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Agardhfjellet Formation

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Coordinates:78°18′N15°48′E/ 78.3°N 15.8°E/78.3; 15.8
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Agardhfjellet Formation
Stratigraphic range:Oxfordian-Berriasian
~157.9–141Ma
Geologic map of central Svalbard with the formation in dark blue
TypeFormation
Unit ofAdventdalen Group
Sub-unitsOppdalsåta & Slottsmøya Members
UnderliesRurikfjellet Formation
OverliesKnorringfjellet Formation
Lithology
PrimaryMudstone
OtherDolomite
Location
Coordinates78°18′N15°48′E/ 78.3°N 15.8°E/78.3; 15.8
Approximate paleocoordinates69°36′N16°18′E/ 69.6°N 16.3°E/69.6; 16.3
RegionSvalbard
CountryNorway
ExtentCentral Spitsbergen Basin

TheAgardhfjellet Formationis ageologic formationinSvalbard,Norway.It preservesfossilsdating back to theOxfordiantoBerriasianstages, spanning theLate Jurassic-Early Cretaceousboundary.[1]The formation contains the Slottsmøya Member, a highly fossiliferous unit (Lagerstätte) where manyichthyosaurandplesiosaurfossils have been found, as well as abundant and well preserved fossils of invertebrates.[2][3]

Description[edit]

The formation overlies theKnorringfjellet Formationand is overlain by theRurikfjellet Formation.The formation comprises the lower Oppdalsåta and upper Slottsmøya Members. The Slottsmøya Member, which averages 55 to 60 metres (180 to 197 ft) in thickness in the study area, consists of dark-grey to black silty mudstone, often weathering to paper shale, and discontinuous silty beds with local occurrences of red to yellowishsideriticconcretions as well as siderite and dolomite interbeds.[3]It consists of a mix ofshalesandsiltstoneswhich were deposited in a shallow marine environment, near a patch of deepermarine sediment.[4]The seafloor, which was located about 150 metres (490 ft) below the surface, seems to have been relatively dysoxic, or oxygen-poor, although the diversity of the benthic fauna suggest that these environments were likely not truly anoxic and that oxygen-depletion may have been a seasonal phenomenon.[5][6]Although direct evidence from Slottsmøya is currently lacking, the high latitude of this site and relatively cool global climate of the Tithonian suggest that some sea ice may have been present at least in the winter.[7][8]

These sites represent shallow-watermethane seepswhich were spread over a relatively large geographic area, and like modern day seeps, they supported high biodiversity. Near the top of the member, various assemblages of invertebrates have been discovered; these includeammonites,bivalves,lingulate brachiopods,rhynchonellate brachiopods,tubeworms,belemnoids,tusk shells,sponges,crinoids,sea urchins,brittle stars,starfish,crustaceans,andgastropods,numbering 54 taxa in total. The most common and abundant of these taxa were bivalves and brachiopods, each of which make up 27.8% of the known seep fauna. Several chemosymbiotic species are known, such as the bivalveNucinella.[5]Outside of the cold seeps, several non-seep-restricted invertebrates were also present in abundance.[6]In addition to the invertebrates, the Slottsmøya Member has also revealed a diverse assemblage of marine reptiles, including several taxa ofichthyosaursandplesiosaurs.Many of these specimens are relatively complete and in articulation, which is rare among Jurassic marine fossil sites.[6]It thus provides a unique and detailed glimpse into the boreal seas of the Late Jurassic. As it spans the Jurassic-Cretaceous boundary, it is also important to understanding how marine ecosystems changed going into the Cretaceous.

Paleobiota[edit]

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are insmall text;crossed outtaxa are discredited.

