Murray Basin
The Murray Basin is a shallow sediment basin in south-eastern Australia. It stretches across parts of New South Wales, Victoria and South Australia and is named after the Murray River that runs through it.
How it formed: One idea is that a sinking slab of oceanic crust to the north pulled the land down, creating a hollow that became the basin. This slab broke off and was pushed beneath the Australian Plate as it moved north. The sinking slab left a trace in the Earth's mantle, and the basin moved slowly south over the last 50 million years. Some scientists think the basin will keep moving south and may eventually disappear under the Southern Ocean. Computer models suggest the surface could be pulled down by about 200 meters and spread over a wide area.
The basin began after Australia separated from Antarctica and slowly sank to form the basin floor. It was gradually filled with sediments during the Cenozoic Era, up to about 600 meters thick.
Rock layers and seas: From the Paleocene to the Eocene, western areas were flooded and deposited sands like the Warina Sand. Later, silt and clay were laid down (Olney Formation). A small sea incursion in the Late Eocene created the Buccleuch Formation. The Renmark Group (formerly Knight Group) includes several sequences. In the Late Oligocene to mid Miocene, the Murray Group formed with marl and limestone in deeper waters and Geera Clay in shallower areas. Deeper-water rocks include the Ettric, Winnanbool and Mannum formations in South Australia, with Gambier Limestone in the south. When sea levels changed, some deposits moved west over other rocks.
From the Upper Miocene to the Pliocene, the sea rose and fell several times. The western side formed the Murravian Gulf with clay and marl (Bookpurnong Formation), while the east developed Calivil Formation river and lake sands. As the sea retreated in the Early Pliocene, the Loxton Sands formed along the emerging coastline. Some heavy minerals like rutile, zircon and ilmenite are concentrated by waves and are of economic interest.
Pleistocene events and the river’s path: In the Pleistocene, uplift in the Grampians (Victoria) dammed the Murray River, creating Lake Bungunnia, which covered about 40,000 square kilometres and deposited Blanchetown Clay. Heavy rainfall kept the lake full at first, but later drier conditions led to saline lakes and dolomite deposits. The Murray River cut a new route to the sea through Murray Bridge, replacing its old exit at Portland. The lake disappeared around 0.7 million years ago.
Other features: The Pooraka Formation in the northwest formed from erosion and deposited colluvium, including fans and scree slopes. In the flat areas, floodplain clays created the Shepparton Formation. Much of the surface today comes from the Quaternary period. River deposits from the east gradually covered older western marine deposits as shorelines moved inland. The Pleistocene also includes three sand aquifer layers.
This page was last edited on 2 February 2026, at 20:28 (CET).