Contributo alla conoscenza dei terrazzi marini della Liguria fra Genova Nervi e Camogli

This paper focuses on the evidence of past sea levels recognized in a specific tract of the Eastern Liguria coast, located immediately eastward the city of Genoa. From a geological point of view, the study area presents a good uniformity since only Antola Unit, consisting of marls, limestone, calcarenite, sandstone and shale, outcrops here. The geomorphological survey of the coast between Nervi and Camogli, provides well-defined markers of at least two highstands, in the form of a staircase of marine terraces, within an altitude span ranging from present-day sea level to the 34 m contour line. Very often these terraces appear covered by continental sediments or altered from erosion processes, uplift and the strong human impact that affects the study area. Although no patches of the original marine deposit of these terraces have been found yet, they are currently undated and their age attribution is attempted in this paper by means of correlation with dated shorelines. Despite of the underlined difficulties, the altitude of the terraces inner margins were obtained on the base of field measurements and two orders of terraces were identified. The terraced landforms of the upper order (I), with inner margins ranging between 24 and 34 m, are developed with few interruptions along the studied stretch of coast and are also often overlain by continental deposits due to alluvial fan or landslide. The cluster value for the upper order is 27 +1/-6 that is the median value of the measured inner margins with the assumed error, related to the inaccuracy of the measurement instrument (±1 m) and the evaluation of the sediment thickness (+5 m). The second order of terraces are characterized by an elevation of the inner margin ranging between 3-5 m a.s.l. The marker of this order is represented by platform of marine abrasion cut in the rock, without sediments on the surface, often affected by weathering. The upper group of terraces could be attributed to the MIS 5.5 highstand for correlation with a dated shoreline 30 km eastward the study area; consequently the lower group are in this hypothesis attributed to MIS 5.3 or 5.1. Another hypothesis, based on the correlation with the Western Liguria data, attributes the lower order to the M.I.S. 5.5 and the upper order to a previous isotopic stage. Considering the available data, the authors don't draw any conclusion about the geodynamic behaviour of the study area. In fact a different uplift rate would derive from each of the two proposed hypotheses and consequently a different vertical displacement for the two tracts of coast.