Henry W. Posamentier¹

(1) Veritas Exploration Service, Calgary, AB

ABSTRACT: Mid-Shelf Lowstand and Transgressive Systems Tract Deposits of Southeast Asia: Examples from Offshore Java and Malaysia

Lowstand and transgressive systems tract deposits on the northwest Java shelf are documented based on an integrated analysis of 3D seismic, shalllow-penetration seismic data, well-log, and conventional core data. These data show that incised valley systems formed during sea-level lowstand extend in excess of 200-500 km inboard of the shelf margin. They range from 2-5 km wide and up to 40 m deep. These incised valleys seem to have formed during only the lowest of lowstand times during relatively short intervals. The distinguishing attribute of these features are distinctive incised dendritic drainage networks, tributary to principal trunk incised valleys. Other lowstand alluvial systems, developed during lesser sea-level lowstands, are not incised and lack tributary drainage networks. Because of low wave energy in this area, and because of rapid transgression, lowstand alluvial deposits appear to be well preserved, and overlain primarily by transgressive muds.

In addition to mud-prone, upper incised valley fill, deposits of transgressive systems tracts appear to be dominated in this area by shelf ridges. These deposits are interpreted to have been formed by tidal current erosion of the substrate and subsequent re-deposition of these sediments into shelf ridges. The shelf ridge deposits commonly overlie ravinement surfaces and are sand prone. These features range from 0.5-4 km wide, 3-10+ km long and up to 15 m thick, and are asymmetric and markedly linear. Their asymmetry suggests that these features have migrated along the sea floor, likely over a transgressive or flooding surface. They have been observed as isolated bodies as well as in clusters.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado