Origin and distribution of surface sediments in the Grgur Channel, Adriatic Sea, Croatia

Granulometric, mineralogical and morphological investigation of the sea-bottom sediments in the Grgur Channel has revealed fi ve sediment types, the most frequent of which are muds containing some amount of coarse fractions (sand and gravel). The coarsest fractions are predominantly composed of recent shell fragments. Unexpected well rounded carbonate gravel was found SE of Prvić Island in 83 m of water. This gravel was presumably transported, shaped and deposited during a sea-level lowstand, by stream and/or in a beach environment. Fine-grained fractions have a siliciclastic composition and suggest a predominant terrigenous origin. One part of the fi ne-grained fraction originates from the recent subaerial weathering of fl ysch outcrops, and the other from previously active (during a lower sealevel), subaerial erosion of presently submerged fl ysch outcrops. As a result of the rapid Late Pleistocene–Holocene transgression, the investigated sediments are now below the present wave-base. Due to a presumed very low or even negligible rate of recent sedimentation in the study area, older sediments in the Grgur Channel remain uncovered and bioturbated by burrowing organisms. Therefore, analyzed surface sediments from the Grgur Channel are considered as a mixture of recent and subrecent deposits. From this investigation, a new seabed sediments map of the Grgur Channel was produced, as an improvement on the existing sedimentological map of the Kvarner area.