Identification of Guayatayoc Basin river patterns (northern Argentinean Puna): implications for a chronological landform history

LOPEZ STEINMETZ, R.L.; GALLI, C.I.; CHAYLE, W.

Mendoza

Congreso; 18th International Sedimentological Congress; 2010

International Associations of Sedimentologist

The endoreic-evaporitic Guayatayoc basin is located in the northwest part of the Argentinean Andes, between 65°20?W - 66°35?W and 22°24?S - 24°00?S. This region is arid and has desert weather; rainfalls are less than 300mm per year. The feeding rivers of the basin, only and episodically, flow during the summer monsoons. The waterbody of Guayatayoc Lake, the lowest drainage point of the basin, reaches an altitude of 3400 meters above the sea level and it is included within the eastern border of the Puna Geologic Province (González et al., 2000). The determination of the most important spatial arrangement of the stream channels in the basin landscape has been based on several important factors like slope and structure without forgetting other factors as weather. However the adjusted and anomalous river patterns are mainly produce by slope and structure (Twidale, 2004). Some slope linked river patterns in the Guayatayoc basin, such as parallel arrangements, are well represented in the plains zones of Coranzuli ignimbrite, as well as the subparallel streams in the highest parts of the quaternary glacis located at the west side of the Sierra de Santa Victoria. Several radial patterns can be recognized in basin borders zones and also have been observed around basin waterbodies. Distributary patterns are well developed in quaternary alluvial fans like Las Burras and generally in the west slops of the Sierra de Aguilar. On the other side, there are quite a lot of examples showing structure linked straight arrangements in large areas dominated by parallel, angular, trellis and segments of other patterns which can be considered linear patterns on a local scale. Some of those straight streams, arranged on the quaternary alluvial deposits, are demonstrating a neotectonic activity. In some parts of Coranzuli ignimbrite plains, angular and trellis patterns are well represented too. Annular arrangements characterize the surrounding drainage in the vicinity of the Miocene volcanoes. Scares of relatively recent direction change of subparallel and dendritic streams were identified in the quaternary alluvia of Cangrejo subriver basin. Evidences of recent structural activity, which are controlling arrangements, are also identified by the present divergence of the distributary drainage closed to the town of Abra Pampa and throughout Pastos Chicos subriverbasin. Morever, some examples of anomalous fluvial designs, considering the stream flows as subsequent-obsequent, can be referred in several outcrops. An example of them is the Ordovician outcrop situated at the NNE of the Huancar village. Anabranching streams, which characterize aggradational plains, are often represented in the dominion of angular-trellis patterns. This arrangement association, angular-anabranching, is only verified in ignimbrite lithologies, even though such kind of plains are not present aggradational environments. The areas of the Guayatayoc basin which have possible aggradational environments are the alluvial fans mouth of Miraflores and Las Burras rivers, although Las Burras fan does not seem active. Finally, some conspicuous examples of anabranching patterns were also found in the present alluvial sediments which are filling up the southern zone of Pastos Chicos river.