LE EOLIANITI DELL’ISOLA D’ELBA: I DEPOSITI DEL PROMONTORIO DEL M. CALAMITA E DEL GOLFO DI VITICCIO

Abstract

M. D’Orefice et al., The Elba Island eolianites: The deposits of the Mt. Calamita promontory and the Viticcio Gulf. (IT ISSN
0394-3356, 2007).
This paper is focused on some deposits of aeolian origin outcropping in the western coast of the Mt. Calamita promontory (southeastern sector of the Elba island) and in the Viticcio Gulf (central- northern sector of the Elba island). The aeolian deposits lie unconformably on the ancient, modeled rocky coasts of the substrate, and also occur inside the pre-existing river valleys, sometimes as far as
100 m a.s.l.
The aeolianites are built up mainly by coarse to medium-sized sands and to a lesser extent by fine gravel. They have an open-work
fabric; nevertheless, most of intergranular pores are filled by two generations of carbonatic cements, which can make the rock cementsupported. Inside the aeolianites, characteristic sedimentary structures are clearly recognizable: they consist essentially in a tabular-planar cross-stratification. High angle foresets dipping landward and tangent to the base level are prevailing. Each set is affected internally by several reactivation surfaces, and is truncated by low angle erosional surfaces dipping seaward. The aeolian deposits are also characterized by second-order sedimentary structures, which consist in vertical and sub-horizontal intra-sedimentary calcite-cemented concretions. Along the coastline, particularly on the flat coasts, the upper surface of the aeolianites shows peculiar erosional micro-forms, consisting mainly in vertical tubules. Also erosional macro-forms are present, such as kamenitza and rock pools. Frequently, the aeolian deposits are interbedded with rubefied paleosols and with slope breccias, built up by polygenetic and heterometric angular clasts.
Petrographical analysis allowed us to classify the eolianites as bioclastic quartz-sandstones. In fact, their main components are carbonate bioclasts, silicate clasts, and lithic fragments. Bioclasts derive from shell fragments of lamellibranchs, gastropods, echinoderms, briozoans, nodular red algae, and benthonic foraminifera. These latter mostly account for species belonging to a temperate to warm, intertidal marine paleoenvironment. Silicate clasts consist mainly in quartz and feldspar grains, with minor amounts of micas, spinel, hematite, and clinopyroxene. The two-dimension morphometrical analysis performed on quartz grains suggests a certain degree of uniformity among the studied occurrences, in particular with the sphericity and roundness parameters. Lithic fragments mostly count quartz-sandstones, along with minor amounts of granitic l.s. and quartzitic rocks. The quantitative ratios of lithics are nearly constant from an outcrop to another, without any correspondence with the lithology of their respective hydrographical basin.
Dipping of the aeolian deposits under the current sea level, together with their erosion by the present marine dynamics, demonstrate
that aeolianites originated during a low standing phase of the sea level. During this time span, a sandy bottom progressively emerged
from the sea and acted as a feeding area for these deposits. Results of the radiocarbon age measurements performed on some
palaeosoils interbedded between the aeolian deposits, along with chronological data on archaeological materials found inside these
palaeosoils, as reported in literature, allow us to assign the studied aeolianites to the two cold stages of the last glacial (isotope stage 4
and 2). Thus, the age of these deposits can be attributed to the Upper Pleistocene.