Tag Archives: Middle Fork

Statemap Field Blog, Dec 10-12, 2013

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Hello all!

Well, we did have a winter weather event last Friday that was still on the ground in the field area the following Tuesday.  Roads were fairly clear to Clinton, but between Clinton and Shirley it was still mostly patches of snow and ice.  North of Shirley, the roads were pretty much all covered with snow and ice.  Even “Goldy” (our Jeep) got stuck briefly when Danny decided to stop and check his map almost at the top of a hill.

Tuesday we managed to get to a drainage south of the Middle Fork that had fairly low relief, so were able to climb down the side and follow it on down.  There were some very large footprints in the snow along the valley floor that may have been a feral pig, but don’t know for sure.  It’s amazing how the critters always choose the easiest route.  Their trails are usually pretty good for people too, though they don’t often care about avoiding briar patches.  The snow was pretty crunchy, so fairly good traction.  Having snow on the ground rather evens out the terrain in an odd way, though you have to be poised to catch yourself with every step.  Had some massive sandstone units, but they were blocky and non-calcareous, so we’re in something different than on the north side of the river.

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The next day we managed to make our way north of Shirley to a couple drainages at the head of Indian Creek that we had skipped when we did the lower end.  As it happened it was a pretty good choice because the relief was rather low and the bottom was fairly wide.  Also, it was south-facing which helped to melt the crusty snow and maybe keep us a little warmer.  We saw mostly massive calcareous sandstone units of the Witts Springs though may have gotten into the Bloyd in the higher elevations.  At the end of the day we entered an area that still showed signs of damage from the Jan. 2009 ice storm that coated most of northwest Arkansas with a thick layer of ice and downed many trees–many by the roots.  Witnessed a beautiful sunset on the way out though.  We were near 1400 feet which is about the highest elevation on the quad.  The trees there were still coated in ice from last Friday’s storm.

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Thursday we tried another drainage near the one we hiked on Tuesday.  This one was north-facing and proved to be too steep and narrow a descent to do with so much snow on the ground.  The snow had developed a thick icy crust from thawing and refreezing, and we had to break through it to get traction.  I managed to get up and around on the side of a particularly narrow spot in the creek bed, and was waiting for Danny to follow when I saw him retreating back upstream.  I later found out that he couldn’t find purchase on the icy banks, so decided to return the way we had come.  Since I had gotten farther downstream by breaking through the crusty snow and climbing down the steep side, I had no choice but to climb back up that way.  I found that going on up was less hazardous than going back down toward the creek, so I continued to climb up the side and by the time I drew even with Danny was probably 100 feet higher.  I could barely see him down there, but managed to get a photo of him climbing up the drainage.  We’ll have to try that one again when the snow is gone!

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After that, we got a few points on Weaver Creek were it leaves the western edge of the map, and headed back to Little Rock.  Hope this clears up by next week!  Until then, see you on the ice-covered outcrop!

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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 Nov. 25-27, 2013

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Hello all!

A cold rain on Monday was freezing on the trees, so we explored some of the many undeveloped road networks in Fairfield Bay, especially along Dave Creek and down to the lake on the east side of the map.

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Not quite sure what we’re in here, but there is a calcareous sandstone massive not too far above lake level which could indicate that we’re still in the Witts Springs even though this is south of the lineation along the Middle Fork.  We’re getting a lot of strong southerly dips along the north edge of the lake which indicate there is a fault along that lineation, unfortunately the lake covers it.  Too bad this detailed geologic mapping was not done prior to 1963!

Tuesday we finished up the upper end of Big Branch.  The ice was still on the branches when we started, but soon began to melt which made it seem like it was raining again until about noon.

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At first, we thought we were finding additional Witts Springs/Cane Hill contacts, which was surprising since we were so far above where we had them downstream last week.  But we definitely had a thin-bedded sandstone that was shaly near the top beneath a classic basal Witts Springs sandstone.

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Or did we?  As it turned out, the thin-bedded sandstone was only about 40-60 feet thick and was above at least two other massive sandstone units.  Another Cane Hill look-alike!  That’s why you always have to look at the entire section, or you may miss something!

