Category Archives: Notes From The Field

Link

2014-02-11 046

Hello all! Sorry I haven’t blogged in awhile. I’ve been so busy trying to complete the maps for this year by the June 30th deadline.  But, I am proud to announce that the Geologic Maps for Shirley and Fairfield Bay are now published and available on our website!  Click below to view and download the maps.

http://www.geology.ar.gov/maps_pdf/geologic/24k_maps/Shirley.pdf http://www.geology.ar.gov/maps_pdf/geologic/24k_maps/Fairfield%20Bay.pdf

The process to create these maps takes an entire year. I kept you updated each field week from July to April last year, so I thought you might be interested to know how we take the raw data we collected in the field and use it to make a map. First of all, it’s a collaborative effort.  It takes a lot of people who specialize in various disciplines working together to make this product.  Basically, drawing the map starts with the notes we took in the field.  At each point, we tried to identify the rock formation exposed there.  Sometimes this was difficult, especially in the southern portion of the Boston Mountains Plateau where we worked this year. These rocks are all so similar–mostly sandstone and shale.  Nevertheless, if you cover as much ground as we did, you begin to discern similarities in the rock types and bedding structures, and can make formation calls based on those similarities.  Many of the points are taken on what we considered to be contacts between different formations.  These points are used to hand draw contact lines on a blank topographic base map. 2014-07-11 0032014-07-11 007 These lines are continued into areas where the contacts may not be exposed, because we assume lateral continuity of these units.  Many times there are topographic breaks along these contacts which can help us draw the lines in areas of poor exposure or in areas we just didn’t get to.  Structural lines are drawn along the trace of faults or other structures at the surface in areas where we saw the hallmarks of faulting such as deformation bands and non-vertical joints.  Also, the many strike and dip measurements we took were plotted on the map and helped determine orientation of faults and other structures, such as the axis of a monocline.  Once all the lines were neatly drawn on the topo, it was scanned into the computer and georeferenced to the grid of all quads in the state.  Next, each line was painstakingly digitized in ArcView by one of our cartographers, in this case Brian Kehner.  The digitized map was then added to a layout that Danny created in Adobe Illustrator. 2014-07-11 008

The layout includes descriptions of each formation developed from our field notes and are specific to each quad.  A correlation of map units, a generalized stratigraphic column, an inset map of the locations of the field points, a symbol chart, and a rose diagram of the frequency of each joint direction are also added to the layout.  A cross-section based on formation thickness is hand drawn, digitized, and placed along the bottom of the layout. Formations are symbolized by color and an abbreviation.  Sometimes photos are added to balance the layout.  Also plotted are any quarries or pits we found or were in the economic commodities database we keep at the Survey.

2014-07-11 012 After we have a reasonably good map, it’s printed and set out for staff review.  They really let us have it, but this editing process always greatly improves the maps.  After two or three revisions, we finalize it and send it to the USGS by June 30 to fulfill the requirements of the STATEMAP grant.  Whew!  What a relief!Geologic Map of Shirley red1 Geologic Map of Fairfield Bay red This year, as in years past, I have designed a commemorative STATEMAP t-shirt.  I’m taking orders until July 25th if anyone is interested.  They are available for the cost of the shirt you choose plus the printing.  Please email me at richard.hutto@arkansas.gov for details. AGS14_shirt_front (1)AGS14_shirt_back (1) Now we get ready to head back out again to our new field area.  This year we’ll be mapping the Parma, Prim, and Greers Ferry quads.  I’m breaking in a new field partner this time out.  Andrew Haner says he’s looking forward to seeing some of the Arkansas wilderness.   I just hope the snake count is low this year.  From what I’ve see so far, the ticks seem to be at an all time high.  I’ll try to keep you posted, but will be out of the office four days a week this year.  That will leave little time for blogging.  So until my next post, I’ll see you on the outcrop! Richard Hutto

