GSA Connects 2021 in Portland, Oregon

Paper No. 44-8
Presentation Time: 3:15 PM


PAZZAGLIA, Frank and FISHER, James, Earth and Environmental Sciences, Lehigh University, 1 W Packer Ave, Bethlehem, PA 18015

Exhibiting numerous examples of steep-walled gorges carved transverse to structure through hard rock, the Apennines have inspired research on the development of transverse drainages summarized in a seminal paper by Walter Alvarez in 1999. We evaluate competing models of transverse drainage development, as well as the underlying dynamic and tectonic processes responsible for Apennine topography, by assembling the rate of base level fall (τ-U) and associated channel χ-z data of ten catchments draining the Apennine pro-wedge using a channel stream power-based linear inverse approach. The model employs the simplifying assumption of uniform uplift and erosion at the catchment scale, but accounts for variable rock erodibility as the first-order determinant of regional, mean channel steepness. Accordingly, local deviations in channel steepness are represented in the model as transient, upstream-propagating waves of base level fall originating at the catchment mouth. Modeled timing, rate, and unsteadiness of these base level falls are broadly consistent with geologic data indicating that the Apennines emerged impulsively at ~2.5 Ma at rates ranging from ~0.2-0.3 mm/yr in the north and central to rates of ~0.7 mm/yr in the south. Segmented χ-z plots suggest that the uplift may not be uniform at the catchment scale, and/or area-growing drainage integration or area-diminishing drainage captures have occurred in the past 3 Ma. Model results support syn-deformation, foreland-propagating superposition for transverse drainage development in the northern and north-central Apennines where an intact Adriatic slab remains. In contrast further south where a slab window separates the Adriatic slab from the base of the Apennine wedge, dynamic uplift prevails and the transverse drainages have developed in response to regional superposition and integration of catchments through spillover and headwater capture processes. The rates of rock uplift modeled in this study, when integrated for surfaces or stratigraphic deposits that have experienced minimal erosion since their formation, results in cumulative uplift ranging from ~900 m to ~1800 m for the central and southern Apennines respectively, both consistent with recent, independent estimates of surface uplift from paleo-elevation studies.