New 2D seismic data acquired in the Mentelle Basin by Geoscience Australia in 2008-09 has been used for a seismic facies study of the post-rift succession. The Mentelle Basin is a large deep to ultra deep-water, frontier basin located on Australia's southwestern margin about 200 km southwest of Perth. The study focused on the post-rift sequences deposited following the breakup between Australia and Greater India. Stratigraphic wells DSDP 258 and DSDP 264 provide age and lithological constraints on the upper portion of the post-rift succession down to mid-Albian strata. The depositional environment and lithology of the older sequences are based on analysis of the seismic facies, stratal geometries and comparisons to the age equivalent units in the south Perth Basin.

Fourteen seismic facies were identified based on reflection continuity, amplitude and frequency, internal reflection configuration and external geometries. They range from high continuity, high amplitude, parallel sheet facies to low continuity, low amplitude, parallel, subparallel and chaotic sheet, wedge and basin fill facies. Channel and channel fill features are common in several facies along with a mounded facies (probably contourite) and its associated ponded turbidite fill. A progradational sigmoidal to oblique wedge facies occurs at several stratigraphic levels in the section. A chaotic mound facies, probably comprising debrite deposits, has a localised distribution.

During the Valanginian to Hauterivian breakup on the south‐western margin, the Mentelle Basin was

characterised by extensive syn‐depositional volcanism. Sedimentary packages comprising interbedded marine

sands and silty clays were deposited predominantly in the western Mentelle Basin surrounded by paleo‐highs

or areas of non‐deposition. Marine‐deltaic sediments prograded from the east and south into the main post‐

rift depocentre. Post‐breakup thermal subsidence began in the Hauterivian with sedimentation dominated by

a widespread high continuity, parallel sheet facies. From the Aptian through to Campanian, considerable

accommodation space was created in the western Mentelle Basin. Sediments deposited during this period are

characterised by several parallel to divergent sheet facies in the eastern Mentelle Basin and to the south these

grade into a time‐equivalent prograding deltaic wedge facies. A regionally extensive, shelf‐slope wedge facies

occurs to the west of the Margaret Hinge Zone which separates the shallow‐ and deep‐water parts of the

Mentelle Basin. Sedimentation rates in the Albian were very high (>45 m/my) with an intra‐slope basin

developing over the western Mentelle Basin. The Albian section is characterised by an extensive basin‐fill

facies occurring throughout the western Mentelle Basin and in the northern part of the eastern Mentelle

Basin. These two facies both comprise deep marine black mudstones, recovered by DSDP 258.

Towards the end of the Albian period an open marine environment was established across the Mentelle Basin

and clastic sedimentation switched to carbonate sedimentation with the deposition of Turonian and

Cenomanian chalks and Santonian to Campanian chalks and limestone. In the Middle Eocene, the margin of

the Mentelle Basin collapsed resulting in flexure along the Margaret Hinge Zone and rapid deepening of the

western Mentelle depocentre. The deep marine carbonate sedimentary section corresponding to this period is

often condensed, discontinuous and extensively eroded. It is characterised by several extensive channelised

sheet facies in the eastern Mentelle Basin and channelised sheet and mound facies in the western Mentelle

Basin. Carbonate chalk and ooze slump deposits just west of the Margaret Hinge Zone are probably associated

with Eocene fault reactivation and margin collapse in the region.

Seismic facies analysis of the post‐rift sequences in the Mentelle Basin has contributed to a better

understanding of the depositional history and sedimentation processes in the region, as well as provided

additional constraints on regional and local tectonic events.

Abstract presented at the 2010 Australian Earth Science Convention (AESC).