2 sedimentary rocks

Question 1

sedimentary rock basics

Answer 1

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

Question 2

Origins of Sedimentary rocks

Answer 2

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

Question 3

Where do the materials for sedimentary rocks come from?

Answer 3

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

Question 4

Weathering types:

Answer 4

rain, snow, ocean, rivers, ice, wind, water, other rocks

Question 5

Weathering vs erosion

Answer 5

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)

Question 6

Physical weathering: ice wedging

Answer 6

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)

Question 7

Talus cones

Answer 7

Piles of rock debris accumulating at base of a cliff
Ice wedging breaks the rocks
Gravity pulls the fragments down

Question 8

physical weathering: sheeting, unloading, exfoliation

Answer 8

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——-
n

Question 9

physical weathering minor pieces

Answer 9

Minor: Heat
Minor: Crystal Growth
Minor: Plant growth

Question 10

Chemical weathering

Answer 10

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

Question 11

Chemical weathering: acid hydrolysis

Answer 11

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

Question 12

Chemical weathering: oxidation and dissolution and hydrolysis

Answer 12

-Dissolution and hydrolysis
-Oxidation
Rust
Fe2+ is converted into Fe3+
Hematite is the most common oxidized secondary mineral
Hematite is usually red

Question 13

why is sea water salty

Answer 13

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

Question 14

Chemical weathering factoids

Answer 14

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?

Question 15

Physical+ chemical weathering

Answer 15

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

Question 16

Transportation(erosion) and Deposition

Answer 16

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)

Question 17

Lithification

Answer 17

Turning loose sediment into rock
The two C’s
-Compaction
-Cementation

Question 18

Lithification: compaction

Answer 18

-Reduction of pore space between particles (less water and air space because of pressure)
-Because of the weight of overlying sediment

Question 19

Lithification: cementation

Answer 19

Mineralization within pore space (fills cracks)
Glues the grains together
Common cements
CaCo3 (calcite)
SiO2 (silica)
Uncommon cement
Iron oxide (rust, essentially)

Question 20

Classification of sedimentary rocks

Answer 20

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

Question 21

Clastic sedimentary rock: materials and grain size classification

Answer 21

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

Question 22

Common Clastic sedimentary rocks: conglomerate and breccia

Answer 22

Conglomerate
Grain size >2 mm
Conglomerate
-Rounded clasts(pieces in between glue)
Breccia
-Angular clasts(pieces in between glue)

Question 23

Common clastic sedimentary rock: sandstone

Answer 23

Sandstone
Sand-sized particles (2mm – 1/16 mm)
Usually made of quartz grains (stronger than feldspar)
Sometimes with feldspars, other minerals

Question 24

Common clastic sedimentary rock: mudstone and shale

Answer 24

Mudrock
Silt or mud sized particles (<1/16mm)
Siltstone
Shale or Mudstone
dnk: shale breaks into clean plates, mudstones ate kind of lumpy

Question 25

classification of grains

Answer 25

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)

Question 26

Where would we find these types of sedimentary rocks?

Answer 26

close to source: conglomerate
middle: sandstone:
far from the source: mudstone

Question 27

Depositional environment
What was the environment where the sediments were deposited?

Answer 27

IT MATTERS!

High energy
Large grain size
Low energy
Small grain size