NOTES ON APPLIED GEOLOGY

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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