Stratigraphy and palaeoenvironmental significance of the loess deposits on Susak Island (Dalmatian archipelago)

Abstract

The loess of Susak Island is the most impressive aeolian deposit in the Dalmatian archipelago as it reaches about twenty metres in thickness. The base of the sedimentary sequence consists of a shore platform, which in the southern part of the island is covered by late Middle Pleistocene fossil dunes. Elsewhere, the shore platform has been affected by gelifraction and is covered by slope waste deposits. Above these, a thick sequence of aeolian deposits occurs, composed in the lower part of cross laminated sandy loam and thick loess cover, interstratified with a level reworked by running water and slightly developed chernozems. The upper part of the sequence has been strongly affected by anthropogenic reworking in historical times. The loess is composed of unweathered, subrounded quartz, feldspar, mica and limestone granules. The heavy mineral association is mainly from metamorphic paragenesis and has the same composition as the sediments of the Po plain. The aeolian sediments are rather homogeneous and composed mainly of coarse silt. They are coarser in comparison with those of Losinj Island (12 km northeast of Susak) which are typical silty loess, indicating a wind direction from southwest to northeast. On the basis of the pedostratigraphic data, loess sedimentation is referred to the first Pleniglacial period of the Upper Pleistocene. The loess of Susak Island originated, in a dry environment, by wind deflation of the Po river sediments. The quick progradation of alluvial and deltaic deposits towards the east-southeast, due to the sea level drop, provided large barren areas exposed to wind erosion.