Monthly Archives: January 2018

Geopic of the week: Skolithos

 

st. pete skolithos

Skolithos is a common type of trace fossil that has been found in rocks as old as 541 million years.  Trace fossils are not the fossilized remains of organisms but rather the burrows, footprints, and other structures that resulted from the animal’s activities.

In the case of skolithos, it’s widely believed that a vermiform (resembling a worm) animal created the straight, vertical, tube structures.  These worm-like critters probably lived by filtering plankton from the turbulent water of a shallow marine environment.  The vertical tubes may have been a dwelling place to retreat to, though their specific purpose is not known.

In the above picture, captured in north central Arkansas, a sandstone has weathered to reveal skolithos traces permeating the approximately 460 million year old rock.  This example is from an exposure of the St. Peter Formation, Buffalo National River Park, Marion County, Arkansas.

To see more views of skolithos traces from Arkansas click here

New Publication: Geologic Road Guide to Highway 10

 

01-Overview

The Geologic Road Guide to Arkansas State Highway 10, a Geotour of the Southern Arkoma Basin Fold Belt and Related Ouachita Mountain Tectonic Zones by Drs. Richard Cohoon (Emeritus), Jason Patton (Associate), and Victor Vere (Emeritus), Professors of Geology at Arkansas Tech University, is now available for download on the Arkansas Geological Survey’s website.  Here’s the link:

http://www.geology.ar.gov/roadside_geology_series/rgs02.htm

The route begins at Petit Roche Plaza in the River Market District of downtown Little Rock. “Petit Roche” was the name given to the first rock outcrop early explorers encountered on their way up the Arkansas River.  It is near this outcrop that the eastern end of Arkansas State Highway 10 (AR-10) is now located.  From here, you will tour the 139-mile length of AR-10 to its western terminus at the Oklahoma state line, just past Hackett.  This route traverses a beautiful and geologically diverse cross section through the mountains of western Arkansas.  The stretch from Ola to Hackett is designated as an Arkansas Scenic Byway.

An overview of the physiography of Arkansas, the concept of geologic time, and the rock formations and structural regions encountered along AR-10 introduce the reader to the detailed Road Guides that follow.  The Road Guides describe the rock outcrops and geologic features along particular sections of the route.  They contain many wonderful color photographs and color-coded geologic maps to help travelers understand the landscape passing outside their windows.  Travelers are encouraged to get out of their vehicle at several places to have a look at the rocks, perhaps gaining a new appreciation of their significance.  An illustrated glossary defines words and concepts that may be unfamiliar to those without an earth science background.  Appendices direct the traveler to several interesting side trips just off the main route and detail the characteristics of the gas and coal resources in the Arkoma Basin.

image

This Geotour is written to be of interest to the general public, to students of geology, and to professional geologists who want to gain a more in-depth understanding of this beautiful and geologically complex region.  So the next time you’re thinking of taking a scenic drive through the mountains of western Arkansas, consider traveling AR-10.  And don’t forget to take along the Geologic Road Guide to make your drive more enjoyable and informative.

Richard Hutto

Geo-pic of the week: Pyrite

pyrite

(FOV approx. 3 mm, photo by Stephen Stuart)

Pyrite, also known as Iron Pyrite (FeS2), is the most common sulfide mineral. Its most frequent crystal structure is cubic, as seen in the picture above. It also forms octahedral (8 sided) and dodecahedral (12 sided) structures. Its brassy-yellow color and metallic luster can sometimes cause it to be mistaken for gold, hence the nickname “fool’s gold”. While it may look like gold, it is much lighter and harder. Typically pyrite cannot be scratched with a knife.

Pyrite is found in many counties in Arkansas. It is used in the production of sulfuric acid, although its use is declining. The primary value of this mineral currently is as a collectible specimen. Individual crystals are commonly found up to 1 inch in diameter.