Geology of Late Miocene clayey sediments and distribution of palaeosol clay minerals in the north-eastern part of the Cappadocian Volcanic Province (Araplı-Erdemli), central Anatolia, Turkey

Abstract

The study area is situated in the Araplı-Erdemli (Kayseri) area in the north-eastern part of the Cappadocian Volcanic Province (CVP), central Anatolia. The Late Miocene series comprises lacustrine and fluvial deposits interbedded with ignimbrites and lava flows. The Late Miocene Mustafapaşa member of the Ürgüp Formation comprises yellow to red mudstone that alternates with thin sandstone beds in the north-eastern part of the CVP. This unit continues upward through the Cemilköy ignimbrite palaeosol layers (comprising altered Cemilköy ignimbrite, vertisol and well-developed palaeosol layers), the Gördeles ignimbrite and red palaeosol layers, and includes two fallout levels; it is overlain by the Kızılkaya ignimbrite. The Mustafapaşa member is dominated by smectite±illite±chlorite, whereas the altered Cemilköy ignimbrite is predominantly kaolinite±smectite±chlorite. The underlying lower level of the Gördeles ignimbrite contains palaeosol layers, and continues upward through smectite-dominated layers. Alteration of feldspars and glass shards in the Cemilköy and Gördeles ignimbrites resulted in the depletion of soluble alkaline elements (such as Ca, Na and K) from these ignimbrites downward to the Mustafapaşa member, and palaeosol levels (Bayramhacılı member) in the Araplı area favoured precipitation of smectite in an alkaline environment. However, the absence of these elements in these ignimbrites may have resulted in the enhancement of Al+Fe/Si-favoured precipitation of kaolinite in an acidic environment. Conversely, palaeosol of the Erdemli area consists of smectite±illite±chlorite. Micromorphologically, flaky smectite rims illite in both the Araplı and Erdemli areas and this can be explained by the release of K and Al during desorption of feldspar. Additionally, higher Ni, Co and Cr_2O_3 values in the mudstone samples of the Mustafapaşa member and palaeosol levels, the presence of iron oxide and partially chloritised pyroxene and hornblende, together with ophiolitic and metamorphic grains, indicate that the basin also accumulated ophiolitic and metamorphic rock fragments in its sediment supply. This suggests that the Araplı area in the southern part of the CVP has undergone erosion, and that the present-day Erdemli area was close to the shallow-lake depositional environment of the northern part of CVP.