Tag Archives: Bloyd Formation

Notes from the Field: Weathers and Delaney Quadrangles

 

Parthenon in Felkins Creek

Parthenon Sandstone overlying Brentwood Limestone on Felkins Creek, Weathers quadrangle

Recently, geologists at the Arkansas Geological Survey (AGS) completed geologic mapping of the Weathers and Delaney quadrangles in northwest Arkansas. These quadrangles are part of the U. S. Geological Survey’s 7.5-minute topographic series and cover an area of approximately 120 square miles. This project was made possible by a grant from the National Cooperative Geologic Mapping Program of which STATEMAP is a part. This year marks the 25th year of STATEMAP projects in Arkansas and represents an unprecedented commitment to gathering data on the geologic features of our State. STATEMAP was established in 1992 by an act of Congress to encourage the states to map their geology at the 1:24,000 scale. The first grant received by the Arkansas Geological Survey, then known as the Arkansas Geological Commission, was for a proposal in fiscal year 1994.  Since that time, eighty, 1:24,000-scale geologic maps have been completed, including the Weathers and Delaney quads.

Printed copies of the new geologic maps (and many others) are available at the AGS office in Little Rock for $12.50, but they are also available as a free download in .pdf form on our website. Here’s the link to the Delaney Quadrangle:

https://www.geology.arkansas.gov/docs/pdf/maps-and-data/geologic_maps/24k/Delaney.pdf

Geologic Map of Delaney Quadrangle

And here’s the link to the Weathers Quadrangle:

https://www.geology.arkansas.gov/docs/pdf/maps-and-data/geologic_maps/24k/Weathers.pdf

Geologic Map of Weathers Quadrangle

STATEMAP, which is administered by the U. S. Geological Survey, provides Arkansas with federal dollars through an annual grant proposal process. These funds are matched by the AGS which then performs all the work necessary to produce new geologic maps for the State. This year’s grant enabled the AGS to hire a geologist and to partially cover expenses incurred during field work. Garry Hatzell and staff geologist Richard Hutto worked together as a team during the data collection and map production phases of the project. This team approach has worked well for the AGS during its long history of geologic mapping, both for safety and efficiency.

The goal of STATEMAP is to classify bedrock exposed at the surface into recognizable units, such as formations and members, based on a common lithology—basically, an areal inventory of surface materials. Unfortunately, bedrock outcrops are few and far between in our State because so much of the surface is covered by alluvium (stream deposits) or colluvium (slope deposits). Since we are mapping the bedrock geology, we have to find ways to see through this cover and infer what is beneath it. We do map certain types of surficial deposits in some areas, however. Along the valleys of mature streams for instance, alluvium and terrace deposits are mapped. On steep hillsides, various types of debris flows considered to have moved in the recent past are mapped as landslides. Structural features, such as faults or folds, that offset or deform rock units are also described and mapped. In areas where the bedrock is covered, these relationships are inferred from data gathered nearby where outcrops are better.

Landslide in Atoka near Frog BayouParthenon Boulders in Kings River

Recent landslide in the Atoka Formation on the Delaney quad (left) and boulders of Parthenon sandstone in Kings River on the Weathers quad (right)

For this reason, much of our data collection efforts are concentrated on stream beds. There, erosional processes have typically removed soil and loose rock leaving sporadic, well-exposed outcrops of bedrock to study. Also, following a streambed allows us to see strata from bottom to top (or vice versa) which puts each formation in context with others. Locating and describing the physical contacts between formations is one of the most important things we do while mapping. Because formations are laterally extensive, disparate points taken on similar contacts can be connected across the mapping area to delineate each formation. Drawing these contact lines between formations in the correct location is a major focus of the mapping process.

Parthenon/Brentwood at Kings River FallsParthenon/Brentwood in Crosses Creek

Contact between the Parthenon and Brentwood Members of the Bloyd Formation on the Weathers quad at Kings River Falls (left) and on the Delaney quad in Crosses Creek (right)

Currently, the AGS’s STATEMAP projects are focused on the Ozark Plateaus Province, part of the Interior Highlands Physiographic Region located in the northern part of the State. The Ozark Plateaus in Arkansas consist of three broad surfaces that have developed due to differential erosion of Paleozoic sedimentary rocks on the southern flank of the Ozark Dome. Weathers and Delaney lie within the Boston Mountains Plateau, the southernmost and highest of these three surfaces. On these quads, over 1000 feet (305 meters) of Mississippian to Pennsylvanian (Chesterian, Morrowan, and Atokan) carbonate and clastic rocks are exposed. These rocks formed from sediment deposited in distal to near shore marine, tidal, deltaic, and fluvial environments.

