View source for Folkeslunda Limestone

{{Short description|Limestone and mudstone formation}}
{{Infobox rockunit
| name           = Folkeslunda Limestone
| image          =
| caption        =
| type           = [[Formation (stratigraphy)|Formation]]
| age            = [[Darriwilian]]<br>([[Lasnamägi]])<br>{{fossil range|463.5|460.9}}
| period         = Darriwilian
| prilithology   = [[calcarenite|Calcarenitic]] [[limestone]]
| otherlithology = [[Mudstone]]
| namedfor       = [[Folkeslunda]], [[Öland]]
| namedby        = Jaanusson
| year_ts        = 1960
| location_ts    = [[Långlöt]] & [[Runsten]], Öland
| coordinates_ts = {{coord|56|43|38.4|N|16|43|01.9|E|display=inline}}
| thickness_ts   = 
| region         = ''In situ'': [[Dalarna County|Dalarna]], [[Jämtland County|Jämtland]], [[Öland County|Öland]] & [[Östergötland County|Östergötland]]<br>''Ex situ'': [[Mecklenburg-Vorpommern]], [[Lubusz]] & [[Kuyavian-Pomeranian Voivodeship|Kuyavia-Pomerania]]
| country        = {{SWE}}<br>''Ex situ'':<br>{{GER}}<br>{{POL}}
| coordinates    = {{coord|58.0|N|15.0|E|display=inline,title}}
| paleocoordinates = {{coord|36.0|S|8.3|W|display=inline}}
| unitof         = 
| subunits       = 
| underlies      = [[Furudal Limestone]]
| overlies       = [[Seby Limestone]]
| thickness      = {{convert|0.99|-|3.51|m|ft|abbr=on}}
| extent         = Patches from [[Jämtland]] (N) via [[Siljan Ring|Siljan]] (C) to [[Öland]] (SE)
| area           = 
| map            = {{Location map+ | Sweden
| relief = 1
| width   = 250
| float   = center
| places  =
  {{Location map~ | Sweden
  | lat_deg = 58.0
  | lon_deg = 15.0
  | mark = Dark Green 004040 pog.svg
  | marksize = 10
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  {{Location map~ | Sweden
  | lat_deg = 57.0
  | lon_deg = 14.0
  | mark = Dark Green 004040 pog.svg
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  {{Location map~ | Sweden
  | lat_deg = 63.0
  | lon_deg = 14.5
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  {{Location map~ | Sweden
  | lat_deg = 56.7
  | lon_deg = 16.7
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  {{Location map~ | Sweden
  | lat_deg = 60.9
  | lon_deg = 15.0
  | mark = Dark Green 004040 pog.svg
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}}
| map_caption    = 
}}

The '''Folkeslunda Limestone''' is a thin [[limestone]] and [[mudstone]] [[Formation (geology)|geologic formation]] of [[Sweden]]. The formation crops out on the island of [[Öland]] to the east of [[Kalmar]], where Folkeslunda is located. Other exposures of the formation are in [[Dalarna County|Dalarna]], [[Jämtland County|Jämtland]] and [[Östergötland County|Östergötland]]. The Folkeslunda Limestone was deposited in an open marine [[depositional environment|environment]] with an estimated water depth of {{convert|150|to|200|m|ft}} in a eustatically transgressive phase.

The formation preserves [[fossils]] dating back to the late [[Darriwilian]] ([[Lasnamägi]] stage in the regional stratigraphy) of the [[Middle Ordovician]] [[Period (geology)|period]], dating to 463.5 to 460.9 Ma. Several genera of [[nautiloid]]s, [[trilobite]]s, [[brachiopod]]s and [[ostracod]]s were found in the maximum {{convert|3.51|m|ft}} thick formation.

Erratic blocks of the same formation are also found in Germany ([[Mecklenburg-Vorpommern]]) and along the [[Vistula River]] in [[Bydgoszcz]] and in [[Żary]], [[Lower Silesia]], Poland.

