Preservation of Modern and MIS 5.5 Erosional Landforms and Biological Structures as Sea Level Markers: A Matter of Luck?

Abstract

The Mediterranean Basin is characterized by a significant variability in tectonic behaviour, ranging from subsidence to uplifting. However, those coastal areas considered to be tectonically stable show coastal landforms at elevations consistent with eustatic and isostatic sea level change models. In particular, geomorphological indicators—such as tidal notches or shore platforms—are often used to define the tectonic stability of the Mediterranean coasts. We present the results of swim surveys in nine rocky coastal sectors in the central Mediterranean Sea using the Geoswim approach. The entire route was covered in 22 days for a total distance of 158.5 km. All surveyed sites are considered to have been tectonically stable since the last interglacial (Marine Isotope Stage 5.5 [MIS 5.5]), because related sea level markers fit well with sea level rise models. The analysis of visual observations and punctual measurements highlighted that, with respect to the total length of surveyed coast, the occurrence of tidal notches, shore platforms, and other indicators accounts for 85% of the modern coastline, and only 1% of the MIS 5.5 equivalent. Therefore, only 1% of the surveyed coast showed the presence of fossil markers of paleo sea levels above the datum. This significant difference is mainly attributable to erosion processes that did not allow the preservation of the geomorphic evidence of past sea level stands. In the end, our research method showed that the feasibility of applying such markers to define long-term tectonic behaviour is much higher in areas where pre-modern indicators have not been erased, such as at sites with hard bedrock previously covered by post-MIS 5.5 continental deposits, e.g., Sardinia, the Egadi Islands, Ansedonia, Gaeta, and Circeo. In general, the chances of finding such preserved indicators are very low.

Sea Caves and Other Landforms of the Coastal Scenery on Gozo Island (Malta): Inventory and New Data on Their Formation

“…However, no datable fossil remains or even forms of rock biodegradation referable to lithodomes were found, which could be due to the low resistance of the limestones in which the cave is developed. This poor quality of rock masses suggest that these fossils were not preserved over a long time, as reported by [45,46]. The fact that rounded gravels are not cemented could raise doubts, related to the fact that the studied deposit is totally composed by uncemented clasts, and MIS5.5 deposits are usually cemented [44].…”

Dipping Tidal Notches (DTN): Exposed vs Sheltered Morphometry

“…These models were used to compare MTNs and DTNs at the reviewed sites. These high-resolution (HR) images were taken above and below the waterline, as described in Furlani et al [36] using GoPro Hero 6 Black cameras. A total of 154 images of the emergent part and 534 of the submerged part were acquired and processed separately using the software Agisoft MetashapeTM (Agisoft LLC, St. Petersburg, Russia) to produce the dense point cloud and 3D model of the cave, according to the DP technique.…”

A Multi-Hazard Historical Catalogue for the City-Island-State of Malta (Central Mediterranean)

“…These are, from youngest to oldest: Upper Coralline Limestone; Greensand; Blue Clay; Globigerina Limestone and Lower Coralline Limestone. As a result of this tectonic and geological setting, the archipelago is home to a varied suite of landforms that include: limestone plateaux; high cliffs; drowned coastlines (rias); drowned and erosional shorelines; highly incised former river valleys (widien), up to several kilometres long and tens of metres deep, and a 14 km long horstand-graben sequence extending north-north-west from the Great Fault (Alexander 1988;Furlani et al 2017;Gauci and Scerri 2019;Furlani et al 2021). Malta's climate is typical of the semi-arid Mediterranean, with hot dry summers and warm wet winters.…”