Intr.phys.Geol.

8/13/2019 Intr.phys.Geol.

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Powerpoint PresentationEarth: An Introductionto Physical Geology, 7e

Tarbuck & Lutgens


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Sedimentary Rocks

Earth - Chapter 6

Stan Hatfield and Ken PinzkeSouthwestern Illinois College


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What is a sedimentary rock?Sedimentary rocks are products of

mechanical and chemical weatheringThey account for about 5 percent (byvolume) of Earths outer 10 miles Contain evidence of past environments

Provide information about sedimenttransport

Often contain fossils


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What is a sedimentary rock?Sedimentary rocks are important for

economic considerations because theymay contain

Coal Petroleum and natural gas Sources of iron, aluminum, and

manganese


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Turning sediment into rockMany changes occur to sediment after itis depositedDiagenesis all of the chemical, physical,and biological changes that take placeafter sediments are deposited

Occurs within the upper few kilometers ofEarths crust


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Turning sediment into rockDiagenesis

Includes Recrystallization development of more

stable minerals from less stable ones Lithification unconsolidated sediments are

transformed into solid sedimentary rock bycompaction and cementation

Natural cements include calcite, silica, andiron oxide


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Types of sedimentary rocks Sediment originates from mechanicaland/or chemical weatheringRock types are based on the source of thematerial

Detrital rocks transported sediment assolid particles

Chemical rocks sediment that was oncein solution


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Detrital sedimentary rocksThe chief constituents of detrital rocksinclude

Clay minerals Quartz Feldspars

MicasParticle size is used to distinguish amongthe various types of detrital rocks


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Detrital sedimentary rocksCommon detrital sedimentary rocks (inorder of increasing particle size)

Shale Mud-sized particles in thin layers that are

commonly referred to as laminea

Most common sedimentary rock


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Shale containing plant remains


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Detrital sedimentary rocks Sandstone

Composed of sand-sized particles Forms in a variety of environments Sorting, shape, and composition of the grains

can be used to interpret the rocks history Quartz is the predominant mineral


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Detrital sedimentary rocks Conglomerate and breccia

Both are composed of particles greater than

2mm in diameter Conglomerate consists largely of rounded

gravels Breccia is composed mainly of large angular

particles


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Conglomerate


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Breccia


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Chemical sedimentary rocksConsist of precipitated material that wasonce in solutionPrecipitation of material occurs in twoways

Inorganic processes Organic processes (biochemical origin)


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Chemical sedimentary rocksCommon chemical sedimentary rocks

Limestone Most abundant chemical rock Composed chiefly of the mineral calcite Marine biochemical limestones form as coral

reefs, coquina (broken shells), and chalk(microscopic organisms) Inorganic limestones include travertine and

oolitic limestone


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Coquina


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Fossiliferous limestone


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Dolostone Typically formed secondarily from limestone

Chert Made of microcrystalline quartz Varieties include flint and jasper (banded

form is called agate )


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Evaporites Evaporation triggers deposition of chemical

precipitates Examples include rock salt and rock gypsum


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Coal Different from other rocks because it is

composed of organic material Stages in coal formation (in order)

1. Plant material 2. Peat 3. Lignite 4. Bituminous


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Successive stages in coal formation


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Classification of sedimentary rocksSedimentary rocks are classifiedaccording to the type of materialTwo major groups

Detrital Chemical


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Classification of sedimentary rocksTwo major textures are used in theclassification of sedimentary rocks

Clastic Discrete fragments and particles All detrital rocks have a clastic texture

Nonclastic Pattern of interlocking crystals May resemble an igneous rock


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Sedimentary environmentsA geographic setting where sediment isaccumulatingDetermines the nature of the sedimentsthat accumulate (grain size, grain shape,etc.)


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Sedimentary environmentsTypes of sedimentary environments

Continental Dominated by erosion and deposition

associated with streams Glacial Wind ( eolian )

Marine Shallow (to about 200 meters) Deep (seaward of continental shelves)


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Sedimentary environmentsTypes of sedimentary environments

Transitional (shoreline) Tidal flats Lagoons Deltas


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Sedimentary environmentsSedimentary facies

Different sediments often accumulateadjacent to one another at the same time

Each unit (called a facies ) possesses adistinctive set of characteristics reflecting

the conditions in a particular environment The merging of adjacent facies tends to be

a gradual transition


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Sedimentary facies


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Sedimentary structuresProvide information useful in theinterpretation of Earth historyTypes of sedimentary structures

Strata , or beds (most characteristic ofsedimentary rocks)

Bedding planes that separate strata Cross-bedding


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Sedimentary structuresTypes of sedimentary structures

Graded beds Ripple marks Mud cracks


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Fossils: Evidence of past lifeBy definition, fossils are the traces orremains of prehistoric life now preservedin rockFossils are generally found in sediment orsedimentary rock (rarely in metamorphicand never in igneous rock)


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Fossils: Evidence of past lifeGeologically fossils are important forseveral reasons

Aid in interpretation of the geologic past Serve as important time indicators Allow for correlation of rocks from

different places


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Natural casts ofshelled invertebrates


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Dinosaur footprint in limestone


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End of Chapter 6

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