THE KASKASKIA PALEOKARST OF THE NORTHERNROCKY MOUNTAINSANDBLACK HILLS,NORTHWESTERN U. S. A.

Arthur N. Palmerand MargaretV. Palmer

Department of EarthSciences. State University ofNew York. Oneonta. NY 138204015

ABSTRACT: The Kaskaskia paleokarst, part of the Mississippian-Pennsylvanian unconformity in North America, is typified by sink­holes, fissures, and dissolution caves at and near the top of the KaskaskiaSequence (Madison limestone and equivalents) and is coveredby basal Absaroka siliciclastics (Chesterian to Morrowan). In the Rocky Mountains and Black Hills of the northwestern U. S. A. it post­dates earlier features produced by sulfate-carbonate interactions, including breccias, dissolutionvoids, bedrock alteration, and mineraliza­tion. Both the paleokarst and earlier features have been intersected by post-Laramidecaves. Ore deposits, aquifers, and petroleum reser­voirs in the region are also concentrated along both the paleokarst horizons and earlier sulfate-related features. Each phase of karstmodified and preferentially followed the zones of porosity and structural weakness left by earlier phases, producing an interrelated com­plex of now-relict features. All should be considered together to explain the present aspect of the paleokarst

INTRODUCTION

The extensiveerosion surfaceof late Mississippianto early Pennsylvanian age in North Americaseparates theKaskaskiaand Absaroka Sequences. IneasternNorth Americatheunderlying Mississippian strataare nearlyall siliciclastic,but in theRockyMountains and Basin and Rangeprovincesof the western U. S. and in southwestern Canada they aremainlycarbonates (Madison Limestone and equivalents) inwhich dissolution playeda majorgeomorphic role.Localre­liefon theunconformityisas muchas50meters. Wherepaleo­reliefwas highest,thewestern exposures of theMississippiancarbonates contain numerous dissolution fissures, sinkholes,and caves, which form the Kaskaskia paleokarst, the mostclearlyexposed relict karst system of North America. Thesekarst openings were filled mainly by basal Pennsylvanianquartzarenites and shales of the Amsden Formation andequivalents.

TheKaskaskiapaleokarst isnota simpleburiedkarstsurface. It includes a variety of diagenetic, dissolution, andcollapse features that greatlypre-date the main karst eventFurthermore, Cenozoic cavedevelopment has modified andexhumed manyof the Paleozoic features. The paleokarst hasbeen described in manyregional studies, including thoseofMcKee and Gutschick (1969) for the Redwall Limestone inArizona, Meyers (1988) in NewMexico, DeVoto (1988) fortheLeadvilleLimestone in Colorado, andRoberts (1966) andSando(1974,1988)for the Madison Limestone of theNorth­ernRockies. Its continent-wide context hasbeendescribed byM. Palmerand A Palmer (1989).

This paper, a discussion of work in progress, de­scribes the various Kaskaskia paleokarst features and theirrelationships. The genetic andpetrographic complexityoftheKaskaskia paleokarstis difficult to recognize in the field, be­causeweathering has mutedor destroyed manyof thedetailsin surface exposures. With the aid of observations in relictcaves, in which rock and sediment textures are more easilydiscerned, an attempt is madehere to establish the geologic

Carbonates and Evaporites. v. 10, no. 2, 1995, p. 148-160

settingand chronology of the manydiscrete events that pro­ducedthe paleokarst Field examples are cited mainly fromSouth Dakotaand Wyoming, but many of the concepts arevalid throughout the entire western exposure of the Missis­sippiancarbonates.

REGIONALSETTING

Although themargins ofNorthAmericaexperiencedtectonic activity during the Mississippian Period, the conti­nental interiorwas rather stable,and shallow-water carbon­ates were deposited over broad areas. In western NorthAmerica, Kinderhookian and Osagean carbonates were de­posited in the region that now extends from Montana andNorthDakotato NewMexico and Arizona. In contrast,car­bonates didnot dominate in eastern NorthAmericauntil theMeramecian. Widespread late Mississippian regression ex­posed most of these rocks throughout North America, andkarst formed where carbonates were present at the surface

.(Fig.1).Renewed upliftofstructurally positive areas,suchastheTranscontinental Arch, promoteddeeperosion thatinmanyplaces extended through theentire Mississippian section. Onmid-continent structural highs,karst formed not onlyin Mis­sissippian carbonates, but also in rocksas old as Cambrian.Theresultingerosion surface typically contains sinkholes, fis­sures, and caves filled with discontinuous red, yellow, andblackpaleosol overlain bybasalsiliciclastics of the AbsarokaSequence.

The post-Kaskaskia erosion surface was buried bychiefly deltaicand estuarine sediments, which filledvalleys,surfacedepressions, andnearlyall caves ofMississippian age.The basal beds (Amsden Formation and equivalents) weretransgressiveanddiachronous, rangingfromlateMeramecianin western Wyoming andsouthwestern Montana toMorrowanin eastern Wyoming and western SouthDakota(Fig.2). Sub­aerial exposure was lengthiest in the east (up to 34 millionyears), and both the duration of exposure and the magnitudeofkarst features diminish westward (Sando1988).

AN. PALMER ANDM.V. PALMER

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to the main karst event The effects on surrounding carbon­ates aredescribed below, withpetrographic evidence for theprocesses responsible. Notall evidence is equallyconvincing,butthecumulative weightofnumerous observations pointstothe influence of sulfate-carbonate interactions.

Carbonate breccias.--The Madison and its equivalents con­tainprominent breccias that constitute as muchas25-30% ofthe thickness of the carbonate section. Breccias are concen­tratedin several distinct zones in the upperhalfor thirdofthecarbonate section. Theyhaveoften been erroneously viewedas "karstbreccias" formed bythe collapse of cavesand otherdissolution features associated with the unconformity. How­ever, mostof the breccias and theircalcareous matrixare cutbythe post-Kaskaskia karstand are considerably older.

Themostwidelyrecognized feature of theKaskaskiapaleokarst is the dissolution surface that truncates theMissis­sippian carbonates. Thissurface cutsdiscordantlyacross olderkarst-like features that includeearlydissolution voids, brec­cias, calcitic boxwork zones, and bedrock alteration, whichresulted from earlier interaction between carbonates andinterbedded sulfates. In turn, the main paleokarst has beenintersected and modified by Cenozoic caves that formed inresponse to renewed groundwater circulation during and af­ter Laramide orogeny. Interspersed within this long historywere various stages of calcite, quartz, and ore deposition incavities. Figure3 is an idealized cross section that illustratesthe spatialrelationships of the majorkarst-related features inthe BlackHills.In a broadsense, the Kaskaskia paleokarst isnota simpleburiedkarst, butis instead theproduct ofa com­plex sequence of dissolution, diagenesis, precipitation, anddetritalfilling that spansmorethan 300million years.

Figure 1. Location map of the study area, showing the ap­proximate boundaries ofthe lateMississippian karst surface(white), bordered by theshoreline to thenorth andwest, shelfmargin tothewest. andTranscontinental Arch (Madison Lime-­stone notdeposited) to thesoutheast. Laramide tectonic fea­tures mentioned intext:1 =BighornBasin;2 = PowderRiverBasin; 3 =Black Hills. Geomorphic features mentioned intext:A = Lewis andClarkCaverns; B = Bighorn Canyon andHorsethief-Bighorn Caves; C =Jewel andWind Caves. Pa­leogeographyfrom more detailed maps by Craig andConnor(1979) andSando (1988). State boundaries are shownfor reference.

