Megalake
A megalake (pl. megalakes) is a very large lake. The term “megalake” is generally used to describe very large prehistoric waterbodies. There is no formal definition but according to Quade.[1], megalake systems from around the world are characterized by a series of diagnostic features, such as multiple well-defined shoreline benches, wave-rounded beach gravels where coarse material is present, landscape smoothing by lacustrine sediment, large-scale deltaic deposits, and in places, tufas encrusting shorelines. In the case of the megalakes from the geologic record, some of the landscape features (e.g., shoreline benches) are difficult to observe as younger rocks cover the lake deposits. In this case, these old megalakes can be identified using interpolations of lacustrine sediment packages (with characteristic non-marine fauna), that can be observed in outcrops or using seismic data that can identify large-scale deltaic deposits in the sub-surface.
Types
Three types of megalakes are generally encountered in the geological record: ice-dammed megalakes, flooded continental depression megalakes, incipient ocean sea-lakes and tectonically trapped sea-lakes.
Ice-dammed megalakes
Ice-dammed lakes are a type of Proglacial Lake formed where mountain glaciers or ice sheets block the flow of water. Presently relatively small ice-dammed lakes are found in mountainous regions at the terminations of mountain glaciers.
Much larger waterbodies, dubbed ice-dammed megalakes, are found in the recent geologic record - closely linked to large ice sheets that due to their considerable weight, caused landmasses to subside. Ice-dammed megalakes formed at the end of ice ages when retreating ice sheets and glaciers provided a source of meltwater. These megalakes tend to be shallow and have elongated shapes (because they develop in valleys or along the edge of the ice sheet).
Best examples: Agassiz megalake[2], Ojibway megalake[2], West Siberian Lake, Lake Komi, the White Sea Basin Lake, the Baltic Lake[3] (Ancylus Lake) and Missoula lake[2].
Ice-dammed megalakes are often associated with cataclysmic outburst floods that occur when the weight of the megalake’s water mass overcomes the ice dam, either by breaking it or by lifting it. In some cases, these cataclysms repeated multiple times, creating spectacular erosional landscapes preserved today (e.g., Channeled Scablands). In contrast, in the case of the most significant outburst floods, it is hypothesized that they induced brief planet-wide cooling events[4].
Flooded continental depression megalakes
The flooded continental depressions are land-locked areas in the interior of a continent that get flooded when wet climate episodes occur in generally dry climate regions. Due to normally dry climatic conditions, the continental depressions don't develop drainage networks and in wet periods large volumes of water can accumulate in these depressions. These megalakes tend to be wide and shallow and are often associated with large deltaic systems.
Best examples: Sahara megalakes Chad[5] and Timbuktu[6], Megalake Makgadikgadi[7], Megalake Bungunia[8], "Jilantai-Hetao" Megalake[9]
Incipient ocean sea-lakes
Continental rift areas can form depressions that fill with water and become rift lakes (e.g., Lake Baikal, Lake Tanganyika, Lake Malawi). These generally long and narrow lakes can expand and connect to the ocean to form rift seas (e.g., Red Sea). This process can be reversed, and the rift seas can become megalakes (e.g., Red Sea during the Ice Ages).
Tectonically trapped sea-lakes
Marginal seas or bays can become isolated from the ocean if tectonic uplift or volcanic activity close the sea straits. Once isolated these aquatic realms can maintain an outflow of excess water flowing into the global ocean (e.g., Lake Nicaragua) or they become completely land-locked, if they have a deficit of water (e.g., Caspian Sea).
Some of the largest megalakes in earth history were formed when epicontinental seas and fragments of former ocean became completely surrounded by land. These megalakes tend to consist of very deep basins, separated by internal shallow sills. The trapped sea megalakes can last for millions of years and they can develop their own endemic fauna, derived from survivors of the marine fauna that once inhabited them, and often they can experience reconnections with the global ocean. Due to their long lifespan and isolation, these megalakes. Best examples: Paratethys Megalake[10], Pannon Megalake[11], Lago-Mare megalakes system[12], Pebas-Amazon mega-wetland system[13], Parana basin megalake.
