BRIEF NOTE ON NEW DATA RELATED TO THE CHRONOSTRATIGRAPHIC LOCATION OF CUMAOVASI VOLCANICS

This study was made in order to contribute for reviewing Neogene stratigraphy proposed in previous studies (Figure 2a, b, c, d) based on new K/Ar ages obtained from acidic volcanics in Çubukludağ section (Figure 1a, b) of the Akhisar Depression (Kaya, 1979). Starting with Early Miocene extension, the infill of Çubukludağ half graben under the control of İzmir fault proposed by Kaya et al. (2007) (ancestor of Tuzla fault proposed by Emre et al., 2005) Is formed by deposits of Bahçecik, Yeniköy and Tahtalı formations from bottom to top and of Cumaovası volcanics (Figure 2e). The lower part of Bahçecik formation symbolizing the Early Miocene deposition does not crop out over the area, because Tuzla fault has generated a depression. The observable part of the sedimentary deposit is formed by lacustrine and fluvial deposits consisting of lignite layers at bottom and by the overlying crimson-maroon lacustrine fan delta deposits with distinctive contacts which reflect a probable unconformity. Algal limestone interlayers symbolizing temporal lacustrine deposit take place within fan delta. Yeniköy formation which unconformably overlies Bahçecik formation and evolves from alluvial environment into lacustrine environment, and Tahtalı formation (Göktaş, 2013) which is formed from bottom to top by alluvial, fluvial and lacustrine deposits reflect Middle Miocene sedimentation (Figure 2e). At the main explosion phase of phreatomagmatic Cumaovası volcanism which began in lacustrine environment and where Yeniköy formation was deposited in, the western side of the basin was enclosed with the emplacement of multi layered ignimbrites following the base surge deposition. Then, Tahtalı formation was deposited to the east of the volcanic axis trending in NE-SW direction. Upper Miocene alluvial fan delta deposits overlying Cumaovası volcanics with angular unconformity forms the youngest Neogene infillings of the study area.