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]
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
Bony fish
Placoderms
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
Sponges
Sponges of the Gravel Point Formation
|
Genus |
Species |
Presence
|
Material |
Notes |
Images
|
Parallelopora
|
P. winchelli
|
|
[1]
|
A stromatoporoid.
|
|
Tentaculitans
Trilobites
|
|
|
Color key
|
|
Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
|
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