This study aimed to identify the clay minerals in Holocene aged unconsolidated fluviolacustrine sediments in the Moralli Stream system and to reveal the source of the clay minerals. The bulk rock and clay fraction analyses were performed by X-ray diffraction method (XRD) to determine the minerals in the fluvio-lacustrine sediments. As a result of bulk rock analysis, amphibole, feldspar, calcite, quartz, mica, pyroxene and clay mineral assemblage, and the clay fraction analysis, illite, kaolinite, chlorite, smectite, mixed-layer chlorite-smectite minerals were determined in the surface sediments. It was concluded that illite, kaolinite, chlorite and smectite minerals detected in the sediments are derived from amphibole, feldspar, mica and pyroxene group minerals found in volcanic, metamorphic and sedimentary rocks outcropped in the study area and subjected to various weathering processes. The illite mineral associated with the chlorite mineral detected in the coastal sediments of Van Lake indicates that the illite mineral is of detrital origin and was transported by the Moralli stream and deposited on the shore of Lake Van. In addition, kaolinite, chlorite and smectite clay mineral associations detected in coastal sediments indicate that the volcanic material found in Lake Van has the characteristics of a volcanic barrier lake, has been altered in situ or they may have formed as a result of the decomposition of other volcanic rocks in the source area and was transported and deposited in the basin.

Keywords: Lake Van, Moralli Stream system, Fluvio-lacustrine sediments, Clay mineralogy