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Sedimentary rocks are formed by the physical and chemical breakdown of pre-existing rocks, which can be of igneous, metamorphic, or sedimentary origin. The particles from these rocks are carried by agents such as rivers, oceans, winds, and rain runoff, and when the transporting current is not strong enough, these particles are deposited in a process called sedimentation. Sedimentary rocks are found in various environments, including arid regions, river valleys, cliffs, and human-made locations like quarries. In Australia, sedimentary rocks containing tiny zircon crystals dating back 4.0-4.2 billion years have been discovered in Western Australia. Additionally, Zebra rock, a type of sedimentary rock, is found in the Ord River area of Western Australia, and the country is also known for its opals found in the outback.
| Characteristics | Values |
|---|---|
| Age | Sedimentary rocks in Australia vary in age, with some dating back to 4.0-4.2 billion years ago, and others being as young as the Cretaceous period. |
| Formation | Sedimentary rocks are formed through clastic, chemical, or biogenic sedimentation. |
| Types of Sedimentation | Clastic sedimentation occurs when particles washed off eroding rocks are carried by rivers, oceans, winds, or rain runoff and then drop out when the energy of the transporting current is not strong enough. Chemical sedimentation occurs when material is dissolved in water and chemically precipitates from it. Biogenic sedimentation occurs when living organisms extract ions from water to create shells and bones. |
| Composition | Sedimentary rocks can be composed of any mineral due to their detrital nature. Common minerals include clay, quartz, feldspar, and carbonate minerals. |
| Environments | Sedimentary rocks are found in various environments, including arid regions, river valleys, cliffs, hillsides, quarries, and road cuttings. |
| Classification | Sedimentary rocks can be classified according to the climate and/or the geometrical arrangement of the sediments. |
| Preservation | The structures and textures found in sedimentary rocks allow for their preservation and provide clues about the environment of deposition. |
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What You'll Learn
- Sedimentary rocks are found in river valleys, cliffs, hillsides, and quarries
- The oldest sedimentary rocks in Australia are in Western Australia
- Sedimentary rocks are formed by the breakdown of pre-existing rocks
- Sedimentary rocks are classified by the climate and geometry of the sediments
- The three types of sedimentary rock formation are clastic, chemical, and biogenic
Sedimentary rocks are found in river valleys, cliffs, hillsides, and quarries
Sedimentary rocks are formed from deposits of pre-existing rocks or pieces of once-living organisms that accumulate on the Earth's surface. These rocks often exhibit distinct layering or bedding, creating picturesque landscapes, particularly in desert regions. Sedimentary rocks are classified into three main groups: Clastic, Biologic, and Chemical.
In Australia, sedimentary rocks can be found in various locations, including river valleys, cliffs, hillsides, and quarries. The geology of the country encompasses a diverse range of rock types, spanning over 3.8 billion years. One notable location for sedimentary rocks in Australia is the Adelaidean province in South Australia, specifically in the region between Adelaide and the Flinders Ranges. This area boasts an almost complete sedimentary record of the late Proterozoic era. The Adelaidean succession includes groups such as the Callanna and Burra, which feature sedimentary deposits like basic volcanic rocks, evaporitic sediments, and carbonate rocks.
Sedimentary rocks are also present in the river valleys of Australia. River valleys provide a path for the transportation and deposition of sediments, contributing to the formation of sedimentary rocks over time. The sedimentation process involves the accumulation of mineral or organic particles, which can be transported and deposited by water, wind, glaciers, or other agents. This process is crucial in understanding the formation of sedimentary rocks in river valleys and other similar environments.
Cliffs in Australia, such as the iconic Cliffs of Dover, also showcase sedimentary rocks. The geology of these cliffs is shaped by the deposition and cementation of materials on the Earth's surface and within water bodies. The processes of sedimentation and erosion play a significant role in forming the cliffs' distinctive features. Additionally, sedimentary rocks can be found on hillsides in Australia. Hillside sedimentary rocks can be a result of the accumulation and compaction of sediments over time, forming solid rock layers.
Lastly, quarries in Australia are another source of sedimentary rocks. Quarrying activities expose large amounts of rock, including sedimentary rock layers. These quarries provide insights into the geological history of the region and contribute to the understanding of the Earth's crust and natural resources. Australia's quarries, along with its river valleys, cliffs, and hillsides, offer a diverse range of locations to study and appreciate the country's sedimentary rock formations.
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The oldest sedimentary rocks in Australia are in Western Australia
The geology of Australia is incredibly diverse, including almost all known rock types and spanning a geological time period of over 3.8 billion years. The country's geology can be divided into several sections, including Archaean cratonic shields, Proterozoic fold belts and sedimentary basins, and Phanerozoic metamorphic and igneous rocks.
The oldest dated minerals in Australia are tiny zircon crystals found in sedimentary rocks in Western Australia, dating back 4.0 to 4.2 billion years. These ancient crystals are highly valuable and are mined on a large scale, contributing significantly to the country's wealth. The Yilgarn block, located in the southwest of the country, is particularly notable for its ancient rocks, with the oldest known rocks being sialic crust that formed between 4.3 and 3.7 billion years ago.
