Stratigraphy of the Volcanic Products Around Nemrut Caldera: Implications for Reconstruction of the Caldera Formation

Abstract

The volcanological development of the Nemrut stratovolcano, located near the southwestern tip of Lake Van in eastern Turkey, is subdivided into three stages: pre-caldera, post-caldera and late stages. Two ignimbrite flows have been recognized in the pre-caldera stage. The earlier of the two occurred after basaltic lavas formed along extensional fissures. The latter, which forms the main subject of this paper, was a major flow associated with the development of the Nemrut caldera. The pyroclastic deposits of the Nemrut volcano in the pre-caldera stage are divided into three phases on the basis of palaeosols that separate them. The first phase includes plinian pumice falls and a pyroclastic flow deposit. The major ignimbrite occurs in the second pyroclastic phase and is here subdivided into three sub-layers based on colour, internal grading, size of pumice and lithic clasts, and the degree of welding. The third and last pyroclastic phase was dominated by plinian pumice and ash-fall deposits. The occurrence of palaeosols between pyroclastic phases suggests that there were periods of inactivity between the eruptions. Formation of the Nemrut caldera is thought to have resulted from eruptions of pyroclastic materials with a volume of about 62.6 km(3).