Just wanted to let you know that the Statemap 2014-15 field mapping project has resulted in the publication of three new geologic maps. These are the Parma, Prim, and Greers Ferry quadrangles. Reduced images are posted below. These should be available as .pdfs on our website in the near future. I’ll keep you posted!
Greers Ferry Quadrangle
Also, I would like to thank the many people who helped with data collection in the field this year, without whom this project would have been impossible.
Andy Haner Danny Rains
Angela Chandler Stefanie Domrois
Doug Hanson Ty Johnson
Now it’s off to the Brownsville quad for next year!
Dye tracing is a tool commonly used by geologists to monitor how water moves through the ground. The above picture is from a study the Arkansas Geological Survey conducted for local residents in Izard County, Arkansas. Dye was added to water to track the path of farm runoff entering the groundwater through a sinkhole.
The test consists of pouring brightly colored, non-toxic dye into water before it enters the ground. Charcoal packets, capable of detecting low concentrations of the dye, are placed in nearby springs and wells. After some time has passed, the packets are analyzed to see where the water and dye travelled after soaking into the ground.
Because the earth is often their laboratory, geoscientists have to come up with creative approaches to studying inaccessible places. Besides, there’s just something satisfying about dyeing large quantities of water bright colors.
Pictured above is a weathering style called honeycomb weathering. Honeycomb is a type of differential weathering that produces a Swiss cheese appearance on the rock’s surface that can be quite striking. This example is from a sandstone outcrop (Prairie Grove member) at Devil’s Den State Park in northwest Arkansas.
Honeycomb weathering has been observed in many rock types, from igneous to sedimentary, forming in wet and dry environments. It has even been noted in man-made structures. Despite being common, the causes of honeycomb weathering are poorly understood. Some studies have linked its formation to exposure to salt in coastal regions, but that doesn’t explain its occurrence in north Arkansas.
In this instance, some clever bats have taken advantage of one of the pits in the rock and are using it as a sleeping shelter.
For more views of honeycomb weathering click here.
The features that crisscross the surface of the sandstone pictured above are deformation bands. They are micro faults that form where the bedrock is under strain. They typically develop near larger faults and the orientation of the bands is determined by the orientation of the stresses acting on the rock.
The grains along deformation bands have been crushed, rotated, and reorganized. The resultant bands are harder and less permeable than the rock they formed in, which causes them to stand in relief when the rock weathers.
Geologists look for deformation bands as indicators that a fault may be nearby. This photo was taken in Van Buren County, Arkansas on the downthrown block of a normal fault.
Above is the fossil remains of a marine organism called a conical nautiloid. These were common in the shallow sea that covered Arkansas during much of the Paleozoic era 540 to 250 million years ago. This one was collected from shale of the Pitkin Formation in pieces over a period of years as it weathered slowly out of the outcrop.
Conical nautiloids are extinct now, but they are the evolutionary forerunner of the sleeker, more deft coiled nautiloids that thrive in the ocean today. They were marine predators, akin to squid, except that they had a shell. They used their shells for protection, buoyancy, and as a means of propelling themselves through the water by squeezing a stream of water out of the empty chambers like a jet.
It’s common to find conical nautiloid fossils that are smaller than a pinky finger; however, some have been unearthed in Arkansas that were as long as 8 feet.