The formation, especially the Slottsmøya Member, has provided an abundance of marine fossils dating to the Late Jurassic-Early Cretaceous.[3]

The timeline below follows stratigraphic data provided in Delsett et al. 2018 and Roberts et al. 2020.[9][10]

NannopterygiusArthropterygiusArthropterygiusArthropterygiusUndorosaurusPliosaurusOphthalmothuleSpitrasaurusSpitrasaurusDjupedaliaColymbosaurus

Vertebrates[edit]

Bony fish[edit]

Bony fishfrom the Agardhfjellet Formation
Genus Species Location Member Material Notes Images
Leptolepis[11] L. nathorsti Oppdalssåta & Lardyfjellet Members

Plesiosaurs[edit]

Plesiosaursfrom the Agardhfjellet Formation
Genus Species Location Member Material Notes Images

Tricleidus

T. svalbardensis

Slottsmøya Member

Reassigned to the genusColymbosaurusafter further analysis[12]

Colymbosaurus C. svalbardensis Slottsmøya Member A colymbosaurinecryptoclidid,also known from theKimmeridge Clay
Djupedalia D. engeri Slottsmøya Member A cryptoclidid plesiosaur
Ophthalmothule O. cryostea Slottsmøya Member Extensive skeletal material including a complete cranium A cryptoclidid plesisosaur which has unusually large orbits.[10]
Spitrasaurus S. wensaasi Slottsmøya Member A cryptoclidid plesiosaur related toOphthalmothule
S. larseni
Pliosaurus P. funkei Slottsmøya Member Known from two partial skeletons A largethalassophoneanpliosauridwhich was informally known as "Predator X" prior to being named. This species is notable for having unusually large paddles in comparison to its body size.

Ichthyosaurs[edit]

Ichthyosaursfrom the Agardhfjellet Formation
Genus Species Location Member Material Notes Images
Cryopterygius C. kristiansenae Slottsmøya Member Junior synonym ofUndorosaurus gorodischensis
Undorosaurus U. gorodischensis Slottsmøya Member A single, largely complete specimen A largeplatypterygiineichthyosaur,also known from theRussianVolga.[13]
Janusaurus J. lundi Slottsmøya Member Junior synonym ofArthropterygius lundi
Palvennia P. hoybergeti Slottsmøya Member Junior synonym ofA. hoybergeti
Keilhauia K. nui Slottsmøya Member Anomen dubiumreferred toA. sp. cf. chrisorum
Arthropterygius A. lundi Slottsmøya Member Several specimens of varying ages, previously referred to several other genera A widespread genus ofophthalmosauridichthyosaur, also known from Canada, Russia, and Argentina. Is present both before and directly after the Jurassic-Cretaceous Boundary.[14]
A. hoybergeti
A. chrisorum
Nannopterygius N. borealis Slottsmøya Member An ophthalmosaurid ichthyosaur present in early Cretaceous strata. This genus is also known from the Kimmeridge Clay and from fossil sites in the Volga.[15]
Brachypterygius B. sp. Slottsmøya Member Partial skull Referred toBrachypterygiusby Angst et al. (2010)[16]

Invertebrates[edit]

An unnamedgalatheidsquat lobsteris known from a single, poorly preserved fragment.[5]

Cephalopods[edit]

Largebelemnoidarm hooks are known.[17]

Cephalopodsfrom the Agardhfjellet Formation
Genus Species Location Member Material Notes Images
Craspedites[18] C. okensis Slottsmøya Member
C. originalis
Borealites B. rossicus Slottsmøya Member
B. sp.
Hectoroceras H. kochi Slottsmøya Member
H. sp.
Kachpurites K. sp. Slottsmøya Member
Surites S. spasskensis Slottsmøya Member
S. spasskensoides
S. tzikwinianus
S. mesezhnikovi
Tollia T. tolli Slottsmøya Member

Echinoderms[edit]

Echinodermsfrom the Agardhfjellet Formation
Genus Species Location Member Material Notes Images
Chariocrinus C. sp. Slottsmøya Member A form ofisocrinidcrinoid
Hemipedina H. sp. Slottsmøya Member A species ofpedinoidsea urchins related to the extantCaenopedina
Polarasterias P. janusensis Slottsmøya Member Nearly complete specimen Aforcipulatidsea star
Savignaster S. septemtrionalis Slottsmøya Member Apterasteridsea star
Ophiogaleus O. sp. Slottsmøya Member Aophiacanthidbrittle star
Ophioculina O. hoybergia Slottsmøya Member An ophiurinebrittle star

Bivalves[edit]

Remains of possibleanomiidclams have been found which are as yet undescribed.

