2 sedimentary rocks Flashcards
sedimentary rock basics
Cover ~75% of the continents
Cover nearly all the ocean floor
Record of life
Host rock for
Oil
Gas
Coal
Metals
Gemstones
Make Utah famous
Origins of Sedimentary rocks
Formed from the activity of surface fluids (water, ice, air/wind)
Formed of sediments
Where do the sediments come from?
Mechanical and chemical breakdown of pre-existing rocks
Where do the materials for sedimentary rocks come from?
Weathering
Of previous rocks into small pieces called sediment
Erosion/Transportation
Of sediment/dissolved minerals
Deposition
Of sediment/dissolved minerals
Lithification
Transformation into solid rock
Weathering types:
rain, snow, ocean, rivers, ice, wind, water, other rocks
Weathering vs erosion
Weathering
-Breakdown and alteration of rocks on the Earth’s surface
Aided by hydrosphere and atmosphere
Erosion
-Removal of debris produced by weathering breakdown
Aided by hydrosphere and atmosphere (and gravity)
Physical weathering: ice wedging
MAJOR: Ice Wedging(most common way to physically weather a rock)
Frozen water expands, forcing rock apart
Necessary conditions
Water (duh)
Cracks
Temperature fluctuation
Creates talus cones
MAJOR: Sheeting (aka unloading or exfoliation)
Talus cones
Piles of rock debris accumulating at base of a cliff
Ice wedging breaks the rocks
Gravity pulls the fragments down
physical weathering: sheeting, unloading, exfoliation
MAJOR: Sheeting (aka unloading or exfoliation)
Release of confining pressure on deeply buried rocks
Expansion creates cracks
Rocks break along these cracks
Conditions:
Rock formed deep in the crust
Usually intrusive or metamorphic
Overburden (rocks above) removed (look at slide for picture)
——- ——n——-
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physical weathering minor pieces
Minor: Heat
Minor: Crystal Growth
Minor: Plant growth
Chemical weathering
Minerals are destroyed or altered by chemical reactions
Often, secondary minerals are formed
Two main types:
-Dissolution
Mineral completely dissolves into water
Halite (salt)
Gypsum
Special subtype:
Acid Hydrolysis
-Oxidation
Chemical weathering: acid hydrolysis
Acid Hydrolysis
When H+ ions attack the minerals
Water that is slightly acidic
Examples: Cave formation, acid rain
(what happens to feldspar)
-Major: Feldspar weathering
Secondary mineral formation
Clay is a HYDRATED mineral
feldspar+acidic water=dissolved materials and clay(parts that don’t dissolve away)
water becomes acidic after it hits and runs over the earth
Chemical weathering: oxidation and dissolution and hydrolysis
-Dissolution and hydrolysis
-Oxidation
Rust
Fe2+ is converted into Fe3+
Hematite is the most common oxidized secondary mineral
Hematite is usually red
why is sea water salty
C. Rivers that flow into the ocean have high concentrations of salts from the chemical weathering of feldspars
D. Evaporation concentrates salts in the ocean water
Chemical weathering factoids
Certain elements (Na, K, Ca, Mg) will dissolve into water
Why is seawater salty?
Certain elements (Al, Fe, Si) get left behind
Stable in the soil
Feldspars weather to CLAY
NaAlSi3O8 (feldspar)
Which elements get carried out to the ocean?
Which get left behind to form clay?
Physical+ chemical weathering
physical weathering breaks up the solid rock increasing the surface area
more surface for the water to attack chemically.
them together is the most rapid type of weathering
Transportation(erosion) and Deposition
Transportation
Dispersal of solid particles and ions
By gravity and fluids
Deposition
Settling of solid particles and ions out of the transporting fluid (precipitate out of fluid)
Lithification
Turning loose sediment into rock
The two C’s
-Compaction
-Cementation
Lithification: compaction
-Reduction of pore space between particles (less water and air space because of pressure)
-Because of the weight of overlying sediment
Lithification: cementation
Mineralization within pore space (fills cracks)
Glues the grains together
Common cements
CaCo3 (calcite)
SiO2 (silica)
Uncommon cement
Iron oxide (rust, essentially)
Classification of sedimentary rocks
Composition
What is it made of?
Texture
3 main categories
Clastic
-Fragments of other rocks
-Cemented together
Chemical/Biochemical
-Chemical precipitates
Organic
-Carbon-rich remains of once-living organisms
Clastic sedimentary rock: materials and grain size classification
Materials
-Mineral grains
-Rock fragments
-Cementing material
Classified by GRAIN size
-Conglomerate: rather large 2<c<16mm
-Sandstone: medium1/16<s<2mm
-Mudrock: tiny sand like pieces<1/16mm
Common Clastic sedimentary rocks: conglomerate and breccia
Conglomerate
Grain size >2 mm
Conglomerate
-Rounded clasts(pieces in between glue)
Breccia
-Angular clasts(pieces in between glue)
Common clastic sedimentary rock: sandstone
Sandstone
Sand-sized particles (2mm – 1/16 mm)
Usually made of quartz grains (stronger than feldspar)
Sometimes with feldspars, other minerals
Common clastic sedimentary rock: mudstone and shale
Mudrock
Silt or mud sized particles (<1/16mm)
Siltstone
Shale or Mudstone
dnk: shale breaks into clean plates, mudstones ate kind of lumpy
classification of grains
Closer to source(original rock it broke off from)
-Large
-Angular
-Poorly sorted (wide variety)
-Feldspar-rich: hasn’t been thoroughly attacked by hydrolysis yet
Farther from source
-Small
-Rounded(been smacked around)
-Well sorted
-Quartz rich (quartz lasts)
Where would we find these types of sedimentary rocks?
close to source: conglomerate
middle: sandstone:
far from the source: mudstone
Depositional environment
What was the environment where the sediments were deposited?
IT MATTERS!
High energy
Large grain size
Low energy
Small grain size
