8 - batuan sedimen.pdf

8/10/2019 8 - Batuan Sedimen.pdf

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Pertemuan ke 7

Material Penyusun Bumi

BATUAN SEDIMEN


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Menurut Selley (1988), Sedimentologi

sebagaimana didefinisikan oleh Wadell (1932)

adalah : Study of Sediments, sedangkan

sedimentsitu sendiri menurut Chambers

Dictionary (1972) adalah what sett les at the

bot tom of l iqu id : deposi t .

Pendahuluan


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BATUAN SEDIMEN

Dibentuk dari batuan yang telah ada oleh (gaya

dlm geologi) pelapukan gaya air,

pengikisan angin batuan hancur diangkut

diendapkan di tempat yang rendah (sungai,

danau, rawa, laut)

Batuan lunak

diagenesis (kompaksi,sementasi oleh larutan karbonat, silisium)

keras


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BATUAN SEDIMEN

Beberapa (larutan)mengendap secara langsung

oleh reaksi kimia garam (NaCl); gipsum

(CaSO4nH2O);

(larutan) Diendapkan dengan pertolongan jasad

baik tumbuhan maupun hewan

Ciri utama batuan sedimen adalah berlapis dan

pada awalnya diendapkan secara mendatar


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Sejak Stones Age (Zaman batu : Paleo -Meso - Neolitikum):

Tidak langsung pemahaman sedimentologi. Eksplorasi/pencarian batu sebagai bahan

mentah/ raw material untuk alat, terutamabahan dari batuan sedimen : Flint, SilicifiedLimestone, Chert, Silicified wood/tuff.

Penggunaan batuan sedimen : batupasir,batugamping batulempung sebagai bahanbamgunan : Pyramid, bangunan-bangunan diMesopotamia, Bagdad, Romawi dll.

1.Rangkuman Perkembangan Sedimentologi

Pendahuluan


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Dewasa ini keterpaduan makro denganmikrosedimentologi menghasilkan

pemahaman menyeluruh tentang evolusi

suatu cekungan dalam konteks

Geodinamika :

Sequence stratigraphy

Provenance

Geohistory


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2. Geologi dan Ilmuilmu Dasar Lainnya

GEOLOGI

KIMIA FISIKA

BIOLOGI

KIMIA FISIKA

PALEONTOLOGI


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3. Sedimentologi Sebagai Ilmu Dasar dan

Hubungannya dengan Ilmu-ilmu Dasar

Lainnya

Pendahuluan

Sedimentologi

Kimia

Fisika

Biologi

(Modifikasi dari Selley, 1988)

Pelapukan,

DiagenesaSedimen

Autochtone

PaleoekologiPaleoenvironment

Transportasi,Pengendapan

Bio Kimia


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Eluvium; batuan yang terbentuk akibat

penghancuran dan tidak larut, diendapkan tidak

jauh dari sumbernya

Alluvium; batuan sedimen yang diendapkan

setelah mengalami transportasi

Sifat utama batuan sedimen adalah berlapis-

lapis dan pada awalnya diendapkan secara

mendatar.

Ketebalan lapisan berbeda-beda ?cm s/d?meter; di dekat muara sungai umumnya tebal

makin ke arah laut menipis dan ahirnya

hilang membaji


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Dekat pantai umumnya berbutir kasar ke arah

laut makin halus.Batupasir batulempung

batugamping

Terjadinya lapisan; karena perbedaan ukuran

butir, perbedaan warna (komposisi); perbedaan

kekerasan

Dibandingkan batuan beku, batuan sedimen

merupakan tutupan kecil (5%) dari dari kerak

bumi


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Bongkah 200 mm 2000 mm

Kerikil kasar 20 mm 200 mm

Kerikil halus 2 mm 20 mm

Pasir kasar 0,2 mm 2 mm

Pasir halus 0.02 mm 0,2 mm

Geluh/lanau 0,002 mm 0.02 mm

Lempung Kurang dari 0,002 mm


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Pemahaman Tentang Cekungan Sedimen

(Sedimentary Basin)

Cekungan (Basin):

Pemahaman Umum (General Perception) Geomorphological Term

Genetic View

Mekanisme Pembentukan Cekungan


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1. Cekungan (Basin)

Berdasarkan aspek geomorfolagi,

cekungan (basin) didefinisikan sebagai :

suatu w ilayah dengan suatu ben tukben tang alam (rel ief) r endah atau negatif

(= cekung >< pos it i f = cembung) d ik eli l in gi

o leh suatu ben tuk (rel ief) t inggian.

