Geomorphology of the Montenegro slope (eastern Adriatic Sea): A tale of slump scars, corals and a chimney forest

The submarine slope offshore Montenegro is a segment of the eastern slope of the Southern Adriatic Sea, which represents the current foredeep basin of the Dinaride-Hellenide fold-and-thrust belt. In this part of the Adriatic Sea shelf is 10 to 40 km wide and is receiving only a limited amount of clastic sediments. The N-NW-trending shelf break has a water depth of about 400 m, over 200 m deeper than the last sea-level low-stand because of the foreland subsidence. The submarine morphology of the Montenegro slope has been investigated using a high-resolution multibeam bathymetry. The slope appears carved by a set of closely spaced canyons that only rarely scratch the shelf break. A drainage system connected to the slope canyons is not visible on the shelf, and the canyons appear to be originated by the coalescence of multiple landslide scars. The incised canyons are closely spaced along the slope, suggesting a high maturity of the drainage system, in accordance with a destructive-type slope, dominated by mass wasting. In the head of one of the southernmost canyons a field of fossil chimneys has been exhumed by erosion at the seafloor. The stable carbon isotope signature indicates that these chimneys originated because of hydrocarbon fluid seepage within the sedimentary cover. A small field of pockmarks is present at the shelf edge, not far from the fossil chimneys, and located in an intra-canyon position, between canyon headscarps that incised the shelf break. The co-existence of chimneys and pockmarks suggests the occurrence of long-lasting fluid flow in the slope. The system of focussed fluid flow might have played a pivotal role in destabilizing the slope sediments, promoting landsliding. Standing and abated chimneys, together with their rubble and other nearby hardgrounds, have become habitat to relevant benthic fauna in the poorly sedimented slope. Megabenthic cnidarian assemblages are commonly found, also including the emblematic cold-water corals Madrepora oculata, Desmophyllum pertusum, and D. dianthus, the octocoral Callogorgia verticillata, the antipatharian Leiopathes glaberrima, and sponges.