Timing of past glaciation at the Sierra de Aconquija, northwestern Argentina, and throughout the Central Andes

Abstract

Advances in cosmogenic nuclide exposure dating have made moraines valuable terrestrial recorders of palaeoclimate. A growing number of moraine chronologies reported from the Central Andes show that tropical glaciers responded sensitively to past changes in precipitation and temperature over timescales ranging from 10 3 to 10 5 years. However, the causes of past glaciation in the Central Andes remain uncertain. Explanations have invoked insolation-modulated variability in the strength of the South American Summer Monsoon, teleconnections with the North Atlantic Ocean, and/or cooling in the Southern Hemisphere.The driver for these past climate changes is difficult to identify, partly due to a lack of dated moraine records, especially in climatically sensitive areas of the southern Central Andes.Moreover, new constraints are needed on precisely where and when glaciers advanced. We use cosmogenic 10 Be produced in situ to determine exposure ages for three generations of moraines at the Sierra de Aconquija, situated at 27°S on the eastern flank of the southern Central Andes. These moraines record glacier advances at approximately 22 ka and 40 ka, coincident with summer insolation maxima in the sub-tropics of the Southern Hemisphere, as well as at 12.5 ka and 13.5 ka during the Younger Dryas and the Antarctic Cold Reversal, respectively. We also identify minor glaciation during Bond Event 5, also known as the 8.2 ka event. These moraines register past climate changes with high fidelity, and currently constitute the southernmost dated record of glaciation on the eastern flank of the Central Andes. To contextualise these results, we compile 10 Be data reported from 144 moraines in the eastern Central Andes that represent past glacier advances. We re-calculate exposure ages from these data using an updated reference production rate, and we re-interpret the moraine ages by taking the oldest clustered boulder age (after the exclusion of outliers attributed to nuclide inheritance) as closest to the timing of glacier advance-an approach for which we provide empirical justification. This compilation reveals that Central Andean glaciers have responded to changes in temperature and precipitation. We identify cross-latitude advances in phase with insolation cycles, the last global glacial maximum, and episodes of strengthened monsoonal moisture transport including the Younger Dryas and Heinrich Stadials 1 and 2. Our results from the Sierra de Aconquija allow us to constrain the southerly limit of enhanced precipitation associated with Heinrich Stadials at ~25°S. More broadly, our findings demonstrate at both local and regional scales that moraines record past climate variability with a fine spatial and temporal resolution.3

Late Quaternary Tectonics, Incision, and Landscape Evolution of the Calchaquí River Catchment, Eastern Cordillera, NW Argentina

“…Increased erosional efficiency could reduce surface slopes across the southern Puna within the thick‐skinned orogenic wedge, driving active shortening in the wedge interior (Davis et al, ; Whipple, ; DeCelles et al, 2011). Although there have likely been changes in humidity in the CRC at millennial and 100‐kyr frequencies (e.g., Bookhagen et al, ; D'Arcy et al, ; Tofelde et al, ), the overall trend in the interior of the Eastern Cordillera has been towards orographically driven aridity (e.g., Bywater‐Reyes et al, ), and the Pucará basin has been arid enough to sustain aridisols and pavement development for at least the last ~151 ka. Increases in erosional efficiency therefore do not provide a sufficient explanation for internal, out‐of‐sequence deformation.…”

“…Interannual variability in precipitation is significant (±75%), and driven primarily by ENSO and the Tropical Atlantic Sea‐surface Temperature Variability (Trauth et al, ). Cooler and more humid periods occurred throughout the Quaternary (Bobst et al, ; Fritz et al, ), increasing landslide‐frequency (Trauth et al, ), expanding glacial (D'Arcy et al, ; Haselton et al, ) and periglacial (May & Soler, ) zones, and increasing overall catchment erosional efficiency (Bookhagen & Strecker, ). Glacial advances are linked to summer insolation when the South American Summer Monsoon is strongest, with local advances at ~44 ka in the Sierra de Quilmes (Zech et al, ) and ~40 ka in the Sierra Aconquija (D'Arcy et al, ).…”

Observations and dynamical implications of active normal faulting in South Peru

“…An important recent development that aides estimating the fault slip rates is the proliferation of moraine age estimates from cosmogenic radionuclide dating in the study region [Smith et al, 2005;Rodbell et al, 2009;Jomelli et al, 2014;Ward et al, 2015;D'Arcy et al, 2019]. Ice covered a large fraction of the Altiplano in the last major glacial, depositing moraines and drift sheets.…”

Last glacial maximum deglaciation of the Southern Velebit Mt. (Croatia): insights from cosmogenic 36Cl dating of Rujanska Kosa

“…40 mm ka −1 ; Table 3). Another uncertainty arises during the interpretation of a moraine landform age from the dated boulders in deciding whether to take the oldest boulder age within a cluster or weighted average age of boulders after the exclusion of outliers (e.g., Putkonen and Swanson 2003;Heyman et al 2011;Applegate et al 2012;Çiner et al 2017;D'Arcy et al 2019). In this study, we used the oldest boulder age as the age of the landform, assuming that the erosion of boulders in karstic terrains and degradation of moraines in humid environments are the two most important factors that influence the age.…”