Effects of Syn-depositional Tectonics on Platform Geometry and Reservoir Characters in Miocene Carbonate Platforms of Central Luconia, Sarawak

摘要

It is commonly assumed that the Miocene carbonate platforms of Central Luconia, Sarawak developed and grew on a stable substratum. This paper documents evidence of syn-depositional tectonic movements in the ‘Mega Platform’ in the northern part of the Central Luconia Basin. Detailed 3D seismic interpretation techniques consisting of spectral decomposition, acoustic impedance opacity rendering, and structurally oriented semblance filtering were used to better constrain geological processes affecting, controlling and modifying the evolution and demise of the platform. Syn-depsositional tectonic movements impacting stratigraphy architecture at a scale sufficient to fragment or break up a platform occurred during platform growth. Depending on the magnitude of the movements, carbonate platforms responded in different ways: (1) Platform fragmentation and permanent separation of part of the platform; this happened in the southern part of the mega- platform early on in its growth history. Two smaller platforms separated from the main one and continued growing as separate entities. (2) Step subsidence and infill of new accommodation space; part of a platform subsides but the surviving part generates sufficient sediment volume to fill in the new accommodation space through progradation. A flat platform is eventually restored over the whole or part of the initial platform surface. (3) Step subsidence and contraction of a platform; part of a platform subsides but the surviving platform does not have the capacity to produce the sediment volume required to fill in the new accommodation space. The down-stepped part of the platform eventually drowns. Faulting not only created topography as a template for the initiation of carbonate platform deposition but also as pedestals for the localization of backstepped platforms. Cessation of syn-depositional faulting may create tectonic quiescence period that instigated progradation as a result of deceleration of accommodation-space production.