FALL 2005GEOLOGY 285:INTRO. PETROLOGYDr. Helen LangDept. of Geology & GeographyWest Virginia UniversitySandstone ClassificationSandstones with less than 15% mud, arecalled Arenites, use the front triangleQLFPercent Mud MatrixNaming ArenitesQFLSandstone Classification15% to 50% mud,called Wackes, use middle triangleQLFNaming Wackes15% to 50% mudQFL“Textural Maturity” of a Ss• A measure of the progress of a clasticsediment in the direction of chemical, mineralogical and textural stability• Affected by processes that take a long time• Maturity increases with total input of kinetic energy– time of transport, distance of transport– energy of mediumIncreasing “Textural Maturity” is indicated by:• clay removal• increased sorting• increased rounding• breakdown (absence) of unstable fragments• breakdown (absence) of unstable mineralsImmature Sandstones - limited transport, rapid deposition and burial• Lots of muddy matrix• poorly sorted• poorly rounded fragments and grains• lots of unstable lithics and unstable minerals• mostly wackes• deposited in convergent margin settings, arc-trench gapSuper-mature Sandstones• Clean (no mud matrix)• well-sorted• well-rounded grains• mostly quartz grains• quartz arenites• Cratonic, typically recycled, formed in beach or other high energy environmentIncreasing Textural Maturity• Wackes - immature• Litharenites• Arkoses• Subarkose and sublitharenite• Quartz arenites -
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