Geomorphological dynamic changes during the Holocene through ephemeral stream analyses from Northwest Argentina

- A review of Holocene antecedents from semiarid valleys from NW Argentina was made.
- Eighteen ephemeral streams in Tafí Valley were selected by its Holocene representativeness.
- Geomorphological, archaeological, chronological and paleoenvironmental data were applied.
- Anthropic and climatic influence over Holocene evolution was analyzed.
- Paleoenvironmental evolutionary reconstruction was made and related with regional and global data.

This paper studies the changes in the geomorphological dynamics recorded in 18 ephemeral streams located on the east side of Loma Pelada (Tafi Valley), a part of the Sierras Subandinas (Northwest Argentina). The applied methodology is based on photointerpretation, field survey, and descriptions of the Holocene alluvial fillings dated by tephras, archaeological artefacts, and absolute datings. The records show a coupled system of slope-terrace-alluvial fans resulting from the environmental changes of four alternating aggradation/degradation stages. The oldest stage (1) was generated by climatic causes and covers Early to Mid-Holocene (ca. 13,000-10,000 BP to ca. 4200 BP). After the incision of these accumulations, a new aggradation stage (2) was triggered by anthropogenic activity occurring from right before 2500 BP to the 15th century. During that time human occupations of the Tafí Valley were intense. Two wetter events occurred around 4200 and 2800 BP in the area, related to global cooling phases. Lastly, two more recent phases (3 and 4) are associated with the climatic variability of the LIA and the Present Warm Period. The results highlight the sensitivity of headwater catchments of dry subtropical mountainous areas to climate changes, anthropogenic impact, and their relationship with global climatic data.