Gravel Point Formation

The Gravel Point Formation is a geologic formation in western Michigan, United States. It preserves fossils dating back to the middle Devonian period and correlates with the Long Lake Limestone and Alpena Limestone.^[1]

Gravel Point Formation
Stratigraphic range: Middle Devonian (Givetian)[1] PreꞒ Ꞓ O S D C P T J K Pg N
Fossiliferous limestone from the Gravel Point Formation
Type	Geological formation
Unit of	Traverse Group
Lithology
Primary	Limestone
Location
Region	Michigan
Country	United States

Description

The Michigan Basin was a shallow marine shelf during the middle Devonian, located between 30º South and 20º North latitude in central Laurasia. According to stratigraphic and paleontological examination, the sediments of the Gravel Point Formation were deposited in a shallow lagoonal reef environment.^[1]

Fossil content

Vertebrates

Acanthodians

Acanthodians of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Gyracanthus	G. sp.	South Point (Gravel Point), Little Traverse Bay, Charlevoix County.[2]	A single specimen (UMMP 1329).[2]	A gyracanthid.

Bony fish

Bony fish of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
?Onychodus	?O. sp.	South Point (Gravel Point), Little Traverse Bay, Charlevoix County.[2]	A single specimen (UMMP 14370).[2]	An onychodontiform.

Placoderms

Placoderms of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Holonemiid		South Point (Gravel Point), Little Traverse Bay, Charlevoix County.[2]	A single specimen (UMMP 3129).[2]

Invertebrates

Several species of ostracods, an unidentified arthropod 'hook', crinoid columnals and several species of polychaetes and scolecodonts are known from the formation.^[1]

Brachiopods

Brachiopods of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Atrypa	A. corrugata		[1]
Douvillina	D. sp.	Lower part of the formation.[3]	2 specimens.[3]
Heteralosia	H. sp. B		2 pedicle valves.[3]
Leptalosia	L. radicans		[3]	Also found in the Norway Point, Alpena, Four Mile Dam, Genshaw, Arkona and Hungry Hollow formations.
Longispina	L. emmetensis		[3]	Also found in the Alpena Limestone and Four Mile Dam Formation.
Mucrospirifer	M. latus		[1]	A spiriferid.
	M. sp.		[1]	A spiriferid.
Oligorhachis	O. oligorhachis		[3]	Also found in the Four Mile Dam Formation.
Orthopleura	O. sp. A	"Large Atrypa zone".[3]	One specimen (U.S.N.M. no. 124258).[3]
	O. sp. B	"Upper Blue shale".[3]	One specimen (U.S.N.M. no. 124280).[3]
Pentamerella	P. aftonensis	Gorbut Member.[3]
	P. alpenensis		[3]	Also found in the Alpena Limestone and Four Mile Dam Formation.
	P. sp. D		A small collection of large shells (the largest being 38 millimeters).[3]
Pholidostrophia	P. geniculata		[3]	Also found in the Alpena, Widder and Hungry Hollow formations.
Pseudoatrypa	P. keslingi		[1]
Schuchertella	S. anomala		[3]	Possibly also found in the Four Mile Dam Formation.
Strophodonta	S. costata		[1]	A strophomenid.
	S. cf. S. erotica		[1]	A strophomenid.
	S. erratica		[3]	Also found in the Alpena Limestone and Four Mile Dam Formation.
	S. fissicosta	Upper part of the formation.[3]		Also found in the Four Mile Dam Formation.
	S. nanus		[3]	Also found in the Alpena Limestone and Four Mile Dam Formation.
	S. titan titan		[3]	Also known from the Alpena Limestone.
Truncalosia	T. gibbosa		[3]	Also found in the Alpena, Genshaw, Norway Point, Petoskey and Potter Farm formations, the Arkona Shale and the Hamilton Group.
Tylothyris	T. subvaricosa		[4]	Also found in the Cedar Valley, Milwaukee, Mineola, Bell, Rockport Quarry, Ferron Point, Genshaw, Alpena, Norway Point and Potter Farm formations.

Bryozoans

Bryozoans of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Fenestellapolypore	F. magnifica		[1]	A fenestellid.

Cnidarians

Cnidarians of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Aulocystis	A. alectiformis		[5]	Also found in the Alpena Limestone.
	A. fenestrata	6 specimens.[5]		Also found in the Alpena Limestone.
Aulopora	A. conferta		[5]	Also found in the Bell, Ferron Point, Genshaw, Alpena, Four Mile Dam, Potter Farm, Petoskey and Hungry Hollow formations.
	A. socialis	Upper part of the formation.[5]
Favosites	F. mammilatus		[1]	A tabulate coral.
Pachyphragma	P. concentricum		[5]	Also found in the Ferron Point, Four Mile Dam and Alpena formations.
	P. erectum		[5]	Also found in the Potter Farm and Petoskey formations.

Sponges

Sponges of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Parallelopora	P. winchelli		[1]	A stromatoporoid.

Tentaculitans

Tentaculitans of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Tentaculites	T. sp.		[1]	A tentaculitid.

Trilobites

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.

Trilobites of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Ancyropyge	A. romingeri	"Longispina emmetensis zone".[6]
Dechenella	D. (Basidechenella) pulchra		[6]	Also found in the Alpena Limestone and Dock Street clay of the Four Mile Dam Formation.
Eldredgeops	E. rana alpenensis		[6]	Originally reported as Phacops rana alpenensis. Also found in the Alpena Limestone.
Greenops	G. aequituberculatus		[6]	Also found in the Norway Point and Four Mile Dam formations.
	G. traversensis		[6]	Also found in the Dock Street clay of the Four Mile Dam Formation.
Phacops	P. rana alpenensis		[6]	Reassigned to the genus Eldredgeops.
Proetus	P. (Crassiproetus) traversensis		[6]	Also found in the Four Mile Dam Formation.

Flora

Algal colonies are known from the formation.^[1]

Acritarchs

Acritarchs of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Lophosphaeridium	L. sp.		[1]
Tasmanites	T. sp.		[1]

Plants

Plants of the Gravel Point Formation
Genus	Species	Presence	Material	Notes	Images
Ancyrospora	A. sp.		Miospores.[1]

See also

• Earth sciences portal
• Michigan portal
• Paleontology portal

• List of fossiliferous stratigraphic units in Michigan