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PENGETAHUAN CEKUNGAN

BATUBARA DAN GMB DI INDONESIA

(GEO-330314)

Modifikasi dari kuliah yang disamaikanoleh Dr. Budhi Kuswan Susilo, S.T., M.T.


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Pengaruh Deformasi Tektonik

Pada Pembentukan Cekungan


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What are Sedimentary Basins?

Holes in the ground where sediment accumulates

Global distribution: Sub-aerial and submarine


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Sedimentary basins – definition

Large areas of positive accommodation in which

sediments can accumulate to considerable

thickness and be preserved for long geological

time periods.


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Thickest sediment accumulations are 15 to 20 km

Tend to form in enclosed basins supplied by major rivers

World’s Thickest Sediment Accumulations


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Basin classification – plate tectonics

1. Type of crust on which the basin rests

2. The position of the basin relative to plate

margins

3. Where the basin lies close to a plate margin, the

type of plate interaction occurring during

sedimentation


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Types of plate margins:

1. Convergent (subduction)2. Divergent (rifts, mid -oceanic ridges)

3. Transform (offset mid -oceanic ridges)


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Basin classification

I. Intraplate basins (pre-rift)

II. Divergent-margin basins (syn-rift)

III. Intraplate basins (post-rift)

IV. Convergent-margin basins

V. Collision and post-collision basins

VI. Strike-slip basins


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EaES 350-13 11

Sedimentary basins

Extension

• Rift basins develop in continental crust and constitute the incipientextensional basin type; if the process continues it will ultimatelylead to the development of an ocean basin flanked by passivemargins, alternatively an intracratonic basin will form

• Rift basins consist of a graben or half-graben separated fromsurrounding horsts by normal faults; they can be filled with bothcontinental and marine deposits

• Intracratonic basins develop when rifting ceases, which leads to

lithospheric cooling due to reduced heat flow; they are commonlylarge but not very deep


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EaES 350-13 13


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Plate Tectonics & Sedimentation

•A. Explains geosynclines (now obsolete)

–1. miogeosyncline = shelf; eugeosyncline =slope & rise

•B. Divergent margins

–1. 2 plates separating

–2. uplift = mantle plume

–3. extension = rift valley development•1. normal faulting & down dropping

•ii. eventually forms ocean basin

–4. coarse immature sediments deposited;alluvial, fluvial, lacustrine

–5. aulacogens may develop & fill•i. fluvial & deltaic deposits fill basin

–6. junction coalesce to form ocean basin•i. evaporites, marine sediments

–7. seafloor spreading develops & pelagicoozes


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Active Rifting


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Rifting and Origin of Ocean Basins

• Active Arms marked by:

– High heat flow

– Normal faulting

– Frequent shallow earthquakes

– Widespread basaltic volcanism

Rift valley widening leads to the development of

new seaways and evaporite belts

In Ocean, it leads to the formation of sedimentdeposition and development of Passive

continental margins


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The East Africa Rift Zone


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The growth of oceanic basin


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Growth of ocean basin – contd.


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Growth of ocean basin – contd.


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Oceanic Rift Basin


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Oceanic Rift

Basin


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Passive

ContinentalMargin Basin


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Mississippi & Connecticut-Hudson Valleys--

Inactive


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Rio Grande Rift--Active

Properties of crust and upper mantle beneath the Rio Grande. Pure shear model is

probable explanation, with a "taffy-like" thinning of the lower crust and the upper crust

faulting in many places to produce the rift valley. This contrasts to "simple shear"

model wherein a single, large detachment fault controls continental rifting.

