Back
to Top

 
  • Share this page on Facebook
  • Print this page

Late Jurassic to the Present Day

Late Jurassic to Cretaceous (ca. 150-65 Ma): break-up of Gondwana

 Paleocene Pebble Point Formation unconformably overlying Cretaceous Otway Group at Moonlight Head,Otway Basin.

Paleocene Pebble Point Formation unconformably overlying Cretaceous Otway Group at Moonlight Head,Otway Basin.

The Gippsland, Bass and Otway basins form part of the Southern Rift System, which formed as a result of rifting and continental breakup of the Australian and Antarctic continents. During the late Jurassic – Early Cretaceous (150–120 Ma) early rift-fill lacustrine and fluvial sediments and minor volcanics (Casterton Formation and Crayfish Group) were deposited in a series of half-grabens formed in the Otway, and possibly Bass, basins as part of the Gondwana breakup. Rifting and associated sag continued through to the end of the Albian (95Ma) resulting in a thick, volcaniclastic-rich sequence of nonmarine greywackes, mudstones and minor coals (Eumeralla Formation and Strzelecki Group). These fluvial successions are today exposed in several basement highs (Otway and Strzelecki ranges).


With the onset of sea-floor spreading between Australia and Antarctica during the Late Cretaceous Cenomanian, the terrestrial to marginal marine Sherbrook Group was deposited in the Otway  Basin. This contrasts with the lacustrine rift-fill sediments of the Emperor and Golden Beach subgroups in the Gippsland Basin, associated with the development of the Tasman Sea rift during the Cenomanian to Early Campanian (95–80 Ma). The Bass Basin persisted as a failed rift, with nonmarine sedimentation continuing until the Eocene (Eastern View Group).


 Cretaceous-Paleogene unconformity at Pebble Point, Otway Basin.

Cretaceous-Paleogene unconformity at Pebble Point, Otway Basin.

At the basin margins, subsidence was balanced by major uplift of the coastal hinterland represented by the Great Dividing Range in Victoria. The area to the north east of the range was not uplifted, but became the Murray Basin and was filled with mainly marine sediments (Millewa Group).


Palaeocene to Recent (65 Ma-present day): paralic sedimentation, stream incision and basaltic volcanism

The Late Cretaceous uplift began a cycle of incision and lateral erosion that continues to the present day. Sediments eroded from the highlands were transported onto the wide coastal plain as well as further offshore. The coastal plain environment of the Gippsland Basin included large swamps and marshes, parts of which were later converted into coal beds that are regarded as the main source rocks for the basin’s economic oil and gas accumulations. In the Latrobe  Valley, the geological and climatic conditions from the Eocene to the Miocene were favourable for the generation of extremely thick brown-coal measures (Latrobe Group). Marine clastic sedimentation continued in the Otway Basin (Wangerrip and Nirranda groups) until the Oligocene.


 Pleistocene dune rock overlying Miocene Port Campbell Limestone and Oligocene Gellibrand Marl at Gibsons Steps, Otway Basin.

Pleistocene dune rock overlying Miocene Port Campbell Limestone and Oligocene Gellibrand Marl at Gibsons Steps, Otway Basin.

From the early Oligocene onwards, deposition of marine siliciclastic sediments ceased in the offshore and was followed firstly by the accumulation of fine-grained clay-rich, then by prominently fossiliferous cool-water carbonates. Nonmarine sedimentation prevailed in the Murray Basin, becoming marine in the Oligocene. Episodes of tectonism have repeatedly modified the sedimentary pile of the southern basins into a complex structural system, reflecting the rift architecture of Victoria’s basins.


Within the last two million years small scale volcanic eruptions (Newer Volcanics) have had a major impact on the Victorian landscape. About 400 volcanoes have produced extensive basalt flows forming a thin veneer (generally less than 50m) covering much of western Victoria. The basalt plains consist of superimposed valley flows and volcanic centres with associated basaltic aprons.