Le variazioni ambientali nell’area di Vado Ligure dal Neolitico ad oggi

Abstract

Carobene L., Firpo M. & Rovere A., The environmental variations in the Vado Ligure area from the Neolithic age until present (IT ISSN 0394-3356, 2008).
Seismic profiles and 13 drilling cores were studied in the Vado Ligure Gulf, in front of the Segno river delta. The study area is located
4-5 Km SW from Savona, along the western Ligurian coast. The Holocene transgression highlighted by the surveys was related to the
variations of the landscape in the last 8-9000 years; this period corresponds to the beginning and the development of the Neolithic.
Subaerial (Fig. 1) and marine (Fig. 2) morphological features were taken into account in order to compare the recent evolution of the
study area with the most important Quaternary events, such as eustatism and tectonic activity. These two events are documented by 5
orders of marine terraces comprised between 185 and 35 m a.s.l.; this allowed us to conclude that the tectonic rising rates of the study
area during Quaternary have been low, and successively decreased. This evidence supported the assertion that the study area has
been substantially stable during Holocene. Moreover, systems of Quaternary faults have conditioned the direction of crests and the
drainage patterns. The cores, 10 of which were made in the marine part of the study area, allowed us to recognize the substratum, that
is constituted by lower Pliocene marly clays, by the continental deposits referable to the low eustatic stand (Würm) and by the marine
sedimentary body of the Holocene transgression (Fig. 8). The marine deposits of the Tyrrhenian transgression (Stage 5.5) are absent.
25 C14 datings provided calibrated ages comprised between 8225 and 510 yrs BP; the data were used to obtain the chronostratigraphy of the marine deposit (Fig. 12). The correlation of the results obtained by the seismic profile analysis (Fig. 4), by the sedimentological study of the drilling cores (Fig. 5) and by the C14 datings allowed us to recognize a transgressive phase, which ended 6000 yrs
BP; a period of relative eustatic standing (from 6000 to 5000 yrs BP); a subsequent period of progradation (from 5000 to 1800 yrs BP)
and, finally, the period of the interglacial high eustatic stand that continues to the present (Fig. 14). The whole sedimentary marine body reaches a thickness of about 14 meters. The various stages of the eustatic sea level rise were reconstructed along a geologic profile that continues landward. The seismic profile was documented by the alignment of 9 cores; this allowed us to recognize the shorelines dated 8000 BP (-12 m), 7000 BP (-6,5 m), 6000 BP (-3 m), and 5000 BP (-1,5 m) (Fig. 14). On the basis of these data an eustatic curve was obtained (Fig.15) and the large modifications of the landscape caused by the Holocene transgression were recognised. About 9000 yrs BP a large surface with a low inclination spread landward for at least 1 Km; taking into account the improvement of the climate, this plain could be used for agriculture. However, in the space of 3000 years, the plain was flooded by the rising sea level, while the valley floor of the Segno river became inhospitable, because it began to be flooded by continuous inundations. After a period of relative stability, that had lasted since 5000 yrs BP, the continued accumulation of debris along the coast caused the progradation of both the emerged and submerged beaches and the contemporaneous aggradation of the alluvial plain of the Segno river. This drove the ancient inhabitants to live and build mainly on the hillsides, mainly in the terraced surfaces. Starting from 8000 yrs BP till present, the coastline became again relatively stable; in the sea bottom the deposition of the sedimentary sequence relative to the last eustatic
interglacial peak began. The alluvial plain of the Segno river became stable again or useful for agriculture, even if not in a permanent
way. The reduction of space and the probable increase in the population lead to the use of deforestation; this started with the washing
of the hillsides and the erosion of soils, as documented by the thick silty-clayey body that rapidly formed in the marine area.