Scientists aboard a Greenpeace ship have discovered that a massive coral reef near the mouth of the Amazon extends further than thought, overlapping areas where French company Total plans to drill for oil.

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 – more than the entire proven reserves in the Gulf of Mexico.

In 2013, 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, but the discovery of a massive coral reef just 28km from the blocks has thrown environmental approval for drilling into doubt.

The Amazon Reef is a unique biome that includes giant sponges and rhodoliths – calcareous algae that form habitat for reef creatures. It is also thought to contain dozens of undiscovered species.

Environmentalists say it would be irreparably damaged if drilling for oil begins.

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