Four Mile Dam Formation

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Four Mile Dam Formation
Stratigraphic range: Middle Devonian (Givetian)[1]
File:An examination of the Devonian fishes of Michigan fig-5-full.png
Vertebrate remains from the Four Mile Dam Formation.
TypeGeological formation
Unit ofTraverse Group[1]
Lithology
PrimaryLimestone
Location
RegionMichigan
CountryUnited States
Type section
Named byCooper & Warthin[2]
Year defined1941[2]

The Four Mile Dam Formation, also called the Four Mile Dam Limestone, is a geologic formation in Michigan. It preserves fossils dating back to the middle Devonian period.

File:An examination of the Devonian fishes of Michigan fig-1-full.png
Stratigraphy of the Devonian deposits of the northern part of the Lower Peninsula of Michigan, showing the Four Mile Dam Formation[1]

Fossil content

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Vertebrates

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Acanthodians

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Acanthodians reported from the Four Mile Dam Formation
Genus Species Presence Material Notes Images
'Acanthodii' Unidentified "Two partial fin spines (JS 120, JS 121)".[1] "Distinct from named acanthodians (Gyracanthus, Machaeracanthus, and Oracanthus) and chondrichthyans (Tamiobatis and Acondylacanthus) reported from Michigan".[1]
File:An examination of the Devonian fishes of Michigan fig-5-a.png

Conodonts

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Conodonts reported from the Four Mile Dam Formation
Genus Species Presence Material Notes Images
Acodina A. formosa [3] Also found in the Detroit River, Traverse, Dundee, Bell, Alpena and Norway Point formations.
Belodella B. devonicus [3] Also found in the Detroit River, Traverse, Antrim, Alpena and Norway Point formations.
Icriodus I. latericrescens latericrescens [3] Also found in the Traverse, Bell, Ferron Point, Genshaw, Newton Creek, Alpena, Norway Point, Potter Farm and Thunder Bay formations.
Ozarkodina O. willsi [3] Also found in the Detroit River, Traverse, Antrim, Dundee, Alpena and Norway Point formations.
Polygnathus P. varcus [3] Also found in the Traverse, Antrim, Alpena, Norway Point and Thunder Bay formations.

Placoderms

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Placoderms reported from the Four Mile Dam Formation
Genus Species Presence Material Notes Images
?Macropetalichthys ?M. sp. "A partial head shield (32M)".[1] A petalichthyid.
File:An examination of the Devonian fishes of Michigan fig-8-a.png
?Mylostoma ?M. sp. 39 specimens, including potential juveniles.[1]
File:An examination of the Devonian fishes of Michigan fig-5-b.png
'Placodermi' Unidentified "One specimen of an armour plate (JS 4)".[1]
File:An examination of the Devonian fishes of Michigan fig-5-c.png
Protitanichthys P. rockportensis "One specimen of an armor fragment (JS 101)".[1] A coccosteid.

Invertebrates

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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.

Brachiopods

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Brachiopods reported from the Four Mile Dam Formation
Genus Species Presence Material Notes Images
Douvillina D. distans Four Mile Dam, Thunder Bay River, Alpena County, Michigan.[4] Also found in the Hungry Hollow Formation and Logansport Formation.
Leptalosia L. radicans Four Mile Dam, Thunder Bay River, Alpena County, Michigan.[4] Also found in the Norway Point, Gravel Point, Alpena and Genshaw formations.
Longispina L. emmetensis Dock Street clay member.[4] Also found in the Alpena Limestone and Gravel Point Formation.
Megastrophia M. gibbosa Four Mile Dam, Thunder Bay River, Alpena County, Michigan.[4] Also found in the Hungry Hollow Formation and Logansport Formation.
Oligorhachis O. oligorhachis Four Mile Dam, Thunder Bay River, Alpena County, Michigan.[4] Also found in the Gravel Point Formation.
Pentamerella P. alpenensis Dock Street clay member.[4] Also found in the Alpena Limestone and Gravel Point Formation.
P. sp. C Dock Street clay.[4] A complete specimen.[4]
Protoleptostrophia P. lirella Dock Street clay member.[4] Also found in the Norway Point Formation and Alpena Limestone.
Schuchertella S. anomala Possibly the Dock Street clay member.[4] Also found in the Gravel Point Formation.
S. sp. Four Mile Dam, Thunder Bay River, Alpena County, Michigan.[4]
Spinulicosta S. mutocosta Four Mile Dam, Thunder Bay River, Alpena County, Michigan.[4] Also found in the Bell, Rockport Quarry, Ferron Point, Beebe School, Thunder Bay and Potter Farm formations.
Strophodonta S. erratica Dock Street clay member.[4] Also found in the Alpena Limestone and Gravel Point Formation.
S. fissicosta Dock Street clay member.[4] Also found in the upper Gravel Point Formation.
S. nanus Dock Street clay member.[4] Also found in the Alpena Limestone and Gravel Point Formation.
S. paula Dock Street clay member.[4] Also found in the Alpena Limestone.
S. sp. B Dock Street clay member and overlying crystalline limestone beds.[4] Several specimens.[4]
Rhipidomella R. penelope traversensis Thunder Bay River, Alpena County, Michigan.[4]

