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Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus , [ 1 ] chunks, and smaller grains of rock broken off other rocks by physical weathering . [ 2 ]
Further erosion eventually reduces these landforms to piles of bouldery rubble as known as rock labyrinths. The tepui of South America are a type of sedimentary tableland composed of erosional outliers of flat-lying Precambrian quartz arenite sandstone that tower over the surrounding jungle underlain by crystalline basement rocks. [3] [4]
Clastic rocks are classified according to their predominant grain size and their composition. In the past, the term "Clastic Sedimentary Rocks" were used to describe silica-rich clastic sedimentary rocks, however there have been cases of clastic carbonate rocks. The more appropriate term is siliciclastic sedimentary rocks.
A conglomerate or any clastic sedimentary rock that consists of a single rock or mineral is known as either a monomict, monomictic, oligomict, or oligomictic conglomerate. If the conglomerate consists of two or more different types of rocks, minerals, or combination of both, it is known as either a polymict or polymictic conglomerate.
Arenite (from the Latin arena, "sand") [1] is a sedimentary clastic rock with sand grain size between 0.0625 mm (0.00245 in) and 2 mm (0.08 in) and containing less than 15% matrix. [2] The related adjective is arenaceous. The equivalent Greek-derived term is psammite, though this is more commonly used for metamorphosed sediments.
Breccia is composed of coarse rock fragments held together by cement or a fine-grained matrix. [5] Like conglomerate, breccia contains at least 30 percent of gravel-sized particles (particles over 2mm in size), but it is distinguished from conglomerate because the rock fragments have sharp edges that have not been worn down. [6]
Clastic dikes (also known as sedimentary dikes) are vertical bodies of sedimentary rock that cut off other rock layers. They can form in two ways: When shallow unconsolidated sediment is composed of alternating coarse-grained and impermeable clay layers the fluid pressure inside the coarser layers may reach a critical value due to lithostatic ...
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.