Landscape response to late Pleistocene climate change in NW Argentina: Sediment flux modulated by basin geometry and connectivity

Abstract

Fluvial fill terraces preserve sedimentary archives of landscape responses to climate change, typically over millennial timescales. In the Humahuaca Basin of NW Argentina (Eastern Cordillera, southern Central Andes), our 29 new optically stimulated luminescence ages of late Pleistocene fill terrace sediments demonstrate that the timing of past river aggradation occurred over different intervals on the western and eastern sides of the valley, despite their similar bedrock lithology, mean slopes, and precipitation. In the west, aggradation coincided with periods of increasing precipitation, while in the east, aggradation coincided with decreasing precipitation or more variable conditions. Erosion rates and grain size dependencies in our cosmogenic 10 Be analyses of modern and fill terrace sediments reveal an increased importance of landsliding compared to today on the west side during aggradation, but of similar importance during aggradation on the east side. Differences in the timing of aggradation and the 10 Be data likely result from differences in valley geometry, which causes sediment to be temporarily stored in perched basins on the east side. It appears as if periods of increasing precipitation triggered landslides throughout the region, which induced aggradation in the west, but blockage of the narrow bedrock gorges downstream from the perched basins in the east. As such, basin geometry and fluvial connectivity appear to strongly influence the timing of sediment movement through the system. For larger basins that integrate subbasins with differing geometries or degrees of connectivity (like Humahuaca), sedimentary responses to climate forcing are likely attenuated.

Short-lived increase in erosion during the African Humid Period: Evidence from the northern Kenya Rift

“…Climate change in the tropics and subtropics associated with rapid changes in erosion, soil thickness, and vegetation cover is the focus of many recent research efforts to better understand the impact of environmental change on landscapes (e.g., Pelletier et al, 2015;Schildgen et al, 2016). Paleo-environmental changes recorded by proxy indicators in marine and terrestrial sediments may serve as powerful proxies of landscape response to both present-day climate variability and future climate change (e.g., deMenocal et al, 2000;Shanahan et al, 2015).…”

Climatic controls on debris‐flow activity and sediment aggradation: The Del Medio fan, NW Argentina

“…In particular, the tributary catchments in the arid sector north of Volcán host thick fluvial fill terraces and fans (abandoned surfaces standing up to 150 m above the modern river level), while catchments in the subhumid sector south of the Del Medio fan record only limited deposition in the vicinity of the confluence with the Rio Grande. Landslides are known to occur throughout the Humahuaca Basin, both north and south of the fan, with more frequent, low‐volume landsliding events observed in wetter regions today [ Paolini et al ., ] and more frequent landsliding proposed to have occurred during wetter periods in the past across the region [ Trauth et al ., ; Bookhagen et al ., ; Haselton et al ., ; Schildgen et al ., ].…”

“…To characterize the processes and local conditions that have led to aggradation in the Del Medio catchment, we combine field observations with measurements of in situ produced cosmogenic 10 Be in sand and pebbles. Differences in cosmogenic nuclide concentrations between sand and pebbles are thought to be related to the dominant erosional mechanisms [ Belmont et al ., ; Aguilar et al ., ; Codilean et al ., , ; Carretier et al ., , and references therein; Schildgen et al ., ], with landslides releasing larger grains with lower 10 Be concentrations. In an effort to establish a chronology of the most recent activity on the fan, we determine exposure ages by measuring 10 Be concentrations of boulder surfaces and depth profiles.…”

Measuring Decadal Vertical Land-level Changes from SRTM-C (2000) and TanDEM-X (~ 2015) in the South-Central Andes

“…1) to identify and measure areas of dh in gravel-bed channels specifically and then across the landscape. Here, steep gradients in elevation (~1-4 km), rainfall (~0.1-1 m/yr), and vegetation (sub-tropical forests and croplands to arid, succulent-covered slopes) cause high rates of mass transfer (Bookhagen and Strecker, 2012;Savi et al, 2016;Schildgen et al, 2016), further influenced by climate change (Castino et al, 2016a(Castino et al, , b, 2017 and anthropogenic modification (gravel mining and weirs). To conclude, we discuss caveats driven by remaining uncertainties prevalent in spaceborne DEMs collected over complex topography.…”

“…8), we see that these automated measurements can be correlated with additional sources. For Río Grande, the steep knickpoint at the Del Medio fan Schildgen et al, 2016) causes a major zone of incision immediately followed by aggradation where the material is deposited. Fieldwork has indicated that 15 some of this incision is man-made, caused by attempted removal of aggrading material coming from the productive (e.g., debris flows cf.…”