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 150 to 200 metres (490 to 660 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, dating to 463.5 to 460.9 Ma. Several genera of nautiloids, trilobites, brachiopods and ostracods were found in the maximum 3.51 metres (11.5 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.

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.

Most of the island of Öland consists of Ordovician sediments, where Folkeslunda is located, the namesake for the formation. 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.

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. 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.

The unit is 2 metres (6.6 ft) thick in the Vikarby section and 2.6 metres (8.5 ft) thick in the Kårgärde section of the western Siljan Ring. In the Lunne section of Jämtland the unit is between 0.99 and 3.51 metres (3.2 and 11.5 ft) thick.

The base of the formation is formed by a 15 centimetres (5.9 in) 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. Other parts of the formation contain finely nodular lime mudstones and mudstones, 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. The eustatic sea level change globally during deposition of the Folkeslunda Limestone was a transgression, 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 150 to 200 metres (490 to 660 ft).

Erratic boulders belonging to the formation have been found in Mecklenburg-Vorpommern, Germany and Lubusz and Kuyavia-Pomerania, Poland. 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.

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.

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).

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
	Arionoceras	A. lotskirkense	Löts Kyrka, Öland	In situ
			Mecklenburg-Vorpommern	Erratic block
	Bactroceras	B. angustisiphonatum	Mecklenburg-Vorpommern	Erratic block
	Cyrtendoceras	C. hircus	Öland	In situ
	Nilssonoceras	N. latisiphonatum	Öland	In situ
	Orthoceras	O. bifoveatum	Öland	In situ
		O. regulare	Öland	In situ
		O. scabridum	Södra Bäck, Öland	In situ
	Oonoceras	O. priscum	Vistula River, Bydgoszcz	Erratic block
	Phthanoncoceras	P. ellipticum	Lerkaka, Kalmar	In situ
			Vistula River, Bydgoszcz	Erratic block
			Żary, Lower Silesia
	Plagiostomoceras	P. fragile	Böda, Stora Mossen, Öland	In situ
	Polygrammoceras	P. oelandicum	Folkeslunda, Öland	In situ
	Richardsonoceras	R. gerhardi	Lerkaka, Kalmar
	Troedssonella	T. endoceroides	Öland	In situ
	Clinoceras	sp.	Vistula River, Bydgoszcz	Erratic block
	Cochlioceras	sp.	Sjöstorp, Öland	In situ
			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
	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
			Kårgärde, Dalarna
	Sigmobolbina		Östergötland
Lingulata	Biernatia	B. holmi	Kårgärde, Dalarna	In situ
	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

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