The Amazon River originated as a transcontinental river around 11 million years ago and took its present shape approximately 2.4 million years ago. These are the most significant results of a study on two boreholes drilled in proximity of the mouth of the Amazon River by Petrobras, the national oil company of Brazil. A team from the Institute for Biodiversity and Ecosystem Dynamics (IBED) of the University of Amsterdam, the University of Liverpool and Petrobras used this new oceanic data to reconstruct the history of the Amazon River. The study was published in the scientific journal Geology in July 2009.

Sediment fan of the Amazon River in the Atlantic Ocean. (University of Amsterdam)

New ecosystem comes to light

Until recently, a sediment column around 10 kilometres thick from the Amazon deep-sea fan (a sort of underwater delta), proved a hard nut to crack, and scientific drilling expeditions such as the Ocean Drilling Program could only reach a fraction of it. Recent exploration efforts by Petrobras lifted the veil, and sedimentological and paleontological analysis on samples from two boreholes, one of which was 4.5 kilometres below sea floor, now give insight into the history of both the Amazon River and the Amazon deep-sea fan. Prior to this publication the exact age of the Amazon River was unknown. This research has large implications for our understanding of South American paleogeography and the evolution of aquatic organisms in Amazonia and the Atlantic coast. The origin of the Amazon River 11 million years ago in fact represents a defining moment: a new ecosystem came into being which at the same time formed a geographic divisor.

The importance of river sediment

Sediment aprons in the proximity of major rivers often hold continuous records of terrestrial material accumulated by the river over time. These records provide a unique insight into the historic climate and geography of the land. In the past, scientific drilling expeditions such as the Ocean Drilling Program tried to learn more about the Amazon River. However they only succeeded in extracting and analysing a fraction of the sediment. The information retrieved from this 4.5-kilometre borehole represents a scientific breakthrough and stresses the value of cooperation between academia and industry.

Publication information

J. Figueiredo, C. Hoorn, P. van der Ven and E. Soares. ‘Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin'. Geology, 37, 619-622.

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Source: University of Amsterdam