Structural Style and Evolution of the Sumatran Forearc Basins

Proceedings, Indonesian Petroleum Association
Thirty-Fifth Annual Convention & Exhibition, May 2011

Structural Style and Evolution of the Sumatran Forearc Basins

M. Ma’ruf Mukti*, Satish C. Singh*, Nugroho D. Hananto*, Dibakar Ghosal*, Ian Deighton**
* Institut de Physique du Globe de Paris
** TGS

Abstract
In the last few years, there has been significant interest in hydrocarbon exploration in the Sumatran fore arc basins. Over ten thousand kilometers of seismic reflection data were acquired from Aceh Basin in NW to Enggano Basin in SE by TGS in 2008-2009, covering the full length of the Sumatran fore arc basins. These data were complemented by earthquake and tsunami studies funded by Western Geco, CGGVeritas and various academic institutions acquiring data (including deep seismic reflection, refraction, bathymetry, heat-flow) covering the whole subduction system, from the oceanic crust to the fore arc basin margins. While refraction data provide insight for large-scale crustal velocity structures, deep seismic reflection data of Western Geco and CGGVeritas provide precise positioning of the plate boundary and continental Moho, which is extremely important for understanding the basin evolution. Densely spaced TGS seismic profiles allow us to map the basement and important sedimentary horizons on a basin scale. The crust beneath the fore arc basin is thin (~20 km) and thickens towards Sumatra mainland. Fore arc basement architecture exhibits extensional structures and deposition of probably Late Eocene – Early Oligocene syn-rift sediments. Post-rift sediments may have been deposited in grabens and slopes during Late Oligocene – Early Miocene. These grabens exhibit transtensional structures. The inversion of old structures could be related to the transpressional strike-slip fault zone. This episode is followed by marked subsidence during Middle – Late Miocene, overprinting older depocenters. Traces of local tectonics are observed, indicating other factors contribute to deformation within the fore arc basins. For example, compression due to strike-slip faults can be observed within the Simeulue and Aceh Basins.Similar features can also be observed in the southern part of Mentawai Basin. Mud diapirism seems to be present in the fore arc basin and involve sedimentary units of Pliocene – Recent deposits. The deformation zone, previously interpreted as Mentawai strike-slip fault, may also be interpreted as backthrust development along re-activated old structures with minor strike-slip component and associated mud diapirism.

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