Corals

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Corals reported from the Four Mile Dam Formation
Genus Species Presence Material Notes Images
Aulocystis A. cooperi [5] Also found in the Plum Brook shale, Silica shale and Potter Farm Formation.
A. jacksoni Dock Street clay member.[5] Also found in the Silica Shale, Ferron Point Formation, Petoskey Formation, Hungry Hollow Formation, Widder Shale, Wanakah shale and Centerfield Limestone.
Aulopora A. conferta [5] Also found in the Bell, Ferron Point, Gravel Point, Genshaw, Alpena, Potter Farm, Petoskey and Hungry Hollow formations.
A. gregaria [5] Also found in the Genshaw Formation, Alpena Limestone and Petoskey Formation.
Pachyphragma P. concentricum Dock Street clay member.[5] Also found in the Ferron Point Formation, Gravel Point Formation and Alpena Limestone.

Gastropods

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Gastropods reported from the Four Mile Dam Formation
Genus Species Presence Material Notes Images
Anematina A. conica Upper limestone unit.[2] An elasmonematid.
A. mellaria Upper limestone unit.[2] An elasmonematid, very rare in the Four Mile Dam Limestone.
Bembexia B. (Genuspira) nodosa Upper limestone unit.[2] About 35 specimens.[2] An eotomariid and the most abundant gastropod in the formation.
Dictyobembix D. bella Upper limestone unit.[2] 5 specimens.[2] An eotomariid.
Mourlonia M. lirata Upper limestone unit.[2] An eotomariid.
Murchisonia M. (Murchisonia) subulata Upper limestone unit.[2] A murchisoniid, extremely rare in the formation.
Naticopsis N. sp. Upper limestone unit.[2] A neritopsid, extremely rare in the formation.
Palaeoscurria? P.? sp. Upper limestone unit.[2] 3 poorly preserved ventral molds.[2] A metoptomatid.
Platyceras P. (Platyceras) bartlettense Dock Street Clay Member.[2] A platyceratid.
P. (Euthyrachis) indianense Dock Street Clay Member.[2] A platyceratid.
P. (Orthonychia) variabilis Upper limestone unit.[2] A platyceratid.
Pseudozygopleuridae? Genus A Genus A sp. A Upper limestone unit.[2] Relatively numerous steinkerns.[2]
Pseudozygopleuridae? Genus B Genus B sp. B Upper limestone unit.[2] One very poorly preserved steinkern with a few small shell patches (YPM 23684).[2]
Spiroscala S. sp. Upper limestone unit.[2] One specimen (UMMP 47377).[2] An eotomariid.
Straparollus S. (Philoxene) sp. Upper limestone unit.[2] 3 poorly preserved specimens.[2] An euomphalid.
Trepospira T. (Angyomphalus) bella Upper limestone unit.[2] A raphistomatid, very rare in the Four Mile Dam Limestone.
Turbinilopsis T. anacarina Upper limestone unit.[2] Abundant specimens.[2] An anomphalid.

Sponges

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Sponges reported from the Four Mile Dam Formation
Genus Species Presence Material Notes Images
Anostylostroma A. anacolumna On Thunder Bay River.[6] A stromatoporoid.

Trilobites

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Trilobites reported from the Four Mile Dam Formation
Genus Species Presence Material Notes Images
Cordania C. rara [7]
Dechenella D. (Monodechenella) macrocephala [7] Also found in the Hamilton Group.
D. (Basidechenella) rowi [7] Also known from the Hamilton Group.
Eldredgeops E. rana [7] Originally reported as Phacops rana. Also found in the Hamilton, Hungry Hollow, Widder, Plum Brook, Prout, Ten Mile Creek, Alpena, Norway Point and Gravel Point formations.
File:Phacops rana.jpg
Greenops G. aequituberculatus Dock Street clay member.[7] Also found in the Norway Point and Gravel Point formations.
G. traversensis Dock Street clay member.[7] Also found in the Gravel Point Formation.
Phacops P. rana [7] Reassigned to the genus Eldredgeops.
Proetus P. (Crassiproetus) traversensis [7] Also known from the Gravel Point Formation.

See also

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References

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