THE GEOMORPHOLOGICAL DEVELOPMENT OF EPHEMERAL AND RELICT RIVER VALLEY SYSTEMS IN THE NORTH PART OF THE IRAQI WESTERN DESERT

This research project provides a geomorphological and geological analysis of ephemeral and relict river valley systems in the north part of the Iraqi Western Desert. The area surveyed covers approximately 30 000 km2 and is one of the remotest and least studied parts of the Arabian Peninsula. Part of the reason for the lack of research in this area in recent years has been the ongoing security problems and all fieldwork undertaken for this thesis was carried out with the support of armed guards and police. In addition much of the work on the geology and geomorphology of the region is in confidential files commissioned by oil companies, and in MSc and PhD theses held in Iraqi Universities. A significant part of this work and indeed many scientific papers, are only available in Arabic. Therefore a major element of the work for this thesis has been to translate this material and make the results available in English for the first time. The study demonstrates that the present surface of the Iraqi Western Desert overall forms an incised plateau developed during two phases of continental erosion and deposition during the Tertiary and Quaternary periods. The first phase started after Oligocene uplift formed an older plateau within the Oligocene Tayarat formation. This plateau is characterized by denudation processes associated with a semiarid climate, including the formation of subsurface hollows and caves. The second phase, which began after the last Alpine Orogenic movement, and includes the Pliocene and Quaternary periods, formed a younger plateau developed on the Zahra formation. This younger plateau is characterized by processes indicative of climatic fluctuations from wet to arid and semiarid, which induced denudation in places and deposition in others. However, in terms of the geomorphological landforms present in the Western Desert they can be broadly divided into: i) Structural and erosion-denudation forms ii) Accumulation forms Lithology landform in these two categories has resulted in the production of a new geomorphological map of the Iraqi Western Desert. A key component of this map uses the drainage networks. Four distinct drainage systems were identified: 1. The valleys which descend from west to east. These valley systems are located to the south and south east town of Rutba 2. The valleys which descend from south to north. These lie to the west and southwest of Rutba and are controlled by the north to south strike of exposed Palaeogene strata. 3. The valleys which descend from east south to north west, located north of the Garaa area like Ratga and Akash. 4. The valleys which descend from east to west. These valley systems are located to the south and south west town of Rutba, like Swab and Wallaj valleys. Investigation of these four networks established that they were relict systems that still carried ephemerally active misfit rivers and stream. The overall control on their form was the alternating sequences of variable strength rocks that were exposed and eroded as part of the uplift of an anticlinorium (Houran) and anticline (Garaa), associated with the Alpine Orogeny .However, the unclearing Structures were much older and can be traced back to Permian tectonic processes. The drainage of the Western Desert, therefore, is antecedent and controlled by Tertiary and Quaternary tectonics. The rivers appear to have active throughout the Pleistocene incising into the Western Desert plateaux. Highest incision rates probably occurred during more pluvial periods in the Pleistocene which may have been coincident with glacial marine in the Northern Hemisphere. The contemporary rivers are misfit within larger valleys although still subject to flash floods under the right metrological conditionMinistry of Higher Education and Scientific Research Baghdad, Ira