Fluvial dynamics and 14 C- 10 Be disequilibrium on the Bolivian Altiplano

Hippe, Kristina; Gordijn, Tiemen; Picotti, Vincenzo; Hajdas, Irka; Jansen, John D.; Christl, Marcus; Vockenhuber, Christof; Maden, Colin; Akçar, Naki; Ivy-Ochs, Susan (2019). Fluvial dynamics and 14 C- 10 Be disequilibrium on the Bolivian Altiplano. Earth surface processes and landforms, 44(3), pp. 766-780. Wiley 10.1002/esp.4529

[img] Text
Hippe_et_al-2019-Earth_Surface_Processes_and_Landforms.pdf - Published Version
Restricted to registered users only
Available under License Publisher holds Copyright.

Download (2MB) | Request a copy

Determining sediment transfer times is key to understanding source‐to‐sink dynamics and the transmission of environmental signals through the fluvial system. Previous work on the Bolivian Altiplano applied the in situ cosmogenic 14C‐10Be‐chronometer to river sands and proposed sediment storage times of ~10–20 kyr in four catchments southeast of Lake Titicaca. However, the fidelity of those results hinges upon isotopic steady‐state within sediment supplied from the source area. With the aim of independently quantifying sediment storage times and testing the 14C‐10Be steady‐state assumption, we dated sediment storage units within one of the previously investigated catchments using radiocarbon dating, cosmogenic 10Be‐26Al isochron burial dating, and 10Be‐26Al depth‐profile dating. Palaeosurfaces appear to preserve remnants of a former fluvial system, which has undergone drainage reversal, reduction in catchment area, and local isostatic uplift since ~2.8 Ma. From alluvium mantling the palaeosurfaces we gained a deposition age of ~580 ka, while lower down fluvial terraces yielded ≤34 ka, and floodplains ~3–1 ka. Owing to restricted channel connectivity with the terraces and palaeosurfaces, the main source of channel sediment is via reworking of the late Holocene floodplain. Yet modelling a set of feasible scenarios reveals that floodplain storage and burial depth are incompatible with the 14C‐10Be disequilibrium measured in the channel. Instead we propose that the 14C‐10Be offset results from: (i) non‐uniform erosion whereby deep gullies supply hillslope‐derived debris; and/or (ii) holocene landscape transience associated with climate or human impact. The reliability of the 14C‐10Be chronometer vitally depends upon careful evaluation of sources of isotopic disequilibrium in a wide range of depositional and erosional landforms in the landscape.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences
08 Faculty of Science > Institute of Geological Sciences > Exogenous Geology

UniBE Contributor:

Akçar, Naki

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0197-9337

Publisher:

Wiley

Language:

English

Submitter:

Naki Akçar

Date Deposited:

25 Nov 2019 14:26

Last Modified:

25 Nov 2019 14:26

Publisher DOI:

10.1002/esp.4529

BORIS DOI:

10.7892/boris.135179

URI:

https://boris.unibe.ch/id/eprint/135179

Actions (login required)

Edit item Edit item
Provide Feedback