Tag Archives: Cane Hill

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 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. 8-13, 2013

Hello all!

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Silence of the cicadas

Signs that summer is almost over despite the continued warm temperatures include the silencing of cicada calls one at a time.  A welcome turn of events!

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More “crazy-bedding” in the upper Imo

This week was a long one because we worked in two different field areas.  On Monday and Tuesday we were back on Tick Creek looking at the last two major eastern drainages.  Found good Cane Hill/Imo contacts in each and a fairly consistent
irregular-, channel-bedded sandstone unit with abundant soft-sediment deformation near the top of the Imo.  It’s so irregular that I was calling it “crazy-bedded” before long. 

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“Crazy-bedding” in the upper Imo

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Yet more “crazy-bedding” in the upper Imo

There was also a section in the middle of the Cane Hill that was so perfectly cut by its east/west joint that it formed a smooth wall on the north side of the creek.  There was a parallel joint face on the south side, but it was not nearly as well exposed.

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Danny views joint face “wall” in Cane Hill

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Buttresses on Bear Creek

On Tuesday evening we joined Angela Chandler and Lea Nondorf, also of the Survey, on Bear Creek in Marshall to work on several other projects the rest of the week.  One ongoing project is to try to resolve edge-matching issues whenever we get a chance.  This involves gathering new data in boundary areas between quads that were mapped by different people or who used a different stratigraphy.  This week we were also looking for localities in the Imo interval for an upcoming field trip that Angela, Erin Smart and I are leading this spring for the GSA (Geological Society of America) conference in Fayetteville.  While looking at various road cuts, we also took new points on an area in the corner of four quads.  

Angela in front of lower Imo sandstone at the type section

Angela and Danny at the foot of the basal Witts Springs sandstone near Bryan Mountain

Wednesday and part of Thursday we looked at several possible field trip stops in the Imo, none of which seemed particularly suitable for one reason or another.  Mostly this is because the Imo doesn’t tend display good outcrops in this area due to its shaley composition and its typically being covered by the flaggy sandstone of the Cane Hill above.  We did visit the type section which is in Sulphur Springs Hollow to see if that could be used as a stop, but deemed the area too rugged unless a very small, sturdy group of geologists sign up.   A type section is an area where a formation or rock unit is first described and studied in detail.  In this case the type section was proposed then summarily  abandoned, but there are those working hard to see it reinstated eventually.

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Coalified wood prints in Imo sandstone at the type section

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Crinoids in red, fossiliferous Imo limestone at the type section

Another project that we are working on for the National Park Service is a compilation of all the quad maps along the Buffalo National River. Our agency and the US Geological Survey have each done about half of the quads in that area.  Most of the quads mapped by our agency did not include the higher terrace levels above the river–some as high as 200 feet!  This week we were able to get points on a few more of these terraces on the Snowball quad. 

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Smart Bluff above Arnold Bend on the Buffalo River

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Calcite fracture-fillings used as building stones in St. Joe

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Quartz crystal encrusted Boone chert used as building stones in St. Joe

We looked in Arnold Bend Thursday afternoon, and differentiated several terrace levels there, then on the way back to town, we stopped at a roadcut on Hwy. 65 that Angela knew about where there are quartz crystals growing in fractured Boone limestone and chert.  Danny had stopped at St. Joe on a previous field trip and so directed us there to see the quartz and calcite crystals encrusted on some of the old building stones in town.  These stones were no doubt found nearby along the several mineralized fault zones in the area.

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Early morning fog on Bear Creek

The next morning there was fog on Bear Creek and we headed up to Jamison Bluff to look for Plattin in the riverbed where it had been mapped previously.  This is part of the 6 mile section of the Buffalo between Woolum and Margaret White Bluff that dries up during the summer.  All we could find was St. Joe, so that part of the map remains as is. 

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Jamison Bluff along the Buffalo River

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River crossing at Woolum on the Buffalo River

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Looking down on Skull Bluff on the Buffalo River

 We crossed the Buffalo at Woolum and walked along the top of Skull Bluff to the Nars Cemetery most of which was covered with a terrace deposit (along with almost impenetrable black locust, cedar and briars).  

And of course, we couldn’t leave the area without a quick trip to “the Nars” itself for Danny and Lea to see for the first time.

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“The Nars”. Buffalo River left, Richland valley right.

“The Nars” is an almost sheer rock wall in the Boone formed as an erosional remnant between the valleys of the Buffalo River and Richland Creek.  Quite impressive as usual.  After that we had to get back to Little Rock and “the real world”.  See you next week.     

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