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July 31, 2016 Weekly Geology Guess

July 31, 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
Minerals and Rocks – The Good Life from the Ground
“If it ain’t grown, it has to be mined”


Alabama Geological Column

Alabama Pre-Cambrian Rocks are the oldest in the state and are generally metamorphosed.  This also includes our igneous intrusives.  Very little, if any, life forms exist in these rocks, probably due to the heat and pressure involved with the metamorphism.

We will now enter the land of the Welch Cambria (tribe).

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 critter assemblages but also some type of plate tectonics or mountain building going on.


Cambrian Period

“the Cambrian Period began about 541 to 485 million years ago (Ma), when hard-shelled creatures first appeared in abundance”  Wikipedia

With the Cambrian period we have the appearance of the first hard shelled animals in relatively warm shallow seas with polar ice was absent for much of the period along with the break up of the supercontinent Pannotia.

>>>>>  If you enjoy puzzles and mysteries come and dive into the geologic swimming pool that has no end, the water is fine.

Alabama Cambrian Period

Alabama Cambrian Period rocks include the Ketona Dolomite, Conasauga Formation, to name a few.

“During the Cambrian, the land that is now Alabama lay south of the Earth’s equator along the edge of the Iapetus Ocean. Rising sea levels during the Late Cambrian produced a thick sequence of sedimentary rocks that contain a smattering of marine life, including fossils of trilobites and brachiopods. Although not shown on this map, rocks formed from these marine sediments can be found across parts of northern Alabama.”

Cambrian Fossils

Show below are a few representative fossils and sketches of Cambrian fossils.
“Chordates are animals possessing a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail for at least some period of their life cycles.”  Chordate – Wikipedia, the free encyclopedia

“Trilobites (pronunciation: /ˈtrləˌbt, ˈtrɪ, l/;[2][3] meaning “three lobes”) are a fossil group of extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period (521 million years ago), and they flourished throughout the lower Paleozoic era before beginning a drawn-out decline to extinction when, during the Devonian, all trilobite orders except the Proetids died out. Trilobites finally disappeared in the mass extinction at the end of the Permian about 250 million years ago. The trilobites were among the most successful of all early animals, roaming the oceans for over 270 million years.[4]”


“Stromatolites (/strˈmætəlts, strə/[1][2]) or stromatoliths (from Greek στρώμα, strōma, mattress, bed, stratum, and λίθος, lithos, rock) are layered bio-chemical accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms (microbial mats) of microorganisms, especially cyanobacteria.[3] Fossilized stromatolites provide ancient records of life on Earth by these remains, some of which date from more than 3.5 billion years ago”  Some are still with us in Sharks Bay, Australia.

“Brachiopods, phylum Brachiopoda, are marine animals that have hard “valves” (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection.”  One group has survived until today, lingula.

“Dickinsonia is an iconic fossil of the Ediacaran biota. It (roughly) resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth is consistent with a bilaterian affinity,[3] though some have suggested that it belongs to the fungi, or even an “extinct kingdom“.

And some are just ????.

“The Devil is in the Detail”

This is what is so exciting about geological science.  It is like an endless mystery movie.


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 Ordovician Period.


Enjoy the adventure!





PS:  I will be on family vacation from August 5 to August 12, 2016, so, pending body-mind-spirit, there may or may not be a weekly Geologic Guess

Randall McDaniel, PG
“Your Rock Doctor”

Cambrian diorama.

Cambrian diorama.

Cambrian - Middle, Pikaia-chordate, 12-08-2007. by Nobu Tamura.

Cambrian – Middle, Pikaia-chordate, 12-08-2007. by Nobu Tamura.

Cambrian Trilobites. By John Alan Elson - httpwww.3dham.com3dtribcol, GFDL, httpscommons.wikimedia.orgwindex.phpcurid=17847332

Cambrian Trilobites. By John Alan Elson – httpwww.3dham.com3dtribcol, GFDL, httpscommons.wikimedia.orgwindex.phpcurid=17847332

Cambrian, Trilobite, Ogygopsis klotzi. 500mya. from everystockphoto

Cambrian, Trilobite, Ogygopsis klotzi. 500mya. from everystockphoto

Cambrian, Algae.

Cambrian, Algae.

Cambrian Stromatolites. Pika Formation (Middle Cambrian) near Helen Lake, Banff National Park, Canada, 08-05-2009. Wilson44691

Cambrian Stromatolites. Pika Formation (Middle Cambrian) near Helen Lake, Banff National Park, Canada, 08-05-2009. Wilson44691

Cambrian, brachiopod.Tucson, US.

Cambrian, brachiopod.Tucson, US.

Cambrian, DickinsoniaCostata. from zmescience

Cambrian, DickinsoniaCostata. from zmescience

Cambrian critter.

Cambrian critter.

Cambrian critter.

Cambrian critter.

AL Geo. Map, Valley and Ridge

Alabama Geologic Map, Valley and Ridge Physiographic Province

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