Cekungan Sedimen


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2. Cekungan Sedimen (Sedimentary Basin)

Persepsi Umum (General Perception)

mendefinisikan : suatu tempat berben tuk

cekungan d imana sed imen d iendapkan.

Genetic definition : Menurut Allen danAllen(1990) Sedimentary basins are

regions of pro longed subsidence of

earths su rface.

Cekungan Sedimen


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Mekanisme penyebab subsidence

(penurunan) berkaitan dengan proses yang

terjadi pada lithsfera dimana lithosfera ini

terdiri atas beberapa lempeng, maka

cekungan sedimen sangat berkaitan erat

dengan pergerakan lempeng lempeng


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3. Klasifikasi Cekungan Sedimen :

Menurut Allen dan Allen (1990) cekungan

cekungan sedimen (sedimentary basins)

telah diklasifikasikan berkaitan dengan jenis

substratum lithosfera (seperti : kontinental,

oceanic, atau transisi), kedudukannya pada

batas batas lempeng (plate boundary)

seperti intra cratonic, plate margin.

Cekungan Sedimen


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Mekanisme Sedimentasi

Proses dan Siklus SedimentasiPelapukan

Erosi

Transportasi

PengendapanSifat sifat Fluida, Aliran dan Sedimen

Sifat Fluida :

- Densitas

- Viskositas

Jenis Aliran (f lows) : Arus (current)

- Laminar : t ract ion current

- Turbulen : low & high densi ty turb id i ty cur rent


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Bed Roughness

Pergerakan Partikel:

- rolling

- bounching

- suspension



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Siklus dan Proses Sedimentasi

Sedimentary Rocks : product of provenance and process

Siklus dan Proses Sedimentasi (Modifikasi dari Selley, 1988)

Siklus

Proses

Metamorphic Rocks

IgneousRocks

Weathering

Erosion Transportation

Uplift

Deposition

P >>T>>

SolidState

P >>T>>

Melting

Diagenesis &

LithificationSedimentary

Rocks

:


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Weathering / Pelapukan

Biological Weathering

Physical Weathering

Chemical Weathering

Product Of Weathering : - Solute

- Residual

The Solutes : Soluble fraction of rock which arecarried in water.

The Residual : Insoluble products of weathering

(boulders to colloidal clay particles.


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Biological Weathering : organisme : fraksi

halus

Tumbuh tumbuhan

Mikroorganisme

=> Soil yang terbentuk tebal dan kaya akan

materi organik.



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Physical Weathering : Fraksi Kasar

a. Freeze weathering: perkolasi air melaluirekahan, butiran dan kristal batuan : polarclimate.

b. Insolation weathering: typical of hot arid climate: sahara. Kontras perubahan temperatur hariandingin mencapai 25o C (malam dan siang) yang

menyebabkan batuan pecah pecah.



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Physical Weathering : Fraksi Kasar

C. Hydration and Dehydration weathering :prosesperubahan kejenuhan dan kekurangan airmemperngaruhi terutama pada butiran lempungyang mengalami pengkerutan (shrinkage)

membentuk rekahan (cracks). Daerah Tropis /Tropical Climate

d. Stress release weathering : Terjadi pada batuanbersifat brittle yang mengalami penimbunan

sehingga batuan di bawahnya mengalamitekanan (Overburdan Pressure). Pada saatoverburdan tererosi, maka akan terjadipengurangan tekanan dan timbul release yangmenyebabkan terjadinya frakturasi.