The Pilbara block in the northwest is also home to ancient rocks, with some of the oldest being between 3.3 and 3.5 billion years old. These rocks consist of basic (alkaline) volcanics and acid volcanics, providing insights into the geological history of the region. The Gawler craton and Willyama Block are also of Archaean to Proterozoic age, flanked by Proterozoic orogenic belts and sedimentary basins.
In Western Australia, the granite cliff known as Wave Rock was formed over 2,700 million years ago and stands at an impressive 14 metres high and 110 metres long. Uluru, formerly known as Ayers Rock, is another iconic rock formation in Central Australia, laid down in an inland sea approximately 500 million years ago. The rock covers 3.3 square kilometres and rises 345 metres above the plains, making it a significant landmark in the region.
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Sedimentary rocks are formed by the breakdown of pre-existing rocks
Sedimentary rocks are formed by the accumulation or deposition of sediments, i.e. the breakdown of pre-existing rocks or pieces of once-living organisms that accumulate on the Earth's surface. This accumulation is followed by cementation, the process by which clastic sediments become lithified or consolidated into hard, compact rocks, usually through the deposition or precipitation of minerals in the spaces among the individual grains of sediment.
Clastic sedimentary rocks are made up of pieces (clasts) of pre-existing rocks loosened by weathering. These rocks have particles ranging in size from microscopic clay to huge boulders, and their names are determined by the clast or grain size. The smallest grains are called clay, then silt, then sand, and grains larger than 2mm are called pebbles.
Biochemical (biogenic) sedimentary rocks are created when organisms use materials dissolved in air or water to build their tissue. Examples include most types of limestone, which are formed from the calcareous skeletons of organisms such as corals, mollusks, and foraminifera, and coal, formed from vegetation.
Chemical sedimentary rocks form through chemical precipitation, which begins when water travels through rock and dissolves some of the minerals. These minerals are then carried away from their source and eventually redeposited, or precipitated, when the water evaporates.
Sedimentary rocks are classified into three groups: clastic, biologic, and chemical. The overall composition of the Earth is very similar to that of meteorites, and it is thought that the Earth originally formed from planetesimals composed largely of metallic iron and silicates.
In Australia, sedimentary rocks containing the oldest dated minerals (4.0-4.2 billion years) in the form of tiny zircon crystals have been found in Western Australia.
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Sedimentary rocks are classified by the climate and geometry of the sediments
Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They are often deposited by rivers and buried in lakes and oceans, where they lose water and become cemented to form rock.
Sedimentary rocks are classified into two main categories: clastic and chemical. Clastic sedimentary rocks are made up of pieces of pre-existing rocks, loosened by weathering and transported to a basin or depression where sediment is trapped. Clastic rocks are classified by grain shape, size, and sorting. They include siltstone, sandstone, conglomerate, and shale.
Chemical sedimentary rocks, on the other hand, are precipitated from water saturated with dissolved minerals. They are classified mainly by the composition of minerals in the rock. Examples of chemically precipitated rocks include the limestones found in the Ord River area of Western Australia, which are composed of crystalline carbonates.
Sedimentary rocks can also be classified according to the climate in which they occur and the geometrical arrangement of the sediments. For example, Ardisol forms in dry climates and can develop layers of hardened calcite, while zebra stone, a type of claystone, forms in highly oxidizing environments.
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The three types of sedimentary rock formation are clastic, chemical, and biogenic
Sedimentary rocks are found in a variety of locations in Australia, including river valleys, cliffs, hillsides, quarries, and road cuttings. The country's geology includes almost all known rock types from various time periods spanning over 3.8 billion years.
Sedimentary rocks are classified into three main types: clastic, chemical, and biogenic. Clastic sedimentary rocks, also known as detrital sedimentary rocks, are formed from pieces of bedrock and sediment derived primarily by mechanical weathering. They are classified by grain shape, size, and sorting, with the size of the clasts indicating the energy available during transport. For example, large fragments like boulders suggest high-energy processes such as avalanches, while smaller grains like silt or clay may be deposited by wind.
Chemical sedimentary rocks, on the other hand, are formed when pre-existing bedrock is weathered by chemical reactions in water, the atmosphere, or the biosphere. These reactions dissolve the rock, transporting the dissolved elements or ions in water. The rocks are then precipitated from water saturated with these dissolved minerals and classified based on their mineral composition.
Biogenic sedimentary rocks, a subtype of chemical sedimentary rocks, are formed with the help of biological processes. Biochemical sedimentary rocks, such as limestone, are formed from ions dissolved in water, but biological processes, like the use of dissolved minerals by marine organisms to build shells, play a role in extracting the dissolved materials. When these organisms die, their hard parts settle as sediment, becoming buried, compacted, and cemented into rock. Biogenic chert, for example, forms on the deep ocean floor from the accumulation of microscopic organic shells, which can be silica-based or calcareous.
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Frequently asked questions
Sedimentary rocks in Australia can be found in river valleys, cliffs, and hillsides. They are also found in human-made exposures such as quarries and road cuttings.
Some examples of sedimentary rocks found in Australia include zebra rock, shale, and limestone.
Sedimentary rocks are formed by the physical and chemical breakdown of pre-existing rocks, which can be of igneous, metamorphic, or sedimentary origin.
The structures and textures found in sedimentary rocks give clues to the environment of deposition, allowing geologists to assign parts of a deposit to a particular sedimentary facies.
