MAP OF THE GEOLOGICAL AND GEOMORPHOLOGICAL SITES OF THE MALFATANO COAST IN SW SARDINIA: A CONTRIBUTION TO THE KNOWLEDGE OF THE ISLAND’S GEODIVERSITY

Abstract

C. Cannillo et al., Map of the geological and geomorphological sites of the Malfatano coast in SW Sardinia: a contribution
to the knowledge of the Island’s geodiversity. (IT ISSN 0394-3356, 2005).
The area between Cape Malfatano and Cape Spartivento is emblematic of Sardinia’s geology, especially with respect to the
Palaeozoic basement, whose lowermost part, the Bithia formation (Precambrian-lower Cambrian?), crops out in this sector. Compared
to the tectonic setting typical of the outer zone of the Sardinian segment of the South-European Hercynian chain, this sector constitutes an anomaly, in which the metamorphism and deformation are more pronounced than in the Sulcis-Iglesiente region as a whole.
Another interesting feature of this area is the granitoid rock outcrop (Cape Spartivento orthogneiss) dated to the Sardic Phase of the
Middle Ordovician that, elsewhere in the Sardinian Hercynian basement, is represented essentially by volcanic products.
The geosites have been classified according to genetic processes (stratigraphic, metamorphic, magmatic, structural) whose importance has been evaluated on the basis of their being exemplary of geological evolution, of their chronostratigraphic, palaeoenvironmental and educational value.
Based on these criteria a number of geosites have been identified, where the following features can be observed:
- the Cape Spartivento orthogneiss, of special interest because of the effects created by intense Hercynian deformation (penetrative
schistosity with pronounced stretching lineation of the deformed crystals);
- the lithologic sequences of the Bithia Formation, with mylonitic and cataclastic bands, outcrops of stretched pebble metaconglomerate, again produced during Hercynian deformation phases, and layers of metalimestone;
- the significant genetic, magmatic and lithologic aspects of Hercynian granites;
- the intrusive relationships of the Hercynian granitoid rocks with the metamorphic basement and of later dyke intrusions intersecting
the contacts;
- ductile deformation structures in the Hercynian basement with multiphase folding especially at the mesoscopic scale;
- brittle deformation structures sometimes with well exposed slickensides and slickenside striae;
- unconformity between the Hercynian basement of the Bithia Formation and the conglomerate and eolianite deposits, evidence of
ancient marine levels and palaeoclimates during the Late Pleistocene different to present day climates.
The geomorphological sites identified in the area have been grouped together according to the genetic processes that created them
(fluvial, meteoric, gravitational, littoral, eolian, etc.).
On the map a symbol is used to denote the type of geomorphological site (point, linear or areal) defined according to its physical features and level of importance (local, regional, etc.). Sites are numbered and a brief description is provided.
The level of importance has been assigned according to the following evaluation criteria:
- exemplary of geomorphological evolution;
- palaeo-geomorphological evidence;
- educational value;
- scenic value.
As for the geographical and physical features, the geomorphological forms in the Malfatano area were created largely by littoral,
eolian, fluvial, slope and gravitational processes, influenced by littoral processes.
A number of areas have also been delineated on the map that stand out not so much for their specific forms but rather for their landscape qualities and geomorphological interest as a whole. These include the Malfatano Ria, a cove where the coastline is submerging, the Bay of Tuaredda and some tracts inland, the extension of the submarine relief, characterized by ridges, peaks, deep incisions and bizarre forms of erosion on meta-sandstone and meta-siltstone, granite and orthogneiss.
The map of the geological and geomorphological sites described summarizes the results of a comprehensive investigation that entailed accurate small scale surveying and photointerpretation of the geo- and geomorphic sites along the Malfatano coast. A number of interesting examples have been identified that are evidence of the area’s significant geodiversity.