Transcript Sedimentary Rocks I. Sedimentary rocks

Earth Materials
Sedimentary Rocks
• I. Sedimentary rocks are formed from
pieces of other rock; from organic material;
or from chemicals out of solution.
• a. Sediments: loose particle from the
weathering (breakdown) of pre-existing
rocks or organic materials.
•
ex. Shells, sand, pebbles, mud
• II. There are 2 main groups of
sedimentary rocks:
Clastic rocks (from fragments of rock)
and Non-clastic rocks (from chemical or
organic processes)
• 1. Clastic sedimentary rocks.
• a. Classified by size of particles. (clay, silt,
sand, etc)
• b. rocks are named according the particle
size, and not by the composition.
• c. Clastics have cement to hold the
particles together. (such as calcite, iron
oxide and silica )
The cement is the youngest part of the
rock. The sediments can be a huge
assortment of ages.
• d. Lithification is the process of becoming
sedimentary rock (loose sediments
becoming rock), which involves:
– compaction due to pressure or weight of
overlying sediments (clay becomes shale), or
– Cementation by precipitation of minerals in
pore spaces from waters carrying ions in
solution (siltstone, sandstone, conglomerate)
e. The size of the sediments indicate the
environment of formation
• 2. Non-clastic: (chemical/biochemical)
a. Chemical rocks: precipitation of
minerals from water in lakes, in the sea, in
caves, and in hot springs.
– Evaporites form from the evaporation of water
(usually seawater). Rock salt , and
– Precipitates when ions come out of solution
in water: ex. limestones
• b. Organic rocks, usually coal (from
plants) and various limestones with shell
fragments.
• ex. Coquina (fossil shells cemented together;)
and Chalk (made of microscopic planktonic
organisms; fizzes readily in acid)
• c. Limestones can be chemical, bioclastic
or a combination of both.
• II. Sedimentary rocks form a thin veneer
on top of the non-sedimentary continental
crust,
• 1.Weathering creates sediments that build
up.
2. MOST sedimentary rocks form in quiet
water, because the particles are carried by
rivers and deposit in slow areas of the
river, in lakes, deltas and in the ocean.
3. Stratification is the creation of layers.
– occurs because new sediments are
deposited on top of older ones in
horizontal layers.
4. Fossils are almost only found in
sedimentary rock Metamorphism and
melting destroy the imprint, bone, and
trace fossils.
• New York has different types of salt and
gypsum deposits. How did they get here?