Application of NAA to develop a chemostratigraphy of volcanic deposits on Nisyros and Telos, Greece

Abstract

Deposits formed by explosive volcanic eruptions offer remarkable reliability when used as time-markers. Especially in time periods where radiometric dating is not applicable, sequences of volcanic layers can be used instead for relative dating. At the very least, a perfect synchronization can be established for every place where a certain volcanic layer is present. This paper deals with the development of a chronology for quaternary sediments on the island Telos. It is based upon the volcanic sequences of the islands Nisyros, Giali, and Kos. The eruptions left their traces also on the non-volcanic island Telos. During the Quaternary period, i.e., the last 1.5 million years, it has been inhabited by several groups of mammals, including elephants. These elephants underwent an outstanding dwarfing process. The time span necessary for this evolutionary process is not known and the use of the volcanic chronometer should contribute significant information to that question. Highly conveniently, at Telos itself no volcanic activity took place, but there are deposits from the eruptions mentioned above. Neutron Activation Analysis has already proven most useful for setting up an analytical database for the identification by “chemical fingerprinting” of volcanic eruption products by their element concentration patterns. A suitable number of elements, in particular As, Ba, Ce, Cr, Co, Cs, Eu, Fe, Hf, K, La, Lu, Na, Nd, Rb, Sb, Sc, Sm, Ta, Tb, Th, U, Yb, Zn, Zr, is determined after one irradiation and two measurement cycles. The results show that a clear distinction between the eruption deposits of interest is possible and the sequencing of the deposits on Telos leads to the intended time scale.