Sedimentary RocksSedimentary Rocks

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Sedimentary rocksSedimentary rocks form from pre‐existing rock particles:particles:

i• igneous, 

• metamorphic or 

• sedimentary. 

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Sedimentary rocksSedimentary rocksThe parent rock undergoes:

• WEATHERING

• TRANSPORTATION 

• DEPOSITION

• LITHIFICATION : COMPACTION, CEMENTATION.LITHIFICATION :  COMPACTION, CEMENTATION.

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Sedimentary rocks

• WEATHERING by chemical and/or physical mechanisms into smaller particles. 

• These particles are TRANSPORTED by ice, air or water to a region of lower energy called a sedimentary basinto a region of lower energy called a sedimentary basin. 

• DEPOSITION takes place as a result of a lowering of p ghydraulic energy, organic biochemical activity or chemical changes (e.g., solubility).

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Once deposited, the sediments are LITHIFIED(turned into rock) through(turned into rock) through 

COMPACTION (decrease in rock volume due to weight of overlying sediment) anddue to weight of overlying sediment) and 

CEMENTATION (chemical precipitation in b t i hi h " l " th kpore spaces between grains which "glues" the rock 

together).

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• Sediments may be rock particles such as mud, sand or pebbles which are usually d i d i h b i ddeposited in the sea by rivers and waves. 

• The weight of the overlying sediments will• The weight of the overlying sediments will compact those found below. 

• Over time, the compacted sedimentsbecome sedimentary rocks. 

• Sometimes, these sedimentary rocks may be uplifted as a result of plate movementsuplifted as a result of plate movements forming mountain, eg. The Himalayas. 

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Sedimentary rocksSedimentary rocks

Sedimentary rocks are formed at the surface ofSedimentary rocks are formed at the surface of the Earth:

• either in water or 

• on land. 

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Th l d l ti fThey are layered accumulations of: 

sedimentssediments,fragments of rocks, minerals, orminerals, or animal orplant material.

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Sediment = loose particulate material (clay, sand, gravel, etc.).

Most sediment is derived from the weathering (breakdown) of pre‐existing rocks.

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Sediment becomes sedimentary rock throughSediment becomes sedimentary rock through lithification, which involves: 

• Compaction due to pressure or weight of l i dioverlying sediments 

• Cementation by deposition of minerals in pore spaces from waters carrying ions in p p y gsolution 

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Types of Sedimentary RocksTypes of Sedimentary Rocks

• Clastic (Detrital) and 

• Nonclastic (chemical) 

sedimentary rocks.

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Clastic sedimentary rocks (also called terrigenous or d t it l)detrital)

Clastic sedimentary rocks are derived from the weathering of pre‐existing rocks which haveweathering of pre‐existing rocks, which have been transported to the depositional basin. 

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They have a clastic (broken or fragmental) texture consisting of:texture consisting of: 

• Clasts (larger pieces such as sand or gravel)• Clasts (larger pieces, such as sand or gravel) • Matrix (mud or fine‐grained sediment surrounding the clasts)surrounding the clasts) 

• Cement (the glue that holds it all together), such as the following minerals:such as the following minerals: – calcite – iron oxide– iron oxide – silica 

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Clastic sedimentary rocksClastic sedimentary rocks

are accumulations of clasts, 

little pieces of broken up rock whichlittle pieces of broken up rock which 

h il d d b "li hifi d" bhave piled up and been "lithified" by 

compaction and cementation.

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NonclasticNonclastic (Chemical sedimentary rocks)Chemical sedimentary rocks) ::Many of these form when Many of these form when

standing water standing water evaporates,evaporates,

leavingleaving dissolved minerals behind.dissolved minerals behind.leavingleaving dissolved minerals behind. dissolved minerals behind.

These are very common inThese are very common in arid landsarid landsThese are very common in These are very common in arid lands.arid lands.

Thick deposits of Thick deposits of salt and gypsum salt and gypsum can form due can form due to repeated flooding and evaporation over to repeated flooding and evaporation over long long periods of timeperiods of time..

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periods of timeperiods of time..

Non‐clastic sedimentary rocks (also called chemical and biochemical sedimentary rocks)y )

They were formed by being precipitated from a l ti b tisolution or by evaporation.

h k f i hi h d i i l b i f• These rocks form within the depositional basin from chemical components dissolved in the seawater. 

• These chemicals may be removed from seawater and made into rocks by chemical processes or withand made into rocks by chemical processes, or with the assistance of biological processes (such as shell growth).growth). 

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BY CRYSTALLISATION FROM DISSOLVED MINERALS

Crystallisation of dissolved minerals in a shallow part of the sea.

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NonclasticNonclastic (Chemical sedimentary rocks)Chemical sedimentary rocks)

Clastic sedimentary rocks:Clastic sedimentary rocks:

Clastic sedimentary rocks are named according to the grain size f h di i lof the sediment particles. 

• Sandstone: grains ranging in size from 2mm to g g g1/16 mm.

• Shale: grains ranging in size from 1/16 mm S a e g a s a g g s e o / 6to <1/256 mm. 

