05_Geology & Sample Description

7/31/2019 05_Geology & Sample Description

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NOTES ONAPPLIED GEOLOGY


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BEDDING

Bed :

Sedimentation unitgreater than 1cm.

Lamina:

Sedimentation unitsmaller than 1cm.

Interbedded:between two things


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STRATIGRAPHY

Stratigraphic unit

A naturally occuring body of rock or rockmaterial which is distinguished from

adjoining rock on the basis of some statedproperty or properties.

1.Lithostratigraphic unit.

2.Biostratigraphic unit.3.Chronostratigraphic unit.

4.Geochronologic unit.


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Lithostratigraphic Unit

(( is a stratum or body of strata,generally layered which conforms

to the law of superposition and isdistinguished and delimited on thebasis of lithic characteristics and

stratigraphic position.))


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Nature of Lithostratigraphic Units

Type section andlocality.

Independence frominferred Geologichistory.

Independence from

time concepts.


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Boundaries

Are placed at positions oflithic change.

Boundaries in lateral lithologic change.

Correspondence with generic units.


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Lithostratigraphic boundaries


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Rank of Lithologic Units


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Formation

It is the fundamental unit inlithostratigraphic classification.

Content:

A formation should posses some degree ofinternal 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.


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Lithostratigraphic Nomenclature

Compound character:

Geographic +Lithic term+ Rank.

Geographic + Rank.Geographic + Lithic + Rank.

Use of Simple lithic terms.

Misuse of well known name.


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Clay Minerals

A term reserved for those constituents of aclay which give it its plastic properties. They

are hydrous aluminosilicates.

Generally occur as minute, platy, rarely fibrouscrystals.

Some contain loosely bonded cations which canbe easily exchanged.

Ability to loose or take up water. Produced by the degradation of other silicates.

Both two and three layered types are known.


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The sheets of clay minerals


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Clay minerals (continue)

Layers of Al - O/OH are called gibbsite.

Layers of MgO/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.


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I. Kandit Group

Members have two layeredstructure consisting of a silicatetrahedral sheet linked to analumina octahedral sheet bycommon O/OH ions.

No replacement occur for Si

or Al. The structure formula is

(OH)4Al2Si2O5. e.g Kaolinite


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II. Smectite Group

Members have a threelayered structure.

Have ability for Al and Siexchange.

Have ability for absorbingwater.

e.g Montmorillonite(Mg,Ca)O.Al2O3.5SiO2.nH2O


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Three layered structure.


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Diagensis

Pre-Burial changes:

1. Burrowing organismseffect.

2. Adjustment to eH andpH.

3. Adjustment to majorcations.

4. Development ofAuthigenic menerals.

Early-Burial changes

1. Continuation of 2 & 3.

2. Oxidation of carbonaceous

material.3. Continuation of compaction.

4. Probable initiation ofconcretions.

5. Start of primary cementation.6. Some conversation of

aragonite to calcite, anddevelopment of dolomite.


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Diagensis(continue)

Late Burial Changes:

Cease of eH and pHadjustments.

Completion of compaction.

Authigenic mica & chlorite.

Completion of concretions

development andcementation.

Replacement of aragoniteby calcite; dolomitization.


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Sedimentary Rock Types

Rocks formed from material derived

from pre-existing rocks byprocesses of denudation, together

with material of organic origin.


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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).


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3. Texture

Sediments with visible graine size:1. Size,

2. Sorting,

3. Roundness,

4. Sphericity. Sediments with crystalline appearance.

estimate crystallinity:

1. Microcrystalline

2. Cryptocrystalline3. Succrose

Sediments without recognizable size at ordinarymicroscope:

Descripe the morphology of the cutting.


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Dunham Classification

Depositional texturenot recognized.

Crystalline carbonate.


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Mud supported


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Grain supported


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Dunham ClassificationDepositional

texture notrecognisable

Depositional texture recognisable

Originalcomponentsboundtogetherduringdeposition

Original components not bound together duringdeposition.

Lacks mud

and is grainsupported

Contain mud (particles 10%

grains


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Dunham Classification


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5. Hardness

Hardness is a reflection of degree ofcementation.

1. Soft or friable

2. Moderately hard; fairly cemented.

3. Hard; moderately cemented.

4. Very hard; well cemented.


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6. Porosity

Porosity could be estimated from hardness andcementation.

Archi classification matrix porosity

I. Compact, dense, hardII. Chaiky, earthy, soft.III. Sugary, loose, poorly cemented. Visible porosityA. No visible pores w/ 10x

B. Visible w/ 10xC. Visible w/ eye.D. Larger than 2 mm


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7. Minor constituents


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Oil Shows DescriptionA. In Normal Light

PercentageNo visible stain

Poor stain

Fair stain

Good stain

40%


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Oil Shows DescriptionA. In Normal Light

Distribution Uniform Scattered Spoty Streaked Shade

V. Light LightMedium Dark Very dark Hue

Green Yellow Brown Black


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Oil Shows DescriptionB. Under UV Light

IntensityNo florescence

Faint

Dull

bright


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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


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05_Geology & Sample Description

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