Clarence Moreton Basin
Encyclopedia
The Clarence Moreton Basin is a Mesozoic
sedimentary basin
on the easternmost part of the Australian continent. It is located in the far north east of the state of New South Wales around Lismore
and Grafton
and in the south east corner of Queensland
. It formed by oblique extension of the underlying Paleozoic New England Orogen basement. It consists of continental deposits, starting with a small amount of Triassic
coal beds, and then mostly Jurassic
and Cretaceous
sedimentary rocks. The basin covers 16000 square kilometers. The basin was named when the Clarence Basin (named after the Clarence River
and Moreton Basin in Queensland were proved to be one structure.
The first rocks in the Clarence Moreton Basin of New South Wales are the Chillingham Volcanics. These are from some time in the Triassic period, and for a band north and south of Chillingham
. They consist of cobbles at the base, Rhyolite, lithic rhyolitic tuff, and shale. The Nymboida Coal measures extend from Nymboida
to Kangaroo Creek. They consist of lithic sandstones (wackes, minor arenites), siltstone, polymictic conglomerate, coal, rhyolitic tuff, and basalt. The total thickness is over 1000 meters. The outcrop is 90 square kilometers, and it forms a north west trending band 29 km long on the southwest tip of the basin. Fossils reveal a date of middle Triassic. A lower part is called Cloughers Creek Formation. The Basin Creek Formation includes the coal mined at Nymboida. The Bardool Conglomerate forming a 180 m thick layer, is also a unit in the coal measures. The conglomerate includes a 15 m thick layer of basalt exposed at Copes Creek.
The Red Cliff Coal Measures are from late Triassic. It forms a belt 2.5km wide and 19km long from Buchanans Head trough Red Cliff. The Evans Head Coal measure are correlated with these, but are further up the north coast at Evans Head
.
The basin was next uplifted and eroded and then deepened considerably and Bundamba group rocks form a complete V shape on both sides of the basin. In the northern parts the rock is mostly friable sandstone, but in the south it is divided into conglomerate below and siltstone above. The Laytons Range Conglomerate rests on the basin floor and extends from Baryulgil, to Nymboida. The conglomerate often appears as a cliff. The Corindi Conglomerate is a local name for a hailstone sized gravel near Corindi. The Mill Creek Siltstone. are often olive green or yellow-brown with bright red joint planes.
The Marburg subgroup extends for 225 km along the western side of the basin into Queensland from Corindi. It is mostly clay cemented cross bedded quartz sandstone, but this is interbedded with claystone
and shale. At the base is the Blaxland Fossil Wood Conglomerate Member at Blaxlands Creek. The fossil wood is in the form of horizontal tree trunks up to 18 m long and 600 mm diameter. The fossilization process replaced the wood with limonite
and hematite
. The Towallum Basalt is a 15 meter thick layer near Nymboida, Glenreagh and Moleton trig station overlying the Marburg formation. The Walloon Coal Measures forms a U shape around the east, south and west sides of the basin. It consists of claystone, shale, siltstone, arenite
s, and coal seams and the plant fossils in it show a Jurassic age.
The next layer of rocks in the basin forming a nested U shape in its exposure is the Kangaroo Creek Sandstone. This sandstone has saccharoidal texture, and glistens white and cream. This is not due to angular sand grains, but results from silica crystallization. It is up to 150 m thick.
The Grafton Formation is the sedimentary unit in the core of the basin. It is the youngest of the beds being between Late Jurassic and early Cretaceous. It occurs from Grafton
to Casino
consisting of soft sandstone, siltstone and claystone. Dolerite has intruded this at Glenugie Peak, and near Banyabba.
Rifting along the east coast of Australia commenced and uplifted the eastern side of the Clarence Moreton Basin. This resulted in the splitting off of the Lord Howe Rise
and the opening of the ocean floor.
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
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...
on the easternmost part of the Australian continent. It is located in the far north east of the state of New South Wales around Lismore
Lismore, New South Wales
Lismore is a subtropical town in northeastern New South Wales, Australia. Lismore is the main population centre in the City of Lismore local government area. Lismore is a regional centre in the Northern Rivers region of the State.-History:...
and Grafton
Grafton, New South Wales
The city of Grafton is the commercial hub of the Clarence River Valley. Established in 1851, Grafton features many historic buildings and tree-lined streets. Located approximately 630 kilometres north of Sydney and 340 km south of Brisbane, Grafton and the Clarence Valley can be reached...
and in the south east corner of Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
. It formed by oblique extension of the underlying Paleozoic New England Orogen basement. It consists of continental deposits, starting with a small amount of Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
coal beds, and then mostly Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
and Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
sedimentary rocks. The basin covers 16000 square kilometers. The basin was named when the Clarence Basin (named after the Clarence River
Clarence River (New South Wales)
The Clarence River is situated in northeastern New South Wales, Australia. The river originates on the watershed that marks the Queensland border. After flowing south and northeast for 394 km it then empties into the Pacific Ocean at Iluka/Yamba. On its journey it passes through the towns of...
and Moreton Basin in Queensland were proved to be one structure.
