Tephra in caves: Distal deposits of the Minoan Santorini eruption and the Campanian super-eruption

Abstract

Tephra deposits in caves are not only significant as stratigraphic markers. The comparatively sheltered position of cave environments, protected from rainfall, may preserve original distal tephra deposition features, unlikely to have survived in the open landscape. Most reported findings of tephra in caves are from the Campanian super-eruption, which originated in the area of Naples (Italy). These findings facilitate evaluation in different caves of facies variability and modes of tephra deposition, derived from the same eruption. The Campanian volcanic event, about 40,000 years ago, was the largest eruption in Europe and the Mediterranean region during the late Pleistocene. Another major volcanic event during the Quaternary was the more recent Santorini eruption in the eastern Mediterranean (Aegean Sea) during the Late Minoan cultural period, approximately 3600 years ago. This was the largest Holocene eruption in the region, but tephra deposits in caves from this event appear to be very rare. We present here the first ever finding of a visible tephra layer from the Minoan Santorini eruption in a cave. The pure tephra, situated in the Pelekita cave in eastern Crete near Kato Zakros, has a thickness of up to 9 cm. Geochemistry analyses of major elements by electron probe micro-analysis (EPMA) and trace elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) prove the tephra to be derived from the Minoan Santorini eruption. Radiocarbon dating also fits the time frame of this eruption. Our findings indicate that the tephra layer in the Pelekita cave is an air-fall deposit. The lower boundary of the tephra layer is sharp and wavy, draping over the underlying irregular cave surface. Particle size distribution of the tephra is bimodal and typical for suspended aeolian transport. The consistently smaller size of heavier feldspar particles adjacent to larger but lighter volcanic glass particles, in thin sections of undisturbed samples, corroborate emplacement of the tephra inside the Pelekita cave from high-altitude fallout.