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Figure 21 Frequency of the kind of grain shapes described with the SEM: A) conchoidal fractures, B) linear grooves, C) V-shaped pits, D) dish shaped concavities, E) upturned plates, F) pitted microreliefs (“orange peel” surface). SEM images of quartz grain surfaces: a) rounded coarse silt grain; b) sub-rounded grain with dish-shaped concavity and silica plastering; c) rounded fine sand grain with upturned silica plates and “orange peel” surface; d) close-up of the same surface; e) euhedral quartz grains with poorly smoothened corner; f) V- shaped holes.

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Fig.2: Structural map of central Apennines (The square shows the area of the field trip). The tectonic activity led to the progressive cutting of river valleys and to the circulation and/or rising of carbonate waters through faults. Variations of the base level, with a consequent increase of fluvial incision in the cold and aggradation phases and precipitation of carbonates in the warm phases, can be related to climatic oscillations. Precipitation of the calcareous tufas occurred only in the fluvial tracts with inputs of carbonate water, at least partly derived from hydrothermal rising (Capezzuoli et al., 2005).

Fig. 3: Geological map of Siena province (1:100,000)

In the tables below, climatic trends, as well as Soil Taxonomy pedoclimatic classification (Soil Survey Staff, 1999) according to a simulation with the Epic model (Costantini et al., 2002) are reported.

Water table type: absent, erosion: absent, runoff: medium, internal drainage: well drained, rooting depth: deep 300

Fig.6: Geological sketch of Poggio del Comune and San Gimignano. Tcv: vugghy limestone, “Calcare Cavernoso” formation (Triassic); Pco: Marine sands (Early Pliocene); tvl: Travertines. Red lines are the direct faults.

Localization and picture of Profile V03P6. The lithological discontinuities between the buried argic horizons and the aeolian deposits is clear in the picture. LOU SHULL Uy ULIe Lies VII VPUUIUS Y )- The aeolian nature of the parent material of the upper part of profile is testified by the particular setting of the soil, in a small in-filled doline on the summit of an isolated limestone hill, thus in a “natural dust trap”. The doline bottom is flat and sized about 80x100m; the surrounding slopes are only some meters high and have an inclination of a few percents, as the doline is almost completely in-filled. The soil is classified as a Haplic Cambisol (Eutric, Siltic, Chromic) over Cutanic Luvisol (Hypereutric, Profondic, Clayic, Rhodic) over Luvic Nitisol (Eutric, Rhodic) according to WRB (F.A.O. et al., 2006), which reflects the striking polycyclic characteristics of the soil, with a deep, strongly developed nitic horizon overlaid by much less pedogenised horizons. UTS - STS: Soil region: Land system: Land Land Unit: Elevation: Slope: Land use: Land form hm: Land element Substratum: Parent Characters and

Scanning electron microscope (SEM) examination of quartz grains surfaces of benchmark soils was lone on fine sand grains (50-250 um), following Krinsley and Doornkamp (1973). For a statistica ount, 30 quartz grains per sample were observed by SEM. Each grain was evaluated for shape yresence of 6 mechanical forms (conchoidal fractures, linear grooves, V-shaped pits, dish-shaped oncavities, upturned plates, pitted microreliefs) and presence of 3 chemical forms (deep cavities silica solutions, silica precipitation). The following features were used to identify eolian grains: i oundness of the grains, 11) presence of upturned plates of silica, iii) characteristic orange-pee surface, with small dissolution pits. Colluvial-alluvial grains were identified by angular or sub- meular shapes, V-shaped pits, conchoidal fractures and linear grooves. v ey

The spectrophotometer used for the Vis-NIR spectroscopy was the FieldSpec 3Hi-Res (ASDi), which has a spectral range between 350-2500 nm. The measurements of the soil Vis-NIR spectrum was carried out in laboratory, with the ASD contact probe (artificial light) on 2 mm fine earth. Before scanning, we calibrate the spectrophotometer with a Spectralon® white tile. The spectrum of each sample was the mean of 20 measured spectra. A total of 22 soil horizons, already recognized as aeolian deposits (11) and buried argic horizons (11), were scanned. A k-means cluster analysis was carried out on all the spectra. We decided to use 2 cluster groups, so as to highlight an eventual Vis-NIR spectrum discrimination between soil horizons developed on aeolian deposits and the rest of soil horizons. Cluster 1 grouped the buried argic horizons, whereas cluster 2 grouped the horizons developed on the Aeolian deposits. Only the cluster group of 3 horizons did not reflects the nature of the deposits. The horizon Bw1 of the profile SO2P21 (aeolian- colluvial deposits, STOP 1) belonged to cluster 1 (non aeolian), whereas the horizons 2Bt1 of the profile SO2P21 and 2Bt of SO2P2 (buried argic horizons, STOP 2) belonged to cluster 2 (aeolian). This result confirms the unclear origin of these horizons, which already showed both aeolian and colluvial contributions.

Figure 21 – uploaded by Simone Priori

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