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.
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.
Fossil content Vertebrates Acanthodians Acanthodians of the Gravel Point Formation Genus Species Presence Material Notes Images GyracanthusG. sp.South Point (Gravel Point), Little Traverse Bay, Charlevoix County.A single specimen (UMMP 1329). 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.A single specimen (UMMP 14370). An onychodontiform.
Placoderms Placoderms of the Gravel Point Formation Genus Species Presence Material Notes Images HolonemiidSouth Point (Gravel Point), Little Traverse Bay, Charlevoix County.A single specimen (UMMP 3129).
Invertebrates Several species of ostracods, an unidentified arthropod 'hook', crinoid columnals and several species of polychaetes and scolecodonts are known from the formation.
Brachiopods Brachiopods of the Gravel Point Formation Genus Species Presence Material Notes ImagesAtrypaA. corrugataDouvillinaD. sp.Lower part of the formation.2 specimens.HeteralosiaH. sp. B2 pedicle valves.LeptalosiaL. radicansAlso found in the Norway Point, Alpena, Four Mile Dam, Genshaw, Arkona and Hungry Hollow formations.LongispinaL. emmetensisAlso found in the Alpena Limestone and Four Mile Dam Formation.MucrospiriferM. latusA spiriferid.M. sp.A spiriferid.OligorhachisO. oligorhachisAlso found in the Four Mile Dam Formation.OrthopleuraO. sp. A"Large Atrypa zone".One specimen (U.S.N.M. no. 124258).O. sp. B"Upper Blue shale".One specimen (U.S.N.M. no. 124280).PentamerellaP. aftonensisGorbut Member.P. alpenensisAlso found in the Alpena Limestone and Four Mile Dam Formation.P. sp. DA small collection of large shells (the largest being 38 millimeters).PholidostrophiaP. geniculataAlso found in the Alpena, Widder and Hungry Hollow formations.PseudoatrypaP. keslingiSchuchertellaS. anomalaPossibly also found in the Four Mile Dam Formation.StrophodontaS. costataA strophomenid.S. cf. S. eroticaA strophomenid.S. erraticaAlso found in the Alpena Limestone and Four Mile Dam Formation.S. fissicostaUpper part of the formation.Also found in the Four Mile Dam Formation.S. nanusAlso found in the Alpena Limestone and Four Mile Dam Formation.S. titan titanAlso known from the Alpena Limestone.TruncalosiaT. gibbosaAlso found in the Alpena, Genshaw, Norway Point, Petoskey and Potter Farm formations, the Arkona Shale and the Hamilton Group.TylothyrisT. subvaricosaAlso 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 FenestellapolyporeF. magnifica A fenestellid.
Cnidarians Cnidarians of the Gravel Point Formation Genus Species Presence Material Notes ImagesAulocystisA. alectiformisAlso found in the Alpena Limestone.A. fenestrata6 specimens.Also found in the Alpena Limestone.AuloporaA. confertaAlso found in the Bell, Ferron Point, Genshaw, Alpena, Four Mile Dam, Potter Farm, Petoskey and Hungry Hollow formations.A. socialisUpper part of the formation. FavositesF. mammilatus A tabulate coral. PachyphragmaP. concentricumAlso found in the Ferron Point, Four Mile Dam and Alpena formations.P. erectumAlso found in the Potter Farm and Petoskey formations.
Sponges Sponges of the Gravel Point Formation Genus Species Presence Material Notes Images ParalleloporaP. winchelli A stromatoporoid.
Tentaculitans Tentaculitans of the Gravel Point Formation Genus Species Presence Material Notes Images TentaculitesT. sp. A tentaculitid.
Trilobites
Trilobites of the Gravel Point Formation Genus Species Presence Material Notes ImagesAncyropygeA. romingeri"Longispina emmetensis zone".DechenellaD. (Basidechenella) pulchraAlso found in the Alpena Limestone and Dock Street clay of the Four Mile Dam Formation.EldredgeopsE. rana alpenensisOriginally reported as Phacops rana alpenensis. Also found in the Alpena Limestone.GreenopsG. aequituberculatusAlso found in the Norway Point and Four Mile Dam formations.G. traversensisAlso found in the Dock Street clay of the Four Mile Dam Formation.PhacopsP. rana alpenensisReassigned to the genus Eldredgeops. ProetusP. (Crassiproetus) traversensis Also found in the Four Mile Dam Formation.
Flora Algal colonies are known from the formation.
Acritarchs Acritarchs of the Gravel Point Formation Genus Species Presence Material Notes Images LophosphaeridiumL. sp. TasmanitesT. sp.
Plants Plants of the Gravel Point Formation Genus Species Presence Material Notes Images AncyrosporaA. sp. Miospores.
See also
List of fossiliferous stratigraphic units in Michigan
References