Mudrocks_etc

Mudrocks,OrganicDeposits,andotherRareSedimentsMudrocks—SiltsandClays FormedfromweatheringofprimaryMinerals Accountsfor60ofallsiliclasticsedimentaryrocks Mostformfrominsoilsuponcontinents SomeformfromalterationbygroundAndmarinewatersSilts–EolianDepositionAirborneSiltsinaDustStormDustStormStratford,TX1935;TheDustBowlEraExtendedperiodsofDustStormeventscanleadtosignificantaccumulationofsilts,especiallyinlowareasPleistoceneageaccumulationofsiltsinthecentralU.S.A.Requiresfairlydryclimate,wind,andalotofsiltsizematerialWhenSiltsizedustaccumulatesassediment,itiscalled“LOESS”.LoessinNepalRiverGravels,SeetheChannel?LoessLayerPleistoceneLoessmantlesthelandscapeinpartsofIowa,U.S.A.EarlyPermianHalgaitoFm.,SoutheasternUtah,U.S.A.Ismademostlyofsilt,soitmaybealoessiteLatePennsylvanianageMaroonFm.Colorado,U.S.A.LoessiteBentonitesAlteredvolcanicashfalldepositsBentonitesBentonitesBentonitesaremostlypreservedinlowareasBentonitesAlterationofVolcanicAshesreleasessilicaIntosolution,leavingmontmorillonite Toothpaste Paint Filler DrillingMudsWhatbecomesofthefreesilica?SomeofthefreesilicaisusedtoformDIATOMITESANDDIATOMACEOUSEARTHDIATOMSaresinglecelledphotosynthesizersthatusesilicainsolutiontomakeaskeletonDIATOMskeletonsaremadeofa“mineralloid”calledopalA.OpalAisamorphoussilicawithlotsofWatersofhydration:SiO2nH2OAlthoughsoftandnotchemicallystableOpalAisbeautifulandusedinjeweleryWhenOpalAisburied,putunderpressureFromoverlyingsedimentsandheated,watersofhydrationareexpelledtoformMicrocrystallinequartz,orchert:SiO2ORGANICMATTERINTHESEDIMENTARYRECORDOfallSiliciclastics,mudrocksholdthelargestamountofO.M.MostMudrockshave2%O.M.byweight3kindsofOrganicMatter Humus–soilorganicmatter Peat–organicmatteraccumulatedinfreshorbrackishH2O Sapropel–lowoxygenenvironments,finelydisseminatedBlackShales–3to10%weight%OrganicmatterIncorporatesapropellicorganicmatterBlackShalesaccumulateinsluggish,poorlycirculatedmarineEnvironments(anoxia).AbundantinEarth’sPast.EpiericSeasOilShales 25weight%organicmatter AlmostalloftheO.M.iskerogen,derivedfromALGAE “Cracks”togivepetroleumat350degreesCelcius Notallare“shales”becausemanydepositsareformedinFinegrainedcarbonate ImportantsourceofEnergyaroundtheworldTheMostFamousOil“Shale”youmightknowIstheEoceneageGreenRiverFormationAbiglakesysteminColorado,Wyoming,andPartsofUtah.AlternatingperiodsofalgalBloomsandcarbonateprecipitationfromtheWatercolumn.AnoxicbottomwaterresultedInexquisitelypreservedfossilfishandplantsCoalsCoals–Havegreaterthan70%organicCarbonDerivedalmostentirelyofplantO.M,soitisDominantlyPeattypeorganicmatterCoalRankingPeat–NoRank,unconsolidated,semicarbonizedplantremainswithhighmoisturecontent.NotCoalLignite–lowestrank.Browntobrownishblackcoalswithhighwatercontentandcommonlyreatinsmuchofthestructuresofthewoodyplantfragments.Subbituminouscoals–betweenligniteandbituminouscoalBituminouscoals–hard,blackcoalswithverylittlewaterandhighCcontent.Alternatingbrownandblackbands.Anthracite–Hard,black,“glassy”anddensecoalwith>90%Carbon.Exhibitsconchoidalfracture.Typicallyonlyfoundinveryancientcoals(Carboniferousage).BandedIronFormationsPreserverecordofimportanteventinEarthhistoryImportantsourceofindustrialiron.BandedIronFormations