Sedimentary Rock Classification

1. Lecture #1

2.  studying sediments
 derive information on the depositional conditions;
rock unit
 relation of the individual rock units in a basin into
a coherent understanding of the evolution of the
sedimentary sequences and basins
 Earth's geological history as a whole

3.  Sedimentary rocks are formed in places where
there has been water at one time.
 Dead animals, plants, and pieces of rocks or
minerals are carried to these places by wind,
water, ice, or even gravity.

4. Rock Process

5.  Types of rock that are formed by the
deposition of material at the Earth's surface
and within bodies of water
 Indicators of geological processes,
environment (tectonic event), and geological
history.
 Contain of mineral resources such as coal,
petroleum, natural gas, iron, gold, aluminum,
uranium, diamond etc.

6. Weathering
 Erosion
 Transportation
 Deposition
 Diagenesis

7.  All of the chemical, physical and biological
changes that take place after sediments are
deposited.
 Occurs within the upper few kilometers of earth’s
crust
 Consist of:
 Lithification : unconsolidated sediments are
transformed into solid sedimentary rocks by
compaction and cementation
 Natural cements include calcite, silica and iron
oxide.

8.  Sediment originates from mechanical and/or
chemical weathering.
 Based on the source of material:
i. Detrital (Siliciclastic) sediments: sediment
transported as solid particles
ii. Chemical Sediments : sediment that was once
in solution
iii. Biogenic, Biochemical and Organic sediments
iv. Volcanoclastic sediments.
coal

9.  The chief constituents of detrital rocks include:
 Clay minerals
 Quartz
 Feldspars
 Micas
Chert Breccia: The angular clasts in this
breccia are chert fragments. The matrix is an
iron-stained mix of clay through sand-size
particles. The specimen is about two inches
(five centimeters) across.
 Particle size is used to distinguish among the
various types of detrital rocks.

10. Size Range (mm) Particle Name Sediment
>256
64-256
4-64
2-4
Boulder
Cobble
Pebble
Granule
Gravel
1/16 - 2 Sand Sand
1/256 – 1/16
<1/256
Silt
Clay
Mud

11. Consist of precipitated material that was
once in solution
Precipitation of material occurs in two
ways:
 Inorganic processes
 Organic processes (biochemical origin)

12.  Limestone
 Most abundant chemical rock
 Majority composed by mineral calcite
 Marine biochemical limestone form as coral reefs,
coquina (broken shells), and chalk (microscopic
organisms)
 Inorganic limestones include travetine (limestone
dissolves in place and is redeposited in another) and
oolitic (small rounded particles or grains &
look like fish eggs)

13.  Example for inorganic processes:
 Chert
 Made of microcyrstalline quartz
 Varieties include flint and jasper (banded
form is called agate)
Evaporites
Evaporation triggers deposition of chemical
precipitates
Ex: rock salt and rock gypsum

14. Clastic
60%
Chemical Biogenic
50%
60%

18. Cross Bedding

19. Siliciclastic rocks Chemical rocks Biochemical rocks
Boulders
Cobbles
Oolitic rocks
Pebbles
Intraclast rocks
Granules
Sand
Dolomite (Dolostone)
Silt
Clay
Micrites
Fossilliferous rocks
Pelletal rocks
Chalk
Chert
Rock Salt (Halite)
Gypsum
Peat and Coal
Gravel:
Breccia /
Conglomerate
Carbonate Rocks
Other chemical Rocks
Other Biochemical
Rocks

26. Rock
streaked by
oil. Ventura
County, CA.
USGS photo