Chemosynthesis and Chemosymbiosis in the Fossil Record: Detecting Unusual Communities Using Isotope Geochemistry

The exploration of chemosynthetic communities in the geologic record over the last ten years has generated a series of sedimentological, tectonic and geochemical criteria that help define a continuum of environments from hot hydrothermal vents to nearshore geothermal deposits. Many of these studies have used stable isotope geochemistry to uncover a depleted carbon signature that characterizes most fossil chemosynthetically derived deposits. Isotope geochemistry (carbon, nitrogen and sulfur) as been an important thread in the story of the discovery of modern chemosynthetic communities, as well, adding to understanding of the biogeochemistry of these ecosystems. With increasing awareness of the prominence of these communities, not just as a biological novelty, but as a fundamental component of life on Earth (and perhaps elsewhere), the drive to develop geochemical proxies for chemosynthetic taxa in the fossil record intensifies. Increased ability to recognize these communities provides access to a second tier of paleobiological questions, including ideas of evolutionary history and selective advantage.