STAGES OF PALEOKARST DEVELOPMENT

Stage 1: Sulfate-carbonate interactionTheuppermost twobreccia zonesare ratherconcor-

The Madison Limestone and its equivalents origi- dant with neighboring beds and contain subrounded tonallycontained considerable gypsum and anhydrite that are subangular clasts generally less than a meter in longestdi­now largely absent in areas of structural uplift. During the mension, withsutured interpenetrating boundaries anddetri­middle Mississippian, thesesulfates were dissolved, altered, tal matrix(Fig. 3, #1). Thesebreccias havebeen interpretedand replaced duringbriefperiodsof subaerial exposure prior bySando(1974, 1988) as the product of interstratal dissolu-

149

KASKASKIA PALEOKARST, NORTHERN ROCKIES ANDBLACK HIILS

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Figure 3. Idealized cross section through theMadi­sonLimestone in thesouthern BlackHills, showingresults of multiple stages of karst and related pro­cesses. Vertical range of diagram is roughly 150meters, but horizontal scale is unspecified. Basinmargin is toward the right. M == Madison (locallyPahasapa) Limestone; A =Amsden equivalent (lo­callyMinnelusa Fm.); C =major chert horizon. 1 =uppermost sulfate solution breccia; 2 = lower sul­fate solution breccia, withredoxboundary;3 =dis­cordant angular breccias (formed by sulfate wedg­ing)with calcite matrix; 4 =mosaic sulfate solutionbreccias near basin margin; 5 =mosaic breccias(from anhydrite hydration) with yellow-brown cal­citeveinsandboxwork; 6 =quartz-lined nodules; 7=middle Mississippian solutionvoids (resultingfromH

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earlyphase ofmixing-zone cavedevelopment, withauthigenic carbonate sediment; 9 = lateMississip­pianpaleokarst surface, withsinkholes andfissures;10 = fissures andcavesfilled withallogenic Penn­sylvanian clastics; 11 =Cenozoic caves, which in­tersect early breccias andpaleokarstfeatures; 12 =exhumed late Mississippian caves; 13 =possibleMississippian mixing-zone caves, not filled withPennsylvanian sediment, enlarged by Cenozoic cavedevelopment.

Figure 4. Solution-collapse breccias inupperMadison Lime­stone (Jewel Cave, southwesternBlackHills), showingformerredox boundary (light grayabove andredbelow). Clasts be­lowboundary havebeenalmost entirely recrystallized toredcalcite.

tion of evaporites during development of the post-Kaskaskiakarst, because they correlate with evaporites present in thesubsurface throughoutmuchofthe Madison Limestone in thenorthern Rockies (see also Andrichuk 1955). In Wyomingthe matrix is lithologically similarto the fill in the paleokarstfeatures at thetop oftheMadison, which suggests thatevapcritedissolution was contemporaneous with development of themain karst surface(Sando 1988).

In the southwestern BlackHills the lowerof the twobreccias is dividedbya sharp sub-horizontal redoxboundary,which probably coincided roughlywith the contemporary wa­ter table (A Palmer and M. Palmer 1989).The boundary ismarked by an abruptcolor change from light gray above toyellow-brown and red below (Fig.3, #2; Fig. 4) and containswavy irregularities withamplitudes ofuptoa meter. Evidently,reducing conditions below the boundaryproduced iron sul­fides that were later oxidized during subaerial exposure. Be­lowthe boundary the clastshavebeenrecrystallized to amor­phousredbodies highlyveined withyellow-brown calcite. Thecolor is impartedby micron-sized crystalsof iron oxide thatcoatfragments ofprobable bacterial filaments, as wellas sparselimonite bodiesthat are pseudomorphic afterpyrite. The ver­tical extent and relativepositions of the clasts indicate thattheyfell fromthe ceilings ofdiscontinuous voidsthat werenomorethan 1-3metershigh. In SouthDakotathe lowerbrecciapre-dates the mainkarst event,as shownby the sharp discor­dant boundaries where they were intersected by dissolutionfissures from the karst surface, and by the absence of the yel­low-brown calcitewithinthePennsylvanian fill (seelaterdis­cussion of allogenic clasticfill).

Lower in the section there are discontinuous brec­ciascomposed of a chaoticassortmentof angularclasts up toseveral decimeters (rarelymeters) in length thatare supportedbya yellow-brown matrixsimilarto that of the reducingzonedescribed above (Fig.3, #3; Fig. 5). The breccias extenddis-

150

A.N.PALMER ANDM.V. PALMER

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apparently not sitesof gypsum brecciation today.

Margins of structural basins (e.g, WIlliston Basin,Fig.1) containedenough meteoric groundwater flow to dis­solve sulfates, despitethe fact that infiltration was limitedbythe dry climate of the region during the middle Mississip­pian. Mosaic brecciaswith stylolitic contactsare common intheseareas (Fig. 3, #4), but the previously described chaoticbreccias areabsent The uppermost mosaicbrecciasappeartohaveformed in collapsezoneswhereevaporites weredissolvedby meteoric water. The matrix of these breccias consistsofauthigenic sand-sized pink and whitecarbonatesediment Inthe lower partsof thebreccias, belowthe Mississippian watertableand in relatively anoxicconditions, the matrix consistsofyellow-brown calcitecorrelative with that of the discordantbreccias farther down-dip. This matrix projects into Ceno-

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Subaerial brecciation byevaporative sulfatecrystal­lization and later replacement of sulfates by calcite can beobserved in many dry cavestoday(palmer 1995). However,under phreatic conditions where evaporation is absent, theprecipitation of sulfates requires changes of temperature orphase.We propose the following process to explain the dis­cordantbreccias: rising warm groundwater dissolved anhy­drite at depth, and gypsum precipitated closer to the surfaceas the water cooled, causingbrecciation by crystalwedging.At near-surface temperatures, gypsum is less soluble thananhydrite and is the stablephasein all but low-humidity sub­aerial environments (Fig.6). Coolingbelow about30 DC re­duces the solubility of gypsum and enhances its crystalliza­tion from the rising water.

30

ToeFigure 6. Solubility of gypsum and anhydrite vs. tempera­ture, with simultaneous calcite saturation, at lowpressuresandactivity of water =1.0.Dashed linesshowinstability ofanhydrite at low temperatures and instability of gypsum athightemperatures. Warm water canriseandprecipitate less­soluble gypsum as it cools. Values calculated from equilib­rium constants recommended by Wigley (1971) for gypsum,andPlummer and Busenburg (1982)for calcite and relatedspecies, andfrom thermodynamic valuesofWoods andGarrels(1987)for anhydrite.