References
- ↑ Quade, J.; Dente, E.; Armon, M.; Ben Dor, Y.; Morin, E.; Adam, O.; Enzel, Y. (2018). "Megalakes in the Sahara? A Review". Quaternary Research. Cambridge University Press. 90 (2): 253–275. Bibcode:2018QuRes..90..253Q. doi:10.1017/qua.2018.46. Retrieved 8 November 2022. Unknown parameter
|s2cid=ignored (help) - ↑ 2.0 2.1 2.2 Harrison, Stephan; Smith, David E.; Glasser, Neil F. (2019). "Late Quaternary meltwater pulses and sea level change" (PDF). Journal of Quaternary Science. 34 (1): 1–15. Bibcode:2019JQS....34....1H. doi:10.1002/jqs.3070. Unknown parameter
|s2cid=ignored (help) - ↑ Krinner, G.; Mangerud, J.; Jakobsson, M.; Crucifix, M.; Ritz, C.; Svendsen, J.I. (2004). "Enhanced ice sheet growth in Eurasia owing to adjacent ice-dammed lakes". Nature. 427 (6973): 429–432. Bibcode:2004Natur.427..429K. doi:10.1038/nature02233. PMID 14749827. Unknown parameter
|s2cid=ignored (help) - ↑ Murton, Julian B.; Bateman, Mark D.; Dallimore, Scott R.; Teller, James T.; Yang, Zhirong (2010). "Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean". Nature. 464 (7289): 740–743. Bibcode:2010Natur.464..740M. doi:10.1038/nature08954. PMID 20360738. Unknown parameter
|s2cid=ignored (help) - ↑ Schuster, Mathieu; Roquin, Claude; Moussa, Abderamane; Ghienne, Jean-François; Duringer, Philippe; Bouchette, Frédéric; Durand, Arnaud; Allenbach, Bernard (2014). "Shorelines of the Holocene Megalake Chad (Africa, Sahara) investigated with very high resolution satellite imagery (Pléiades) : example of the Goz Kerki paleo-spit". Revue Française de Photogrammétrie et de Télédétection (208): 63–68. doi:10.52638/rfpt.2014.114.
- ↑ Drake, Nicholas; Candy, Ian; Breeze, Paul; Armitage, Simon; Gasmi, Nabil; Schwenninger, Jean-Luc; Peat, David; Manning, Katie (2022). "Sedimentary and Geomorphic evidence of Saharan megalakes: a synthesis". Quaternary Science Reviews. 276: 107318. Bibcode:2022QSRv..27607318D. doi:10.1016/j.quascirev.2021.107318. Unknown parameter
|s2cid=ignored (help) - ↑ Podgorski, Joel E.; Green, Alan G.; Kgotlhang, Lesego; Kinzelbach, Wolfgang K.H.; Kalscheuer, Thomas; Auken, Esben; Ngwisanyi, Tiyapo (2013). "Paleo-megalake and paleo-megafan in southern Africa". Geology. 41 (11): 1155–1158. Bibcode:2013Geo....41.1155P. doi:10.1130/G34735.1. Retrieved 8 November 2022.
- ↑ Stephenson, A.E. (1986). "Lake Bungunnia — A Plio-Pleistocene megalake in southern Australia". Palaeogeography, Palaeoclimatology, Palaeoecology. 57 (2–4): 137–156. doi:10.1016/0031-0182(86)90011-8. Retrieved 8 November 2022.
- ↑ Fahu, Chen; Yuxin, Fan; Madsen, D.B.; Xi, Chun; Hui, Zhao; Liping, Yang (25 September 2008). "Preliminary study on the formation mechanism of the "Jilantai-Hetao" Megalake and the lake evolutionary history in the Hetao region". Quaternary Sciences. 28 (5): 866–873. Retrieved 8 November 2022.
- ↑ Palcu, Dan Valentin; Patina, Irina Stanislavovna; Șandric, Ionuț; Lazarev, Sergei; Vasiliev, Iuliana; Stoica, Marius; Krijgsman, Wout (2021). "Late Miocene megalake regressions in Eurasia". Scientific Reports. Nature. 11 (1): 11471. Bibcode:2021NatSR..1111471P. doi:10.1038/s41598-021-91001-z. PMC 8169904 Check
|pmc=value (help). PMID 34075146 Check|pmid=value (help). - ↑ Geary, D.H.; Magyar, I.; Müller, P. (2000). "Ancient Lake Pannon and its endemic molluscan fauna (Central Europe; mio-pliocene)". Advances in Ecological Research. 31: 463–482. doi:10.1016/S0065-2504(00)31025-X. ISBN 9780120139316.
- ↑ Andreetto, F.; Aloisi, G.; Raad, F.; Heida, H.; Flecker, R.; Agiadi, K.; Lofi, J.; Blondel, S.; Bulian, F.; Camerlenghi, A.; Caruso, A.; Ebner, R.; Garcia-Castellanos, D.; Guibourdenche, V.; Gvirtzman, Z.; Hoyle, T.M.; Meijer, P.T.; Moneron, J.; Sierro, F.J.; Travan, G.; Tzevahirtzian, A.; Vasiliev, I.; Krijgsman, W. (2021). "Freshening of the Mediterranean Salt Giant: controversies and certainties around the terminal (Upper Gypsum and Lago-Mare) phases of the Messinian Salinity Crisis". Earth-Science Reviews. 216 (103577): 103577. Bibcode:2021ESRv..21603577A. doi:10.1016/j.earscirev.2021.103577. Unknown parameter
|s2cid=ignored (help) - ↑ Hoorn, Carina; Boschman, Lydian M; Kukla, Tyler; Sciumbata, Matteo; Val, Pedro (2022). "The Miocene wetland of western Amazonia and its role in Neotropical biogeography". Botanical Journal of the Linnean Society. 199 (1): 25-35. doi:10.1093/botlinnean/boab098.
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