Advertisements

Statemap Field Blog, April 7-9, 2014

2014-04-07 006

Hello all,

Well, this is the last week of field work for the 2013-14 season.  Of course, there’s always more one would like to have a look at, but we have to stop sometime.  On Monday, we started down by the M&NA railroad bridge at Shirley.  The big fault that makes the SW/NE lineation goes through here somewhere, but it’s difficult to say where exactly.  There are lots of non-vertical joints and deformation bands in the area, which are all good fault signs, but nothing very definitive.  The area north of the bridge is about as thick as it could possibly be with greenbriers –only passable with much effort and many scratches.  We saw very thick-bedded sandstone there which we took for Witts Springs that day, but when we came back on Wednesday, we decided it may be north of the fault, and therefore would be Imo.  We have Imo across the valley, so it’s not out of the question to have it here, but it may be just a relatively thin slice.  There are many cut and fill channel beds there, some of them with very nice soft-sediment deformation at the margins.

On Tuesday we finished up some loose ends in the northwest corner of the Shirley quad.  After we climbed way down in a hollow that had an old tornado track going through it, Danny realized he had lost his camera somewhere.  We hiked back up to the Jeep to see if it was there (it wasn’t), then retraced our steps from earlier that morning.  Still nothing.  He remembered the last time he had used it was in that horrible briar patch the day before, so after we climbed out again, we headed back there.  Sure enough, in the thickest part of the patch, where he had been practically crawling to get through, a briar had reached in his carrying case and pulled it out.  It was still dangling there about a foot off the ground right on the river bank.  At least we got it back!

Deformation bands in massive sandstone near Middle Fork north of Shirley2014-04-07 017

2014-04-09 026 2014-04-09 011On Tuesday afternoon, we went down a drainage on the west side of Middle Fork looking for more signs of a fault we have traced from the Old Lexington quad.  We definitely found a lot of deformation bands in the Witts Springs massives down there and figure there might be as much as 80 feet of throw on the fault.

2014-04-08 0192014-04-08 027Wednesday was our last day in the field this year, and we spent most of our time on the Middle Fork just north of Shirley where we had left off on Monday.  Did look like the fault goes through there because we found very-thick bedded massives on the north side (Imo) and shale interbedded with very thin-bedded sandstone on the south side (Cane Hill).  Our last couple of hours we spent getting points in several road cuts in and around Shirley.  We took a final photo in front of the town sign.

2014-04-08 048 (2)2014-04-09 047This will be Danny’s last year out in the field with me, so I’d like to take this opportunity to thank him for putting up with me and the sometimes horrendous field conditions we’ve faced together the last five years.   Looks like I’ll have to break in a new field partner next year, so should be interesting.  Now comes the time of year when we have to sit in the office and draw the maps, create the layouts, and finish the database, all to be turned in to the USGS by June 30.  It seems like a long time, but we’re always editing down to the last minute.  By the time we make it back out in the field, it will be mid-July, so the ticks and snakes will be out in full force, it will be nice and hot, and all the vegetation will be full grown.  At least that gives us something to look forward to.  Until then, I’ll see you in the office.  After that, I’ll see you on the outcrop!

 

 

 

Statemap Field Blog, March 31-April 2, 2014

 

2014-04-01 075

Hello all!

Another great week in the field.  Signs of spring are everywhere, and unfortunately the field season is drawing to a close.  We skipped around all over the Fairfield Bay quad this week, still trying to trace the very thick-, massive-bedded sandstone that we’re calling the base of the Bloyd for now.  Just off the eastern edge of the Fairfield Bay quad is a locally famous outcrop of that sandstone that was supposedly visited by Hernando Desoto himself in 1542.  Whether or not that’s true, it is a very impressive bluff shelter known as the Indian Rock House.  A lot of eroded material was removed from the floor of the shelter when the adjacent Indian Hills Golf Club was built, leaving behind the fine sandstone amphitheater we see today.   One could see how this formation could later become a natural bridge if erosion continues along the joint set parallel to the bluff face.  If that interior arch were to fall out, then the remaining one would form a bridge.  This is how most of the sandstone natural bridges in Arkansas are formed.  Lots of graffiti has been scratched into the friable rock over the years, including some that may have been carved by native people.

