Semester 2, 2008-2009

petrologi
2 SKS teori
1 SKS praktikum
by:
hill. gendoet hartono
Senin, jam 09.50 – 10.40
jam 10.45 ...
Clastic Rocks - Hand Specimens
 Breccias: angular particles
 Conglomerates: rounded particles
 Sandstones
 Quartz sand...
Sedimentary Rocks
 Detrital/Siliciclastic Sedimentary Rocks




conglomerates & breccias
sandstones
mudstones

 Carbo...
Detrital Sediments & Sedimentary
Rocks
gravel
&
conglomerate

sand
&
sandstone

clay, silt
&
mudstone
Types of sedimentary rocks
Chemical rocks – sediment

from ions that were once in
solution

Detrital rocks –sediment

tr...
Detrital sedimentary rocks

 Constituents of detrital rocks can
include
Clay minerals
Quartz
Feldspars
Micas

 Parti...
Detrital sedimentary rocks

Mudrocks: grains less than .06 mm
 1. Mud: small particles easily kept in
suspension
 Settl...
Mudrock (Shale) containing plant fossils
lamellae

Fossil Leaves Wilkes Barre, PA
Detrital sedimentary rocks

Sandstones
 Made of sand-sized particles .064 – 2
mm … Sand is a size!
 Forms in a variety ...
Sandstone (note large number of quartz grains)
Classifying Sandstones

Photomicrograph of quartz rich sandstone (Arenite)
Grains subangular to subrounded, sandstone is p...
Types of Sandstone
 Quartz Arenite >90% quartz grains
 Beach and dune deposits

 Arkoses >25% feldspar, angular, poor
s...
Detrital sedimentary rocks
Conglomerate and breccia
 Both composed of particles > 2mm in
diameter
 Conglomerate consist...
Conglomerate
Breccia (shattered rock accumulates at the base of a cliff)

Note sharp angular clasts
Energy
 Coarse sediments are deposited in high
energy (fast water) environments such as
under breaking waves at the beach...
Outcrop of conglomerate
with cobble-sized clasts
interbedded with sandstone

Conglomerates are fastwater sediments
“High E...
Chemical sedimentary rocks
 Precipitated material once in solution
 Precipitation of material occurs two
ways:
Inorgani...
 Common chemical sedimentary rocks
Limestone
 Most abundant chemical rock
 Made of the mineral calcite CaCO3
 Marine ...
Coquina
Fossiliferous limestone
Note shells and lime matrix
Chalk Outcrops in SE USA

Chalk
Hand Specimen
Inorganic Chemical Sediments
Ooids under microscope

Oolitic Limestone - Bahama Shoals
Oolitic Limestone - Hand Specimen
 Other chemical sedimentary rocks
 Chert
 Made of microcrystalline quartz
 Usually deposited as siliceous ooze in deep...
 Other chemical sedimentary rocks
 Dolostone (made of mineral Dolomite)
 Like Calcite, but some Ca is replaced by Mg

T...
Evaporation

How to make Dolomite
6_19

Limestone

Seawater enriched
in Mg2+

Mg2+ -rich seawater circulates
Dolostone
thr...
http://www.ndsu.nodak.edu/instruct/ashworth/coursework/g410/evaporites/saltbeds.jpg

 Common chemical sedimentary
rocks

...
Chemical sedimentary rocks
 Common chemical sedimentary rocks
 Coal
 Different from other rocks because
it is composed ...
Stages in coal formation
Sedimentary Environment

 Is the geographic setting where
sediment accumulates

 Determines nature of sediment that
accu...
Character of detrital sediments depends on time, distance,
and energy. For 6_5
example, in streams:

Particles are large a...
Clastic wedges
Sediment Maturity

Sediment Maturity is
indicated by decreasing
clay content, increasing
degree of size sorting,
and incre...
We can recognize past floods

Floods change the local
conditions
6_6

Fine-grained sediment
on floodplain
Older sediment

...
 Types of sedimentary environments
 Continental
 Streams

 cross beds from ripples, fine mud w/ cracks
on floodplain
...
 Types of sedimentary environments
Transitional (shoreline)
 Tidal flat Sands w/ symmetrical ripples

Lenses of tidal ...
A picture glossary of sedimentary

Turbidite: underwater landslide
= graded bedding
environments
 Sedimentary Facies
Different sediments accumulate
next to each other at same time
Each unit (called a facies) possesse...
Some facies in an oversimplified drawing

Abyssal Ooze

Stillwater muds

Nearshore sands
Sedimentary structures

 Tell us something about past

environments
 Types of sedimentary structures
Strata, or beds (m...
Strata- Bedding Planes
Fine Scale Bedding- Lamellae
Recognizable Sedimentary Structures
 Types of sedimentary structures 1

