Identification of Knickpoints in Littoral Basins of Argentine Patagonia: Geomorphic Markers in a Passive Margin

Knickpoints are an expression of disequilibrium in a fluvial system and they occur in both alluvial and bedrock rivers. A significant amount of research in the past decade around the globe demonstrated the usefulness of the knickpoints as geomorphic markers, specially in active margins, which due to its formation is related to tectonic, climatic and geomorphic processes. However, less attention is paid to the fluvial systems in well-developed along the passive coastal margin as the Atlantic Ocean coast in Patagonia. For the first time in this region, knickpoint analysis together with hypsometric curves and longitudinal stream profiles studies were conducted to understand the landform evolution in coastal basins along the passive margin in Bustamante and Solano Bays (Chubut province, Patagonia, Argentina) during the recent past. The methodology employed digital elevation models (DEMs) and satellite images which have been processed by ArcGIS software using such specific tools as (1) ArcHydro and knickpointfinder, (2) CalHypso, and (3) TopoToolbox (which contains a set of MATLAB functions) to complete the proposed studies. A total of 590 knickpoints were identified along longitudinal fluvial profiles in 18 basins. The results suggest that knickpoints frequency and density vary according to the lithological-structural and tectonic conditions, and it is possible to separate two sectors in the study area, in both the northern and the southern portion, being the southern zone more dynamic linked to active alignments in the depocenter of the San Jorge Gulf. This work provides a method for using knickpoints as geomorphic markers in coastal basins associated to the Atlantic Ocean margin.