Andrés Bilmes

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.

Late Cenozoic Landforms and Landscape Evolution of Península Valdés

The present landscape of the Peninsula Valdes is the result of a complex interrelation between climatic (aeolian deposition, windblown processes, glacial and interglacial cycles, pluvial and fluvial processes), tectonic, and eustatic controls that had work in the Andean foreland during the late Cenozoic. Based on a geomorphological approach, which includes new descriptions, interpretations, and hierarchically classification of the main landforms of this region, together with previous geomorphological surveys, the Peninsula Valdes area was grouped in three major geomorphologic systems: Uplands and Plains, Great Endorheic Basins, and Coastal Zone. Based on the interrelationship among these three geomorphological systems the landscape evolution of the late Cenozoic of Peninsula Valdes could be summarized in five main stages: (1) development of fluvial and alluvial systems during the Pliocene early Pleistocene; (2) closed basin formation associated to tectonic processes during the early middle Plesitocene; (3) first marine transgressions during the late Pleistocene; (4) flooding of the gulfs and construction of the peninsula in the late Plesitocene–Holocene; (5) final flooding in the region during the middle Holocene.

Late Cenozoic of Península Valdés, Patagonia, Argentina

The Península Valdés region is situated in an intraplate position of the South American Plate, in the Patagonian foreland close to the Argentine Continental shelf. This region has a complex geotectonic evolution that started more than 400 Ma and involves the conformation of Northern Patagonia as a part of Gondwana during the Paleozoic, the opening of the Atlantic Ocean during the Mesozoic and the configuration of the Andean margin during the Cenozoic. At different scales, the interplay between climate, tectonic, sea-level, and volcanic processes, set the sedimentary routing system that had governed the final geologic records of the Península Valdés region and control the transfer of terrigenous sediments from source to sink. The stratigraphic record of the region was not only influenced by local factors. Processes developed far away from Península Valdés, both in the Southern Andes or in the continental shelf had influenced the late Cenozoic record of this region.

Climatic, Tectonic, Eustatic, and Volcanic Controls on the Stratigraphic Record of Península Valdés

The Peninsula Valdes region is situated in an intraplate position of the South American Plate, in the Patagonian foreland close to the Argentine Continental shelf. This region has a complex geotectonic evolution that started more than 400 Ma and involves the conformation of Northern Patagonia as a part of Gondwana during the Paleozoic, the opening of the Atlantic Ocean during the Mesozoic and the configuration of the Andean margin during the Cenozoic. At different scales, the interplay between climate, tectonic, sea-level, and volcanic processes, set the sedimentary routing system that had governed the final geologic records of the Peninsula Valdes region and control the transfer of terrigenous sediments from source to sink. The stratigraphic record of the region was not only influenced by local factors. Processes developed far away from Peninsula Valdes, both in the Southern Andes or in the continental shelf had influenced the late Cenozoic record of this region.