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Saharan Palaeohydrology
Kevin White1, Nick Drake2, Simon Armitage3, Ahmed El-Hawat4, Mustafa Salem5
1University of Reading, UK2King’s College London, UK
3Royal Holloway, University of London, UK4Gayounis University, Benghazi, Libya
5Al Fatah University, Tripoli, Libya
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Introduction
Reconstructing Saharan palaeohydrology is of importance because
1. Impact on modern water resources
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Introduction
Reconstructing Saharan palaeohydrology is of importance because
1. Impact on modern water resources
2. Export of mineral aerosol
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Introduction
Reconstructing Saharan palaeohydrology is of importance because
1. Impact on modern water resources
2. Export of mineral aerosol
3. Impact on human migration out of Africa
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Lacustrine sediments widespread throughout the region, but when were the highstands and how large was the area inundated?
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Field-based surveys are difficult in this terrain
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Remote sensing enables fieldwork to be targeted to important palaeoenvironmental sites
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Multispectral optical remote sensing enables identification of outcrops of lacustrine sediments rich in sulphates and carbonates
3 km
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Radarsat
Landsat ETM+
5 km
But heavily silicified limestones can only be identified by radar
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Well developed cyclical sedimentation around the margins of the basin (over 500m a.s.l.)
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Five limestone/sand cycles are found throughout the Fazzan basin, but only the top cycle is young enough to fall within the range of OSL dating (420 +/- 34 ka)
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Coquinas (340m a.s.l), death assemblages representing nearshore beach ridges (113 ±10, 107 ±6, 97.7 ±5.1)
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Interdunes in the Ubari sand sea (ca.500m a.s.l.), higher mesas 118 +27–20, 47 +17–13 and 14.3 +1.7–1.7 ka. Dark humic palaeolake sediments in the base of interdunes 9.12 +0.09-0.14, 8.31 +/- 0.5 BP 8.42 +0.04-0.12, 6.69 +0.03-0.05, 5.94 +/- 0.4, 3.36 +/- 0.45 ka
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Shorelines preserved adjacent to escarpment
Shorelines dated and their heights determined using DGPS
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200 km
Maximum lake area (from SRTM3 DEM) is 134,617 km2, drainage basin area is 450,000km2 (ca. 1/3rd catchment)
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Though not as big as Lake MegaChad (344,320 km2), Lake MegaFazzan is second largest Palaeolake in the Sahara
500m 527m
340m
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Associated archaeology
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• Modelling studies show that, in the vicinity of large water bodies, 6% lake cover affects the climate as much as orbital forcing (Coe and Foley 2003)
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• Remote sensing and DEM analyses enable palaeohydrological reconstruction of Lake MegaFazzan
• Its maximum size was about 134,617 km2
• Evidence of highstands at 420, 120, 74, 47, 30, 14 and 10 ka• 4 as yet undated lacustrine cycles that are older than 420 ka• Wet during much of the Early Holocene; however, evidence
of abrupt shifts to arid conditions at 9.8, 7.4 and 6.0 ka• Further study of relationship with highstands in surrounding
basins is critical to understanding Saharan palaeoenvironments
Conclusions