Geological formation
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]
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]
Several species of ostracods , an unidentified arthropod 'hook', crinoid columnals and several species of polychaetes and scolecodonts are known from the formation.[ 1]
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.
Color key Notes Uncertain or tentative taxa are in small text ; crossed out taxa are discredited.
Algal colonies are known from the formation.[ 1]
^ a b c d e f g h i j k l m n o p q r Mohan, Joseph (November 2013). "A Paleoenvironmental Analysis of the Middle Devonian Gravel Point Formation, Western Michigan" . The Professional Geologist . 50 (6): 12–16. ^ a b c d e f 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 . ^ a b c d e f g h i j k l m n o p q r s t 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 . ^ 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 . ^ a b c d e f 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 . ^ a b c d e f g Stumm, Erwin (1953). "Trilobites of the Devonian Traverse Group of Michigan" (PDF) . University of Michigan Press - Museum of Paleontology .