Sedimentary rocks
Modified from www.matsuk12.us/1768201159295920/lib/.../Sedimentary_rocks.ppt and www.geo.utep.edu/pub/ellis/geol1303/sed_rocks.ppt
Relative abundances of major rock types exposed at the Earth's surface.http://gsabulletin.gsapubs.org/content/121/5-6/760/F2.expansion
Why a sedimentary rock study is important for ENGINEERS ?
Sedimentary Rocks
Weathering
Erosion
Transport
Deposition
Sediments
Lithification
Weathering
The sediments that make up sedimentary rocks are produced by:
Mechanical & Chemical Weathering
Mechanical Weathering
Thermal stress
Frost weathering
Hydroric action
Biological weatering
Chemical Weathering
Oxidation (rusting)
Dissolution (Acid rain)
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
WaterWind
IceGravity
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
Clastic Rocks Chemical Rocks
vs.
Difference: TextureClastic Texture
vs.
Chemical (Crystalline Texture)
Clastic Rock Composition
Clastic Rocks• Lithic Fragments• Quartz• Clay Minerals• Fossil Fragments• Rust Minerals• Orthoclase• Muscovite / Biotite
Clastic Rock Texture
Clastic Texture• Grain Size• Grain Sorting• Grain Rounding• Sediment Maturity
Grain Size
Detrital Rock Names(Based Primarily on Grain Size)
Sand Sized: Sandstone
Gravel Sized:Conglomerate
Siltstone Shale
Mud Sized:Mudstone
Grain Size Factors : Deposition Energy (environment) and Transportation Path
Sorting
Sorting Factor : Deposition Energy (environment)
Grain Roundness
Roundness Factor : Transportation path (environment)
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
Clastic (Detrital) Sedimentary Rocks
Grain Size Roundness Sorting Composition Name
Rounded Moderate to
poor Fragments of any rock type CONGLOMERATE
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
Clastic Sedimentary Rock ID
• Compacted and cemented from detrital sediments
• Formation processes: Transportation, deposition, compaction, and cementation
• Fossil-fuel bearing rocks
• Classified based on particle size
• Shale: The most abundant clastic rocks
Clastic Sedimentary Rocks (Keynotes)
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
• Precipitated from chemical solutions and/or accumulated chemical, biological matter
• Classified based on composition and texture
• Limestone:: The most abundant nonclastic sedimentary rocks
• Common texture: Crystalline, microcrystalline, skeletal, oolitic, massive
Chemical Sedimentary Rocks (Keynotes)
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
Exercises P48
Exercises P50