Prerift and synrift sedimentation during early fault segmentation of a Tertiary carbonate platform, Indonesia

Eocene carbonate deposits of the Barru area, Sulawesi, Indonesia, provide a rare insight into sedimentation prior to and during propagation of normal faults to the surface. Three main successions; late prerift, latest prerift /earliest synrift and synrift, are characterised by distinctive facies asso ciations and sequence development. Shallow water foraminiferal shears and i ntervening lower energy depositional environments occurred during the late prerift in areas which latter formed footwall highs and hangingwall depocen tres, respectively. During the latest prerift/earliest synrift, shallow wat er shelves deepened laterally into slope environments in developing hanging wall depocentres. In both these sequences, sections in developing hangingwa ll areas are thickest, deepen up-section and thin laterally towards growing footwall highs. Active faulting resulted in rapid drowning of hangingwall depocentres and massive reworking of material derived from collapse of the platform margin and adjacent shallow water/emergent footwall highs. Differential subsidence, controlling water depths and accommodation space, types of carbonate producers and active faulting were the main factors affe cting depositional environments and facies distributions. Carbonate produce rs are extremely sensitive indicators of depositional water depth and energ y, hence rapid lateral and vertical facies variations in the Barru area pro vide quantifiable insight into environmental changes prior to and during ac tive faulting. (C) 1999 Elsevier Science Ltd. All rights reserved.