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Sedimentary Rock Classification
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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…