Gun River Formation Explained

Gun River Formation
Type:	Geological formation
Age:	Early Silurian (Llandovery)
Namedby:	Schuchert and Twenhofel
Year Ts:	1910
Subunits:	Lachute Member Innomée Member Sandtop Member Macgilvray Member
Underlies:	Menier Formation
Overlies:	Merrimack Formation
Thickness:	85 to 100 meters

The Gun River Formation is a geologic formation in Quebec. It preserves fossils dating back to the early Silurian period.

Description

The formation is divided into 4 members (from the base up): the Lachute, Innommée, Sandtop and Macgilvray members. The formation was deposited some 40–80 km offshore from the stable Laurentian craton, underwater at depths of 30 to 60 meters.^[1]

Fossil content

Vertebrates

Conodonts
Genus	Species	Presence	Material	Notes	Images
Anticostiodus	A. fahraeusi	Anticosti Island.^[2]
	A. boltoni	Anticosti Island.
Icriodella	I. deflecta			Probably instead belongs to the Jupiter Formation.

Invertebrates

Brachiopods
Genus	Species	Presence	Material	Notes	Images
Brachyprion		Sandtop and Macgilvray Members.		A strophomenid.
Coolinia		Sandtop and Macgilvray Members.
Fenestrirostra	F. glacialis	Lowermost part of the formation.^[3]		A rhynchonellidalso found in the Merrimack Formation.
	F. pyrrha	Lachute Member.		A rhynchonellid.
'Gotatrypa	'G. sp.	Innommée Member.
Hyattidina		Sandtop to Macgilvray Members.		An athyrid.
Joviatrypa		Uppermost Macgilvray Member.
Kulumbella	K. xacta	Upper Macgilvray Member.^[4]		A pentamerid.
Mendacella		Innommée Member.		A dalmanellid.
Meristina		Innommée Member.
Pentamerus	P. palaformis	Top of the formation (uppermost Macgilvray Member).^[5]		Also found in the Jupiter Formation.
Stegerhynchus
Stricklandia	S. gwelani	Top of the formation (Macgilvray Member).		Also found in the Jupiter Formation.
	S. sp.	Innommée Member.	A509 (7 broken valves on a slab).	Also found in the uppermost Merrimack Formation.
Sypharatrypa	S. sp.	Innommée Member.

Bryozoans
Genus	Species	Presence	Material	Notes	Images
Phaenopora	P. superba			Also found in the Becscie Formation.^[6]
Ptilodictya	P. canadensis		USNM 143039.
	P. sulcata		USNM 143039, 143050; YPM 3063/98, 3063/104.

Corals
Genus	Species	Presence	Material	Notes	Images
Acidolites	A. arctatus	^[7]		A heliolitid.
Brachyelasma
Crassilasma
Helicelasma
Palaearaea		Cap aux Goélands (Uppermost Macgilvray Member).	Small colonies.	The only rugosan coral known from the formation, also found in the Menier formation.
Paleofavosites	P. capax		Multiple colonies.^[8]	A tabulate coral.

Crinoids
Genus	Species	Presence	Material	Notes	Images
Dendrocrinus
Eumyelodactylus		Macgilvray Member.
Laurocrinus		Macgilvray Member.
Stupatocrinus		Macgilvray Member.

Sponges
Genus	Species	Presence	Material	Notes	Images
Camptodictyon				A stromatoporoid.
Clathrodictyon				A stromatoporoid.

See also

• List of fossiliferous stratigraphic units in Quebec

References

• Web site: Fossilworks: Gateway to the Paleobiology Database. ((Various Contributors to the Paleobiology Database)). 17 December 2021. 25 March 2022. https://web.archive.org/web/20220325060448/http://www.fossilworks.org/cgi-bin/bridge.pl?action=home. dead.

Notes and References

1. Copper . Paul . Long . Darrel G. F. . Jin . Jisuo . 2012 . The Early Silurian Gun River Formation of Anticosti Island, eastern Canada: A key section for the mid-Llandovery of North America . Newsletters on Stratigraphy . 45 . 3 . 263 . 10.1127/0078-0421/2012/0024 . 0078-0421.
2. Zhang . Shunxin . Barnes . Christopher R. . July 2000 . Anticostiodus, a new multielement conodont genus from the Lower Silurian, Anticosti Island, Quebec . Journal of Paleontology . en . 74 . 4 . 662–669 . 10.1666/0022-3360(2000)074<0662:AANMCG>2.0.CO;2 . 59056082 . 0022-3360.
3. Jin . Jisuo . Caldwell . W. G. E. . Copper . Paul . March 1990 . Evolution of the Early Silurian rhynchonellid brachiopod Fenestrirostra in the Anticosti Basin of Quebec . Journal of Paleontology . 64 . 2 . 214–222 . 10.1017/s0022336000018370 . 132248649 . 0022-3360.
4. Jin . Jisuo . Copper . Paul . May 1998 . Kulumbella and Microcardinalia (Chiastodoca) new subgenus, Early Silurian divaricate stricklandiid brachiopods from Anticosti Island, eastern Canada . Journal of Paleontology . 72 . 3 . 441–453 . 10.1017/s0022336000024185 . 132809506 . 0022-3360.
5. Jin . Jisuo . Copper . Paul . Late Ordovician and Early Silurian pentamerid brachiopods of Anticosti Island, Québec, Canada . Palaeontographica Canadiana.
6. Larger Cryptostome Bryozoa of the Ordovician and Silurian, Anticosti Island, Canada . SEPM Society for Sedimentary Geology . 2022-09-18 . www.jstor.org . 1300852 . en.
7. Dixon . O. A. . January 1986 . The heliolitid coral Acidolites in Ordovician–Silurian rocks of eastern Canada1 . Journal of Paleontology . en . 60 . 1 . 26–52 . 10.1017/S002233600002148X . 130759173 . 0022-3360.
8. Lee . Dong-Jin . Noble . James P. A. . July 1990 . Reproduction and life strategies in the Paleozoic tabulate coral Paleofavosites capax (Billings) . Lethaia . en . 23 . 3 . 257–272 . 10.1111/j.1502-3931.1990.tb01452.x . 0024-1164.