2014-04-01 0802014-03-31 013

On Tuesday, we finished up our field work on the lake.  We still had a couple islands we needed to visit, and the entire south side of the lake is so steep that access by land would be difficult.  We were excited to find more old river terraces on the islands, including one that would have been deposited on a cut-off meander in the area of Harpers Cove.  The deposit is about 80 feet above and over a half mile north of the current river channel (before the lake was there, that is).  The high end of the range for the downcutting rate for the Colorado River in the western Grand Canyon is 16 centimeters/1000 years, and I think we can all agree that downcutting there probably exceeds that in Arkansas.  Using that rate, an estimated 152,000 years would have passed since that terrace was deposited.  That gravel has been there a long time!  Of course, cutting off the meander would have stranded that deposit at that time, but don’t forget that this stream is developed in bedrock, so meander cut-off would be a fairly infrequent event.  To get a better estimate of these events, methods such as luminescence dating are being developed to age date the sand in these stranded river terraces.  With this new technology, perhaps someday we will know when these terraces were deposited.

2014-03-31 0182014-04-01 053

2014-04-01 023

2014-04-01 0352014-04-01 005

On the south side of lake below Stevens Point is a good example of a modern landslide, and a bit of a cautionary tale.  Sometimes clearing trees for roads and houses can have catastrophic results.  The photo tells the story.  The major part of this landslide occurred March 28, 2005 just after a road was cleared from the house down to the lake.  Most of the material at the edge of the lake on the north side of Hunter Mountain is there as a result of old landslides, therefore any development in this area can cause it to become unstable, as evidenced here.  That’s why part of our project includes mapping areas where landslides have occurred.

2014-04-01 049

Speaking of Hunter Mountain, we ran across one of the now ubiquitous gas well pads up there, and I thought you might be interested to know the function of each piece of typical well head production equipment.  At each wellhead is a set of valves that regulate the flow of gas.  These are often controlled remotely, thus the solar panels which power the system.  The big tanks near them contain hydrogen sulfide which is introduced into the gas right away to give it a strong odor.  This odor is, of course, quite useful to determine if there are any gas leaks since natural gas is odorless.  From the wellhead, the gas flows to the separators which remove any fluids contained in the gas.  This fluid could include heavy hydrocarbons, but is mostly produced water.  These fluids are stored in large tanks which are built inside a berm.  The berm is designed to hold 1 1/2 times the capacity of one of the storage tanks in case of a spill.  The level in the tanks is also monitored remotely and emptied on a regular basis.  From here, the gas is piped to a compression station where it undergoes further treatment.   Then it is sent through a transmission line and on to your house.  It’s not pretty, but for now, we have to have it.

2014-04-02 0102014-04-02 0112014-04-02 012

Well, next week will be the last of our field season.

Until then, see you on the outcrop!

 

Statemap Field Blog March 24-26, 2014

Taphoni (honeycomb weathering) in massive sandstone.

Taphoni (honeycomb weathering) in massive sandstone.

Hello all!

Sorry about that long hiatus, but I had a couple of extra projects the last couple months that took a lot of extra time.  We’ve been in the field almost every week except for March 3-5 during the 3 inch snow in Van Buren County.  We’ve mostly worked on the Fairfield Bay quad during the last few weeks.  This week was spent tracing a very thick-bedded, massive sandstone unit through the town of Fairfield Bay itself.  It is quite an impressive bluff-former and actually underlies almost the entire Mountain Ranch golf course.

2014-03-24 017

Danny descending treacherous massive sandstone outcrop

2014-03-24-002.jpg

Danny contemplating how this massive sandstone can all but disappear a few hundred yards north of here

 

2014-03-24 028

Grotto in massive sandstone

2014-03-25 001

Most hillsides are composed of a thick sequence of very thin sandstone/siltstone and shale–easily erodible

 

Apparently some structure or perhaps a change in depositional environment made this sandstone climb up 200 feet to the east.  There it forms the cap of the ridge on which the small town of Fairfield Bay sits.  Moving east again, It underlies the Indian Hills Country Club where weathering (and earth-moving equipment) has produced the famous Indian Rock House on the golf course there.  Underlying that massive across the entire area is a very thick sequence of very thin-bedded sandstone/siltstone/shale.  A lot of the roads built in this unit have formed deep gullies making some of them impassable.  Still, there is better access in this area than most that we map, so we’re thankful for that.  Only about two weeks left of the field season.  We’ll probably be jumping around a lot to work out problem areas on both quads during that time.

