Agardhfjellet Formation

Agardhfjellet Formation
Stratigraphic range: Oxfordian-Berriasian ~157.9–141 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Geologic map of central Svalbard with the formation in dark blue
Type	Formation
Unit of	Adventdalen Group
Sub-units	Oppdalsåta & Slottsmøya Members
Underlies	Rurikfjellet Formation
Overlies	Knorringfjellet Formation
Lithology
Primary	Mudstone
Other	Dolomite
Location
Coordinates	78.3°N 15.8°E / 78.3; 15.8
Approximate paleocoordinates	69.6°N 16.3°E / 69.6; 16.3
Region	Svalbard
Country	Norway
Extent	Central Spitsbergen Basin

The Agardhfjellet Formation is a geologic formation in Svalbard, Norway. It preserves fossils dating back to the Oxfordian to Berriasian stages, spanning the Late Jurassic-Early Cretaceous boundary.^[1] The formation contains the Slottsmøya Member, a highly fossiliferous unit (Lagerstätte) where many ichthyosaur and plesiosaur fossils have been found, as well as abundant and well preserved fossils of invertebrates.^[2][3]

Description

The formation overlies the Knorringfjellet Formation and is overlain by the Rurikfjellet 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 yellowish sideritic concretions as well as siderite and dolomite interbeds.^[3] It consists of a mix of shales and siltstones which were deposited in a shallow marine environment, near a patch of deeper marine 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-water methane seeps which 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 include ammonites, bivalves, lingulate brachiopods, rhynchonellate brachiopods, tubeworms, belemnoids, tusk shells, sponges, crinoids, sea urchins, brittle stars, starfish, crustaceans, and gastropods, 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 bivalve Nucinella.^[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 of ichthyosaurs and plesiosaurs. 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

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa 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]

Vertebrates

Bony fish

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

Plesiosaurs

Plesiosaurs from the Agardhfjellet Formation
Genus	Species	Location	Member	Material	Notes	Images
Tricleidus	T. svalbardensis		Slottsmøya Member		Reassigned to the genus Colymbosaurus after further analysis[12]
Colymbosaurus	C. svalbardensis		Slottsmøya Member		A colymbosaurine cryptoclidid, also known from the Kimmeridge 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 to Ophthalmothule
	S. larseni
Pliosaurus	P. funkei		Slottsmøya Member	Known from two partial skeletons	A large thalassophonean pliosaurid which 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

Ichthyosaurs from the Agardhfjellet Formation
Genus	Species	Location	Member	Material	Notes	Images
Cryopterygius	C. kristiansenae		Slottsmøya Member		Junior synonym of Undorosaurus gorodischensis
Undorosaurus	U. gorodischensis		Slottsmøya Member	A single, largely complete specimen	A large platypterygiine ichthyosaur, also known from the Russian Volga.[13]
Janusaurus	J. lundi		Slottsmøya Member		Junior synonym of Arthropterygius lundi
Palvennia	P. hoybergeti		Slottsmøya Member		Junior synonym of A. hoybergeti
Keilhauia	K. nui		Slottsmøya Member		A nomen dubium referred to A. sp. cf. chrisorum
Arthropterygius	A. lundi		Slottsmøya Member	Several specimens of varying ages, previously referred to several other genera	A widespread genus of ophthalmosaurid ichthyosaur, 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 to Brachypterygius by Angst et al. (2010)[16]

Invertebrates

An unnamed galatheid squat lobster is known from a single, poorly preserved fragment.^[5]

Cephalopods

Large belemnoid arm hooks are known.^[17]

Cephalopods from 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

Echinoderms from the Agardhfjellet Formation
Genus	Species	Location	Member	Material	Notes	Images
Chariocrinus	C. sp.		Slottsmøya Member		A form of isocrinid crinoid
Hemipedina	H. sp.		Slottsmøya Member		A species of pedinoid sea urchins related to the extant Caenopedina
Polarasterias	P. janusensis		Slottsmøya Member	Nearly complete specimen	A forcipulatid sea star
Savignaster	S. septemtrionalis		Slottsmøya Member		A pterasterid sea star
Ophiogaleus	O. sp.		Slottsmøya Member		A ophiacanthid brittle star
Ophioculina	O. hoybergia		Slottsmøya Member		An ophiurine brittle star

Bivalves

Remains of possible anomiid clams have been found which are as yet undescribed.

