Seismik Stratigrafi MIGAS [PDF]

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SEISMIC STRATIGRAPHY



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KlasikUnconformity •



Angular unconformity is used when layers below are clearly tilted or folded and then eroded before deposition continues on the eroded surface



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Disconformity is used when beds above and below are parallel but a well-developed erosional surface can be recognized, by irregular incision, soil development, or basal gravel deposits on top. Paraconformity is used for obscure unconformities where correlation with time markers elsewhere indicates missing strata, even though no evidence of a gap is present locally. Nonconformity is used for deposition of bedded strata on unbedded (usually igneous or metamorphic) basement.



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Seismic Stratigraphy, Vail et al., 1977



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Definisi



•Seismik Fasies adalah unit atau paket pola-pola refleksi yang teramati pada sekuen seismik. •Hubungan perlapisan dengan refleksi terminasi: •Toplap : refleksi terminasi yang menumpu permukaan erosi yang berada di atasnya/ hiatus.



ke



arah



•Onlap : refleksi terminasi yang menumpu ke permukaan miring (maju ke depan). •Downlap (berada di bagian bawah): refleksi terminasi miring yang menumpu ke permukaan horisontal/miring.



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Stratal Termination Sequence Boundary (SB) toplap



onlap



onlap downlap



Erosional Truncation Sequence Boundary (SB)



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Downlap Surface



Apparent Truncation



Asosiasi Seimik Fasies



Basin



Slope



Intraslope Basin



Slope/shelf Break



Shelf



Physiographic Areal/ Seismic Refelction Characters



mound



sheet drape



hummocky



concordant



discontinuous



continuous



discontinuous



variable



moderate to high



variable



Upper Reflection Terminations



onlap



concordant



truncations&onlap



toplap



toplap & truncation



local toplap



Lower Reflection Terminations



bidirectional downlap



some onlap



random downlap



downlap



downlap



local downlap



External Form Internal configuration Reflection Continuity Reflection Amplitude



chaotic basin-fill slope front fill chaoticclinoform hummocky



apparent



wedge



tabular



divergent



concordant



continuous



continuous



continuous



moderate to high



moderate



moderate to high



(Mitchum et al., 1977)



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Horizontal



Parallel



CONFIGURATION REFLECTION



Inclined Undulating Clinoform



Sub-parallel



Regular Migrating Irregular



Divergent/Convergent Angular



INTERNAL REFLECTION CHARACTER



Lenticular



Discordant



Contorted Hummocky Chaotic



Reflection Free Continuous REFLECTION CONTINUITY



Discontinuous Variable High



REFLECTION AMPLITUDE



Moderate Low



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Reflection Configuration: Paralel & Subparalel HORIZONTAL



REGULAR MIGRATING



SUBPARALLEL



INCLINED



PARALLEL



UNDULATING



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IRREGULAR



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Parallel & Sub-Parallel • Parallel and Sub-Parallel : Stable basin plain, Subsiding shelf: Even & Wavy • Divergent : variation in the rate of deposition, progressive tilting of depositional surface



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Reflection Configuration: Clinoform



SIGMOID



CLINOFORM



OBLIQUE



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SHINGLED



PARALLEL



Clinoform • Sigmoid : low sediment suplay, relatively rapid subsidence, rapid rise in sea level. • Oblique : progradation pattern, small channelfill configurations. • Shingled : prograding into shallow water • Parallel : progradation pattern



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Reflection Configuration: Discordant ANGULAR



LENTICULAR



CONTORTED



DISCORDANT



HUMMOCKY



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CHAOTIC



Discordant • Hummocky : pro delta, inter-delta; shallow marine • Chaotic : slump structure, cut-and-fill channel complexes, highly faulted, folded, contorted zones • Contorted : slump structure • Angular & Lenticular : Large cross bedding Eni Indonesia



Reflection free • • • • • •



Homogeneous shales, sanndstone etc., Nonstratified Highly contorted Steeply dipping lithologic unit Large igneous masses Salt features



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Reflection Configuration



FREE/ TRANSPARENT DIVERGENT/CONVERGENT



DISCONTINUOUS



DISCONTINUOUS



REFLECTION CONTINUITY



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CONTINUOUS



Geometry (3D forms) BENTUK FACIES (2-D)



UNIFORM



WEDGE



CONVEX UPWARD



CONVEX DOWNWARD



DOUBLY CONVEX



SHEET WEDGING



MOUND



UNIT FASIES (3-D )



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LENS



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Terminasi Refleksi • (Te) Truncation adalah terminai lateral suatu lapisan akibat terpotong dari batas pengendapan aslinya. • (O) Onlap adalah baselap dimana lapisan yang awalnya horisontal laps-out pada permukaan yang mulanya miring atau lapisan yang awalnya miring laps-out updip pada lapisan yang lebih miring. • (D) Downlap adalah baselap dimana lapisan yang awalnya miring terminates downdip pada bidang yang awalnya horisontal atau miring. • (T) Toplap adalah lapout pada batas atas sekuen pengendapan. Toplap mencerminkan nondepositional hiatus sedang erosional trunction mencerminkan bidang erosi. • (C) Concordance dapat terlihat pada batas atas dan bawah sekuen. Pada bagian atas hubungan yang konkordan dapat dikenali dari kesejajaran lapisan dengan lapisan di bawahnya yang pada awalnya horisontal, miring atai tidak teratur.



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Jenis dan notasi ABC untuk konfigurasi internal sekuen seismik adalah : • Paralel (P), subparalel (Sp), divergent (D), chaotic (c), reflection-free(Rf), mounded (M), sigmoid (S), oblique (Ob), comples sigmoidoblique (SO),shingled (Sh),, hummocky clinoforms (HC), Even (E), Wavy (W), Regular (R), Irregular (IR), Uniform (U), Variable (V), Draped (Dr), Lenticular (L), Disrupted (D), Contorted (Co). Eni Indonesia



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Model Sekuen Stratigrafi •Sekuen stratigrafi adalah studi stratigrafi yang berhubungan dengan kerangka waktu pengendapan dalam kaitannya perubahan siklus muka laut (global/regional) . •Setiap sekuen pengendapan terdiri dari perulangan perlapisan yang dibatasi oleh permukaan erosi (UC) atau hiatus atau permukaan yang selaras (C) (Van Wagoner et.al., 1987). •Sekuen dibatasi secara regional oleh ketidakselarasan (UC) atau permukaan keselarasan (C) (Mitchum et.al., 1977). •Elemen penting dalam menentukan pola-pola sekuen stratigrafi adalah shelf/slope break.



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Sequence Stratigraphy Diagram SMST (Shelf Margin Systems Sract) HST (Highstand Systems Tract) SB.2 (Sequence Boundary 2)



SB.1 (Sequence Boundary 1)



TST (Transgressive Systems Tract) MFS (Maximum Flooding Surface) PGC/LSW (Prograding Complex/ Lowstand Wedge) SFC (Slope Fan Complex) BFF (Basin Floor Fan)



Vail et al, 1987



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