Vardebukta Formation

Vardebukta Formation
Stratigraphic range: Induan ~251.9–251.2  Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Formation
Lithology
Primary	Conglomerate
Other	Sandstone, lime mudstone, packstone
Location
Coordinates	77°00′N16°12′E / 77°N 16.2°E / 77; 16.2
Approximate paleocoordinates	41°00′N9°24′E / 41.0°N 9.4°E / 41.0; 9.4
Region	Svalbard
Country	Norway
Vardebukta Formation (Svalbard)

The Vardebukta Formation is a geologic formation in Norway. It preserves fossils dating back to the Induan stage (early Early Triassic). ^[1] Outcrops are known from the Hornsund area but also from Bellsund and Isfjorden areas. ^[2]

Subunits

The Vardebukta Formation is divided into the Urnetoppen Member and the overlying Wibebreen Member. Both members are of marine origin. They were deposited in a sublittoral to shallow-neritic environment. ^[2] The Vardebukta Formation represents the oldest Mesozoic formation in Svalbard. ^[3]

Urnetoppen Member

The Urnetoppen Member, which is approximately 30 meter thick in the Hornsund area, consists of greenish shales, siltstone and fine-grained sandstone, occasionally with clay-ironstone nodules. In the Hornsund area, it rests paraconformably on the Permian Kapp Starostin Formation. The Urnetoppen Member is correlated with the Deltadalen Member of the Vikinghøgda Formation, which is of Dienerian (late Induan) age. ^{[2] [4]}

The top of the Urnetoppen Member contains the so-called Brevassfjellet Myalina beds, a 5–6 meter thick, fossiliferous conglomerate.

Wibebreen Member

The Wibebreen Member is ca. 90–100 meter thick in the Hornsund area. It consists of black to light-grey coloured shales, marly shales, arenaceous marls and siltstone. The lower part of this member contains mainly siltsone layers. The locally developed Skilisen Retzia Limestone belongs to the uppermost part of the Wibebreen Member. The Wibebreen Member is overlain by the Smithian (early Olenekian) aged Lusitaniadalen Member (="Sticky Keep Member") of the Vikinghøgda Formation. ^[2]

Paleobiota

Fossiliferous layers of the Vardebukta Formation are concentrated to the uppermost part of the Urnetoppen Member (Brevassfjellet Myalina beds). These Dienerian aged beds have yielded the bivalves Myalina and Anodontophora , crinoids, conodonts, numerous isolated fish remains, and trace fossils. ^{[2] [3] [5]}

Fish

The isolated fish teeth of bony and cartilaginous fishes have been described from the Brevassfjellet Myalina Bed (upper Urnetoppen Member of the Vardebukta Formation) of Hyrnefjellet, Hornsund. ^{[2] [3] [6]} The bony fish teeth are mostly tentatively referred to Saurichthys sp. ^[7]

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.

Chondrichthyes of the Vardebukta Formation
Taxon / Genus	Species	Subunit	Notes	Images
Acrodus	A. spitzbergensis [2] [3]	Brevassfjellet Myalina Bed	An acrodontid hybodontiform shark. Only known from isolated teeth	Hybodus
Hybodus	H. microdus [2] [3]	Brevassfjellet Myalina Bed	A hybodontid hybodontiform shark. Only known from isolated teeth
	H. sasseniensis [2] [3]	Brevassfjellet Myalina Bed	A hybodontid hybodontiform shark. Only known from isolated teeth
	H. sp. [3]	Brevassfjellet Myalina Bed	A hybodontid hybodontiform shark. Only known from isolated teeth
Lissodus	L. angulatus [3]	Brevassfjellet Myalina Bed	A lonchidiid hybodontiform shark (previously referred to as Polyacrodus angulatus [2] )
Palaeobates [8]	P. sp.	Brevassfjellet Myalina Bed	An acrodontid hybodontiform shark. Only known from isolated teeth
Edestidae [2]	Gen. et sp. indet.	Brevassfjellet Myalina Bed	A eugeneodont holocephalian. Only known from two incomplete teeth

See also

• List of fossiliferous stratigraphic units in Norway

References

1. Vardebukta Formation at Fossilworks.org
2. Birkenmajer, Krzysztof; Jerzmańska, Anna (1979). "Lower Triassic shark and other fish teeth from Hornsund, South Spitsbergen". In K. Birkenmajer (ed.). Results of the Polish Spitsbergen Expeditions, Part 10. Studia Geologica Polonica 60. pp. 7–38.
3. Błażejowski, Błażej (2004). "Shark teeth from the Lower Triassic of Spitsbergen and their histology" (PDF). Polish Polar Research. 25 (2): 153–167.
4. Mørk, Atle; Elvebakk, Geir; Forsberg, Arne W.; Hounslow., Mark W.; Nakrem., Hans Arne; Vigran, Jorunn Os; Weitschat, Wolfgang (1999). "The type section of the Vikinghøgda Formation: a new Lower Triassic unit in central and eastern Svalbard" . Polar Research. 18 (1): 51–82. Bibcode:1999PolRe..18...51M. doi:10.1111/j.1751-8369.1999.tb00277.x. ISSN   0800-0395.
5. Salamon, Mariusz; Gorzelak, Przemysław; Hanken, Nils-Martin; Riise, Henrik Erevik; Ferré, Bruno (2015). "Crinoids from Svalbard in the aftermath of the end−Permian mass extinction" (PDF). Polish Polar Research. 36 (3): 225–238. doi:10.1515/popore-2015-0015. S2CID   130751392.
6. Brinkmann, Winand; Romano, Carlo; Bucher, Hugo; Ware, David; Jenks, Jim (2010). "Palaeobiogeography and stratigraphy of advanced gnathostomian fishes (Chondrichthyes and Osteichthyes) in the Early Triassic and from selected Anisian localities (Report 1863–2009)" (PDF). Zentralblatt für Geologie und Paläontologie, Teil II. 2009: 765–812..
7. Błażejowski, Błażej; Duffin, Christopher J.; Gieszcz, Piotr; Małkowski, Krzysztof; Binkowski, Marcin; Walcak, Michał; McDonald, Samuel; Withers, Philip J (2013). "Saurichthys (Pisces, Actinopterygii) teeth from the Lower Triassic of Spitsbergen, with comments on their stable isotope composition (δ¹³C and δ¹⁸O) and X−ray microtomography" (PDF). Polish Polar Research. 34 (1): 23–38. doi:10.2478/popore-2013-0007.
8. Stensiö, Erik (1918). "Notes on some fish remains collected at Hornsund by the Norwegian Spitzbergen expedition in 1917". Norsk Geologisk Tidsskrift. 5 (1): 75–78..