https://en.bharatpedia.org/w/index.php?action=history&feed=atom&title=PalaeochannelPalaeochannel - Revision history2026-09-06T23:00:24ZRevision history for this page on the wikiMediaWiki 1.43.6https://en.bharatpedia.org/w/index.php?title=Palaeochannel&diff=421497&oldid=prevAjay Kumar: Created a new article2023-08-29T16:04:55Z<p>Created a new article</p>
<p><b>New page</b></p><div>{{Short description|An inactive river or stream channel that has been filled or buried}}<br />
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In geology, a '''palaeochannel''', '''palaeovalley''', or '''palaeoriver''' (US spellings '''paleo-''') is the remnant of an inactive river or stream channel that has been filled or buried by younger [[sediment]]. The sediments that the ancient channel is cut into or buried by can be unconsolidated, semi-consolidated, consolidated or [[Diagenesis|lithified]]. The word ''palaeochannel'' is formed from ''palaeo'' 'old' and ''channel''.<br />
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== Recognition ==<br />
A palaeochannel is distinct from the [[overbank]] deposits of currently-active river channels, including ephemeral water courses that do not regularly flow (such as the [[Todd River]], Central [[Australia]]) because the [[river bed]] is filled with sedimentary deposits unrelated to the normal bed load of the current drainage pattern.<br />
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Many palaeochannels are arranged on old drainage patterns, distinct from the current drainage system of a catchment. For example, palaeochannels may relate to a system of rivers and creeks that drained east–west while the current drainage direction is north–south.<br />
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Palaeochannels can be most easily identified as broad [[erosion]]al channels into a basement that underlies a system of depositional sequences, which may contain several episodes of [[Deposition (geology)|deposition]] and represent [[meander]]ing [[peneplain]] streams.<br />
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Thereafter, a palaeochannel may form part of the [[regolith]] of a region and although it is unconsolidated or partly consolidated, it is currently part of the [[erosion surface|erosional surface]].<br />
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Palaeochannels can also be identified according to their age. For example, there are deposits of Tertiary [[lignite]]s in the [[Tertiary]] river systems preserved on top of [[Archean|Archaean]] basement in the [[Yilgarn Craton]] of [[Western Australia]].<ref>{{cite journal |last1=Anand |first1=R. |last2=Paine |first2=M.|title= Regolith Geology of the Yilgarn Craton, Western Australia |journal=Australian Journal of Earth Sciences |volume=49 |issue=1 |pages=3–162 |date=2002 |doi=10.1046/j.1440-0952.2002.00912.x |s2cid=129930657}}</ref> The river systems have laid in place for 15 to 50 million years and would be considered palaeochannels.<br />
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Palaeochannels can be identified using [[Aeromagnetic survey|airborne electromagnetic surveys]], as the coarse-grained sediments are more electrically resistive than surrounding materials.<ref name=Knight22>{{Cite journal |last1=Knight |first1=Rosemary |last2=Steklova |first2=Klara |last3=Miltenberger |first3=Alex |last4=Kang |first4=Seogi |last5=Goebel |first5=Meredith |last6=Fogg |first6=Graham |date=2022-12-01 |title=Airborne geophysical method images fast paths for managed recharge of California's groundwater |url=https://iopscience.iop.org/article/10.1088/1748-9326/aca344 |journal=Environmental Research Letters |volume=17 |issue=12 |pages=124021 |doi=10.1088/1748-9326/aca344 |s2cid=253605188 |issn=1748-9326}}</ref><br />
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== Formation ==<br />
Paleochannels form when river channels [[aggradation|aggrade]] and so deposit sediment on their bed. For the channel deposits to be preserved, the flow must not occupy and erode them again. Examples of what may cause long-term preservation include the channels being in a net-depositional environment and/or being in a subsiding [[sedimentary basin]]. Paleochannels may also be preserved in the short-term on non-net-depositional [[floodplain]]s in which the river migrates or [[avulsion (river)|avulses]] away from its previous course. The preservation is short-term because unless the channel deposits are buried, flow will eventually reoccupy its formerly-occupied course, reworking and [[erosion|eroding]] the channel deposits.<br />
