Chapter 4: section 4

FORMATION OF SEDIMENTARY ROCKS

Igneous rocks are the most common rocks.
However, these rocks mostly exist underneath the surface of the Earth.

FORMATION OF SEDIMENTARY ROCKS

They come from already existing rocks.

Sedimentary rocks form when sediments are pressed and cemented together, or when minerals form from solutions.

STACKED ROCKS

Sedimentary rocks often form as stacked layers.

The older layers are at the bottom and the newest layers are on top of an undisturbed stack.

CLASSIFYING SEDIMENTARY ROCKS

To classify a sedimentary rock, determine its composition and texture.

Sedimentary rocks can be made out of any material in nature.

Sedimentary rocks are classified as:



Detrital
Chemical
Organic

DETRITAL SEDIMENTARY ROCKS

Detrital – “to wear away”

They are made from broken fragments of other rocks.

The loose sediments are compacted and cemented together to form solid rock.

They are named according to shape or size.

Conglomerate – rounded sediments

Breccia – sediments with sharp angles

DETRITAL SEDIMENTARY ROCKS
-
-
-
-
Weathering
Erosion
Compaction
Cementation

DETRITAL SEDIMENTARY ROCKS

Weathering – breaks rocks into smaller pieces when a rock is exposed to air, water, or ice.

Erosion is the movement of weathered material.

DETRITAL SEDIMENTARY ROCKS
-
-
-
-
Erosion moves sediments to a new location where they are then deposited.
Layer upon layer of sediments will build up.
Pressure from the upper layers will push down on the lower layers.
If the sediments are small, they will stick together and form solid rock in the process of compaction .

DETRITAL SEDIMENTARY ROCKS

If sediments are large, pressure alone can’t make them stick together.

These large sediments must be cemented together.

Cementation occurs when minerals such as quartz, calcite, and hematite are deposited between the pieces of sediment.

CHEMICAL SEDIMENTARY ROCKS

Chemical sedimentary rocks form when dissolved minerals come out of a solution or when liquid evaporates.

You may see salt deposits at the bottom of a glass when salt water evaporates.

ORGANIC SEDIMENTARY ROCKS

Rocks made of the remains of once living things are called organic sedimentary rocks.

Example:

Shells - Help form fossil-rich limestone.

Chalk – shells

Coal – When dead plants are buried under other sediments in swamps.

If a rock is made completely out of shell fragments, the rock is called coquina.