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founded in 1995 in Vancouver (British Columbia, Canada). Hosted at the University of Lyon 1 (France).
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New radiolarian data from CHENAILLET-MONTGENEVRE ophiolite (French-Italian Alps) : click here
Radiolarians and siliceous rocks
Radiolarians are unicellular planktonic marine organisms, absorbing silica from the marine environment and constructing tiny skeletons
(diameter 0.2 mm, see picture) according to well-defined geometric patterns. Radiolarian
fossils are known from the early Phanerozoic to the present (550 million years)
and, with an immense diversity of taxa which evolved rapidly, they have a significant
biochronological interest. Unlike calcareous skeletons, they do not undergo
total dissolution with water depth and can accumulate differentially on deep
seafloors. They are in fact considered as the "background" pelagic sediment
during the Paleozoic and Mesozoic eras.
As a result of their deposition,
radiolarians have generated accumulations of biogenetic oozes that have evolved
through diagenesis into sedimentary rocks called radiolarian cherts or radiolarites (picture).
These rocks are widely distributed in mountain ranges exposing
geological units of oceanic affinities, therefore radiolarian
micropaleontology has become a significant tool in geological surveys and studies. Plate tectonics
movements such as subduction/accretion processes have thrust layers of oceanic
crust capped by radiolarian-rich sediments into mountain ranges. In some orogens composed of a patchwork
of various lithospheric fragments such as the North-American Cordillera, radiolarian cherts directly reveal the existence and the age range of ancient ocean
basins (ridge to trench model, see figure). In doing so, they provide a mean to predate the timing of closure and
deformation of these basins, a key to the understanding of their geodynamic history.
Radiolarians being also present in lithologies such as siliceous shales, mudstones, argillites and pelagic carbonates, they provide a regional stratigraphic and
structural tool used in Cordilleran geological mapping, mining exploration,
as well as academic research related to the study of ancient oceanic environments.
Radiolarians are unicellular planktonic marine organisms, absorbing silica from the marine environment and constructing tiny skeletons
(diameter 0.2 mm, see picture) according to well-defined geometric patterns. Radiolarian
fossils are known from the early Phanerozoic to the present (550 million years)
and, with an immense diversity of taxa which evolved rapidly, they have a significant
biochronological interest. Unlike calcareous skeletons, they do not undergo
total dissolution with water depth and can accumulate differentially on deep
seafloors. They are in fact considered as the "background" pelagic sediment
during the Paleozoic and Mesozoic eras.