Greenpeace said that a coral reef near the mouth of the Amazon extends further than previously thought and its findings would be published soon by the scientific journal Frontiers in Marine Science.
The research could further complicate plans by oil companies to explore an area that some geologists say could hold up to 14 billion barrels of petroleum, or more than the entire proven reserves in the Gulf of Mexico.
"Now that we know that the Amazon coral overlaps the perimeter of Total's two blocks, the Brazilian government has no choice but to deny the license for the company to explore for oil in the region," Greenpeace said in a statement.
Total led a group including Britain’s BP Plc and Brazilian state-run oil company Petrobras in buying five exploration blocks in the Foz do Amazonas basin in 2013, but the discovery of a massive coral reef just 28 kilometers (17 miles) from the blocks has thrown environmental approval for drilling into doubt. As the operator, Total is responsible for applying for environmental licenses.
Representatives for Total did not immediately reply to requests for comment on the Greenpeace statement.
Brazil’s environmental regulator Ibama has repeatedly refused to accept Total's environmental impact study. Last August Ibama warned that it needed more information or it would suspend the French oil firm's license application.
Environmentalists said potential oil leaks in the Foz do Amazonas basin, named for its location near the mouth of the Amazon river, could wreak havoc in the rainforest in Brazil's far northern Amapá state in addition to harming the reef.