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Uluru (Ayers Rock) is a large sandstone formation in Northern Territory, Australia.. Sedimentary rocks can be subdivided into four groups based on the processes responsible for their formation: clastic sedimentary rocks, biochemical (biogenic) sedimentary rocks, chemical sedimentary rocks, and a fourth category for "other" sedimentary rocks formed by impacts, volcanism, and other minor processes.
Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition. Sediments and sedimentary rocks are characterized by bedding , which occurs when layers of sediment, with different particle sizes are deposited on top of each other. [ 1 ]
Metamorphic rocks are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism, meaning to "change in form". The result is a profound change in physical properties ...
While features of some ancient apparent stromatolites are suggestive of biological activity, others possess features that are more consistent with abiotic (non-biological) precipitation. [17] Finding reliable ways to distinguish between biologically formed and abiotic stromatolites is an active area of research in geology.
A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'. Of the many rhythmites in the geological record, varves are one of the most important and illuminating in studies of past climate change.
The geology of the southwest includes old rocks, the 3.6 billion year old Morton Gneiss and the Paleoproterozoic Sioux Quartzite, overlain by the Cretaceous sedimentary sequence that includes the Dakota Sandstone, Niobrara Formation, and Pierre Shale, and is continuous across much of the western Midwest to the eastern slopes of the Rocky Mountains.
The following is a list of rock types recognized by geologists.There is no agreed number of specific types of rock. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type.
The margins of the Canadian Shield have been covered by sedimentary rocks, such as in Michigan where a series of sediments has filled in the Michigan Basin. [4] The exposed sections are often where glaciers have removed this overlying regolith to reveal the underlying glacially scarred crystalline rock.