122 From the Cosmos and Back: Quantifying Processes and Rates of Landscape Change

This session explores how methods such as cosmogenic nuclides, apatite (U-Th)/He thermochronometry, U-series geochemistry, luminescence, and chemical mass balances quantify relationships between climate, tectonics, and erosion.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 212AB

Constraining landscape evolution in the eastern Amazon region

Paper number: 122-11
Program: Technical Sessions
Time: 4:25 PM – 4:45 PM

Authors

Abstract

The Amazon landscapes are the tapestry for the most biodiverse continental ecosystem on Earth. Changes in these landscapes have consequences not only for water, sediment, and nutrient routing, but also for the biogeography and biodiversity of the region. Rivers simultaneously form barriers and corridors for the distribution of terrestrial and aquatic species, respectively. Therefore, constraining their reorganizations can not only help constrain landscape evolution, but also provide a blueprint for biogeographic studies. However, the timing of drainage network reorganizations is under-constrained and highly debated. Many deposits are too old for luminescence dating and/or too shallow for the cosmogenic nuclide burial dating approach assuming complete shielding. Furthermore, few quantifiable mechanisms have been proposed to explain recurring drainage reorganizations in the region that can consistently explain river captures and drainage divide migration. In this work, we use cosmogenic isotopes in shallow sedimentary deposits from abandoned river networks in Central Amazonia. Using a numerical approach to solve for burial ages, we account for muogenic production and recover Mio-Pliocene ages. These ages are consistent with previously published ages of lateritic duricrusts in the region, the timing of base level fall detected in the topographic inversion of fluvial profiles, and the ages of aquatic and terrestrial species isolated due to drainage reorganizations. To explore what mechanisms can explain the widespread drainage reorganizations in this area, we use numerical landscape evolution models. We find that the outcropping of hard rocks triggers widespread drainage network reorganizations and patterns of drainage divide migration consistent with those seen in the eastern Amazon. These data reveal that combining numerically modeled cosmogenic nuclide ages, topographic analysis, and numerical landscape evolution models offer a powerful combination to decipher the evolution of the Amazon’s river networks, linking landscapes and life. 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414270

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