== Description ==
Ordovician sedimentary rocks are exposed in patches across the southern half of Sweden. The northernmost exposure is surrounding the [[Siljan Ring]], a [[Devonian]] [[Impact craters in Sweden|impact crater]] in [[Dalarna County|Dalarna]]. Other outcrops are found west and south of [[Örebro]], northeast of [[Livköping]]{{clarify|Lidköping or Linköping?|date=April 2021}}, west and southwest of [[Skövde]] and surrounding [[Falköping]]. Underlying the [[Granby crater]], west of [[Linköping]], the Ordovician has a larger exposure. The southernmost Ordovician outcrops are situated in [[Skåne]], due east of [[Lund]] and at the southeastern tip of Sweden.<ref name=Geomap>Bergman et al., 2012</ref>

Most of the island of [[Öland]] consists of Ordovician sediments, where [[Folkeslunda]] is located, the namesake for the formation.<ref name=Folkeslunda>[https://alltpaoland.se/platser/folkeslunda-gravfalt/ Folkeslunda, Öland]</ref> Previous names for the formation were Upper Grey Orthoceratite Limestone, Chiron Limestone, Centaurus Limestone and Schroeteri Limestone (lower part). The type section is located in the southeastern part of the parish of [[Långlöt]] and the northeastern part of the parish of [[Runsten]] on Öland. The best section of the unit on Öland is in a quarry close to the road from [[Vedby]] to [[Bäcklunda]], east of [[Hornsjön]].<ref name=Ebbestad2007-p17>Ebbestad et al., 2007, p.17</ref>

The formation is the uppermost unit in the traditional Orthoceras Limestone of Sweden, overlying the [[Seby Limestone]] and the Folkesunda Limestone is overlain by the [[Furudal Limestone]].<ref name=Ebbestad2007-p10>Ebbestad et al., 2007, p.10</ref> The Folkeslunda Limestone dates to the [[Lasnamägi]] stage, part of the Purtse, belonging to the Virunian in the regional stratigraphy of Sweden, corresponding to a late [[Darriwilian]] age of the Middle [[Ordovician]].<ref name=Ebbestad2007-p11>Ebbestad et al., 2007, p.11</ref>

The unit is {{convert|2|m|ft}} thick in the Vikarby section and {{convert|2.6|m|ft}} thick in the Kårgärde section of the western Siljan Ring.<ref name=Holmer1989-p11>Holmer, 1989, p.11</ref> In the Lunne section of [[Jämtland]] the unit is between {{convert|0.99|and|3.51|m|ft}} thick.<ref name=Ebbestad2007-p17/><ref name=Karis1982-p70>Karis & Larsson, 1982, p.70</ref>

== Lithologies ==
[[File:Diversity evolution of Ordovician zooplanktonic organisms compared with global eustatic sea-level curve.png|left|thumb|200px|Eustatic sea level of the Ordovician]]
The base of the formation is formed by a {{convert|15|cm|in}} thick grey [[calcarenite|calcarenitic]] [[limestone]] bed, which is overlain by thin-bedded calcarenitic and [[calcilutite|calcilutitic]] limestones. The upper half of the formation consists of thick-bedded calcarenitic limestones. In Kårgärde, the formation comprises medium-bedded, coarse-grained, grey to dark grey [[limestone]]s with [[chamosite|chamositic]] grains in some beds.<ref name=FWKargarde>[https://paleobiodb.org/classic/displayCollResults?collection_no=192380 Kårgärde] at [[Fossilworks]].org</ref> Other parts of the formation contain finely nodular lime [[mudstone]]s and mudstones,<ref name=FWVikarbyn>[https://paleobiodb.org/classic/displayCollResults?collection_no=192378 Vikarbyn] at [[Fossilworks]].org</ref> and thick-bedded, coarse grained, in part [[coquina|coquinoid]] grey to dark grey limestones.

The [[depositional environment]] of the limestone has been interpreted as reef platform [[facies]].<ref name=Ebbestad2007-p44>Ebbestad et al., 2007, p.44</ref> The [[eustatic sea level]] change globally during deposition of the Folkeslunda Limestone was a [[Transgression (geology)|transgression]],<ref name=Chen1991-p7>Chen & Lindström, 1991, p.7</ref> and based on the low implosion rate of fossil shells during fossilization, the water depth at time of deposition of the Folkeslunda Limestone has been estimated at {{convert|150|to|200|m|ft}}.<ref name=Chen1991-p14>Chen & Lindström, 1991, p.14</ref>

