The Fur Formation is a marine geological formation of Ypresian (Lower Eocene Epoch, c. 56.0-54.5 Ma) age which crops out in the Limfjord region of northern Denmark from Silstrup via Mors and Fur to Ertebølle, and can be seen in many cliffs and quarries in the area. The Diatomite Cliffs (moler in Danish) became a World Heritage Site in 2026. Fossils found in the Fur Formation are primarily housed at the Fossil and Mo-clay Museum on Mors Island, the Fur Museum on Fur Island, and the Natural History Museum of Denmark (formerly named Geological Museum) in Copenhagen.
Geology The Fur Formation is a unit of diatomitic sediment approximately 60 meters thick consisting of diatoms and clay minerals with up to 180 layers of volcanic ash.Pedersen, G.K. & Surlyk, F. 1983: The Fur Formation, a late Paleocene ash-bearing diatomite from northern Denmark. Bulletin Geological Society of Denmark, 32, 43-65. In Danish literature the formation has informally been referred to as the moler (Ler means clay). The diatomite comprises 2/3 opal tests of diatoms and 1/3 clay, interbedded with layers of volcanic ash and a few limestone horizons ('cementstones'), and has exceptionally complete fossil preservation.
It is known for its abundant fossil fish, insects, reptiles, birds and plants. The Fur Formation was deposited just above the Palaeocene-Eocene boundary, about 55 million years ago, and its tropical or sub-tropical flora indicate that the climate after the Paleocene-Eocene Thermal Maximum was moderately warm (approximately 4-8 degrees warmer than today).
Glacial activity has moved and folded all exposed moler in a complicated pattern which permits very precise mapping of glacial movement at the end of the last ice age, and has, due to the ash layers, created a useful pedagogical case for studying tectonics.
Members The Fur Formation is divided into two members: The lower Knudeklint Member was named for a location on the island of Fur. The upper Silstrup Member was named for a location in Thy. The stratigraphy exposed at Knudeklint constitutes the unit that containing the Paleocene/Eocene boundary informally named Stolleklint Clay, which grades up into the Fur Formation.
Paleontological significance Fossils of great diversity and unique preservation exist here, dating to only 10 million years after the 'great extinction' of dinosaurs, ammonites, etc.) This site shows a most unusual, if not unique, diversity of life from both ocean and land, with extremely good preservation of details rarely seen elsewhere, therefore allowing for very reliable reconstruction of palaeobiology. The vast majority of the "Danekræ" fossils (fossils that are considered of national importance and covered by a special law) found since 1990 have been found in the Mo-clay area.Bonde, N., Andersen, S., Hals, N., and Jakobsen, S.T. (2008). Danekræ - Danmarks bedste fossiler. Copenhagen: Gyldendal. 224 pp.
Birds The Fur Formation preserves the earliest diverse Paleogene bird fauna known, with over 30 species, including some near complete, some preserved in 3-D, and some excellent bird-fossils (even with feathers and chromatine). Most are the earliest known representatives of their orders (e.g. Trogons, Swifts, Ibises) and all are terrestrial birds.Pedersen, G. K., Pedersen, S. A. S., Bonde, N., Heilmann-Clausen, C., Larsen, L. M., Lindow, B., Madsen, H., Pedersen, A. K., Rust, J., Schultz, B. P., Storey, M. og Willumsen, P. S. 2012: Molerområdets geologi – sedimenter, fossiler, askelag og glacialtektonik. Geologisk Tidsskrift 2011, pp. 41–135,
