06.struktur sedimen

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    06 Struktur Sedimen

    Petrologi Batuan Karbonat

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    Kerangka Materi

    Pendahuluan: Struktur Sedimen Primer

    Definisi

    Burrows

    Borings

    Geopetal fabrics

    Fenestral fabrics

    Stromatactics

    Lamination

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    Pendahuluan:

    Struktur Sedimen Primer

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    PRIMARY SEDIMENTARY STRUCTURES

    Primary sedimentary structures are physical and/or biological

    features formed during the process of sediment deposition.Generally such structures are best seen in outcrop, core, orpolished hand sample, but smaller features such as borings orfenestral fabrics are both readily apparent in thin section andimportant to recognize. Their identification can improve

    interpretations of depositional environments and can alsohelp to decipher patterns and timing of diagenesis.

    The characteristic features for the recognition andinterpretation of primary sedimentary structures are providedin the figure captions. Diagenetic sedimentary structures, such

    as hardgrounds, soil crusts, or stylolites, are covered in theappropriate diagenetic chapters.

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    Definitions

    Borings - Openings created in relatively rigid rock, shell, or other material by boring organisms.The rigid host substrate is the feature that distinguishes borings from soft-sediment burrows.

    Burrow porosity - Feature created by organic burrowing in relatively unconsolidated sediment,in contrast to borings. Most burrows collapse, become filled with sediment, or are back-filled bythe burrow-forming organism itself.

    Fenestrae (fenestral fabric) - Primary or penecontemporaneous gaps in rock framework largerthan grainsupported interstices. Such features may be open pores or may have been partially orcompletely filled with internal sediment and/or sparry cement. Fenestrae occur as somewhatrounded features of spherical, lenticular, or more irregular shapes; their large size in comparisonto normal interparticle openings and their multigranular roofs, floors, and other margins are keycharacteristics. Fenestrae are commonly somewhat flattened parallel with the laminae. They

    may, however, be round or very irregular, and some are elongate in a vertical dimension.Although isolated fenestrae occur in sedimentary carbonates, it is more common to find many inclose association. Fenestrae are generally associated with microbial mats and result fromshrinkage, gas formation, organic decay, trapping of air through swash-zone wave action, orother synsedimentary processes (Choquette & Pray, 1970).

    Geopetal structure - Any internal structure or organization of a rock indicating originalorientation such as top and bottom of strata. Common examples are internal sedimentaccumulating on the floor of a cavity which it partly fills, or solution-collapse residue that hasfallen to the bottom of a vug or cave.

    Stromatactis - A cavity structure common in muddy carbonate sediments, typically 3 to 10 cm indiameter, characterized by a flat floor and an irregular roof. The floor of this former cavitytypically is overlain by peloidal internal sediment; the remaining void is filled with marinecement or later sparry cement. These poorly understood vugs have been attributed to the decayof unknown soft-bodied organisms, to gas formation in impermeable sediments, to gravitysliding and shear, to the alteration of sponges and sponge holdfasts, and to several other causes.

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    Burrows

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    Burrow

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    Burrow

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    Burrow

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    Burrow

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    Borings

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    Boring

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    Boring

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    Boring

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    Boring

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    Boring

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    Boring

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    Boring

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    Geopetal Fabrics

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    Geopetal

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    Geopetal

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    Geopetal

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    Fenestral Fabrics

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    Fenestral fabrics

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    Fenestral fabrics

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    Fenestral fabrics

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    Fenestral fabrics

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    Stromatactics

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    Stromatactics

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    Stromatactics

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    Laminations

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    Lamination

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    Lamination

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    Eroded Surface Contact

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    Terima Kasih

    Ada Pertanyaan?Minggu Depan:

    Semen

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    Geopetal

    Geopetal structure in bivalve boring in coral; bivalve shell

    visible; Matmor Formation (Middle Jurassic), southern Israel.

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