Download Chemical sedimentary rocks

The rock cycle
In the view of EARTH MATERIALS
‫ד"ר חנן גינת‬
‫ד"ר ירון פינצי‬
The rock cycle in the view
of internal and external
PROCESSES
external
Internal
The external
processes
Weathering
Transportation
Deposition
Solidifying
Weathering
The destructive processes that
change the physical and chemical
characteristics of rocks at the
earth's surface.
Physical Weathering – mechanical
breakdown of large rocks into
smaller rocks is called mechanical
weathering
Physical weathering does not
involve chemical changes to rock.
Mechanical weathering results from the disintegrating action of high or low
temperature, large changes of temperature, frost, or the impact of windborne sand or water
Changes in a rock's composition due to
exposure to the atmosphere and water is called
chemical weathering.
Factors which effect the rate of chemical weathering are:
1. The particle size and the surface area
2. Climate
3. Type of rock
Chemical weathering can be solution by water, hydrolysis
reactions, oxidation and other chemical processes.
Biogenic Weathering – Caused by plants or animals
- roots
- digging
- Involving in chemical
processes
‫זיהוי סוגים שונים של בלייה‬
‫‪2‬‬
‫‪1‬‬
‫‪4‬‬
‫‪3‬‬
5
-Write the main factors of the
Weathering process
7
9
6
8
9
11
10
12
In which areas we can find the maximum physical and/or chemical weathering?
Transportation of the weathering products
Can be by:
1. Streams and
rivers (fluvial)
2. By wind
(Aeolian)
3. By ice and
glaciers
(glacial)
4. By sea
currents
Water in streams transport:
1. Raking pebbles
2. Floating materials
3. Dissolving materials
The amount and characteristic of the loaded
materials depend on:
1. Intensity of floods
2. Available loaded materials from the
weathering processes
3. The type of the stream/river
4. Characteristic of the catchments area
Loaded
alluvial
sediments
during
floods
The fluvial process
valleys
Wide river
highlands
angular
rounded
Pebbles transport by the
stream and change their
shape and size (physical
weathering).
What are the factors that
influence the amount of change?
Clastic sediments are also characterized by the degree of particle
sorting, and by the roundness of their grains, which usually implies
something about the distance and mode of transport.
Transport of sand grains by winds – the aeolian process
Characteristic of transport:
1. Small grains
2. No pebbles
3. Deposit mostly in dunes
Different kinds of dunes depends on the
wind direction and intensity, the topography
and the plants
Transport by ice – the glacial process
Glaciers are large masses of snow, recrystallized ice and rock debris that
accumulate in great quantities and begin to flow outwards and downwards
under the pressure of their own weight
The Glacial features
The glacial materials can be in
different sizes – from boulders
to clay grains.
Signs in the rocks
Deposition will be in:
-Front moraines
-Side moraines
-Medial moraines
And other remnants will be U
shaped valleys and fiords
Transport by sea
currents
Most fine sediments
can be transferred long
distances
Reconstruction of the
Geological History from a
geological cross section
A movie: Flood in the
Isaron 18.1.2010
The rock cycle
In the view of EARTH MATERIALS
Different types of bedding
Graded beds form when a
rapidly flowing turbid
slurry of water and mixed
clasts, usually in a river or
stream, slows down on
entering a larger body of
water and the largest
clasts settle first.
Cross bedding in ripples and
dunes is formed by the
migration of sand up the
shallow, windward face and
down the steep, leeward face
windward face.
Planner bedding
Gradded bedding
Cross bedding
By wind
By stream
Bedding and stratification are
the hallmark of sedimentary
rock. The layers, or strata, are
built up from the
accumulation of particles of
various sizes and
arrangements. These
particles formed during the
breakdown and transport of
pre-existing rock, or by
precipitation from ions in
solution.
Sediments and sedimentary
rocks, like those in the Grand
Canyon preserve records of past
climatic, environmental, and
biological change on the Earth.
Sedimentary environments on land are:
fluvial (stream), lacustrine (lake), glacial, aeolian.
Where the land meets the sea typical environments are:
Beach, Estuary, Delta, Lagoon, Tidal Flat.
In the ocean some common sedimentary environments are:
Reef, carbonate shelf, submarine canyon.
In some lakes, sediments are
deposited in annual cycles called
varves. The light colored silty
layers were deposited when rivers
flowed into the lake, while the dark
clay rich layers formed when the
lake was frozen over.
Lithification (Solidification)
Particle size is the primary basis for classifying clastic sediments and
sedimentary rocks, regardless of the mineralogy of the clasts.
Clastic rocks
Loose sediments are transformed into
rock, that is they are lithified, by
compaction, recrystallization, and
cementation. Together, these changes
are commonly referred to as diagenesis.