Bivalves from the Agardhfjellet Formation
Genus	Species	Location	Member	Material	Notes	Images
Pseudotrapezium	P. aff. groelandicum		Slottsmøya Member		An arcticid clam 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		A lucinid clam
Cretaxinus	C. hurumi		Slottsmøya Member		A thyacirid clam
Camptonectes	C. spp		Slottsmøya Member		A pectinid clam 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

Serpulids from the Agardhfjellet Formation
Genus	Species	Location	Member	Material	Notes	Images
Propomatoceros	P. sp.		Slottsmøya Member		A serpulid tube worm
aff. Pyrgopolon	aff. P. nodulosum		Slottsmøya Member		A serpulid tube worm which forms mass accumulations in the Echinoderm Bed
Nogrobs	N. sp.		Slottsmøya Member

Brachiopods

Brachiopods from the Agardhfjellet Formation
Genus	Species	Location	Member	Material	Notes	Images
Lingularia	L. similis		Slottsmøya Member		The most abundant species of brachiopod that is present in Slottsmøya
Ptilorhynchia	P. mclachlani		Slottsmøya Member		A rhynchonellide brachiopod

Gastropods

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

See also

• List of fossiliferous stratigraphic units in Norway
• Tithonian formations
• Berriasian formations

References

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. Agardhfjellet Formation at Fossilworks.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. ISSN 0029-196X.
5. Hryniewicz, 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. Delsett, L.L.; Novis, L.K.; Roberts, A.J.; Koevoets, M.J.; Hammer, O.; Druckenmiller, P.S.; Hurum, J.H. (2015). "The Slottsmøya marine reptile Lagerstätte: 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. S2CID 130478320.
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. PMC 6187996. PMID 30345178.
10. Roberts, 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. PMC 7120097. PMID 32266112.
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 of Undorosaurus, 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. S2CID 91912834.
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. PMC 6497043. PMID 31106052.
15. Nikolay G. Zverkov; Megan L. Jacobs (2020). "Revision of Nannopterygius (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

• Roberts, 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, PMC 7120097, PMID 32266112
• Delsett, L.L.; Roberts, A.J.; Druckenmiller, P.S.; Hurum, J.H. (2019), "Osteology and phylogeny of Late Jurassic ichthyosaurs from the Slottsmøya Member Lagerstätte (Spitsbergen, Svalbard)", Acta Palaeontologica Polonica, 64: 717–743, doi:10.4202/app.00571.2018, hdl:10852/76089
• Delsett, L.L.; Roberts, A.J.; Druckenmiller, P.S.; Hurum, J.H. (2017), "A New Ophthalmosaurid (Ichthyosauria) from Svalbard, Norway, and Evolution of the Ichthyopterygian Pelvic Girdle", PLoS ONE, 12 (1): e0169971, Bibcode:2017PLoSO..1269971D, doi:10.1371/journal.pone.0169971, PMC 5266267, PMID 28121995
• Hryniewicz, K.; Little, C.T.; Nakrem, H.A. (2014), "Bivalves from the latest Jurassic-earliest Cretaceous hydrocarbon seep carbonates from central Spitsbergen, Svalbard", Zootaxa, 3859: 1–66, doi:10.11646/zootaxa.3859.1.1, PMID 25283172
• Roberts, A.J.; Druckenmiller, P.S.; Sætre, G.P.; Hurum, J.H. (2014), "A New Upper Jurassic Ophthalmosaurid Ichthyosaur from the Slottsmøya Member, Agardhfjellet Formation of Central Spitsbergen", PLoS ONE, 9 (8): e103152, Bibcode:2014PLoSO...9j3152R, doi:10.1371/journal.pone.0103152, PMC 4118863, PMID 25084533
• Druckenmiller, P.S.; Hurum, J.H.; Knutsen, E.M.; Nakrem, H.A. (2012), "Two new ophthalmosaurids (Reptilia: Ichthyosauria) from the Agardhfjellet Formation (Upper Jurassic: Volgian/Tithonian), Svalbard, Norway" (PDF), Norwegian Journal of Geology, 92: 311–339, ISSN 0029-196X, archived from the original (PDF) on 2015-09-24, retrieved 2020-07-03
• Knutsen, E.M.; Druckenmiller, P.S.; Hurum, J.H. (2012a), "A new plesiosauroid (Reptilia: Sauropterygia) from the Agardhfjellet Formation (Middle Volgian) of central Spitsbergen, Norway", Norwegian Journal of Geology, 92: 213–234
• Knutsen, E.M.; Druckenmiller, P.S.; Hurum, J.H. (2012b), "A new species of Pliosaurus (Sauropterygia: Plesiosauria) from the Middle Volgian of central Spitsbergen, Norway", Norwegian Journal of Geology, 92: 235–258
• Knutsen, E.M.; Druckenmiller, P.S.; Hurum, J.H. (2012c), "Redescription and taxonomic clarification of 'Tricleidus' svalbardensis based on new material from the Agardhfjellet Formation (Middle Volgian)", Norwegian Journal of Geology, 92: 175–186