COALESCENCE OF ISOLATED CARBONATE PLATFORMS

Isolated carbonate platforms are common in various tectonic settings, especially where fault-controlled bathymetry or compactional highs are rapidly flooded. Isolated platforms may coalesce and become larger composite platforms, especially where: 1) initial platforms are closely spaced, 2) initial bathymetric profiles or long-term aggradation along platform margins does not produce steep profiles with over several hundred meters of relief, 3) adjacent platforms are aligned with paleowind directions, 4) sediment supply from extra-platform sources is high, and 5) carbonate-sediment production is high, but long-term accumulation is low within platform interiors, so that much sediment can be delivered to slope and basin-floor environments.

The growth histories of middle to upper Miocene isolated buildups in the Wonocolo Formation, North Madura area, Indonesian backarc, provide insight into conditions that are conducive to platform coalescence. Five successive growth phases can be identified in numerous Wonocolo buildups across the North Madura study area. Platforms in western parts of the study area record a complex history of coalescence, which reflects their closer spacing and upwind location. In contrast, eastern platforms did not coalesce into larger composite platforms because they were farther apart, were not aligned with paleowind direction, and experienced slightly faster subsidence rates. Volcaniclastic sediment and ash fall from the Indonesian arc may have helped to fill basin-floor settings between individual Wonocolo buildups, which assisted progradation and coalescence of some platforms. For the Wonocolo buildups, there also is no clear relationship between platform-top area or the tendency for platforms to coalesce.