151

cordantlyacrossthebeddingovera vertical rangeofup to40m, and in places theywiden laterallyin a crudelystratiformpattern, particularly below major chert horizons. Clast dis­placements are rarelymorethan a meter, and theiroriginalfitrelative to adjacent clasts and bedrock can easily be recon­structed. Displacement trajectories, including upwardmove­mentfromthehostbedrock, showthat theclastswerewedgedapart by crystalgrowth.The chaoticbreccias grade into thesurroundingbedrockas mosaicbreccias, in which there hasbeenverylittlerelativemovementbetween clasts. Thesechar­acteristics suggestthat the breccias were formed by the dis­ruptive influence of sulfate crystallization within fractures,and that the original matrix consisted of sulfates that havesincebeenreplacedbytheyellow-brown calcite. This replace­ment apparentlyresulted from (1) reduction of sulfates andaccompanying production of Ca" and RC03' in thepresenceof organic carboncompounds, and/or (2) dissolution of sul­fates,whichincreasedtheCa" concentration enoughtocausecalcite to precipitate by the common-ion effect. Faintcathodoluminescent bandingofthecalcitemayindicatea var­ied redox history. The discordantbreccias are concentratedalong the flanksof structural highs,whererising groundwa­ter wasfedbyrechargeeitherfromup-dipinftltration or fromoverpressured zones in the basins. Modem analogs may in­cludethe numerous brecciapipesin thesouthwestern flankofthe Black Hills, which extend from the Mississippian intooverlying strata as young as Cretaceous (Gott et al. 1974).Such pipes serveas pathways for risinggroundwater but are

Figure5. Breccia dike with angular clastsexposed intheWallsofJewel Cave.

KASKASKIA PALEOKARST, NORfHERNROCKIESAND BLACKHll.LS

zoic caves as boxwork veins (Fig. 3, #5; Fig. 7). The lowerbrecciasprobablyformedby the hydrationof anhydrite in re­sponse to meteoric groundwatercirculation during early ex­posure.

Figure 7. Boxwork composed ofyellow-brown calcite veinsandfriable altered bedrock, Wind Cave, southeastern BlackHills.

The isotopic signature of the yellow-brown calcitematrix variesconsiderably (Fig. 8). In the angular discordantbreccias, where the matrix is thickest, SIlO=-10 ±1%0 andSI3C =-5.5 ±1%o, comparedto bedrockvaluesofSIlO=+3 to-50/00 and SI3C =+3 to -20/00. Calciteveins in the mosaicbrec­ciashaveSIlO= -13 to -210/00 and SI3C =4.5 to-7.50/00. Theselight ratios suggest high-temperature fractionation; but al­though a hydrothermal origin for the matrix calcitescannotruledout, their shallow, earlydiageneticorigincastsdoubtonsuch an interpretation. The thinnest calcite veins have thelightest isotopicratios, yetthey formed along basin marginswherehigh-temperature groundwaters wereleastlikely. Thesethin veins formed in areas of extensive anhydrite hydrationand~S oxidation (discussed later). Isotopicfractionation wasfavored bythe occurrenceof severalsequentialreactions,someof which were exothermic. For example, hydrationof anhy­drite yields4 kcal/mole, and oxidationof aqueous~S yieldsa remarkable202kcal/mole(calculatedfromenthalpyvaluesreportedby Woods and Garrels 1987). Isotopic ratios in car­bonatesafter sulfates are frequentlyreportedto haveisotopicratios lighter than their thermal history would suggest (see,for example,Pierre and Rouchy 1988).

Early dissolution voids.-- Cenozoic caves that intersect thezone of former Mississippian sulfates haveassimilatedmanypreexistingvoids, masking the original voidcharacter.How­ever,where extensive collapseof ceilingor wall rock has oc­curred in these caves, especially along faults, many freshlyexposed bedrock surfaces contain dissolution voids that areclearly pre-Laramide (Fig. 3, #7). They consist of isolatedpocketsup to severalmeters in diameterand lined (especiallyalong their wallsand floors) with brecciatedbedrockencasedin a matrix of yellow-brown calcite that is petrographically

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A.N.PALMER AND M.V. PALMER

identical to that of the angular Mississippian-age breccias.Evidently these voids are Mississippian relics of sulfate-re­lateddiagenesis. Thebreccialiningof thesevoids is notcom­patiblewithan originby the simple dissolution of sulfates. Itis more likely that carbonates were dissolved by hydrogensulfideand/orsulfuric acid,as in thefollowing model. Reduc­tion of sulfates lowerin the section produced ~S, whichmi­gratedupwardeitherbyadvection in aqueous form,or as ris­ing gas bubbles. Mixing of waters of differing ~S contentproduces solutions thatareundersaturated withrespecttodis­solved carbonate minerals,eventhough thetwooriginalsolu­tions are at saturation (palmer 1995). Isolated dissolutionpockets at various levelscanbeproduced in thisway. It is alsoprobable that the~S eventually reachedoxygenated waterator near the water table,whereit couldbe oxidized to sulfuricacid,causingvigorous carbonate dissolution. A liningof 100­300 um dolomite rhombs, whichoutlines the originaldiss0­lutionvoids, is presentonlyon the faces of the breccia clastsadjacent to the voids. This shows that the brecciation post­datedthe dissolution of the voids. It is likely that the wedgingtookplaceas a byproduct of sulfuric aciddissolution of lime­stone, where the (Ca++)(S04=) activity product became highenoughtocauseprecipitation ofsecondarygypsum. Suchpro­cesses havebeen observed in many cavernous carbonates inthe semi-arid western U. S. (Egemeier 1981; Hill 1987).

Bedrock alteration andboxwork:«- Calciteveinsof the lowerbreccias projectas resistantboxwork into theCenozoic caves(Fig. 3, #5; Fig. 7). It constitutes a densegrid of thin inter­sectingveinsbetween which the bedrock has been removedbyweathering (A. Palmer and M. Palmer1989). Most veinsareroughly normalto thebedding, butsomeare located alongbedding planes and others show splayed or ramp-like pat­terns. Vein spacingvaries from a few centimeters to severaldecimeters. Intervening voids average about 10cm deep,al­though in placesthey exceedhalf a meter. The bedrock be­tween veinsis lessresistanttoerosionnotsimply because it islesscrystalline than the calciteveins, butbecause it has beenconsiderably altered to a friable sand consisting of calcitepseudomorphs aftergypsum with a sparsecementof second­ary quartz. Much of the original carbonate bedrock was re­movedby~S-~S04 dissolution, leaving manymillimeter­sizedporeswitha matrixof100pm quartzsurroundingformerdolomite rhombs. Wheretheyhavebeenexposed to subaerialweathering thesezonescontainabundantiron oxides, whichproducebright yellows and reds, particularly in the wallsofCenozoic caves. In placesa whitesiliceous zoneseparates thefriable outer bedrock from the unaltered bedrock beneath.Thesefeatures are the products of alteration by sulfuric acid,as shownby the presence of similarfeatures in the vicinity ofoxidizingpyritecrystals in carbonaterocksinmanyotherfieldareas. It is within the siliceous zone that the boxwork veinsterminatein thedirection of the unaltered bedrock. Precipita­tion of secondary silicamay have beenfavored by an abruptdrop in pH, where infiltratingwater from evaporative envi­ronmentsat thesurface encountered thelow-pH zonesaroundthe sulfatebodies. However, the presence of fossil bacterial

(?) filaments within the silica, and the local abundance ofredox reactions, suggest that silicaprecipitation could havebeenmediated by microorganisms.

This alteredbedrock between boxwork veinsdisin­tegrates and falls by its own weight, especially in zones ofcondensation moistureandperiodic rises in watertable. WindCave, South Dakota, exhibits the finest and most extensiveknown examples of boxwork in the world. Although someboxwork veinsin the caveappearto follow consistent trendsoverdistances of several tensof meters, theirorientations donot correlate over larger distances. They showlittle relationto tectonic fractures. Scattered pseudomorphs after anhydritein the intra-vein bedrock supportthe view that the boxworkzones wereoriginallyrich in anhydrite and are of diageneticorigin.

