prinsip dasar stratigrafi

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PRINSIP DASAR PRINSIP DASAR STRATIGRAFI STRATIGRAFI

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Prinsip Dasar Stratigrafi

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  • PRINSIP DASAR STRATIGRAFI

  • PRINSIP DASAR STRATIGRAFI

    Gambaran tentang bermacam jenis batuan dan strukturnya adalah mengikuti aturan atau pengertian mengenai hubungan dan kejadian geologinya. Dalam hal ini adalah letak antara tubuh batuan, dan sifat hubungannya yang menyangkut umur, urutan kejadian, dan sejarah pembentukannya.

  • BEBARAPA PRINSIP DASAR STRATIGRAFI YANG PENTING :

    1. HUKUM STENOa. SUPERPOSISIb. HORISONTALITAS/KEDATARANc. KESINAMBUNGAN

    2 UNIFORMITARIANISME

    3. HUKUM WALTHER

    4. FASIES

  • a. SUPERPOSISI

    Modified statement

    Law of Superposition : The younger strata at the top in an undisturbed sequence of sedimentary rocks (Anthony, 1955)

    " DALAM KEADAAN NORMAL, SUATU LAPISAN BATUAN YANG LETAKNYA DIATAS SATUAN LAPISAN YANG LAIN, SELALU BERUMUR LEBIH MUDA DARIPADA LAPISAN BATUAN DIBAWAHNYA .

    HUKUM-HUKUM STENO (1669)

  • In an undisturbed rock sequence, the bottom layer of rock is older than the layer above it, orThe younger strata at the top in an undisturbed sequence of sedimentary rocks.

  • Undisturbed strata

  • Disturbed strata

  • Disturbed strata

  • Penekanan pada :

    waktu diterjemahkan hubungan yang bersifat fisik, antar perlapisan

    strata/lapisan, bukan batuan

    - kondisi normal, belum mengalami gangguan

  • b. HORISONTALITAS / KEDATARAN

    Modified statement :

    Law of Horizontality Sedimentary strata are laid down nearly horizontally and are essentially parallel to the surface upon which they accumulate (Anthony, 1955)

    Lapisan-lapisan sedimen diendapkan mendekati horisontal dan pada dasarnya sejajar dengan bidang permukaan dimana lapisan sedimen tersebut diendapkan.

    Akumulasi lapisan-lapisan sedimen adalah secara vertikal.

    Susunan lapisan yang kedudukannya tidak horisontal berarti telah mengalami proses geologi lain setelah pengendapannya.

  • c. KESINAMBUNGAN

    Modified statement :

    Law of Original continuity : The original continuity of water-laid sedimentary strata is terminated only by pinching out against the basin of deposition, at the time of their deposition (Anthony, 1955)

    Lapisan sedimen diendapkan secara menerus dan bersinambungan (continuity), sampai batas cekungan sedimentasinya

    Lapisan sedimen tidak mungkin terpotong secara tiba-tiba, dan berubah menjadi batuan lain dalam keadaan normal

    Pada dasarnya hasil suatu pengendapan yakni bidang perlapisan, akan menerus walaupun tidak kasat mata

    Pemancungan : Ketidakselarasan, erosi, morfologi

  • Berhentinya perlapisan akibat erosi/morfologi

  • Berhentinya perlapisan akibat ketidakselarasan

  • Berhentinya perlapisan akibat erosi/morfologi

  • Berhentinya perlapisan akibat erosi/morfologi

  • Berhentinya perlapisan akibat erosi/morfologi

  • UNIFORMITARIANISM (HUTTON., 1785):Peneliti lain yang mempunyai sumbangan penting dalam stratigrafi adalah JAMES HUTTON (1785).

    Original statement" In examining things present, we have data from which to reason with regards to that which is to happen hereafter. Therefore, upon the superposition that the operations on nature are equable and steady, we rind, in natural appearances, means for concluding a certain portion of time to have necessarily elapsed in the production of these events of which we see the effects (Hutton, p.217)

    Modified statement " The Present is the Key to the Past

    Keterangan:Walaupun kita ketahui bahwa setiap zaman mempunyai ciri yang tertentu, misalnya ZAMAN PERM : umumnya beriklim panas, dan ini berbeda dengan iklim zaman sebelumnya yaitu ZAMAN, KARBON : dimana mempunyai iklim lebih bersifat lembab, namun proses-proses yang membentuk semua gejala Geologi dapat dikatakan sama.Proses di bumi terjadi secara berulang-ulang, membentuk suatu SIKLUS.

  • MODIFIED STATEMENTThe present is the key to the past"The processes (plate tectonics, mountain building, erosion) we see today are believed to have been occurring since the Earth was formed.

  • No vestiges of the beginning, no vestiges of the end Everything changes, only the law of changes does not change

    Perubahan terjadi sangat lambat perubahan besar Proses di bumi terjadi secara berulang ulang siklus Bermacam jenis batuanHUTTONS DOCTRINE OF UNIFORMITY ( Playfair, 1802 )

  • F A C I E S (Greeslv. 1836)

    Pada tahun 1836 seorang ahli dari SWISS bernama A. GREESLY menyebutkan caranya sendiri dalam mempelajari batuan.