GenusSpeciesHigher taxonNotesImagesChascacocoliusC. oscitans?SandcoleidaeOnly known from one wingEocypselusE. vincentiApodiformesMainly known from the London ClayGalliformes indet.UnapplicableGalloanseraeKnown from foot imprints distinct from all other Eocene galliformsLithornisL. vulturinusLithornithidaeFirst complete lithornithid specimen knownMopsittaM. tantaPsittaciformes incertae sedis?Formerly the largest fossil parrot known, however it may actually be synonymous with the ibis RhynchaeitesMorsoravisM. sedilisMorsoravidaeFormerly classed as a charadriiform before being reclassified as a basal member of PsittacopasseresHalcyornithidae indet.UnapplicableEufalconimorphaeOnly known from one humerusPellornisP. mikkelseniMesselornithidaeLimb specialisation indicates it was likely cursorial, redescribed from several complete skeletons which support it being a crown-gruiformScandiavisS. mikkelseniCharadriiformes?Likely a basal member due to features of the postcraniaSeptencoraciasS. morsensisCoraciiformesOne of the earliest rollers, preserved with fish in its stomachSeptentrogonS. madseniTrogonidaeEarliest trogon known
Reptiles Several fossil sea turtles are known from the Fur Formation. In one of them, a large leatherback turtle (Eosphargis breineri)NIELSEN, E. 1963. On the postcranial skeleton of Eosphargis breineri Nielsen. Meddelelser fra Dansk Geologisk Forening, 15, 281–328 remains of soft tissue and skin pigmentation have been recovered A number of well-preserved turtle specimens have been recovered from the formation, two of which have been recognized to be a completely new species of the genus Tasbacka.Karl, H.-V. & Madsen, H. (2012): Tasbacka danica n. sp., A new Eocene marine turtle of Denmark (Testudines: Chelonioidea).- Studia Palaeocheloniologica 4: 193-204 Sea snakes are also known from the formation.HOCH, E. 1975. Amniote remnants from the eastern part of the Lower Eocene North Sea Basin. Colloque International du Centre National de la Recherche Scientifique, Paris, 218, 543–562.Kristensen, H.V., Cuny, G., Rasmussen, A.R., ang Madsen, H., 2012: Earliest record of the fossil snake Palaeophis from the Paleocene/Eocene boundary in Denmark. Bull. Soc. géol. France, 2012, t. 183, no 6, p. 623-627
Palaeophis (Sea snake) Eosphargis brenieri (Leatherback turtle) Cheloniidae and pan-Cheloniidae †PuppigerusNielsen, E., 1959: Eocene Turtles from Denmark, Dansk Geologisk Forening, BD. 14, Hefte 2. p. 96-115 | http://2dgf.dk/xpdf/bull-1959-14-2-96-114.pdf Glarichelys Tasbacka
Fish Fossils of large oceanic teleostean fauna are known from the Fur Formation, possibly including earliest truly deepwater fish, a 'whale-fish'; earliest members of many living families and Tertiary diversity preserved as complete skeletons; including some large and complete specimens (two 'bonytongues', one tarpon).BONDE, N. 1997: A distinct fish fauna in the basal ashseries of the Fur/Ølst Formation (U. Paleocene, Denmark). Aarhus Geoscience, 6, 33–48.
The following taxa are known: GenusSpeciesLocationMemberNotesImages?Analectis?A. sp.FurA turkmenid lampriform.?Antigonia?A. sp.FurA boarfish.ArchaeozeusA. skamolensisFurAn archaeozeid zeiform.?Arius?A. sp.FurA sea catfish.Atheriniformes indet.FurAn atheriniform.Aulostomoidea indet.FurAn aulostomoid.BrychaetoidesB. greenwoodiFurA bonytongue.cf. BrychaetusB. sp.Stolle KlintA bonytongue.ButyrumichthysB. henriciiFurA medusafish.Euzaphlegidae indet.FurA euzaphlegid.ExelliaE. sp.FurAn exelliid percomorph.FurichthysF. fieldsoeiFurA bonytongue.HeterosteoglossumH. foreyiFur, Stolle KlintA bonytongue.HolosteusH. sp.FurA barracudina.Megalopidae indet.FurA tarpon.Mene M. sp.FurA moonfish.MoclaybalistesM. danekrusFurA moclaybalistid tetraodontiform.Muraenidae indet.FurA moray eel.Osteoglossiformes indet.FurA small-sized osteoglossiform.PalaeocentrotusP. boeggildiFurA palaeocentrotid lampriform.Palaeorhynchidae indet.FurA billfish.?Percopsiformes indet.FurA potential percopsiform.PolyspinatusP. fluereFurA beardfish.ProtozeusP. kuehneiFurA protozeid zeiform.RhamphosusR. sp.FurA syngnathiform.RhinocephalusR. sp.FurA hake.?Rondeletia?R. sp.FurA whalefish, possibly a redmouth whalefish.?Salmonidae indet.FurA potential salmonid.?Sardinella?S. sp.FurA clupeid.?Scorpaeniformes indet.FurA potential scorpaeniform.SurlykusS. longigracilisFurAn argentiniform, the most common fish in the Mo-Clay.?Vomeropsis?V. sp.FurA carangid.XosteoglossidX. rebeccaeStolle KlintA bonytongue.
Insects Fauna from land, over 200 species, many are oldest of their families; many with colour spots and eye lenses, some preservation with stridulation (sound) apparatus in grasshoppers, and migratory moth mass mortality.ARCHIBALD, S. B. &MARKARKIN, V. N. 2006: Tertiary Giant Lacewings (Neuroptera: Polystoechotidae): Revision and description of new taxa from Western North America and Denmark. Journal of Systematic Palaeontology, 4, 119–155.LARSSON, S.G., 1975: Palaeobiology and mode of burial of the insects of the Lower Eocene Mo-clay of Denmark. Bulletin of the Geological Society of Denmark, vol. 24 p. 193-209.
GenusSpeciesHigher taxonNotesImagesApachyusA. madseniApachyidaeFirst fossil apachyidCephalallusC. vitaliiSpondylidinaeFirst longhorn beetle from the formationCryptocheilusC. lelejiPepsiniEarliest pompillid wasp knownDanoberothaD. verkleijorumBerothidaeFirst berothid from the formationDanochrysaD. madseniChrysopidaeDanolestesD. moelleriLestoideaA member of Lestoidea of uncertain affinities.DanomantispaD. frandseniMantispidaeIntermediate between Drepanicinae and MantispinaeEodysagrionE. mikkelseniDysagrionidae (Odonata)Member of its own subfamily, EodysagrioninaeEosassulaE. szwedoiNogodinidaeOne of the few nogodinid fossilsFuragrionF. jutlandicusZygopteraBears all wing venation characters of cephalozygopterans, but has a head similar to zygopteransFurochrysaF. alisaeChrysopidaeDistinguished by a long crossveinMesypochrysaM. nielseniChrysopidaeLatest record of the Mesozoic genus MesypochrysaPachycondylaP. rebekkaePonerinaeOne of the earliest fossil ants in an extant genus at the time of descriptionPalaeopsychopsP. quadratusPolystoechotidaeBears stripes along its crossveinsParabaissaeshnaP. ejerslevenseAeshnidaeResembles the Mesozoic BaissaeshnaPseudotettigoniaP. amoenaTettigoniidaePreserves a complete stridulatory organ, with the structure of the organ suggesting that it was able to hear low ultrasoundPrimorilestesP. madseniDysagrionidae (Odonata)ProtheristriaP. roldaeMantispidaeIn the same subfamily as the other mantisfly known from the formation, but otherwise unrelatedRhantusR. villumiDytiscidaeOldest species in the genusStephenbrooksiaS. multifurcataChrysopidaeBears unusual hind wing venationStolleagrionS. foghnielseniCephalozygoptera (Odonata)First odonate known from the early YpresianTriachrysaT. rustiChrysopidaeHas three series of crossveins in its wings, alongside several unrelated genera
Crustacea Extraordinary cirripeds (barnacles), and the only fossil shrimps from Denmark.GARASSINO, A. & JAKOBSEN, S. L. 2005: Morscrangon acutus n. gen. n. sp. (Crustacea, Decapoda, Caridea) from the Fur Formation (Early Eocene) of the Islands of Mors and Fur (Denmark). Atti Societa italiana di Scienze naturali, Museo civico di Storia nataturale, Milano, 146, 95–107.
Molluscs Gari sp. Mytilus sp. Nucula sp.
Land plants Some members of the 'Arcto-Tertiary flora'; some with cuticle preservation and some flowers preserved. Large silicified trunks (up to 9 m) of redwood, and some very soft wood preserved. Some trunks with mussels and barnacles attached. Many seeds and fruits.Sakala, J., & Gryc, V., 2011: A new species of Rhysocaryoxylon (Juglandaceae) from the Lower Eocene Fur Formation of Mors island (northwest Jutland, Denmark). Bulletin of the Geological Society of Denmark, Vol. 59, p 45–49
Diatoms Great diversity of unicellular, marine algae with siliceous (opal) tests, 130 species.HOMANN, M. 1991. Die Diatomeen der Fur Formation. Geologisches Jahrbuch, A 123, 1–285.
Ash layers