Where fresh limestone has been.exposed by recentcollapse or artificial excavation, the boxwork veins can beseentodie outawayfrom thecaves into thesurrounding bed­rockovera distance of less than a meter. Theyare rarelyex­posed in nearby canyon outcrops, except in the vicinity ofdissolution pockets. The boxwork-lined caves therefore ap­pear to havefollowed formeranhydrite zones.

Wehaveobserved boxwork in all stages of develop­ment in the Mississippian San AndresLimestone of centralNew Mexico. Wherecavesintersectbeds of gypsum that aresandwiched between carbonates, theadjacentwallrockis cutbya gridofgypsum veins, someofwhichhavebeenpartiallyreplaced by calcite. Thegypsum appearstohavebeenderivedfrom anhydrite, as it contains lath-shaped crystals that arepseudomorphic afteranhydrite, as wellas residualanhydriteinclusions. Gypsum veins in bedrock adjacent to partly hy­dratedanhydrite are also described by Bundy(1956).

Alongformer basinmargins (e.g.southeastern BlackHills) the upper Madison Limestone contains pod-shapednodular bodies 1-2 m in diameterwith siliceous rinds andboxwork interiors(Fig.3, #6). Upwardtheydecrease in sizeandbecome hollownodules lackingboxwork. Mostnoduleshavesharp contacts with the surrounding bedrock, but theirinternalwallsare encrusted or replaced by a friable networkof euhedral, doubly-terminated 100pm quartz crystals. Thenodules mayrepresentformer isolated sulfatebodiesand aretruncated bythelateMississippiankarst features. Doubly ter­minated, euhedral quartzcrystals arecommon withinthenod­ules.Friedman (1980) considered this crystalhabit tobeevi­dencefor formerevaporites.

In the southeastern Black Hills (formerly the mar­gin of the Williston Basin),a porous varietyof "zebra rock"forms discontinuousbodies uptotwometers indiameter. Thesebodies, which are concentrated belowlow-permeability bedssuchas sabkhadolomites, consistofblades ofyellow-browncalcitethat are sub-parallel to localbedding, spaced 1-2 emapart, andwhichalternatewith tabularvoidslined withclear

153

KASKASKIA PALEOKARST, NORIHERNROCKIES ANDBLACK. HIlLS

scalenohedral calcite(describedbelow as a deep-burial crust).Thezebrarock terminates abruptly in brecciated bedrock. Iso­topicratios are similar to thoseof the yellow-brown brecciamatrix (Fig. 8). The location and morphology of the zebrarock suggestthat it originated as dissolutional voids formedby~S-~SO4 reactions.Subsequently, as calciumand sulfateconcentrations increased, the voids were filled with second­ary gypsum. The gypsum was later replacedby calcite, in asimilarfashion to the matrixof theangularbreccias, andpro­ducing similar isotopic ratios. The void space remaining inthe zebra rock, aftercalcitereplaced the gypsum, originallyrepresented about 50% of the volume, but the laterscalenohedral calcite lining has diminished that percentagebyat leasthalf. The origin of this type ofzebra rockis uncer­tain, although reduction of mineral volume during closed­system replacement of gypsum bycalcitecan producethe0b­servedporosity value.

Stage 2: Late Mississippian karst and caves

The main post-Kaskaskia karst had a rather simplehistorycompared tothatoftheearliersulfate-relatedprocesses,but it stands out boldly in surface exposures because of thevisualcontrastbetween the massive gray Mississippian car­bonates and the overlying red siliciclastics, mostof whicharefriable and recessive. This paleokarst contains the featuresdescribed below.

Meteoric karstfeatures.-- Early Meramecian to Morrowanexposure, 345-312millionyearsago,produceda broadkarstplaincontaining sinkholes andfissures, andunderlain bycaves(Sando 1988; Fig. 2; Fig 3, #9). This was the main phase inthe development of the Kaskaskia paleokarst. No paleokarsthas been observed in the Williston or PowderRiver Basins,but some is present in the Bighorn Basin (McCaleb andWeyhan 1969). Paleokarstremnantsare present in manyex­posures throughoutthe Northern Rockies and BlackHills,for

Figure 9. Paleo-sinkhole in the Kaskaskia karst surface atthe top of the Madison Limestone, Bighorn Canyon, Mon­tana. Theoverlying sandstonesoftheAmsden Formation havebeen almost entirely removed by erosion. Sinkhole is about20 meters wide.

example, in the walls of Bighorn Canyonon the Montana­Wyoming border, wherewide dissolution fissures filled withredAmsden sandstonepenetrate theMadison Limestone. Mostof these fissures are narrow, rarely more than a few meterswide, but up to 50 m deep. Sinkholesare broaderand shal­lower, generally less than 50 m wideand 20 m deep(Fig.9),and areconcentrated in paleo-valleys (Sando1988). Maslyn(1977) described relict karst towers and pinnacles in theLeadville Limestone of Colorado, but these have not beenidentified farther north.

Few exposures of these paleo-sinkholes in presentcanyon walls show evidence of channels that extend belowthe main depression, throughwhich the originalsolventwa­ter could drain; and yet excavation of modem sinkholes in­variably reveals a drain or collapseinto an underlying cave.The closed appearance of many of these paleo-sinkholes isprobably an artifact of exposure only as random cross sec­tions. For the samereason,interconnections with underlyingpaleo-caves areprobably moreabundantthan exposures sug­gest.

A dry climate in the region during the Mississip­pian is suggested by the sparseness of surfacefissures and bythe apparent isolation of caves, as compared to the denseepikarstand tightintegration between surface depressions andcavesthat are typical of humid regions(palmer 1995). How­ever, it is likelythat muchof the surficialkarst was removedbyerosion prior to Absaroka burial, givingthe impression ofa sparserepikarstthan originally existed.

Coresexaminedby Demiralinet al. (1993)containbreccias at and below the Kaskaskia-Absaroka unconformityin the Bighorn Basin. From top to bottom, these brecciaschange from detrital matrix support to clast support. Theyappear to be true karst breccias that formedduring the mainpost-Kaskaskia exposure. They have low porosity and serveaslow-permeabilitybarriers tofluidmigration. Carbonatebrec­ciaswith dolomicrite matrix, lower in the section, are inter­preted to be the product of subaerial exposure prior to themainkarst event(Demiralin et al. 1993).

Mixing-zone caves>- Dissolution caves are abundant belowthepaleokarstsurface and areusuallyconcentrated 60-100mbelow the topof theMadison Limestone (Sando1988; Fig. 3,#12-13). Although mostare (or were) filledwith surface-de­rived siliciclastics, they are poorly integrated with the lateMississippian karst surface, and someseem to havereceivedlittleor no detritus from the surface. Insteadof forming con­tinuous networks, they appear to be isolateddomed cham­bers. Theyare rarelymore than 10 m iI1 heightor more than100m in lateralextent In the wallsofBighornCanyon, Wy0­ming-Montana, manypartly filled cavesareclustered about20-30m below theAmsden/Madisoncontaet (Fig.10).Thesecavesseemto be of whollyphreaticorigin,because theylackvadose features such as canyon-like passages, flutedverticalshafts, and spelean calcitedeposits. Manyliebelow themaxi-

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mum level of entrenchment of nearbyvalleys (Sando 1988).Most of these voidsresemblemixing-zonecaves that form atthe fresh-water/saltwater interface along seacoasts (Mylroieand Carew 1990). The transition from marine to meteoricconditionsthat occurredduring the late Mississippian in thisarea makes such an origin for thesepaleocaves plausible.

