An unusual paleokarst sedimentary rock in the Bohemian Karst (Czech Republic), and its regional tectonic and geomorphologic relationships

摘要

AnunusualtypeofpaleokarstcarbonatesedimentaryrockhasbeenfoundintheBohemianKarst,CzechRepublic.Thiswell-layeredcoarse-crystallinelimestoneisreddishincolorandoccursashorizontalorslightlyinclinedlayersfillingdeeppaleokarstcavitieswithinkarstifiedfaultsinEarlyDevonianmarine-limestonehostrocks.FieldobservationsconfirmthatthesesedimentaryrocksareundoubtedlyyoungerthanthepolyphasedVariscanfolding.PetrographicandgeochemicalstudiesindicatethatthestudiedpaleokarstlimestoneisquitedifferentfromtheSilurianandDevonianlimestones,fromcommoncavespeleothems,aswellasfromthetypicalclasticLateCretaceousandCenozoickarstsedimentsoftheBohemianKarst.Carbonatedelta;13Canddelta;18Ostableisotopicratiosofthepaleokarstlimestone(delta;13Cfrom-4.0to-6.2a€°,delta;18Ofrom-6.2to-8.4a€°PDB),differingbothfrommarineSilurianandDevonianlimestonesandCenozoicsecondarycavecarbonatesofthearea,correspondtoanon-marinedepositionalenvironment.ThepaleomagneticdatasuggestthatmagneticpropertiesofthestudiedrockswereacquiredduringtheEarlytoMiddleTriassic,althoughtheseageshavenotyetbeenconfirmedbyfindsofcontemporaneousmicrofossils.TheonlymicrofossilsthatwereextractedusingdissolutionmethodsconsistofseveralyoungerplantandfaunalremainsincludingangiospermpollengrainspecimensbelongingtothefamilyMyricaceae,likelyTertiaryinage.Theirsporadicoccurrenceisinterpretedastheresultofsecondaryinfiltrationsintothemillimeter-widecracksandcavities,incorrespondencewiththethin-sectiondataondiageneticsuccessions.