A RECORD OF BASE LEVEL FALL FROM DATA-DRIVEN LINEAR INVERSION OF FLUVIAL TOPOGRAPHY AND ITS COMPARISON TO FAULT SLIP AT THE MOUNTAIN FRONT, NORTHERN APENNINES, ITALY

We present a data-driven linear inversion of fluvial topography with variable erodibility and precipitation weighting, tested against a published fault-slip model along the northern Apennines. Results show that the fault slip along the northern Apennine Mountain front has been unsteady beginning ~5 Ma and has grown outwards along strike from a center near Bologna. Based on the detachment-limited stream power model, we used a formal linear inversion of empirically-calibrated river response time and river profile elevations to determine uplift histories. Our model accounts for both variable erodibility by rock lithology and non-uniform distribution of precipitation. Glacio-eustatic base-level fall signals are erased in the Po River before reaching the Apennine rivers. Therefore, the base-level fall histories represent uplift in the Apennine Mountains and subsidence in the Po Plain. Best-fit parameters of profile concavity and channel steepness are taken as fundamental observations and are constrained for each river. Rock uplift is assumed to be spatially uniform and in balance with long-term ¹⁰Be terrestrial cosmogenic nuclide (TCN) erosion rates that range from 0.310 to 0.694 mm/yr. The resultant uplift histories and response time curves exhibit a younging trend towards the northwest along strike from 4.8Ma to 2Ma, temporally and spatially consistent with the emergence of the northern Apennines above sea level and records of long-term exhumation. Base level fall at the mouths of the Enza and Panaro rivers match previously constrained fault slip rates modeled from growth strata and fluvial terrace deposits in the Po foreland. Five of the six drainages in this study display a synchronous decrease of uplift rate in the early Pleistocene. This pattern is coincident with overfilling of the Po Plain and supports a proposed switch from asynchronous thin-skinned deformation along shallow blind thrust structures to synchronous, thick-skinned, regional deformation on the basal Pedeapenninic thrust front (PTF) in the last ~1Ma. These results are a rare example of a comparison between base level fall histories for an active range-bounding fault system assembled from both fluvial topography in the source and growth strata in the sink.