Boston Mountains Plateau from Boston, Ark.

On the Boston Mountains Plateau, looking west toward Delaney from Boston.

In this area, the White River is increasingly being utilized as a public water source. Because of its importance in this regard, there is a lot of interest in gathering baseline data in this watershed. Most of the Delaney quad is drained by the White River, the uppermost reaches of the Middle Fork of the White River, and numerous smaller tributaries of the White. Some small drainages along the west side of the quad and Frog Bayou along the southern edge drain to the Arkansas River. Most of Weathers quad is drained by the Kings River and its tributaries as well as upper reaches of War Eagle Creek and the Buffalo River, all of which contribute to the White. Field work this year included hiking, wading, and swimming about 4.5 miles of the White River and 7 miles of the Middle Fork of the White River on the Delaney quad. 11 miles of the Kings River and 10.5 miles of Felkins Creek were traversed on the Weathers, along with numerous other streambeds on both quads.

Fossiliferous Brentwood in White RiverFossiliferous Brentwood in Cowcumber Creek

Close examination of fossiliferous Brentwood Limestone in White River on Delaney quad (left). Crinoid detritus including spines and cup plates in the Brentwood in Cowcumber Creek on Weathers quad (right)

The most significant structural feature on Weathers is the Russell Ridge Monocline, the axis of which is oriented parallel to other northeast-trending faults and lineations in northwest Arkansas. Presumably these align with regional faulting of Precambrian basement rock. The strata are depressed approximately 200 feet (61 meters) from southeast to northwest across this structure. Various normal faults with throws from 60-100 feet (18-20 meters) were also mapped. In the northwest corner of Delaney, the Drakes Creek Fault, a normal fault that also trends northeast, is downthrown to the southeast approximately 200 feet (61 meters).

Normal fault in Whispering Hollow

Yellow line marking the trace of a normal fault in Whispering Hollow on Weathers. Pitkin (Mp) downthrown to Fayetteville (Mf) approximately 60 feet (18 meters)

The Ozark National Forest occupies parts of the southern two thirds of Delaney and the southern third of Weathers. It is managed by the U. S. Forest Service. Along a reach of the Kings River in the southern part of Weathers is the Kings River Falls Natural Area which is maintained by the Arkansas Natural Heritage Commission.

Kings River Falls

Kings River Falls, the centerpiece of the 1059-acre Kings River Falls Natural Area

Field work commenced on July 16, 2018 and was finished on March 28, 2019 for a total of 75 days. From early April through the end of June, the geologists analyzed field data, classified rock specimens, and wrote descriptions specific to each quadrangle. Contacts and structural features were drawn on a topographic map base both digitally and by hand. Brian Kehner and Kerstein Dunn helped digitize and symbolize the map elements in ArcMap, developed alternative base maps, and integrated field data into our seamless geodatabase. Final layout of the maps was accomplished in Adobe Illustrator by Garry Hatzell, and they were edited by AGS geologic staff.

Prairie Grove in Kings RiverAtoka in Shrader Hollow

Massive calcareous sandstone in the Prairie Grove Member of the Hale Formation in Kings River on Weathers (left). Thin-bedded sandstone in the Atoka Formation in Shrader Branch on Delaney (right)

Special thanks to Ciara Mills for accompanying us in the field several weeks this year. Also to Angela Chandler for writing the proposal and serving as Principal Investigator again this year. Her guidance and support of geologic mapping in the State inspires us all to do great things. Very special thanks to Jerry and Joan Johnson of Madison County whose hospitality and knowledge of the people and places in the mapping area provided invaluable support for our endeavor this year.

Joan, Richard, and JerryAngela

Joan Johnson, Richard Hutto, and Jerry Johnson by Little Mulberry Creek (left) and Angela Chandler on North Sylamore Creek (right)

Next year, STATEMAP is heading farther north to the Salem Plateau where Scott Ausbrooks, Bill Prior, and Garry Hatzell will be mapping the Mammoth Springs quadrangle. So if you see someone up there taking an unusually keen interest in the rocks, be sure to say hello.

Until next time, I’ll see you in the field!

