Alum Shale Formation

This article is about the Cambro-Ordovician rock unit found predominantly in southern Scandinavia. For the Jurassic shale found in England, see Whitby Mudstone Formation.
Alum Shale Formation
Stratigraphic range: Cambrian-Ordovician
TypeGeological formation
Thicknessup to 160 m
Lithology
PrimaryBlack shale
OtherShale, oil shale
Location
CountrySweden, Denmark, Norway

The Alum Shale Formation (also known as alum schist and alum slate) is a formation of black shale of Miaolingian (Middle Cambrian) to Tremadocian (Lower Ordovician) in age found predominantly in southern Scandinavia.[1][2] It is shale or clay slate containing pyrite. Decomposition of pyrite by weathering forms sulfuric acid, which acts on potash and alumina constituents to form alum, which often occurs as efflorescences on the rock outcrop.

As the formation contains kerogen originated from algae, it is also classified as marinite-type oil shale. At the same time it is rich in aromatic hydrocarbon attributed to post-depositional irradiation damage to saturated hydrocarbons, induced by uranium concentration in the shale.[3] Alum shale also contains enhanced levels of radium as a result of uranium decay.[4] Between 1950 and 1989, Sweden used alum shale for the uranium production.[5]

8502 specimens of trilobite-agnostoid fauna were found in the Furongian strata of this formation in Bornholm, Denmark. Most of them are disarticulated sclerites. Described gerena include Ctenopyge, Eurycare, Leptoplastus, Olenus, Parabolina, Peltura, Protopeltura, Sphaerophthalmus, Lotagnostus and Triangulopyge.[6]

  1. ^ Nielsen A.T. & Schovsbo N.H. (2007). "Cambrian to basal Ordovician lithostratigraphy in southern Scandinavia" (PDF). Bulletin of the Geological Society of Denmark. 53: 82–84.
  2. ^ Zhengfu Zhao, Nicolas R. Thibault, Tais W. Dahl, Niels H. Schovsbo, Aske L. Sørensen, Christian M. Ø. Rasmussen, Arne T. Nielsen (13 April 2022). "Synchronizing rock clocks in the late Cambrian". Nature. 13 (1990): 1990. Bibcode:2022NatCo..13.1990Z. doi:10.1038/s41467-022-29651-4. PMC 9007955. PMID 35418121.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ Peters, Kenneth E.; Walters, Clifford C.; Moldowan, J. Michael (2005). The biomarker guide. Cambridge University Press. p. 777. ISBN 978-0-521-83762-0. Retrieved 2009-05-30.
  4. ^ Stranden, E.; Strand, T. (1988). "Radon in an Alum Shale Rich Norwegian Area". Radiation Protection Dosimetry. 24 (1–4). Oxford University Press: 367–370. doi:10.1093/oxfordjournals.rpd.a080304.
  5. ^ Dyni, John R. (2006). "Geology and resources of some world oil shale deposits. Scientific Investigations Report 2005–5294" (PDF). United States Department of the Interior, United States Geological Survey. Retrieved 2009-05-30.
  6. ^ Arne Thorshøj Nielsen, Line Frigaard Andersen (2021). "Furongian (upper Cambrian) trilobites and agnostoids from the Alum Shale Formation of Bornholm, Denmark: revised taxonomy and biostratigraphy" (PDF). Bulletin of the Geological Society of Denmark. 69: 123–213. doi:10.37570/bgsd-2021-69-08. ISSN 2245-7070. Archived (PDF) from the original on 2023-10-26.