Cenozoiccavesin theBlackHills containnumerousupper levels that are clearlyexhumedrelicsof the Kaskaskiapaleokarst, as indicated by the subsidence of red clastic fillinto underlyingpassages, a process that continues today (A.Palmer and M. Palmer 1989;Fig 3, #12; Fig. 11).Other pas­sages in the upper Madison Limestone contain little or noclastic fill and yet have similar geometries as the exhumedpaleocaves (Fig. 3, #13). This observation invites the ques­tion of whether these are enlarged relics of the Kaskaskiapaleocaves that had no fissure infeedersfrom the surfaceandtherefore escaped filling by Pennsylvanian sediment. In thesouthwestern BlackHillstheseupper-level roomsclusteralongthe redoxboundaryin the lowerof the twostratiformbreccias(Fig.4). In the southeastern BlackHills, wherethe stratiformbrecciasare of mosaicpattern, the upper-level caveroomsarestratigraphically lower, possibly indicatingthat thegeochemi­cal zone that hosted the cave origin (possibly a mixing zonebetween freshwaterand saltwater) wasdiscordant to thestrata.Open cavescan surviveat burial depths up to many kilome­ters,as shownbythepersistenceofthe intactdissolution voidsofconfirmed middleMississippian age(described earlier),andso it is feasible for the upper-level cave rooms to have sur­vivedpost-Mississippian burial.

Authigenic carbonate sediment.-- The earliest detritalpaleokarst fill in the late Mississippiandepressions, caves,and dissolution-breccia pocketswas laminatedredand whitecarbonatesandderivedfrom the localcarbonatebedrock(Fig.

Figure 10. Late Mississippian caves in the upper MadisonLimestone, Bighorn Canyon, MYoming, probably formed bythe mixingoffresh waterand saltwater. The contactwiththeoverlyingAmsdenFormation is shown by the upward changefrom cliff to slope. The caves were oncefilled withAmsdensandsbut have beenpartly evacuatedduring entrenchmentofthe sur/acecanyon. Height ofcliff is approximately 25m.

3, #8; Fig. 12). In places these deposits grade laterally intoquartzsands of similar grain size and sorting, whichare con­centratedin thebottomsofcavitiesconnectedto the overlyingpaleokarst surface. Laminae are typically a few millimetersthick, poorly indurated, and interrupted in places by sub-

Figure 11. Upper-level caveroom in Wind Cave, SouthDa­kota, above the level of the wall coatingofpalisade calcitespar. The hole at the upper left, above the person, is a lateMississippian paleo-cave that wasoncefilled withPennsyl­vanian sands, butwhich havemostlyfallen into theCenozoicpassages below. Thedarkupper sur/aces ofbedrockarecoatedwitha layerofthesesandsseveralmillimeters thick.

Figure 12.Laminatedauthigenic sediment ofcarbonate sandin solution-collapse voids (aformer sulfate zone) in the up­per Madison Limestone, WindCave.

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KASKASKIA PALEOKARST, NORIHERNROCKIES ANDBLACK HllLS

roundedcarbonateclasts. Suchdeposits are common onlyinarid or semi-aridclimatesand are forming todayin dry upperlevels of cavesin the BlackHills as the result of dissolutionalonggrainboundaries bycondensation moisture(A Palmerand M. Palmer 1989).Cumulus bodies of whitecalcitein thesedimentindicate by their shape the replacement of originalsulfates. In manyplaces the sedimentexposed in the wallsoflater cavesappears to exhibitcrossstratification, which maylead to the false impression that it was deposited by runningwater. However, in this case, the bedding simplyreflects theinitialdepositional slopes and differential compaction. Clastsof this laminated authigenic carbonate within the allogenicfill, described below, indicateeither multiple stagesof karstor a changeof depositional environment during a singlema­jor karst event

Allogenic clasticfill.- Thepost-Kaskaskia paleokarst fillcon­sistsmostlyof red, yellow, and blacksand,silt, and clay(Fig.3,#10;Fig. 13).Sando(1988)reportedthat the basalfillcon­sistsofred siltstoneand fine sandstone in the BlackHills andMontana, and white to red, medium to coarse sanstone inWyoming, and thatitsageincreaseseastward fromChesteriantoMorrowan. However, detailed examination ofthe fillshowsaconsiderablevarietyoftextures andcomposition. In theBlack

Figure 13. Dissolutionfissure extending downwardfrom theKaskaskia paleokarst surface, filled with red Minnelusa(Amsden equivalent) sandandclasts oflocal limestone andChesterian sandstone (Jewel Cave, South Dakota). The fis­sure has beenintersected by the Cenozoic cave.

Hills the typical Pennsylvanian fill consists of fineto mediumsubrounded quartzsand(60%),undeformed grainsof musco­vite and biotite (20%), feldspar (10%), and chlorite (10%),withtraceamountsofclay, hornblende, andtourmaline. Sandgrainshavea matrixofhematite-rich clay, whichimparts theredcolor. In placesthe lowest beds ofthe fill consistofyellowclayand weathered limestone fragments. The interpretationof this contrastis uncertain. In the deeperfissures the fill in­cludes abundant sub-rounded toangularclastsofquartzarenite,carbonates, and chert. In places the paleofill also containsabundantangularclastsofred or whitequartzarenite fromanunidentified formation of probableChesterian age that onceoverlay the Madison, but which was removed by post­Kaskaskia erosion (Fig.13).Theseclastsareredexceptwheresulfuric acid released by the oxidation of pyrite has leachedtheferricoxidestoformwhitehalos.Angular clastsin the fillare of local origin, but rounded metaquanzite pebbles andfine-grained fragments of silicatemineralswereprobably de­rived from the nearbyTranscontinental Arch, as shown byincreasinggrainsize towardthe southeast In places,strataofnearlypure manganese oxidesup to 50 cm thick and rich infossil bacterial filaments are interbedded with the fill. Themanganesewas probably carried downward in solution fromanoxicorganic-rich pondsor swampson the surface.

It is importantto verify that the paleokarst fill post­dates the yellow-brown calcite matrix of the breccia andboxwork, as a means of ascertainingthat the latter featuresare indeed diagenetic and not byproducts of the main post­Kaskaskia karst event. The abilityof calcitecement to pen­etratethe sediment fillis shown byabundantdeposits ofwhitecalcite as veins, cements, and pore linings described in thenext section. However, extensive mapping of the paleokarsthasshownthattheyellow-brown calciteisentirelyabsentfromthe fill exceptwhereit is containedas olderveinsor noduleswithincarbonate clasts.

Stage 3: Deep-burial deposits

Thepost-Kaskaskia surfacein theNorthernRockiesandBlackHills was coveredbyPennsylvanian toTertiarysedi­ment toan average depthof severalkilometers. Groundwaterwithin the Madison was anoxic, and until Laramide upliftremobilized basinal fluids near the end of the deep-burialphase, the velocity wasalmostnil. Severaldistinctive depos­its can be recognized fromthis interval.

Scalenohedral calcite.-- Voids that werenotcompletely filledwiththebasalAmsden Formation acquireda nearlyisopachousliningofcleartowhitescalenohedral calcite("dogtooth spar'').This calcitecoatedall surfaces, regardless of their lithology,to a thickness of 1-2em, and in a few placesto more than 5cm (Fig. 14).It is brightlycathodoluminescent, with8180 =-17 to -19%0 and 813C = -4 to -50/00, which are characteristicscompatible withtheanoxicconditions and high temperaturesof deep burial. White calciteveins in the red paleokarstfillhave880 =-17.50/00and 83C =-3.5%0± 0.50/00. Althoughthe

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A.N.PALMER ANDM.V. PALMER

157

veinsappear tobecontinuous with the scalenohedral calcite,the isotopic ratios of the veins are most similar to thoseofCenozoic cavelinings (Fig.8).

