Tag Archives: Lost Creek

Statemap Field Blog—Dec. 2-4, 2013

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Hello all!

This week we finished up a few odds and ends on the Shirley quad.  We needed to get to a few suspected outcrops along the north side of the Middle Fork just east of Shirley.  As we were looking for a way to access them, we stumbled upon the Sid Burgess Historic M&NA Trail which starts in downtown Shirley and ends up about a mile distant at the historic Cottrell-Wilson Cemetery.  As luck would have it, this trail happened to access the very areas we needed to see.  If you’re ever in Shirley, it’s definitely worth checking out!

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We saw mostly thin-bedded sandstone and shale units of the same variety as on the south side of the Middle Fork and Weaver Creek upstream.  There are a few low dips toward the lineation, but nothing indicating a major structure.  I’m thinking this may all be the unit above the Witts Springs (Bloyd Formation) brought down to the southeast by a monocline.  The trouble is, we don’t really know what the Bloyd/Witts Springs contact looks like in this area yet.  That’s something we still need to work out.

Tuesday was wet again, but we set out to finish up the southernmost branch of Lost Creek anyway.  Seems to be mostly Witts Springs in there with some Cane Hill at the bottom of the valley.  We saw some great examples of soft-sediment deformation in some of the silty units on the way down.  Soft sediment deformation occurs during sedimentation when the rapid loading of usually more dense, overlying sediments causes the less dense, buried deposits beneath them to become partially liquefied, which forms various types of disruptions in the original bedding.  This can take the form of simple reorientation of the bedding as we have here, to more complex convolute bedding and flame structures.  I took a photo later in the week of a good flame structure in the Bloyd Formation.  Notice where the shale has been squeezed up between the thick, contorted beds of sandstone.

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Several massive calcareous sandstone units in the Witts Springs again illustrated the dramatic difference between outcrops weathered with and without the influence of groundwater.  Notice how rotten the outcrop of massive sandstone in the photo below left appears.  Also note the green color.  There is a layer of moss and lichen growing over almost the entire rock surface, made possible by its relative saturation by groundwater.  These organisms help accelerate the weathering of the rock, and there are places where you can actually see clumps of moss peeling off the surface along with a layer of sand.  This type of chemical weathering is known as chelation and results in the effective removal of the residual iron cement still holding the rock together after the calcite cement has been dissolved by groundwater.  The photo below right shows how “dry weathering” of a boulder of the same material can result in well-defined liesegang bands.  Highly concentrated iron has cemented these bands within the massive sandstone, and without the influence of groundwater, they are preferentially resistant to weathering, leaving them in bold relief.

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On Friday, we looked at some of the last steep areas we haven’t vistited north of the Middle Fork east of Shirley.  Definitely still have Witts Springs right down to the river there, but there is also a thin- to very thick-bedded unit above it that is probably in the Bloyd.  We saw a fairly recent landslide above the river composed of material from that upper unit.  There was also a good cut and fill channel bed exposed in that unit as well.

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It was warm enough for the critters to be out again this week.  Just when I thought it was safe to put my foot down anywhere I pleased, I nearly stepped on a moccasin.  That’s him slinking back in his hole.  We also saw a western slimy salamander (plethodon albagula?) under some storm debris, which was subsequently replaced.

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Hopefully the warm weather holds out, but the forecast says the bottom may drop out on Friday.  We’ll see!

Until next week, see you on the outcrop!

 

STATEMAP Field Blog August 26-28, 2013

Hello all!

This week was a hot one, so we did some creek work, but also did some road work.  Went up a section of lower Lost Creek on Monday.  Narrowed down the Cane Hill/Imo to a fairly small area.Danny on Cane Hill in Lost CreekSand on shale in the Imo on Lost Creek

Saw more nice trace fossils in the Imo.

Trace fossils in ImoTrace fossils in the Imo

Got a few points on the Middle Fork where it leaves the Shirley quad and enters Greers Ferry Lake.

Thin-bedded sandstone in Middle Fork Little Red RiverThin-bedded sandstone in Middle Fork Little Red River

Quarry near Fairfield BayAlso, took points on a 4 different shale pits or quarries.

Green persimmons
The persimmons aren’t quite ripe yet!

Deformation bands in massive sandstoneFound these deformation bands right by Highway 16 near Fairfield Bay.  These bands are associated with structural features like faults and folds.  They form in more coarsely grained sandstone when the stress crushes the individual sand grains along a plane, then recrystallizes to form a slightly more resistant lithology, that when weatherd, stand in slight relief.   We will keep looking in this area for more clues and hopefully figure out what the rocks are trying to tell us!

