{{Short description|Interior drainage basin in Libya}} The '''Fazzan Basin''', or '''Fezzan Basin''', is a large [[endorheic basin]] in Libya. It has no outlet to the sea and contains large areas of desert or semi-arid land. It is one of two basins in southern [[Libya]] on the northern flanks of the [[Tibesti Mountains]] in the central [[Sahara|Sahara desert]], the other being the [[Kufra|Kufra Basin]], further to the east.<ref name=Bridges>{{cite book|author1=Bridges, Edwin Michael |title=World Geomorphology|url=https://books.google.com/books?id=-ZCyyxIZPaIC&pg=PA41 |year=1990 |publisher=Cambridge University Press|isbn=978-0-521-28965-8 |pages=41–42}}</ref>

==Formation== The Fazzan Basin is situated on the junction between two [[Plate tectonics|tectonic plates]]. Collision between these occurred in the [[Paleozoic]] period and caused thickening of the Earth's crust, which then [[Isostasy|downwarped]] under its own weight to form a depression in the ground, the Fazzan Basin. Since then, there has been a deposition of "continental intercalaire" and other continental rocks, and large quantities of water have been trapped in underground [[aquifer]]s. An outcrop of [[basalt]] occurs between the Fazzan and the Kufra Basins, and both are overlaid by sand.<ref name=Bridges/>

The climate of this region has varied greatly in the past, with pluvial and dry periods alternating; the current arid phase averages less than {{convert|20|mm|in|1|abbr=on}} of precipitation per year.<ref name=Armitage/> During its geologic history, the Fazzan Basin has on at least four occasions during the [[Pleistocene]] been inundated with water to form a large lake.<ref name=Armitage/> On each occasion, a thick layer of limestone was deposited. Armitage et al. (2007) estimated that two of these events occurred earlier than 400,000 years ago, another one was in [[MIS 11]] (~400,000 years ago) and a further one in [[MIS 5]] (between 130,000 and 80,000 years ago).<ref name=Armitage>{{cite journal |author=Armitage, S.J. |author2=Drake, N.A. |author3=Stokes, S. |author4=El-Hawat, A. |author5=Salem, M.J. |author6=White, K. |author7=Turner, P. |author8=McLaren, S.J. |year=2007 |title=Multiple phases of North African humidity recorded in lacustrine sediments from the Fazzan Basin, Libyan Sahara |journal=Quaternary Geochronology |volume=2 |issue=1–4 |pages=181–186 |doi=10.1016/j.quageo.2006.05.019 |hdl=2381/11455 |hdl-access=free }}</ref> Geye and Thiedig (2008) recognise further lake sedimentation periods in [[MIS 9]] and [[MIS 7]]. They have also estimated that the lake extended to {{convert|100000|km2|mi2|0|abbr=on}} in MIS 11, and this was when it was at its maximum size. By MIS 5, the lake was reduced to {{convert|1400|km2|mi2|0|abbr=on}} and less than {{convert|100|km2|mi2|0|abbr=on}} during the most recent iteration in the [[Holocene]].<ref>{{cite journal |author=Geyh, Mebus A. |author2=Thiedig, Friedhelm |year=2008 |title=The Middle Pleistocene Al Mahrúqah Formation in the Murzuq Basin, northern Sahara, Libya evidence for orbitally-forced humid episodes during the last 500,000 years |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=257 |issue=1–2 |pages=1–21 |doi=10.1016/j.palaeo.2007.07.001}}</ref> However, Armitage et al. (2007), citing Brooks et al. (2003), put the Holocene lake area at {{convert|76250|km2|mi2|0|abbr=on}}.<ref name=Hublin>{{cite book|editor1=Hublin, Jean-Jacques |editor2=McPherron, Shannon P.|title=Modern Origins: A North African Perspective |url=https://books.google.com/books?id=GyYt3Ogx5AQC&pg=PA38 |year=2012 |publisher=Springer Science & Business Media|isbn=978-94-007-2929-2 |pages=38–39|doi=10.1007/978-94-007-2929-2_3|chapter=Spatial and Temporal Variation in the Nature of Pleistocene Pluvial Phase Environments Across North Africa|last1=Smith|first=J. R.}}</ref> Although there is some disagreement about the exact timing and the size of Lake Megafazzan, both authorities agree that there has been no [[Lacustrine deposits|lacustrine]] activity between MIS 5 and the Holocene. The MIS 5 deposits include fossils of ''[[Cerastoderma glaucum]]'', which indicates that the water was probably [[Brackish water|brackish]].<ref name=Hublin/>

==Lake Megafazzan== During the [[Miocene]], Libya was drained by two large rivers systems, both flowing into the [[Mediterranean Sea]], the [[Wadi Nashu]] River in the west and the [[Sahabi River]] in the centre and east. In the late Miocene and early [[Messinian]], increased volcanic activity in northeastern Libya resulted in the damming back of the Wadi Nashu, which caused water to accumulate in the Fazzan Basin, forming the proto-Lake Megafazzan during humid periods.<ref name=Drake>{{cite journal |author=Drake, N.A. |author2=El-Hawat, A.S. |author3=Turner, P. |author4=Armitage, S.J. |author5=Salem, M.J. |author6=White, K.H. |author7=McLaren, S. |year=2008 |title=Palaeohydrology of the Fazzan Basin and surrounding regions: The last 7 million years |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=263 |issue=3–4 |pages=131–145 |doi=10.1016/j.palaeo.2008.02.005 }}</ref>

==References== {{Reflist}}

[[Category:Endorheic basins of Africa]] [[Category:Sedimentary basins of Africa]] [[Category:Geology of Libya]]