Understanding the Neogene history of Amazonia is essential for understanding the evolution of the rainforest. This is one of the most species diverse areas on Earth. The PI seeks a better understanding about the paleogeography of the Amazon. He wishes to determine if during the Miocene (25-5 Ma) the Amazon was a shallow sea inundated from the north by the Caribbean Sea, or whether it was a giant freshwater lake. The PI also wishes to determine if the temperature 17-14 Ma was 3-4° Celsius higher than today as it was at higher latitudes. Commensurate with these hypotheses is whether plant diversity was greater in the Miocene than today. The PI will study two areas in the Llanos (with 4500 meters of stratigraphy) and one site in Urumaco (with 9000 meters of stratigraphy), Colombia. The PI wishes to determine whether the Amazon was flooded by the Caribbean Sea from the north, or alternatively if the Amazon was a giant freshwater lake during various intervals of the Miocene Epoch. Palynology and sedimentology will be used as a proxy to identify a shallow sea or freshwater lake. There will likewise be a study of Middle Miocene (17-14 Ma) temperature to determine if it was tied to a major global warming event using the TEX86 method. Oxygen isotope analysis of coexisting mammalian tooth enamel and fish scales will also be evaluated. This project includes a well-developed international collaboration involving scientists from the USA, Colombia, Panama, Brazil, and Holland. Training of a graduate student and a postdoctoral researcher represents important components of this grant. Their careers will greatly benefit from international networking opportunities and the extended exchange of ideas with PI and collaborators of this grant. This research will be useful for biologists working in the Amazon, climate modelers, plant physiologists, conservationists and evolutionary biologists. Chronostratigraphic results of this project will improve the geological community?s understanding of the regional structural geology and tectonics.
Why is Amazonia so species rich? Was Amazonia covered by a shallow sea in recent times? When neotropical savannas evolved? Does tropical latitudes warm during global warming events? This set of questions represent a major puzzle to understand the dynamics of tropical ecosystems, and in the face of the current anthropogenic climate change they are especially relevant today. In order to attempt responding these questions we performed three set of analysis including 1) the study of the pollen and spore content of ~300 rock samples that were taked both from a rock core drilled in the tropical savannas of Colombia, and from extensive outcrops in western Venezuela, 2) the study of the environment where the sediments that produced the rock were accumulated, and 3) the study of the Oxygen isotopic content of the enammel of ~13 Million-year old fossil mammals from Central Colombia. Our research yielded three major findings Eastern Amazonia was covered at least eight different times by a shallow sea in a period that spanned from 19.8 to 12.5 million years ago. Six of those events were short-lived (less than one million years in duration), and two events were long lived (more than two million years). There has not been any more marine floodings over the past 12.5 million years. It is hard to imagine how the extensive forests that cover Amazonia today were covered by a shallow sea only a few million years ago. What impact these events had on the evolution of the plants and animals inhabiting the region today is still a major puzzle, that we plan to address in a future research. Neotropical savannas expanded only over the past 2-3 Million years. In other words, the savanna ecosystem is a very recent one and expanded at the expense of tropical forests. We need to understand the causes of this expansion. An initial hypothesis indicates that an increase in rainfall seasonality driven by the onset of the glaciation in the northern hemisphere could be the trigger of the expansion. Mean annual temperature of the Neotropics increased by 2-7 degrees Celsius during the global warming of the Middle Miocene (~15 Million years ago), the last major global warming of the past 65 Million years. This warming is associated to a large increase in CO2. This result indicates that even though the tropics warm during global warming, it does not warm as much as temperate and polar regions, suggesting that there could be a differential temperature response across latitude of a CO2-driven warming.
