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

Introduction

Reconstructing Saharan palaeohydrology is of importance because

1. Impact on modern water resources

Introduction

Reconstructing Saharan palaeohydrology is of importance because

1. Impact on modern water resources

2. Export of mineral aerosol

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

Lacustrine sediments widespread throughout the region, but when were the highstands and how large was the area inundated?

Field-based surveys are difficult in this terrain

Remote sensing enables fieldwork to be targeted to important palaeoenvironmental sites

Multispectral optical remote sensing enables identification of outcrops of lacustrine sediments rich in sulphates and carbonates

3 km

Radarsat

Landsat ETM+

5 km

But heavily silicified limestones can only be identified by radar

Well developed cyclical sedimentation around the margins of the basin (over 500m a.s.l.)

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)

Coquinas (340m a.s.l), death assemblages representing nearshore beach ridges (113 ±10, 107 ±6, 97.7 ±5.1)

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

Shorelines preserved adjacent to escarpment

Shorelines dated and their heights determined using DGPS

200 km

Maximum lake area (from SRTM3 DEM) is 134,617 km2, drainage basin area is 450,000km2 (ca. 1/3rd catchment)

Though not as big as Lake MegaChad (344,320 km2), Lake MegaFazzan is second largest Palaeolake in the Sahara

500m 527m

340m

Associated archaeology

• 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)

• 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