The first rocks in the Clarence Moreton Basin of New South Wales are the Chillingham Volcanics. These are from some time in the Triassic period, and for a band north and south of Chillingham
Chillingham, New South Wales
Chillingham is a small village approximately 14 km northwest of Murwillumbah in the Tweed Valley, New South Wales, Australia. The Rous River, a tributary of the Tweed River, flows through the town....
. They consist of cobbles at the base, Rhyolite, lithic rhyolitic tuff, and shale. The Nymboida Coal measures extend from Nymboida
Nymboida, New South Wales
Nymboida is a rural village located in the Northern Rivers region of New South Wales, Australia. It is located about 21 kilometres south-west of Coutts Crossing, 44 kilometres south-west of Grafton and approximately 687 km north of Sydney. Nymboida is close to the challenging and popular white...
to Kangaroo Creek. They consist of lithic sandstones (wackes, minor arenites), siltstone, polymictic conglomerate, coal, rhyolitic tuff, and basalt. The total thickness is over 1000 meters. The outcrop is 90 square kilometers, and it forms a north west trending band 29 km long on the southwest tip of the basin. Fossils reveal a date of middle Triassic. A lower part is called Cloughers Creek Formation. The Basin Creek Formation includes the coal mined at Nymboida. The Bardool Conglomerate forming a 180 m thick layer, is also a unit in the coal measures. The conglomerate includes a 15 m thick layer of basalt exposed at Copes Creek.
The Red Cliff Coal Measures are from late Triassic. It forms a belt 2.5km wide and 19km long from Buchanans Head trough Red Cliff. The Evans Head Coal measure are correlated with these, but are further up the north coast at Evans Head
Evans Head, New South Wales
Evans Head is a town in the Northern Rivers region of New South Wales, Australia in Richmond Valley Shire. At the 2006 census, Evans Head had a population of 2,631 people. It is 726 kilometres north of Sydney, and 11 kilometres east off the Pacific Highway from Woodburn...
.
The basin was next uplifted and eroded and then deepened considerably and Bundamba group rocks form a complete V shape on both sides of the basin. In the northern parts the rock is mostly friable sandstone, but in the south it is divided into conglomerate below and siltstone above. The Laytons Range Conglomerate rests on the basin floor and extends from Baryulgil, to Nymboida. The conglomerate often appears as a cliff. The Corindi Conglomerate is a local name for a hailstone sized gravel near Corindi. The Mill Creek Siltstone. are often olive green or yellow-brown with bright red joint planes.
The Marburg subgroup extends for 225 km along the western side of the basin into Queensland from Corindi. It is mostly clay cemented cross bedded quartz sandstone, but this is interbedded with claystone
Claystone
Claystone is a geological term used to describe a clastic sedimentary rock that is composed primarily of clay-sized particles ....
and shale. At the base is the Blaxland Fossil Wood Conglomerate Member at Blaxlands Creek. The fossil wood is in the form of horizontal tree trunks up to 18 m long and 600 mm diameter. The fossilization process replaced the wood with limonite
Limonite
Limonite is an ore consisting in a mixture of hydrated iron oxide-hydroxide of varying composition. The generic formula is frequently written as FeO·nH2O, although this is not entirely accurate as limonite often contains a varying amount of oxide compared to hydroxide.Together with hematite, it has...
and hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...
. The Towallum Basalt is a 15 meter thick layer near Nymboida, Glenreagh and Moleton trig station overlying the Marburg formation. The Walloon Coal Measures forms a U shape around the east, south and west sides of the basin. It consists of claystone, shale, siltstone, arenite
Arenite
Arenite is a sedimentary clastic rock with sand grain size between 0.0625 mm and 2 mm and contain less than 15% matrix. The related adjective is arenaceous...
s, and coal seams and the plant fossils in it show a Jurassic age.
The next layer of rocks in the basin forming a nested U shape in its exposure is the Kangaroo Creek Sandstone. This sandstone has saccharoidal texture, and glistens white and cream. This is not due to angular sand grains, but results from silica crystallization. It is up to 150 m thick.
The Grafton Formation is the sedimentary unit in the core of the basin. It is the youngest of the beds being between Late Jurassic and early Cretaceous. It occurs from Grafton
Grafton, New South Wales
The city of Grafton is the commercial hub of the Clarence River Valley. Established in 1851, Grafton features many historic buildings and tree-lined streets. Located approximately 630 kilometres north of Sydney and 340 km south of Brisbane, Grafton and the Clarence Valley can be reached...
to Casino
Casino, New South Wales
Casino is a town in the Northern Rivers area of New South Wales, Australia, with a population of 9,400 people . It lies on the banks of the Richmond River and is situated at the junction of the Bruxner Highway and the Summerland Way....
consisting of soft sandstone, siltstone and claystone. Dolerite has intruded this at Glenugie Peak, and near Banyabba.
Rifting along the east coast of Australia commenced and uplifted the eastern side of the Clarence Moreton Basin. This resulted in the splitting off of the Lord Howe Rise
Lord Howe Rise
The Lord Howe Rise is an underwater plateau that extends from southwest of New Caledonia to the Challenger Plateau, west of New Zealand. To its west is the Tasman Basin and to the east is the New Caledonia Basin. Lord Howe Rise has a total area of about 1,500,000 square km, and generally lies about...
and the opening of the ocean floor.