The presence of intact scalenohedral calciteis use­ful in determining whetheror not the paleofill has remainedundisturbed since the early Pennsylvanian. Some paleofilldeposits in cavesand surface exposures were clearlydisturbedduringCenozoic uplift, faulting, and erosion. In thesedepos­its thescalenohedra1 calciteis broken anddiscontinuous, andin manyplacesit is entirelyabsent The scalenohedral calciteis also distinctfrom the yellow-brown diagenetic calcitethatpre-datedthe paleokarst, as it coatsthe earliercalcitespar invugs, andcovers erosional orcollapsesurfaces thatintersectedthe earliercalciteduring post-Kaskaskia exposure.

It is interesting tonote that thescalenohedral calcitealsolinessomeof the upper-level rooms andgalleries in cavesthatareusuallypresumed tobepost-Laramide, butonlywherethecalcitehas beenprotected fromdissolution bya coating ofinsolublepost-Mississippian sediment thataccumulated withinthecaves. Thepresence of thecalcitesupports theidea thatatleast someof the upper-level cavities are of post-Kaskaskiaorigin and are intactsurvivors of deepburial.

Euhedral quartz> Euhedralquartzcrystals upto several mil­limeters longweredeposited inandaroundfaults in theMadi­sonLimestone. Mostare of 100JIm sizeand confined to nar­rowfractures,but the largestare located in Mississippian-agevoids and are superposed on the scalenohedral calciteas caps

up to a millimeter thick,or as a coatingup to 5 mm thickoncrystalline hematitecores. Quartz crystals are generallyvis­ibleonlywherecollapse has exposed the voids in the wallsofCenozoic caves. Theirlargecrystal size,concentration aroundfaults, superposition on older scalenohedral calcite, and ab­sence on the dissolutional walls of Cenozoic cavesindicatesthat they were probably deposited by thermal water duringthe firststagesof Laramide orogeny.

Sulfide ores.-- Sulfide ores,particularly galena and sphaler­ite, are abundant in paleokarst voids in the CentralRockiesbutare sparsein the Northern Rockies and BlackHills. Likethe quartz, they are probably of early Laramide age. Theyhavebeendescribed in detail elsewhere (e.g. Tschauder andLandis 1985; DeVoto 1988).

Stage 4: Post-Laramide cave development

Post-Kaskaskia karst features were intersected byCenozoic dissolution caves whenhydraulic gradients in areasofLaramide upliftbecame steepenough to allowsubstantialthrough-flow of water in the Mississippian strata. Althoughsomecaves in the Madison Limestone are integral parts ofthepresentgroundwater flow pattern,mostare relicsthatareoutof adjustment with the presentdrainage.The lattercavesare concentrated in the upperhalf of the Mississippian car­bonates, within the zoneof paleokarst and earlierdiageneticfeatures (Fig. 3). Examples include the caves of the BlackHills in South Dakota, Horsethief and Bighorn CavesalongtheMontana-Wyoming border, and Lewisand ClarkCaveinMontana (Fig. 1). In theBlackHills, mostcavesare ofprob­ablePaleocene and Eoceneage,as shownby the fact that thepresenttopography on thePaleozoic rocksis nearlyidenticalto that of the late Eocene surface. This surfacewasburiedbyOligocene sediments and has beenexhumedby late Tertiaryerosion. It is likely that the caves formed prior to the Oli­gocene, when hydraulic gradients were steepest (A. PalmerandM.Palmer, 1989). Thesecaveshaveundergone consider­ablelater modification bymobilization of detritalfill, calciteprecipitation, and subaerial weathering. In prominently frac­tured beds the cavesconsist of networks of fissure-like pas­sageways, whereas in massivecarbonates theyconsistofbroadarchedrooms. In theBlackHills,forexample, thelowest cave

Figure 14. A record ofkarst-related events exposed by localcollapse inthewalls ofJewel Cave, South Dakota: A =brec­ciated bedrock with yellow-brown calcite matrix; B = redPennsylvanian quartz sandfilling a lateMississippian paleo­cave; C =white calcite deposited during deep burial, liningapocketthatwasnotcompletely filled by thePennsylvaniansand (the white calcite is normally a coating withscalenohedral terminations, buthere itcompletelyfillsa nar­rowpocket); D =late Tertiary palisade crust ofcalcite, whichlines thewalls ofthepresent cave; E =cavewall. The sharpcontact at the base of the palisade crust is the Cenozoicsolutional wall of the cave that truncated all the olderfea­tures.

KASKASKIA PALEOKARST, NORTHERN ROCKIES AND BLACK HILLS

levels in thedolomitic limestones consist of fissure networks,and the upperlevelsconsistof archedroomsin the relativelypurelimestones thatoverliea conspicuous cherthorizon (Fig.3). The caves intersect deep fissures filled with Pennsylva­niansediment, which extenddownward from theunconformityas muchas 50 m (Fig. 13). In placesthe fill is smearedandslickensided as the resultofLaramideor late Cenozoic fault­ing.

The origin and morphology of the Cenozoic caveshavebeendescribed elsewhere (Tullis andGries1938; Howard1964; Campbell 1977; Bakalowicz etal. 1987; A. PalmerandMPalmer 1989), sothefollowing paragraphs merelydescribetherelation between thesecaves andtheKaskaskiapaleokarstThe origin of the Cenozoic cavesis still debated. Someau­thorsarguefor a simplemeteoric originas the resultof arte­sianflow, othersfavor thermalwaters, and still othersinvokelocalrecharge through the overlying surface. All three sce­nariosare feasible, but it is mostlikelythat the sourceof ag­gressive water evolved with time, beginning with thermalsources and progressing toward regional artesian and localinfiltration. Regardless, the caves simplyrepresentenlarge­mentofvoids and high-permeability zonesthat datefrom theMississippian. Cenozoic cavesare concentrated in preciselythosebeds most affected by earlybrecciation and alteration,which in turn werethosemostaffected by the late Mississip­pian karst event (Fig. 3). These caves include some of theworld's largest For example, Jewel Cave, in the southwest­ern Black Hills,contains 170km of integratedmappedpas­sageways.

The scalenohedral calcitecrust is visible in Ceno­zoiccaves mainly in surfaces exposed by collapseor bysub­sidence of sedimentfrom intersected chambers of Mississip­pian age, but it never covers the dissolution surfaces of theCenozoic cavesthemselves (Fig.14).Duringthe lateTertiaryand Quaternary, water-filled caves in most of the NorthernRockies and Black Hills acquired a palisadecalcitecrust upto tensofcentimeters thick thatcontains manyredand blackdetritalimpurities (Fig. 14,D). In theBlackHills thiscalciteis isotopically distinctfrom earliercalcites (0180 =-12.5to-180/00ando13e =-2.5 to -7%0), andis generally interpreted tobe of thermal origin (Bakalowicz et al. 1987; Fig. 8). Thiscalcitemayin factrepresenta thermalevent,or merely a risein temperaturecaused bystagnation ofgroundwater afterburialof the overlying landscape by Oligocene sediment At WindCave, in the southeastern Black Hills, the crust dates backonlyto thePleistocene, and it is stillbeingdeposited today inthe lowestlevelsat a rather cool 14 DC (Fordet al. 1993). Inothercaves, suchasJewelCave, Pliocene faults havedisruptedmanyofthecavecrusts(forexample, at Jewel Cave). Deposi­tion of manganese oxides and silica along faults that post­datethecavedevelopment indicates an influxofwarmanoxicwaterfromdepth.

