An exhumed river channel is a ridge of

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

that remains when the softer flood plain

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

eroded Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. Erosion is disti ...

away. The process begins with the deposition of sand within a

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

channel (typically a

meander A meander is one of a series of regular sinuous curves in the Channel (geography), channel of a river or other watercourse. It is produced as a watercourse erosion, erodes the sediments of an outer, concave bank (cut bank, cut bank or river cl ...

ing river) and mud on the adjacent

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

. Eventually the channel is abandoned and over time becomes buried by flood deposits from other channels. Because the sand is porous (grain-to-grain contact leaves spaces between),

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...

flows more easily through the sand than through the mud of the floodplain deposits. Minerals (typically

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

) can cement the grains together converting the loose sand into sandstone. Meanwhile, pressure from overlying

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s compresses the floodplain mud converting it to mudstone. Millions of years later, erosion can remove the softer, less cemented mudstone and leave the more resistant sandstone as a sinuous ridge. Thus, an exhumed river channel is a form of

inverted relief Inverted relief, inverted topography, or topographic inversion refers to landscape features that have reversed their elevation relative to other features. It most often occurs when low areas of a landscape become filled with lava or sediment t ...

: what was previously low is now high, and vice versa. Exhumed channels are important indicators for ancient stream flow direction. Some of the best examples of exhumed river channels occur in the Ruby Ranch Member of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Cedar Mountain Formation The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid-Cretaceous. The formation was named for Cedar Mountain (Utah), Cedar Mountain in northern Emery Cou ...

southwest of

Green River, Utah Green River is a city in Emery County, Utah, United States. The population was 847 at the 2020 census. History The city of Green River is located on ancestral Ute lands, in the home locale of the Seuvarits/Sheberetch band of Ute people. The ...

. Within the Cedar Mountain Formation in this part of Utah, fluvial

s filling paleochannels within it are cemented by

. Because of this cementation, the sandstone filling these paleochannels are considerably more resistant to erosion than the

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

and

that enclose them. As a result, differential erosion preferentially removes the shale and mudstone and exposes these paleochannels as ridges.Williams, R.M.E., T.C. Chidsey, Jr., and D.E. Eby, D.E., 2007, ''Exhumed paleochannels in central Utah - analogs for raised curvilinear features on Mars'', in G.C. Willis M.D. Hylland, D.L. Clark, and T.C. Chidsey, Jr., eds., pp. 220-235, Central Utah - diverse geology of a dynamic landscape. Publication 36, Utah Geological Association, Salt Lake City, Utah.Harris, D.R. 1980
''Exhumed paleochannels in the Lower Cretaceous Cedar Mountain Formation near Green River, Utah.''

Brigham Young University Brigham Young University (BYU) is a Private education, private research university in Provo, Utah, United States. It was founded in 1875 by religious leader Brigham Young and is the flagship university of the Church Educational System sponsore ...

Geology Studies 27:51–66.

References

{{reflist

References

See also