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Late Holocene storm deposit and boulders on the island of Mana (NP Kornati, central Adriatic, Croatia)

The Upper Cretaceous bedrock surrounding a shallow inlet in the central part of the southern cliff on the island of Mana (NP Kornati, central Adriatic, Croatia) is built of alternating thin to thick bedded mostly micritic limestones, which are inclined to the south-west. Subvertical fractures within the limestones are arranged decimeters to meters apart, which together with the bedding discontinuities define fragments of carbonate layers. The storm deposit has an irregular semi-circular shape (80x60 m) which covers an area of ~3500 m2, wherein the central part is of the estimated thickness of >2 m. The deposit is composed of unsorted pebbles, cobbles, and boulders, on which, in some places, there are still attached erosional remnants of the reddish-brown calcrete. In the frontal SE part of the storm deposit there are meter-sized boulders that are clearly imbricated to the SE. At the edges of the valley, there are solitary boulders, some of which are located up to ~15 meters above sea level and some have traces of boring marine organisms, which prove the submarine origin of the boulders. Preliminary storm waves modelling indicates that this part of the central Adriatic is exposed to the extreme southern to southeastern waves formed by strong Sirocco wind, which are necessary for the erosion of the rocky coast and displacement of the meter-sized limestone boulders up to 100 m from the coastline. Slightly concave southern cliff of the island of Mana and the shallow inlet in the central part of the cliff, probably can additionally channelize the storm waves, that could detach the boulders from fragmented carbonate bedrock at the bottom of the shallow inlet and surroundings, and displace the boulders inland.

Rocky shore, Holocene, extreme waves, coarse-clastic sediment, coastal boulders

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