Linking mid-scale distributive fluvial systems to drainage basin area: geomorphological and sedimentological evidence from the endorheic Gastre Basin, Argentina

Abstract

The analysis of mid-scale distributive fluvial systems (DFS) provides an opportunity to study fluvial depositional patterns in sedimentary basins in a manner similar to megafans, but under the more homogeneous external conditions that control small alluvial fans from the source area to the depositional area. Four mid-scale Quaternary DFS and the areas of their drainage basins were analysed with the aim of understanding and predicting the mechanism and magnitude of fluvial fan deposition. These DFS were located in the Gastre Basin, Argentina, an endorheic basin that has evolved during the Quaternary under relatively uniform climatic and tectonic conditions. Using a geomorphological and sedimentological approach, the measured areas of the DFS were compared with the calculated areas using different regression equations for variables such as the drainage basin area and the drainage basin slope. The results suggest a moderate to high percentage of deviation in all cases, indicating that at an intermediate scale the size of the DFS is not solely a function of the size of the drainage basin. Adjacent DFS with similar depositional areas and catchment bedrock lithologies were linked with very different drainage basin areas and vice versa. This study suggests that the horizontal accommodation space, determined by the incision and distribution of previous deposits, and the drainage basin slope may also influence the size of mid-scale DFS.