EVIDENCE FOR LATE QUATERNARY FAULTING IN THE RENO RIVER VALLEY, NORTHERN APENNINE MOUNTAINS, ITALY

The region south of Bologna, Italy in the northern Apennine Mountains is seismically active; however no published geologic map shows faults cutting Quaternary deposits. As part of the RETREAT effort to characterize the tectonic evolution of the northern Apennines, a detailed study of strath terraces along the Reno River (Fiume Reno) upstream from Bologna provides evidence for the nature and timing of late Quaternary tectonic activity in this region. Soil development, sedimentology, morphology and 14C dates of terrace deposits was used to correlate terrace straths along a 25 km section of the Reno River (Bierma et al., 2004). Using this detailed correlation combined with exposed strath elevations, longitudinal profiles were constructed for five of the six terrace units within the valley. Poor strath exposure precluded construction of profiles for the Qt7 unit. The profiles do not exhibit simple, parallel concave up morphologies. Instead, they are characterized by numerous knickpoints as well as intervals of both up and downstream divergence between different units. Such complexity suggests that their morphology is not a function of simple base level fall or regional uplift, rather it is likely due to deformation along relatively localized structures, both at the mountain front (Pazzaglia et al., this meeting) and in the interior of the range. In the areas of Lama di Reno and Panico, the longitudinal profile of the 12 – 19 ka Qt6 terrace is abruptly (across a distance of ~ 30 m) offset by 9 and 12 m respectively. While there are no exposures of these offsets, they coincide with similarly trending (NE) bedrock faults as well as knickpoints and sharp bends (notably 60 degrees at Panico) in the modern channel. Other smaller offsets are common for this and other terrace units and also coincide with knickpoints and or high channel sinuosity. Calculated slip rates on Qt6 offsets (0.5 – 1 mm/yr) are slightly lower than the Qt6 average incision rate (0.8-2 mm/yr) for the entire length of the river. These data provide evidence for widespread, relatively low-slip Quaternary faulting along the entire length of the Reno River.