sediment ology 11
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Definitions
Sedimentary Rocks
Defined as a geologic unit or rock unitproduced from physico-chemical
weathering of lithosphere .Sedimentary deposit
A body of solid materials accumulate at or
near surface of the earth under low T, Pwhich normally characterise thisenvironment
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Definitions
Sedimentary petrology
Is the microscopic and megascopicinvestigation of sedimentary rocks
Sediments
Sediments in its ordinary means solid
materials that had settled down from astate of suspension in a liquid but ingeological mean it is not limited.
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Sedimentology
DefinitionThe branch of geology that deals of
studying of sedimentary rocks;description, classification, genesis,diagenesis and their economicimportance.
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The classification of sedimentaryrocks
* The terrigenous sediments are those particles were originally derived from the earth ( mudrocks, siliciclastic sands and
conglomerates )* The pyroclastic sediments are the products of volcanic activity, include ashes, tuffs, volcaniclastic sands and agglomerates.* The residual sediments are those left in place after weathering,
include the laterites and bauxites.* The organic sediments are those which are composed of organic
matter of both animal and vegetal origin, include skeletal limestone and coal.
* The chemical sediments are those which form by direct precipitation in a subaqueous environment, include evaporite gypsum and rock salt , as well as tufa and perhaps some lime
mud.
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The classification of sedimentaryrocks
The five genetic classification still not solve all rock classification problem e.g phosphatized bone beds
are chemical, organic or residual deposits, and so on ?The five main genetic classes of sedimentary rocks can be divided
into two separate categories: the allochthonous and the autochthonous deposits.
** The allochthonoussediments are those which aretransported into the environment in which they are deposited. Theyinclude the terrigenous and pyroclastic, with rare reworkedcarbonates.
** Theautochthonoussediments are those which form withinthe environment in which they are deposited. They include thechemical, organic and residual classes.
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Internal Organization andStructures of sedimentary
Introduction:
To understand whatthe meaning of
structures ofsedimentary rocks
we well made a rapidcomparison betweentexture and structure
StructuresTextures
Largerorganizationalunits,
are seen orstudied best in
the outcrop
the grain tograinrelation,
seen or studiedbest in thin
section.
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Geological importance ofsedimentary structures:
a. They can be used to ascertain
sedimentary stratigraphic sequence.
b. They can be used to determine paleo-
current, paleo-slope.
c. They aid to determine agent of
transportation.
d. They aid to determine paleogeoraphy
and paleo-climate.
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Classification of sedimentarystructures
primaryorMechanicalorPhysicalstructuresare those formed at the time ofsediment accumulations or deposition, they maybe either; Hydrodynamic(produced by actionof current) or Hydro plastic( syn-
sedimentary deformation )
Chemical or diagenetic or secondary st.
are those formed after rock depositionOrganic or biogenic:are formed during the
depositional process by action of organisms.
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Characterization and restrictionof sedimentary structures:
sedimentary structures are independent ofrock composition or lithology .
examples : Graded bedding or cross
bedding characterize s.s and l.s, whileMud cracks occur only in cohesive mudsand stromatolites occur only in carbonatesediments.
Ripple do not form neither in a clay nor incoarse sand or gravel.
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Classification of sedimentarystructures
The most common classification ofsedimentary structures based on theagent or the environment of deposition,other is based on the morphology.
(see pettijohn page 101)
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Classification of sedimentarystructures
Inorganic StructurePrimary Structures(Mechanical)
A. Beddingstratification
B. Bedding internal structures
C. Beddingplane structures (on sole)
d. Beddingplane structures (on surface)
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Classification of sedimentarystructures
Inorganic Structure Secondary Structures (chemically)
A. solution Structures 1.stylotites
2. corrosion zone 3. vugs
B. Accretionary st. Crystal aggregatesC. Composite structure
Geodes, Sepatria
Cone in cone
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Primary structures
is the common and universal;Bedding or stratification primary structures.
It is the arrangement of bed into layers stratified rock it meansedimentary rocks.
