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

River profile inversion and cosmogenic nuclide burial ages of shallow sedimentary deposits in the Eastern Amazonia

Paper number: 122-10
Program: Technical Sessions
Time: 4:10 PM – 4:25 PM

Authors

Abstract

The Amazon River Basin has the largest drainage area and the richest biodiversity of freshwater species in the world. However, the timing and mechanisms of its landscape evolution remain unclear. The formation of the Amazon River (i.e., the trunk river) as a transcontinental conduit (i.e., Andes to Atlantic), for example, is an open topic, with a wide range of possible ages. Studies with a focus on the Western Amazonia date the formation to the Pleistocene-Pliocene, whereas Late Miocene ages are obtained from offshore sediments in drill cores in the Amazon Fan. Therefore, ages that help reconstruct the basin’s evolution and the fluvial system in the Eastern Amazon are lacking (i.e., the Lower Amazon River). For example, no known sediment deposit dates to the Miocene or even Pliocene. In this study, we shed light on this topic, coupling results of cosmogenic nuclide-derived erosion rates, burial age of deposits in the region of eastern Amazonia, and numerical modeling. We hypothesize that the lower Amazon River must have incised in response to the formation of the Amazon River (i.e., the connection of the current Western and Eastern Amazonia), leading to the downcutting of the Lower Amazon River in the East. We hypothesize that it drove the incision and consequently the base-level fall of its tributaries. Using 10Be and 26Al concentrations from quartz-bearing samples of tributary rivers in the Northern border of the Lower Amazon River, we calculated erosion rates from riverbed samples and burial ages in deposits in riverbanks. The calculated erosion rates vary from 2.8 m/Myr to 30 m/Myr. The erosion rates will be used as a proxy to model the inversion of river profiles’ topography in the basins in which we aim to find the best incision parameters and base level fall variables. These parameters will be used to obtain the age of the latest base-level fall in the tributaries and possibly correlate to the Amazon River Formation. The burial ages are estimated using a numerical approach that considers continued production of nuclides in buried samples, mainly by muons.

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

doi: 10.1130/abs/2025AM-414218

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