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Chemical Weathering : Fraksi Halus

Pelapukan terjadi oleh proses rekasi kimia

dan penyebab reaksinya hampir seluruhnya

oleh air. Reaksi kimia terjadi antara air

dengan unsur unsur pada mineral dan batuan.

Karbonat : CaCO3

CaCO3+ 2H2O H2CO3+ Ca(OH)2

H2CO3

H2O + CO2



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Reaksi yang sama terjadi pada mineral K-

Feldspar :

2KAlSi3O8 + 2H+ + 9H2O Al2Si2O5(OH)4 +

2K+ +4H2SiO4

Reaksi tersebut menghasilkan mineral lempung

Kaolinit.


Chemical Weathering


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Chemical Weathering


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Laterite : Berasal dari kata later(latin) = brick (bata).Pertama kali diajukan oleh Buchanan (1807 dalamSelley, 1988) untuk red soils di Deccan Plateau(Basalt Plateau) India, hasil dari pelapukan kimiapada basalt.

China Clay / Kaolin : Pelapukan Kimia yangmenghasilkan hydrate aluminisilicate clay mineral(Al2O3.2SiO2.2H2O) yang dikenal sebagai kaolinite.

Bauxie : suatu residual weathering terdiri atasaluminium hydroksida. Nama Bauxite berasal darisuatu tempat di Perancis : Les Baux. Mineral bauxiteterbentuk dari hasil hydrolysis mineral lempungterutama kaolinite.

H2O + Al2O3.2SiO2.2H2OAl2O3.nH2O.2SiO2.2H2O


Chemical Weathering


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Erosion

Removal of weathering product.

Penyebabnya : - Gravity- Running Water

- Wind

- Glacial / Gletser


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Transportation

Pengangkutan suatu material (partikel) dari suatutempat ke tempat lain oleh suatu gerakan media(aliran arus) hingga media dan material (partikelberhenti.

Mekanisme gerakan ; oleh aliran arus fluida atau

angin. Fluida sifat-sifatnya ditentukan oleh densitas dan

viskositas. Hukum Stokes membahas hubungansettling velocity dengan densitas dan viskositas :

21

18

)(d

gPPW

=

Dimana W = settling velocity.

= perbedaan densitaspartikel dan fluida

= viskositas fluida

d = diameter partikel

g = percepatan gravitasi

)( 1 PP


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Jenis Aliran / FlowTerdapat dua jenis aliran : - Laminar

- Turbulen

Kedua jenis aliran ini dapat ditentukan dengan

nilai Reynolds (Reynolds Number)

U dpR =

Dimana :

R = Reynolds Number U =kecepatan partikel d =diameter partikel p =densitas partikel

= viskositas fluida


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Aliran Laminar (Laminar Flow) R = rendah ().


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Dalam Laminar terbentuk : tractive current

sedangkan Turbulent (Density) : Low and HighDensity turbidity current


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Pergerakan Partikel : - Rolling

- Bounching / Saltation- Suspention


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Bed forms and Sedimentary structure for

different flow regimes.


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Berbagai Jenis Proses Sedimentasi

a. Traction : - Unidirectional tractioncurrent : fluvial

- Bidirectional traction

current : marine

b. Turbidity : - Low density turbiditycurrent

- High density turbidity current

c. Gravitasional : - Debris Flow

- Grain flow

- Fluidized flow


Berbagai Jenis Proses Sedimentasi


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Proses Proses Sedimentasia. Traction Current :

Unidirection of traction current : fluvial

Bidirection traction current : shallow marine

b. Turbidity / Density Current : Low and HighDensity Turbidity Currents

c. Gravitation Debris Flow

Grain Flow

Fluidized Flow


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Pembagian batuan sedimen berdasarkan

genetik

1. Terbentuk secaramekanik; batuan yang terdiri

dari bagian atau fragmen batuan sedimen

klastika (breksi, konglomerat (kelompok

psefit), batupasir, (kelompok psemit);batulempung, kelompok (pelit) dll)