== Erratic boulders ==
Erratic boulders belonging to the formation have been found in [[Mecklenburg-Vorpommern]],<ref name=FWMecklenburg>[https://paleobiodb.org/classic/displayCollResults?collection_no=89413 Erratic block Mecklenburg-Vorpommern] at [[Fossilworks]].org</ref> Germany and [[Lubusz]] and [[Kuyavian-Pomeranian Voivodeship|Kuyavia-Pomerania]], Poland.<ref name=FWLubusz>[https://paleobiodb.org/classic/displayCollResults?collection_no=89470 Erratic block Lubusz] at [[Fossilworks]].org</ref><ref name=FWKuyavia>[https://paleobiodb.org/classic/displayCollResults?collection_no=89471 Erratic block Kuyavia-Pomerania] at [[Fossilworks]].org</ref> The German boulder was described by Schlotheim (1820) and Boll (1857). Boll's collection is fortunately preserved at the regional [[Müritz Museum]] of [[Waren (Müritz)|Waren]], Mecklenburg. Dzik (1984) described and illustrated Ordovician nautiloids of the erratic boulders in Poland.<ref name=Kroger2004-p58>Kröger, 2004, p.58</ref>

== Paleontology ==
With respect to both fauna and lithology, the unit in the Siljan District resembles its development on Öland. The fauna shares many common species with the Seby Limestone, but is also distinct with respect to the cephalopods and hyolithids. Faunal differences with respect to the underlying formation were notes in the [[phosphate|phosphatic]] [[brachiopod]] fauna, although the dominant species is the same as in the Seby Limestone. Trilobites from the Folkeslunda Limestone were described by Holm (1883) and Törnquist (1884), while Janusson (1957) described ostracods. Species of nautiloid cephalopods were reported by Holm in 1896, Troedsson (1931, 1932), and Kröger (2004). Biostratigraphically, the Folkeslunda Limestone spans the ''[[Pygodus serra]]'' [[conodont]] zone and the ''[[Eoplacoghnathus reclinatus]]'' subzone.<ref name=Ebbestad2007-p17/>

=== Correlations ===
The ''[[Eoplacoghnathus reclinatus]]'' subzone extends from the lowermost part of the Folkeslunda Limestone into the lower part of the Furudal Limestone. The subzone index
species is not common outside [[Baltoscandia]] but has been recorded from a few localities in eastern North America (Bergström 1973), Argentina (Albanesi & Ortega 2002), and China (Zhang 1998).<ref name=Ebbestad2007-p32>Ebbestad et al., 2007, p.32</ref>

=== Fossil content ===
[[File:Orthoceras_BW.jpg|right|thumb|250px|Interpretation of ''Orthoceras'']]
[[File:Middle Ordovician South Polar paleogeography - 460 Ma.png|right|thumb|250px|Paleogeography of the late Middle Ordovician. The Folkeslunda Limestone was deposited around 30°S]]
The following fossils have been found in the rocks belonging to the formation:

