Earth Sciences Seminar: Dr Mark Bunch

Abstract

Draining the shelf

The now submerged continental shelf of the Gippsland Basin records a terrestrial drainage system active during the latest ice age.  An integrated study comprising interpretations of sedimentological and geophysical surveys produced a map of the Pleistocene barrier bars and drainage channels in 2003.  These features are now enhanced by interpretation of 3D seismic survey data. 

The channel system is distributed as the ‘negative’ of petroleum field areas, limiting the opportunity for ‘ground truth’. This leads to two hypotheses: ongoing structural inversion of existing petroleum traps at depth acted to ‘push’ channels away, or; intervening zones of relatively high differential compaction subsidence acted to ‘pull’ channels towards.

No evidence has been found to confirm the former. Regarding the latter, the loci of drainage channels appear to correspond well with regions of the thickest post-Eocene stratigraphy.  This suggests underlying differential compaction has acted to anchor lowstand drainage over time.