rate of carbonate removal can be reca lcu-lated as an average lowering of the karst surface, a queapni-k tity known as the karst denudation rate. princ Various methods have been devised for the direct measurement of denudation rate (summarized by white, 2000). Te rate of surface lowering can be measured di-rectly on exposed rock surfaces using embedded reference pins and a precision micrometer (High and Hanna, 1970). Te micrometer works best on bare rock surfaces. Most In th limestone dissolution takes place under a soil mantle. A calci technique to measure dissolution rates in soil is to bury rock carefully weighed plaques of limestone for a known time, react then re-excavate and weigh them again (Gams, 1981). evap On the scale of the entire drainage basin, it is pos-sible to estimate denudation rate by a mass balance cal-culation using the volume of water leaving the basin and analy the concentration of dissolved carbonates contained in Figu the water. Te denudation rate is then given by L more com I NG: a K rb A on R a S teT o D ckEs N , U is D t A heTIe O n N sit removing insoluble 10e -12 fs o tr the units given. Because the ma i s n s balanc ( e i . e e q . ua- D, 1 K N 1a]ry T Q(t)H(t)dt LA ptRJ'i In this equation, Dn is the denudation rate in m3km2yr1 (numerically equivalent to the more common unit of mm/ka), A is the basin area in km2, NL is the fraction of the basin underlain by carbonate rocks, ? is the density of carbonate rock in gcm3, tR is the period of record in years, q(t) is the instantaneous discharge in m3s-1 (i.e. the hydrograph) and H(t) is the instantaneous (Ca + Mg) hardness in gcm3 (i.e. the chemograph). Te constant, K, contains unit conversions and has the value t,ioKn, rceoqnutiarienss c uonittincuoonuvserseicoonrsd sanodf bhoatsh thdeis vchalaureg e1 a0n-1d2 for the units g eh tahrednmesasssw bhaiclahn acree e nqoutatoifonen reaqvuailraebslec,o an tvinaruioetuys orfe caopr-ds of both disc ps rwoxhiimcha taioren sn hoat voef tbeenena vpariolapbolse,d a. variety of approximations have be If the reaction between infltrating water and car-Ibfo tnhaet er eraoctki oant t bhe tbwaese no fi nthfeil terpaitkinargs tw isa atessru amnded c taor breoancaht e e iqsu ailsisburmiuemd, toh er edaecnhudeqatuiiolnib raiutem c,a tnh eb ed ecanlucdualattieodn frraotme c fesr s(tW prhinitcei,p 1le9s8 (4w).hite, 1984). rock at the b be calcula Dn = M cal Kc K1 K p34lK 2rCa 2f2 CO2 1 P3 CO2 (P-E) [2] In t, h Dis e iq uation, D is th le den ud ation rat e in a m l i m s t/ ka. M in al is the molecular weight of calcite (or a weighted m it x o f th e m olr eec ula r we igh ts oef c ialcit net a n d do lo mreite) ans d ir is th e r ock dheen s ity in gc m3 . The K s’ s. a re th e usual equilibrium constants for carbonate reactions and the ?’s are the activity coef e a cients. P-E (precipitation minus evapo tra nspiration) k i s the ar n e n mual runo s e in s m t d m e/yr Many of the ear pl ier measur) e . ments e o cf k ea r st denue -dation rates were reviewed and analyzed by Smith and Atkis n cson (1976). A se lt e hctio n of m e , re recb en let de a sta ar e disp lay ed in Figure th . in e r c i h do sen examples i e n rnclude d ar ta from each of the three measurement methods described above and t hese give comparable results. e v a e regid o inal environmen ts representu e ted in Figure 1 include arid, al m -pine, northern, and temperate. Denudation rates vary by a factor of 5-10 within each group but the groups are almost completely overlapping. Local conditions at the sampling site, including soil cover, available water, and rock lithology, all contribute so that local site variation masks regional scale variations. Tere is also the question of how denudation rates have changed in response to climatic fuctuations of the Pleistocene. For the regional scale landscape evolution of interest in this paper, he molecular and dolomite tants for carb itation minus rates were re recent data ar three measur The regional e perate. Denu almost compl soil cover, av asks regional 46 TIME in KARST – 2007 EVOLUTION AND AGE RELATIONS OF KARST LANDSCAPES 70 * t^\ _ _ 5 60 st E rn • E M — * •¦^ * * | 40 1 * . i_ o 30 i l • t rtj * 1 20 J C • ¦ Q 10 1 t i i ¦ i 0 * KB k Hs C-Y AK S-S DATA SET about the best that can be said is that exposed karst surfaces in the Appala-chian Mountains would be lowered by dissolution at a rate of 20-30 mm/ka. Fig. 1: measured denudation rates. All data have been converted to units of mm/ ka. KR – mt. Kräuterin, Austria (buried tablets) (zhang et al., 1995). LG – Logatec doline, Slovenia (buried tablets) (Gams, 1981). hS – hochschwab massif, Austrian Alps (buried tablets) (Plan, 2005). C-y – Cooleman Plain and yarrangobilly Caves area, New South Wales, Australia (microerosion meter) (Smith et al., 1995). AK – southeastern Alaska (microerosion meter) (Allred, 2004). S-S – Saltfellet-Svartisen area, northern Norway (mass balance) (Lauritzen, 1984). RATES OF VALLEy DEEPENING Regional rivers draining through areas of fuviokarst cut normal valleys in the clastic rocks that overlie, under-lie, or border the karstic rocks and may appear as sur-face streams in valleys cut into the karstic rocks. Meas-urements of the downcutting rates of larger rivers are difcult because many of them, in their lower reaches, are at grade with a sediment load balanced against the discharge. Lowering of the bedrock channel can be very slow. A few data are given in Table 1. Lowering rates in the tectonically stable Appalachians fall in the same 20-30 mm/ka range as is found for denudation of karst sur-faces. Only one example, the Bighorn Basin in western United States is a factor of ten higher and may represent a higher rate of tectonic uplif. tab. 1. downcutting Rate of Some moderate-Size Rivers Small tributary streams that fow from surround-ing non-karstic lands onto the karst and then sink at the contact with the soluble rocks seem to have a much higher rate of channel lowering. Some direct micrometer measurements in the beds of sinking streams are given in Table 2. Sinking stream waters are generally highly un-saturated so that sinking streams downcut rapidly into the carbonate rock at their sink points. Similar measure-ments at spring outlets produce much smaller numbers. Te highest values yet reported were for a muskeg-drain-ing stream in Alaska (Allred, 2004) where there is an im-plication that organic acids may also play a role. Name and Location Rate (mm/ka) Reference Bighorn River, Wyoming 350 Stock et al. (2006) East Fork, Obey River, Tennessee 30 Sasowsky et al. (1995) Anthony & Granger (2004) Green River at Mammoth Cave, Kentucky 30 Granger et al. (2001) Juniata River, Newport, Pennsylvania 27 Sevon (1989) New River at Pearisburg, Virginia 27 Granger et al. (1997) TIME in KARST – 2007 47 wILLIAM B. wHITE tab. 2. downcutting Rate in Small Karst Streams Name and Location Rate (mm/ka) Reference Cataract Cave, southeast Alaska County Clare, Ireland Muskeg Infow Cave, southeast Alaska Slate Cave, southeast Alaska Yarrangobilly, NSW, Australia 137 500 400 1670 1080 180 200 Allred (2004) High and Hanna (1970) Allred (2004)) Allred (2004) Smith et al. (1995) CAVE DEVELOPMENT IN FLUVIOKARST Caves – here considered to be master trunk caves related to surface base-level streams – have a three-stage development. (1) Te initiation phase is the evolution of an initial mechanical fracture to a critical-size protoconduit about one centimeter in aperture. (2) Te enlargement phase takes the protoconduit up to the meters to tens of meters diameter of a typical cave passage. (3) Te stagnation and decay phase is that period afer the cave passage has been drained and abandoned by lowering base levels. As the stagnation phase progresses, entrances are developed and process of collapse, speleothem growth, and sediment in- INITIATION .STAGE o _i 8 l 3 4 O U 2 0 flling choke of the once continuous conduit. Deepening of surface valleys breaks the cave into fragments. Te initiation phase is almost purely chemical. Nearly saturated water percolates