Chronostratigraphic and lithologic features of the Tiber River sediments (Rome, Italy): Implications on the post-glacial sea-level rise and Holocene climate

Abstract

Rapid and permanent granulometric changes within the clastic sedimentary deposits of the Tiber River are directly linked to changes in sediment transport capacity and give insight on climate fluctuations and related sea-level oscillations during Late Pleistocene–Holocene times. In this work, we investigate the stratigraphic features of the sedimentary fill of the Tiber River channel as far as 30 km from the coast, and of one tributary, the Grottaperfetta stream. Through direct observation and core sampling of ten, 30 to 80 m deep boreholes, and the analysis of a large number of stratigraphic log data, we reconstruct a series of transverse sections and correlate them along a longitudinal profile of the Tiber River course. We provide geochronologic constraints to the deposition of distinct lithostratigraphic units by means of 8 newly acquired 14C ages and 21 previously reported ages of intercalated peat layers and wood fragments. Moreover, we review and select 28 radiocarbon ages fromliterature on the deposits of the Tiber River in the coastal plain, in order to reconstruct the aggradational history throughout the distal portion of the basin. Finally, we provide curves of sediment aggradation vs. time during the last 19,000 yr for the different investigated portions of the Tiber River course. We compare them to sea-level curves from the literature. To perform this comparison, we use a rigorous geotechnical approach to estimate the subsidence due to sediment compaction, andwe apply a correction to the Present-day elevation of the dated samples of organic material interbedded with the sedimentary deposits. Two significant sedimentary events at around 13,800 yr BP and 7500 yr BP, marked by sharp stratigraphic and granulometric changes, are recognized and correlate to important variations in the rate of sea-level rise. Moreover, we show evidence of an erosional event coupled to a reversal of the granulometry (increase in gain size of sediments) affecting the whole investigated tract of the Tiber River channel between 5500 and 3500 yr BP and discuss its possible causes. In particular, we discuss whether besides the change in capacity of transport due to a climatic change, also a drop in sea level, in the order of 2–3 meters, may have occurred in this time span, either in response to an increase in global ice volume, glacial isostatic adjustment, or local tectonic uplift.