Nicolle Rager, NSF


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Red Sea-Ocean Beginning

•Deep axial trough, broadshallow shelf

–Miocene (5-25mya) evaporites(over 4km thick) below shelf

–Evaporties probably overlie

thin, stretched continental crust –Evaporite deposition end 5mya- connection to Indian seaestablished

–Open ocean water led toflourishing plankton

–Biogenic seds give way laterallyto thin terrigenous clays, sands,

gravels from eroding flanks

Stephen A. Nelson


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Intracratonic Basin


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Intracratonic Basins


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EaES 350-13 39

Sedimentary basins

Collision

• Forearc basins form between the accretionary prismand the volcanic arc and subside entirely due to

sediment loading; like trench basins, their fill dependsstrongly on whether they are intra-oceanic or proximal toa continent

• Backarc basins are extensional basins that may form

on the overriding plate, behind the volcanic arc• Retroarc foreland basins form as a result of

lithospheric loading behind a mountainous arc under acompressional regime; they are commonly filled with

continental deposits


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ARC Morphology/Terminology


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Forearcs


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Trenches and Accretionary Wedges


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EaES 350-13 57


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I) Tectonics and Sedimentation

•A. Can explain sedimentarysequence with plate tectonicmodels

•B. Cratonic sedimentation –1. craton = stable continentalinterior, positive relief

–2. thin sedimentary sequences,unconformities

–3. positive relief leads to erosion& unconformities

–4. sedimentary sequence = ~ 1km of Paleozoic and Mesozoic rks

•i. l.s, s.s., sh = shallow marine,fluvial-deltaic

•5. local development of basins &arches

•i. origin of basins = failed rifts?=Michigan basin

Wiley.com

Alberta Geol Society

II) Geosynclines


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) y

•A. Trough that parallels continental margin = geosyncline –1. subdivided in miogeosyncline & eugeosyncline –2. miogeosyncline

•i. = shallow marine ls & ss adjacent to craton•

ii passes to deep water lithologies –3. eugeosyncline•i. deep marine sediments, submarine volcanics, volcaniclastic sediments•ii. tectonically deformed

–4. no explanation of how geosynclines formed

Steven Dutch


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Steven Dutch


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Steven Dutch


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III) Plate Tectonics & Sedimentation

• C. Convergent margins

– 1. cont-cont collision = uplift & coarse clastic debris, fluvial

deposits

– 2. oceanic-oceanic collision = island arc

• i. submarine volcanism & turbidites, shales, pelagic oozes

– 3. ocean-continent collision = continental margin arc

• i. felsic batholiths, silicic volcanics

• ii. immature seds = alluvial & fluvial ss

• ii. accretionary wedge, melange


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III) Plate Tectonics & Sedimentation

• D. Transform Margin

– 1. strike slip motion

– 2. irregularities produce local extension &

compression

– 3. typical of southern California

• i. may develop sediment-starved basin

•

ii. eventually infilled


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EaES 350-13 65

Sedimentary basins

Transtension

• Strike-slip basins form in transtensional regimes and are usuallyrelatively small but also deep; they are commonly filled with coarse

facies (e.g., alluvial fans) adjacent to lacustrine or marine deposits


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Woods Hole


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EaES 350-13 68


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Accommodation SpaceSea-Level Change

Tectonic Uplift / Subsidence

Basins form through Tectonic Subsidence


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Very little of a typicalunderformed basin is

accessible by surface sampling

/ mapping

S i i R fl ti I i


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12 km

Ninian Fault Block, North Sea

vertical exageration x3 to x4

Seismic Reflection Imaging

A


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Sistem progradasi pengendapan deltaik Lower Kutai Basin (Allen et al., 1998)

Penampang progradasi sistem deltaik dan pengendapan batubara

di lingkungan Delta Plain di Lower Kutai Basin (Allen et al., 1998)

A

B

B

A

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A B

Distributary Channel pada ModelPengendapan Coal Swampdi Delta Plain, Lower Kutai Basin (a)(Allen et al., 1998) and Sangatta Deltaik (b)

Tipe endapan pembawa batubara:1. Overbank deposits (coal swamp)2. Splay deposits

3. Levee deposits4. Channel deposits

B A

A B

a.

b.

cross section


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Pembentukan splitting Middle Seam akibat migrasi channel secara lateral

PIT Hatari (Rahmad, B., 2001, dalam Diessel, 1992) 75

Jenis-jenis sedimen pembawa batubara


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j p

A B

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Levee deposits Channel deposits

Channel deposits

Channel deposits

Channel depositsChannel deposits

Channel depositsSplay deposits Overbank deposits(swamp)

Sangata Seam