See you on the outcrop!

2014-03-26 009

Danny actually seeing through the groundcover to the rock beneath the Mountain Ranch golf course

 

 

 

 

 

Statemap Field Blog, Dec 16-18, 2013

2013-12-17 001

Hello all!

Well, it’s been a week and a half since the snow came down, and there are plenty of shady areas where it’s still on the ground.  We started out on the east side of the map in Deadland Hollow, even though it was north-facing, because we knew we could get to it fairly easily.  If anything, the snowy areas may even have been a little more treacherous this week, because it’s thawed and frozen so many times that it’s more like solid ice now.  After that we went all the way over to the west side of the map and got a few points in a small drainage south of Weaver Creek.

2013-12-16 001

On Tuesday we walked from the lake to the top of Dave Creek in an undeveloped part of Fairfield Bay.  Saw some really good worm burrows in a thin- to medium-bedded sandstone  near where the creek reaches the lake.  Some of these burrows crossed bedding planes, so the rate of sedimentation must have been fairly rapid during deposition of this unit.  2013-12-17 0102013-12-17 030

Above that, we were in fairly continuous outcrops of calcareous sandstone, including some beds of “zebra rock” (see previous two posts).  We can only surmise that we are again in the Witts Springs Formation, which is interesting in that it’s still at the surface south of that Weaver Creek/Middle Fork lineation.  This probably means that if the lineation formed due to a fault at the surface, there is minimal offset.  More likely, it indicates the lineation formed along a monocline at the surface perhaps indicating a fault at depth in the basement rock.  Anyway, we had several hundred feet of calcareous sandstone along the creek, some of which exhibited large scale cross-bedding.

2013-12-17 0392013-12-17 045

We’re still working on that Bloyd/Witts Springs contact, but probably did cross it somewhere in that upper end.  There may even be some Atoka up there, but if so, it will be in sparse exposures at the very highest elevations.  If the Bloyd proves to be several hundred feet thick here as it has been on other quads to the west, the only Atoka may be on the southern third of the Fairfield Bay quad south of the southwest/northeast lineation that goes through the upper end of Greers Ferry Lake.  This is almost undoubtedly a fault at the surface based on the steep dips we’ve been seeing on the north edge of the lake.

On Wednesday, we started at the lake again and went up a small drainage on the eastern edge of the map.  Had a great view of Sugar Loaf Mountain when we started that morning.

2013-12-18 001

Well, I hate to say it, but this will be the final blog of this field season.  I have a major test and a GSA field trip to prepare for this spring, so I need to devote all my time to that right now.  It’s been fun to write it, and I hope I’ve given you a better idea of what range of effort goes into making a “simple” geologic map.  We’ll keep going out until mid-April, then we’ll have about 10 weeks in the office to draw and digitize the two maps, add descriptions of the rock units, a cross section, stratigraphic column, joint diagram, and correlation of map units.  If all goes according to plan, we’ll turn the finished maps into the USGS on June 30 to fulfill our grant requirements.  The Shirley and the Fairfield Bay quads should be up on our website as a .pdf by mid-July.  By that time, we’ll be back in the field battling ticks and snakes next season–probably on the Parma and Greers Ferry quads.  Who knows, maybe I’ll start blogging again!  Until then, see you on the outcrop!

Statemap Field Blog, Dec 10-12, 2013

2013-12-10 021

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.

2013-12-10 0432013-12-10 045

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.

2013-12-11 0312013-12-11 0152013-12-11 0122013-12-11 004

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!

2013-12-12 0042013-12-12 0222013-12-12 022 (2)

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!

2013-12-11 064

 

 

Statemap Field Blog—Dec. 2-4, 2013

2013-12-02 031

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!

2013-12-02 0112013-12-02 0152013-12-02 018

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.

2013-12-03 0072013-12-04 019

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.

2013-12-03 015

2013-12-03 034

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.

2013-12-04 0052013-12-04 0142013-12-04 0152013-12-04 020

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.

2013-12-04 0032013-12-03 046

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!