The results of a sedimentological study of the beaches and the inner shelf between Capo Testa and Punta di Li Francesi are herein reported. The aim of the work was to understand provenance, dispersion and sediments dynamics. In the littoral parts oriented NE-SW (beaches of La Liccia, Rena Maiore, Buredaggia, Lu Litarroni, Naracu Nieddu, Lu Tuvunatu) a tendency of dispersion in direction NE-SW is evident from the analysis of the mean size along the shoreline, whereas this direction is opposite at a depth of 10 meters, according with the results of the study of the energy fluxes. By mapping these data, dispersion controlled by clockwise circulation cells, whose form and extension are strongly conditioned by the conformation of the sea-floor, is delineated. In the physiographic units oriented NW-SE (beaches of Vignola, and La Colba) longshore transport oriented SE-NW prevails. Furthermore, in the sector comprised between Capo di M.ti Russu and Punta di Li Francesi, the sedimentological parameters indicate the existence of relict sediments at a bathymetric depth of 20 meters, that are scarcely related to the present dispersion. By means of heavy mineral analysis lithogenic provenance of sediments was recognised to be from intrusive, volcanic and metamorphic rocks. A clear predominance of Epidote, in its most diffuse variety Pistacite, on Clinozoisite, as well as Amphiboles (Green Hornblende) and Pyroxenes was observed. Other minerals present in minor amounts are: Granates, Zircon, Picotite, Anatase, Andalusite, Staurolite, Sillimanite, Olivine, Tourmalin, Titanite, Rutile and Brookite, with low percentages of Apatite. High percentages of heavy minerals are observed on the top of the dunes, diminishing on the berms and relatively increasing on the shoreline, if transects perpendicular to the beach are considered. In the submerged beach the highest concentrations have been observed at the foot of the bars. On the shoreline, in general, an increase in percentage can be observed from North to South.
Caratteri sedimentologici e dinamica delle spiagge e della piattaforma interna tra Capo Testa e Punta di li Francesi (Sardegna Settentrionale)
DEMURO, SANDRO;IBBA, ANGELO
2004-01-01
Abstract
The results of a sedimentological study of the beaches and the inner shelf between Capo Testa and Punta di Li Francesi are herein reported. The aim of the work was to understand provenance, dispersion and sediments dynamics. In the littoral parts oriented NE-SW (beaches of La Liccia, Rena Maiore, Buredaggia, Lu Litarroni, Naracu Nieddu, Lu Tuvunatu) a tendency of dispersion in direction NE-SW is evident from the analysis of the mean size along the shoreline, whereas this direction is opposite at a depth of 10 meters, according with the results of the study of the energy fluxes. By mapping these data, dispersion controlled by clockwise circulation cells, whose form and extension are strongly conditioned by the conformation of the sea-floor, is delineated. In the physiographic units oriented NW-SE (beaches of Vignola, and La Colba) longshore transport oriented SE-NW prevails. Furthermore, in the sector comprised between Capo di M.ti Russu and Punta di Li Francesi, the sedimentological parameters indicate the existence of relict sediments at a bathymetric depth of 20 meters, that are scarcely related to the present dispersion. By means of heavy mineral analysis lithogenic provenance of sediments was recognised to be from intrusive, volcanic and metamorphic rocks. A clear predominance of Epidote, in its most diffuse variety Pistacite, on Clinozoisite, as well as Amphiboles (Green Hornblende) and Pyroxenes was observed. Other minerals present in minor amounts are: Granates, Zircon, Picotite, Anatase, Andalusite, Staurolite, Sillimanite, Olivine, Tourmalin, Titanite, Rutile and Brookite, with low percentages of Apatite. High percentages of heavy minerals are observed on the top of the dunes, diminishing on the berms and relatively increasing on the shoreline, if transects perpendicular to the beach are considered. In the submerged beach the highest concentrations have been observed at the foot of the bars. On the shoreline, in general, an increase in percentage can be observed from North to South.
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