Timing and nature of alluvial fan and strath terrace formation in the Eastern Precordillera of Argentina

Sixty-eight 10Be terrestrial cosmogenic nuclide (TCN) surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper-arid San Juan region of the Argentine Precordillera. This region is tectonically active, and numerous fault scarps traverse Quaternary landforms. The three study sites, Marquesado strath complex, Loma Negra alluvial fan and Carpintería strath complex reveal a history of alluvial fan and strath terrace development over the past ∼225 ka. The Marquesado complex Q3m surface dates to ∼17 ± 3 ka, whereas the Loma Negra Q1ln, Q2ln, Q3ln, Q4ln, and Q5ln surfaces date to ∼24 ± 3 ka, ∼48 ± 2 ka, ∼65 ± 13 ka, ∼105 ± 21 ka, and ∼181 ± 29 ka, respectively. The Carpintería complex comprises eight surfaces that have been dated and include the Q1c (∼23 ± 3 ka), Q2c (∼5 ± 5 ka), Q3ac (∼25 ± 12 ka), Q3bc (∼29 ± 15 ka), Q4c (∼61 ± 12 ka), Q5c (∼98 ± 18 ka), Q6c (∼93 ± 18 ka), and Q7c (∼212 ± 37 ka). 10Be TCN depth profile data for the Loma Negra alluvial fan complex and Carpintería strath terrace complex, as well as OSL ages on some Carpintería deposits, aid in refining surface ages for comparison with local and global climate proxies, and additionally offer insights into inheritance and erosion rate values for TCNs (∼10 × 104 10Be atoms/g of SiO2 and ∼5 m Ma−1, respectively). Comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the Carpintería and Loma Negra areas with only younger alluvial fan surfaces preserved both to the north and south. These data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages, which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region.