• First chronostratigraphic study of the Marquesado, Loma Negra, and Carpintería surfaces.
  • More than seventy 10Be and OSL dates on fifteen alluvial fan and strath terrace surfaces.
  • Three 10Be depth profiles measured to investigate potential erosion rate and inheritance issues.
  • Regional correlation of alluvial fan and strath surface ages indicate modulation by climate.

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

Kathryn Hedricka, Lewis A. Owena, Thomas K. Rockwellb, Andrew Meigsc, Carlos Costad, Marc W. Caffeee, Eulalia Masanaf, Emilio Ahumadad

a Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA
b Department of Geological Sciences, San Diego State University, San Diego, CA 92182, USA
c College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
d Department of Geology, Universidad Nacional de San Luis, 5700 San Luis, Argentina
e Department of Physics, Purdue University, West Lafayette, IN 47907, USA
f Department Geodinamica ia Geofisica, Universitat de Barcelona, Spain


Location of detailed study areas
A) Location of detailed study areas. Yellow star on the overview map marks the location of the main image. Note the extensive bajada (yellow) developed east of the mountain front. White areas are the areas investigated in this study. Red lines delineate the observed track of fault scarps on strath terrace and alluvial fan surfaces. MF = Marquesado Fault, RF = Rinconada Fault. Base image from GoogleEarth. B) Schematic section showing the general tectonic setting of the study area following Meigs (2012; pers. comm.). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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 × 10410Be 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.

Quaternary Science ReviewsKathryn Hedrick, Lewis A. Owen, Thomas K. Rockwell, Andrew Meigs, Carlos Costa, Marc W. Caffee, Eulalia Masana, Emilio Ahumada,Timing and nature of alluvial fan and strath terrace formation in the Eastern Precordillera of Argentina, Quaternary Science Reviews, Volume 80, 15 November 2013, Pages 143–168http://dx.doi.org/10.1016/j.quascirev.2013.05.004