Graded beds: waning flow (flood, turbidite)
 Se...
Graded Beds – grains fine upward
Note: Beds were tilted from horizontal after deposition
Recognizable Sedimentary Structures

 Ripples

Irregularities in bottom sediment lead to
ripples
Asymmetric types indic...
Cross Beds – ripples in cross section

 In cross section these look like lines
at an angle to the horizontal – “cross
bed...
Slabs of eroding sandstone with ripple marks
Cross bedding in Sand Dune deposits
Navaho Sandstone

Sand Dune? Look for Frosted Grains

Shoreline of
an interior
seaway
...
Recognizable Sedimentary Structures

 Types of sedimentary structures 3
 Non-marine

Mud Cracks – floodplains, playas
...
Mud Cracks: clay layer shrinks during drying, curls
upward; cracks fill next flood
Mudcracks indicate drying events.
Geologists can determine if rocks overturned.
Sedimentary Environments
 Sediments are formed in many different
environments

 Each have characteristic appearance
toda...
Fresh Water Facies
Streams (includes big Rivers), with
floodplains and levees, called fluviatile. The
Point Bar Sequence i...
Point-bar Sequence:

Deposits Associated with
Meandering Streams
Meandering
Stream

OxBow

Floodplain

http://hays.outcrop...
Point Bar Sequence
Fines of Floodplain
Crossbeds of Bar

Gravel of bed

Erosion
Terms for Marine (i.e. Ocean) Environments
6_27
and some characteristic sediment facies

Continental
shelf

Shallo
w
marin...
Facies changes due to rising sea level - water getting deeper everywhere
River

6_29
Direction

of migration
of shoreline,...
Fossils: Evidence of past life
 By definition, fossils are the traces or
remains of prehistoric life now preserved in
roc...
Fossils: Evidence of past life
 Geologically fossils are important for
several reasons
 Aid in interpretation of the geo...
3 Billion Year Old Algal Mounds (Stromatolites) Australia

CO2 in
O2 out
Natural casts of
shelled invertebrates in limestone
Dinosaur footprint in mudstone
Dilophosaurus Jurassic Park Dennis Neary and Peter Dodson
Petrologi 9-klastika
Petrologi 9-klastika
Petrologi 9-klastika
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Petrologi 9-klastika

