engleski

Morphology of volcanic particles from Quaternary loess deposits of Susak Island, Croatia

Quaternary sediments of the Susak Island, owing to their great thickness (more than 90 m) on a relatively small area, represent one of the most impressive phenomenon among other Adriatic islands and wider. They consist mostly of loess with interbeds of sandy layers, paleosols, carbonate concretions and three tephra horizons (Bognar et al. 2003). The main characteristics of these distinct volcanic layers are glass particles (vitroclasts), higher content of pyroxenes compared to surrounding sediment and presence of idiomorphic biotite. The middle tephra (TF2) and the youngest tephra (TF3) show similar morphology of some pyroxenes, namely idiomorphic clinopyroxene crystals (possibly augite) which is quite different from the oldest tephra (TF1) that contains „saw-toothed” clinopyroxene grains. Vitroclasts from all three tephras are pale yellow to light brown, weathered and fragile, often with patches of secondary ferrous minerals covering their surface. Vitroclasts from the middle tephra (TF2) show more elongated habitus and vesicular textures as seen on SEM images as well as on polarizing microscope photos. Based on the optical dating of loess below and on top of the tephra layer the youngest tephra (TF3) is between 28, 0 ± 2, 2 and 26, 6 ± 2, 1 ka old and middle tephra (TF2) is between 35, 5 ± 2, 7 and 33, 9 ± 2, 6 ka old (preliminary and uncorrected age results). Based on the age of the loess directly above Mende Base paleosol in Hungary (Frechen et al. 1997), which was correlated with Susak reddish-brown forest paleosol (Bognar et al. 2003), the oldest tephra (TF1) under that sequence is estimated to be significantly older than the last interglaciation.

Susak Island; loess; tephra; morphology; volcanic particles

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