What is the Neogene?
The Earth is about 4.6 billion years old—and a lot of history has happened here. One of these chapters is the Neogene period, which occurred between 23 and 2.5 million years ago. It was during this time that large mountain ranges such as the Himalayas, the Alps, and the Andes were formed.
But what few people know is that during the Neogene, the Amazon also underwent surprising transformations.
The Amazon was once invaded by the sea.
Millions of years ago, what is now a dense forest was once an environment partially covered by salt water. Over the course of 23 to 5 million years during the Miocene epoch, a subdivision of the Neogene, the Caribbean Sea occasionally overflowed into large areas of the Western Amazon region via natural waterways.
These “visits” from the sea left important marks: fossils of shark teeth, shells, microalgae, and small crustaceans have been found in sediments in the region. These are clues that one day, the sea was where dolphins and giant trees live today.
Figure 1. Geological time. Source: Mundo Educação. Avaiable at: https://mundoeducacao.uol.com.br/geografia/escala-tempo-geologico.htm.
The sea that helped shape the Amazonian biodiversity.
These marine incursions not only changed the landscape but also influenced the biodiversity of the Amazon. The mixing of fresh and salt water created unique environments where new species could emerge and adapt.
A good example is the pink river dolphin and freshwater stingrays—animals that originated from marine ancestors and, over time, adapted to life in Amazonian rivers.
Figure 2. Pink river dolphin. Avaiable at: https://noticias.uol.com.br/meio-ambiente/ultimas-noticias/redacao/2020/02/06/fim-de-moratoria-de-pesca-ameaca-boto-rosa-da-amazonia-diz-biologa.htm
What does science say?
A study was conducted by researcher Lilian Leandro, which involved the analysis of calcareous and organic microfossils, along with geochemical data. The goal was to better understand how and when salt water influenced the region.
The area analyzed was the Solimões Basin in the Western Amazon. The data revealed evidence of salt content in the samples, suggesting that there was a new stage of sea flooding at the end of the Miocene epoch, which runs counter to the previous notion that this event occurred solely at the start of the period.
Figure 3. Microfossils analyzed. Avaiable at: https://pubs.geoscienceworld.org/gsa/geology/article/50/4/465/610675/Multi-proxy-evidence-of-Caribbean-sourced-marine
Figure 4. Paleogeography of nothern South America in the middle to late Miocene. Avaiable at: https://pubs.geoscienceworld.org/gsa/geology/article/50/4/465/610675/Multi-proxy-evidence-of-Caribbean-sourced-marine
Where did all this salt water come from?
Studies indicate that these floods have their source in the Caribbean Sea. The significance of the Caribbean's impact on the Amazon is underscored, underscoring its pivotal role in shaping the Amazon's geological history, including its terrain, weather patterns, and biodiversity. Examining these past occurrences provides insight into how the Amazon originated and why it is so distinctive, uncovering the fact that the sea is also an integral component of the world's largest rainforest's history.
References
LEANDRO, Lilian M. et al. Multi-proxy evidence of Caribbean-sourced marine incursions in the Neogene of Western Amazonia, Brazil. Geology, v. 50, n. 4, p. 465–469, 2022. Disponível em: https://pubs.geoscienceworld.org/gsa/geology/article/50/4/465/610675/Multi-proxy-evidence-of-Caribbean-sourced-marine.
MONTERA, Luciana. Neógeno. Campo Grande: Universidade Federal de Mato Grosso do Sul, 2021. Disponível em: https://faeng.ufms.br/neogeno/.
MUNDO EDUCAÇÃO. Escala de tempo geológico: o que é, como funciona, tabela. Disponível em: https://mundoeducacao.uol.com.br/geografia/escala-tempo-geologico.htm.
SACEK, Victor; MUTZ, Sebastian G.; BICUDO, Tacio C.; DE ALMEIDA, Renato P.; EHLERS, Todd A. The Amazon paleoenvironment resulted from geodynamic, climate, and sea-level interactions. Earth and Planetary Science Letters, v. 605, p. 118033, 2023. Disponível em: https://www.sciencedirect.com/science/article/pii/S0012821X23000468.
