petropetrolologigi2 SKS teori2 SKS teori1 SKS praktikum1 SKS praktikum

by:by:hill. gendoet hartonohill. gendoet hartono

Semester 2, 2007-2008Semester 2, 2007-2008

Senin, jam 09.50 – 10.40Senin, jam 09.50 – 10.40 jam 10.45 – 11.35jam 10.45 – 11.35

Sedimentary Sedimentary RocksRocksBatuan SedimenBatuan Sedimen

Sediments and Sedimentary RocksSediments and Sedimentary Rocks

Rock Cycle

What is a sedimentary rock?What is a sedimentary rock?• Sedimentary rocks result from mechanical

and chemical weathering• Comprise ~ 5% of Earth’s upper crust• About 75% of exposed rocks• Contain evidence of past environments

• Record how sediment is transported• Often contain fossils

Fossil Fish - 50 Million Year Old Lakes in southern WyomingFossil Fish - 50 Million Year Old Lakes in southern Wyoming

Sedimentary Rock made of fine-grained mudstone.Sedimentary Rock made of fine-grained mudstone.

These fish tell us the Wyoming climate50 million years ago.

OverviewOverview►sediment productionsediment production►types of sediment and sedimentary types of sediment and sedimentary

rocksrocks►sediment transport and depositionsediment transport and deposition►depositional systemsdepositional systems►stratigraphic architecture and basinsstratigraphic architecture and basins►chrono-, bio-, chemo-, and sequence chrono-, bio-, chemo-, and sequence

stratigraphystratigraphy►Earth historyEarth history

Sedimentary rocks are Sedimentary rocks are the product of the the product of the creation, transport, creation, transport,

deposition, and deposition, and diagenesis of detritus diagenesis of detritus and solutes derived and solutes derived

from pre-existing rocks.from pre-existing rocks.

creation

solutes

Steps Involved in Steps Involved in Formation of Clastic Formation of Clastic Sedimentary RockSedimentary Rock

Weathering

Erosion

Transport

Deposition

Lithification --Compaction --Cementation

WeatheringWeathering

Steep terrain accelerates Steep terrain accelerates erosionerosion

Turbidity Turbidity CurrentsCurrents

6_116_11

Ions weather out of rock,are transported bygroundwater to sediment layers below

Ion-richground-water

Ions transportedto lake or ocean

Dissolved ions precipitateto form cement betweensediment grains

Water enters pore spaces between sediment grains

Diagenesis includes:Diagenesis includes:

RecrystallizationRecrystallization – growth of stable – growth of stable minerals from less stable onesminerals from less stable ones

LithificationLithification – loose sediment is – loose sediment is transformed into solid rock by transformed into solid rock by compaction and cementationcompaction and cementation

Natural cements: calcite, silica, and Natural cements: calcite, silica, and iron oxide. Formed from ions in iron oxide. Formed from ions in solution in water. solution in water.

►DiagenesisDiagenesis – chemical and physical changes – chemical and physical changes that take place after sediments are depositedthat take place after sediments are deposited

►Diagenesis varies with composition Diagenesis varies with composition

LithificationLithification

►Compaction: As more sediments are piled Compaction: As more sediments are piled on top, compaction drives out the excess on top, compaction drives out the excess water.water.

►Cementation: Precipitation of chemicals Cementation: Precipitation of chemicals dissolved in water binds grains of a dissolved in water binds grains of a sediment together.sediment together.

►Remember where the dissolved chemicals Remember where the dissolved chemicals come from?come from?

Compaction and Compaction and CementationCementation

of Clastic Sediment into of Clastic Sediment into RockRockOverburden

Sediment

Compaction Cementation

Lithification and compaction of Lithification and compaction of shaleshale

NB volume loss during compaction

► Source areaSource area - the locality from which the - the locality from which the sediment was derived: factors used to evaluate sediment was derived: factors used to evaluate source area include source area include rock typerock type, , environment of environment of depositiondeposition, , directiondirection ( (paleocurrentspaleocurrents) and ) and distancedistance from source areafrom source area

► Depositional environmentDepositional environment – where sediment – where sediment is deposited. It is deposited. It can be determined by looking can be determined by looking at at sedimentary structuressedimentary structures (including fossils), (including fossils), the the bed shapebed shape and and vertical sequencesvertical sequences within within the sedimentary layers, and the sedimentary layers, and grain compositiongrain composition

Sedimentary environments & plate tectonic Sedimentary environments & plate tectonic settingssettingsConvergent boundariesConvergent boundaries – coarse-grained clastic – coarse-grained clastic

sediments with abundant volcaniclastic and felsic sediments with abundant volcaniclastic and felsic materialmaterial

Sedimentary environments & plate tectonic Sedimentary environments & plate tectonic settingssettings

