Tidal notches (Tn) along the western Adriatic coast as markers of coastal stability during late Holocene

In this paper, we present and discuss the spatial distribution of Tidal notches (Tn) along the western sector of Adriatic Sea as a marker of the coastal stability during late Holocene. Specifically, a 3.97 km long coastal reach at the Mt. Conero area has been investigated in relation to its geological and geomorphological pecularieties such as: i) active, low rates uplift; ii) active coastal plunging cliff; iii) diffuse gravity-induced instability of the rocky cliff and consequent presence of coastal landslides of different type, size and state of activity. The identification and location of Tn has been conducted on July 2016 by means of a snorkel survey along a route encompassing the toe of the Conero coastal cliff, allowing the investigation of the tidal zone and recognition of the morphotypes above and below the sea level. Time-lapse images with frame rate of 1 s were collected along the entire route. The best quality frames were used to precisely clusterize the coastal geomorphological features, and to precisely locate the recognized Tn. The snorkel survey was supported by detailed geomorphological surveys and geo-structural investigations from inland. This multifaceted approach allowed to identify and precisely locates Tn, other than to establish relationships among their morphometric features and other specific coastal morphotypes recognized in the field. Tns have been observed for the first time in the study area. Although the rocky coastal cliff is affected by active uplift and several active landslides of different types, sizes and depth, the Tn location and elevation suggests that i) late Holocene vertical deformations due to tectonic are negligible for the whole coastal sector analysed; ii) gravitaty-induced vertical deformations involving bedrock are negligible during at least the last couple of centuries in the coastal stretches where they are preserved.