The rapid post-LGM sea-level rise resulted in fast migrations and changes of sedimentary environments in present-day shallow continental shelves. In the northern Adriatic the last transgression submerged the vast alluvial plain of the Po river and its Apennine, Alpine and Dinaric confluences. The Gulf of Trieste represents the northeasternmost part of the Adriatic Sea, where the Holocene change from alluvial to shallow marine sedimentary environments was already observed in sedimentary cores. As high-resolution geophysical methods have been increasingly applied for investigation of seabed sediments in the last few decades, we wanted to use them to study the Holocene transgression in the Gulf of Trieste. We used these methods, mostly the sub-bottom sonar, to correlate the acoustic and sedimentary facies of various Late Quaternary deposits. We also used high-resolution acustic and seismic profiling of seabed sediments of the Gulf of Trieste to study the tectonic activity, to determine the thickness of the Holocene marine sediments and to determine the sound velocity through Late Quaternary deposits. Our results show that in the Gulf of Trieste, terrestrial, transgressive and marine sediments can be differentiated on the basis of their acoustic facies. The sedimentary environment of terrestrial sediments can be determined from geophysical and sedimentological data. Dating results show that fluvial sedimentation in the study area persisted at least until the Younger Dryas and that deposition of transgressive sediments took place in the Early Holocene. While we did not find direct indicators of tectonic activity, we did consider Late Pleistocene fluvial channels as geomorphic indicators of tectonic activity. These indicators do not correlate with the measured vertical motion rates on the Slovenian coastline, which indicates that the recent vertical motion is not expressed in the sedimentary record. Instead, the recent vertical movement rates may result from surface deformation above a locked thrust. The thickness of Holocene marine sediments in the Gulf of Trieste is variable, but generally the thickness decreases away from the coast, where the thickest successions are located. Holocene marine sediments in the Slovenian part of the Gulf of Trieste are usually thicker than 5 meters. Sound velocity in thin (up to 20 meters thick) Late Quaternary successions predominantly depends on the sediment grain-size. Additionally, the presence of gas greatly influences the sound velocity.
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