Divergent boundariesDivergent boundaries - - thick wedges of gravel thick wedges of gravel and coarse sand along margins,with lake bed and coarse sand along margins,with lake bed deposits and associated evaporite rocks deposits and associated evaporite rocks possible in bottoms of rift valleyspossible in bottoms of rift valleys

What is the economic What is the economic importance of sedimentary importance of sedimentary

rocks?rocks?► They are important for economic reasons They are important for economic reasons

because they containbecause they contain►CoalCoal►Petroleum and natural gasPetroleum and natural gas►Iron, aluminum, uranium and manganeseIron, aluminum, uranium and manganese►Geologists use them to read Earth’s historyGeologists use them to read Earth’s history

Remember this when we talk about correlation. Note how beds pinch out or are offset by faults

SEDIMENTARY ROCKSSEDIMENTARY ROCKS

►WEATHERING PROCESSES BREAK WEATHERING PROCESSES BREAK ROCK INTO PIECES, ROCK INTO PIECES, SEDIMENTSEDIMENT, READY , READY FOR TRANSPORTATION DEPOSITION FOR TRANSPORTATION DEPOSITION BURIAL LITHIFICATION INTO NEW BURIAL LITHIFICATION INTO NEW ROCKS. ROCKS.

CLASSIFYING SEDIMENTARY CLASSIFYING SEDIMENTARY ROCKSROCKS

► THREE SOURCESTHREE SOURCES► Detrital (or clastic) sedimentDetrital (or clastic) sediment is composed of is composed of

transported solid fragments (or transported solid fragments (or detritus)detritus) of pre- of pre-existing igneous, sedimentary or metamorphic existing igneous, sedimentary or metamorphic rocksrocks

► Chemical sedimentChemical sediment forms from previously forms from previously dissolved minerals that either precipitated from dissolved minerals that either precipitated from solution in water , or were extracted from water by solution in water , or were extracted from water by living organismsliving organisms

► OrganicOrganic sedimentarysedimentary rock consisting mainly of rock consisting mainly of plant remains plant remains

CLASTIC SEDIMENTARY CLASTIC SEDIMENTARY ROCKSROCKS

CLASSIFIED ON GRAIN OR PARTICLE SIZECLASSIFIED ON GRAIN OR PARTICLE SIZE

►ShalesShales: finest-grained: finest-grained►SandstonesSandstones: medium-grained: medium-grained►ConglomeratesConglomerates – Breccias: coarse- – Breccias: coarse-

grainedgrained

SHALESSHALES

►SHALES: SHALES: finest-grained – composed of finest-grained – composed of very small particles (from <0.004-0.063 very small particles (from <0.004-0.063 mm)mm) 50% of all sedimentary rocks are Shales50% of all sedimentary rocks are Shales Consist largely of Clay minerals Consist largely of Clay minerals Subcategories: Claystones; Siltstones; Subcategories: Claystones; Siltstones;

MudstonesMudstones Economic value: building material; china Economic value: building material; china

and ceramics; spark plug housingsand ceramics; spark plug housings

SANDSTONESSANDSTONES► SANDSTONES: SANDSTONES: medium-grained; particle-medium-grained; particle-

size (0.063-2 mm)size (0.063-2 mm)► 25% of all sedimentary rocks fall into this 25% of all sedimentary rocks fall into this

category category ► Three major kinds of Sandstone, based on Three major kinds of Sandstone, based on

mineral composition and appearance:mineral composition and appearance: Quartz AreniteQuartz Arenite: >90% quartz grains : >90% quartz grains ArkosesArkoses : more Feldspar minerals : more Feldspar minerals GraywackesGraywackes :quartz and feldspar grains, and :quartz and feldspar grains, and

volcanicsvolcanics► Economic value: glass; natural reservoirs Economic value: glass; natural reservoirs

for oil, gas, and groundwaterfor oil, gas, and groundwater

CONGLOMERATES - CONGLOMERATES - BRECCIASBRECCIAS

►CONGLOMERATESCONGLOMERATES AND BRECCIASAND BRECCIAS::►The coarsest of all the detrital The coarsest of all the detrital

sedimentary rocks sedimentary rocks ►Composed of particles >2 mm in Composed of particles >2 mm in

diameter diameter Conglomerate - the particles are rounded Conglomerate - the particles are rounded Breccia - the particles are angularBreccia - the particles are angular

CHEMICAL SEDIMENTARY CHEMICAL SEDIMENTARY ROCKSROCKS

►TWO CATEGORIES:TWO CATEGORIES:

INORGANIC CHEMICAL SEDIMENTARYINORGANIC CHEMICAL SEDIMENTARY

ORGANIC CHEMICAL SEDIMENTARYORGANIC CHEMICAL SEDIMENTARY

INORGANIC CHEMICAL INORGANIC CHEMICAL SEDIMENTARY ROCKSSEDIMENTARY ROCKS

►Formed when dissolved products of Formed when dissolved products of chemical weathering precipitate from chemical weathering precipitate from solution solution