    Modified statement" The term facies designates the differences, whatever they may be between formations of the same age; the differences may be either in petrographic composition. resulting the nature of the substances deposited, or paleontologic differnces, resulting from the living conditions of the animal and plant fossils "." FACIES are then difinitely the different kinds of deposite, sedimentary or other, which can be produced simultaneously, at a given geological moment, just as is the case at the present time. One then speaks of the various facies of a formation as one would speak of the different deposits of modern times ".

    Keterangan .Greesly mulai melihat fosil sebagai bagian batuan, tidak berdiri sendiri sebagaimana peneliti sebelumnya.

  • WALTHER LAW (Walther, 1894)

    Modified statement" In other words facies that occur in a conformable vertical core sequence were formed in laterally adjacent depositional environment ".Note" It is specialty important to note as MIDDELTON (1973) pointed out, that Walther's Law applies only to successions without major erosional or non depositional breaks. There it is extremely important to recognize such erosional or non depositional breaks in a vertical sequence".

    KeteranganFASIES yg pada dasarnya berarti perbedaan ciri paleontologi dan batuan pada umur yg sama, namun dalam praktek pengenalannya di lapangan sulit dikerjakan pada daerah tropis. Hal ini karena terbatasnya bentang singkapan. Oleh karena itu pemakaian Hukum Walther ini menolong kita dalam menafsirkan perubahan fasies yg bersifat lateral dan perubahan ciri paleontologi dan batuan dalam susunan vertikal. Tetapi pengertian bahwa perubahan vertikal adalah sama dgn perubahan fasies adalah pengertian yg salah, karena susunan vertikal menunjukkan urutan waktu yg berbeda (superposisi), yg tdk sesuai dgn pengertian facies menurut GREESLY.

  • Walthers Law

  • A SandNonmarine Member XShale ZB SandUnits are defined by lithologyRock Units vary in space and timeBoundaries are subjectiveLithostratigraphy

  • Unconformity and correlative conformityDownlap surface and correlative conformityUnit 1Unit 2Unit 3Units based on physically observable stratal surfacesUnits vary in space onlyRepresent natural stratigraphic divisions (genetically related)Chronostratigraphy

  • Alluvial PlainCoastal PlainForeshore/Upper ShorefaceShoreface/ShelfHypothetical Cross SectionLithostratigraphy and Chronostratigraphy

  • Correlation Styles

  • *Walthers Law: In a conformable succession, the same succession of facies that is present horizontally is present vertically. Recognition of non-conformable successions is one of the foundations of sequence stratigraphy. Conformable successions involve the stacking of facies in order of their natural association. However, not all such successions are gradational some may involve sharp or erosional contacts between facies (as in channelized facies). **The significant distinction is that the key surfaces which subdivide the section chronostratigraphically time-line surfaces do not simply duplicate lithologic or facies boundaries. They may be obvious or subtle, and depending on their scale may not be immediately recognizable from a single dataset. *A hypothetical cross section, waiting to be subdivided by the unsuspecting geoscientist.*Irrespective of which parasequence model one adopts, correlation by lithostratigraphic and chronostratigraphic techniques can result in major differences in ones interpretation of reservoir architecture.

    We have probably all seen examples like this. Because so many stratal bodies are not simply tabular layers, recognition of stacking patterns and interpretation of progradation/retrogradation is essential for improving ones chances of correctly correlating these units. Note that this applies both early in the life cycle (imagine predicting the others from the first well) and later (correctly planning a waterflood). *Biostratigraphy is one of the most important tools for chronostratigraphy, but bio- and chronostratigraphy are not the same!

    This slide illustrates some of the varied types and uses of biostratigraphic data. Note at left a conventional range chart for the microfossil types occuring in this section; in the center, a set of graphs of abundance of particular groups as a function of depth. Interpretation of paleobathymetry derives from environmental ranges of forms and assemblages, and combines with recognition of significant patterns such as condensed sections and sequence boundaries to give a specific and predictive interpretation of depositional cycles.

    More on this later.

    RFW NOTES: 1.Biostratigraphic units, based on criteria that differ fundamentally from those for lithostratigraphic or chronostratigraphic units; as such, boundaries of the three kinds of units may or may not coincide.2.Units characterized by fossil content; boundaries diachronous (upper/lower boundaries rarely synchronous surfaces, lateral boundaries never synchronous).3.Biozone, fundamental biostratigraphic unit; boundaries are surfaces that e.g. mark the lowest or highest occurrence, increase or decrease in abundance of one or more components of the fauna or flora, or change in the character of individual taxa (e.g. coiling change in forams). Several kinds of biozones are recognized, two types noted herea)Range biozone: Boundaries are the horizons of lowest and highest stratigraphic occurrence of specified taxa (FAD tamilis LAD abies, TS - MFS).b)Abundance biozone: Boundaries defined by marked changes in relative abundance of preserved taxa (U. peregrina acme zone), controlled by e.g. paleoecology (i.e.HS).4. Also note trend in FODs, trend in LODs, peak abundance/diversity, peak reworked.