Geological Society of America

T136 The Andes from Top to Bottom

Monday, 16 October 2023
1:30 PM - 5:30 PM
326

DRAINAGE EVOLUTION IN THE AMAZON FORELAND BASIN DURING UPLIFT OF THE ANDES

Paper number: T136-3
Program: Technical Sessions
Time: 1:55 PM – 2:10 PM

Authors

Brian Horton Presenting Author
University of Texas at Austin, Austin, TX
Inigo Wahnfried
Amazonas Federal University, Manaus
Gustavo Kiefer
Brazil Potash, Manaus
André O. Sawakuchi
University of São Paulo, São Paulo
Sherilyn Fritz
University of Nebraska - Lincoln, Lincoln, NE
Paul A. Baker
Duke University, Durham, NC
Sebastian Gomez
University of São Paulo, São Paulo, Butanata
Mauricio Parra
University of São Paulo, São Paulo
Lily Jackson
School of Energy Resources, University of Wyoming, Laramie, WY
Claudia L. Banks
University of Texas, Austin, TX
E. Gabriela Gutierrez
University of Texas, Austin, TX
Cristian Vallejo
Escuela Politécnica Nacional, Quito
Cleverson G. Silva
Fluminense Federal University, Niterói

Abstract

Detrital zircon results from modern rivers and ancient fluvial deposits help define the paleodrainage history of the Amazon River and South American foreland during uplift of the Andes. The continental-scale Amazon, Orinoco, and Magdalena fluvial drainage systems have impacted erosion, sediment dispersal, biodiversity, and climatic-tectonic interactions in the Andean fold-thrust belt and foreland basin. South America is well suited for provenance studies employing detrital zircon U-Pb geochronology because of age-diagnostic sources, including the Andean magmatic arc, retroarc fold-thrust belt, and Amazonian cratonic basement provinces.

New results from ~100 samples of fluvial basin fill and modern rivers in the Amazon headwaters of Ecuador and Peru demonstrate the spatial and temporal changes in detrital input from different source areas. U-Pb ages of modern river samples show both first-cycle igneous and metamorphic detritus as well as recycled sedimentary detritus from the magmatic arc, fold-thrust belt, and cratonic basement. Within foreland basin fill, U-Pb age distributions demonstrate a drainage reversal from cratonic to Andean sources during the Late Cretaceous-earliest Cenozoic initiation of Andean uplift. Thereafter, Cenozoic exhumation of the Andean orogenic belt resulted in greater input from the growing fold-thrust belt relative to the magmatic arc.

New U-Pb results from ~20 subsurface samples near Manaus, Brazil (~2200 km east of the Andes) show complex changes in source contributions that reflect abrupt alternations between local and regional derivation. These major drainage reorganization events may be related to Andean uplift, intracratonic uplift of basement arches, regional-scale marine incursions, or episodic generation of dynamic topography.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-390363

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