Abstract/Summary

This paper reviews previous research on Lake Megafazzān, a giant lake that has periodically existed in the Fazzān Basin since the late Miocene. The aim is to develop a chronology for the development and demise of this giant body of water. In the Late Miocene Libya was dominated by two large river systems that flowed into the Mediterranean Sea, the As Sahābi river draining central and eastern Libya and the Wadi Nāshu river draining much of western Libya. As the Miocene ended, volcanic activity blocked the Nāshu river in Late Miocene or Early Messinian times, forming a sizeable closed basin in the Fazzān for the first time that would have developed a substantial lake during humid periods. The fall in base level associated with the Messinian desiccation of the Mediterranean Sea promoted extension of river systems throughout much of Libya and, as a result, Wadi Barjuj appears to have expanded its headwaters westwards, capturing much of what is now the southern Fazzān from Wadi Nāshu. The channel was then blocked by continued volcanic activity some time between 4 and 2 Ma, increasing the size of the Fazzān Basin by about half. The Fazzān Basin contains many Pleistocene to Recent palaeolake sediment outcrops that demonstrate evidence of lacustrine conditions during numerous interglacials spanning a period greater than 750 ka. The middle to late Pleistocene interglacials were humid enough to produce a giant lake of about 135,000 sq. km. Later lake phases were smaller, the interglacials less humid, developing lakes of a few thousand square kilometres.