Clastic rocks–made of cemented
sediments—are classified by their grain
sizes.
http://www.volcanoworld.org/vwdocs/vwlessons/lessons/Sedrocks/Sedrocks9.html
The story of different kind of bedding
Use page 7 to identify the size and
)roundness of the grains)
What are the main types of sedimentary rocks?
Classified into three
groups include the types
of particles they contain.
Clastic rocks
built from grains that have
been cemented as a rock
Biogenic rocks
built from remains of plants or
animals, mostly from the sea
Chemical sedimentary
rocks – were formed in an over
saturated liquid (as lagoon or salty
lakes)
Deposition Environment of Clastic and Biogenic Rocks
High Lands
stream
200m
Conglomerate
Continental
shelf:
chalk
Limestone
Dolomite
Clay
Volcano
Clay
Chert
lake
Marl
Clay
Limestone
Clay
Limestone
Sandstone
Marl
Dolomite
Chalk
Chert
―Black‖ Sea
Shallow
sea
Very Shallow
Deep Ocean
Reconstruction of the
Geological History from a
geological cross section
A movie: Flood in the
Isaron 18.1.2010
Fossils
A fossil is any evidence of a plant or animal that
has been preserved in the Earth’s rocks
The importance of fossils:
1. Giving more details about the Environment of
the plant/animals
2. Compare about the Time Scale.
3. Giving data about the development of animals
and/or plants through evolution
How can we classify the fossils ?
1. By the parts of
the animal that
were fossilized;
- Body fossils
(Shells, bones,
teeth)
- Trace fossil –
footstep, burrow
2. By the kind of
the Animal or
plant:
Shell, snail,
Dinosaur….
1. Identify the fossils
2. Classify the fossils to
groups.
3. Try to identify to the
environments in which the
animals were fossilized
3. The age of the animal
Young …..some thousands of
years
or Old…. some millions
4. By the kind of rocks that include the fossils
Soft rocks (clay)
Or hard rock
(limestone)
Body fossils and trace fossils are uncovered
Creation of Biogenic Rocks
1. The animal or the plant dies
2. The skeleton or the shell lie on the fine
sediments on the floor of the sea, lake or swamp.
3.The skeleton or the shell
is buried under the
surface and becomes
hard.
4. Most of the biogenic materials dissolve and are
deposited on the bottom of the sea
5. By compression process the soft sediment becomes a hard rock
6. The sea dries out and the rocks on the sea
floor are uncovered.
The Rock
Biogenic materials
Environment
Limestone
Shelf, marine snails, carbonate
foraminifera
Shallow sea
Marl
Shallow sea rich with clay
Chalk
Nano-plankton
Open sea
Chert
Diatomite and Radiolaron
Deep Sea
Or: Chemical change
Carbonate
foraminifera
Big fossils in limestone
Chalk
Chert
Diatomite
Chemical Sedimentary rocks
When water washes over and through rocks, some of the minerals from
the rocks are dissolved and carried in the water. When the water
evaporates or the minerals precipitate out of it the chemical
sediment (the previously dissolved minerals) are deposited. These
sediments go through the same lithification process as detrital
sedimentary rocks
Chemical sedimentary rocks form when mineral solutions, such as sea
water, evaporate. Examples include the evaporite minerals such as halite
and gypsum.
The needed conditions to create chemical sedimentary rock:
1. Saturated water
2. Hot climate
3. Evaporation > Precipitation
Dolomite
(Ca,Mg)C03
Gypsum
CaSO4(2H2O)
2/3 of the liquid
was evaporated
Salt
Na Cl
9/10 of the liquid
was evaporated
Crystallization from saturated liquid
The Natural Environments
Lagoon
A bay inshore from an enclosing reef or
island paralleling a coast.
Close lake in hot climate
Open lake
Bardawill Lagoon
Close lake
The chemical sedimentary rocks have high economic value
Sedimentary rocks are economically important in that they can be
used as construction material. In addition,
Chemical rocks as gypsum and salt are
mined in quarrys
‫בדרך להר המלח‬
‫הדנקילים – מלח ומים חמים עשירים במינרלים‬
‫חוצבים מלח‪...‬או מפעלי ימת המלח‪...‬‬
Metamorphic rocks and processes
New rock textures and new mineral assemblages
develop when rocks are subjected to elevated
temperatures and pressures. Changes that take place
while the rock is still solid are called metamorphism.
Metamorphic changes start at about 150oC (equivalent to a depth within
the Earth of 5 km) and cease around 800oC where the rocks start to melt.
The Pietà, Michaelangelo's most famous
statue, was carved from marble, a
metamorphic rock from the Carrara quarries in
Italy.
What are the three types of metamorphism?
The processes that cause changes in texture and in mineral
assemblage in metamorphic rocks are mechanical deformation and
chemical recrystalization.
The origin rocks
Granite
Limestone
Metamorphosed rocks
Gneiss
Marble
Schist
Clay
Sandstone
Quartzite
And Some times with new
metamorphic minerals
Schist Garnet
Tourmaline Mica Schist
Pore fluids allow dissolved
minerals to be transported and reprecipitated elsewhere; they also
speed up chemical reactions.