Richard Hutto

 Team Ozark

Garry Hatzell and Richard Hutto—out standing in the field

Cannon Creek Waterfall at Parthenon/Brentwood Contact

Notes from the Field-Durham Quadrangle

 

Geologic Map of the Durham Quadrangle, Madison and Washington Counties, Arkansas

Geologic mapping of the Durham 7.5-minute quadrangle in northwest Arkansas was recently completed by the STATEMAP field team.  STATEMAP in Arkansas is currently focused on detailed 1:24,000-scale mapping in the Ozark Plateaus Region in north Arkansas.  It is accomplished through a cooperative matching-funds grant program administered by the US Geological Survey.   Field work was performed between July and February, and included hiking/wading/swimming the entire 12-mile stretch of the upper White River located on the quad.  Previous mapping delineated five stratigraphic units for the 1:500,000-scale Geologic Map of Arkansas, but at the 1:24,000 scale, we were able to draw ten. Further division is possible, but several units were considered too thin to map on the available 40-foot contour interval.

You can download your own copy of the map at this link:

http://www.geology.arkansas.gov/maps_pdf/geologic/24k_maps/Durham.pdf

 

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Generalized Stratigraphic Column of Durham Quadrangle

The Drakes Creek Fault, which runs diagonally from the southwest corner to the northeast corner, is the most striking feature on the map.  It is part of a major structural feature in northwest Arkansas, forming a lineament that can be traced at the surface for over 45 miles.  The Drakes Creek displays normal movement, is downthrown to the southeast, and offsets strata an average of 230 feet.  Associated with the fault on the northwest side is a large drag fold. There, rocks parallel to the fault are deformed such that units typically present at higher elevations away from the fault bend down to a much lower elevation next to the fault.  Erosion along this side of the fault has exposed the core of the fold along Fritts Creek, Cannon Creek, and other places.

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Detail of Cross-section of Durham Quadrangle

The Durham quad is far-removed from areas of previous STATEMAP projects in north Arkansas.  We completed work on the Mountain View 1:100,000-scale quad last year, ending on the Brownsville quad near Heber Springs.  Focus has now turned to the Fly Gap Mountain 1:100K quad as the next high-priority area.  When completed, we will have continuous 1:24K coverage for a large portion of the central Ozark Plateaus Region.  The Durham quad was an appropriate choice to begin mapping in this area due to its proximity to designated type sections for many of the formations in north Arkansas.  This facilitated easy comparisons between our field observations on Durham with the classic outcrops where these formations were first described.  Initial field investigations included locating, describing, and sampling these historic outcrops near Fayetteville. We visited many places the names from which the stratigraphic nomenclature we still employ was derived.  These places have such names as: Bloyd Mountain, Kessler Mountain, Lake Wedington, Cane Hill, Prairie Grove, Brentwood, Winslow, and Woolsey.  Having seen the stratigraphy in these areas firsthand better prepares us to track changes in lithology and sedimentation as we continue to map to the east and south of Durham in the coming years.

The following images were taken during this year’s field season and are arranged in stratigraphic order from youngest to oldest:

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Liesegang boxworks–Greenland Sandstone.  Mapped into the Atoka Formation

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Asterosoma trace fossils–Trace Creek Shale of the Atoka Formation

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Kessler Limestone just below the Morrowan/Atokan Boundary–mapped into the Dye Shale of the Bloyd Formation

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Parthenon sandstone resting on the Brentwood Limestone, both of the Bloyd Formation.  The Parthenon was also mapped into the Dye

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Mounded bioherms in the Brentwood Limestone

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Tabulate coral colony in the Brentwood Limestone

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Herringbone cross-bedding in calcareous sandstone–Prairie Grove Member of the Hale Formation

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Goniatitic Ammonoids in calcareous sandstone–Prairie Grove

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South-dipping sandstone in the White River south of the Drakes Creek Fault–Cane Hill Member of the Hale Formation

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Soft-sediment deformation–Cane Hill

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Pitkin Limestone, below the Cane Hill near West Fork—Mississippian/Pennsylvanian Boundary

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A cluster of solitary Rugose corals–Pitkin Limestone

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Wedington Sandstone of the Fayetteville Shale at West Fork

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Base of the Wedington–mapped into the upper Fayetteville Shale

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Large septarian concretion–lower Fayetteville Shale

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Pyritized Holcospermum (seed fern seed-left) and goniatitic ammonoid (right)–lower Fayetteville Shale

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Boone Formation, along the White River in the northwest corner of the Durham quadrangle

This year, we’re moving east to map the Japton and Witter quads. Wish us luck as we begin a new field season.  We’ll try to keep you apprised, so until next time, we’ll see you in the field!

