Tag Archives: Witts Springs

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, Nov. 18-20, 2013

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Hello all!

Well, another great week to look at rocks!  We explored about a five mile stretch of Big Branch, definitely the biggest drainage left unexplored on the Shirley quad at this point.  Quite a bit of Cane Hill in the bottom, then several hundred feet of Witts Springs above.  The rocks near its confluence with Weaver Creek are dipping strongly southeast, and the Cane Hill actually dives into the subsurface there.

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Still haven’t decided if the big structure in Weaver Creek valley is a fault or just a really big monocline, but we’re leaning toward monocline right now because we still haven’t seen a real break in the rocks.  Of course, faults typically become covered because the fractured rock is preferentially eroded.  It just seems less and less likely that there is a fault there with each drainage we do that should cut across it.

Monday we walked in the lower end and got several strong SE dips in the Cane Hill.  Then we discovered an outstanding outcrop of basal Witts Springs sandstone, that we thought was a very large boulder at first because of the advanced state of the sort of “dry weathering” that usually affects the massive Witts Springs boulders after they become separated from groundwater, usually along joints, as they slide downslope.  This includes well-developed honeycomb taphoni, well-defined liesegang banding, and case-hardening of the surface.  In the bluff face, solutionally-enlarged joints can form fracture caverns, and spalling near the base can form bluff shelters.  All of this can happen under the influence of groundwater of course, but that kind of saturation usually leads to a punky or rotten texture in the rock, and forms very steep, covered topography.  The really spectacular outcrops occur when lack of groundwater slows down the weathering to a grain-by-grain process.  This is what I call “dry weathering”.  After walking up both sides and along the top, we concluded that it was indeed part of a continuous outcrop that was probably protected from groundwater penetration by its joint system.  I dubbed it “Castle Rock” because of its many turrets and towers.

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Speaking of weathering, on Tuesday we saw a classic example of preferential weathering along beds of sandy limestone interbedded with limey sandstone.  When these beds are freshly exposed, they form light and dark bands within a smooth face of massive sandstone.  We refer to this informally as “zebra rock”.  The light bands are more limey, the dark bands less.  As weathering progresses, chemical weathering breaks down the more limey areas at an accelerated rate simply because there is more reactive material in that rock than in the sandier beds around it.  When weathered, these areas form long horizontal hollows or pits in the massive sandstone.

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We informally refer to this weathering pattern as “Prairie Grove weathering” after a Member of the Hale Formation in northwest Arkansas that most typically exemplifies this trait.  The base of the Witts Springs Formation is an equivalent unit to the Prairie Grove Member, and often massive sandstones within the Witts Springs will display this type of weathering as well.  Though not definitive, this characteristic can be used to help us determine if a given outcrop is within the Witts Springs.

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As we made are way up the Big Branch, we ran into our old nemesis: the February 5, 2008 tornado track.  This is the one that was on the ground for 122 miles in Arkansas and killed 14 people.  We’ve crossed it’s track on several maps, and it never ceases to amaze how destructive it was.

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I’ll be back next week.  Until then, 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

Statemap Field Blog, Sept. 23-25, 2013

Hello all!

Another good week in the field!  Temperatures are getting low in the morning, but still warming up in the afternoon.  We started out by finishing up the rest of Tick Creek at the north edge of the map.  Got the lower Cane Hill sandstone up Files Hollow and again on the east side of Tick.2013-09-23 001  2013-09-23 014Still have good channel-bedded Imo below in the creek bed with a shale unit between the two.

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Tuesday and Wednesday we finished up the lower end of Indian Creek.  There were several massive-bedded sandstone units that had cut down into lower units of thin- to medium-bedded sandstone interbedded with shale.

This is probably all in the Witts Springs Formation, but we won’t know for sure until we see more of the rock in the area.  One of the indications that it is Witts Springs sandstone is the characteristic curved reentrant at creek level.  This is caused by exfoliation or spalling of curved sheets of rock due to more rapid dissolution of the calcareous cement near the creek.  The Witts Springs sandstone is typically more calcareous than overlying formations.    2013-09-24 0452013-09-24 060

You never know when you might see a classic example of a sedimentary structure while hiking around.  This week we saw some good examples of load casts in the creek float.  A sand deposit formed an irregular bulge as it pressed down (loaded) into the mud below.  Later lithification preserved the cast of that shape on the bottom of the sandstone bed.

