Tephrostratigraphy and tephrochronology in the Philippi peat basin, Macedonia, Northern Hellas (Greece)

摘要

Three tephra layers have been identified in the upper 15 m of a 190-m section of peat beneath the Philippi fen. They provide significant lithological and chronological markers throughout the fen and the Aegean region. The upper tephra (PhT1) consists of shards of a transparent calcalkaline felsic glass and fragments of plagioclase, augite, hypersthene, and rare hornblende, magnetite, apatite and quartz. Peat directly beneath PhT1 gave a radiocarbon approximate age of 13, 000 yr. The middle tephra layer (PhT2), which resembles PhT1 in chemistry and petrography but contains more crystals and lithic fragments, rests on peat dated ca 18,000 ~(14)C yr BP. The lower tephra (PhT3) has colorless to brown glass shards with a trachytic chemistry and a mineral assemblage of sanidine, sodic plagioclase, biotite, aegirine-augite, hornblende, titanite and apatite. Bracketing radiocarbon ages imply that PhT3 accumulated about ～ 30,000 ~(14)C yr BP. The likely ages of PhT1 and PhT2, together with their mineralogical and chemical characteristics, suggest that these tephras came from the volcanic field of Thera in the Hellenic arc. PhT2 particularly was derived from a major, known explosive eruption ca 18,000 yr BP, the Cape Riva eruption, correlative to the Y-2 tephra layer. Evidence for PhT3 suggests derivation from the Campanian Province of Italy, and correlation with the Campanian Ignimbrite and the Y-5 ash beneath the Mediterranean Sea.