2. Terbentuk secarakimia;batuan yang langsung

mengendap dari larutan yang mengandung

berbagai unsur seperti garamdapur, gipsum,

batugamping


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Batugamping;

Batugamping oolit; tersusun oleh butiran

bundar kecil/halus

Batugamping pisolit; tersusun oleh butiran

bundar agar besar


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Diatomae, geyserit

batubara

gambut/peat

stigmaria /fosil akar

gambut batubara muda/lignit

batubara antrasit grafit


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Struktur sedimen;

Terjadi karena adanya enerji, arah arus, ukuran

butir, lingkungan pengendapan

Macam struktur sedimen : paralel, silang-siur,

gelembur gelombang, grading,


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Bedforms and Sedimentary Structure


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Biogenic Structure


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Sedimentasi vulkanik

Adalah bahan lepas seperti bom, lapili, pasir,

dan debu vulkanik, batuan apung yang

terendapkan dengan media udara

Terbentuk secara primer dari magma

Penggalan lava yang dilemparkan keluar

selama erupsi, akan jatuh di sekitar badan

gunungapi; direkat oleh larutan dan zat tertentuakan terbentuk aglomerat (komponen

membundar) dan breksi vulkanik (komponen

menyudut).


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Sifat Utama Batuan lepas Batuan Padat

PsefitBersifat batuanguling (2 mm)

Taluskerikil

Breksikonglomerat

DIBENTUK SECARA

MEKANIK

PsamitBersifat pasir (2 mm 0,1 mm)

pasir butir kasarPasir butir menengahPasir butir halus

Grauwacke, arkosaBatupasir, flagstone

PelitBersifat lempung

lempung BatulempungSchali/serpih

Mengandung gamping KoralPasir Globigerina

batugamping

DIBENTUK SECARA

Mengandung silisum Lumpur RadiolariaTanah diatomea

Batuan yangmengandung radiolarit

ORGANIK Mengandung karbon gambut LignitBatubara, antrasit

Mengandung besi Bijih besi Limonit

Mengandung fospat Guano, tulang FosforitBreksi tulang

DIBENTUK SECARA

Mengandung gamping

CaCO3, mengendapdr lautan

CaCO3 dan MgCO3pengendapan atau

penggantian

Batugamping

dolomit

KIMIA Mengandung silisium Gel silisium Batuapi, sinter, jasper

Mengandung besi Hidrosol Fe2O3 Batubesi lempung

Mengandung garam Endapan danu garam Gipsum anhidrit, halit,nitrat


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Non Marine : - Alluvial Fan

- Fluvial

- Lacustrine

Delta Coastal

Deep Marine / Deep Water


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Sedimentary Environment


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Sedimentary Environment


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General EnvironmentalSetting:Non marine: fluvial

Rock Description:Pebble conglomerate (wellsorted)

Depositional EnvironmentRepresented:

Channel

Other environments whererock type is typically found:

Any high energy

environment such aschannel, bar or beach facies

Alluvial Fans


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Anastomosing

GeneralEnvironmentalSetting:

Non marine: fluvial

Rock Description:

Breccia-sandstone:mudstone intraclasts inthis sample have only beentransported a shortdistance otherwise theywould have disintegrated.

DepositionalEnvironmentRepresented:

Channel

Other environmentswhere rock type istypically found:

Intraclasts (rip-up-clasts)are common in channel ofevery environment.

General EnvironmentalSetting:

Non marine: fluvial

Rock Description:

Cross-beddedsandstone


Channel

Other environments whererock type is typicallyfound:

High energyenvironments wheremigrating dunes ofmegaripples occur(foreshore, aeolian,channel


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Non marine: fluvial

Rock Description:Ripple cross-beddedsandstone (only lee side ofripple preserved)

DepositionalEnvironmentRepresented:

Channel

Other environments

where rock type istypically found:Any moderate energyenvironment in whichmigrating ripples occur butmost commonly preserved intidal and non-marine facies.


