Marine geology of the Gulf of Trieste (northern Adriatic): Sedimentological aspects

Abstract

The Gulf of Trieste, the northernmost part of the Mediterranean Sea, is a ∼ 20 m deep marine basin influenced by freshwater inflow, bottom sediment resuspension and increasing pollution. The surficial sediments can be subdivided into seven zones on the basis of grain-size and mineral composition. The western part of the gulf consists of up to 70% carbonate shells of various organisms (molluscs, foraminifera and echinoderms). In the inner part of the small bays of Koper, Piran, Muggia and Panzano the surficial sediments consist of clayey silt with approximately 30% carbonate. A part of the carbonate fraction and all the non-carbonate minerals are derived from flysch in the hinterland, while the River Isonzo is the main contributor of these minerals in the northern part of the Gulf of Trieste. The distribution of suspended sediments shows the highest values in the northern part of the gulf, intermediate values in the southeastern part, and lowest values in the southwestern sector in the gulf entrance under the influence of the inflow of western Istrian waters. About one third of the suspended sediment is in the form of organic matter. Sedimentation rates decrease from about 3–5 mm yr −1 within the small bays, to about 1 mm yr −1 in the central part of the gulf, gradually increasing to approximately 2.5 mm yr −1 towards the mouth of the River Isonzo. Depth profiles of Holocene sediments in the inner part of the bays of Koper and Piran reveal a change from fluvial to brackish and marine environments.