along alternative paths in the carbonate rock, slowly enlarging them. Te initiation phase ends when one pathway becomes sufciently large to permit critically undersaturated water to pass completely through the aquifer. As a result, the fnal layout of the conduit system is largely determined during the initiation phase. Te initiation phase is particularly amenable to geochemical modeling and some very elegant models have been constructed (Dreybrodt et al., 2005). Te time scale for the initiation depends on assumed initial conditions but ap-pears to be in the range of 10,000 to 20,000 years. Te enlargement phase is large-ly independent of outside factors. TTeh era eten loafr gremtreantt opfh apsaes siasg lea rwgaelllys independent tc oanf pbaes sadgeesc wriablelds cbayn bthe ed ePsaclrmibeerd- by the Palme Dreybrodt equation (Palmer, 1991). co, - 03 atm . 10 20 30 Time (k-year) 31.56k S = pR 1-C R [3] e rate S o ifs w thaell raetter eoaft wina lclm re/ytrre.a tS ionm e calculation dcmin/yFri.g S.o 2m. e T chalec uralatteiocnosn fsotra npta,s ksa, gwe as taken from was set equal to 2.65 g/cm3. The reaction order, n = meter is the sa dioxide partia Fig. 2: Enlargement phase for typical nate which depends on the carb conduits assuming various carbon dei oexnidlae rpgaermtiael nptr ersasuteress ebxaspeedc otne dth feo r a reasonable ra tPaailms earr-ed sreiyteb-rospdte ecqiufiact,io env. en rough calculations su fficient to allow a master cave to develop. 48 TIME in KARST – 2007 re h fQ2 n The enlargement phase is largely independent of outside factors. The rate of retreat of passage walls can be described by the Palmer-Dreybrodt equation (Palmer, 1991). C n EVOLUTION AND AGE RELATIONS OF KARST LANDSCAPES enlargement are plotted in Fig. 2. TCe rate constant, k, was taken from Palmer (1991). The rock density, ?R was set equal to 2.65 g/cm3. Te reaction order, n = 1, in the fast disso lut ioh n e rea g teim o e f . w T ale o renly en vir onmer n . t aS ll oy sensia - l tive paramo e tter i is t hF e i sa t2 u .ration ca o ten c centratiot n , of c w a alciua m ke carbonate whic h e d t epends o n the carbon dioxi k ,e parti al pressure. Figure 2 shv o ir w o ns the nassa ge es n itlargema e rant re a t t e e rs expected for n a a re asoh n icable range of n C th O e2 pressur es. Ald -though the d ageta ils are sitm e e-sp ecit f e c s, even c r teougf h o c a lculao -tions suggest that 50,000 to 100,000 y e ars a r e suffic ient to allow a ma s ster cac v ie to develop. Ta e relationship between hydraulic gradient, hf/L, discharge, q, and passage radius, R, is given by a form of the Dar rcy-d w ius e ,i sba c i h s equation hf L = 2 fQ 4x2gR5 [4] of 10 or m3/cal sity,/sec n = , i th = 3 _ * 2 L [3] > 7 " \ c e o C th ^ 5 - equatio n Q ge = 0.1 m3/sec 4] = 0.0 en siz are plotted in 0 yst e eleva 1.00 1,50 surface streams can ,rrrt SoSmoem mea mximaxuimu gmradgireandtise tnhtast t chant cbaen s ubpep sourptepdo brtye a given Fsiizgeu croen 3d ufoitr aar es epleoctteiodn ino fF idgiusrceh 3a rfgoer sa. s election of discharges. Because ofB tehcea uloswe ohfy dthrea ulloicw r hesyidstranucleic o rfe sciosntadnucite systemsd, itfhfe reelenvcaetiboent wdiefeenre tnhcee hbeeatdwweeante trhse a hneda dthwea tdeorws and thep drowvindsetrseuafmfi creieancht ehse aodf stuor dfarciev es ttrheeam cas vcea-nf oprrmo-i vide sufcacvieenst dhevaedl otop d breivnee aththe csauvrefa-fcoer mvainllge ypsr o(coers sm. Borye this protchees sf loofw au ftroopmir atchye, scuavrfeasc dee svterleoapm b.e nSeuacth scuarvfeacs eg valleys (voarl mleyorse t ohfate nth ieny t huen vdaelrledyra wina.lls) and drain of the fow from the surface stream. Such caves generally have fatter gradientsU thnalnik teh ke avrasltl esyusr tfhaacte tsh oery suunrdfaecrder vaianll.eys Unrleikmea kina rasst fsiuxrefdacelse voar tsiounrfamcea rvkaelrlse yasn dw hariceh t haer eo continuwouhsilcyh etvhoel vaigneg ,i sc alovceks erdemina.in C asv efsx meda ye lreivdaet iuonp markersr eamnda ianr efi txheed oansl yth fe asturfeasc