Establishing the Chronostratigraphy and Miocene-Pliocene Palaeoenvironmental History of the Fazzan Basin, Libyan Sahara
thesisposted on 14.06.2017, 14:49 by Helena Elizabeth White
The vastness of the Sahara Desert makes it a key region for the study of global climate change. Large and important gaps remain, however, in our understanding of the palaeoenvironmental history of the Sahara due to limited terrestrial evidence. The Fazzan Basin, south-west Libya, is one of a few regions to document North Africa’s palaeohydrological history in the form of lake shorelines and sedimentary deposits. The most extensive of these belongs to the Al Mahruqah Formation, recently upgraded to Group status, which is believed to have been deposited by Lake Megafazzan. Previous dating using OSL/U-series has revealed the deposits to be of Quaternary age. However, the origin and age of the deposits are still subject to ongoing debate with the chronological and palaeoenvironmental framework of Miocene-Pliocene units severely lacking. In order to develop and extend the knowledge of the basin during the Neogene, geochemical and sedimentological analyses have been conducted on deposits from six stratigraphic sections from across the northern Fazzan Basin. Palaeomagnetic dating, which is able to date beyond the range of previous dating techniques, has also been completed. This research provides what is believed to be the only low resolution, long-term palaeoenvironmental record of the central Sahara. Magnetostratigraphic and geochemical assessments question the previously proposed ages of the Al Mahruqah Group revealing that several humid intervals leading to several phases of lake development not only occurred in the Quaternary, but throughout the Miocene and early Pliocene. It is therefore proposed that the main drainage networks of the Fazzan basin were established in the early Miocene and hence ideas originally thought about the geomorphological history of the basin need to be redeveloped. It is hoped this research will not only help to fill the palaeoclimatic void of this important region but also potentially contribute to the understanding of the wider Saharan palaeoclimate.