Fröjel formation

, mid Silurian), the sediments represent an unusually high supply of terrigenous sediment into the shallow carbonate platform that was to become the island of Gotland.cite journal
doi = 10.1007/s10347-005-0050-0
title = Silurian carbonate platforms and extinction events—ecosystem changes exemplified from Gotland, Sweden
year = 2005
author = Calner, Mikael
journal = Facies
volume = 51
pages = 584] Their deposition is coincident with a d13c|link excursion of +3‰.

tratigraphy

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.cite journal
author = Calner, M.
year = 1999
title = Stratigraphy, facies development, and depositional dynamics of the Late Wenlock Fröjel Formation, Gotland, Sweden
journal = GFF
volume = 121
issue = 1
pages = 13–24] (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, which rests unconformably on an erosion surface - a sequence boundarycite journal
author = Calner, M.; Säll, E.
year = 1999
title = Transgressive oolites onlapping a Silurian rocky shoreline unconformity, Gotland, Sweden
journal = GFF
volume = 121
issue = 2
pages = 91–100] - created at a time of low sea level. This erosional surface formed a flat - a rocky shore which was innundated 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.cite journal
author = Calner, Mikael
year = 2002
title = A lowstand epikarstic intertidal flat from the middle Silurian of Gotland, Sweden
journal = Sedimentary Geology
volume = 148
pages = 3–4
doi = 10.1016/S0037-0738(01)00144-0]

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. [cite journal
year = 2005
author = C. Karlsson
title = Provenance studies of the Middle Jurassic strata of the Tornquist Zone in southern Sweden and of storm generated siliciclastic strata of Upper Silurian Burgsvik Formation of southern Gotland, Sweden
journal = Geophysical Research Abstracts
volume = 7]

The sea levels fell as a result of increasing ice buildup in Gondwana, which then occupied the South pole; this caused increased carbonate weathering, and possibly increased organic burial, leading to the positive d13c excursion. [cite journal
doi = 10.1002/gj.1090
title = Early Silurian positive δ13C excursions and their relationship to glaciations, sea-level changes and extinction events
year = 2007
author = Loydell, David K.
journal = Geological Journal
volume = 42
pages = 531 ]

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::cite journal
year = 2002
title = The Silurian Mulde Event and a scenario for secundo–secundo events
journal = Transactions of the Royal Society of Edinburgh: Earth Sciences
volume = 93
pages = 135–154
doi = 10.1017/S0263593302000093]

Palaeontology

Graptolites are abundant in parts of the Svarvare member,cite journal
author = Samtleben, C.; Munnecke, A.; Bickert, T.
year = 2000
title = Development of facies and C/O-isotopes in transects through the Ludlow of Gotland: Evidence for global and local influences on a shallow-marine environment
journal = Facies
volume = 43
issue = 1
pages = 1–38
doi = 10.1007/BF02536983] which also contains Ramphoprionid polychaetes.Citation
author = Eriksson, Mats
year = 2001
title = Silurian Ramphoprionid Polychaetes From Gotland, Sweden
volume = 1
issue = 75
pages = 993–1015
doi = 10.1666/0022-3360(2001)075<0993:SRPFGS>2.0.CO
month = September]

See also

*Geology of Gotland

References