FoliationThe schist
The composition of metamorphic rock is strongly controlled
by the composition of the parent rock, but other factors also
apply.
The growth of new mineral phases during
metamorphism is primarily controlled by
temperature. High temperatures, pressures
and abundant pore fluids result in
metamorphic rocks with large mineral grains
The original structure
Elongated structure after metamorphism
The changes that occur during metamorphism often produce a
texture called foliation. This is caused by the preferential orientation
of newly-formed micaceous minerals
Foliation in low-grade
metamorphic rocks is called
slaty cleavage. Both foliation
and cleavage develop
perpendicular to the direction of
maximum stress
The diagram shows the conditions of pressure and temperature
in which diagenesis, metamorphism, and melting occur in the
Earth's crust.
Metamorphic changes start at about 150oC (equivalent to a depth within the Earth
of 5 km) and cease around 800oC where the rocks start to melt
How do solid rocks change?
As temperature and stress increase on a sedimentary rock, like shale,
different mineral assemblages are formed, ultimately resulting in the
metamorphic rocks slate, phyllite, schist, and gneiss.
What are the metamorphic facies?
For a given rock composition, the assemblages of minerals that are formed
under a specific temperature and pressure are always the same. This fact
allows us to define specific metamorphic facies.
Sedimentary rocks that are saturated with water and subjected to
elevated temperatures and pressures undergo burial metamorphism.
Regional metamorphism
occurs under differential
stress and elevated
temperatures as a result
of the collision of
tectonic plates.
Regionally
metamorphosed rocks
commonly extend over
areas of thousands of
square kilometers
Subduction Zone
Paired metamorphic facies are common in subduction zone tectonic
environments. Ocean floor basalts exposed to variable pressures
and temperatures form well-foliated greenschists and amphibolites,
or weakly-foliated blueschists and eclogites.
Reconstruction of the
Geological History from a
geological cross section
The rock cycle
In the view of EARTH MATERIALS
Summary – the main rocks
and their story
http://www.volcanoworld.org/vwdocs/vwlessons/lessons/Rocks/Rocks8.html
1. Identify Rocks
Environments (page 10)
- Limestone
- Chert
- Granite
- Basalt
2. Why are there so many kinds
- Dolomite
- Gypsum
of sedimentary rocks?
- Marl
- Clay
- Schist
- Salt
- Sandstone
Some definitions:
Normal Fault – A dip-slip fault marked by a generally steep dip along
which the hanging wall has moved downward relative to the footwa
Thrust Fault – fault on which the hanging wall appears to have moved
up-ward, relative to the footwall
Strike slip Fault – A fault which has horizontal movement, or
movement parallel to the strike of the fault plane
Antycline – A fold in which the limbs dip away from the hinge. After
erosion, the oldest rocks are exposed in the central core of the fold
Syncline - fold in rocks in which the strata dip inward from both sides
(limbs) toward the axis
Normal and Thrust Faults
Normal and
thrust faults
and their
influence on the
topography
Strike slip Faults
Complex Geological Structures
Folds
Syncline
Anticline
-Sort the cards of the
Ggeological Structure Puzzle
Exercise: Find the geological structures along the Arava Valley and its margins
The main geological ideas connecting to sedimentary rocks are:
1. Superposition – The lower layer is the older one
2. Horizontal laying – In a body of standing water
the sediments accumulate always horizontal
3. ―The present is the key to understanding the
past‖
…and other principles connecting relationships in
the field
4. ―Chilled zones‖, xenolithes and magmatic pebbles in sedimentary rocks
can help us to know the relative date between magmatic and sedimentary
rocks
5. In a field outcrop metamorphic rock will be always older than its neighbors
6. The shaping of the recent landscape will be always the last stage of the
Geological History
Reconstruction of the
Geological
Field trip to Canyon Shehoret
The Goals
1. Meet the main rock-landscape
units of south Israel and
Jordan
2. Identify rocks near their origin
3. Reconstruct the main stages of
the Geological History of the
region
Geomorphology of Arid Zones
Climate
factors
Amount
of rain
Climate
Time
Geological
structures
Rocks
Geology
―Black box‖
The human
impact
Some remarks for the trip:
1. Leaving Ketura dinning room at 07.30 after breakfast
2. Bring with you walking shoes, Water (ar least 1.5 litter), hat, pen
3. We will work with field notebooks (4-5 stations).
4. Last task will be navigating in coupls
5. Back in Ketura at 14.00.
-Going out side and figure a
geological cross section
between Ketura Hills and
Edom Mountains
Dating rocks
1. Relative dating by field relationships
2. Dating with fossils
3. Accurate dating by radiometric measuring
The rock cycle
In the view of EARTH MATERIALS
Summary – the main rocks
and their story