Morpho-sedimentological map of Chia beaches - SCI ITB042230 “Porto Campana” (SW Sardinia, Mediterranean Sea - Italy)

This paper presents a 1:5,000 scale morpho-sedimentological map of the emerged and submerged area of Chia beaches, located in the ITB042230 “Porto Campana” SCI of Natura2000 network (SW Sardinia, Mediterranean Sea - Italy). The Chia beaches continuity is interrupted by two low rocky headlands which divide it into three areas from NE to SW called Sa Colonia, Campana and Su Giudeu. The map is compiled using sonograms and sedimentological data and it shows the granulometric distribution of the emerged and submerged beach (up to -50m depth). The geological setting is characterized by a Precambrian and Palaeozoic basement formed by metamorphic rocks (ortogneiss and micaceous shales) and granitoid lithotypes. Moreover crops of “Bithia Formation” (Precambian?-Lower Cambrian), formed by phyllites, metasandstones, marbles and basic metavolcanic rocks are observed. On the Palaeozoic basement, Quaternary deposits lie, which are formed from Holocenic and recent beach sands, ancient and recent alluvial deposits related to the main rivers and colluvial deposits on the slope floors. The surface beyond the backshore is characterized by colluvial-alluvial deposits made up of sandy matrix clastic sediments, while the alluvial plains present are composed of sandy-gravelly deposits. The data were collected during four different surveys conducted in 2009. The surveys were conducted by field measurements referred to a geodetic net based on the IGM95 ETRF2000 n.239901 point, located in Monte Filau. The topography of the emerged beach was surveyed with a DGPS system, obtaining the points with xyz coordinates on 1Hz frequency. For the submerged beach, a system of interfaced Reson Navisound 215 echosounder/Omnistar 8300HP DGPS through Reson PDS2000 navigation software, was used, installed on the Novamarine RH580 ship of the “Osservatorio Coste E Ambiente Naturale Sottomarino” (OCEANS) of Chemical and Geological Sciences Department (Cagliari University). The surveys were obtained together on submerged and dry beach on a 50m side grid. In “post-processing mode” all data were processed and filtered to realize a studied area DTM, it permits to realize a detailed topography and bathymetry of the study area, reported on the map. Then a sedimentological survey, along prefixed land-sea transects was carried out. During this survey the following sample were collected: 67 samples from the submerged beach (using 5 liter van veen grab), 42 samples from emerged beach and shoreline and 74 samples from the dune area. Granulometric analysis was made following the ASTM International standard metodology, with sieves spaced on ¼Φ between 2000μm and 63μm (Udden-Wentworth scale, 1922). The grainsize parameters of Folk and Ward (1957): Meansize (Mz), sorting (σI), skewness (SkI) e kurtosis (KG) were obtained for every sample. Moreover an ortophotos analysis was carried out to evaluate the historical and the anthropical evolution of the area that were reported on the map. The sediments were described and mapped and they consist in 5 legend terms: Coarse Sand, Medium-Coarse Sand, Medium Sand, Medium-Fine Sand and Fine Sand. The map also shows rocky outcrops and Posidonia oceanica (L.) Delile meadow coverage. The meadow plays a decisive role in the production, selection and transport of bioclastic sediments and it contains the terrigenous sedimentation between the coastline and its upper boundary.