2 Pengaruh Deformasi Tektonik

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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 incipient extensional basin type; if the process continues it will ultimately lead to the development of an ocean basin flanked by passive margins, alternatively an intracratonic basin will form

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

    • Intracratonic basins develop when rifting ceases, which leads to

    lithospheric cooling due to reduced heat flow; they are commonly large 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 & pelagic oozes

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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 sediment deposition 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

    Continental Margin 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, broad shallow shelf 

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

     –Evaporties probably overlie

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

     –Open ocean water led to flourishing 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 prism and the volcanic arc and subside entirely due to

    sediment loading; like trench basins, their fill depends strongly on whether they are intra-oceanic or proximal to a 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 a compressional 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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