LATE PLEISTOCENE AND HOLOCENE SURFACE DEFORMATION OF THE PO PLAIN, POSSIBLE CONTINUING DEFORMATION OF A FORELAND BASIN

The Po Plain is a foreland basin north of the Italian Apennine Mountains. Extensive Pliocene and early Pleistocene folding and thrust faulting are buried by relatively undeformed younger sediment. Surface deformation is poorly expressed, but appears to be continuing. Geomorphic, sedimentologic, and archeologic evidence near Modena indicates that a surface depression has been filling for > 21 ky. The most obvious geomorphic indication of deformation is the path of the Secchia and Panaro rivers which have an unusual “rectangular” channel pattern where both rivers flow toward each other into the mid fan depression and parallel to each other within the depression. Just upstream of the depression both streams have incised into the fan surface to form terraces. Topographic profiles parallel and perpendicular to the fan axes show that the depression is 2-9 m deep. Radiocarbon-dated sediment on the west and south margins of the depression indicate that the depression was more extensive, but accelerated sedimentation rates have partially filled the low area. Archeology supports this sedimentary information. Surface Roman sites, reticolo centuriale (Roman ditches and agricultural field boundaries, ~2 kya) and a Bronze Age site within 0.5 m of the surface are present on the high area west of the depression indicating a relatively stable landsurface with low aggradation rates during at least the last 3500 years. Roman and older sites are buried by fluvial sediment beneath Modena at the present southern depression margin. Roman and older archeological sites are absent within the depression north of Modena because this poorly drained area may not have been attractive for settlement or sites are deeply buried. The high sedimentation rates of the Po Plain are obscuring the continuing, but subtle, foreland basin deformation.