Late Quaternary landscape evolution of the Tiber River delta plain (Central Italy): new evidence from pollen data, biostratigraphy and C-14 dating

摘要

New data from 45 sediment cores, 35 C-14 datings and numerous pollen analyses were considered for improving the understanding of the stratigraphy of the Tiber River delta plain. Bottom to top, the three recognized units pointed to the following environments: i) continental shelf with fairly noticeable siliciclastic input, ii) coastal plain with spread lagoons and sandy-gravelly beaches and, iii) a capping complex and mostly a paralic sediment suite which records the landscape evolution over the last 18 kyr. The study area, fully emerged until 13 kyr BP, is characterized by the deep and narrow valley incised by the Tiber River during the last glacial sea level low stand. Following its origin the valley underwent partial submersion by sea-water while Tiber River was building up a seaward retrograding bay-head delta. Beginning from 8 kyr BP this feature progradated and at 6 kyr BP changed into a wave-dominated delta which originated a strand plain with two coastal lakes. In Roman times, the most important harbour of the antiquity was built close to the Tiber River mouth. During the Renaissance, an enhanced progradation phase shaped a landscape akin to the present one, apart from some minor changes subsequent to the reclamation of coastal ponds and relic marshes in modern times. The results herein discussed confirm that the post-glacial sea level rise and the Tiber River solid discharge were the two antithetic mechanisms responsible for the landscape evolution of the deltaic area. However, during the last transgression even the antecedent topographhy played an important role, and since Neolithic times the effects of the anthropogenic impact were also noticeable.