Hydrothermal vent fauna and fossilisation
Hydrothermal vents and their associated fauna were first discovered in 1977. An
unusual, diverse fauna thrives around these vents. The dynamic and unpredictable
nature of volcanism, fluid chemistry and temperature around vents mean these faunal
habitats remain for a maximum of -20 years.
This study examines fossilisation of vent fauna from five localities of varying tectonic
setting and age: the Mothra Vent Field, Endeavour Segment, Juan de Fuca Ridge;
'Feather Duster' vent site, 11oN East Pacific Rise; 'MESO' zone, Central Indian Ridge;
Roman Ruins vent site, PACMANUS, eastern Manus Basin; and the Kambia massive
sulphide deposit, Troodos ophiolite, Cyprus.
No shelly fauna (i.e. gastropods or bivalves) were found. The majority of the fossils
found were vestimentiferan tubeworm tubes. Diagnostic features for these include at
least one of the following: surface striations/longitudinal ridges; internal septa and
lateral flange structures. Extensive SEM and mineral mapping have highlighted specific
mineral patterns on fossil worm tube surfaces for both early and late stage fossilised
material. An order of mineralisation is presented for early-mineralised material.
Several new and unique fmds are reported here. A specimen of a predatory (?)
ammonite preserved in pyrite from a late Cretaceous vent deposit provides evidence of
an additional trophic group to fossil vent communities and introduces a new,
challenging palaeoenvironment for ammonites. Delicate internal septa from the interiors
of fossil tubeworm tubes (preserved in silica), suggest the tubeworm Ridgeia piscesae
secretes basal clumps to support its body within the tube. Previously unreported
fossilised soft body parts infer either bacterial inducement of mineralisation of worm
body surfaces, or protection of those surfaces by bacteria.
Stable isotopes of carbon, nitrogen and sulphur were used as an additional tool for the
study of both animal tissues, fossilised worm tubes and sulphide samples. Results for
Ol3C and olsN of animal tissues agreed with previous work. Ol3C and Ol~ for fossilised
material suggest a bacterially fractionated worm signature. 034S values for sulphides
suggest a volcanic source for sulphur, with little evidence for bacterial fractionation.