Only few rare sediments such as Tillite are without internal
stratification, also some Igneous, metamorphic and lava flows arebedded.Stratum: is a layer greater then > 1 cm in thick visually
separable from other layer this is due to change inlithology or to sharp physical break.
Lamination: is restricted to similar units 1 cm in thick.
Fissile, shaly:is applied to shale strata and formed due to arrangement of
micaceous Laminas
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Diagram showing different shapes that can beacquired by beds and laminae and the
corresponding descriptive terms
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Nomenclature of bed accordingto their thickness
According to Meckee and wear
CharacterNomenclatureThickness
FlaggyVery thin bedded1-5 cmSlabbyThin bedded5-60 cm
BlockyThick bedded60-120 cm
MassiveVery thick bedded> 120 cm
The thinner strata are Laminated if 2mm., it named thinly
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Terminology for thickness of bedsand laminae
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Morphological description ofbedding.
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Flow Mechanisms
It is very important to know howparticles will behave when the fluid ismoving.
The physics of this situation isexpressed by the Reynolds equation:R = vdp / Where R is the reynolds numberV: velocity of the particleD: id the diameter of the particleP: is the density of the particle: is the viscosity of the fluid.
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Flow Mechanisms
Reynold number
For low R. number ( 2000) the fluid is
turbulent, generating eddies and vortices flow.--------------------------
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Ripple marks also
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Ripple marksalsoindicate currents, andare preserved onbedding planes
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5) Mud cracksindicate alternate drying and wetting
of the surface
The important idea
the characteristics ofsediments and sedimentary strata tell usabout the past environmental conditions ina particular area & how they changed over
time
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Sole marks
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Flute marks preserved as flute moulds on the lower surfaceof a bed. Flute are arranged parallel to the current. The
current is from L to R.
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Vertical plastic deformational structures
pseudonodule
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Biogenic Sedimentary Structures
Four main types of structure
Biogenic tracks ( vertebrate activities)Biogenic trails (vertebrate homes)
Biogenic burrows ( soft sediments)
Biogenic borings ( hard rocks)All the mentioned features known as trace fossil
or Ichnofossils
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Classification of sedimentarystructures
Organic Structures
A. petrification
B. BeddingC.Miscellaneous
Borings
Casts
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Allochthonous Sediments Classification
Allochthonous sediments consists of the
terrigenous and pyroclastic classes
The allochthonous sediments may conveniently
be classified using the end-member triangle
Studies of modern sediments are predominant
emphasizes grain size and texture rather than
mineral composition
Here we prefer the classification which is based
on the grain size and composition..
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Allochthonous Sediments Classification
Fourmain types of allochthonous sedimentswell now be described. These may be groupedinto the:
Mudrock,Pyroclastic,
Sandstone
Rudaceous.
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Gravel and Conglomerates( Rudaceous Sediments )
Most gravels consist of a framework and void.
The framework is composed ofgravelsizematerial varying from pebble to cobble and
Boulder)
The voids are the openings between theseframework elements, voids are rarely empty,they are generally filled with detritus sand orsmaller size or with a cement.
Gravel with unfilled voids have been termedopenwork gravel or Beach gravel
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Gravel and Conglomerates
Texture of Gravel and Conglomerate
Size of grains
Sorting or modalitySize of gravel
Shape of gravel
Roundnesssurface textures
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Classification of Gravels and conglomerate
Conglomerates and gravels have been classified in various ways.
e.g: boulder conglomerate)Texture (size* Based on cobble conglomerate
e.g: Limestone conglomerate, Chertcomposition* Based on conglomerate
e.g: Ferrugineous conglomerate, Calcareouscement* Based on conglomerate
of depositionagent or to the environment** According to the e.g : beach conglomerate, Fluviatile conglomerate
e.g: Epiclasticfragmentation** Based on the process responsible for conglomerate, Cataclastic conglomerate and Pyroclastic
conglomerate** Based on the origin of the Conglomerates and breccias, there are
those five major categories will shown in table.,Five types
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C l i B i
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Cataclastic Breccias( fault, fold breccia)
* Movement of large masses of rocks past one
onother
* Movement that occurs along a fault surface
give rise to fault breccia
* In case of overthrust, the breccia form thin
blanket along the sole of such overthrust.
