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sedimentology - Sedimentary Rock Classification...

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1 Sedimentary Rock Classification Depositional Environments Sedimentary Structures Sedimentary Rock Classification Depositional Environments Sedimentary Structures February 14, 2002 February 14, 2002 Geology 211, Physical Geology ©Copyright, 2002, Ron Parker Geology 211, Physical Geology ©Copyright, 2002, Ron Parker Geology 211, Physical Geology, ©, 2002, Ron Parker + 5% of rocks in the outer 10 miles of crust. + 75% of rocks exposed at the surface. + Preserve evidence of surficial processes... ! Occurring today ! That occurred in the past Sedimentary Rock Geology 211, Physical Geology, ©, 2002, Ron Parker + Sediment originates from mechanical and/or chemical weathering. + Two major divisions of sedimentary rock. ! Detrital – Made of particles. ! Chemical – Made from dissolved ions that crystallize into solids. Types of Sedimentary Rock Geology 211, Physical Geology, ©, 2002, Ron Parker Detrital Sedimentary Rocks + Sedimentary particles are… ! Eroded from pre-existing rock. : Mechanical weathering : Chemical weathering ! Transported by wind, water or ice. ! Retained in a depositional environment . Geology 211, Physical Geology, ©, 2002, Ron Parker Transport Effects Transport Effects + Sediments are modified by transport. + Sorting – The uniformity of grain size. ! Well-sorted – Uniform grain size. ! Poorly sorted – Wide variety of grain sizes. + Sorting indicates the constancy of environmental energy. ! Well sorted – Uniform energy i.e. a beach ! Poorly sorted – Variable energy i.e. an alluvial fan + Sediments are modified by transport. + Sorting – The uniformity of grain size. ! Well-sorted – Uniform grain size. ! Poorly sorted – Wide variety of grain sizes. + Sorting indicates the constancy of environmental energy. ! Well sorted – Uniform energy i.e. a beach ! Poorly sorted – Variable energy i.e. an alluvial fan Geology 211, Physical Geology, ©, 2002, Ron Parker Transport Effects Transport Effects + Rounding – Relative sphericity. + Sediment grains start out as angular grains. + With transport, sediments bocome more spherical. ! Well-rounded – Long transport distances ! Angular – Negligible transport + Rounding – Relative sphericity.
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