Paleozoic , near
Nossen (
Nossen-Wilsdruff Slate Mountains) The oldest known radiolarites come from the
Upper Cambrian of
Kazakhstan. Radiolarian ooze was sedimented here over a time span of 15 million years into the
Lower Ordovician. The deep water sediments were deposited near the paleoequator and are associated with remnants of
oceanic crust. The dating has been done with
conodonts. In more lime-rich sections four radiolarian faunal associations were identified. The oldest, rather impoverished
fauna dates back well into the second stage of the Ordovician (Arenigian). The youngest fauna consists already of 15 different taxa and belongs to the fifth stage (Lower Caradocian). During the Middle Ordovician (Upper
Darriwilian) radiolarites were formed near
Ballantrae in
Scotland. Here radiolarian cherts overlie
spilites and volcanic rocks. Radiolarites are also found in the nearby
Southern Uplands where they are associated with
pillow lava. The Scottish radiolarites are followed by deposits in
Newfoundland from the Middle and Upper Ordovician. The red
Strong Island Chert for instance rests on
ophiolites. At the
Silurian/
Devonian boundary black cherts (locally called
lydites or
flinty slates) developed from radiolarians mainly in the
Franconian Forest region and in the
Vogtland in
Germany. Of great importance are the
novaculites from
Arkansas,
Oklahoma and
Texas which were deposited at the close of the Devonian. The novaculites are milky-white, thinly-bedded cherts of great hardness; they underwent a low-grade metamorphism during the
Ouachita orogeny. Their mineralogy consists of
microquartz with a grain-size of 5 to 35 μm. The microquartz is derived from the sclerae of
sponges and the tests of radiolarians. During the
Mississippian black
lydites were sedimented in the
Rhenish Massif in Germany. The
Lower Permian of
Sicily hosts radiolarites in limestone
olistoliths, at the same period radiolarites have been reported from northwestern
Turkey (
Karakaya complex of the
Pontides). Radiolarites from the
Phyllite Zone of
Crete date back to the
Middle Permian. The radiolarites from the
Hawasina nappes in
Oman closed the end of the Permian. Towards the end of the
Paleozoic radiolarites formed also along the southern margin of
Laurasia near
Mashad in
Iran.
Mesozoic During the
Triassic (
Upper Norian and
Rhaetian) cherty, platy limestones are deposited in the
Tethyan region, an example being the
Hornsteinplattenkalk of the
Frauenkogel Formation in the southern
Karawanks of
Austria. They are composed of interlayered cherts and
micrites separated by irregular, non-planar bedding surfaces. The cherty horizons have originated from radiolarian-rich limestone layers which subsequently underwent silicification. Similar sediments in Greece incorporate layers with calcareous
turbidites. On local
horsts and farther upslope these sediments undergo a
facies change to red, radiolarian-rich, ammonite-bearing limestones. In central Japan clay-rich radiolarites were laid down as bedded cherts in the Upper Triassic. Their depositional environment was a shallow marginal sea with rather high accumulation rates of 30 meters/million years. Besides radiolarians sponge spicules are very prominent in these sediments. From the
Upper Bajocian (
Middle Jurassic) onwards radiolarites accumulated in the
Alps. The onset of the sedimentation was
diachronous but the end in the
Lower Tithonian rather abrupt. These alpine radiolarites belong to the
Ruhpolding Radiolarite Group (
RRG) and are found in the
Northern Calcareous Alps and in the
Penninic of
France and
Switzerland (
Graubünden). Associated are the radiolarites of
Corsica. The radiolarites of the
Ligurian
Apennines appear somewhat later towards the end of the Jurassic. From the Middle Jurassic onwards radiolarites also formed in the
Pacific domain along the West Coast of
North America, an example being the
Franciscan complex. The radiolarites of the
Great Valley Sequence are younger and have an Upper Jurassic age. The radiolarites of
California are paralleled by radiolarite sedimentation in the equatorial Western Pacific east of the
Mariana Trench. The accumulation of radiolarian ooze on Jurassic oceanic crust was continuous here from the
Callovian onward and lasted till the end of the
Valanginian. , near
Gascoyne Junction, Western Australia in the permanent collection of
The Children's Museum of Indianapolis. The
Windalia radiolarite is a
Lower Cretaceous (
Aptian)
formation in
Western Australia. The formation contains abundant
foraminifera,
radiolaria and
calcareous nanoplankton fossils Locally the varicolored
opaline to
chalcedonic radiolarite is mined and used as an ornamental stone termed
mookaite. At the same time radiolarites were deposited at the
Marin Headlands near
San Francisco. Radiolarites from the Upper Cretaceous can be found in the
Zagros Mountains and in the
Troodos Mountains on
Cyprus (
Campanian). The radiolarites of
Northwestern Syria are very similar to the occurrences on Cyprus and probably have the same age. Red radiolarian clays associated with
manganese nodules are reported from
Borneo,
Roti,
Seram and
Western Timor.
Cenozoic A good example for
Cenozoic radiolarites are radiolarian clays from
Barbados found within the
Oceanic Group. The group was deposited in the time range
Early Eocene till
Middle Miocene on oceanic crust which is subducting now under the
island arc of the
Lesser Antilles. Younger radiolarites are not known – probably because younger radiolarian oozes did not have sufficient time to consolidate. == Use ==