Copyright (c) 2005 Pearson Education Canada, Inc.6-1 PowerPoint Presentation Stan Hatfield....

Copyright (c) 2005 Pearson Education Canada, Inc. 6-1

PowerPoint PresentationStan Hatfield . Southwestern Illinois College

Ken Pinzke . Southwestern Illinois College

Charles Henderson . University of Calgary

Chapter 6a

Sedimentary Rocks: Environments & Processes

PowerPoint Presentation

Stan Hatfield . SW Illinois College

Ken Pinzke . SW Illinois College

Charles Henderson . University of Calgary

Tark Hamilton . Camosun College

Copyright (c) 2005 Pearson Education Canada Inc. 6-2

Sedimentary rocks are products of mechanical and chemical weathering

They account for about 5 percent (by volume) of Earth’s outer 16 kilometres

Contain evidence of past environments• Sediment transport directions• Macro- , Micro- & Trace fossils, evolution, time &

changing ecologies• Stable isotope records of past sea water & climates

What is a sedimentary rock?


What is a sedimentary rock?

Sedimentary rocks are important for economic considerations because they may contain:

• Coal• Petroleum and natural gas• Limestone for cement• Gypsum for plaster & sheetrock• Salt for roads & chemicals• KCl in evaporites & Apatite in phosphate rock for

fertilizers• Sources of iron, aluminum, and manganese


Lithification: Turning Sediment into Sedimentary Rock

Many changes occur to sediment after it is depositedCompactionReduction or recycling of organic compoundsDewateringCementationRecrystallization

Diagenesis – all of the chemical, physical, and biological changes that take place after sediments are deposited, but prior to metamorphism

• Occurs within the upper few kilometres of Earth’s crust at temperatures generally less than 200ºC

• Clays persist in sediments (Micas form in Metamorphism)• Reduction of porosity & permeability


Diagenesis Includes:Recrystallization – • Pressure Solution: grains dissolve at corners• Infilling of porosity• Development of more stable minerals from less

stable ones: Plagioclase Clay + Calcite

Lithification - • Unconsolidated sediments are transformed into

solid sedimentary rock by compaction and cementation

– Cements include calcite, silica, clays, zeolites, iron oxide, pyrite

Lithification: Turning Sediment into Sedimentary Rock


Types of Sedimentary Rocks

Sediment originates from mechanical and/or chemical weathering

Rock types are based on the source of the material

• Detrital sedimentary rocks – transported sediment as solid particles, earlier rocks & minerals

• Chemical sedimentary rocks – sediment that was once in solution

• Biochemical sedimentary rocks – sediment formed or shed from living organisms


Detrital (Clastic) Sedimentary Rocks

The chief constituents of detrital sedimentary rocks include components shed from weathering on land (terrigenous debris):

• Clay minerals: kaolinite, illite, chlorite, smectite• Quartz & Chert• Feldspars (Kspar >> Plagioclase)• Micas: Muscovite, Vermiculite, Chlorite,

Serpentine

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

• Boulders, cobbles, gravel, sand, silt, clay


Detrital Sedimentary Rocks

Particle size is important in the classification of detrital sedimentary rocks.


Shale and other Mudrocks (Argillite, Wackes)• ~60% of all sedimentary rocks, best fossil records!

• Frequently organic rich and the source rocks for hydrocarbons

• Mud-sized particles in thin layers that are commonly referred to as laminae

• Deposited as a result of gradual settling in quiet environments: floodplains, deep lakes, deep ocean basins

• Shale exhibits fissility (splits into thin layers) and mudrock does not (sometimes bioturation or mixing destroys layers)

• Siltstone consists of silt-sized particles as well as mud

• Most common sedimentary rock, but often inconspicuous because they weather recessively and are covered by veg!


Copyright (c) 2005 Pearson Education Canada Inc. 6-10Shale is a type of mudrock. The shale above contains plant fossils.



Sandstone-20% of sedimentary rocks are sandstone; second

only to mudrocks in abundance

-Composed of sand-sized particles

-Forms in a variety of environments and transported by wind and water

-Sorting, shape, and composition of the grains can be used to interpret the rock’s history

-Quartz is the predominant mineral in mature or long system sediments because it is so

durable

-Feldspars & Rock Fragments are abundant in younger immature sediments



Quartz sandstone (bottom) and wind-blown layers of sandstone (above) from Zion National Park (Jurassic Desert!).



Conglomerate and breccia– Both are largely composed of particles > 2mm

– Indicative of high energy currents or steep slopes

– Conglomerate consists primarily of rounded gravels

– Grain supported have been sorted, winnowed, redeposited

– Matrix supported usually just deposited once as a thick slurry or debris flow

– Breccia is composed largely of large angular particles

– Less sedimentary transport

– May result from avalanche or talus in mountainous terrain


Copyright (c) 2005 Pearson Education Canada Inc. 6-14Conglomerate is composed primarily of rounded gravel-size particles.


Copyright (c) 2005 Pearson Education Canada Inc. 6-15Breccia is composed of angular gravel-sized particles.



Chemical Sedimentary Rocks

Consist of precipitated material that was once in solution

Precipitation of material occurs in two ways• Inorganic processes (precipitation, crystallization

from solution in briny or saturated fluids)• Organic processes (biochemical origin)

– Clams grow shells

– Calcareous algae

– Wood in bayous, oxbow lakes

– Fish poop on shelf!


Common chemical sedimentary rocks• Limestone

– Most abundant chemical rock; 10% of all sedimentary rocks

– Composed chiefly of the mineral calcite (CaCO3)

– Marine biochemical limestones form as coral reefs, coquina (broken shells; also called bioclastic grainstone), and chalk (microscopic organisms)

– Inorganic limestones include travertine and oolitic limestone (comprises small spherical grains or ooids formed in high wave-energy environments)


Copyright (c) 2005 Pearson Education Canada Inc. 6-18Bioclastic limestone with shell fragments of biochemical origin.


Copyright (c) 2005 Pearson Education Canada Inc. 6-19Modern coral reef (A) and Paleozoic fossil reef in Arctic Canada (B).


But Reefs form in the Tropics?


Common chemical sedimentary rocks• Dolostone

– Typically formed secondarily from limestone when magnesium replaces some calcium

• Chert– Made of microcrystalline silica (SiO2)

– Occurs as nodules in limestone and as tabular layers (siliceous organisms like diatoms and radiolarians often provide silica related to chert origin)

– Varieties include flint and jasper (banded form is called agate)

– Banded Iron Formation (Hematite & Jasper) from Precambrian evolution of cyanobacteria Free O2



Banded Iron Formation

Precambrian between 3.8 and 1.7 Ga (Archean)


Common chemical sedimentary rocks• Evaporites

– Evaporation triggers deposition of chemical precipitates

– Examples include rock salt (NaCl) and rock gypsum (CaSO4.2H2O), anhydrite (CaSO4), sylvite (KCl; potash, which is used as a fertilizer)

• Phosphate Rock– Phosphate Rock is apatite rich marine sediment also

used as fertilizer

– Forms on sediment starved shelves

– Upwelling and biological activity exceeds clastic input



Common chemical sedimentary rocks• Coal

– Different from other rocks because it is composed of organic material

– Stages in coal formation (in order)

– 1. Accumulation of plant material (often in swamps)

– 2. Partial decomposition into peat

– 3. Shallow burial forming lignite

– 4. Deeper burial forming bituminous coal


Copyright (c) 2005 Pearson Education Canada Inc. 6-24Successive stages in the formation of coal.



End of Chapter 6a

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