Folkeslunda Limestone

The Folkeslunda Limestone is a thin limestone and mudstone 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, Jämtland and Östergötland. The Folkeslunda Limestone was deposited in an open marine environment with an estimated water depth of 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, dating to 463.5 to 460.9 Ma. Several genera of nautiloids, trilobites, brachiopods and ostracods were found in the maximum 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 crater in Dalarna. Other outcrops are found west and south of Örebro, northeast of Livköping, 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.Bergman et al., 2012

Most of the island of Öland consists of Ordovician sediments, where Folkeslunda is located, the namesake for the formation.Folkeslunda, Öland 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.Ebbestad et al., 2007, p.17

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.Ebbestad et al., 2007, p.10 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.Ebbestad et al., 2007, p.11

The unit is thick in the Vikarby section and thick in the Kårgärde section of the western Siljan Ring.Holmer, 1989, p.11 In the Lunne section of Jämtland the unit is between thick.Karis & Larsson, 1982, p.70

Lithologies

The base of the formation is formed by a thick grey calcarenitic limestone bed, which is overlain by thin-bedded calcarenitic and 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 limestones with chamositic grains in some beds.Kårgärde at Fossilworks.org Other parts of the formation contain finely nodular lime mudstones and mudstones,Vikarbyn at Fossilworks.org and thick-bedded, coarse grained, in part coquinoid grey to dark grey limestones.

The depositional environment of the limestone has been interpreted as reef platform facies.Ebbestad et al., 2007, p.44 The eustatic sea level change globally during deposition of the Folkeslunda Limestone was a transgression,Chen & Lindström, 1991, p.7 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 .Chen & Lindström, 1991, p.14

Erratic boulders Erratic boulders belonging to the formation have been found in Mecklenburg-Vorpommern,Erratic block Mecklenburg-Vorpommern at Fossilworks.org Germany and Lubusz and Kuyavia-Pomerania, Poland.Erratic block Lubusz at Fossilworks.orgErratic block Kuyavia-Pomerania at Fossilworks.org The German boulder was described by Schlotheim (1820) and Boll (1857). Boll's collection is fortunately preserved at the regional Müritz Museum of Waren, Mecklenburg. Dzik (1984) described and illustrated Ordovician nautiloids of the erratic boulders in Poland.Kröger, 2004, p.58

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 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.

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).Ebbestad et al., 2007, p.32

Fossil content

The following fossils have been found in the rocks belonging to the formation:

Group Genus Species Location Status Notes Cephalopods Archigeisonoceras A. folkeslundense Öland In situ Kröger, 2004, p.68 Arionoceras A. lotskirkense Löts Kyrka, Öland In situ Kröger, 2004, p.72 Mecklenburg-Vorpommern Erratic block Kröger, 2004, p.73 Bactroceras B. angustisiphonatum Mecklenburg-Vorpommern Erratic block Cyrtendoceras C. hircus Öland In situ King, 1993, p.172 Nilssonoceras N. latisiphonatum Öland In situ Kröger, 2004, p.70 Orthoceras O. bifoveatum Öland In situ Kröger, 2004, p.61 O. regulare Öland In situ Kröger, 2004, p.60 O. scabridum Södra Bäck, Öland In situ Mutvei, 2002, p.158Kröger, 2004, p.62Södra Bäck at Fossilworks.org Oonoceras O. priscum Vistula River, Bydgoszcz Erratic block Phthanoncoceras P. ellipticum Lerkaka, Kalmar In situ Lerkaka, Kalmar at Fossilworks.org Vistula River, Bydgoszcz Erratic block Żary, Lower Silesia Plagiostomoceras P. fragile Böda, Stora Mossen, Öland In situ Kröger, 2004, p.64 Polygrammoceras P. oelandicum Folkeslunda, Öland In situ Mutvei, 2002, p.160Folkeslunda at Fossilworks.org Richardsonoceras R. gerhardi Lerkaka, Kalmar Troedssonella T. endoceroides Öland In situ King, 1993, p.174 Clinoceras sp. Vistula River, Bydgoszcz Erratic block Cochlioceras sp. Sjöstorp, Öland In situ Mutvei, 2002, p.161Sjöstorp, Öland at Fossilworks.org Vistula River, Bydgoszcz Erratic block Żary, Lower Silesia Lituites sp. Kårgärde, Dalarna In situ Trilobites Illaenus I. chiron Kårgärde, Dalarna In situ Pseudoasaphus P. aciculatus Pseudobasilicus P. ?brachyrachis Plectasaphus P. plicicostis Pseudomegalaspis P. patagiata Kårgärde 5.5-6.34, Dalarna at Fossilworks.org Ampyx (Cnemidopyge) sp. Asaphus sp. Żary, Lower Silesia Erratic block ?Lonchodomas sp. Żary, Lower Silesia Erratic block Nileus sp. Kårgärde, Dalarna In situ Remopleurides sp. Östergötland In situ Kårgärde, Dalarna Gastropods Eccyliopterus E. alatus Lerkaka, Kalmar In situ E. declivis Pararaphistoma P. vaginati Sinuites S. vetustus Ostracods Euprimites E. bursa Kårgärde, Dalarna In situ E. effusus Steusloffia S. linnarssoni Laccochilina sp. Östergötland Östergötland at Fossilworks.org Kårgärde, Dalarna Sigmobolbina Östergötland Lingulata Biernatia B. holmi Kårgärde, Dalarna In situ Kårgärde 6.34-6.5, Dalarna at Fossilworks.org Conotreta C. mica C. siljanensis 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 In situ Strophomenata Christiania sp. Kårgärde, Dalarna In situ Kårgärde 4.1-5.5, Dalarna at Fossilworks.org

Folkeslunda Limestone

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