Seismic architecture of a Miocene isolated carbonate platform and associated off-platform strata (Central Luconia Province, offshore Malaysia)

摘要

Rather than being homogeneous and isotropic, many isolated carbonate platforms in the geologic record include internal heterogeneity and complex geometric relations with off-platform strata on their flanks. To better understand stratal architecture of a Miocene isolated platform (Central Luconia, offshore Malaysia), this study integrates core, log and seismic data, revealing stratal terminations and geometries that define several seismic stratigraphic units. A thick in the basal seismic unit, the initial deposits of the carbonate buildup, is 4-5 km across. This thick includes abrupt thinning to the west and east, with onlap onto its flanks, but continues outside of the survey area to the north and south. Above a mappable surface, a less extensive (2 x 5 km) seismic unit represents a backstepped isolated platform (Platform Stage 1). Across a pronounced normal fault on the east/southeast margin of the platform occur marked isochron and seismic character changes, with thicker carbonates on the downthrown (western) block. The northern and western margins are not faulted. A third seismic unit, representing a smaller, elongate (< 1 x 3 km), N-S trending carbonate platform (Platform Stage 2), reflects a second backstep. The top of this unit in core is associated with karst, suggesting subaerial exposure; the surface can be traced off the platform and across the fault, to an (upthrown) area with irregular amplitude and similarity, interpreted to represent karst. These strata and several other reflectors that dim and decrease loop duration away from the buildup ("wings") - sit atop one of a series of north-prograding clinoforms (siliciclastic "wedges"). In turn, two chronostratigraphically distinct wedges that onlap and thin away from the thick of Platform Stage 2 are interpreted to be carbonate (platform stages 3 and 4), and are onlapped by another succession of off-platform clinoforms (interpreted as siliciclastic). All of these strata are capped by another elongate (< 1 x 2 km) seismic unit (Platform Stage 5), before the platform is covered with siliciclastics.