  1. 1. Semester 2, 2008-2009 petrologi 2 SKS teori 1 SKS praktikum by: hill. gendoet hartono Senin, jam 09.50 – 10.40 jam 10.45 – 11.35
  2. 2. Clastic Rocks - Hand Specimens  Breccias: angular particles  Conglomerates: rounded particles  Sandstones  Quartz sandstone: dominated by quartz grains  Arkose sandstone: composed of qtz & fsp grains  Graywacke: dominated by lithic (rock) fragments  Shales: mud and silt particles
  3. 3. Sedimentary Rocks  Detrital/Siliciclastic Sedimentary Rocks    conglomerates & breccias sandstones mudstones  Carbonate Sedimentary Rocks  limestones  dolostones  Other Sedimentary Rocks      evaporites phosphates organic-rich sedimentary rocks cherts volcaniclastic rocks
  4. 4. Detrital Sediments & Sedimentary Rocks gravel & conglomerate sand & sandstone clay, silt & mudstone
  5. 5. Types of sedimentary rocks Chemical rocks – sediment from ions that were once in solution Detrital rocks –sediment transported as solid particles
  6. 6. Detrital sedimentary rocks  Constituents of detrital rocks can include Clay minerals Quartz Feldspars Micas  Particle size is used to distinguish among the various types of detrital rocks
  7. 7. Detrital sedimentary rocks Mudrocks: grains less than .06 mm  1. Mud: small particles easily kept in suspension  Settles only in quiet water  Rock types include Shale: mud-sized particles <.004 mm deposited in thin bedding layers called laminae The most common sedimentary rock 2. Larger mudrock grains called silts silt-sized particles .004-.06 mm Gritty grains can be felt
  8. 8. Mudrock (Shale) containing plant fossils lamellae Fossil Leaves Wilkes Barre, PA
  9. 9. Detrital sedimentary rocks Sandstones  Made of sand-sized particles .064 – 2 mm … Sand is a size!  Forms in a variety of environments  Sorting, angularity and composition of grains can be used to interpret the rock’s history  Quartz is the predominant mineral (due to its durable nature)
  10. 10. Sandstone (note large number of quartz grains)
  11. 11. Classifying Sandstones Photomicrograph of quartz rich sandstone (Arenite) Grains subangular to subrounded, sandstone is poorly sorted Plagioclase grain Making thin sections
  12. 12. Types of Sandstone  Quartz Arenite >90% quartz grains  Beach and dune deposits  Arkoses >25% feldspar, angular, poor sort.  Transform boundaries; exposed granites  Any felsic rock eroded, not transported far  Graywackes Quartz, feldspar, volcanics    Port sorted, angular Erosion of Island Arcs Rift Valley Sediments
  13. 13. Detrital sedimentary rocks Conglomerate and breccia  Both composed of particles > 2mm in diameter  Conglomerate consists largely of rounded clasts  Breccia is composed of large angular particles
  14. 14. Conglomerate
  15. 15. Breccia (shattered rock accumulates at the base of a cliff) Note sharp angular clasts
  16. 16. Energy  Coarse sediments are deposited in high energy (fast water) environments such as under breaking waves at the beach, or in the beds of fast streams.  Fine sediments are deposited in low energy environments, e.g. the slow water of deep lagoons, the abyssal plain, etc.
  17. 17. Outcrop of conglomerate with cobble-sized clasts interbedded with sandstone Conglomerates are fastwater sediments “High Energy” K.E. = 1/2mv2 In fast water, smaller sizes swept away
  18. 18. Chemical sedimentary rocks  Precipitated material once in solution  Precipitation of material occurs two ways: Inorganic processes: the minerals precipitate out of water Organic processes: animals and plants precipitate the minerals to use as shells or skeletons A foraminiferan, a type of microfossil http://www.ucmp.berkeley.edu/collections/micro.html
  19. 19.  Common chemical sedimentary rocks Limestone  Most abundant chemical rock  Made of the mineral calcite CaCO3  Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms)  Inorganic limestones include travertine (caves) and oolitic limestone (Bahamas)
  20. 20. Coquina
  21. 21. Fossiliferous limestone Note shells and lime matrix
  22. 22. Chalk Outcrops in SE USA Chalk Hand Specimen
  23. 23. Inorganic Chemical Sediments Ooids under microscope Oolitic Limestone - Bahama Shoals Oolitic Limestone - Hand Specimen
  24. 24.  Other chemical sedimentary rocks  Chert  Made of microcrystalline quartz  Usually deposited as siliceous ooze in deep oceans (can be diatomaceous) chert Diatomaceous chert
  25. 25.  Other chemical sedimentary rocks  Dolostone (made of mineral Dolomite)  Like Calcite, but some Ca is replaced by Mg The Dolomites, sediments thrust up when the Alps formed
  26. 26. Evaporation How to make Dolomite 6_19 Limestone Seawater enriched in Mg2+ Mg2+ -rich seawater circulates Dolostone through porous limestone Mg2+ replaces some of the Ca2+ in limestone
  27. 27. http://www.ndsu.nodak.edu/instruct/ashworth/coursework/g410/evaporites/saltbeds.jpg  Common chemical sedimentary rocks Evaporites Evaporation triggers deposition of chemical precipitates Examples include rock salt and gypsum
  28. 28. Chemical sedimentary rocks  Common chemical sedimentary rocks  Coal  Different from other rocks because it is composed of organic material  Stages in coal formation (in order) 1. Plant material 2. Peat 3. Lignite 4. Bituminous
  29. 29. Stages in coal formation
  30. 30. Sedimentary Environment  Is the geographic setting where sediment accumulates  Determines nature of sediment that accumulates (grain size, shape, etc.)
  31. 31. Character of detrital sediments depends on time, distance, and energy. For 6_5 example, in streams: Particles are large and irregular, and consist of a variety of lithologies, including the least resistant. Particles are mid-sized and of intermediate sphericity, and include resistant and nonresistant lithologies. HIGHLANDS LOWLANDS Particles are small and nearly spherical, and consist mainly of the most resistant lithologies, such as quartz. NEAR-COASTAL
