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 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 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.
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. 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 thick in the Vikarby section and thick in the Kårgärde section of the western Siljan Ring. In the Lunne section of Jämtland the unit is between thick.

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. 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.

Erratic boulders

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 and Boll. Boll's collection is fortunately preserved at the regional Müritz Museum of Waren, Mecklenburg. Dzik described and illustrated Ordovician nautiloids of the erratic boulders in Poland.

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 and Törnquist, while Janusson described ostracods. Species of nautiloid cephalopods were reported by Holm in 1896, Troedsson, and Kröger. 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, Argentina, and China.

Fossil content

The following fossils have been found in the rocks belonging to the formation:
GroupGenusSpeciesLocationStatusNotes
CephalopodsArchigeisonocerasA. folkeslundenseÖlandIn situ
CephalopodsArionocerasA. lotskirkenseLöts Kyrka, ÖlandIn situ
CephalopodsArionocerasA. lotskirkenseMecklenburg-VorpommernErratic block
CephalopodsBactrocerasB. angustisiphonatumMecklenburg-VorpommernErratic block
CephalopodsCyrtendocerasC. hircusÖlandIn situ
CephalopodsNilssonocerasN. latisiphonatumÖlandIn situ
CephalopodsOrthocerasO. bifoveatumÖlandIn situ
CephalopodsOrthocerasO. regulareÖlandIn situ
CephalopodsOrthocerasO. scabridumSödra Bäck, ÖlandIn situ
CephalopodsOonocerasO. priscumVistula River, BydgoszczErratic block
CephalopodsPhthanoncocerasP. ellipticumLerkaka, KalmarIn situ
CephalopodsPhthanoncocerasP. ellipticumVistula River, BydgoszczErratic block
CephalopodsPhthanoncocerasP. ellipticumŻary, Lower SilesiaErratic block
CephalopodsPlagiostomocerasP. fragileBöda, Stora Mossen, ÖlandIn situ
CephalopodsPolygrammocerasP. oelandicumFolkeslunda, ÖlandIn situ
CephalopodsRichardsonocerasR. gerhardiLerkaka, KalmarIn situ
CephalopodsTroedssonellaT. endoceroidesÖlandIn situ
CephalopodsClinocerassp.Vistula River, BydgoszczErratic block
CephalopodsCochliocerassp.Sjöstorp, ÖlandIn situ
CephalopodsCochliocerassp.Vistula River, BydgoszczErratic block
CephalopodsCochliocerassp.Żary, Lower SilesiaErratic block
CephalopodsLituitessp.Kårgärde, DalarnaIn situ
TrilobitesIllaenusI. chironKårgärde, DalarnaIn situ
TrilobitesPseudoasaphusP. aciculatusKårgärde, DalarnaIn situ
TrilobitesPseudobasilicusP. ?brachyrachisKårgärde, DalarnaIn situ
TrilobitesPlectasaphusP. plicicostisKårgärde, DalarnaIn situ
TrilobitesPseudomegalaspisP. patagiataKårgärde, DalarnaIn situ
TrilobitesAmpyx (Cnemidopyge)sp.Kårgärde, DalarnaIn situ
TrilobitesAsaphussp.Żary, Lower SilesiaErratic block
Trilobites?Lonchodomassp.Żary, Lower SilesiaErratic block
TrilobitesNileussp.Kårgärde, DalarnaIn situ
TrilobitesRemopleuridessp.ÖstergötlandIn situ
TrilobitesRemopleuridessp.Kårgärde, DalarnaIn situ
GastropodsEccyliopterusE. alatusLerkaka, KalmarIn situ
GastropodsEccyliopterusE. declivisLerkaka, KalmarIn situ
GastropodsPararaphistomaP. vaginatiLerkaka, KalmarIn situ
GastropodsSinuitesS. vetustusLerkaka, KalmarIn situ
OstracodsEuprimitesE. bursaKårgärde, DalarnaIn situ
OstracodsEuprimitesE. effususKårgärde, DalarnaIn situ
OstracodsSteusloffiaS. linnarssoniKårgärde, DalarnaIn situ
OstracodsLaccochilinasp.ÖstergötlandIn situ
OstracodsLaccochilinasp.Kårgärde, DalarnaIn situ
OstracodsSigmobolbinasp.ÖstergötlandIn situ
LingulataBiernatiaB. holmiKårgärde, DalarnaIn situ
LingulataConotretaC. micaKårgärde, DalarnaIn situ
LingulataConotretaC. siljanensisKårgärde, DalarnaIn situ
LingulataEoconulusE. cf. clivosusKårgärde, DalarnaIn situ
LingulataEoconulusE. robustusKårgärde, DalarnaIn situ
LingulataHisingerellaH. unguiculaKårgärde, DalarnaIn situ
LingulataMyotretaM. dalecarlicaKårgärde, DalarnaIn situ
LingulataRowellellaR. cf. lamellosaKårgärde, DalarnaIn situ
LingulataScaphelasmaS. micaKårgärde, DalarnaIn situ
LingulataSpinilingulaS. radiolamellosaKårgärde, DalarnaIn situ
LingulataTalasotretaT. deformisKårgärde, DalarnaIn situ
LingulataCyrtonotretasp.Kårgärde, DalarnaIn situ
LingulataPaterulasp.Kårgärde, DalarnaIn situ
LingulataSpondylotretasp.Kårgärde, DalarnaIn situ
LingulataLingulellinaeindet.Kårgärde, DalarnaIn situ
LingulataOrbiculoideinaeindet.Kårgärde, DalarnaIn situ
RhynchonellataNicolellasp.ÖstergötlandIn situ
StrophomenataChristianiasp.Kårgärde, DalarnaIn situ