Bivalvesfrom the Agardhfjellet Formation
Genus Species Location Member Material Notes Images
Pseudotrapezium P. aff. groelandicum Slottsmøya Member Anarcticidclam which constitutes nearly half of the fauna recovered from the seep assemblages.
Mesosaccella M. rogovi Slottsmøya Member
M. toddi
Nucinella N. svalbardensis Slottsmøya Member The most abundant chemosymbiotic species in the Spitsbergen seeps.
Buchia B. sp Slottsmøya Member
Solemya S. cf. woodwardiana Slottsmøya Member A burrowing chemosymbiotic bivalve which is very abundant in the seep sites
Tehamatea T. rasmusseni Slottsmøya Member Alucinidclam
Cretaxinus C. hurumi Slottsmøya Member Athyaciridclam
Camptonectes C. spp Slottsmøya Member Apectinidclam represented by at least two species
Oxytoma O. octavia Slottsmøya Member
Pseudolimea P. arctica Slottsmøya Member
Dacromya D. chetaensis Slottsmøya Member Rare
Goniomya G. literata Slottsmøya Member Rare

Serpulids[edit]

Serpulidsfrom the Agardhfjellet Formation
Genus Species Location Member Material Notes Images
Propomatoceros P. sp. Slottsmøya Member Aserpulidtube worm
aff.Pyrgopolon aff. P. nodulosum Slottsmøya Member Aserpulidtube wormwhich forms mass accumulations in the Echinoderm Bed
Nogrobs N. sp. Slottsmøya Member

Brachiopods[edit]

Brachiopodsfrom the Agardhfjellet Formation
Genus Species Location Member Material Notes Images
Lingularia L. similis Slottsmøya Member The most abundant species ofbrachiopodthat is present in Slottsmøya
Ptilorhynchia P. mclachlani Slottsmøya Member Arhynchonellidebrachiopod

Gastropods[edit]

Gastropodsfrom the Agardhfjellet Formation
Genus Species Location Member Material Notes Images
Ambercyclus A. sp. Slottsmøya Member The most abundant species ofgastropodthat is known from the Slottsmøya seep deposits
Hudlestoniella H. sp. Slottsmøya Member Arissoidgastropod
Cantrainea C. sp. Slottsmøya Member Aturbinidgastropod; it is rare and only known from one of the seep sites

See also[edit]

References[edit]

