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:
i.
ii.
iii.
A formation should posses some degree of
internal homogeneity or distinct features.
One lithic type.
Repetitions of two or more lithic types.
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
•
1.
2.
3.
4.
•
1.
2.
3.
•
Sediments with visible graine size:
Size,
Sorting,
Roundness,
Sphericity.
Sediments with crystalline appearance.
estimate crystallinity:
Microcrystalline
Cryptocrystalline
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 Classification
Depositional
texture not
recognisable
Depositional texture recognisable
Original
components
bound
together
during
deposition
Original components not bound together during
deposition.
Lacks mud Contain mud (particles<20m)
and is grain
supported
Grain
Mud supported
supported
> 10%
grains
Crystalline
carbonate
Boundstone
Grainstone
Packstone Wackstone
< 10%
grains
Mud
stone
Dunham Classification
5. Hardness
1.
2.
3.
4.
Hardness is a reflection of degree of
cementation.
Soft or friable
Moderately hard; fairly cemented.
Hard; moderately cemented.
Very hard; well cemented.
6. Porosity
•
Porosity could be estimated from hardness and
cementation.
•
Archi classification
 matrix porosity
I. Compact, dense, hard
II. Chaiky, earthy, soft.
III. Sugary, loose, poorly cemented.
 Visible porosity
A. No visible pores w/ 10x
B. Visible w/ 10x
C. Visible w/ eye.
D. Larger than 2 mm
7. Minor constituents
Oil Shows Description
A. In Normal Light
• Percentage
 No visible stain
 Poor stain
 Fair stain
 Good stain
40%
Oil Shows Description
A. In Normal Light
• Distribution
 Uniform
 Spoty
• Shade
 V. Light
 Medium
 Very dark
• Hue
 Green
 Yellow
 Brown
 Black
Scattered
Streaked
Light
Dark
Oil Shows Description
B. Under UV Light
• Intensity
 No florescence
 Faint
 Dull
 bright
Oil Shows Description
B. Under UV light
•


•



•





Distribution
Uniform
Spoty
Shade
V. Light
Medium
Very dark
Hue
Blue
white
Yellow, Orange
Gold
Brown
Scattered
Streaked
Light
Dark
C. Cuts & D. Residual ring
• Stream cut:
 Immediate
 Fast
 Slow
• Discoloration
 Very slow
 Slow
 Fast
• Crush cut
 Poor
 Fair
 Good
• Allow the solvent to
evaporate,
describe the
fluorescence of the
ring as well as the
color of the ring in
the day light.