Geopic of the week: Travertine falls

Travertine Fall over St. Peter ss, Searcy County

Pictured above is a travertine falls.  It looks like a waterfall except that, rather than being water, it’s composed of solid rock.

Travertine is made of calcite which also forms stalactites and stalagmites.  Like those familiar cave features, travertine falls form by precipitation from water; the water is flowing in a creek, over a ledge instead of dripping from a cave ceiling.  As the travertine precipitates in layer upon layer, it begins to take on the appearance of flowing rock.

Dripstone features like these only form in areas where the groundwater carries a high load of dissolved carbonate minerals.  This one was photographed in Searcy County, Arkansas, not far from the Buffalo National River, near the contact between the St. Peter and Plattin Formations.

For another view of this travertine falls click here

Geopic of the week: Breccia

Dolostone breccia (1) corrected

A Breccia is a rock made up of angular rock fragments mixed with finer sediment.  The one above was deposited about 450 million years ago (Ordovician) in a shallow sea in what is now the Ozark highlands, north of Mountain View, Arkansas.

Breccias can form by a variety of processes such as landslides, volcanic eruptions, storm events, cave and sinkhole collapses and others.  This one likely formed during a storm.  Turbulent ocean waves and currents washed fragments of marine organisms (dark gray) into calmer water where marine mud (light gray) had recently accumulated.  The turbulence ripped some of the mud up and mixed it with the organic material.

Breccias are just one of many clues, recorded in rocks, that help geologists understand how the earth has changed through time: a story that itself constantly evolves as new rock is unearthed and studied.

For more views of breccias click here

Statemap 2014-15 Update

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Hello all,

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!Parma

Parma Quadrangle

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Prim Quadrangle

Prim boulder (cannonball concretion) in Sugar Camp Creek

Greers Ferry Layout

Greers Ferry Quadrangle

Old Terrace deposit underlying Greers Ferry, AR

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.

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Andy Haner                                                        Danny Rains

 

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Angela Chandler                                                                     Stefanie Domrois

 

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Doug Hanson                                  Ty Johnson

Thanks, everyone!

 

Now it’s off to the Brownsville quad for next year!

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Richard Hutto

Geopic of the week: Dye tracing

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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.