{| class="wikitable sortable"
! Group !! Genus !! Species !! Location !! Status !! Notes
|-
| rowspan=22 | [[Cephalopod]]s || ''[[Archigeisonoceras]]'' || ''A. folkeslundense'' || [[Öland]] || In situ || align=center | <ref name=Kroger2004-p68>Kröger, 2004, p.68</ref>
|-
| rowspan=2 | ''[[Arionoceras]]'' || rowspan=2 | ''A. lotskirkense'' || [[Löts Kyrka]], [[Öland]] || In situ || align=center | <ref name=Kroger2004-p72>Kröger, 2004, p.72</ref>
|-
| [[Mecklenburg-Vorpommern]] || Erratic block || align=center | <ref name=Kroger2004-p73>Kröger, 2004, p.73</ref>
|-
| ''[[Bactroceras]]'' || ''B. angustisiphonatum'' || [[Mecklenburg-Vorpommern]] || Erratic block || align=center | <ref name=FWMecklenburg/>
|-
| ''[[Cyrtendoceras]]'' || ''C. hircus'' || [[Öland]] || In situ || align=center | <ref name=King1993-p172>King, 1993, p.172</ref>
|-
| ''[[Nilssonoceras]]'' || ''N. latisiphonatum'' || [[Öland]] || In situ || align=center | <ref name=Kroger2004-p70>Kröger, 2004, p.70</ref>
|-
| rowspan=3 | ''[[Orthoceras]]'' || ''O. bifoveatum'' || [[Öland]] || In situ || align=center | <ref name=Kroger2004-p61>Kröger, 2004, p.61</ref>
|-
| ''O. regulare'' || [[Öland]] || In situ || align=center | <ref name=Kroger2004-p60>Kröger, 2004, p.60</ref>
|-
| ''O. scabridum'' || [[Södra Bäck]], [[Öland]] || In situ || align=center | <ref name=Mutvei2002-p158>Mutvei, 2002, p.158</ref><ref name=Kroger2004-p62>Kröger, 2004, p.62</ref><ref name=FWSodra>[https://paleobiodb.org/classic/displayCollResults?collection_no=87727 Södra Bäck] at [[Fossilworks]].org</ref>
|-
| ''[[Oonoceras]]'' || ''O. priscum'' || [[Vistula River]], [[Bydgoszcz]] || Erratic block || align=center | <ref name=FWKuyavia/>
|-
| rowspan=3 | ''[[Phthanoncoceras]]'' || rowspan=3 | ''P. ellipticum'' || Lerkaka, [[Kalmar County|Kalmar]] || In situ || align=center | <ref name=FWLerkaka>[https://paleobiodb.org/classic/displayCollResults?collection_no=89255 Lerkaka, Kalmar] at [[Fossilworks]].org</ref> 
|-
| [[Vistula River]], [[Bydgoszcz]] || rowspan=2 | Erratic block || align=center | <ref name=FWKuyavia/>
|-
| [[Żary]], [[Lower Silesia]] || align=center | <ref name=FWLubusz/>
|-
| ''[[Plagiostomoceras]]'' || ''P. fragile'' || Böda, Stora Mossen, [[Öland]] || In situ || align=center | <ref name=Kroger2004-p64>Kröger, 2004, p.64</ref>
|-
| ''[[Polygrammoceras]]'' || ''P. oelandicum'' || [[Folkeslunda]], [[Öland]] || rowspan=2 | In situ || align=center | <ref name=Mutvei2002-p160>Mutvei, 2002, p.160</ref><ref name=FWFolkeslunda>[https://paleobiodb.org/classic/displayCollResults?collection_no=87730 Folkeslunda] at [[Fossilworks]].org</ref>
|-
| ''[[Richardsonoceras]]'' || ''R. gerhardi'' || Lerkaka, [[Kalmar County|Kalmar]] || align=center | <ref name=FWLerkaka/>
|-
| ''[[Troedssonella]]'' || ''T. endoceroides'' || [[Öland]] || In situ || align=center | <ref name=King1993-p174>King, 1993, p.174</ref>
|-
| ''[[Clinoceras]]'' || sp. || [[Vistula River]], [[Bydgoszcz]] || Erratic block || align=center | <ref name=FWKuyavia/>
|-
| rowspan=3 | ''[[Cochlioceras]]'' || rowspan=3 | sp. || [[Sjöstorp]], [[Öland]] || In situ || align=center | <ref name=Mutvei2002-p161>Mutvei, 2002, p.161</ref><ref name=FWSjostorp>[https://paleobiodb.org/classic/displayCollResults?collection_no=87732 Sjöstorp, Öland] at [[Fossilworks]].org</ref>
|-
| [[Vistula River]], [[Bydgoszcz]] || rowspan=2 | Erratic block || align=center | <ref name=FWKuyavia/>
|-
| [[Żary]], [[Lower Silesia]] || align=center | <ref name=FWLubusz/>
|-
| ''[[Lituites]]'' || sp. || Kårgärde, [[Dalarna County|Dalarna]] || In situ || align=center | <ref name=FWKargarde4.1/>
|-
