Climate changes and the formation of fluvial terraces in central Amazonia inferred from landscape evolution modeling

Author(s)

do Prado, Ariel Henrique ; de Almeida, Renato Paes ; Galeazzi, Cristiano Padalino ; Sacek, Victor ; Schlunegger, Fritz

• Document type: Journal article
• Source: EARTH SURFACE DYNAMICS; v. 10, n. 3, p. 15-pg., 2022-06-02.

Abstract

Climate changes have been considered an essential factor controlling the shaping of the recent alluvial landscapes in central Amazonia, with implications for explaining the biogeographic patterns in the region. This landscape is characterized by wide floodplains and various terrace levels at different elevations. A set of older terraces with ages between 50 and > 200 ka occupy the higher portions of central Amazonia, whereas multiple terraces next to floodplains occur at lower elevations and display ages of a few thousand years. These lower terraces, referred to as middle-lower terraces, reveal what can be perceived as a stochastic pattern both in space and time. Despite the widespread occurrence of these geomorphic features, no process-oriented analysis has been conducted to explain their formation. Here, we develop a landscape evolution model referred to as SPASE (Sedimentary Processes and Alluvial Systems Evolution) to explicitly account for fluvial erosion and deposition in combination with lateral channel migration to explore the controls on terrace development. The model results show that the higher terraces were deposited under the condition of a higher base level for the basins upstream of the confluence between the Solimoes and Negro rivers. The subsequent decrease in the base level initiated a phase of gradual incision, thereby resulting in the current fluvial configuration. The model also predicts that high-frequency climate changes resulted in the construction of middle-lower terraces at various elevations which, however, are all situated at lower elevation than the higher terrace levels. Our model shows that dry-to-wet shifts in climate, in relation to the modern situation, yield a landscape architecture where middle-lower terrace levels are better preserved than wet-to-dry changes in climate, again if the current situation is considered as reference. Finally, our results show that fast and widespread landscape changes possibly occurred in response to high-frequency climate changes in central Amazonia, at least since the Late Pleistocene, with great implications for the distribution and connectivity of different biotic environments in the region. Because of this short timescale of response to external perturbations, we suggest that the streams in central Amazonia possibly also respond in rapid and sensitive ways to human perturbations. (AU)

• FAPESP's process: 18/02197-0 - Integrated quantitative models for quaternary fluvial sedimentation and the distribution of the varzea and terra firme biomes in Western and central Amazonia
• Grantee: Ariel Henrique Do Prado
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 18/23899-2 - Trans-Amazon Drilling Project: origin and evolution of the forests, climate, and hydrology of the South American tropics
• Grantee: André Oliveira Sawakuchi
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 17/06874-3 - Fluvial dynamics and sedimentary deposits in the Amazon channel: providing tools to decipher the paleogeographical evolution of Amazonia and deposits of large anabranching rivers in the rock record
• Grantee: Cristiano Padalino Galeazzi
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 16/03091-5 - CHARACTERIZATION OF HETEROGENEITIES AND MODELING OF RESERVOIR ANALOGUES IN FLUVIAL AND EOLIAN DEPOSITS
• Grantee: Liliane Janikian Paes de Almeida
• Support Opportunities: Regular Research Grants