--> Wings and Wedges: Architecture of a Miocene Carbonate Buildup and Associated Basinal Strata: Central Luconia Province, Offshore Sarawak, Malaysia

AAPG ACE 2018

Datapages, Inc.Print this page

Wings and Wedges: Architecture of a Miocene Carbonate Buildup and Associated Basinal Strata: Central Luconia Province, Offshore Sarawak, Malaysia

Abstract

Cenozoic isolated carbonate platforms of Southeast Asia include more than two hundred Miocene equatorial buildups in the Central Luconia province alone. Although they form productive reservoirs, the aspects of stratal heterogeneity - external form and internal architecture - remain ambiguous. To explore seismic-scale stratal complexity, two cores and well log suites penetrate a Miocene carbonate buildup and associated basinal strata to provide calibration for interpretation of its seismic stratigraphy and architecture.

The data reveal a lower seismic unit with extent of at least 4-5 km across, with shelf margins exposed in part of the survey area. Above a regionally mappable surface, a less extensive (2 x 5 km) seismic unit represents a backstepped platform. Across a pronounced normal fault, this second platform stage includes marked isochron and seismic character changes, with thicker carbonates on the downthrown block. The east/southeast margin of the platform is defined by this fault, and is in turn onlapped by northward-thinning wedges, presumably siliciclastic, present only east of the fault. A third seismic unit, representing a smaller, elongate (< 1 x 3 km) carbonate platform, is onlapped by several distinct wedges that thin away from the buildup (likely carbonate), and which are in turn onlapped by northward-thinning (siliciclastic?) wedges in the basin. The major fault offsets these strata locally; the fault tip passes into folds with stratal terminations on the crest, suggesting syndepositional deformation. The succession is capped by another elongate (<1 x 2 km) seismic unit (a fourth platform stage) that appears to interfinger with adjacent basinal strata. A small (< 1 km2) pinnacle caps the succession before the platform is covered with siliciclastics.

Although step-wise backstepping is the most pronounced stratal motif, seismic-scale intra-carbonate architecture includes considerable geometric heterogeneity. Likewise, superposition and cross-cutting relations between buildup and basinal strata document that platform “wings” alternating with basin-fill wedges were deposited during overall platform growth, rather than post-dating the platforms. Beyond sea-level influences, stratal relations indicate a pronounced structural control on heterogeneity in both platform and basinal parts of the succession. The results demonstrate the complex controls on carbonate platform growth and interactions with basinal silciciclastics.