* Crush conglomerate are produced by deformation of brittle, closely jointed rocks.
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Landslides and slump Breccia
* Most slump breccia are formed due to
simple gravitational srtess
* They are localy and quantitavely
unimportant.
* Slump and landslides occur either
subarial or saubaqueous
* landslides are related to slope,
structure and lithology
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Impact or fallback Breccias
* Shown in a few terrestrial impact Craters.
* Seen through the effects of shock
metamorphism ( effect of shock on qz)
* Shatter cones in basement quartzites
and features attributable to shock metamorphism in the breccia
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Internal fabric of gravel and conglomerate:
Gravels tend to have a preferred orientation.
It has been observed that a flatter stone
have up current dip.Imbricationsalso have been observed in
both fluvial and marine gravels.
The long axesof the pebble are said to be
oriented in the direction of the currentflow.
P d l t d
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Pseudoconglomerates andpseudobreccias
* Formed due to the weathering of diabases and related rocks (rounded
boulders of exfoliation surrounded by
clays)
* Sandstone packed with many rounded
concretionary bodies.
* Limestone consists entirely of algal balls-
pebbely sized concretionally structure
oncollites.
* diagenetic processes produces a pseudo-
breccias in some l.s
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Diagenesis of conglomerates
Conglomerates, like all sedimentary rocks undergomodifications after deposition as lithification, solution ext..
Lithification,the addition of a cement lead to
binds the constituents clasts together.Solution;when intrastratal solution begin to
play, it dissolve the contact between pebbles,and finally give stylolitic boundaries
Lead to deformationMechanical pressures:of pebbles some quartz or quartzite displayfractures or micro-fault
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Type of Sphericity
F t t l th t it f th
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Factors control the maturity of thesediments
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Rock components of detrital sediments
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Uses and Economic importance of
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Uses and Economic importance ofSandstone
Sandstone deposits can be a beautiful part of the naturalenvironment and apart of the breath-taking views at many naturalparks and preserves.
Mined sandstone can be cut, polished and carved for many uses. Itis used as ornamental rocks for buildings, monuments, gravestones, bookends, beverage coasters, tiles and many other possible
uses.Sandstone can also provide silica for glass production.
Some mineral ores are found in sandstone. concentrate in uraniumminerals in sandstone deposits and many uranium ore bodies arethe result.
Heavy minerals such as rutile, gold, diamonds and others can befound in sandstones from prehistoric placer deposits that are nowworked for their economic value.
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Economic Importance
1.Many sands and sandstones are economic resources
as abrasive. Raw materials in chemical, glass and
metallurgical industries, as constructive material, both
building stones and as ingredient of plaster and concrete.
2. Some sandstone constitute important reservoirs for
natural gas, oil and artesian water
3. Some placer sands are a source of ore minerals and
gem.
4. Sand erosion and deposition are of engineering
importance on beaches, in river and in dune area.
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Academic Importance:
* They help for understanding the geologic
history;
* Their composition consider as clue to
provenance .
* Their directional structure are guide to paleo
-current.* Their geometry and internal structure shed
light on depositional environment.
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Mud rocks
Definition:
The term mud is illdefined and looselyused. In recent deposits sedimentsreferred to as a mixture of wet clay withcertain amount of silt and sand.
If lithified equivalent is termed
mudstone.
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MUDSTONE & CLAYSTONE
Claysare sediments with particles < .0039 mm.If lithified it give claystones.
Siltshave a grain size between .0039-.00625
mm. If lithified it give siltstones. Shaleis another term applied to fine grained
sediments, it does not differentiate silt fromclay-grade sediments. Shaley or fissile
phenomena is due to traces of mica aligned onlaminae.
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Type of Clay Minerals
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Type of Clay Minerals
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