a. sediment source and history b. formation of sedimentary rocks c. types of sedimentary rocks d....
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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
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