In a few places nearly the entire sequence ofpaleokarst dissolution and precipitation features is visible, as

shown in Fig. 14.Brecciated bedrock (A) is truncated by lateMississippian caves, whichwere filledbyPennsylvanian de­trital sediment (B). Surfaces of cave-wall pockets that werenotcompletely filledbysedimentwerecovered bydeep-burialscalenohedral calcite(C). Thosepockets were intersected byCenozoic caves, which exposed thescalenohedral calcite, and,finally, the palisade calcitecrust(0) was deposited acrossthetruncated edgesof all the previous features.

Someresearchers (e.g.Bridges 1982) havesuggestedthat the sediment-filled voids interpreted here as part of themainKaskaskia paleokarst actually consistofsubsidence fea­turesproduced byCenozoic dissolution ofMississippian car­bonates. Although this process can be documented to a lim­itedextent in somecaves, it almost invariably represents re­activation of existing Kaskaskia paleokarst The distinctioncanbemadebyobserving thepresence or absence ofan intactdeep-burial crustof the white to clear scalenohedral calcite,which linestheMississippian voidsthatwerenotentirelyfilledbyPennsylvanian sediment In a few placesthescalenohedralcalcitecrust is disrupted or absent wherepaleofill has sub­sidedintoCenozoic caves, but thereare somanyexamples ofintactcrust that thepre-Laramide ageof thepaleokarst is un­equivocal.

Because evaporites within the Madison are presentin basins but absent in present-day uplifts, several authors(e.g. Roberts 1966) haveconcluded that they wereremovedbyactivecirculation ofgroundwater resultingfromLaramideuplift. However, the diagenetic and other features producedbyinteraction between thesulfates and carbonates are unam­biguously cut by the Kaskaskia karst surface, so there is noquestion that theevaporites in mostcurrentsurface exposureswereremoved earlier in the Mississippian Period. It is note­worthy that most of the areas uplifted during the Laramidewere also relative highsduringtheMississippian, havingbeenpositive features since the Precambrian. Evaporite dissolu­tion continues todayat depth (Busby et al. 1983; Back et al.1983).

CONCLUSIONS

Few of the interrelated features discussed here areproducts of actualpost-Kaskaskia karst processes. However,this "true" paleokarst can neitherbe described norexplainedadequately without reference toearliersulfate-relatedprocessesandlater (post-Laramide) caveorigin.Eachprocess modifiedearlierfeatures andwas also guidedbythem,and thisinterde­pendence complicates any attempt to isolate the individualkarstevents. Itmaybemoreappropriate toreferto theassem­blageofrelictfeatures at and near the toIfOftheMississippiancarbonates as the "Kaskaskia paleokarstsystem."

The importance of interbedded sulfates within thecarbonates shouldnotbe underestimated. Theywererespon­siblefor manyof the dissolution, brecciation, alteration, anddepositional features near the topof the Kaskaskia Sequence,

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which in tum servedas targets for all subsequent karst pro­cesses; in fact, theycontinueto provide someof themostper­meable zones in the Paleozoic strataof the western U. S.

Although this paper focuses on the northwesternexposures of theKaskaskiapaleokarst, similarsuitesofrelictdepressions and caves,multiplebrecciation events, diageneticalteration, and mineralization are alsopresentat this horizonin the Centraland SouthernRockies and in the Colorado Pla­teau. Moreover, similar features are characteristic of othermajor paleokarst zones, such as the Sauk paleokarst at andbelowthe Early-Middle Ordovician unconformity, which isthemostextensive paleokarstsystem in NorthAmerica(Har­ris 1971; Kyle 1976; Mussman et al. 1988; Furman 1993).Many carbonate breccias in other strata, traditionally inter­pretedas the resultofcaverncollapse, wereactually producedby reduction and dissolution of evaporites (Dravis and Muir1993). The evolutionary details and environments of thesepaleokarstzonesprobably do notprecisely match thoseof theKaskaskia paleokarst, but theyare likelyto sharemanyof thesameprocesses and relationships.

ACKNOWLEDGMENTS

Field and laboratory workfor this projectwas sup­portedby the BlackHills Parks and Forests Association andby the Research Foundation of the State University of NewYork. Our ideas have been enhanced by discussions withMichael Wiles, Rickard Olson, and Thomas Miller of theNationalPark Service, DerekFord of McMaster University,FrankSnocker ofChadronStateCollege, 1.PaulGriesofSouthDakotaSchool ofMinesand Technology, FredLuiszerof theUniversity of Colorado, R Mark Maslyn of Littleton, Colo­rado, and J. MichaelQueenofRichmondville, N.Y. JamesL.Carew of the University of Charleston made many sugges­tions that improvedthe clarityof the text.

REFERENCES CITED

ANDRICHUK, 1. M., 1955, Mississippian Madison Groupstratigraphyand sedimentation in Wyoming and south­ern Montana: American Association of Petroleum Ge­ologists Bulletin, v. 39, p. 2170-2210.

BACK,W.,HANSHAW, B. B. ,PLUMMER, L. N., RAHN,P. H, RIGHTMIRE, C. T.,and RUBIN, M., 1983, Pro­cessand rateofdedolomitization: Masstransferand 14Cdating in a regional carbonate aquifer: Geological So­cietyofAmerica Bulletin, v. 94,p. 1415-1429.

BAKALOWlCZ, M. J., FORD, D. C., MILLER, T. E.,PALMER, AN., and PALMER, M. V., 1987,thermalgenesis of dissolution caves in the Black Hills, SouthDakota: Geological Society ofAmerica Bulletin, v. 99,p.72-99.

BRIDGES, L. W. D., 1982,Rocky Mountain Laramide-Ter­tiary subsurface solutionvs. Paleozoic karst in Missis­sippian carbonates: Wyoming Geological AssociationGuidebook, 33rdAnnualFieldConference, p. 251-264.

BUNDY, W. M, 1956, Petrology of gypsum-anhydrite de­positsin southwestern Indiana:Journal ofSedimentaryPetrology, v. 26, p. 240-252.

BUSBY, J. E, lEE, R W., and HANSHAW, B. B., 1983,Major geochemical processes related to the hydrologyof the Madisonaquifersystemand associated rocks inparts ofMontana, South Dakota,and Wyoming: U. S.Geological SurveyWater-Resources Investigations Re­port 834093, 171p.

CAMPBElL, N.P.,1977,Possible exhumedfossil caverns inthe Madison Group (Mississippian) of the northernRockyMountains: a discussion: National Speleologi­calSociety Bulletin, v. 39, p. 43-54.

CRAIG, L. C., and CONNOR, C. W., (eds.), 1979,Paleotectonic investigations of the Mississippian Sys­tem in the UnitedStates: U. S. Geological SurveyPro­fessional Paper 1010,559 p.

DEMIRALIN, A S., HURLEY, N.E, and'OESLEBY, T.W.,1993, Karst breccias in the MadisonLimestone (Mis­sissippian), Garland Field, Wyoming, in Fritz, RD.,Wilson, 1.L., and Yurewicz, D. L., Paleokarst relatedhydrocarbon reservoirs: Society for Sedimentary Geol­ogy, CoreWorkshop No. 18,p. 101-118.

