BSR occurrence along the Sunda margin: evidence from seismic data

Abstract

The occurrence of bottom simulating reflections (BSRs) along the Sunda margin off Indonesia is investigated for the first time using seismic reflection data from three surveys conducted across the subduction zone and the forearc domain off southern Sumatra to central Java. BSRs commonly concur with the base of the thermodynamically stable hydrate zone and are thus an important indicator for gas hydrates. Along the Sunda Arc, BSR occurrence is restricted to the forearc domain in regions likely to represent a focussing of fluid flow, such as the forearc basin slopes or anticline structures. Dissociation of gas hydrates due to uplift along anticline structures may be an important secondary cause of BSR formation. The absence of BSRs in the forearc basin center despite continuous sedimentation to ensure carbon supply may be related to the very high sedimentation rate (>0.4 km/Ma) which causes unused carbon to pass through the stability zone even for a high rate constant of methanogenesis. In addition, the interbedding of low- and high-permeability layers renders fluid flow across layering ineffective. No BSR phases could be detected along the accretionary prism or the outer high, although the P– T regime would allow a potential BSR to lie within the accretionary sedimentary column.