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As we approached the southwest/northeast topographic lineation along the Middle Fork at the mouth of Indian Creek, we began to see more and more signs of a major structure.  Aside from a 5 to 7 degree southeast dip, there was an increasing abundance of deformation bands in the massive sandstone.   Also, we began to see a lot of non-vertical joints and small faults.  Took photos of a couple of fault planes with the slickensides still evident.2013-09-25 013  Slickensides are the parallel grooves or scratches left behind on the fault plane caused by the abrasion of one rock surface against another.  They are typically smooth in the direction of movement and rough in the opposite direction, so can indicate which way the fault moved.  Unfortunately there is no way to estimate throw, or the amount of offset on the fault, without knowing which formations are on either side.  That’s why we’ll have to be extra thorough in that area.  There’s probably a big fault somewhere along that lineation, but we’ve yet to find it so far.

By the way, Indian Creek must have gotten its name from the number of moccasins lying around.

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We’re taking a little hiatus next week so will be at least two weeks ’til the next installment.

See you on the outcrop!

Snake count: at least 4

Tick attacks: still severe

Statemap Field Blog, Sept. 16-18, 2013

Hello all!

Another great week in the field!  Temperatures are coming down some which makes things much more bearable.  Monday we came down from Fox and crossed the Middle Fork at Lydalisk.  Went as far south on the old railroad grade as we could then worked our way back, getting points along the way.  Still finding the Imo near the bottom of the valley.   The river was so low that we could actually cross it on foot to get a drainage on the east side.  The first good outcrops we found there were the lower Cane Hill.   There were good examples of taphoni in the rocks there.  Commonly known as “honeycomb weathering”, taphoni is caused by weathering processes in many rock types and under many conditions.  In the Cane Hill it typically affects the thin-bedded sandstones in dry areas beneath overhangs and is probably due to differential dissolutioning of the cement by groundwater.  This process also causes the concave structures as noted in previous blogs.

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The next two days we started at the upper end of Indian Creek and worked our way down.  Lots 2013-09-17-019_thumb.jpgof Fayetteville shale production going on in this area, which means good roads for us!  Seemed to be in Witts Springs sandstone the entire stretch, so not a lot of contacts.  Definitely had a lot of dipping rock and signs of  a large fault further south including deformation bands and non-vertical joints.  Located a couple small faults with what we think is minimal offset along the creek and adjacent hollows.

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Cottonmouth in dry creek bed.

Did have a few encounters with our reptile friends.  We always leave them be so maybe word will spread among their kind that we mean no harm.  It’s worked so far!

See you on the outcrop!

Snake count: 2

Tick attacks: severe

Statemap Field Blog, Sept. 3-5, 2013

Hello all!

Well, it warmed up again this week, but at least the humidity stayed lower.  Definitely getting a more golden quality to the sunlight in the evenings now, and the mornings are almost pleasant—maybe fall is just around the corner! 

Kinder Slough on Middle ForkSpent this week exploring lower Tick Creek which is one of the larger tributaries on the north side of the Middle Fork north of Shirley.  I can attest that this creek is aptly named.  It seemed that every plant above ankle high must be covered in them.  Danny and I mapped the upper end of this creek in the 2011-12 field season on the Fox quad.  It was all Cane Hill there with a cap of Witts Springs near the top.  This week we found Imo in the main channel a couple miles from its confluence with the Middle Fork, but haven’t found the contact with the Cane Hill yet.  Will look closer to the north edge of the map next week. 

Flood debris in lower Tick CreekAccording to local landowners, there was a 6-inch deluge at the end of May that washed out many of the access roads.  We could corroborate this after seeing all the large trees and other debris that had been piled up in the creek bed by the flood.  It looks like the entire valley may have been filled with water during that event.  Another good reason not to build anything in the floodplain of these steep-sided, narrow hollows in the Ozark uplands.  Where Still Hollow empties into Tick Creek, a small delta had developed during the flood event.Alluvial fan in Tick Creek 

There was also fresh cutting of the alluvial deposits along the stream bank which plainly showed a typical fining upward sequence.

 

Typical Cane Hill in small drainage to Middle ForkWe walked up quite a few side drainages along Middle Fork and Tick Creek to see if we could catch a glimpse of the Imo as it reaches the bottom of the Middle Fork valley, but the breakdown of the Cane Hill and Witts Springs above has covered it almost entirely.  That left us with thin-bedded Cane Hill sandstone as the lowest unit that produced a decent outcrop in these smaller branches. 

Slide block in creek bedMaybe we’ll get lucky when we hike up the sides of the Middle Fork north of this area.  We did see a large slide block that had fallen into the creek bed and was weathering away virtually intact.  If we had encountered that rock in isolation without the adjacent outcrop, we may have thought there was a fault close by due to the extreme inclination.  As it was, it’s just an interesting footnote to be filed away then used to cast aspersions on future structural theories based on similarly dipping rocks. 

 

What we did see of the Imo upstream in Tick Creek has a lot of interesting lithology (rounded siltstone concretions and coalified wood prints in shale) and bedding structures (soft sediment deformation).  Can’t wait to see what we’ll find upstream!

Snake count: 1

Tick attacks: severe