Geology

Sedimentary Rock Classification Depositional Environments Sedimentary Structures

Sedimentary Rock
+ 5% of rocks in the outer 10 miles of crust. + 75% of rocks exposed at the surface. + Preserve evidence of surficial processes...

February 14, 2002
Geology 211, Physical Geology Geology 211, Physical Geology ©Copyright, 2002, Ron Parker ©Copyright, 2002, Ron Parker

! Occurring today ! That occurred in the past
Geology 211, Physical Geology, ©, 2002, Ron Parker

Types of Sedimentary Rock
+ 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.
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
+ Sediments are modified by transport. + Sorting – The uniformity of grain size. + Sorting indicates the constancy of environmental energy.
! Well-sorted – Uniform grain size. ! Poorly sorted – Wide variety of grain sizes.

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

! Well sorted – Uniform energy i.e. a beach ! Poorly sorted – Variable energy i.e. an alluvial fan
Geology 211, Physical Geology, ©, 2002, Ron Parker

Geology 211, Physical Geology, ©, 2002, Ron Parker

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Transport Effects
+ Maturity – Unstable minerals (feldspars, micas) are removed with transport and by chemical weathering.
! Immature sediments ! Mature sediments
: Contain unstable grains : Indicate short transport or arid conditions : Only stable grains