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== Geological importance ==<br />
Palaeochannels are important to geology for a number of reasons:<br />
* Understanding movements of [[fault (geology)|faults]], which may redirect river systems and so form stranded channels that are, in essence, palaeochannels.<br />
* Preserving Tertiary, [[Eocene]] and [[Holocene]] sediments and [[fossil]]s within them, important locations for [[palaeontology]], [[palaeobotany]] and [[archaeology]]. <br />
* Preserving evidence of older erosional surfaces and levels, which is useful for estimating the net erosional budget of older [[regolith]].<br />
* Preserving sedimentary records, which is useful for understanding climatic conditions, including various [[isotope geology|isotopic]] indicators of past rainfall, temperatures and climates, used to understand [[climate change]] and [[global warming]].<br />
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==Examples==<br />
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There is a large palaeovalley underneath [[Anangu Pitjantjatjara Yankunytjatjara]] (APY lands) in the remote north-west of [[South Australia]].<ref name="Lysaght 2021">{{cite web | last=Lysaght | first=Gary-Jon | title=Map of APY Lands translated to 'empower' First Nations people, giving them greater voice | website=ABC News|publisher=[[Australian Broadcasting Corporation]] | date=28 January 2021 | url=https://www.abc.net.au/news/2021-01-28/apy-lands-geological-map-translated-to-empower-aboriginal-groups/13093900 | access-date=29 January 2021}}</ref><br />
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== Economic importance ==<br />
Palaeochannels can host economic [[ore]] deposits of [[uranium]],<ref>{{cite web|url=http://crcleme.org.au/RegExpOre/MulgaRock.pdf |first1=G.B. |last1=Douglas |first2=C.R.M. |last2=Butt |first3=D.J. |last3=Gray |title=Mulga Rock Uranium and Multielement Deposits, Officer Basin, WA |date=2003 |publisher=CRC LEME, [[CSIRO]] Exploration and Mining |accessdate=2006-03-07}}</ref> [[lignite]], [[precious metal]]s such as [[gold]] and [[platinum]], heavy minerals such as [[tin]], [[tungsten]], and [[iron ore]] preserved as paleo-[[placer deposit|placer]] deposits.<br />
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Palaeochannels have been proposed as a mechanism for [[Aquifer storage and recovery|managed aquifer recharge]] in California.<ref name=Knight22/><ref>{{multiref|{{cite news |first=Erica |last=Gies |title=California Could Capture Its Destructive Floodwaters to Fight Drought |newspaper=New York Times |date=7 January 2023 |url=https://www.nytimes.com/2023/01/07/opinion/california-flood-atmospheric-river-drought.html}}|{{cite thesis |first=Amy LeVan |last=Lansdale |title=Influence of a coarse-grained incised-valley fill on groundwater flow in fluvial fan deposits, Stanislaus County, Modesto, California, USA |date=2005 |type=Masters |publisher=Michigan State University |doi=10.25335/M5G44J01D |url=https://d.lib.msu.edu/etd/33813}}<br />
|{{cite journal |last1=He |first1=Xiaogang |last2=Bryant |first2=Benjamin P. |last3=Moran |first3=Tara |last4=Mach |first4=Katharine J. |last5=Wei |first5=Zhongwang |last6=Freyberg |first6=David L. |title=Climate-informed hydrologic modeling and policy typology to guide managed aquifer recharge |journal=Science Advances |volume=7 |issue=17 |pages=eabe6025 |date=2023 |doi=10.1126/sciadv.abe6025 |pmid=33883132 |s2cid=233349426 |url=}}}}</ref><br />
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== See also ==<br />
* [[Sedimentology]]<br />
* [[Erosion]]<br />
* [[Ore genesis]]<br />
* [[Paleoshoreline]]<br />
* [[Placer mining]]<br />
* [[Uranium ore deposits]]<br />
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== References ==<br />
{{reflist}}<br />
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{{Rivers, streams and springs}}<br />
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[[Category:Sedimentary structures]]</div>Ajay Kumar