Sediment and Sedimentary rock,Significance of sedimentary rocks

Sediment: An accumulation of loose mineral grains, such as boulders, pebbles, sand, silt or mud, which are not cemented together.

1. SOMALI NATIONAL UNIVERSITY
FACULTY OF SCIENCE-
GEOLOGY DEPARTMENT
LECTURER: GEO .Abdirahman Mayow Abdirahiin
B.sc, M.sc Geology(Int)

2. Sedimentary
petrology-II

3. OUTLINE OF THE
COURSE
CONTENT!
PETROLOGT-2

4. CHAPTER 1Pre-existing Rocks to Sediment
Weathering and Erosion
Physical vs. Chemical Weathering
CHAPTER 2Sediment to Sedimentary Rocks
•Transportation
•Deposition
•Lithification
CHAPTER 3 Types of texture
•clastic
•non-clastic
CHAPTER 4Classifying Sedimentary Rocks
Detrital/Clastic Sedimentary Rocks:
Inorganic/Chemical Sedimentary Rocks
Organic/Biochemical Sedimentary Rocks
CHAPTER 5Depositional Environments
Continental
Transitional
Marine
CHAPTER 6Sedimentary Structures
AND PRACRTICAL RECORD WRITING OF SEDIMENTARY PHYSICAL / MEGASCOPIC ROCK SPECIMEN

5. CHAPTER 7
Overview of Metamorphism and Metamorphic rocks
Principle Factors of Metamorphism
Types of Metamorphism
CHAPTER 8 Classification of Metamorphic rocks
Texture is further subdivided into two types:
Foliated and/or Layered Fabrics
Non-foliated and/or Massive Fabrics
The Major Metamorphic Rock Types

CHAPTER 9
 METAMORPHIC ZONE AND FACIES CONCEPTS
CHAPTER 10
MEGASCOPIC PRACTICAL OF METAMPRHIC SPECIMEN

6. Sedimentary
Rocks

7. Sediment and Sedimentary rock
Sediment: An accumulation of loose mineral grains, such as boulders, pebbles, sand,
silt or mud, which are not cemented together.
Mechanical and chemical weathering produces the raw materials for soil and
sedimentary rock.
Sediment may be detrital or chemical, and sedimentary rocks may form by the
deposition of particles or by biologic activity.
Sediment can be carried a considerable distance from its source, eventually coming
to rest in a depositional environment: ( Continental , Transitional , Marine ).

8. Sediment and Sedimentary rock
Sedimentary rock: Rock that forms either by the cementing together
of fragments broken off pre-existing rock or by the precipitation of
mineral crystals out of water solutions at or near the Earth’s surface.
Sedimentary rocks make up only about 5% of the Earth’s crust. As
a result, sedimentary rocks cover about 75% of continents.
Many sedimentary rocks have high economic value. Oil and gas
form in certain sedimentary rocks.

9. Significance of
sedimentary rocks:
Cover more than 75% of the Earth’s surface
but they are less than 5% of the Earth’s mass.
Provide a record of ancient tectonic events
(e.g., mountain building and erosion).
Fossil record-evolution of life.
Major reservoirs of groundwater, oil, coal.
History of past climate changes..

10. •1. Weathering: Transform the solid rock into smaller fragments
•2. Transportation: Transport the sediments by sliding down slopes, being
picked up by the wind, or by being carried by running water in streams,
rivers, or ocean currents.
•3. Deposition: Sediment is deposited when the energy of the transporting
medium becomes too low to continue the transport process.
•4. Lithification (Diagenesis): Lithification is the process that turns sediment
into rock.
The major processes forming the clastic
sedimentary rocks:

11. Physical or Mechanical Weathering:
The process in which a rock breaks into smaller grains or pieces
called detritus (disintegration, i.e. without change in its chemical
composition).
Many different phenomena contribute to physical weathering such
as:
•Jointing – Exfoliation – Frost wedging – Root wedging, Salt
wedging – Diurnal temperature change, Thermal expansion –
Animal attack

12. CONT..
•EXFOLIATION :
Exfoliation weathering occurs when outer layers of rocks
break off and the released pressure causes rock to
expand and break. The formation in California called
Half Dome is a well known example of exfoliation
weathering.