| rowspan=11 | [[Trilobite]]s || ''[[Illaenus]]'' || ''I. chiron'' || rowspan=6 | Kårgärde, [[Dalarna County|Dalarna]] || rowspan=6 | In situ || align=center rowspan=3 | <ref name=FWKargarde6.5/>
|-
| ''[[Pseudoasaphus]]'' || ''P. aciculatus''
|-
| ''[[Pseudobasilicus]]'' || ''P. ?brachyrachis''
|-
| ''[[Plectasaphus]]'' || ''P. plicicostis'' || align=center | <ref name=FWKargarde4.1/>
|-
| ''[[Pseudomegalaspis]]'' || ''P. patagiata'' || rowspan=2 align=center | <ref name=FWKargarde5.5>[https://paleobiodb.org/classic/displayCollResults?collection_no=192379 Kårgärde 5.5-6.34, Dalarna] at [[Fossilworks]].org</ref>
|-
| ''[[Ampyx (trilobite)|Ampyx (Cnemidopyge)]]'' || sp. 
|-
| ''[[Asaphus]]'' || sp. || [[Żary]], [[Lower Silesia]] || Erratic block || align=center | <ref name=FWLubusz/>
|-
| ''?[[Lonchodomas]]'' || sp. || [[Żary]], [[Lower Silesia]] || Erratic block || align=center | <ref name=FWLubusz/>
|-
| ''[[Nileus]]'' || sp. || Kårgärde, [[Dalarna County|Dalarna]] || In situ || align=center | <ref name=FWKargarde5.5/>
|-
| rowspan=2 | ''[[Remopleurides]]'' || rowspan=2 | sp. || [[Östergötland County|Östergötland]] || rowspan=2 | In situ || align=center | <ref name=FWOstergotland/>
|-
| Kårgärde, [[Dalarna County|Dalarna]] || align=center | <ref name=FWKargarde4.1/>
|-
| rowspan=4 | [[Gastropod]]s || rowspan=2 | ''[[Eccyliopterus]]'' || ''E. alatus'' || rowspan=4 | Lerkaka, [[Kalmar County|Kalmar]] || rowspan=4 | In situ || align=center rowspan=4 | <ref name=FWLerkaka/>
|-
| ''E. declivis''
|-
| ''[[Pararaphistoma]]'' || ''P. vaginati''
|-
| ''[[Sinuites]]'' || ''S. vetustus''
|-
| rowspan=6 | [[Ostracod]]s || rowspan=2 | ''[[Euprimites]]'' || ''E. bursa'' || rowspan=3 | Kårgärde, [[Dalarna County|Dalarna]] || rowspan=6 | In situ || align=center rowspan=3 | <ref name=FWKargarde5.5/>
|-
| ''E. effusus''
|-
| ''[[Steusloffia]]'' || ''S. linnarssoni''
|-
| rowspan=2 | ''[[Laccochilina]]'' || rowspan=3 | sp. || [[Östergötland County|Östergötland]] || align=center | <ref name=FWOstergotland>[https://paleobiodb.org/classic/displayCollResults?collection_no=2937 Östergötland] at [[Fossilworks]].org</ref>
|-
| Kårgärde, [[Dalarna County|Dalarna]] || align=center | <ref name=FWKargarde5.5/>
|-
| ''[[Sigmobolbina]]'' || [[Östergötland County|Östergötland]] || align=center | <ref name=FWOstergotland/>
|-
| rowspan=16 | [[Lingulata]] || ''[[Biernatia]]'' || ''B. holmi'' || rowspan=16 | Kårgärde, [[Dalarna County|Dalarna]] || rowspan=16 | In situ || align=center rowspan=16 | <ref name=FWKargarde4.1/><ref name=FWKargarde6.5>[https://paleobiodb.org/classic/displayCollResults?collection_no=192033 Kårgärde 6.34-6.5, Dalarna] at [[Fossilworks]].org</ref><ref name=FWKargarde5.5/>
|-
| rowspan=2 | ''[[Conotreta]]'' || ''C. mica''
|-
| ''C. siljanensis''
|-
| rowspan=2 | ''[[Eoconulus]]'' || ''E. cf. clivosus''
|-
| ''E. robustus''
|-
| ''[[Hisingerella]]'' || ''H. unguicula''
|-
| ''[[Myotreta]]'' || ''M. dalecarlica''
|-
| ''[[Rowellella]]'' || ''R. cf. lamellosa''
|-
| ''[[Scaphelasma]]'' || ''S. mica''
|-
| ''[[Spinilingula]]'' || ''S. radiolamellosa''
|-
| ''[[Talasotreta]]'' || ''T. deformis''
|-
| ''[[Cyrtonotreta]]'' || sp.
|-
| ''[[Paterula]]'' || sp.
|-
| ''[[Spondylotreta]]'' || sp.
|-
| [[Lingulellinae]] || indet.
|-
| [[Orbiculoideinae]] || indet.
|-
| [[Rhynchonellata]] || ''[[Nicolella]]'' || sp. || [[Östergötland County|Östergötland]] || In situ || align=center | <ref name=FWOstergotland/>
|-
| [[Strophomenata]] || ''[[Christiania (brachiopod)|Christiania]]'' || sp. || Kårgärde, [[Dalarna County|Dalarna]] || In situ || align=center | <ref name=FWKargarde4.1>[https://paleobiodb.org/classic/displayCollResults?collection_no=192380 Kårgärde 4.1-5.5, Dalarna] at [[Fossilworks]].org</ref>
|-
|}

