origins of the Ubari/Awbari lakes

[Sam Rutherford]

I have heard all the stories (I think), but is there a definitive description of their creation, continued existence etc.?

Cheers, Sam.

[Richard Washington]

Palaeohydrology of the Fazzan Basin and surrounding regions: The last 7 million yearsHere is a summary of an article on the palaeo drainage of Libya.....Author(s): Drake NA (Drake, N. A.)1, El-Hawat AS (El-Hawat, A. S.)2, Turner P (Turner, P.)3, Armitage SJ (Armitage, S. J.)4, Salem MJ (Salem, M. J.)5, White KH (White, K. H.)6, McLaren S (McLaren, S.)7

Source: PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY Volume: 263 Issue: 3-4 Pages: 131-145 Published: JUN 23 2008


Abstract: We have integrated information on topography, geology and geomorphology with the results of targeted fieldwork in order to develop a chronology for the development of Lake Megafazzan, a giant lake that has periodically existed in the Fazzan Basin since the late Miocene. The development of the basin can be best understood by considering the main geological and geomorphological events that occurred thought Libya during this period and thus an overview of the palaeohydrology of all Libya is also presented. The origin of the Fazzan Basin appears to lie in the Late Miocene. At this time Libya was dominated by two large rivers systems that flowed into the Mediterranean Sea, the Sahabi River draining central and eastern Libya and the Wadi Nashu River draining much of western Libya. As the Miocene progressed the region become increasingly affected by volcanic activity on its northern and eastern margin that appears to have blocked the River Nashu in Late Miocene or early Messinian times forming a sizeable closed basin in the Fazzan within which proto-Lake Megafazzan would have developed during humid periods. The fall in base level associated with the Messinian desiccation of the Mediterranean Sea promoted down-cutting and extension of river systems throughout much of Libya. To the south of the proto Fazzan Basin the Sahabi River tributary know as Wadi Barjuj appears to have expanded its headwaters westwards. The channel now terminates at Al Haruj al Aswad. We interpret this as a suggestion that Wadi Barjuj was blocked by the progressive development of Al Haruj al Aswad. K/Ar dating of lava flows suggests that this occurred between 4 and 2 Ma. This event would have increased the size of the closed basin in the Fazzan by about half, producing a catchment close to its current size (-350,000 km(2)). The Fazzan Basin contains a wealth of Pleistocene to recent palaeolake sediment outcrops and shorelines. Dating of these features demonstrates evidence of lacustrine conditions during numerous interglacials spanning a period greater than 420 ka. The middle to late Pleistocene interglacials were humid enough to produce a giant lake of about 135,000 km(2) that we have called Lake Megafazzan. Later lake phases were smaller, the interglacials less humid, developing lakes of a few thousand square kilometres. In parallel with these palaeohydrological developments in the Fazzan Basin, change was occurring in other parts of Libya. The Lower Pliocene sea level rise caused sediments to infill much of the Messinian channel system. As this was occurring, subsidence in the Al Kufrah Basin caused expansion of the Al Kufrah River system at the expense of the River Sahabi. By the Pleistocene, the Al Kufrah River dominated the palaeohydrology of eastern Libya and had developed a very large inland delta in its northern reaches that exhibited a complex distributary channel network which at times fed substantial lakes in the Sirt Basin. At this time Libya was a veritable lake district during humid periods with about 10% of the country underwater. (C) 2008 Elsevier B.V. All rights reserved.

[Sam Rutherford]

Well, that's cleared that up then!? :confused1:

Erm, any chance of something a little simpler and practical?!

Cheers, Sam.

[Richard Washington]

What, from scientists?!
Nick Drake at Kings College is the guy to ask. I'll get on to him....

[Sam Rutherford]

Hi Richard,

Cheers!

Sam.

[Richard Washington]

Sam,
Nick's reply is below. I have copied the abstract of the paper onto the thread - there's more from that paper if you want....

Hi
I take it you mean the lakes that still contain water. If so little or
nothing has been done on them as far as I am aware. They are groundwater
fed vestiges of more numerous lakes in the sand sea that have now dried
up. We have done a bit on them.

Parker, A.G., Harris, B.M., White, K.H., *Drake, N.A*. (2008) Phytoliths
as indicators of grassland dynamics during the Holocene from lake
sediments in the Ubari Sand Sea, Fezzan Basin, Libya. /Libyan Studies,
/39,/ /29-40.

Abstract
This study presents the first phytolith study from the Saharan region. Phytolith analysis shows the potential of reconstructing grassland dynamics during the Holocene, refining our knowledge of palaeoecosystems in the Ubāri Sand Sea, Libya. The lake sediments studied range in age between 3273-9440 cal. BP. Tree cover was very low around 3273-3436 and 6678-6796 cal. BP, and the landscape was dominated by C4 grasslands around 6678-6796 cal. BP, shifting to a more mixed C3-C4 grassland community around 3273-3436 cal. BP. These differences may be caused by the older sample being deposited during the onset of a brief arid period, but a similar phytolith assemblage could arise due to a more pronounced seasonality in the climate, with C3 grasses dominating late and early in the growing season when the climate is cooler and less arid, and C4 grasses becoming dominant in the hot, dry summer season.