Lacustrine couplet-lamination: evidence for Late Pennsylvanian seasonality in central equatorial Pangaea (Stephanian B, MÅ¡ec Member, Central and Western Bohemian basins)

Bulletin of geosciences

Sýkorová I¹  Laurin J¹  Lojka R¹  Matysová P¹  Matys Grygar T¹ 

关键词: lamination;    cyclicity;    freshwater lake;    dispersed organic matter;    siderite;    palaeoclimate;   

DOI  :  

来源: Czech Geological Survey

【 摘 要 】

Alargefreshwaterlakeformed(lakearea>5000km2)duringtheStephanianB(tilde;304My)periodoftheLatePennsylvanianinthecentral-eastequatorialPangaeaandcoveredasubstantialpartofthecontinentalLatePalaeozoicbasinsinthecentralBohemianMassif(theCzechRepublic).LacustrinemudstonesoftheMÅ¡ecMemberwereacquiredfromtwoshallowboreholes80kmapartandwereanalysedforlaminationstructureandperiodicity,mineralcompositionanddispersedorganicmatter,inordertoobtainmoredetailedinformationonthepalaeoenvironmentalchangewithanearannualresolution.Twohydrologicalstatesofthelakewereidentified,includinghighlake-levelperiodswithdysoxicconditionsonthelakefloor,underapermanentlythermallystratifiedhypolimnionfavouringorganicmatterproductionandstorageduringperiodsofcondensedsedimentationproducinganirregularlaminationpattern.Aseriesofcontinuousregularcoupletlaminationreflectconditionsofpartially,possiblyseasonallystratifiedhypolimnionwithadvancedlake-watermixingandorganicmatteroxidation.Thecoupletlaminationresultsfromanalternationoforganic-claylaminae,consistingofvariableproportionsofautochthonousalgalandmicrobialorganicremnants,withdetritalsiltlaminaeaccompaniedbyauthigenicsideriteandhumifiedorburntterrestrialplantdebris.Similarlyasinsomemoderntropicallakes,suchregularhigh-frequencyvariationsinsedimentsupplysuggestseasonalchangesinrainfalltoberesponsibleforcoupletformation.Coupletthicknessdistributionshowsstatisticallysignificantperiodicities,resemblingmultiannualtomultidecadalscalesobservedinrecentsedimentarchives,andsoindirectlysupportsseasonalityinprecipitationinPangaeanlow-latitudes,atleastduringpartoftheStephanianB.

【 授权许可】

Unknown