The Amazon paleoenvironment resulted from geodynamic, climate, and sea-level interactions

The northern South American landscape evolved in response to complex interactions between geo-dynamic processes, climate, and sea-level oscillations, culminating in formation of the Amazon River. Although the history of this drainage basin was investigated in previous studies, the controlling factors on its depositional environment before Amazon River formation remain elusive. Based on existing sedi-mentologic and paleontologic observations and new numerical models, we show that Andean mountain building, evolving climate, and eustatic sea-level oscillations controlled the transition from intermittent marine to lacustrine environmental conditions in Amazonia before the onset of the transcontinental river. Our numerical simulations show that the incorporation of an evolving climate contributed to the short-ening of the time interval between the end of marine influence in Western Amazonia and the onset of the transcontinental Amazon River during the late Miocene. Additionally, our numerical scenarios indi-cate that sea-level oscillations created intermittent marine incursions in central and western Amazonia only when negative dynamic topography induced by mantle convection was taken into account. After the establishment of the transcontinental river, the numerical scenarios produced no further marine in-cursions in central and western Amazonia, despite continued sea-level oscillation. We propose that this environmental evolution influenced regional biodiversity and the sedimentation history in northern South America, and explains the formation and disappearance of aquatic environments before the onset of the transcontinental Amazon River.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

This study reveals that the formation of the Andes, climate evolution, and sea-level oscillations were the controlling factors for the transition from intermittent marine to lacustrine environments in the Amazon before the formation of the transcontinental river. It is also found that the evolving climate shortened the time interval between the end of marine influence and the onset of the transcontinental Amazon River.