• Conglomerate: coarse (64 mm to >256 mm), roundedConglomerate: coarse (64 mm to >256 mm), rounded grains 

• Breccia: coarse (2mm to 64 mm), angular grains19

Sandstone rocks

• Sandstone is one of the most common sedimentary rocks. 

i d f d i d d f ld k d h• It is made from sand grains eroded from older rocks, cemented together and then hardened into new rock. 

• They often form in layersThey often form in layers.

• They are often used as building stones. 20

Sandstone rocksDistinctive features:

C l• Colour:Buff to brownish; sometimes reddish, due to presence of iron oxides, or greenish, due to presence of glauconite.

• Composition:Sand grains (quartz), cemented by secondary silica or calcite.

• Field associations:Compound and / or cemented ancient beach, river, delta, lake d d t d itand desert deposits. 

Occurs as thick, stratified beds in sedimentary sequences, often showing current or dune bedding.

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Shale Rocks

• Formed from clay that is compacted together by pressure. 

• They are used to make bricks and other material that is fired 

in a kiln.

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Shale Rocks• Spilts easily into thin plates along well‐defined planes parallel to theSpilts easily into thin plates along well defined planes parallel to the 

original stratification. Buff to grey very fine‐grained silty rock. 

• Colour:Colour:Buff to various shades of grey.

• Texture and granularity:g yFine‐grained.

• Composition:Complex mixture of microscopic clay minerals, plus mica and quartz.

• Field associations:D i d f i t d d it it i t di tDerived from ancient mud deposits, it occurs in most sedimentary sequences with fine sandstone and limestone.

• Varieties:• Varieties:Probably mudstone.

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ShaleShale

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ShaleShale

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Mudstone or Shale 

• These are simply just mud hardened intoThese are simply just mud hardened into rock. 

• They consist of much finer particles than dsand .

• They often contain fossils. 

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MarlC bli di t k ti ll d lCrumbling sedimentary rock, sometimes called clayeylimestone, 

including various types of 

calcareous clays and fine‐grained limestonescalcareous clays and fine‐grained limestones.

• Marls are often laid down in freshwater lakes and are usually soft earthy and of a white grey greenare usually soft, earthy, and of a white, grey, green or brownish colour. 

• They are used in cement‐making and as fertilizer.

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MarlMarl

Green MarlGreen Marl Red MarlRed Marl

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Conglomerate Rocks

• They are made up of large sediments like sand and pebbles. 

• The sediment is so large that pressure alone cannot hold the rock together; it is also cemented together g ; gwith dissolved minerals. 

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Conglomerate RocksDistinctive features:

Boulders, pebbles, or shingle, set in fine‐grained matrix, sometimes resembling coarse concrete.

Colour:Variable, depending on the type of rock fragments.

Texture and granularity:Variable.

Composition:Rounded rock fragments set in a fine‐grained matrix.

Field associations:Derived from beach, lake and river deposits of boulders, pebbles and gravel. Often found near deposits of sandstoneand arkose.and arkose.

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ConglomerateConglomerate

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BRECCIABRECCIA• Distinctive features:

Similar to conglomerate, but rock fragments are angular and i fi i d iset in fine‐grained matrix.

• Colour:Variable, depending on the type of rock fragments.

• Texture and granularity:g yAngular fragments of rock set in fine grained matrix.

• Composition:Fragmented rocks of any kind can form breccia. The matrix is normally fine sand or silt, cemented by secondary silica ornormally fine sand or silt, cemented by secondary silica or calcite.

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BRECCIABRECCIA

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Classification Sedimentary Rock

Composition Depositional EnvironmentRock Environment

Cl ti Sh l Cl d/ ilt S fl d l i iClastic (Detrital)

Shale Clay and/or silt Swamp, floodplain, river bottom

Sandstone Sand Beach, desert

Conglomerate Various-sized Riverbedgpebbles

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Sedimentary rocksSedimentary rocks

• are generally stratified, fine‐grained.

• Many sedimentary rocks also contain fossils.

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Jurassic sandstone from the USA, notice the layers. Each layer is a record of an event in the past. Made from small grains of the minerals quartz and feldspar. 

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How can you spot a Sedimentary rock?

• Sedimentary rock will often have layers or bands across thembands across them. 

• It will often contain fossils which are• It will often contain fossils which are fragments of animals or plants preserved within the rock Only sedimentary rockswithin the rock. Only sedimentary rocks contain fossils.

• The rock will tend to scrape easily and often crumble easily.crumble easily. 

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Wasson's Bluff, Nova Scotia. Notice the layers of sediments.

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Chemical sedimentary rocks• Evaporite chemical sedimentary rocks form as waterevaporates from a lake or ocean.

• During the process of evaporation, water molecules change from the liquid phase to the gas phase,change from the liquid phase to the gas phase, 

• but atoms such as calcium, sodium, and chlorine are l f b hleft behind.

• As a result the remaining water becomes enriched• As a result, the remaining water becomes enrichedin these atoms which begin to precipitate from the water.

