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Jeremie Lee
Geol 212
fossil paper
P.I.
12 September, 2012
Late Devonian Formations and Their Fossils of Utah, Idaho, and Montana.
Early Devonian rocks in Idaho, Montana, and Utah are practically nonexistent. The area was
above sea level during this time, consequentially deposits have eroded away. Later Devonian
rocks in Idaho, Montana, and Utah are mostly shallow to moderate-depth marine sediments.
(Figure 1.1North America during the late
Devonian. Taken from, sciencedirect.com)
There are a handful of formations in
the area representing the Devonian. They are the Jefferson, the Three Forks, the Water Canyon,
Darby, and Milligen formations. With the Three Forks and the Jefferson formations being the
most productive (Link).
The Jefferson formation of the late Devonian is a well developed reef in east-central
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Idaho. There are many fossils that are found in this formation. The colonial rugose coral, which
has a shell made of calcite, making it easy to fossilize. Tabulate corals, which are similar in
appearance to honeycomb. They also have an exoskeleton made of calcite.
(Figure 2.1 Tabulate corals. Taken from, http://www.fallsoftheohio.org/Tabulate_Corals.html)
(Figure 3.1 Devonain Brachiopod. Taken from, uky.edu)
Gastropods from the phylum molluscsa, more commonly known as snails or slugs. A sponge
species Hormospongia. Brachiopods, marine animals that have hard shells that open like a valve.
Last, Stromatoporoids reef-forming invertebrates. These species are common among the
Jefferson Formation (Isaacson).
(Figure 4.1 Stromatoproids. taken from, inyo.coffeecup.com)
The Three Forks
formation in the late
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Devonian is a fossiliferous shale. The formation contains Brachiopods, hard shelled animals that
open like a valve. Along with Nautiloids, which were the main predatory animals of the late
Devonian. Also Nautaloids have a large diversity of shell shapes and forms.
(Figure 5.1 Nautaloids. Taken from, rationalskepticism.org)
Ammonites, also found in the Three Forks formation are marine invertebrates with a spiral
shaped shell. Ammonites and Nautiloids are fast moving invertebrates with well developed
sensory organs (Link).
(Figure 6.1Ammonites. Taken from,
thejournal.ie)
The Water Canyon formation near Bear lake Idaho is a dolomatic sandstone. It was
named after a tributary of the Green Canyon near Logan Utah. This formation is home to
Eocrinoids an extinct class of echinoderms.
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(Figure 7.1 Eocrinoid. Taken from, fossilscapes.com)
Trilobites are also found, they form one of the earliest known groups of Arthropods. Most
Trilobites died out during the late Devonian. They were one of the most successful of the early
animals (Link).
(Figure 8.1 Trilobite. Taken from, facweb.bhc.edu)
The Darby formation is a Dolomite Shale found North and West of the Tetons. During
the late Devonian the formation produced unidentifiable Gastropods. Gastropods are commonly
known as snails and slugs.
(Figure 9.1 Devonain Gastropod. Taken from,
louisvillefossils.blogspot.com)
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The Milligen formation of the late Devonian appears near Ketchum Idaho, below the
Wood River formation. The formation during the late Devonian produced Brachiopods. Hard
shelled animals with valves (Link).
(Figure 10.1 Brachiopods. Taken from, britannica.com )
In Idaho, Montana, and Utah the late Devonian was home to a plethora of marine
animals. Some of which were the most sophisticated of their kind. After the Devonian sea levels
begin to regress, taking all of the fauna living within its depths with it.
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Work Cited
Link, Paul. "fossils in Idaho." Digatal Atlas of Idahon.pag. Digital Atlas of Idaho. Web. 12 Sep
2012. <http://imnh.isu.edu/digitalatlas/geo/fossils/fossils.htm>.
Springer, Dale. "The Devonian in Idaho, Utah, and Montana, US." The Paleontology Portal.
N.p., 05/21/2006. Web. 12 Sep 2012.
Isaacson, Peter. LATE DEVONIAN SHELLY FOSSILS FROM THE JEFFERSON FORMATION,
GRANDVIEW CANYON, EAST-CENTRAL IDAHO. Diss. Web.
<https://gsa.confex.com/gsa/2012AM/finalprogram/abstract_213409.htm>.