  32. 32. Clastic wedges
  33. 33. Sediment Maturity Sediment Maturity is indicated by decreasing clay content, increasing degree of size sorting, and increasing rounding of grains within the deposit Poorly sorted Well sorted Sorting refers to the range of particle sizes in the sediment Well-sorted - uniform grain size Poorly-sorted - mixture of grain sizes immature OCNG 251 mature Texas A&M University Oceanography
  34. 34. We can recognize past floods Floods change the local conditions 6_6 Fine-grained sediment on floodplain Older sediment 1 Pre-flood Bounders on bottom, sands and muds suspended Flood water Erosion of uppermost fine-grained sediment 2 Flood stage Flood: One source of Graded Bedding 3 Post-flood Fining-upward flood deposit Bedding plane is an erosional surface
  35. 35.  Types of sedimentary environments  Continental  Streams  cross beds from ripples, fine mud w/ cracks on floodplain  Lakes – Fine parallel lamellae - Varves  Wind (dunes) well sorted, frosted grains  Glacial Ice: Poorly sorted, unstratified  Marine  Shallow (< 200 meters deep) carbonate-rich sands, muds  Deep (seaward of continental shelves) microfossils, volcanic ash, turbidites
  36. 36.  Types of sedimentary environments Transitional (shoreline)  Tidal flat Sands w/ symmetrical ripples Lenses of tidal creek muds  Lagoons – including Bays behind Barrier Islands. Organic rich black muds and sands  Deltas Complex, e.g. Sandstones w/ large foresets at seaward face
  37. 37. A picture glossary of sedimentary Turbidite: underwater landslide = graded bedding environments
  38. 38.  Sedimentary Facies Different sediments accumulate next to each other at same time Each unit (called a facies) possesses a distinctive characteristics reflecting the conditions in a particular environment The merging of adjacent facies tends to be a gradual transition
  39. 39. Some facies in an oversimplified drawing Abyssal Ooze Stillwater muds Nearshore sands
  40. 40. Sedimentary structures  Tell us something about past environments  Types of sedimentary structures Strata, or beds (most characteristic of sedimentary rocks) -bedding planes that separate strata caused by variation in deposition
  41. 41. Strata- Bedding Planes
  42. 42. Fine Scale Bedding- Lamellae
  43. 43. Recognizable Sedimentary Structures  Types of sedimentary structures 1 Graded beds: waning flow (flood, turbidite)  Sediments become coarser upward Determines “Right side up”
  44. 44. Graded Beds – grains fine upward Note: Beds were tilted from horizontal after deposition
  45. 45. Recognizable Sedimentary Structures  Ripples Irregularities in bottom sediment lead to ripples Asymmetric types indicate flow direction. Symmetric types formed in tidal areas
  46. 46. Cross Beds – ripples in cross section  In cross section these look like lines at an angle to the horizontal – “cross beds”  Form determined by velocity and size of particles.
  47. 47. Slabs of eroding sandstone with ripple marks
  48. 48. Cross bedding in Sand Dune deposits Navaho Sandstone Sand Dune? Look for Frosted Grains Shoreline of an interior seaway Sandstone deposited in ancient sand dunes Frosted Grains
  49. 49. Recognizable Sedimentary Structures  Types of sedimentary structures 3  Non-marine Mud Cracks – floodplains, playas Also good for right side up
  50. 50. Mud Cracks: clay layer shrinks during drying, curls upward; cracks fill next flood
  51. 51. Mudcracks indicate drying events. Geologists can determine if rocks overturned.
  52. 52. Sedimentary Environments  Sediments are formed in many different environments  Each have characteristic appearance today, features that allow them to be recognized in the geologic record
  53. 53. Fresh Water Facies Streams (includes big Rivers), with floodplains and levees, called fluviatile. The Point Bar Sequence is typical for meandering streams. Cutoffs generate Oxbow deposits. • High gradient streams with high sediment load are Braided. • Lake deposits called lacustrine, generally still waters, often varved deposits if winters cold http://hays.outcrop.org/gallery/rivers/arid_meander?full=1
  54. 54. Point-bar Sequence: Deposits Associated with Meandering Streams Meandering Stream OxBow Floodplain http://hays.outcrop.org/gallery/rivers/arid_meander?full=1
  55. 55. Point Bar Sequence Fines of Floodplain Crossbeds of Bar Gravel of bed Erosion
  56. 56. Terms for Marine (i.e. Ocean) Environments 6_27 and some characteristic sediment facies Continental shelf Shallo w marin e Continental slope Abyssal Plain Dee p ma rine Submarine volcanoes
  57. 57. Facies changes due to rising sea level - water getting deeper everywhere River 6_29 Direction of migration of shoreline, and landward shift of sedimentary facies Time B Shoreline at time B Time A Shoreline at time A Shallow marine Beach River Sea level rising Deep marine Shallow marine Beach Comparison of sediments deposited Deep marine Shallow marine Deposited at time A Deposited at time B REMEMBER: the facies follow the shoreline
  58. 58. Fossils: Evidence of past life  By definition, fossils are the traces or remains of prehistoric life now preserved in rock  Fossils are generally found in sediment or sedimentary rock (very rarely in metamorphic or igneous rocks)
  59. 59. Fossils: Evidence of past life  Geologically fossils are important for several reasons  Aid in interpretation of the geologic past  Serve as important time and environment indicators  Allow for correlation of rocks from different places
  60. 60. 3 Billion Year Old Algal Mounds (Stromatolites) Australia CO2 in O2 out
  61. 61. Natural casts of shelled invertebrates in limestone
  62. 62. Dinosaur footprint in mudstone Dilophosaurus Jurassic Park Dennis Neary and Peter Dodson

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