Geol 285 - Petrology, Dr. Helen M. Lang, West Virginia University, Fall 2005 Sandstone Classification Sandstone Classification after Folk (see handout)based on % of detrital Quartz+Chert (Q), Feldspar (F, plagioclase + orthoclase),Lithics (L, unstable lithic fragments)and % mud matrix Naming Arenites - Sandstones with <15% mud are called Arenites, and are Plotted on the front trianglePlot %Q (quartz + chert), %F (feldspar), %L (unstable lithic fragments) on the front triangleKnow names and their positions! Naming WackesSandstones with 15% to 50% mud are called Wackes, and are Plotted on the middle trianglePlot %Q (Q/Q+F+L), %F (F/Q+F+L), %L (L/Q+F+L) on the middle triangleKnow names and their positions! "Textural Maturity" of a Ss- A measure of the progress of a clastic sediment 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 medium Increasing "Textural Maturity" is indicated by:- clay removal - increased sorting - increased rounding - breakdown (absence) of unstable fragments - breakdown (absence) of unstable minerals Immature 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 - formed in convergent margin settings, arc-trench gap Super-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 environment In order of increasing Textural Maturity- Wackes - immature - Litharenites - Arkoses - Subarkose and sublitharenite - Quartz arenites -
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