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 triangle Plot %Q (quartz + chert), %F (feldspar), %L (unstable lithic fragments) on the front triangle Know names and their positions! Naming Wackes Sandstones with 15% to 50% mud are called Wackes, and are Plotted on the middle triangle Plot %Q (Q/Q+F+L), %F (F/Q+F+L), %L (L/Q+F+L) on the middle triangle Know 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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