New data for the late-antiquity alluvial flooding in the Emilia plain (Italy).

From about forty years a scientific grey-literature (i.e. local publications) exists dealing with the environmental deterioration characterising the late-antiquity period (5th-6th century AD) and with its causal link with a peculiar climate change (the so called “Pauli Diaconi Deluge”) happened at the end of the 6th century AD. The researches performed by the Emilia-Romagna Regional Bureau for the Archaeology (Soprintendenza per i Beni Archeologici) during the last twenty years, especially in the cities of Modena and Bologna, allowed to better define the timing of the sedimentary history in the ancient urban contexts and their related peripheral areas. A series of well defined sedimentary episodes were discovered. A first group was very precocious, developing from the second half of the 1st century AD up to the end of the 4th, and was of a fine dominated kind. The second group (dating from the end of the 5th end the end of the 6th century AD) was of a silty-sandy kind and it developed up to the Common Age (end of the 12th century-beginning of the 13th cent.). Therefore, in both the cities a stratigraphic proof can probably be seen concerning the economical and political crisis of the 3rd century AD, the increasing of alluvial basin fine sedimentation and, finally (around the end of the 6th and the beginning of the 7th century) the true river avulsion activity. A second period of fluvial avulsions dated to the beginning of the middle age. Almost the whole of the geomorphic units up to now preserved in the alluvial plain dated to post roman time. The fine character of the first group of sediments could suggest a partial hillslopes reforestation, whereas the subsequent deposits are surely related to the riverbeds aggradation and avulsion.