What is an authigenic carbonate?
Calcium carbonate (CaC03) composes a skeleton of inorganically precipated marine organisms accumulated on the ocean floor. Around 30 years ago, another type of carbonate was discovered. This so-called « authigenic » carbonate is formed in situ and sometimes covers large areas in the form of crusts or chimneys.
Where are they found?
Authogenic carbonate occurs where gas-rich fluids are emitted into the ocean. The presence of oil reservoirs or large amounts of organic matter buried in marine sediment are often the source of these gases (mainly methane). Communities of microbes in the sediment feed on these fluids near the seabed. It is this intense microbial activity that causes the formation of authogenic carbonates, as well as the development of a whole specific ecosystem composed among others of mussels, clams and tuber worms adapted to these extreme conditions.
Why is it important to study them?
Authogenic carbonates may represent the only vestige of old gaseous fumes on the seabed. The study of their chemical composition is therefore the only way to reconstruct their history. Recent studies have also suggested that the precipitation of these carbonates through geological times may have played an important role in the carbon dioxide cycle, and therefore, to some extent, in the evolution of the climate on Earth.