SEDIMENTARY ROCKS

A. Sediment Source and History

B. Formation of Sedimentary Rocks

C. Types of Sedimentary Rocks

D. Sedimentary Structures and Environments

SEDIMENTARY ROCKS These are composed of particles derived from

pre-existing rocks or by the crystallization of minerals that were held in solutions.

A general characteristic of this group is the layering or stratification.

Type of Sedimentary Rocks Clastic Sedimentary are composed of

particles of pre-existing rocks. These fragments show evidence of transport – rounding of the grains and size sorting.

Chemical sedimentary rocks are the result of either precipitation of solids from solutions (like salt from water) or by organic process, like shells from marine organisms.

Recipe for Sedimentary Rocks Sediment

Clasts: mineral particles from weathering of parent rock

Bioclasts: Shell and coral fragments (calcite or silica)

Chemical Precipitate: (calcite, silica, salts) Accumulation and Preservation

Sedimentation > Erosion Lithification

Compaction Cementation

B. Compaction

C. Cementation

A. After DepositionOverburden

compacts and reduces pore space

Cement from dissolved ions fills some porespace

Creation of Clastic Sedimentary Rocks

Sediment History

Talus slopes Mtn. Streams Beaches Oceans Alluvial Fans Rivers Delta (Plains)

Effects: Rounding, Size, Sorting and Mineralalogy

Clastic Sedimentary Rock Classification (Indicates History and Environment)

Rock Fragments

Unstable Minerals

More Stable Minerals Quartz

Angular Rounded Sub-Angular Rounded

Gravel (and Sand), Poorly Sorted

Sand and Silt, Poorly Sorted

Sand,Well Sorted

Mountains Cliffs, Glaciers

Mountain Streams

Rivers, (Flood Plains)

Beachesand Dunes

Breccia Conglomerate Arkose Quartz Sandstone

Clast Composition

Clast Shape

Clast Size and Sorting

Depositional Environment

Rock Type

Increasing duration of weathering and winnowing out of silt and Clay sized particles (predominantly clay minerals)

Immature Mature

Mud

Clastic Particle Sizes (Wentworth Scale)

Example (mm) (Ø)

Bowling Ball 256 -8

Pool Ball 64 -6

Buck Shot 2 -1

Powder /16 4

1/256 8

Boulder

Cobble

Pebble

Sand

Silt

Clay*

*very small particles are usually clay minerals

GravelKehew, Table 4-3

Sand

Talus Slopes

1. Gravel (boulders, cobbles etc.)

2. Poorly sorted

3. Angular

4. Fragments of rocks and minerals

Mountain Stream (Upstream)

1. Gravel (Cobbles, Pebbles etc.)

2. Poorly sorted

3. Sub-angular(Somewhat rounded)

4. Fragments of Rocks and minerals

Mountain Stream (Downstream)

1. Gravel (Cobbles, Pebbles etc.)

2. Poorly sorted

3. Rounded

4. Fragments of Rocks and minerals

Alluvial Fans

1. Sand

2. Poorly Sorted

3. Sub-angular

4. Many minerals

River in the Plains

1. Sand2. Somewhat

Sorted3. Sub-angular4. Many minerals

Quartz Sandstone: From Beaches and/or Dunes

Delta Silt and Clay i.e., Mud

Deep Sea (Lakes, Oceans) Clay

Fig. 10.30 Clay minerals and quartz

Breccia (#24)

is made of varying sizes of angular fragments cemented together.

Many form as the result of fault movement; others form as the result of rapid and short transportation, such as landslides.

Conglomerate (#17)

are very similar to breccias, but the fragments are rounded.

These rocks form in alluvial fans, stream beds and pebble beaches.

Sandstone (#16) is made up of fine-grained

particles (1/16 –2 mm). The sand grains (often

quartz) are commonly cemented by silica, carbonates, clay or iron oxides.

is identified by its sandy texture – which often translates into a gritty feel

Environments in which sandstones form include beaches, sand bars, deltas and dunes.

Shale (#14) It is the most common

type of sedimentary rock. It is made of silt and clay

sized particles. It is generally very thin-

bedded and splits along the bedding planes.

Normally gray to black, shale may be brown to dark red, depending on the amount of included iron oxide.

form in quiet environments, such as lakes, swamps, deltas and offshore marine.

