Sedimentary Rocks II Sedimentary Rock II. Characteristics of clastic rocks Sedimentary Rock Types 5. Color: presence of key components (can be minor by

Sedimentary Rocks II

Sedimentary Rock II

Characteristics of clastic rocks

Sedimentary Rock Types

5. Color:

• presence of key components

(can be minor by volume)



5. Color:

• BLACK: organic carbon, iron sulfide



5. Color:

• BLACK:abundant dead organismsand stagnant water

(not enough oxygen for decomposition)



5. Color:

• BLACK:

still water:

swamp, lake, deep marine



5. Color: Red or Brown:

Iron Oxide

high O2

(continental)

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6. Lithification:

• transformation of loose sediment into a rock



6. Lithification:


• compaction: degree

(packing and fusion)

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Pre- Post-

Compaction - packing

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Compaction - packing

Compaction - grain fusion

http://www.gly.uga.edu/railsback/PDFimage0208a.jpeg



6. Lithification:


• cementation: composition

silica, calcite, hematite SiO2 CaCO3 FeO2

Quartz grains - Calcite cement

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Plagioclase grains - Calcite cement

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q-quartz grains, o-quartz cement, c-calcite cement



7. Texture:

size, shape and arrangement

of clasts.



Three components:

• grains: the larger particles (sand and larger)



Three components:


• matrix: fine clastic particles deposited with grains



Three components:


• matrix: fine clastic particles deposited with grains

• cement: chemical precipitate that fills voids after deposition

Grains & Cement Grains & Matrix

Levin - Earth Through Time 7th



8. Maturity:

a measure of how long/far

sediment was transported.

two kinds


8a. Textural Maturity:Immature

• large grain size, angular grains, poorly sorted

• intermediates

• small grain size, well rounded,

well sorted

Mature



8b. Compositional Maturity:

Immature - least stable

• rock fragments

• iron/magnesium minerals

• feldspars

• quartz

Mature - most stable


most mature least mature

well rounded angular grains

well sorted poorly sorted

fine grained pebbles & sand

quartz rock fragments

Summary

Characteristics of Clastic Rocks


1. Grain size2. Composition of grains3. Sorting of grains4. Shape of grains5. Color of rock6. Lithification process7. Texture8. Maturity

a. texturalb. compositional

Environmental significance of sandstones



1. Quartz arenite:

• dominance of quartz

• little or no feldspar, mica, or matrix

• grains well rounded, well sorted

• calcite or silica cement

• wide spread thin sand beds


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Quartz arenite :

http://nessus.gunslingers.org/2003-09%20-%20North%20Carolina%20Beach%20and%20California%20Hiking/0047%20More%20Beach-half.jpg


Quartz arenite: tectonic setting

• Beach, far from the mountains



Arkose: (feldspathic wacke)

• contain 25% or more feldspar (pink)

• quartz most abundant (angular)

• calcite, iron oxide cement, or clay matrix

• granitic source

• coarse sand, moderately well sorted


Arkose

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Arkose: tectonic setting

• Physical weathering near granitic mountain



Arkose


Wacke:

• matrix 30% of rock (dark minerals)

• little or no cement

• grains supported by matrix


Wacke

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Wacke: tectonic setting

• Rapid uplift near continent margin


Episodes of depositionTurbidites

Episodes of deposition

Turbidites

OneTurbidite

Turbidites

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Turbidites & Deep Marine Shales


Lithic sandstone:

• quartz, mica, chert, rock frag.

• little feldspar

• 15% matrix or less, rest cement

• intermediate rounding & sorting


Lithic sand(Mekong river)

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Lithic sandstone: tectonic setting

• delta on the edge of a coastal plain




Lithic sand



Beachfar from Mt

Continentalarid

DeepMarine

MatureRiver

Documents

Sedimentary Rocks II Sedimentary Rock II. Characteristics of clastic rocks Sedimentary Rock Types 5. Color: presence of key components (can be minor by