13. CONT…
•Frost wedging :
Frost wedging happens when water filling a crack freezes
and expands (as it freezes, water expands 8 to 11% in
volume over liquid water). The expanding ice imparts a
great amount of pressure against the rock (as much as
30,000 pounds/square inch) and wedges open the crack.

15. Root wedging:
•Happens when plant roots work themselves into cracks, prying
the bedrock apart as they grow. Occasionally these roots may
become fossilized.

16. Root wedging

17. Salt expansion:
which works similarly to frost wedging,
occurs in areas of high evaporation or near-
marine environments. Evaporation causes
salts to precipitate out of solution and grow
and expand into cracks in the rock. Salt
expansion is one of the causes of tafoni, a
series of holes in a rock. Tafoni, cracks, and
holes are weak points that become
susceptible to increased weathering.

18. water abrading rocks

19. Chemical weathering:
•The process in which chemical reactions alter or destroy minerals (i.e.
decomposition) when rock comes in contact with water solutions and/or air.
It involves many processes such as:
•Dissolution – Hydrolysis – Oxidation – Hydration
 affect on minerals:
quartz resists chemical weathering
feldspar survives with rapid erosion or altered to clay mafic minerals and
carbonate minerals usually dissolve…

20. Hydration:
•The simplest reactions that take place in chemical weathering are
the solution of soluble minerals and the addition of water to
substances to form hydrates. Solution commonly involves
ionization. for example, this takes place when gypsum and
carbonate rocks are weathered. Hydration takes place among
some substances, a common example being gypsum and
anhydrite:

21. Dissolution:
•Is a hydrolysis reaction that dissolves minerals in bedrock and leaves the
ions in solution, usually in water. Some evaporites and carbonates, like salt
and calcite, are more prone to this reaction; however, all minerals can be
dissolved. for example, the Aqueous dissolution of calcium carbonate
introduces the carbonate ion into the water, that is, CO3 combines with H
to form the stable bicarbonate, H2CO3:

22. Hydrolysis:
•Weathering of the silicate minerals is primarily a process of
hydrolysis. Much of the silica that is released by weathering forms
silicic acid.
•When subjected to chemical weathering, feldspars decompose to
form clay minerals, which are, consequently, the most abundant
residual products and some silicic acid.

23. •The Goldich Dissolution Series shows chemical weathering rates are associated with
crystallization rankings in the Bowen’s Reaction Series. Minerals at the top of the
Bowen series crystallize under high temperatures and pressures, and chemically
weather at a faster rate than minerals ranked at the bottom.
•Quartz, a felsic mineral that crystallizes at 700°C, is very resistant to chemical
weathering.
•High crystallization-point mafic minerals, such as olivine and pyroxene (1,250°C),
weather relatively rapidly and more completely. Olivine and pyroxene are rarely found
as end products of weathering because they tend to break down into elemental ions.

25. •Oxidation, the chemical reaction that causes rust in metallic iron, occurs
geologically when iron atoms in a mineral bond with oxygen. Any minerals
containing iron can be oxidized.
•The resultant iron oxides may permeate a rock if it is rich in iron minerals.
Oxides may also form a coating that covers rocks and grains of sediment, or
lines rock cavities and fractures.
•If the oxides are more susceptible to weathering than the original bedrock,
they may create void spaces inside the rock mass or hollows on exposed
surfaces.

26. Erosion:
•Erosion is a mechanical process, usually driven
by water, gravity, wind, or ice that removes
sediment from the place of weathering. Liquid
water is the main agent of erosion.

27. Erosion :

28. T
he END