Transcript 3.3 Sedimentary Rocks

Sedimentary Rocks
I. Formation of Sedimentary Rocks
- Sedimentary = “settling”
- Form when solids settle out of a
fluid such as water or air.
- The sediments eventually become
cemented to form rocks.
• Weathering - is a process in which
rocks are physically and chemically
broken down by water, air, and living
things.
• Erosion - involves weathering and the
removal of rock.
• Deposition - when an agent of erosion –
water, wind, ice, or gravity – lose
energy, it drops the sediments.
• Compaction – is a process
that squeezes, or compacts,
sediments.
• Cementation – “glue” - takes place when
dissolved minerals are deposited in the
tiny spaces among sediments.
II. Classification of Sedimentary Rocks
• Can be classified into two main groups
according to they way they form.
1. Clastic Sedimentary Rocks –
composed of weathered bits of
rocks and minerals.
•
•
Classified by particle size.
Conglomerate – made up of rounded
particles.
•
Breccia – made up of angular
particles.
Ex: Shale, Sandstone, Siltstone
Conglomerate
Shale with Plant Fossils
2. Chemical Sedimentary Rocks –
Forms when dissolved minerals
precipitate from water solutions.
(water usually evaporates or boils)
• Ex: Limestone & rock salt.
Fossiliferous Limestone
III. Features of Sedimentary
Rocks
• Unique features are clues to how, when,
and where they formed.
1. In undisturbed rocks, the oldest layers
are found on the bottom and the youngest
at the top.
Law of Superposition
2. Ripple Marks – rock formed along
the beach or stream bed.
3. Mud Cracks - formed when wet mud or
clay dried and shrank, leaving a rock
record of a dry environment.
4. Fossils – traces of remains
of ancient life.
Trilobite
Where is the oldest layer located
on this picture?