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NOTES ON APPLIED GEOLOGY. BEDDING. Bed : Sedimentation unit greater than 1cm. Lamina: Sedimentation unit smaller than 1cm. Interbedded: between two things. STRATIGRAPHY. Stratigraphic unit - PowerPoint PPT Presentation
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NOTES ON APPLIED GEOLOGY
BEDDING
• Bed :
Sedimentation unit greater than 1cm.
• Lamina:
Sedimentation unit smaller than 1cm.
• Interbedded:
between two things
STRATIGRAPHY
• Stratigraphic unit
A naturally occuring body of rock or rock material which is distinguished from
adjoining rock on the basis of some stated property or properties.
1.Lithostratigraphic unit.
2.Biostratigraphic unit.
3.Chronostratigraphic unit.
4.Geochronologic unit.
Lithostratigraphic Unit
(( is a stratum or body of strata, generally layered which conforms to the law of superposition and is
distinguished and delimited on the basis of lithic characteristics and
stratigraphic position.))
Nature of Lithostratigraphic Units
• Type section and locality.
• Independence from inferred Geologic history.
• Independence from time concepts.
Boundaries
Are placed at positions of lithic change.
Boundaries in lateral lithologic change.Correspondence with generic units.
Lithostratigraphic boundaries
Rank of Lithologic Units
Formation
It is the fundamental unit in lithostratigraphic classification.
• Content: A formation should posses some degree of internal homogeneity or distinct features.
i. One lithic type.
ii. Repetitions of two or more lithic types.
iii. Extrem lithic heterogenity.
• Lithic characteristics.• Mappability and thickness.
Lithostratigraphic Nomenclature
• Compound character:
Geographic +Lithic term+ Rank.
Geographic + Rank.
Geographic + Lithic + Rank.• Use of Simple lithic terms.• Misuse of well known name.
Clay Minerals
A term reserved for those constituents of a clay which give it its plastic properties. They
are hydrous aluminosilicates.• Generally occur as minute, platy, rarely fibrous
crystals.• Some contain loosely bonded cations which can
be easily exchanged.• Ability to loose or take up water.• Produced by the degradation of other silicates.• Both two and three layered types are known.
The sheets of clay minerals
Clay minerals (continue)
• Layers of Al - O/OH are called “gibbsite”.• Layers of Mg – O/OH are called “brucite”.• The stacking arrangement of the sheets
determine the clay mineral type, as does the replacement of the Si and Al inons.
I. Kandit Group
• Members have two – layered structure consisting of a silica tetrahedral sheet linked to an alumina octahedral sheet by common O/OH ions.
• No replacement occur for Si or Al.
• The structure formula is (OH)4Al2Si2O5. e.g Kaolinite
II. Smectite Group
• Members have a three – layered structure.
• Have ability for Al and Si exchange.
• Have ability for absorbing water.
• e.g Montmorillonite
(Mg,Ca)O.Al2O3.5SiO2.nH2O
Three – layered structure.
Diagensis
• Pre-Burial changes:
1. Burrowing organisms effect.
2. Adjustment to eH and pH.
3. Adjustment to major cations.
4. Development of Authigenic menerals.
• Early-Burial changes
1. Continuation of 2 & 3.
2. Oxidation of carbonaceous material.
3. Continuation of compaction.
4. Probable initiation of concretions.
5. Start of primary cementation.
6. Some conversation of aragonite to calcite, and development of dolomite.
Diagensis (continue)
• Late – Burial Changes:• Cease of eH and pH
adjustments.• Completion of compaction.• Authigenic mica & chlorite.• Completion of concretions
development and cementation.
• Replacement of aragonite by calcite; dolomitization.
Sedimentary Rock Types
Rocks formed from material derived from pre-existing rocks by
processes of denudation, together with material of organic origin.
Lithological Description
1. Type of formation (Limestone, sandstone, shale…).
2. Colour.3. Texture.4. Cementing material.5. Hardness.6. Porosity.7. Minor components (accessories).8. Staining and fluorescence (oil shows).
3. Texture• Sediments with visible graine size:1. Size, 2. Sorting,3. Roundness,4. Sphericity.• Sediments with crystalline appearance.
estimate crystallinity:1. Microcrystalline2. Cryptocrystalline3. Succrose• Sediments without recognizable size at ordinary
microscope:Descripe the morphology of the cutting.
Dunham Classification
• Depositional texture not recognized.
• Crystalline carbonate.
Depositional texture recognized
• Depositional texture recoginized.
• Original components bound together
• Boundstone.
Mud supported
Grain supported
Dunham ClassificationDepositional texture not recognisable
Depositional texture recognisable
Original components bound together during deposition
Original components not bound together during deposition.
Lacks mud and is grain supported
Contain mud (particles<20m)
Grain supported
Mud supported
> 10% grains
< 10%grains
Crystalline carbonate
Boundstone Grainstone Packstone Wackstone Mud stone
Dunham Classification
5. Hardness
Hardness is a reflection of degree of cementation.
1. Soft or friable
2. Moderately hard; fairly cemented.
3. Hard; moderately cemented.
4. Very hard; well cemented.
6. Porosity
• Porosity could be estimated from hardness and cementation.
• Archi classification matrix porosityI. Compact, dense, hardII. Chaiky, earthy, soft.III. Sugary, loose, poorly cemented. Visible porosityA. No visible pores w/ 10xB. Visible w/ 10xC. Visible w/ eye.D. Larger than 2 mm
7. Minor constituents
Oil Shows DescriptionA. In Normal Light
• Percentage No visible stain Poor stain Fair stain Good stain
40%
Oil Shows DescriptionA. In Normal Light
• Distribution Uniform
Scattered Spoty
Streaked• Shade V. Light Light Medium Dark Very dark• Hue Green Yellow Brown Black
Oil Shows DescriptionB. Under UV Light
• Intensity No florescence Faint Dull bright
Oil Shows DescriptionB. Under UV light
• Distribution Uniform Scattered Spoty Streaked• Shade V. Light Light Medium Dark Very dark• Hue Blue white Yellow, Orange Gold Brown
C. Cuts & D. Residual ring• Stream cut:ImmediateFastSlow• DiscolorationVery slowSlowFast• Crush cutPoorFairGood
• Allow the solvent to evaporate, describe the fluorescence of the ring as well as the color of the ring in the day light.
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