The Fröjel Formation is a ten-metre thick siliciclastic unit lying in the

carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...

sequence of

Gotland Gotland (; ; ''Gutland'' in Gutnish), also historically spelled Gottland or Gothland (), is Sweden's largest island. It is also a Provinces of Sweden, province/Counties of Sweden, county (Swedish län), Municipalities of Sweden, municipality, a ...

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

. Deposited some during the mid Homerian (late Wenlock, mid

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

), the sediments represent an unusually high supply of terrigenous sediment into the shallow

carbonate platform A carbonate platform is a Sedimentary rock, sedimentary body which possesses topographic relief, and is composed of Autochthon (geology), autochthonic calcareous deposits. Platform growth is mediated by Sessility (zoology), sessile organisms whose ...

that was to become the island of Gotland. Their deposition is coincident with a excursion of +3‰.

Stratigraphy

The formation, nine to eleven metres thick in total, contains two subdivisions, the Svarvare Mudstone Member, two to three metres thick, which is overlain by the Gannarve Siltstone Member, seven to eight metres in thickness. (This is also known as the Silte Siltstone, but does not form part of the Slite Group.) The water depth was decreasing as the Gannarve member was deposited, so the member shows evidence of shallowing up. The formation is overlain with an

oolite Oolite or oölite () is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. Strictly, oolites consist of ooids of diameter 0.25–2 millimetres; rocks composed of ooids larger than 2 mm are called pis ...

, which rests

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

on an erosion surface – a sequence boundary – created at a time of low sea level. This erosional surface formed a flat – a rocky shore which was inundated by the sea at times, but was also subject to subaerial rainfall. Calcium carbonate penetrated the underlying sediment (the top of the Gannarve member), altering the existing dolomitic siltstone.

Formation

The Svarvare member was deposited during the end of a sea level highstand; the Gannarve member was subsequently deposited when falling sea levels exposed land, increasing the influx of terrigenous material. Deposition occurred under storm conditions. The sea levels fell as a result of increasing ice buildup in

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

, which then occupied the South pole; this caused increased carbonate weathering, and possibly increased organic burial, leading to the positive excursion.

Exposure

The formation is no longer exposed at the surface; it is only known from drill cores.Detailed geological map differentiating members is available on second page of: :

Palaeontology

Graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian ( Miaolingian, Wuliuan) through t ...

s are abundant in parts of the Svarvare member, which also contains Ramphoprionid

polychaete Polychaeta () is a paraphyletic class of generally marine Annelid, annelid worms, common name, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called c ...

References

{{DEFAULTSORT:Frojel Formation Geologic formations of Sweden Silurian System of Europe Silurian Sweden Formations Geography of Gotland County

Stratigraphy

Formation

Exposure

Palaeontology

See also

References