►Most common types:Most common types: Inorganic limestones and chertsInorganic limestones and cherts: :

precipitates directly from seawater and precipitates directly from seawater and fresh waterfresh water

EvaporitesEvaporites:: precipitates when ion-rich precipitates when ion-rich water evaporates water evaporates

DolostonesDolostones:: Origin is still in debate Origin is still in debate

INORGANIC - LIMESTONESINORGANIC - LIMESTONES

►LimestonesLimestones - - account for 10% - 15% of account for 10% - 15% of all sedimentary rocks formed from Calcite or all sedimentary rocks formed from Calcite or Calcium Carbonate (CaCOCalcium Carbonate (CaCO33).).

► Formed as pure carbonate muds accumulate on the sea floorFormed as pure carbonate muds accumulate on the sea floor

► Also formed on land:Also formed on land: TufaTufa - a soft spongy inorganic limestone that forms where - a soft spongy inorganic limestone that forms where

underground water surfacesunderground water surfaces TravertineTravertine - - forms in caves when droplets of carbonate-rich forms in caves when droplets of carbonate-rich

water on the ceiling, walls and floors precipitate a carbonate rockwater on the ceiling, walls and floors precipitate a carbonate rock

ORGANIC LIMESTONESORGANIC LIMESTONES► Formed with calcite from marine environment: CaCOFormed with calcite from marine environment: CaCO33 shells shells

and internal/external skeletons of marine animals and internal/external skeletons of marine animals

► CoquinaCoquina - “crushed” shell fragments cemented with CaCO - “crushed” shell fragments cemented with CaCO33 ► ChalkChalk - made from billions of microscopic carbonate- - made from billions of microscopic carbonate-

secreting secreting organisms organisms ► Coral ReefsCoral Reefs - Formed from the skeletons of millions of tiny - Formed from the skeletons of millions of tiny

invertebrate animals who secrete a invertebrate animals who secrete a calcite-rich calcite-rich material. Live “condo” style material. Live “condo” style while algae acts while algae acts as the cement to create as the cement to create the large structures the large structures called “reefs”.called “reefs”.

► Organic ChertOrganic Chert - formed when silica-secreting microscopic - formed when silica-secreting microscopic marinemarine

► organisms die (organisms die (radiolariaradiolaria {single-celled {single-celled animals} and animals} and diatomsdiatoms {skeletons of singled-celled {skeletons of singled-celled plants})plants})

► Flint - Flint - an example of an Organican example of an Organic Chert Chert

ORGANIC SEDIMENTARY ORGANIC SEDIMENTARY ROCKSROCKS

► Coal Coal -- Organic sedimentary rock consisting mainly of Organic sedimentary rock consisting mainly of plant remains plant remains

► Formation: Formation: Burial of decaying vegetationBurial of decaying vegetation;; Increasing pressure from the overlying layers expels water, Increasing pressure from the overlying layers expels water,

CO2 and other gases;CO2 and other gases; Carbon accumulates.Carbon accumulates.

► Peat Peat -- formed early in the process, when the original plant formed early in the process, when the original plant structurestructure

can still be distinguished. can still be distinguished. ► LigniteLignite - - a more hardened form of Peat a more hardened form of Peat► BituminousBituminous - - more pressure and more heat produce this moderately more pressure and more heat produce this moderately

hard coal. hard coal. ► AnthraciteAnthracite - - the hardest coal - formed from metamorphic processes the hardest coal - formed from metamorphic processes

under extreme heat and pressure - Hard - Shiny - the under extreme heat and pressure - Hard - Shiny - the mostmost

desired as an energy resource.desired as an energy resource.

SEDIMENTARY SEDIMENTARY ENVIRONMENTSENVIRONMENTS

► LakesLakes► LagoonsLagoons► RiversRivers► Ocean bottomsOcean bottoms► EstuariesEstuaries► Salt FlatsSalt Flats► PlayasPlayas► Glacial Glacial

environmentsenvironments

SEDIMENTARY PROCESSESSEDIMENTARY PROCESSES

►LITHIFICATIONLITHIFICATION::► As sediment is As sediment is buriedburied several kilometers beneath the surface, several kilometers beneath the surface,

heatedheated from below, from below, pressurepressure from overlying layers and from overlying layers and chemically-active waterchemically-active water converts the loose sediment into solid converts the loose sediment into solid sedimentary rock sedimentary rock

► CompactionCompaction - volume of a sediment is reduced by - volume of a sediment is reduced by application of pressure application of pressure

► CementationCementation - - sediment grains are bound to each sediment grains are bound to each other by materials originally dissolved during other by materials originally dissolved during chemical weathering of preexisting rocks chemical weathering of preexisting rocks typical chemicals include silica and calcium carbonatetypical chemicals include silica and calcium carbonate..