Rocks

B. Sedimentary Rocks

What are sedimentary rocks formed from?

Where do sedimentary rocks form?

How do you turn sediment into rock?

Sedimentary rocks are formed from sediments

What are sediments?

When the process called weathering attacks rocks near or at the surface, the rocks are broken into fragments.

This fragmentary material is called sediment.

Sediments come in different shapes and sizes:

•Boulders Silt

•Pebbles mud

•Gravel clay

•Sand

Depositional Environments for Sediments or

Where sediments are deposited after they are transported

Where sediments accumulate:

a- alluvial fans h-deltas

b- Glaciers i- tidal flats

c- rivers j- continental shelf

d- dunes k-continental slope

e- lakes L-abyss

f- lagoons m-reefs

g- estuaries

There are three major deposition settings: continental, marginal marine, and marine

How do sediments become Sedimentary Rocks?•form by the lithification of unconsolidated sediments.

•lithification is a process of compaction and cementation

What sediments produce what rocks?

Sediment• Sand• Mud• Silt• Clay• Rounded gravel• Angular gravel

Rock•Sandstone•Mudstone•Siltstone•Shale•Conglomerate•Breccia

These are called Detrital sedimentary rocks: because they are made of detritus or solid particles of other rocks

Chemical Sedimentary Rocks

Sometimes material is dissolved in water as the rocks are weathered.

This material is transported to lakes and oceans where it can reform into minerals and rocks by:

• inorganic chemical reactions

•or the activities of organisms (organic).these are often called biochemical sedimentary rocks

Chemical sedimentary Rocks (inorganic)

Sometimes when water evaporates, the dissolved chemical precipitate out minerals.

e.g. Rock salt ( NaCl )

Rock Gypsum ( CaSO4.2H2O )

Chert (SiO2) is a hard rock is is made of microscopic crystals of quartz. (can also be bio-chemical)

It comes in several colored varieties

flint (Black)jasper (brown/red)novaculite (white)agate (banded)

Rock salt Rock gypsum

Chert

Coal

Chemical Sedimentary Rocks

Bio-Chemical sedimentary Rocks (organic)

These are formed by living organisms

Chert can be made from the accumulations of silica shells

Coal is formed from woody land plant material

Limestone (fossilifereous) ( CaCO3) is formed from the accumulation of seashells

Limestone (chalk) ( CaCO3) is formed from the accumulation of microscopic shells

Limestone (fossiliferous) Limestone (chalk)

Bio-chemical Sedimentary Rocks

Some common Sedimentary Rocks you will have to learn.

Sandstone* Limestone (chalk)

Conglomerate*

Siltstone

Breccia*

Shale*

Mudstone*

Chert*

Coal*

Rock Salt

Limestone (fossiliferous)* * = must know for test

Sedimentary Structures: Crossbedding = desert sand dune

Sedimentary Structures:Ripple marks = streams, lake shores

Sedimentary Structures: Fossils = environment, age, comparison