4. Importance of Sedimentary Rx
1) Form 75% of exposed rx at
surface (outcrops)
- compose only 5% of total crust
2) Contain clues to reconstruct
past environments on Earth
11. Detrital Rock Process
1) Weathering
2) Erosion (transportation)
3) Deposition (sediment settles)
4) Lithification – turning sediment
into rock (“lithos” = rock)
(after sediment is buried)
12. Types of Lithification Processes
a) Compaction
- most effective on fine-grained rx
(ex: shale)
Exception: St. Peters Sandstone
Starved Rock State Park, IL
14. Sedimentary Rx Classification
2) Chemical – named based on
composition
Ex: calcite = limestone
halite = rock salt
plant remains = coal
15. Chemical Sedimentary Rocks
a) Inorganic – formed by chemical
reactions in environment
Ex: evaporites – rock gypsum,
rock salt
Ex: Travertine (limestone)
16. Inorganic Chemical Sed. Rx
Calcite:
*Limestone = mostly marine origin
Travertine = speleothems
Oolitic Limestone = tidal flats
* Most abundant chemical
sedimentary rock
30. Clues
3) Composition – minerals present
Two most common minerals found
in sedimentary rocks are _____
and ______ .
31. Variety of minerals:
Ex: quartz, K-spar, plagioclase
feldspar, mafic minerals, rock
fragments
- very little chemical weathering
- indicates rapid deposition close
to source area
Ex: arkose in alluvial fan
34. Sedimentary Structures
a) Bedding – layering w/in rock
Bedding plane – flat surfaces
along which rx tend to break or
separate
- separates different episodes of
deposition
35. Bedding
i) Laminar bedding – horizontal
layers
- usually deposited in calm energy
environment
Ex: shale, some sandstones
36. Bedding
ii) Graded bedding – sorted by
size
- occurs w/sudden decrease in
velocity
Ex: turbidity currents, alluvial fans
44. Clues
5) Fossils – evidence of
prehistoric life
Fossil record is incomplete
- shows remarkable pattern of
change from simple to complex
life forms
45. Steps to becoming a fossil
Step 1: Death
Step 2: Hard parts – bones, teeth,
shells (Who you are!)
Step 3: Rapid burial (Where you
die!)
Step 4: Time (prehistoric)
46. Fossils
Fossil record biased towards
marine environment
- abundant life in oceans
- many critters have hard parts
- lots of sediment for quick burial
52. Lithofacies map
For a particular moment in
geologic time, rocks indicate the
landscape
1) Map out the areas where each
rock type is found & draw
boundaries
53. Lithofacies map
2) Look at the lithologies (rock
types) & compare them to:
- nearby rx
- geometry of rock unit
3) Determine the original
depositional environment