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What we took for the basal sandstone massive may actually have been the uppermost sandstone massive in the Witts Springs.  As we hiked on downstream, we did eventually find the actual Witts Springs/Cane Hill contact that lined up much better with the points we already had.

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Wednesday, it was so cold the moisture being wicked up certain grasses was making “frost flowers”.

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We walked up the lower end of Little Creek along the western edge of the map.  We had already seen the upper portion when we mapped Old Lexington, and it seems to be all Witts Springs in there.  We saw some good examples of “zebra rock” and “Prairie Grove weathering” in some of the massive sandstone units (see previous blog).

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Some of the calcareous sandstone is also fossiliferous, and I was lucky enough to find a good rugose coral weathering out in one fossiliferous zone.

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Well, looks like winter is here to stay!  At least I don’t have to watch for snakes anymore!  Until next week, see you on the outcrop!

STATEMAP Field Blog Oct. 21-23, 2013

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Hello all! 

Another good week in the field!  Continued fairly dry fall weather means we’re still in the big drainages this week.  Finished up in Weaver Creek on Monday.  Still have the channel-bedded mostly shaly unit in the valley and the thin- to very thick-bedded sandstone unit on the southeast side of the valley.  Got to see the thickness of the alluvial cover in the high wall of a shale pit in the middle of the valley.  The owner states that the pit is 60 feet deep and is shaly to the bottom.  That’s a lot of shale!   The sandstone above it is at least that thick and probably more like 100 feet.  Still seeing channel beds within the sandstone unit as well.  A ribbon snake crossed our path heading toward the water. 

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The next day, we tried to cross the Middle Fork as we have done in past weeks, but there is already too much water in it.  There are some deep hollows on the east side that we needed to get to, but after fording the river proved impracticable, we resigned to going north on highway 9 and dropping off the top edge of the valley.  At least we started from the lowest saddle.  It was a fairly easy descent with a few washed out 4-wheeler trails helping out.  We knew right away we were in Witts Springs when we reached the bottom, but were surprised by how low the contact was when we reached the Cane Hill.  When we reached the river valley, we decided to follow a slough upstream to the next drainage on the east side.  This looked like the best route on the map, but was actually a thick canebrake with very few places to cross the slough.  We had a hard time getting in the upper end of this drainage a few weeks ago, and the lower end proved no different.  We were rewarded by finding a lot of deformation bands along non-vertical joints in the Witts Springs, and a drop of about a hundred feet in the contact with the Cane Hill between the drainages, which are only separated by about a mile.  At best may be a monocline in there.  On the way out we nearly ran over what I hope is the last moccasin of the season sunning on a very steep hillside above the drainage.  We gave him as wide a berth as we could and continued back to the river bottom.  This time we tried to avoid the slough and stayed closer to the river where the switch cane was thinner.  We backtracked up the hollow we came down earlier, then climbed back up the side to the highway.  So to summarize, river unfordable so drove around, hiked down 420 feet, bushwhacked a mile through canebrake, hiked up 320 feet, saw deformation bands, back down 320 feet, avoided snake, hiked a mile through woods, climbed back up 420 feet.  What a day!  

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On Wednesday we started on the west side of the river downstream of where we were the day before, and walked up one of two remaining large drainages before the river turns northeast at Shirley to follow the lineament.  We were rather surprised to find Imo near the mouth of the hollow.  This would make it the southernmost exposure of Imo mapped to date.  Saw good exposures of Cane Hill, which is mostly sandy through here, on the way to a classic example of the basal Witts Springs sandstone complete with exfoliation weathering. 

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Once we got out of there, it was back to Little Rock and back to reality. 

Oh, and I almost forgot.  I found this graph on the USGS website and thought you might find it interesting.  You can see that flood event on the last day of May this year that we are still seeing evidence of.  Apparently it was right up there with some of the biggest recorded events on the Middle Fork in that area.   

Stages on the Middle Fork at Shirley

Looks like we’ll be in the office next week, so next installment in two.  Until then, I’ll see you on the outcrop!

Tick attacks: very light

Snake count: 2

Statemap Field Blog–Oct 7-9, 2013

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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