DEVOTO, R R., 1988, Late Mississippian paleokarst,Leadville Formation, Colorado, in James, N. P., andChoquette, P. W., (eds.), Paleokarst: Springer-Verlag,NewYork, p. 278-305.

DRAVIS, J. J., and MUIR, I. D., 1993,Deep-burial breccia­tion in the Devonian UpperElk Point Group,RainbowBasin, Alberta, western Canada, in Fritz, R D., Wil­son, 1.L., and Yurewicz, D. L., Paleokarstrelated hy­drocarbon reservoirs: Society forSedimentary Geology,CoreWorkshop No. 18,p. 119-166.

EGEMEIER, S. J., 1981,Cave development by thermalwa­ters: National Speleological Society Bulletin, v. 43, p.31-51.

FORD, D. C., LUNDBERG, J., PALMER, A N., PALMER,M. v; SCHWARCZ, H. P., and DREYBRODT, w.,1993, Uranium-series datingofthe drainingofan aqui­fer: the exampleofWindCave,BlackHills,SouthDa­kota: Geological Society ofAmericaBulletin, v.105,p.241-250.

FRIEDMAN, G.M, 1980,Dolomite is an evaporite mineral:evidence from the rock record and from sea-marginalpondsof theRed Sea, in Concepts and models of dolo­mitization, Zenger, D.H., Dunham,1.B.,andEthington,R L., (eds.): Society of Economic Paleontologists andMineralogists Special Publication 28, p. 69-80.

FURMAN, E C., 1993, Formation of east Tennessee KnoxMVTbodies byhypogenetic- interstratal-evapcrite-TSR-

sulfuric acidkarstification, in Shelton,K. L., and Hagni,R D., (eds.): Geology and geochemistryofMississippi­valley-type ore deposits: University of Missouri, Rolla,Missouri, p. 133-148.

GOTT, G. B.,WOLCOTT, D.E., and BOWLES, C. G., 1974,Stratigraphy of the InyanKara Group and localizationof uranium deposits, southern Black Hills, South Da-

159

KASKASKIA PALEOKARST, NORfHERN ROCKIES AND BLACK HILLS

kota and Wyoming: U. S. Geological Survey Profes­sional Paper763, 130p,

HARRIS, L. D., 1971,A lowerPaleozoic paleoaquifer -- theKingsport Formation and Mascot Dolomite of Tennes­seeand southwest Virginia: Economic Geology, v. 66,p.735-743.

IllLL, C. A, 1987, Geology of Carlsbad Cavern and othercaves in the Guadalupe Mountains, New Mexico andTexas: NewMexico Bureau of Minesand Mineral Re­sources, Bulletin117,150p.

HOWARD, A D., 1964,Model forcaverndevelopment un­der artesian ground water flow, with special referenceto theBlackHills: National Speleological Society Bul­letin, v. 26, p. 7-16.

KYLE, J. R, 1976,Brecciation, alteration, and mineraliza­tion in the central Tennessee zinc district: EconomicGeology, v.71,p. 892-903.

MASLYN, R M, 1977,Fossil tower karstnearMolasLake,Colorado: TheMountain Geologist, v. 14,no. I, p. 17­25.

MCCALEB, J. A., and WEYHAN, D. A, 1969, Geologicreservoir analysis, Mississippian Madison Formation,Elk Basin field, Wyoming-Montana: American Asso­ciation ofPetroleum Geologists Bulletin, v. 53, no. 10,part I, p, 2094-2113.

MCKEE, E. D., and GUTSCHICK, R C., 1969, History ofthe Redwall Limestone of northern Arizona: Geologi­cal Society of AmericaMemoirs, v. 114, 726 p.

MEYERS, W. J., 1988, Paleokarstic features in Mississip­pian limestones, New Mexico, in James, N. P., andChoquette, P. w., (008.), Paleokarst: Springer-Verlag,New York, p. 306-328.

MUSSMAN, W. J., MONTANEZ, 1. P., and READ, J. F.,1988, Ordovician Knox paleokarst unconformity, Ap­palachians, inJames, N.P.,andChoquette, P.W., (008.),Paleokarst: Springer-Verlag, New York, p. 211-228.

MYLROIE, J. E., and CAREW, J. L., 1990, The flank mar­gin model fordissolution cavedevelopment in carbon­ateplatforms: EarthSurface Processes andLandforms,v. 15,p. 413-424.

PALMER., AN., 1995,Geochemical models forthe originofmacroscopic solution porosity in carbonate rocks, inBudd, D. A., Harris, P. M., and Saller, A., (eds.),Unconformities in carbonatestrata: theirrecognition andthesignificance ofassociated porosity: American Ass0­ciation ofPetroleum Geologists, Memoir 63, p. 77-101.

PALMER, A. N., and PALMER, M. V., 1989,Geologic his­toryof the BlackHills caves, South Dakota: National

Speleological Society Bulletin, v. 51, p. 72-99.PALMER, M V., and PALMER., AN., 1989, Paleokarst of

theUnitedStates, inBosak, P., Ford,D. C., Glazek, J.,and Horacek, I., (eds.), Paleokarst: Prague andAmsterdam, Academia and Elsevier, p. 337-363.

PIERRE, C., and ROUCHY, J. M, 1988,Carbonate replace­mentsaftersulfate evaporites in themiddleMiocene ofEgypt: Journal ofSedimentary Petrology, v. 58,p. 446­456.

PLUMMER, L. N., and BUSENBERG, E., 1982, The solu­bilities of calcite, aragonite, and vaterite in CO2-H,,osolutions between 0"and 90"C and an evaluation oftheaqueous model for the system CaC03-C02-~O:

Geochimicaet CosmochimicaActa, v.46,p.1011-1040.ROBERTS, A E., 1966, Stratigraphy of the Madison Group

nearLivingston, Montana, and discussion of karstandsolution-breccia features: UnitedStatesGeological Sur­vey, Professional Paper52B,p. BI-B22.

SANDO, W. J., 1974, Ancient solution phenomena in theMadison Limestone (Mississippian) of north-centralWyoming: U.S.Geological SurveyJournal ofResearch,vA, no. 2, p. 133-141.

SANDO, W. J., 1985,Revised Mississippian timescale, west­ern interior region, conterminous United States: U. S.Geological Survey Bulletin 1605-A, p. AI5-A26.

SANDO, W. J., 1988, Madison Limestone (Mississippian)paleokarst: a geologic synthesis, in James, N. P., andChoquette, P.w., (008.), Paleokarst: Springer-Verlag,New York, p. 256-277.

TSCHAUDER, R J., andLANDIS, G. P., 1985, LatePaleo­zoic karst development and mineralization in centralColorado, inDeVoto, R R, (00.), Sedimentology, dolo­mitization, karstification, and mineralization of theLeadville Limestone (Mississippian), centralColorado:Fieldtripguidebook, Society forEconomic Paleontolo­gistsand Mineralogists, Section 6, p. 79-91.

TULLIS, E. L, and GRIES, J. P., 1938, BlackHills caves:BlackHillsEngineer, v.24, p. 233-271.

WIGLEY, T.M L., 1971, Ionpairingand water quality mea­surements: Canadian Journal ofEarthScience, v.8,p.468-476.

WOODS, T. L., and GARRELS, R M., 1987, Thermody­namic values at low temperature for natural inorganicmaterials: an uncritical summary: Oxford Univ. Press,New York, 242p.

Received: September 5,1995Accepted: October 11,1995

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