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Tube worms and specialized gastropods are present as well. One of the most
striking aspects of the cold-seep bivalves is their large size. The bivalves
found in the seeps are normally several times larger than any bivalves found
in the surrounding, non-seep deposit sediment.
Since these early discoveries, a variety of cold-seep faunas, mainly of
Mesozoic and Cenozoic vintage, have been identified in the geological
record. Yet research into modern and ancient cold-seep accumulations is still
in its infancy. To date, research efforts have been largely observational; we
have little or no theory from which to predict the geographic placement, bi-
ological makeup, or temporal duration of these deposits.
A large number of cold-seep regions have now been identified. Many
are associated with deep-sea plate tectonic settings, although they also occur
on the margins of continents, at the base of underwater cliffs, and at oil and
gas seeps on the continental slope.
The fauna surrounding vents and seeps is normally characterized by an
unusual taxonomic assemblage. Some researchers have proposed that vent/seep
faunas are long-lived groups composed of many relict taxa of great geological
antiquity. This implies that vent/seep faunas have been largely immune to the
mass extinction events that have so profoundly affected the rest of our planet's
biota. If so, the vent/seep fauna may be the most insulated group of animals on
earth from mass extinction events, being largely self-sufficient except for a need
for oxygen. This fauna might be able to survive even catastrophic meteor im-
pacts and other planetary calamities. Vent and seeps may thus be important fau-
nal reserves or refuges, "lost worlds" retaining archaic forms. An important and
still unresolved question is whether the vent/seep areas are also seed stocks for
evolutionary innovation and planetary repopulation following a mass extinc-
tion event. Are these faunas units of evolutionary innovation, where new types
of life first atise? Are they regions of relict taxa? Are they sites impervious to
mass extinction, and therefore storehouses of diversity?
Fossil cold-seep areas are most commonly recognized from Tertiary de-
posits. Far fewer have been recognized from Mesozoic deposits, and only
small numbet are yet recognized from Paleozoic deposits. Verena Tunnicliffe
