INTEGRATED SEDIMENTOLOGICAL ANALYSIS: THE EOCENE OF THE BASS BASIN

Abstract

The Eocene section in the Bass Basin comprises the upper part of the siliciclastic coal- bearing Eastern View Group and the thin but regionally extensive Demons Bluff Formation.

An integrated sedimentological study utilising core analysis, log analysis, palynology, coal maceral studies and geochemistry, together with sequence stratigraphy, has been used to determine Eocene sedimentation styles in the basin.

The most likely environment during deposition of the Upper Eastern View Group was a tide- dominated delta consisting of a complex mixture of distributary channels, strandline sand bars, peat swamps and shallow lagoons, the sedimentary successions resulting from a complex interplay between sea- level, tectonics and sediment supply. A major coal- forming episode occurring in the interval 48- 51.5 m.y. is related to oscillations of sea- level following a major highstand.

A locally developed progradational unit, Konkon Sandstone, comprising two sandy parasequences separated by a very thin shaly interval is recognised at the top of the Eastern View Group in the northwestern sector of the basin and reaches a maximum thickness of 140 m.

The Demons Bluff Formation is a diachronous unit consisting dominantly of siltstone probably deposited in a barred basin with anaerobic conditions.