Snake count: 2

Tick attacks: severe

STATEMAP Field Blog—August 19-21, 2013

Hello campers!

Well, much drier this week, but of course the heat is back!

We’re still working on the Shirley quad this week.  Started out Monday by dropping down a steep side drainage off Nubbin Ridge nearly to the Middle Fork, then right back up another one.  Got good points at the base of the Witts Springs and Cane Hill.  The Imo is at the bottom of the valley but the very large boulders eroding at the top cover most of it.  Relief was around 400 feet.

Tuesday and Wednesday we were back in the headwaters of Lost Creek.  There are many branches to this creek, and there seems to be a fairly large structure crossing them approximately east/west.  Could be a fault, or maybe just a fold of some kind—will take much more data collection to be sure.  We did observe a repeating sequence from higher elevations to lower—now we just have to figure out which formation they are in!  In the Ozarks, the Pennsylvanian-aged rocks are a series of sandstone and shale units deposited in a shallow marine environment.  That means they are all very similar to each other and the differences are subtle and vary from place to place.  To differentiate one formation from another, we depend a lot on context, which means we must take meticulous notes on each outcrop in the hopes we can see a pattern in the stratigraphy that matches something known.  We’re starting in the northwest corner of Shirley because we’ve already mapped the surrounding quads in that area, so have a pretty good idea of the geology there.  Things are getting more complicated as we reach the structure because the strata are displaced somewhat from one side to the other.  We will continue to add points next week in order to discover what the rocks are doing there.

ripple beds

ripple beds

Since I’ve mentioned some of the formations in the area and how difficult they are to differentiate, let me discuss one that has stayed fairly consistent across the Boston Mountains Plateau.  The Cane Hill is a Member of the Hale Formation, and its type section is in northwest Arkansas.  It is typically very thin- to thin-bedded, ripple-bedded, very fine-grained sandstone with interbedded shale and thicker shale units.  There are abundant trace fossils in the Cane Hill including asterosoma which is a somewhat star-shaped feeding burrow.

Trace Fossils:

Asterosoma:

concave solutioning in thin-bedded Cane HillBluffs of this sandstone often affected by a particular weathering phenomenon where the cement holding the sand together actually solutions out which lets the individual grains fall away eventually forming a concave structure.  I have included a good set of photos of the Cane Hill and a few of its characteristic structures.  It is getting to be over 300 feet thick as we continue to map toward the southeast.

See you next week!

Snake count: 2

Conostichus count: 1

Tick attacks: moderate to heavy

STATEMAP Field Blog August 12-14, 2013

Hello campers!

Rather wet in the Shirley quadrangle this week.  Rain over the weekend brought the Middle Fork up, and we crossed it on the old train bridge at Shirley on Monday.  About three miles upstream, there are a couple washouts and parts of the old railroad bed have slumped into the river.  We managed to get around all that, but then ran into a gate at Bear Branch.  That was the drainage we needed to get anyway, so we hiked up and got a Witts Springs/Cane Hill contact in the ditch of an old road.  At that point the rain caught up with the thunder we’d been hearing for a while and we got soaked through, but not for the last time this week.      

The next day we did some work in the headwaters of Lost Creek.  Again the day looked threatening.  We started down the drainage and almost immediately found the trace of a small fault (probably).

We traced it though a couple more side drainages, and got soaked again around noon.  It continued to rain on and off the rest of the afternoon.  We did see some good examples of Asterosoma, ripple bedding, and sandstone concretions (“Prim boulders”).  Also saw what I think is a native spider lily for the first time.  Ended the day by climbing 300 feet up one side drainage, followed a bench over to another, and climbed back down to the main drainage, then 500 feet back up to the Jeep (Goldy).  All was wet and slippery.


The next day the sun came out and the air was much cooler and drier.  What a relief!  We started by going to an area marked “Chimney Rocks” on the map.  It is near the the top of a mountain where a massive sandstone unit has weathered along its joints to form several large blocks and pedestals which are slowly creeping downslope away from the bluff from which they originate.  The weathering of the pedestals slows down tremendously once they detach from the face because they simultaneously become disconnected from groundwater. The area, though small, is very scenic, and I took many photos. 

After that we drove to the bottom of Good Spur Hollow and walked upstream and down until we ran out of time and had to get back to Little Rock.  Couldn’t ask for better field weather on Wednesday.  Hope it holds out!

See you next week!

Snake count: 1

Tick attacks: low to moderate