Gravel Point Formation
Stratigraphic range:
Fossiliferous limestone from the Gravel Point Formation
TypeGeological formation
Unit ofTraverse Group
Lithology
PrimaryLimestone
Location
Region Michigan
Country United States

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

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
GenusSpeciesPresence MaterialNotesImages
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
GenusSpeciesPresence MaterialNotesImages
?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
GenusSpeciesPresence MaterialNotesImages
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
GenusSpeciesPresence MaterialNotesImages
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
GenusSpeciesPresence MaterialNotesImages
Fenestellapolypore F. magnifica [1] A fenestellid.

Cnidarians

Cnidarians of the Gravel Point Formation
GenusSpeciesPresence MaterialNotesImages
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
GenusSpeciesPresence MaterialNotesImages
Parallelopora P. winchelli [1] A stromatoporoid.

Tentaculitans

Tentaculitans of the Gravel Point Formation
GenusSpeciesPresence MaterialNotesImages
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
GenusSpeciesPresence MaterialNotesImages
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
GenusSpeciesPresence MaterialNotesImages
Lophosphaeridium L. sp. [1]
Tasmanites T. sp. [1]

Plants

Plants of the Gravel Point Formation
GenusSpeciesPresence MaterialNotesImages
Ancyrospora A. sp. Miospores.[1]

See also

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Mohan, Joseph (November 2013). "A Paleoenvironmental Analysis of the Middle Devonian Gravel Point Formation, Western Michigan". The Professional Geologist. 50 (6): 12–16.
  2. 1 2 3 4 5 6 Stack, Jack; Sallan, Lauren (2018-09-20). "An examination of the Devonian fishes of Michigan". PeerJ. 6 (2): e5636. doi:10.7717/peerj.5636. PMC 6151260. PMID 30258725. S2CID 52843222.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Imbrie, John (1959). "Brachiopods of the Traverse group (Devonian) of Michigan. Part 1, Dalmanellacea, Pentameracea, Strophomenacea, Orthotetacea, Chonetacea, and Productacea. Bulletin of the AMNH ; v. 116, article 4". hdl:2246/1258. {{cite journal}}: Cite journal requires |journal= (help)
  4. ↑ Rogers, Frederick S.; Pitrat, Charles W. (May 1987). "Distribution of Tylothyris (Brachiopoda) and its occurrence in the Traverse Group (Middle Devonian) of Michigan". Journal of Paleontology. 61 (3): 494–507. doi:10.1017/S0022336000028651. ISSN 0022-3360. S2CID 130922140.
  5. 1 2 3 4 5 6 Watkins, J. Lloyd (1959). "Middle Devonian Auloporid Corals from the Traverse Group of Michigan". Journal of Paleontology. 33 (5): 793–808. ISSN 0022-3360. JSTOR 1300915.
  6. 1 2 3 4 5 6 7 Stumm, Erwin (1953). "Trilobites of the Devonian Traverse Group of Michigan" (PDF). University of Michigan Press - Museum of Paleontology.


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