Nonmarine - overbankRock Description:Horizontal-wave beddedsandstone and mudstone.The lenses of sandstone areprobably vestiges of ripples

DepositionalenvironmentRepresented:

Overbank (splay or

floodplain)Other environmentswhere rock type istypically found:

Tidal flats and shallowoffshore facies wherefluctuating energy conditionsare frequent.

Anastomosing


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Non marine: fluvial

Rock Description:Granular sandstoneDepositional EnvironmentRepresented:

Channel

Other environmentswhere rock type is typicallyfound:

Clean well sorted granularsandstones also common inhigh energy beach and barfacies


Non marine: fluvial

Rock Description:Pebble-conglomerate (well sorted)Depositional EnvironmentRepresented:

Channel


Any high energy environment suchas channels, beach or bar facieswhere fine sediment is selectivelyremoved


Non marine: fluvial

Rock Description:Pebble conglomerate (well sorted)Depositional EnvironmentRepresented:

Channel


Any high energy environmentsuch as channel, bar or beachfacies

Anastomosing


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BEACH

General Environmental Setting:Marine shoreface - beach

Rock Description:Parallel bedded-rippledsandstone. Note horizontalburrow near bottom (probablyPaleophycus)


Upper shoreface/beachOther environments where rocktype is typically found:

Paleophycus burrows only foundin marine environments. Marineshoals, washovers, tidal deltas


Rock Description:Clean sandstone with distinctparallel bedding. Burrows absent.


Shoreface/beachOther environments where rock typeis typically found:

Clean sand areas subject to high-velocity currents such as exposedembayment shoals, upper portionsof tidal deltas, washovers, fluvialand tidal point bars, channel

bottoms and distributary mouth


Rock Description:Bioturbated sandstone. Original rock-interbedded clean sandstone andmudstone.

Depositional EnvironmentRepresented:Foreshore to offshore

Other environments where rock typeis typically found:

Interbedded clean sandstone and shaletypical of lower foreshore to offshoreenvironments or tidal areas whereperiodic high current velocities occur.Vertical burrows typical of transitionalmarine environments where filter

feeders are dominant.


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Rock Description:Parallel and cross-beddedsandstone



Areas with moderate to highvelocity currents such asmarine shoals, upperportion of tidal deltas,washovers, fluvial and tidalpoint bars, channelbottoms, distributary

mouth bars.


Rock Description:Granular, well sortedconglomerate. Note theabsence of any fine sandymatrix and good granular

porosity. This rock wouldmake an excellent petroleumreservoir.


Gravel beach-shorefaceOther environments where rocktype is typically found:

Areas of moderate to highcurrent velocity such as

braided streams, offshore bars.


Marine shoreface - beach

Rock Description:sandstone with root structures (R)


Backshore area of beach


Sandy vegetated environmentssuch as splays, washovers, dunes,point bars

BEACH


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Rock Description:Sandstone with abundant burrowstructures destroying all primaryphysical sedimentary structures. Typeof fossil is uncertain, possiblyChondrites orMacaronichnus

segregatus

Depositional Environment Represented:In the Gates Formation this trace fossil

was found only in sandstonesdeposited in very shallow marine(intertidal) settings such as beachesand bars in distributary channels.

Other environments where rock type istypically found:Not found in other environments

BEACH


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Crevasse

General Environmental Setting:Nonmarine - overbank

Rock Description:Horizontal-wave beddedsandstone and mudstone. The

lenses of sandstone are probablyvestiges of ripplesDepositional EnvironmentRepresented:

Overbank (splay or floodplain)Other environments where rocktype is typically found:

Tidal f lats and shallow offshorefacies where fluctuating energyconditions are frequent.


Nonmarine - overbank

Rock Description:Horizontal-ripple cross-laminated

sandstone with mudstone partings.Only lee side of ripples preserved


Overbank deposit (levee or splay).


