Tag Archives: Prim boulder

Statemap 2014-15 Update

2014-08-04 006

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: Prim boulders

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Prim boulder is a name given to curious, round, often nearly spherical sandstone boulders that are common in the area around the town of Prim in Cleburne county, Arkansas.  Though the town of Prim boasts a noteworthy abundance of these unusual specimens, they actually have been found within a 100 mile area from Newton to White county.  The one pictured here is still attached to the outcrop of sandstone:  Many are found laying around at the surface, the rock from which they came having long ago weathered away. 

Geologists believe these formed by precipitation of calcite and iron minerals from ground water.  The calcite and iron minerals precipitate in concentric bands and make that part of the sandstone more resistant to weathering so that the boulders remain after the rest of the sandstone has eroded away. 

If you are interested in seeing Prim boulders for yourself there are many on display around the community of Prim within easy sight from highway 263.  

Statemap Field Blog–Oct 7-9, 2013

2013-10-07 005

Hello all!

Well, it was good to be back in the field again after a week of “vacation” (painting my daughter’s bedroom).  The weather is really getting a lot nicer now, and the ticks have almost given up.  We’re still working on the larger tributaries to the Middle Fork, so that they will be done by the time the dry season ends.  The Middle Fork is still low enough for us to cross it easily which is good because road access on the north side of the river turned out to be very limited.

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We finished up the last two big drainages that flow south into the Middle Fork east of Shirley.  Mostly a big stack of massive-bedded, calcareous sandstone, but little sign of the shalier Cane Hill which is still prominent along the river to the west.  This might suggest that the Cane Hill is either faulted out or that the tilt of the rocks to the southeast brings the Witts Springs to a lower elevation near the large southwest-northeast trending fault just to the south along the river.  Whichever it is, we’ll need more data to determine.  We did see a good example of travertine precipitating on some of the thin-bedded calcareous sandstone.  Slightly acidic groundwater is solutioning the calcium carbonate (calcite) with which this particular sandstone is cemented.  It is then precipitated where the water seeps out of the rock, in this case along a joint.  This lets us know that the adjacent rocks are calcareous, which in turn may help us determine what formation it’s in.2013-10-08 009 

We also saw some good deformation bands, which as I’ve said in a previous post is one of the signs that a fault is nearby.  These were in float, and though I looked high and low, I couldn’t find the source.  Certainly evidence of a lot of stress in these rocks!

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2013-10-09 004The other drainage we looked at is north of Shirley and is extremely steep and badly overgrown.  The sides were so boxed in we couldn’t come down the main channel, and had to try a side branch.  We did make it down that way, but with great difficulty.  Once we got to the bottom, we could only get within about 40 feet of the Witts Springs/Cane Hill contact in the main channel, because the lower end was boxed in as well.  We usually don’t give up until we get our point, but this one was deemed impenetrable.  The break is visible in the contours, so shouldn’t be too difficult to draw in anyway.  On the way down the side branch, I spied a round rock or “Prim boulder”.  These are definitely coming out of the Witts Springs.

2013-10-09 009Also saw more deformation bands, this time way up at the top of a 40 foot massive of basal Witts Springs sandstone.  That band you see in the close-up is about 6 inches wide!  The last photo is the Cane Hill in the box canyon below the contact.  The sheer bluff of massive Witts Springs sandstone was visible on both sides above.  I was rewarded by finding a large patch of muscadines on the way out.  They continue to get sweeter each week!  Wish I could have stayed to fill a bucket, but had to make do with a pocketful.  Made a nice snack during the hike back to the Jeep.  This is definitely a banner year for the muscadine crop!

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Hope y’all have a good week, and see you on the outcrop!

Tick attacks: mild