== See also ==
{{div col|colwidth=25em}}
* [[List of fossiliferous stratigraphic units in Sweden]]
* [[Alum Shale Formation]], Scandinavia
* [[Letná Formation]], Czech Republic
* [[Fezouata Formation]], Morocco
* [[San Juan Formation, Argentina|San Juan Formation]], Argentina
* [[Sella Formation]], Bolivia
{{div col end}}

== References ==
{{reflist|2}}

=== Bibliography ===
<!--Most recent first-->
* {{citation |last1=Bergman |first1=S. |last2=Stephens |first2=M.B. |last3=Andersson |first3=J. |last4=Kathol |first4=B. |last5=Bergman |first5=T. |year=2012 |title=Bedrock map of Sweden, scale 1:1 million |publisher=Sveriges geologiska undersökning |pages=K.423}}
* {{citation |last1=Ebbestad |first1=Jan Ove |last2=Wickström |first2=Linda |last3=Högström |first3=Anette |year=2007 |title=9th meeting of the Working Group on Ordovician Geology of Baltoscandia IGCP503 Ordovician Palaeogeography and Palaeoclimate Regional Meeting |publisher=Sveriges geologiska undersökning |pages=1–112 |issn=0349-2176 |isbn=978-91-7158-788-6}}
* {{citation |last=Kröger |first=Björn |year=2004 |title=Revision of Middle Ordovician orthoceratacean nautiloids from Baltoscandia |url=https://www.app.pan.pl/archive/published/app49/app49-057.pdf |journal=[[Acta Palaeontologica Polonica]] |volume=49 |pages=57–74 |accessdate=2020-05-30}}
* {{citation |last=Mutvei |first=Harry |year=2002 |title=Connecting ring structure and its significance for classification of the orthoceratid cephalopods |url=http://webaccess.app.pan.pl/archive/published/app47/app47-157.pdf |journal=[[Acta Palaeontologica Polonica]] |volume=47 |pages=157–168 |accessdate=2020-05-30}}
* {{citation |last=King |first=A.H |year=1993 |title=The Fossil Record - Mollusca: Cephalopoda (Nautiloidea) |publisher=Chapman & Hall, London |pages=169–188 |isbn=0-412-39380-8}}
* {{citation |last1=Chen |first1=Jun-yuan |last2=Lindström |first2=Maurits |year=1991 |title=Cephalopod Septal Strength lndices (SSI) and depositional depth of Swedish Orthoceratite limestone |journal=[[Geologica et Palaeomologica]] |volume=25 |pages=5–18}}
* {{citation |last=Holmer |first=Lars E |year=1989 |title=Middle Ordovician phosphatic inarticulate brachiopods from Våstergotland and Dalarna, Sweden |journal=[[Fossils and Strata]] |volume=26 |pages=1–172 |doi=10.18261/8200374254-1989-01 |isbn=82-00-37425-4}}
* {{citation |last1=Karis |first1=Lars |last2=Larsson |first2=Kent |year=1982 |title=Jämtland Road Log |publisher=N.N. |pages=64–76}}

== Further reading ==
<!--Most recent first-->
* B. Kröger, Y. Zhang, and M. Isakar. 2009. Discosorids and Oncocerids (Cephalopoda) of the Middle Ordovician Kunda and Aseri Regional Stages of Baltoscandia and the early evolution of these groups. Geobios 42:273-293
* D. H. Evans. 2005. The Lower and Middle Ordovician cephalopod faunas of England and Wales. Monograph of the Palaeontographical Society 623:1-81
* J. Dzik and G. N. Kiselev. 1995. The Baltic nautiloids ''Cyrtoceras ellipticum'' Lossen 1860, ''C. priscum'' Eichwald 1861, and ''Orthoceras damesi'' Krause 1877. Paläontologische Zeitschrift 69(1/2):61-71
* V. Jaanusson. 1963. Lower and Middle Viruan (Middle Ordovician) of the Siljan district. Bulletin of Geological Institutions of the University of Uppsala 42(3):1-40
* V. Jaanusson. 1962. The Lower and Middle Viruan sequence in two borings in Östergotland, central Sweden. Bulletin of Geological Institutions of the University of Uppsala 38(9):1-30
* V. Jaanusson. 1960. The Viruan (Middle Ordovician) of Öland. Bulletin of the Geological Institutions of the University of Uppsala 38:207-287

[[Category:Geologic formations of Sweden]]
[[Category:Ordovician System of Europe]]
[[Category:Ordovician Sweden]]
[[Category:Ordovician southern paleotemperate deposits]]
[[Category:Darriwilian]]
[[Category:Limestone formations]]
[[Category:Mudstone formations]]
[[Category:Open marine deposits]]
[[Category:Paleontology in Sweden]]
[[Category:Paleontology in Germany]]
[[Category:Paleontology in Poland]]