oef ltahned kscaarspte l afnaldlsc arpoeu for whipch atshee iang teh eis claovcke’esd hiins.t oCrayv aesn dm iasy t hreid pe huapswe ainrd with tecotnocneic-c uopnltifn,u obust coothnedruwiti sies rferamgamine nftxeedd a sa st hteh es surface tlearnmdsc oafp eim faplolsr taarnocuen das t hbeiomlo. gTiciasl ihs atbhiet astt,a tghnea -fi Unfortunately, the details of the conduit decay of the conduit depends on local circumstances does not lend itself to numerical analysis. AGE RELATIONSHIPS IN THE PLATEAU FLUVIOKARST SETTING ten in the valley walls) and drain off Fig. 3: Supportable hydraulic hea s a function of conduit erraadliluys hfoarv vea rfiloautst edri sgchrardgieesn. Tts et hdaanr ctyh-We eisbach friction factor, f = 100. Te gravitational acceleration, g = 9.8 msec-1. hitciohn a arned c doenctianyu pohuassley inev tohlev cianvge,’ sc haivsetosr y and is the phase y ifne awthuircehs eonf ttrhaen ckeasr astr el adnedvsecloaped f oanr d the once-continu-rdo uws ictho ntedcutiot nisicf ruapglmifet,n bteudt aosththerew suisreface lowers and val-tlehyesm d.e eTpheins. iIsn ttheerm stsa ogfn iamtipoonr taanndced eacs abyio logical habitat, cth ee nftnraln csteasg ae ries dvevrye liomppeodr atanndt.t hUenfortunately, the de-atcaeil sl owf tehres caonndd vuaitl ldeeycsa yd eoefp thene .coInd uit depends on local l csitracguem ist avnecreys idmopeos rntaont tl.en d itself to numerical analysis. Te Cumberland Plateau is the southern-most extension of the great Appalachian plateaus that extend from New york State into Alabama. Te Cumberland Plateau in Tennessee and Alabama is an upland of low-dip Mis-sissippian rocks. Te plateau is capped with a highly re-sistant quartzite which provides a reference elevation at about 550 to 600 meters. Te denudation of the resistant quartzite is very slow, 3-5 mm/ka, according to Anthony and Granger (2004). Te plateau is bounded by a pro-nounced escarpment into which deep valleys (known locally as “coves”) have been incised. At the base of the western escarpment is a karst surface known as the Highland Rim. Te doline surface of the Highland Rim ex-tends into many of the deeper coves. Mississippian limestones underlie the valley walls of the coves and much of the Highland Rim (Fig. 4). Te downcutting rate of one incised valley, that of the East Fork of the Obey River in north-central Tennessee was frst calculated from magnetic reversals in the sediments of one of the caves in the valley wall (Sasowsky et al., 1995). Tis number was revised when cosmogenic isotope dating of the same cave showed that TIME in KARST – 2007 49 wILLIAM B. wHITE Fig. 4: Schematic cross-section through the western escarpment of the Cumberland Plateau. Ticknesses of individual beds are nominal values; bed thicknesses vary considerably over short distances (milici et al., 1979). the paleomagnetic measurements referred to an earlier Cumberland River reversal (Anthony and Ganger, 2004). Te revised value Highland Rim. of 30 mm/ka (Table 1) is similar the downcutting rate of other moderate size rivers and also very similar to the expected denudation rate. Te Highland Rim surface at the base of the western escarp-ment has nearly eroded to the bottom of the carbonate sequence. It all about 150 meters of limestone have been removed. If the Highland Rim is raised according to the 30 mm/ka denudation rate, approximately 5 million years ago, the erosion surface was at the top of the limestone. Te sediments in Big Bone Cave were dated at 5.7 Ma (Anthony and Granger, 2004) and it was claimed that this date represents a time when the was fowing at the elevation of the AGE RELATIONSHIPS IN APPALACHIAN VALLEy FLUVIOKARST SETTING Te karst surfaces of the Great Valley and Valley and Ridge Provinces of the folded Appalachians are breached anticlines. Deep erosion along the anticlines has exposed the Ordovician and Cambrian limestones and dolomites which now form the valley foors. Te more resistant quartzites on the fanks of the anticlines remain as long nearly-parallel ridges