Lecture 9: Surface Processes: chemical and physical weathering and sedimentary rocks
Sedimentary Rocks Weathering Erosion Transport Deposition Sediments Lithification.
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Transcript of Sedimentary Rocks Weathering Erosion Transport Deposition Sediments Lithification.
Sedimentary Rocks
Weathering
Erosion
Transport
Deposition
Sediments
Lithification
WeatheringThe sediments that make up sedimentary rocks are produced by:
Mechanical & Chemical Weathering
Mechanical Weathering
Chemical Weathering
MineralStability
Products of Weathering
• Lithic (Rock) Fragments(granite, basalt, schist, etc.)
• Dissolved Ions(Calcium, Potassium, Sodium, etc.)
• Rust Minerals (Hematite, Goertite, etc.)
• Clay Minerals(Bentonite, Montmorillonite, etc.)
• Residual Minerals(Quartz, Orthoclase, Muscovite, etc.)
Erosion & Transport
WaterWindIce
Gravity
Deposition
Lithification
Sediment
Rock
Cementation
Typical Cement:•Calcite•Quartz
Sedimentary RocksIdentification
Note: Use the same terms to describesediments & sedimentary rocks.
Only difference is lithification!
Rock Identification is based on:
•Composition
What minerals make up the rock?
•Texture
What is the shape, size and orientation of the mineral grains that make up the rock?
Major Difference:Crystalline vs. Clastic
Types of Sedimentary Rocks
Detrital Rocks Chemical Rocks
vs.
Difference: TextureDetrital (Clastic
Texture)
vs.
Chemical (Crystalline Texture)
Detrital Rock Composition
Detrital Rocks• Lithic Fragments• Quartz• Clay Minerals• Fossil Fragments• Rust Minerals• Orthoclase• Muscovite / Biotite
Detrital Rock Texture
Clastic Texture• Grain Size• Grain Sorting• Grain Rounding• Sediment Maturity
Grain Size
•Gravel2mm
•Sand1/16 mm
•Mud - Silt1/256 mm
•Mud - Clay
Detrital Rock Names
(Based Primarily on Grain Size)
Sand Sized: Sandstone
Gravel Sized:Conglomerate
Siltstone Shale
Mud Sized:Mudstone
Sorting
Grain Roundness
Gravel Sized Detrital Rocks
(Subdivided Based on Grain Roundness)
Breccia
Conglomerate
Maturity
Mature•Well Sorted•Well Rounded•All Quartz
Immature•Poorly Sorted•Angular grains•Mixed Compositionincluding clay
Sandstones
(Subdivided based on maturity)
Quartz SandstoneArkose (Sandstone)
Lithic Sandstone Greywacke
Sandstones Under a Scope
Clastic (Detrital) Sedimentary Rocks
Grain Size Roundness Sorting Composition Name
Rounded Moderate to
poor Fragments of any rock type CONGLOMERAT E
Gravel-sized (> 2 mm)
Angular Moderate to
poor Fragments of any rock type BRECCIA
Rounded Well All Quartz - usually white to tan QUARTZ
SANDSTONE
Sub-rounded to
Angular
Moderate to poor (few
grains >2mm)
Feldspar (usually orthoclase), micas, quartz, and other minerals
ARKOSE (Arkosic Sandstone)
Sub-rounded
Moderate to well
Quartz, lithic fragments, and other minerals
LITHIC SANDSTONE
Sand-sized (visible grains up to 2 mm)
Rounded to angular
Moderate Quartz and rock fragments mixed
with >15% clay; often gray colored GRAYWA CKE SANDSTONE
Silt-sized (feels gritty)
(to small to see)
Well Clay and quartz (but usually too
small to see) SILTSTONE
Clay (but usually too small to see); Massive
MUDSTONE Clay-sized
(feels smooth) (to small to
see) Well
Clay (but usually too small to see); Breaks into semi-flat layers
SHALE
Detrital Sedimentary Rock ID
Chemical Rock Texture
Crystalline Texture
• Coarse• Fine
Chemical Sedimentary Rocks
(Names based primarily on composition)
Basic Rock Name• Limestone• Chert• Rock Salt• Rock Gypsum• Peat or Coal
Composition• Calcite• Quartz (silica)• Halite• Gypsum• “Carbon” / Plant Remains
Chemical Rocks(Names based mainly on
composition)
LimestonesCrystallineLimestone
Chalk
Fossiliferous Limestone
Chemical Rocks (cont.)Evaportites
RockGypsum
Rock Salt
Coal
Chert
Chemical, Biochemical & Organic Sedimentary Rocks
Composition Texture Name
Crystalline - medium to coarse (visible) grains CRYSTALLINE
LIMESTONE
Crystalline - grains too small to see MICRITE
Abundant fossils in a fine- to coarse-grained crystalline matrix FOSSILIFEROUS
LIMESTONE
Calcite (acid reaction)
Fine-grained powder, earthy smell (often black, gray, or white) CHALK
Dolomite (acid reaction)
Crystalline - fine to coarse grained DOLOSTONE
Crystalline - grains too small to see; conchoidal fracture CHERT Quartz (scratches
glass) Fine-grained powder, earthy smell (no acid reaction) (often white) DIATOMITE
Gypsum Crystalline - fine to coarse grained ROCK GYPSUM
Halite (tastes salty)
Crystalline - fine to coarse grained ROCK SALT
Fibrous, brownish plant material; soft PEAT Plant Remains
(Carbon) Dense, black masses; depending on grade may be dull to vitreous; lower grades may contain minor fossils
COAL
Chemical Sedimentary Rock ID
Sedimentary Rocks on Earth