Not found in other environments



Rock Description:Horizontal and ripple cross-

laminated sandstone with mudstonepartings


Overbank (levee or splay)


Alternating low (mudstone) andmoderate energy (sandstone) such astidal or subtidal facies or facies

characterized by periodic flooding


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Crevasse



Rock Description:Horizontal bedded siltstone withmudstone laminae. This rock consists

of varves of light coloured siltstoneand darker mudstone


Lacustrine. True varves are the resultof seasonal climatic changes





Rock Description:fragment preserved on beddingplane. Such fragments are

common in overbank deposits.Depositional EnvironmentRepresented:





Rock Description:Convolute (soft-sediment structures)and horizontal bedded sandstone. Note

the syn-depositional fault near the baseDepositional EnvironmentRepresented:

Channel of proximal crevasse-splay


Any moderate to high energy faciescharacterized by rapid deposition.


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Crevasse


Rock Description:Lenticular bedded siltstoneand mudstone


Overbank (lake, distal splay,levee)

Other environments where rocktype is typically found:

Any low energy environment inwhich there is a periodic influxof coarse sediment (flood orstorm events) such as tidal,shallow offshore or lake facies.


Rock Description:Horizontal bedded mudstone andcross-bedded sandstone. Base ofcore is composed of rip-up-clasts.This core has been interpreted asthe result of a single flood withcurrents declining from base to thetop.


Crevasse-splayOther environments where rock typeis typically found:



Rock Description:Massive siltstone. The absenceof bedding may be the resultof rapid deposition,bioturbation, rooting or rapidde-watering. Alternativelybedding may be present butnot visible to the unaided eye


Crevasse-splay, levee orlacustrine.


Not found in other


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Lake Deposit


Rock Description:Convolute (soft-sedimentstructures) and horizontalbedded sandstone. Note the syn-

depositional fault near the baseDepositional EnvironmentRepresented:

Channel of proximal crevasse-splay


Any moderate to high energyfacies characterized by rapid

deposition


Rock Description:Massive siltstone. The absence ofbedding may be the result ofrapid deposition, bioturbation,

rooting or rapid de-watering.Alternatively bedding may bepresent but not visible to theunaided eye


Crevasse-splay, levee orlacustrine.

Other environments where rock

type is typically found:


Rock Description:Rooted sandstone. Roots havelocally disrupted bedding

Depositional Environment

Represented:Levee or exposed floodplain


Roots provide evidence for at leastperiodic emergence


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Levee Deposit


Rock Description:Intraformational conglomerate(breccia). The core is composedof rip-up-clasts of siltstone


Crevasse-splayOther environments where rocktype is typically found:

Not found in otherenvironments


Rock Description:Convolute (soft-sedimentstructures) and horizontal bedded

sandstone. Note the syn-depositional fault near the base


Channel of proximal crevasse-splayOther environments where rock typeis typically found:

Any moderate to high energy faciescharacterized by rapid deposition.


Rock Description:Rippled siltstone and sandstonewith local rooting. Note the

siliceous concretions at the baseDepositional EnvironmentRepresented:

Levee or crevasse-splayOther environments where rock typeis typically found:



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Marine Offshore

General Environmental Setting:Marine offshore to transitional zone

Rock Description:Fine grained sandstone and mudstone.Bioturbation and compaction. May locallycontain gas-disrupted bedding.

Depositional Environment Represented:Shoreface to shallow offshore.

Other environments where rock type istypically found:

Any moderate to low energy environmentincluding lakes, lagoons and shallowmarine environments.

General Environmental Setting:Marine offshore transitional zone

Rock Description:

Alternating parallel bedded very finegrained sandstone and mudstoneDepositional Environment Represented:

Lower most shoreface - offshoreOther environments where rock type istypically found:

Any low energy environment such as alake, lagoon, bay or offshore mari


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Non Marine Overbanks


Rock Description:

CoalDepositional EnvironmentRepresented:

Peat-forming wetland (mire:marsh or swamp)




Rock Description:

Intraformational conglomerate(breccia). The core is composed ofrip-up-clasts of siltstone





Rock Description:

Lenticular bedded siltstone andmudstone

Depositional Environment Represented:Overbank (lake, distal splay, levee)


Any low energy environment inwhich there is a periodic influx ofcoarse sediment (flood or stormevents) such as tidal, shallow offshore


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Non Marine Overbanks


Rock Description:Horizontal bedded mudstone andcross-bedded sandstone. Base of

core is composed of rip-up-clasts.This core has been interpreted asthe result of a single flood withcurrents declining from base to thetop.





