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ABSTRACT: Seismic expression of Karst developed on Miocene-Lower Pliocene carbonate platform (Terumbu Limestone), East Natuna Sea, Indonesia

Martono, Dwi , Pertamina, Jakarta, Indonesia

Karst is distinct topography formed by meteoric dissolution of carbonate strata that is characterized by sink holes, caves, and subsurface drainage. Well developed karst topography is often associated with major sequence boundaries and may enhance porosity and permeability. Well developed karst topography is recognized on top of a thick carbonate platform (Middle Miocene-Lower Pliocene Terumbu Formation) in the East Natuna Sea. Major karsting on top of the platform indicates that a major relative fall in sea level exposed the platform prior to platform drowning and burial by deep-water siliciclastics of the Muda Formation. Karst is well developed over topographic high areas of the platform, especially on the backstepped Pliocene buildups. Seismic recognition criteria for karst include: 1) rugosity and termination of reflectors at the top of carbonate, 2) intraformation collapse and faulting, 3) seismic diffractions at the karst surface, 4) chaotic seismic facies at or below the karst surface, 5) sag of younger siliciclastics into collapse structures, 6) similar scale and geometry of karst features compatible with geologic analogs. Interpretation of regional 2D seismic data subdivided the platform into twelve seismic sequences. Seismic facies were qualitatively mapped for each sequence based on distinct seismic character and geometry. Seismic interval attributes were extracted for each sequence (amplitude and correlation coefficient) and can be used as a method to quickly and quantitatively map karst distribution for each sequence.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia