Palaeochannel

Source: Wikipedia, the free encyclopedia.

Aerial view of exhumed fluvial palaeochannel, Emery County, Utah. The erosion of softer surrounding mudstone left this palaeochannel as a sandstone ridge.[1]

In the

tectonics and diagenesis during their geologic history after deposition. The abandonment of an active fluvial channel and the resulting formation of a palaeochannel can be the result of tectonic processes, geomorphologic processes, anthropogenic activities, climatic changes, or a variable and interrelated combination of these factors.[2][3]

Palaeochannel versus palaeovalley

In practice, the term palaeochannel has often been used both interchangeably and inconsistently with the terms palaeovalley and paleovalley. This has led to both potential and actual confusion in the published literature and studies of groundwater and mineral resources associated with palaeochannels.

lacustrine, estuarine, or marine deposits.[4] Finally, even when filled largely by fluvial sediments, the channel deposits that fill a palaeochannel comprise only a small fraction of a valley fill, which mainly consists of the deposits of other fluvial environments.[7] The nomenclature of palaeochannels must reflect their actual physical character, origin, and evolution if their relationship to mineral and groundwater resources is to be properly understood.[4][5] Thus, it is recommended[4][5][8]
that palaeochannel be used for an inactive channel formed by a river; palaeochannel deposits for the sediments that infill a palaeochannel; and palaeovalley for a valley incised by an ancient river.

Formation

The avulsion of an active river or stream is the most common fluvial process resulting in the formation of palaeochannels. It is the process by which flow diverts out of an established river channel into a new permanent course on the adjacent floodplain. An avulsion can be either a full avulsion, in which in which all of the discharge is transferred out of the parent channel to a new one, or partial avulsion, in which only a portion of the discharge is transferred to a new one. Only the full avulsion results the formation of a palaeochannel. Partial avulsions result in the formation of anastomosing channels when the divided active channels rejoin downstream and distributary channels when the divided active channels do not rejoin downstream.[9]

At least three broadly different types of avulsions, (a) avulsion by annexation; (b) avulsion by incision; and (c) avulsion by progradation, are recognized. First, an avulsion by annexation is an avulsion in which an existing active channel is appropriated or if an existing abandoned channel is reoccupied. Second, an avulsion by incision is an avulsion in which a new channel is created by the scouring into the floodplain surface as a direct result of the avulsion. Finally, an avulsion by progradation is an avulsion that results in the formation of an extensive deposition and multi-channeled distributive network. Of these types of avulsions only the avulsion by incision results in the complete abandonment and preservation of a fluvial channel as a palaeochannel.[9]

The exact environmental conditions that favour incisional avulsions remain unsettled. However, it is generally agreed that they are promoted by a) rapid aggradation of the main channel and floodplain; b) wide unobstructed floodplain and down-valley drainage; and c) frequently recurring floods of high magnitude. In many floodplains, these conditions and frequent avulsions are correlated with superelevated alluvial ridges and river stages.[9]

The event or factor that can trigger a specific avulsion may be either external or internal to a river system and quite varied. Factors external to a river system that might cause an avulsion include fault activity, sea-level rise, or an increase in flood peak discharge. Factors internal to a river system that might cause an avulsion include sediment influx, breakout along animal pathways, and blockage by ice jams, plant growth, log jams, and beaver dams.[10]

Recognition

A variety of techniques have been used to recognize and map palaeochannels. At first, surficial data from aerial photography, soils maps, topographic maps, archaeological surveys and excavations, and field observations were integrated with subsurface data from geological and engineering borings and cores to recognize and map palaeochannels.[11][12] As the importance of coarse-grained fluvial deposits associated with palaeochannels as sources of groundwater and favoured conveyance of subsurface water became appreciated, geophysical techniques sensing the physical properties of underlying ground and bedrock and groundwater and other fluids contained within them became more important and widely used.[13][14] For example, palaeochannels can be identified using airborne electromagnetic surveys, as the coarse-grained sediments are more electrically resistive than surrounding materials.[15] Also, lidar, more sophisticated remote sensing techniques, digital analysis, including computer modeling, of data were added to the various techniques used to detect and map palaeochannels.[14]

Geological importance

Palaeochannels are important to the Earth sciences because the palaeohydrology of the prehistoric rivers that created them can be reconstructed from their morphology, and the sediments or sedimentary rocks filling palaeochannels often contain dateable material, fossils, and palaeoenvironmental proxies. The data derived from the analysis of their morphology and the fossils and palaeoenvironmental proxies can be used to study changes in regional palaeohydrology, palaeoclimates, and palaeoenvironments over geological and historic time scales.[16] The morphology and distribution of palaeochannels can also be used to reconstruct the types, prehistory, and geometry of tectonic deformation, such as faulting, folding, uplift, and subsidence within an area.[17]