Rock Description:Rippled siltstone and sandstone with

local rooting. Note the siliceousconcretions at the base

Depositional Environment Represented:Levee or crevasse-splay




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NON MARINE


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NON MARINE

General Environmental Setting:Non marine: fluvial

Rock Description:Granular sandstone

Depositional Environment Represented:Channel

Other environments where rock type is typicallyfound:

Clean well sorted granular sandstones alsocommon in high energy beach and bar facies


Rock Description:Conglomerate

Depositional Environment Represented:Braided channel


Such coarse conglomerates are restricted tovery high energy channels. In mass flowdeposits the degree of rounding of clastsevident in this sample will not occur.


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NON MARINE


Rock Description:Pebble-conglomerate (well sorted)



Any high energy environment such aschannels, beach or bar facies where finesediment is selectively removed.


Rock Description:Pebble conglomerate (well sorted)



Any high energy environment such aschannel, bar or beach facies


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Sh f


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Shoreface


Rock Description:Bioturbated sandstone. Originalrock-interbedded clean sandstoneand mudstone.


Represented:Foreshore to offshore


Interbedded clean sandstone andshale typical of lower foreshore tooffshore environments or tidalareas where periodic high currentvelocities occur. Vertical burrowstypical of transitional marine


Rock Description:Clean sandstone with distinct parallelbedding. Burrows absent.

Depositional Environment Represented:Shoreface/beach


Clean sand areas subject to high-velocity currents such as exposedembayment shoals, upper portions oftidal deltas, washovers, f luvial andtidal point bars, channel bottoms anddistributary mouth bars.


Rock Description:Parallel-to-burrowed sandstone.Burrow are horizontal formssimilar toPaleophycus


Represented:Shoreface. The alternation ofparallel bedded sandstone in whichburrows are rare to absent withdensely burrowed zones suggestsconsiderable variation insedimentation rates, probablyassociated with storm/fairweatherdeposition.

Other environments where rock type is

Shoreface


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Shoreface

General Environmental Setting:Marine offshore transitionalzone

Rock Description:Alternating parallel bedded very

fine grained sandstone andmudstoneDepositional EnvironmentRepresented:

Lower most shoreface - offshoreOther environments where rocktype is typically found:

Any low energy environmentsuch as a lake, lagoon, bay oroffshore

General Environmental Setting:Marine offshore transitional zone

Rock Description:Horizontal bedded and bioturbatedsandstone. Burrows are similar toPaleophycus


Shoreface - moderate energyenvironment. Presence of laminaeof mudstone indicate periods of lowenergy


Any moderate energy environmentbut with burrows is typical of lower

Shoreface


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Shoreface

General Environmental Setting:Marine offshore transitionalzone

Rock Description:Bioturbated very fine grainedsandstone and mudstone

Bioturbation has largelydestroyed initial depositionalenvironment


Lower shorefaceOther environments where rocktype is typically found:

Predominance of fine sedimentindicates low energy

environment which to ether


Rock Description:Cross-bedded sandstone


Upper shoreface or distributarychannelOther environments where rock typeis typically found:

Moderate to high current velocityareas such as marine shoals, f luvialand tidal point bars, channelbottoms, distributary mouth bars,tidal inlets, tidal deltas and shelfsand ridges.


Rock Description:Parallel bedded-rippledsandstone. Note horizontalburrow near bottom (probably

Paleophycus)Depositional EnvironmentRepresented:


Paleophycus burrows onlyfound in marine environments.Marine shoals, washovers, tidaldeltas.


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Shoreface


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Shoreface


Rock Description:Granular, well sorted conglomerate.Note the absence of any fine sandymatrix and good granular porosity. This

rock would make an excellentpetroleum reservoir.

