Murray Basin
Encyclopedia
The Murray Basin is a Cenozoic
sedimentary basin
in south eastern Australia. The basin is only shallow, but extends into New South Wales, Victoria and South Australia. It takes its name from the Murray River
which traverses the Basin from east to west.
After Australia separated from Antarctica the Murray Basin was formed. The basin floor only subsided slowly over time. The basin became filled with up to 600 m of sediments during the Cenozoic.
From Paleocene
to Eocene
the western side was flooded with sea water and deposited the Warina sand. The sea withdrew and later in the Eocene silt and clay of the Olney Formation were deposited. One minor sea incursion resulted in late Eocene resulted in the Buccleuch Formation in South Australia. The is group of deposits is termed the Renmark Group and was earlier known as Knight Group.
The sea level rose again in Late Oligocene
to mid Miocene forming the Murray Group of sediments, with marl
and limestone
in the deeper locations, and the Geera Clay in the shallow waters. The rock units formed in the deeper water included the Ettric Formation, the Winnanbool Formation and the Mannum Formation limestone with Gambier Limestone in South Australia. When sea level fell again in mid Miocene the deposited Geera clay and Olney Formation moved westward over the limestone.
During Upper Miocene to Pliocene
the sea rose and fell several times. The first sea rise formed the Murravian Gulf and resulted in clay and marl in the west called the Bookpurnong Formation, and Calivil Formation river and lake sand in the east. When the sea retreated in Early Pliocene, the Loxton Sands also informally known as Loxton-Parilla Sands were formed on the beach on the shore of the emergent land. Locally heavy minerals
have been concentrated by wave action including rutile
zircon
and ilmenite
forming economic mining opportunities.
The Murray River
became dammed by uplift of over 250 meters in the Grampians
in Victoria during the Pleistocene
about 2.5 Mya. The dam formed Lake Bungunnia, which reached 40000 km2 and deposited the Blanchetown Clay therein. Higher rainfall of at least 500 mm per year kept the lake filled at first, but during later times rainfall was insufficient and saline lakes formed, depositing dolomite. Even today some saline lakes remain as a remanent of the vast lake. The Murray River carved out a new path to the sea via Murray Bridge replacing its previous exit at Portland, Victoria
. The lake was gone by about 0.7 Mya.
The Pooraka Formation formed in the north west due to increased erosion resulting in colluvium
depositing. The colluvium forms fans, cones and scree slopes, and often contains clay and breccia. In the flat areas the Shepparton Formation also resulted from river deposits of floodplain clay.
Most of the existing surface dates from Quaternary
period. The river deposits from the east have been progressively overlaying the marine deposits further west, as the shore line receded. Within the Pleistocene
deposits are three layers of sand that are aquifers, deposited during higher rainfall periods of the interglacial
s. The floodplain deposits from the current rivers are the Coonambidgal Formation, however this term is used informally for the older Pleistocene flood deposits as well. During the dryer glacial periods the area was arid.
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
sedimentary basin
Sedimentary basin
The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification...
in south eastern Australia. The basin is only shallow, but extends into New South Wales, Victoria and South Australia. It takes its name from the Murray River
Murray River
The Murray River is Australia's longest river. At in length, the Murray rises in the Australian Alps, draining the western side of Australia's highest mountains and, for most of its length, meanders across Australia's inland plains, forming the border between New South Wales and Victoria as it...
which traverses the Basin from east to west.
After Australia separated from Antarctica the Murray Basin was formed. The basin floor only subsided slowly over time. The basin became filled with up to 600 m of sediments during the Cenozoic.
From Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
to Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
the western side was flooded with sea water and deposited the Warina sand. The sea withdrew and later in the Eocene silt and clay of the Olney Formation were deposited. One minor sea incursion resulted in late Eocene resulted in the Buccleuch Formation in South Australia. The is group of deposits is termed the Renmark Group and was earlier known as Knight Group.
The sea level rose again in Late Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
to mid Miocene forming the Murray Group of sediments, with marl
Marl
Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...
and limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
in the deeper locations, and the Geera Clay in the shallow waters. The rock units formed in the deeper water included the Ettric Formation, the Winnanbool Formation and the Mannum Formation limestone with Gambier Limestone in South Australia. When sea level fell again in mid Miocene the deposited Geera clay and Olney Formation moved westward over the limestone.
During Upper Miocene to Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
the sea rose and fell several times. The first sea rise formed the Murravian Gulf and resulted in clay and marl in the west called the Bookpurnong Formation, and Calivil Formation river and lake sand in the east. When the sea retreated in Early Pliocene, the Loxton Sands also informally known as Loxton-Parilla Sands were formed on the beach on the shore of the emergent land. Locally heavy minerals
Heavy mineral sands ore deposits
Heavy mineral sands are a class of ore deposit which is an important source of zirconium, titanium, thorium, tungsten, rare earth elements, the industrial minerals diamond, sapphire, garnet, and occasionally precious metals or gemstones....
have been concentrated by wave action including rutile
Rutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...
zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
and ilmenite
Ilmenite
Ilmenite is a weakly magnetic titanium-iron oxide mineral which is iron-black or steel-gray. It is a crystalline iron titanium oxide . It crystallizes in the trigonal system, and it has the same crystal structure as corundum and hematite....
forming economic mining opportunities.
The Murray River
Murray River
The Murray River is Australia's longest river. At in length, the Murray rises in the Australian Alps, draining the western side of Australia's highest mountains and, for most of its length, meanders across Australia's inland plains, forming the border between New South Wales and Victoria as it...
became dammed by uplift of over 250 meters in the Grampians
The Grampians
The Grampians are a set of hills in the Nelson region of New Zealand. Frequented by locals and tourists alike, they are covered in a myriad of tracks ranging from leisurely strolls to relatively taxing steep inclines.-Areas of interest:...
in Victoria during the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
about 2.5 Mya. The dam formed Lake Bungunnia, which reached 40000 km2 and deposited the Blanchetown Clay therein. Higher rainfall of at least 500 mm per year kept the lake filled at first, but during later times rainfall was insufficient and saline lakes formed, depositing dolomite. Even today some saline lakes remain as a remanent of the vast lake. The Murray River carved out a new path to the sea via Murray Bridge replacing its previous exit at Portland, Victoria
Portland, Victoria
The city of Portland is the oldest European settlement in what is now the state of Victoria, Australia. It is the main urban centre of the Shire of Glenelg. It is located on Portland Bay.-History:...
. The lake was gone by about 0.7 Mya.
The Pooraka Formation formed in the north west due to increased erosion resulting in colluvium
Colluvium
Colluvium is the name for loose bodies of sediment that have been deposited or built up at the bottom of a low-grade slope or against a barrier on that slope, transported by gravity. The deposits that collect at the foot of a steep slope or cliff are also known by the same name. Colluvium often...
depositing. The colluvium forms fans, cones and scree slopes, and often contains clay and breccia. In the flat areas the Shepparton Formation also resulted from river deposits of floodplain clay.
Most of the existing surface dates from Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
period. The river deposits from the east have been progressively overlaying the marine deposits further west, as the shore line receded. Within the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
deposits are three layers of sand that are aquifers, deposited during higher rainfall periods of the interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...
s. The floodplain deposits from the current rivers are the Coonambidgal Formation, however this term is used informally for the older Pleistocene flood deposits as well. During the dryer glacial periods the area was arid.