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• Evaporite minerals and rocks tend to form inarid climates 

where the rate of evaporation greatly exceeds rainfall.a a

• Evaporites are light in color and so can be• Evaporites are light in color, and so can be readily recognized, even from a great distance.

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Evaporites are commonEvaporites are common

• where lakes form and then evaporate in a desert (such lakes are referred to as playadesert (such lakes are referred to as playa lakes), or 

• in shallow and warm arms of the oceanadjacent to desert areas.

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Nonclastic (Chemical Sedimentary Rocks)Nonclastic (Chemical Sedimentary Rocks)

• Limestone=composed of the mineral calcite, may contain marine fossils, formed by precipitation from , y p pwater 

Rock salt composed of the mineral halite (salt)• Rock salt= composed of the mineral halite (salt), formed by evaporation

• Rock gypsum= composed of the mineral gypsum, formed by evaporation

• Chert=composed of microscopic mineral grains of quartz, very hard with sharp edges q , y p g

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Limestone Rocks

made from:the mineral calcite which came from the beds of evaporated seas and lakes and sea animal shells.

This rock is used in concrete and is an excellent building stone for humid

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excellent building stone for humid regions.

Limestone

• Limestones are made from fragments of seacreatures that sank to the bottom of ancient tropical seas. 

• Limestones frequently contain fossils.

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Limestones• Limestones are easily identified because they effervesce in diluteLimestones are easily identified because they effervesce in dilute 

hydrochloric acid.

• Often rich in fossils.

• Colour: White to yellowish or grey. Black varieties are rich in hydrocarbons. 

• Composition: Mostly calcium carbonate. 

• Field associations:

Deposited in ancient seas by precipitation or by the accumulation of calcite‐rich shells etc., coral reefs, around hot springs.

• USES: Source of cement, building construction (locally), blackboard chalk.

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Limestone effervesces (fizzes rapidly) when treated with cold dilute hydrochloric acid and is easily scratched by a knife bladehydrochloric acid and is easily scratched by a knife blade. 

Vinegar, which contains acetic acid and water, will also cause limestone to effervesceto effervesce.

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Natural acids in groundNatural acids in ground water can dissolve limestone in the ground, which is why 

caves and other karst‐solution 

features are common in many parts of the world.

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Here we see a stalactite from the limestone cave system a few miles away in Ingleton. 

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DolomiteDolomite

• Dolomite (dolostone) is a sedimentary rock ( ) ycomposed chiefly of magnesium calcium carbonate. 

• It is closely related to limestone both physically and• It is closely related to limestone, both physically and chemically; 

• in fact, when the magnesium content decreases, it is often referred to as magnesian or dolomiticis often referred to as magnesian or dolomiticlimestone. 

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Rock saltCrystals of salt, called rock salt, form on top of the dried soil.

Rock salt is formed when minerals are dissolved in water, then the water evaporates.

As the water evaporates, the salt molecules start to pcling together and grow into larger crystals.

The slower the evaporation the larger the crystals

composed of halite (NaCl)

The slower the evaporation, the larger the crystals.

composed of halite (NaCl). 

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Halite (sodium chloride)comes from the Greek 

h l i " lt" dhalos, meaning "salt" and lithos meaning "rock," and 

is in fact, better known as rock salt. 

Halite is called an evaporite becauseHalite is called an evaporite because 

it is formed by the evaporation of saline water in partially enclosed basinsenclosed basins. 

It is very common worldwide, as a dissolved solution in oceans and many arid region inland lakesand many arid‐region inland lakes.

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Rock Salt

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Gypsum Rocks

• Made up of sulfate mineral and p

• formed as the result of evaporating sea water in massive prehistoric basins. 

• It is very soft and 

• is used to make Plaster of Paris, casts, molds, and wallboards.

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Chert• Chert is usually brown or creamy white andChert is usually brown or creamy white, and 

• it sometimes looks smooth and waxy. (Chert also comes in white and other colors )in white and other colors.) 

• Freshly broken edges may be scalloped or sharp. 

• You can't scratch chert with a nail or knife. Chert is made mostly of extremely tiny crystals of the mineral, quartz.

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Bituminous coalBituminous coal

• Coal is formed from peat which is anCoal is formed from peat, which is an accumulation of decayed vegetation usually associated with swampsassociated with swamps. 

Th f h f i f• The process of the transformation from 

peat to coal is called coalification. 

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In the stages of coalificationIn the stages of coalification, 

• peat is altered to lignite• peat is altered to lignite, 

li it i lt d t b bit i l• lignite is altered to sub‐bituminous coal, 

b bi i l i l d bi i l• sub‐bituminous coal is altered to bituminous coal, and 

• bituminous coal is altered to anthracite coal.

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Non‐Clastic (Chemical)

Classification Sedimentary Rock

Composition Depositional Environment

Non-Clastic(Ch i l)

Limestone Calcite or f t d

Shallow sea, coastline(Chemical) fragmented

shells

Chert (flint) Chalcedony Formed from a silica richChert (flint) Chalcedony (quartz), traces of other minerals

Formed from a silica-rich precipitate in a deep ocean environment.

Bituminous Coal

Plant material Ancient forest or swamp

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