Henry W. Posamentier1
(1) Atlantic Richfield Indonesia, Plano, TX
Abstract: Seismic and lithologic expression of miocene shelf ridges on the south Java sea shelf
Numerous shelf ridge systems have been imaged using 3D seismic volumes across the South Java Sea shelf offshore Indonesia. Individual shelf ridges imaged range from 2-15 m thick, 0.5 to 5 km wide, and 3-20+ km long. These ridges are observed in isolation or in clusters across significant parts of the shelf at several levels within the Miocene. Borehole information, consisting of logs and cores, indicates that these bodies are sand rich. They commonly are characterized by a sharp, well-defined leading edge, and a gradational, poorly-defined trailing edge. In cross-profile these ridges are asymmetric, with the thickest sections close to the leading edge. Log profiles suggest a coarsening-upward lithology closest to the leading edge and a fining-upward lithology towards the trailing edge. The shelf ridges were imaged on 3D seismic data using a combination of seismic reflection and seismic interval attributes. Detailed analysis of the seismic attributes of the ridges suggests the presence of superimposed sand waves that were migrating obliquely towards the leading edge, suggestive of a transport direction. Where the shelf ridges are observed to have migrated across a mud-rich substrate, there is a good possibility for stratigraphic trap assist at the leading edge of these features. These shelf ridge systems are interpreted to have formed as palimpsest deposits on the shelf, subsequent to marine transgression across broad embayments. The sediments comprising these ridges are thought to constitute reworked estuarine mouth sand-prone deposits. As such, they constitute a significant part of the transgressive systems tract in this area.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana