Quantitative Analysis of Carbonate Facies and Depositional Environment Characterization in Syn-Drifting Miocene Carbonates Reservoir of Banggai Basin; Case Study in Collision Zone Between Sula Spur and Sulawesi North Arm Volcanic Arc
Eastern Indonesia consist of a considerably extensive carbonate development which derived from restricted shallow water buildups or even open shelf carbonates. The tectonic controls are followed by growth of carbonates becomes the great interest to carbonate study in Eastern Indonesia. Research area is located in collision zone between Sula Spur and Sulawesi North Arm volcanic arc which happened in Neogene time. The first contact of the Sula Spur and the Asian margin was soon after 25 Ma in north Sulawesi. The embayment was surrounded by a passive continental margin and the Sula Spur was about to make contact with the Sulawesi North Arm volcanic arc marking the beginning of collision of Australia and SE Asia. Subduction rollback began at about 15 Ma into the Jurassic Banda Embayment causing extension of the Sula Spur (Hall, 2012). The extension of Sula Spur was followed by development of two recognized carbonate Formation in the research area, which are platform and reefal carbonates of Minahaki and Mantawa Formation. Regional geology data, core sample data, sidewall core, and routine core analysis were provided to accomplish this research. The best method to be adopted would be the integrated core analysis. In such a method the integrated approach was performed by maximizing the contribution of all available data and information to ensure that all aspects of interpretation are considered accordingly. The integrated core analysis that had been performed including core description, petrography analysis, and lithofacies analysis. After done with integrated core analysis, the research continues by classifying facies and depositional environment. Two main carbonate facies had been identified across the area, which are the organic buildup facies and deep shelf margin facies. The deep shelf margin facies is predominantly consists of muddy wackestone/packstone facies with unsignificant porosity development. The organic build-up facies consists of Grainstone/Floatstone facies with more typical of reefal organism such as coral growth. The deposition of downslope distal facies consists of several coral-algal fragment was also developed adjacent to the area where reefal buildup grows. The grainstone/floatstone facies is interpreted to be a lithological characteristic which develops in the northern part of this research area. It is generally reflected as carbonate organic buildup facies association of Mantawa Formation. However, at southern structure, the lithological characteristics were changed to planthonic globigerinids wackestone-packstone facies which represented the deep shelf margin facies environments of Minahaki Formation. From biostratigraphy examination, the depositional environment ranging from Shelf Lagoon to Organic Buildup Facies for northern structure and Foreslope to Deep Shelf Margin Facies for southern structure. Most of the porosity in buildup facies are secondary vuggy and mouldic pore type of leached coral-algal framework, while in deep shelf facies are fracture and vuggy porosities. The difference on depositional environment from landward to basinward is shown by the increasing thickness of Mantawa reef buildup from NE to SW. Transgression related with relative sea level rise in the Late Miocene time resulted to shutdown the development of Mantawa reef buildup carbonate and subsequently had changed the facies succession into more marine sediments. This Research highlights the quantitative approach of characterizing carbonate facies and depositional environment in complex tectonic regime, which resulting two different main facies that deposited during syn-drifting until collision.
AAPG Datapages/Search and Discovery Article #90336 ©2018 AAPG Asia Pacific Region, The 4th AAPG/EAGE/MGS Myanmar Oil and Gas Conference, Myanmar: A Global Oil and Gas Hotspot: Unleashing the Petroleum Systems Potential, Yangon, Myanmar, November 13-15, 2018