bounding the valleys (Fig. 5). Contemporary surface streams have downcut 50 to 75 meters into the valley surface. Tere must have been a time when the anticlines were frst breached to expose the carbonate rocks to denudation. Figure 6 shows the se-quence of events (without time scale) and includes the recognized erosion surfaces identifed in central Pennsylvania. Te Nittany Valley near State College, Pennsylvania is an interfuve area. Here are found residual soils Fig. 5: Sketch showing topographic relations in central Pennsylvania. Ridges are supported by resistant quartzite; most of the valley foors are underlain by Cambrian and Ordovician carbonate rocks. Afer deike (1961). 50 TIME in KARST – 2007 EVOLUTION AND AGE RELATIONS OF KARST LANDSCAPES Fig. 6: Te evolution of the Nittany valley in central Pennsylvania showing traditional erosion surfaces. Afer Gardner (1980). with thicknesses averaging 50 meters. On the assump-tion that these are let-down soils consisting of the in-soluble residues from the dissolution of the carbonate Although doline plains give the impression of stable erosion surfaces, denudation measurements suggest the rate of lowering is comparable to the rate of downcutting of surface valleys. Te horizontal surface is maintained be-cause of the internal drainage through the dolines. It is, therefore, problematic to attempt to assign and age to karst surfaces. Cave development is very rapid compared with the evolution of the surface landscape. Caves in tectonically rocks, a calculation based on insoluble residue content and bulk density suggests that more than 425 meters of carbonate rock were removed to accumulate this thick-ness of soil (white and white, 1991). On the (quite pos-sibly unreasonable) assumption that the denudation rate has been 30 mm/ka, the removal of 425 meters of car-bonates would require on the order of 14 million years, placing the beginning of what has been a uniform denudation process in mid-Miocene time. Te present relief between the valley foor and the ridge tops is about 250 meters. Te carbonate surface at the beginning of the denudation process would be 175 meters above the pres-ent-day ridge tops. However, the estimated denudation would not include the entire carbonate section so it does not represent the breaching of the anticline which must have taken place earlier. Te accordant ridge-lines of the folded Appalachians are ofen taken to represent the Schooley Peneplain. If these quartzite-topped ridges erode as slowly as similar rocks on the Cumberland Plateau, the limestone would have flled the valley to the level of the ridge tops only 8 – 9 Ma ago. Te age of the Schooley Peneplain would be much less than many ages that have been assigned to it, some setting the age as far back as the Jurassic. Te valley foors which represent the Harrisburg Survey have been dissected by present day streams to produce an internal relief of about 60 meters. Te caves of the Valley and Ridge Province are found within this interval. Some are inlet caves with high gradients due to the rapid downcutting of sinking streams. Others are fragments of base-level conduits. Given the observed rates of stream downcutting, the time span available for the development of these caves is 2 – 3 million years. stable areas serve as better markers of temporarily sta-ble pauses in base level lowering than do either surface streams or the elevations of karst “erosion surfaces”. Tis conclusion has been suspected at least since the work of Davies (1960) but was given much stronger support by recent cosmogenic isotope dating (Granger et al., 1963; Anthony and Granger, 1964). It is also supported by the present geochemical calculations and mass balance arguments. TIME in KARST – 2007 51 wILLIAM B. wHITE REFERENCES Allred, K., 2004: Some carbonate erosion rates of south-east Alaska – journal of Cave and Karst Studies 66, 89-97. Anthony, D.M. & D.E. Granger, 2004: A late Tertiary origin for multilevel caves along the western escarp-ment of the Cumberland Plateau, Tennessee