Black shale, deposited in a offshore basin in a Middle Cambrian sea. Wheeler Shale with trilobite fossil (Elrathia kingii)

Fish scales

C L U E S T O S E D IM E N TA R Y R O C K S

F R A G M E N T A L : C o m p o s e d o f p ie c e s o f ro c ks a n d m in e ra ls

L A R G E P IE C E S (B o u ld e rs ,c o b b le s ,

p e b b le s )

B R E C C IA : C o m p o s e d o f la rg e a n g u la r p ie c e s a n d c la y C O N G L O M E R AT E : C o m p o s e d o f la rg e ro u n d e d p ie c e s a n d c la y

S M A L L P IE C E S (s a n d )

S A N D S T O N E : L o o ks s a n d y (m a y “s h e d ” s a n d g ra in s ) , fe e ls ro u g h ( l ike s a n d p a p e r) ; m a y b e ta n , w h ite , re d , g ra y.

V E R Y S M A L L P IE C E S (c la y, s i l t, m u d )

S H A L E : H a s ve r y th in la ye rs ; o fte n b la c k. M a y h a ve fo s s ils — u s u a ll y im p re s s io n s (n o s h e ll, b u t in d e n ta tio n w ith p a tte rn o f s h e ll) o r c a rb o n ize d fi lm (as fo r p la n ts ) . H a s a d u ll lu s te r . Is s o ft. W h e n ta p p e d w ith a ro d o r o n a ta b le , i t g e n e ra ll y m a ke s a d u ll th u n k.

Chemical Sediments

Weathering & Sediments

Quartz

Na Feldspar

Biotite

Sediments

Weathering

Weathering of Granite

1. Mechanical Weathering forms rock and mineral

fragments of parent rockQuartz

Na Feldspar

Sediments of:Quartz1

Feldspar1

Biotite

Ions4

4. Dissolves some ions (e.g, Ca, Na, K, Mg)

Chemical Weathering2. Converts silicates* to clay3. Oxidizes iron in minerals

(i.e., ferromagnesian minerals)

Clay2

Hematite3

*except quartz

Weathering and Erosion of Hawaii What are the

products of the weathering of Hawaii?

Haleakala Past and Present1.3mya

Hint: Think of the black sands of Hawaii

Sediments from Weathering

• Black sands of basalt and dark minerals • Pyroxene and • Ca-feldspar

• Chemically weathered to• Dissolved ions• Iron oxides, and • Clay (Washed away and

deposited in deep sea)

Maui, Hawaii, 1.3 my old

Chemical Weathering and Erosion

Chemical WeatheringDissolving ionsOxidation iron oxidesClay minerals

Erosion carries sediments to ocean

Kauai: An ancient volcanic island, 4.7 my old

Ocean Water

Deep Ocean Sediments

Chemical and Biochemical Sedimentary Rocks

Sandstone (sand)

Shale (clay)

Limestone (Shell frag. & lime mud)

Back Reef ReefFore Reef

Limestone (CaCO3) (#18)

• Generally it is dense, fine-grained, and usually white to dark gray.

• Its most distinguishing feature is its solubility in weak hydrochloric or acetic acid accompanied by brisk effervescence.

• The environment of deposition if generally warm, shallow seas.

Limestone can be made two ways: Bioclastic: Fragments of

Coral, Algea and Shells Inorganic: precipitated

directly from water It comes in many

different formats

Limestone – Travertine (#22)

Looks sugary with bands of different colours

Created when hot, carbon dioxide rich water dissolve limestone and then cools off to deposit the dissolved calcium carbonate.

Limestone - Fossiliferous

Made primarily of seashells and other aquatic organisms.

Limestone - Chalk

White, soft, and powdery

You could break it part with you hands.

Limestone – Coquina (#19)

Contains nothing but seashells.

Made from old coral refs and shallow seas.

CHERT (#13) It is made from quartz or

silica crystals It is made by replacing the

calcium carbonate in limestone with silica.

It is often the result of the dissolution of volcanic ash and is sometimes found in extensive beds.

It has waxy luster, is translucent, looks glassy and can be any color, but extensive beds are generally white to gray.

It is also used to make blades.

