A high-resolution, two-dimensional seismic survey covering 7500 km² provides an unprecedented view of the evolution of a MiocenePliocene carbonate platform in the East NatunaSarawak Sea, Indonesia. The Segitiga Platform (1400 km²) contains Terumbu Formation carbonate strata as much as 1800 m thick that were deposited in platform interior, reef and shoal margin, and slope to basin environments.

The Segitiga Platform was subdivided into 12 seismic sequences that demonstrate a history of (1) initial isolation, (2) progradation and coalescence, (3) backstepping and shrinkage, and (4) terminal drowning. Interpretations of seismic facies maps for each sequence were used to help illustrate platform history. These seismic facies maps indicate that the Segitiga Platform originated as three smaller platforms on extensional fault-block highs. Deep intraplatform seaways separated these smaller platforms. Progradation of shallow-water carbonates filled the seaways during a phase of coalescence and the three platforms were amalgamated to form a merged composite platform (1400 km²; middleupper Miocene). A rapid relative rise in sea level at the end of Miocene time caused a major backstepping of the carbonate margins (and a concomitant drowning of the adjacent Natuna field carbonate platform to the east) resulting in a platform of greatly reduced size (600 km²) during the lower Pliocene. Rapid subsidence, combined with an eustatic rise at the end of the early Pliocene, caused terminal drowning of the Segitiga Platform. The platform was buried by younger siliciclastics of the Muda Formation.

Eustatic sea level change controlled the timing of sequence-boundary formation, but structural movements modified internal sequence character and facies distribution. Faulting created topography that acted as templates for the initiation of carbonate platform deposition and provided pedestals for the localization of backstepped platforms. Cessation of faulting may have instigated progradation of the platform resulting from the deceleration of accommodation-space production. Regional subsidence may have controlled the location and extent of platform backstepping. Geographic variability in sequence stacking of coeval platform margins is observed over relatively short distances. Progradation is most strongly developed on the leeward side of the platform, but increased accommodation resulting from the rapid local subsidence or changing oceanographic currents also influenced the direction and magnitude of progradation.