  1. ^Connors, Marisa Leigh (2017).Deciphering the Late Jurassic paleoenvironment through Re-Os isotope geochemistry of the Agardhfjellet Formation, Svalbard(Thesis). Colorado State University.
  2. ^Delsett et al., 2019, p.741
  3. ^abcAgardhfjellet FormationatFossilworks.org
  4. ^Hurum, J.H.; Nakrem, H.A.; Hammer, O.; Knutsen, E.M.; Druckenmiller, P.S.; Hryniewicz, K.; Novis, L.K. (2012)."An Arctic Lagerstätte – the Slottsmøya Member of the Agardhfjellet Formation (Upper Jurassic-Lower Cretaceous) of Spitsbergen"(PDF).Norwegian Journal of Geology.92:55–64.ISSN0029-196X.
  5. ^abcHryniewicz, K.; Nakrem, H.A.; Hammer, O.; Little, C.T.S.; Kaim, A.; S., M.R.; Hurum, J.H. (2015)."The palaeoecology of the latest Jurassic–earliest Cretaceous hydrocarbon seep carbonates from Spitsbergen, Svalbard".Lethaia.48(3): 353–374.Bibcode:2015Letha..48..353H.doi:10.1111/let.12112.
  6. ^abcDelsett, L.L.; Novis, L.K.; Roberts, A.J.; Koevoets, M.J.; Hammer, O.; Druckenmiller, P.S.; Hurum, J.H. (2015)."The Slottsmøya marine reptileLagerstätte:depositional environments, taphonomy and diagenesis "(PDF).In Kear, B.P.; Lindgren, J.; Hurum, J.H.; Milan, J.; Vajda, V. (eds.).Mesozoic Biotas of Scandinavia and its Arctic Territories.Geological Society of London, Special Publications. Vol. 434. pp. 165–188.doi:10.1144/SP434.2.S2CID130478320.
  7. ^Galloway, J.M.; Sweet, A.R.; Swindles, G.T.; Dewing, K.; Hadlari, T.; Embry, A.F.; Sanei, H. (June 2013)."Middle Jurassic to Lower Cretaceous paleoclimate of Sverdrup Basin, Canadian Arctic Archipelago inferred from the palynostratigraphy".Marine and Petroleum Geology.44:240–255.Bibcode:2013MarPG..44..240G.doi:10.1016/j.marpetgeo.2013.01.001.
  8. ^Price, Gregory G. (1999)."The evidence and implications of polar ice during the Mesozoic".Earth-Science Reviews.48(3): 183–210.Bibcode:1999ESRv...48..183P.doi:10.1016/S0012-8252(99)00048-3.
  9. ^Delsett, L.L.; Druckenmiller, P.S.; Roberts, A.J.; Hurum, J.H. (October 12, 2018)."A new specimen of Palvennia hoybergeti: implications for cranial and pectoral girdle anatomy in ophthalmosaurid ichthyosaurs".PeerJ.6:e5776.doi:10.7717/peerj.5776.PMC6187996.PMID30345178.
  10. ^abRoberts, A.J.; Druckenmiller, P.S.; Cordonnier, B.; Delsett, L.L.; Hurum, J.H. (2020)."A new plesiosaurian from the Jurassic–Cretaceous transitional interval of the Slottsmøya Member (Volgian), with insights into the cranial anatomy of cryptoclidids using computed tomography".PeerJ.8:e8652.doi:10.7717/peerj.8652.PMC7120097.PMID32266112.
  11. ^Koevoets, Maayke J.; Hurum, Jørn H.; Hammer, Øyvind (17 April 2018)."New Late Jurassic teleost remains from the Agardhfjellet Formation, Spitsbergen, Svalbard".Norwegian Journal of Geology.98(2).doi:10.17850/njg98-2-01.hdl:10852/71055.
  12. ^E. M. Knutsen, P. S. Druckenmiller, and J. Hurum. 2012. Redescription and taxonomic clarification of ‘Tricleidus’ svalbardensis based on new material from the Agardhfjellet Formation (Middle Volgian). Norwegian Journal of Geology 92:175-186
  13. ^Nikolay G. Zverkov; Vladimir M. Efimov (2019)."Revision ofUndorosaurus,a mysterious Late Jurassic ichthyosaur of the Boreal Realm ".Journal of Systematic Palaeontology.17(14): 963–993.Bibcode:2019JSPal..17.1183Z.doi:10.1080/14772019.2018.1515793.S2CID91912834.
  14. ^Zverkov, Nikolay G.; Prilepskaya, Natalya E. (2019)."A prevalence of Arthropterygius (Ichthyosauria: Ophthalmosauridae) in the Late Jurassic—earliest Cretaceous of the Boreal Realm".PeerJ.7:e6799.doi:10.7717/peerj.6799.PMC6497043.PMID31106052.
  15. ^Nikolay G. Zverkov; Megan L. Jacobs (2020). "Revision ofNannopterygius(Ichthyosauria: Ophthalmosauridae): reappraisal of the 'inaccessible' holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution ".Zoological Journal of the Linnean Society.191:228–275.doi:10.1093/zoolinnean/zlaa028.
  16. ^ANGST, D.; BUFFETAUT, E.; TABOUELLE, J.; TONG, H. (2010)."An ichthyosaur skull from the Late Jurassic of Svalbard".Bulletin de la Société Géologique de France.181(5): 453–458.doi:10.2113/gssgfbull.181.5.453.
  17. ^HAMMER, Ø.; HRYNIEWICZ, K.; HURUM, J.H.; HØYBERGET, M.; KNUTSEN, E.M.; NAKREM, H.A. (4 May 2012)."Large onychites (cephalopod hooks) from the Upper Jurassic of the Boreal Realm".Acta Palaeontologica Polonica(58).doi:10.4202/app.2012.0020.
  18. ^Wierzbowski, A.; Hryniewicz, K.; Hammer, Ø.; Nakrem, H.A.; Little, C.T.S. (October 2011)."Ammonites from hydrocarbon seep carbonate bodies from the uppermost Jurassic – lowermost Cretaceous of Spitsbergen and their biostratigraphical importance".Neues Jahrbuch für Geologie und Paläontologie.262(3): 267–288.doi:10.1127/0077-7749/2011/0198.

Bibliography[edit]

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