Depositional Environment Represented:Gravel beach-shoreface


Areas of moderate to high current

velocity such as braided streams,


Rock Description:Sandstone with abundant burrowstructures destroying all primaryphysical sedimentary structures. Type offossil is uncertain, possiblyChondrites orMacaronichnus segregatus

Depositional Environment Represented:In the Gates Formation this trace fossilwas found only in sandstones depositedin very shallow marine (intertidal)settings such as beaches and bars indistributary channels.



Tidal Flat


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Tidal Flat

General Environmental Setting:Marine and transitional marine totidal f lat

Rock Description:bedded sandstone. Lenticularbedded sandstone streaks inmudstone at top.


Tidal flatOther environments where rock typeis typically found:

Low to moderate energy areaswith variable current velocity suchas tidal point bars, marine shoals,splays, lagoons, offshore near fair-weather wave base.

General Environmental Setting:Marine and transitional marineto tidal flat

Rock Description:Massive sandstone with verticalburrows


Intertidal to shallow subtidalareas of shoals.


Shoreface environments ofmoderate wave energy

General Environmental Setting:Marine and transitionalmarine to tidal flat

Rock Description:massive sandstone with thinvertical burrows (probablySkolithos or Arenicolites)


Intertidal to shallow subtidalareas of marine shoals


Sandy, shallow marineenvironments such as tidaldeltas, tidal point bars, tidalflats.

Tidal Flat


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Rock Description:Parallel bedded sandstone withlarge vertical to 'U' shaped burrows

(probablyDiplocrateron orRhizocorallum). Parallel beddingdefined by thin laminae ofcarbonaceous material and reddishbrown siderite pellets


Marine shoal/shoreface.Other environments where rock typeis typically found:



Rock Description:Ripple cross-bedded andconvolute-bedded sandstone

interbedded with mudstoneDepositional EnvironmentRepresented:

Tidal flat to shallow subtidalOther environments where rock typeis typically found:

Areas of alternating high (sanddeposition) and low energy (muddeposition) such as splays or somesubtidal areas influenced by

storms.

General Environmental Setting:Marine and transitional marine totidal flat

Rock Description:Lenticular and flaser bedding:sandstone and mudstone

Depositional EnvironmentRepresented:Typical of tidal f lats


flaser and lenticular beddingindicate both sand and mud areavailable and that periods of at leastmoderate current activity (sanddeposition) alternate with periods ofquiescence (mud deposition). These

Tidal Flat


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Tidal Flat

General Environmental Setting:Marine and transitional marineto tidal flat

Rock Description:Parallel bedded sandstone and

mudstone. Note flame structuresnear base and load casts near topof core


Shallow subtidal to intertidalOther environments where rocktype is typically found:

Load casts and f lame structuresform as a result of differential


Rock Description:Breccia-sandstone: mudstoneintraclasts in this sample have only

been transported a short distanceotherwise they would havedisintegrated.



Intraclasts (rip-up-clasts) arecommon in channel of every environment.


Rock Description:Intraformational conglomerate(breccia). The core is composed

of rip-up-clasts of siltstoneDepositional EnvironmentRepresented:

Crevasse-splayOther environments where rocktype is typically found:

Not found in otherenvironments

Wave Dominated Delta


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Wave Dominated Delta


Rock Description:Cross-bedded sandstone


Upper shoreface or distributarychannelOther environments where rock type istypically found:

Moderate to high current velocityareas such as marine shoals, f luvialand tidal point bars, channelbottoms, distributary mouth bars,


Rock Description:Ripple cross-bedded and convolute-bedded sandstone interbedded with

mudstoneDepositional EnvironmentRepresented:

Tidal flat to shallow subtidalOther environments where rock type istypically found:

Areas of alternating high (sanddeposition) and low energy (mud

)

General Environmental Setting:Marine and transitionalmarine to tidal flat

Rock Description:Parallel bedded sandstone andmudstone. Note flame

structures near base and loadcasts near top of coreDepositional EnvironmentRepresented:

Shallow subtidal to intertidalOther environments where rocktype is typically found:

Load casts and flame

8 - batuan sedimen.pdf

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