Recent alluvial fan developments in Muğla (SW Turkey)

Abstract

The Muğla Polje (SW Turkey), which formed as a result of the Pleistocene activity of the Muğla Fault, is an example of a rift basin with two alluvial fans (the Muğla Fan, 3.33 km2 and the Düğerek Fan, 1.26 km2). This study focuses on the development of these fans through the evaluation of aerial photos, Google-Earth images, the measurements of sedimentary sections, lithological examinations, mineralogical discriminations, and in situ observations. Fractured Jurassic-Cretaceous limestone and upper Miocene-Pliocene clastics have been observed in drainage areas of both fans. In the drainage area of the Muğla Fan, where low strength upper Miocene-Pliocene clastics are abundant, the river incision is higher. As a result, higher amount of sediment supply led to formation of the larger Muğla Fan. Small scale tectonic activities and rainy periods led to the formation of poorly sorted, angular-subangular, and coarser-grained pebblestone-cobblestone deposits, whereas, tectonically quiescent and dry periods were represented by the finer-grained sediments at the apex and upper fan of both fans. They pass into the finer-grained deposits in the downdip direction. Recently, the Muğla and Düğerek fans surface has been covered by urbanization. Man-made channel was built to protect humans from floods, which starts from the apex and extends beyond the distal fan in Polje center. Thus, sediment and water required for fan development have been all cut. Both fan development were initially controlled by nature, such as tectonic activities and climate, and now by humans. Therefore, this study recommends the constant monitoring of the impact of human interference on fan development while regulating the feeding mechanism of fan basin interiors, natural balance of local environment, and urban lives.