Palaeochannels often preserve the form, width, and sinuosity of prehistoric river channels when they were active. This is important in reconstructing prehistoric climate and hydrology because empirical equations developed using data collected from modern rivers and streams can be used to calculate the approximate past hydrologic regime of a palaeochannel and the palaeoclimate associated with it. Such empirical equations also allow the estimation of palaeochannel gradient, meander wavelength, sinuosity, and discharge from a palaeochannel exposed in cross-section in an outcrop.[18][19][20] The sediments or sedimentary rocks filling palaeochannels also often contain dateable material, micro- and megafossils, and palaeoenvironmental proxies. Fine-grained palaeochannel fills containing autochthonous vertebrate fossils may, in extremely favourable ccircumstances, contain unabraded, complete skeletons that are important for understanding habitat-specific palaeofaunas and associated palaeoenvironments.

global warming.[23][24]
Finally, the theoretical equilibrium profiles of rivers and streams provide a datum by which to detect and quantify tectonic processes such as faulting, uplift, and subsidence. Examples of the displacement of palaeochannels by active faulting are shown by the lateral movement along the San Andreas fault where it crosses Wallace Creek in central California,[25][26] and where a fault of the Baton Rouge fault zone vertically offsets a Pleistocene palaeochannel and palaeo-floodplain of the Amite River near Denham Springs, Louisiana.[27]

Palaeochannel-hosted mineral deposits

Economically important mineral deposits may be hosted in palaeochannels and associated fluvial deposits. The most important of these deposits are syndepositional palaeo-placer deposits containing gold,[28][29] cassiterite (tin ore),[30] and platinum group minerals.[31] In addition, diagenetic and postdepositional ores of uranium[32] and iron[33] have been found in palaeochannel fills.

Although layers of

opencast mines and collapsable roof rock in coal adits.[34][35][36]

Palaeochannels and aquifers

Coarse-grained (sandy) palaeochannels and palaeovalleys have been proposed as reservoirs or conduits for the preferential underground flow of fresh water. When they extend offshore beneath the continental shelf, they may either transfer freshwater offshore beneath the shelf, or act as pathways for saltwater intrusion into onshore aquifers. Smaller palaeochannels and palaeovalleys, which are commonly filled with muddy or clayey sediments can act as aquicludes that retard and act as barriers to the movement of groundwater.[37]