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Richard Hutto and Garry Hatzell

Statemap 2015-16 Update

 

Hello all!

Well, another year, another map!  The Brownsville quad is now published (see map below), and a link to it will be posted on our website soon.  This year marks the 22nd anniversary of Statemap, aka the National Cooperative Geologic Mapping Program, in Arkansas.  Statemap is partially funded by a USGS grant, and was established to encourage the states to map their surface geology at the 1:24,000 scale.  To date, our mapping teams have completed thirty-three quadrangles in the West Gulf Coastal Plain and, with the recent publication of the Brownsville quad, forty quads in the Ozark Plateaus.

Geologic map Brownsville, AR

The geology of the area around Greers Ferry Lake has never been mapped in great detail until now.  Previous work had been to produce the 1:500,000-scale Geologic Map of Arkansas.  Because we mapped the Brownsville quad at the 1:24,000 scale, we were able to make some observations new to science.  A fault was discovered that had never been mapped previously.  We named it the Shiloh Fault for the old town, now inundated by the lake, that lies along its trace.  Meanders of the Little Red River channel approached this fault but didn’t cross it, probably due to encountering more resistant rock on the north side of the fault.  The Witts Springs Formation had not been mapped south of the Choctaw Creek Fault before, but we were able to draw in its upper contact with the Bloyd Formation along the Devil’s Fork and several other drainages.

Overturned cross beds in massive sandstone of the undifferentiated Bloyd Formation

As on other quads around Greers Ferry Lake, we continued to find terrace deposits left behind as the Little Red River carved the valley down to its present elevation.  Some of these are stranded as much as 260 feet above the current channel bottom (now located on the bottom of the lake).

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For many years now, our mapping program has focused on completing the Mountain View 1:100,000-scale quad.  This area encompasses thirty-two 1:24,000-scale quads and stretches from Richland Creek to Sylamore Creek on the north side and from the Illinois Bayou to Greers Ferry Lake on the south side.  Now that this area is finished, our Statemap Advisory Committee has decided we should jump over to northwest Arkansas to complete work on the Fly Gap Mountain quad, just west of the Mountain View quad (see map below).

STATEMAP index for blog

So for next year, the Statemap team is going to start work on the Durham quad in the northwest corner of the Fly Gap Mountain quad near Fayetteville.  We’ll have to spend a few weeks getting our feet on the ground, so to speak, because we won’t have the benefit of already mapped quads adjacent.  Fortunately, we will be very close to the type-sections for most of the formations we’ll be mapping, so hopefully, we can study the classic outcrops and trace them into our new field area without too much difficulty.

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A type-section is an area, or even just an outcrop, where a particular formation was first described.  They are named after a local geographic feature.  Formations first described in northwest Arkansas include: the Fayetteville Shale, the Pitkin Limestone, and the Hale Formation which has the Cane Hill and Prairie Grove as members.  Members are smaller, discernable units within a formation.  The type-section for the Bloyd Formation, including the Brentwood, Woolsey, Dye, and Kessler Members, and the Trace Creek, which is the basal member of the Atoka Formation (named for its type locality in Oklahoma), is on Bloyd Mountain near West Fork.

I would like to take this opportunity to thank my field partners that accompanied me this past year.

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I started the year with Ty Johnson, who has since moved into a permanent staff position at the Survey, so congratulations to him!  He was with me for just a year, but we covered a lot of ground together.  He’s now mapping the geology of the Lake Ft. Smith area with an emphasis on landslide mitigation.

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The writer and also principle investigator of the Statemap grant, Angela Chandler, went out a few weeks in the late fall before we could fill the vacancy Ty left behind.  No matter how much I learn, she always manages to teach me something new.

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We hired Garry Hatzell, a recent U of A grad, who started fieldwork in January.  He brings an enthusiastic knowledge of paleontology to the mix, and I look forward to his continued insight into the biostratigraphy of our field areas.

Without the help of these fine folks, we couldn’t have gathered the data or produced the map.  Also, I would have been stuck in the office—a torture for the unrepentant field geologist.

Wish us luck on the Durham quad!  And if you’re in northwest Arkansas during the next twelve months and happen to drive by a Jeep Cherokee with the AGS seal on it, be sure to stop and introduce yourself.

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Until then, I’ll see you on the outcrop!

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Richard Hutto

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!