GYPSUM (#21) It is made of calcium

sulfate It is found in

geographically wide-spread deposits resulting from the evaporation of a body of water, such as ocean basin or playa lake.

It is soft. Gypsum is mined for use

in wallboard and plasters, as an agricultural amendment and to control the set/cure time of Portland cement.

AlabasterSatin Spar

Selenite

Gypsum & Anhydrite (water-less calcium sulfate), Carlsbad, NM

ROCK SALT Is known sodium

chloride It is a deposit resulting

from evaporation of a marine basin or lake.

It is used as a source of chlorine and sodium, as a food supplement, in water softeners and as a road de-icer.

Halite Trona, CA

COAL (#20) Coal is considered a rock,

although it is not composed of minerals, but rather the decomposed remains of large volumes of vegetation that accumulated in a wet, low oxygen environment, such as a swamp or marsh.

Peat, Lignite and Sub-Bituminous & Bituminous are sedimentary varieties of coal and are used as fuels.

Coal (sub-bituminous) out of the Cretaceous Dakota Formation of north-eastern Arizona.

DIATOMITE is composed of the

siliceous shells of microscopic alga called diatoms.

It is light weight and is generally white.

It is used as an abrasive, insecticide, filtering medium, and paint “flattener”.San Manuel, AZ

Dolomite (#23)

Composed of calcium magnesium carbonate

The rock has over 90% carbonate and fossils are rare in these rocks

Does not react with acid.

M O R E C L U E S T O S E D IM E N TA R Y R O C K S

C H E M IC A L : R o c k s a re c rys ta l l in e

L IM E S T O N E S : C o m p o s e d o f c a lc i te a n d a l l W IL L F IZ Z vig o ro u s ly in a c id C rys ta l l in e — L o o k s s u g a r y, u s u a l ly g ra y o r ta n F o s s il i fe ro u s — C o n ta in s s e a s h e lls (u s u a lly) o r o th e r a q u a tic o rg a n is m s T ra ve r t in e — L o o k s s u g a r y w ith b a n d s o f v a r io u s c o lo rs C h a lk — W h ite a n d s o ft ( c o m e s o ff o n h a n d s ) C o q u in a — C o n ta in s a lm o s t n o th in g b u t s e a s h e l ls o r s e a s h e l l fra gm e n ts

C H E R T: C ry p to c ry s ta llin e Q U A R T Z V e r y f in e — c a n N O T s e e c rys ta ls W a x y lu s te r C o n c h o id a l fra c tu re (b re a k s l ik e g la s s ) V e r y h a rd — w i l l e a s ily s c ra tc h g la s s M a y b e A N Y C O L O R (R e d = J a s p e r , B la c k = F l in t, in c lu d e s S i l ic i f ie d W o o d )

G Y P S U M : W h ite , g ra y, c le a r V e r y s o ft — yo u c a n s c ra tc h w ith f in g e rn a i l C le a r s h e e ts , f ib ro u s o r s u g a ry

R O C K S A LT: W h ite to c le a r — c u b ic s h a p e S o ft — y o u c a n s c ra tc h i t w i th f in g e rn a i l T a s te s l ik e ta b le s a l t ( IT IS T A B L E S A L T !)

C O A L : B la c k ; B r i t t le ; L ig h tw e ig h t M a y c o n ta in p la n t fo s s i ls V a r ie t ie s : p e a t, l ig n i te ( in c l . je t) , s u b -b i tu m in o u s , b i tu m in o u s

D IAT O M IT E : W hite V e r y s o ft ( c o m e s o ff o n y o u r h a n d s ) L ig h tw e ig h t W i ll N O T fiz z in H C l a c id (u n l ik e c h a lk )

Sedimentary Structures

Bedding: Sediments are deposited in Horizontal layers (original horizontality)Deeper rocks are older (superposition)

Tilted Sedimentary Rock Layers

La Castilla, Peru

Sedimentary Structures

Other information preserved in sedimentary rocks

Cross Bedding (Dunes)Graded Bedding

(Turbidity Currents)Ripple marks (water or

wind)Mud Cracks (dried lake)Fossils (many

sediments)

Cross Bedding

Indicates current

and directionWindWater

Homework

P. 132 #1,2,3 P. 127 #1- 4