and Kentucky, established by cosmogenic 26Al and 10Be – journal of Cave and Karst Studies 66, 46-55. Davies, w.E., 1960: Origin of caves in folded limestone – National Speleological Society bulletin 22, 5-18. Deike, R.G., 1961: Karst development in Brush Valley, PA – Nittany Grotto Newsletter 9, 121-128. Dreybrodt, w., F. Gabrovšek & D. Romanov, 2005: Pro-cesses of speleogenesis: A modeling approach – Car-sologica, No. 4, 375 p. Gams, I., 1981: Comparative research of limestone solu-tion by means of standard tablets – 8th International Congress of Speleology Proceedings, Bowling Green, Kentucky, USA, p. 273-275. Gardner, T., 1980: Geomorphology of Nittany Valley – Chapter 5 in Soils and Geology of Nittany valley, E.J. Ciolkosz, R.R. Parizek, G. w. Petersen, R.L. Cunningham, T.w. Gardner, J.w. Hatch, & R.D. Shipman, Eds., Te Pennsylvania State University Agronomy Series No. 64, p. 52-75, University Park, PA. Gibbs, M.T., G.J.S. Bluth, P.J. Fawcett, & L.R. Kump, 1999: Global chemical erosion over the last 250 My: Vari-ations due to changes in paleogeography, paleocli-mate, and paleogeology – American journal of Science 299, 811-51. Granger, D.E., D. Fabel & A.N. Palmer, 2001: Pliocene – Pleistocene incision of the Green River, Kentucky, determined from radioactive decay of cosmogenic 26Al and 10Be in Mammoth Cave Sediments – Geo-logical Society of America bulletin 113, 825-836. Granger, D.E., J.w. Kirchner & R.C. Finkel, 1997: qua-ternary downcutting rate of the New River, Virginia, measured from diferential dcay of cosmogenic 26Al and 10Be in cave-deposited alluvium – Geology 25, 107-110. High, D. & F.K. Hanna, 1970:A method for the direct measurement of erosion on rock surfaces – british Geomorpological Research Group technical bulletin No. 5, p. 24. Lauritzen, S.-E., 1984: Some estimates of denudation rates in karstic areas of the Saltfellet – Svartisen Region, North Norway – Catena 11, 97-104. Milici, R.C., G. Briggs, L.M. Knox, P.D. Sitterly & A.T. Statler, 1979: Te Mississippian and Pennsylvanian (Carboniferous) Systems in the United States – Tennessee – U.S. Geological Survey Professional Paper 1110-G, 38 p. Palmer, A.N., 1991: Origin and morphology of limestone caves – Geological Society of America bulletin 103, 1-21. Plan, L., 2005: Factors controlling carbonate dissolution rates quantifed in a feld test in the Austrian Alps – Geomorphology 68, 201-212. Sasowsky, I.D., w.B. white & V.A. Schmidt, 1995: Determination of stream-incision rate in the Appalachian plateaus by using cave-sediment magnetostratigra-phy – Geology 23, 415-418. Sevon, w.D., 1989: Erosion in the Juniata River drainage basin, Pennsylvania – Geomorphology 2, 303-318. Smith, D.I. & T.C. Atkinson, 1976: Process, landforms and climate in limestone regions – Chapter 13 in Geomor-phology and Climate, E. Derbyshire, Ed., John wiley, p. 367-409, London. Smith, D.I., M.A. Greenaway, C. Moses, & A.P. Spate, 1995: Limestone weathering in eastern Australia. Part I. Erosion rates – Earth Surface Processes and Landforms 20, 451-463. Stock, G.M., C.A. Riihimaki, & R.S. Anderson, 2006: Age constraints on cave development and landscape evolution in the Bighorn Basin of wyoming, USA – journal of Cave and Karst Studies 68, 76-84. white, w.B., 1984: Rate processes: chemical kinetics and karst landform development – in Groundwater as a Geomorphic Agent, R.G. LaFleur, Ed., Allen & Un-win, p. 227-248, London. white, w.B., 2000: dissolution of limestone from feld ob-servations – in Speleogenesis, A. Klimchouk, D.C. Ford, A.N. Palmer & w. Dreybrodt, Eds., National Speleological Society, p. 149-155, Huntsville, AL. white, w.B. and E.L. white, 1991: Karst erosion surface in the Appalachian highlands – in Appalachian Karst, E.H. Kastning and K.M. Kastning, Eds. National Speleological Society, p. 1-10, Huntsville, AL. Zhang, D., H. Fischer, B. Bauer, R. Pavuza & K. Mais, 1995: Field tests of limestone dissolution rates in karstic Mt. Kräuterin, Austria – Cave and Karst Science 21, 101-104. 52 TIME in KARST – 2007