Quantitative Geomorphology applied to the distal Salado del Norte River basin, Argentina. Neotectonic and Surface processes in an intracratonic setting

BRUNETTO E.; KRÖHLING, D.; FRANCISCONI, C.; ZALAZAR, M.C.

Nagoya

Congreso; XIX INQUA Congress; 2015

INQUA

Several quantitative tools (mainly an erosion code) were applied with the aim to estimate the relative incidence of surface processes on the landscape of a representative region of the Northern Pampa. It could contribute to analyze the interplay between exogenous and endogenous factors in an intracratonic setting of South America. Swath profiles and frequency histograms from DEM data allowed evaluating the incision of river valleys on elevated plains uplifted by intraplate tectonic deformation. Slope inversion of dells that display a co-linear drainage model and lacustrine deposits located on gentle scarps support the interpretation of the tectonic origin for the uplifted plains. Regional pond and shallow lacustrine sediments, Late Pleistocene in age (ca. 70 ka.BP), were used as a geochronological constrain for the fluvial incision model. Topographic cross-sections and frequency histograms from DEM data suggest two paleosurfaces, which can be interpreted as they were uplifted by Late Quaternary reactivation of faults. These faults limit the San Guillermo and San Cristobal blocks. The best-fit fluvial incision model was obtained for an erodability coefficient K= 1.e-4, a diffusion coefficient D=1.e-9, and m= 0.5 and n= 1.0 parameters. The model reproduces the actual modern topography starting from a low-elevation surface (t=0 yr; slope=0.2 degrees) with an uplift history initiated at 60 ka. It suggests incision rates of 0.25 mm/a and uplift rates of 0.4 mm/a. Maximum incision depth resulted from the difference between maximum and minimum elevations on swath profiles along the river valley, downstream of the knick point, and uplift rates rose from the best-fit model. These estimations evidence highly dynamic surface processes during the Late Pleistocene in an intracratonic setting, which had been previously suggested from geological proxies, where uplift elevations were estimated from the difference between medium elevations of paleosurfaces representatives of the blocks.