Skip to content

August 28, 2016 Weekly Geology Guess

August 28, 2016
Greetings from the Bluff Park   Porch, way up yonder on Shades Mountain (1,109′) in Alabama:

My discussion on Alabama Geology will continue with the Geologic Time Scale or the Geologic Column and the critters that abide within each pigeon holes.

As with most sciences, especially natural sciences, we love to pigeon hole our data.  Most of the pigeon holes have scientific merit and accuracy.  With the Geologic Time Scale we start with the oldest layers and work upward to the youngest layers.

For some of you this will be new, novel, and maybe heretical.

Expedition Earth: Geological time scale
vonian Period

The Devonian Period

The period is named after Devon, a county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found distributed throughout the county was eventually resolved by the defining of the Devonian period in the geological timescale.

Note:  As a geologist we usually do not talk in number of years but in periods, epochs, and eras.

“The Devil is in the Detail”

Not only with each period do we have unique animal and critter assemblages, geography, but also some type of plate tectonics or mountain building is going on.

“The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 419.2 Mya (million years ago), to the beginning of the Carboniferous Period, about 358.9.

Discussion from Wikipedia.

Climate:    “The Devonian was a relatively warm period, and probably lacked any glaciers..”


Paleogeography:    “The Devonian period was a time of great tectonic activity, as Euramerica and Gondwana drew closer together.”  The North American continent was a lively place during the Devonian.  R

    Tectonics:    “In addition to global patterns of change, many important regional activities also occurred. The continents of North America and Europe collided, resulting in massive granite intrusions and the raising of the Appalachian Mountains of eastern North America. Vigorous erosion of these newly uplifted mountains yielded great volumes of sediment, which were deposited in vast lowlands and shallow seas nearby.”

Marine Critters:     bryozoa, brachiopods, hederelloids, microconchidscorals,  “First Sharks”, placoderms, first ammonite mollusks, Trilobites, terrestrial arthropods, Free-sporing vascular plants began to spread across dry land, forming extensive forests.

>    As some of you will notice, as we go up the geologic column the more complex and numerous life becomes.

>    The Devonian Period, Age of Fishes.

Most of the attached images are of Devonian Placoderms and Sharks. Most shark parts are made up of cartilage.  The bony Placoderm heads fossilized more frequently.  R

Alabama Devonian Paleontology and Geology:    “The Devonian is not well represented in Alabama rocks, as at least some of the state was above sea level and subject to erosion. However, a stretch of Devonian rocks called the Frog Mountain Sandstone occurs in eastern Alabama. Formed nearshore in a marine environment, these rocks are reported to contain the first fragmentary traces of land plants in Alabama. Dark-colored marine rocks in northern Alabama (known as the Chattanooga Shale) show that the sea covering most of the state in the Late Devonian contained large areas of deeper, oxygen-poor water. Few organisms could tolerate these conditions. Fossils from these rocks are limited primarily to plant fragments and the remains of animals that swam above the deep, oxygen-starved waters.”  The Paleontology Portal


As with most of my weekly fores into geology, with each topic I could write many papers and dissertations.

Note:  I have intentionally reduced the amount of linked graphics in this email due to the amount of space required and trying to untangle everything the following week has been a mess.


References include:

–    Wikipedia


Editors Note:  It is the intent of this site to keep this discussion as simple as possible, so as to educate the interested general public and not to discuss with the geology crowd the latest geologic theories and nuances.  Thanks, R


“No copyright infringement intended.
The rights belong to their respective owners”
Copyright Disclaimer: Under Section 107 of the Copyright Act 1976, allowance is made for “fair use” for purposes such as criticism, comment, news reporting, teaching, scholarship, and research. Fair use is a use permitted by copyright statute that might otherwise be infringing. Non-profit, educational or personal use tips the balance in favor of fair use.


Author’s Request:  If you see any pictures that you know the source and photographer, let me know immediately.  Thanks!  R

Images have been searched by TinEye Reverse Image Search.


Next time we will venture into the Mississippian Period.


Enjoy the adventure!



Devonian, Late, 390 MYA Map. www.scoles

Devonian, Late, 390 MYA Paleogeography. http://www.scoles

Devonian Arored Fish-2, Dunkleosteus Skull. 03-03-2008. Sam Noble Museum

Devonian Armored Fish-2, Dunkleosteus Skull. 03-03-2008. Sam Noble Museum

Devonian Feeding Frenzy.

Devonian Feeding Frenzy. Dunkleosteus and Devonian Sharks (Anvil & Cladoselachida.)

Devonian Fish, shield, Zanaspis pagei. Turin Hill, Scotland.

Devonian Shield Fish, Zanaspis pagei. Turin Hill, Scotland.

Devonian Jawless Fish, headshield, Stensiopelta, Ukraine.  by Arthur Israel.

Devonian Jawless Fish, headshield, Stensiopelta, Ukraine. by Arthur Israel.


Devonian shark, Cladosalechetyleri1. by unknown

Devonian Shark, Cladoselachida. Public Domain

Devonian Shark, Cladoselachida. Public Domain

Devonian, Anvil Shark. by tumblr_mrccve

Devonian, Anvil Shark. by tumblr_mrccve

Devonian, Anvil Shark. Stethacanthus. paleopedia.

Devonian, Anvil Shark. Stethacanthus. paleopedia.

Devonian. Buzz Saw Shark,   Helicoprion Dimitri Bogdanov-2.

Devonian. Buzz Saw Shark, Helicoprion Dimitri Bogdanov-2. This one puzzled the Paleontologists for decades.

No comments yet

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: