Sedimentary Rock Classification

SEDIMENTOLOGY AND

STRATIGRAPHY

Lecture #1

SEDIMENTOLOGY 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

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.

Rock Process

SEDIMENTARY ROCKS 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.

FORMATION OF SEDIMENTARY ROCKS Weathering

Erosion

Transportation

Deposition

Diagenesis

DIAGENESIS 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.

FOUR BASIC TYPES OF SEDIMENTARY ROCKS

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

DETRITAL SEDIMENTARY ROCKS The chief constituents of detrital rocks include:

Clay minerals Quartz Feldspars Micas

Particle size is used to distinguish among the various types of detrital rocks.

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 CLASSIFICATION FOR DETRITAL ROCKS (SILICICLASTIC)

Size Range (mm)

Particle Name

Sediment

>25664-2564-642-4

BoulderCobblePebbleGranule

Gravel

1/16 - 2 Sand Sand

1/256 – 1/16<1/256

SiltClay

Mud

CHEMICAL SEDIMENTARY ROCKS

Consist of precipitated material that was once in solution

Precipitation of material occurs in two ways:Inorganic processesOrganic processes (biochemical origin)

COMMON CHEMICAL SEDIMENTARY ROCKS

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)

Example for inorganic processes:Chert

Made of microcyrstalline quartz Varieties include flint and jasper

(banded form is called agate)

EvaporitesEvaporation triggers deposition of chemical precipitatesEx: rock salt and rock gypsum

Clastic

60%

50%BiogenicChemical

60%

BEDDING PLANE

Cross Bedding

Siliciclastic rocks Chemical rocks Biochemical rocks

BouldersCobblesPebblesGranulesSandSiltClay

Oolitic rocksIntraclast rocks

Dolomite (Dolostone)

MicritesFossilliferous rocksPelletal rocksChalk

ChertRock Salt (Halite)Gypsum

Peat and Coal

Gravel: Breccia /

Conglomerate

Carbonate Rocks

Other chemical Rocks

Other Biochemical Rocks

DEPOSITIONAL ENVIRONMENT

ESTUARINE ENVIRONMENT

CARBONATE CLASSIFICATION (BASED ON DURHAM)

Rock

streaked by

oil. Ventura

County, CA.

USGS photo

Questions…