Organic matter with various origins is commonly associated with hydrothermal activity. Examples from the terrestrial record include hydrothermally produced petroleum (Simoneit 1988), the possible formation of abiotic organic molecules (Holm 1992), and present-day biological activity around hydrothermal vents and hot springs (Corliss et al. 1979; Reysenbach and Cady 2001). If the conditions for preservation of the organic matter are favourable, hydrothermal deposits could be suitable sites for the detection of extraterrestrial organic matter, for example on Mars (e.g. Simoneit et al. 1998).
The study of hydrothermal deposits in the terrestrial record allows us to gain more knowledge of the distribution of organic matter in various fossil hydrothermal settings. We have investigated fossil hydrothermal deposits on the Isle of Skye in Scotland, where the heat from igneous intrusions (Paleogene dolerite sills) in wet carbon-rich shale (Jurassic) has caused localized hydrothermal activity with the mobilization of organic-rich fluids. Here, the organic matter is accumulated in hydrothermal deposits: It occurs as vesicular hydrocarbon, located in hydrothermal veins together with calcite, chlorite and quartz, and as a cm-dm thick sheet sandwiched between the shale and the intrusive body. Organic matter also occurs in hydrothermally precipitated calcite veins that cross-cuts the igneous intrusion, and in vesicles of the igneous rock.
This is one example from the terrestrial record showing that where organic matter is available, it can be mobilised and concentrated as a result of hydrothermal activity. The same process of carbon concentration could have taken place in ancient martian hydrothermal systems, induced by igneous activity or bolide impacts.
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