See also

References

  1. ^ Hayden, A.T., Lamb, M.P., Fischer, W.W., Ewing, R.C., McElroy, B.J. and Williams, R.M., 2019. Formation of sinuous ridges by inversion of river-channel belts in Utah, USA, with implications for Mars. Icarus, 332, pp.92-110.
  2. ISBN 978-90-481-2641-5
  3. ISBN 978-0-631-20472-5
  4. ^ a b c d e Clarke, J., 2009. Palaeovalley, palaeodrainage, and palaeochannel–what's the difference and why does it matter?. Transactions of the Royal Society of South Australia, 133(1), pp.57-61.
  5. ^ a b c Munday, T., Taylor, A., Raiber, M., Soerensen, C., Peeters, L., Krapf, C., Cui, T., Cahill, K., Flinchum, B., Smolanko, N. and Martinez, J., 2020. Integrated regional hydrogeophysical conceptualization of the Musgrave Province, South Australia. Goyder Institute for Water Research Technical Report Series No. 20/04. Adelaide, SA, Australia, Goyder Institute for Water Research. 108 pp.
  6. ^ Shepard, F.P., 1981. Submarine canyons: multiple causes and long-time persistence. American Association of Petroleum Geologist Bulletin, 65(6), pp.1062-1077.
  7. ISBN 978-1-56576-305-0
  8. ^ Long, J.H., Hanebuth, T.J., Alexander, C.R. and Wehmiller, J.F., 2021. Depositional environments and stratigraphy of Quaternary paleochannel systems offshore of the Georgia Bight, southeastern USA. Journal of Coastal Research, 37(5), pp.883-905.
  9. ^ a b c Slingerland, R., and Smith, N.D., 2004. River avulsions and their deposits. Annual Review of Earth and Planetary Sciences, 32, pp.257-285.
  10. ^ Gibling, M.R., Bashforth, A.R., Falcon-Lang, H.J., Allen, J.P. and Fielding, C.R., 2010. Log jams and flood sediment buildup caused channel abandonment and avulsion in the Pennsylvanian of Atlantic Canada. Journal of Sedimentary Research, 80(3), pp.268-287.
  11. ^ Fisk, H.N., 1944. Geological Investigation of the Alluvial Valley of the Lower Mississippi River. Vicksburg, Mississippi, Mississippi River Commission and Washington, DC, War Department, U. S. Army Corps of Engineers. 78 pp.
  12. ^ El Bastawesy, M., Gebremichael, E., Sultan, M., Attwa, M. and Sahour, H., 2020. Tracing Holocene channels and landforms of the Nile Delta through integration of early elevation, geophysical, and sediment core data. The Holocene , 30(8), pp.1129-1141.
  13. ^ Nimnate, P., Thitimakorn, T., Choowong, M. and Hisada, K., 2017. Imaging and locating paleo-channels using geophysical data from meandering system of the Mun River, Khorat Plateau, Northeastern Thailand. Open Geosciences, 9(1), pp.675-688.
  14. ^
    ISBN 978-3-540-29383-5
  15. ^ Knight, R., Steklova, K., Miltenberger, A., Kang, S., Goebel, M., and Fogg, G., 2022. Airborne geophysical method images fast paths for managed recharge of California's groundwater. Environmental Research Letters, 17(12), no. 124021.
  16. ^ Toonen, W.H., Kleinhans, M.G., and Cohen, K.M., 2012. Sedimentary architecture of abandoned channel fills. Earth surface processes and landforms , 37(4), pp.459-472.
  17. ^ Peakall, J., 1998. Axial river evolution in response to half-graben faulting; Carson River, Nevada, USA. Journal of Sedimentary Research, 68(5), pp.788-799.
  18. ISSN 0097-3270
  19. ISBN 978-0-471-62558-2
  20. ^ Sidorchuk, A.Y., and Borisova, O.K., 2000. Method of paleogeographical analogues in paleohydrological reconstructions. Quaternary International, 72(1), pp.95-106.
  21. ^ Behrensmeyer, A.K., 1988. Vertebrate preservation in fluvial channels. Palaeogeography, Palaeoclimatology, Palaeoecology, 63(1-3), pp.183-199.
  22. ISBN 978-0-226-04155-1
  23. ISBN 978-9-400-73403-6
  24. ^ Simon, S., Gibling, M.R., DiMichele, W.A., Chaney, D.S., Looy, C.V. and Tabor, N.J., 2016. An abandoned-channel fill with exquisitely preserved plants in redbeds of the Clear Fork Formation, Texas, USA: an Early Permian water-dependent habitat on the arid plains of Pangea. Journal of Sedimentary Research, 86, 944–964.
  25. ^ Sieh, K.E. and Jahns, R.H., 1984. Holocene activity of the San Andreas fault at Wallace creek, California. Geological Society of America Bulletin, 95(8), pp.883-896.
  26. ^ Dascher-Cousineau, K., Finnegan, N.J., and Brodsky, E.E., 2021. The life span of fault-crossing channels. Science, 373(6551), pp.204-207.
  27. ^ Shen, Z., Dawers, N.H., Törnqvist, T.E., Gasparini, N.M., Hijma, M.P. and Mauz, B., 2017. Mechanisms of late Quaternary fault throw rate variability along the north central Gulf of Mexico coast: Implications for coastal subsidence. Basin Research, 29(5), pp.557-570.
  28. ^ Taylor, D.H., and Gentle, L.V., 2002. Evolution of deep-lead palaeodrainages and gold exploration at Ballarat, Australia. Australian Journal of Earth Sciences, 49(5), pp.869-878.
  29. ^ Garside, L.J., Henry, C.D., Faulds, J.E., Hinz, N.H., Rhoden, H.N., Steininger, R.C., and Vikre, P.G., 2005. The upper reaches of the Sierra Nevada auriferous gold channels, California and Nevada. in Rhoden, H.N., Steininger, R.C., and Vikre, P.G., eds., pp. 209-235, Geological Society of Nevada Symposium 2005: Window to the World, Reno, Nevada, May 2005. Reno, Nevada, Geological Society of Nevada.
  30. ^ Lericolais, G., Berne, S., Hamzah, Y., Lallier, S., Mulyadi, W., Robach, F., and Sujitno, S., 1987. High-resolution seismic and magnetic exploration for tin deposits in Bangka, Indonesia. Marine Minerals, 6(1), pp.9-21.
  31. ^ Slansky, E., Barron, L.M., Suppel, D., Johan, Z., and Ohnenstetter, M., 1991. Platinum mineralization in the Alaskan-type intrusive complexes near Fifield, NSW, Australia. Part 2. Platinum-group minerals in placer deposits at Fifield. Mineralogy and Petrology, 43(3), pp.161-180.
  32. ^ Kumar, P., Panigrahi, B. and Joshi, G.B., 2016. Palaeochannel controlled Cretaceous sandstone-type uranium deposit of Lostoin area, Mahadek basin, Meghalaya. Journal of the Geological Society of India, 87(4), pp.424-428.
  33. ^ Macphail, M.K. and Stone, M.S., 2004. Age and palaeoenvironmental constraints on the genesis of the Yandi channel iron deposits, Marillana Formation, Pilbara, northwestern Australia. Australian Journal of Earth Sciences, 51(4), pp.497-520.
  34. ISBN 978-1-786-20055-6
  35. ^ Sames, G.P. and Laird, R.B., 1987. Geologic Conditions Affecting Coal Mine Ground Control in the Western United States. US Department of the Interior, Bureau of Mines Report, IC-9172. 30 pp.
  36. ^ Kane, W.F., Milici, R.C. and Gathright, T.M., 1993. Geologic factors affecting coal mine roof stability in the eastern United States. Bulletin of the Association of Engineering Geologists, 30(2), pp.165-179.
  37. ^ White, S.M., Smoak, E., Leier, A.L. and Wilson, A.M., 2023. Small Muddy Paleochannels and Implications for Submarine Groundwater Discharge near Charleston, South Carolina, USA. Geosciences, 13(8), no. 232.
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