Tag Archives: Pennsylvanian

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

Notes from the Field: Japton and Witter Quadrangles

 

Geologic mapping of the Japton and Witter 7.5-minute quadrangles was recently completed by the Arkansas Geological Survey’s STATEMAP field team. In Arkansas, the STATEMAP Program is currently focused on detailed 1:24,000-scale mapping in the Ozark Plateaus Region, located in the northern part of the state.

image

Figure 1. Japton and Witter Quadrangles on the 1:500,000-scale Geologic Map of Arkansas (Haley et al., 1993)

Japton_final-red.jpg

Geologic Map of the Japton Quadrangle, Madison County, Arkansas. Download a digital copy at:

http://www.geology.ar.gov/maps_pdf/geologic/24k_maps/Japton_24k_geologic.pdf

Geological Map of the Witter Quadrangle

Geologic Map of the Witter Quadrangle, Madison County, Arkansas.  Download a digital copy at:

http://www.geology.ar.gov/maps_pdf/geologic/24k_maps/Witter_24k_geologic.pdf

STATEMAP is a cooperative, matching-funds grant program administered by the U. S. Geological Survey. The goal of the program is to classify surface rocks into recognizable units based on a common lithology–basically, an inventory of surface materials. Also, we strive to locate and depict any structural elements that may have deformed the rocks. The rock units are classified into formations and members, and structures are described as synclines, anticlines, monoclines, and faults. During the project, a rich dataset was recorded in the field using a portable data collector/global positioning satellite receiver as well as by traditional methods. This made possible a more detailed depiction of geological and structural features and a more comprehensive description of lithology than previous studies had done. Data collection included:

  • 629 field locations recorded and described in detail
  • 3,385 photographs taken at recorded field locations
  • 72 strike and dip measurements, most depicted on the maps
  • 950 joint orientations, depicted in a rose diagram of strike frequency
  • 1 shale pit
  • 8 springs, previously undocumented
  • 108 rock samples collected and described

The new map is useful to landowners interested in developing their land for personal or commercial purposes, to scientists seeking a better understanding of landscape evolution and geologic history, and to planners responsible for resource development and mitigating environmental impacts.

Angela Chandler, Principal Investigator for the project, wrote the grant for fiscal year 2018 and we received funding adequate to produce two maps.  Two geologists, Richard Hutto and Garrett Hatzell, began their field season last July and after putting in 76 days in the field, concluded that portion of their work in February of this year. The area of investigation lies within the Interior Highlands Physiographic Region in north Arkansas, specifically the Boston Mountains Plateau portion of the Ozark Plateaus Province. Previous work by the AGS in this area had been done in preparation for the 1:500,000-scale Geologic Map of Arkansas by Haley et al. circa 1976 (see Fig. 1). That mapping project delineated five stratigraphic units in this area, but through extensive field reconnaissance, we were able to define ten units on these maps at the 1:24,000 scale. Further division is possible, but several units were considered too thin to depict on the 40-foot contours of the topographic map currently available, or too difficult to delineate by lithology alone.

Several tributaries of the White River are located on these quadrangles including Lollars Creek, Drakes Creek, and War Eagle Creek. The White River is a major water resource in Arkansas and southern Missouri, and as such we need to learn as much as we can about this important watershed. Included in the field work was hiking, wading, or swimming the entire 13-mile stretch of War Eagle Creek located within the Witter quadrangle, the 10 miles of Lollars Creek within the Japton, and many smaller drainages. The reason we concentrate our efforts on stream beds is that there, erosion has typically removed soil and loose rock leaving well-exposed outcrops of bedrock for us to study. Also, being able to see the entire stack of the rock sequence as we move up or downstream helps put each formation in context with the others. Discovering where one formation contacts another is one of the most important things we do while mapping. Because formations are laterally extensive, similar contacts can be connected into a contact line separating one formation from another. Figuring out where to draw these lines on the map is a major goal of the project.

From mid-February through the end of June, we analyzed field data, classified rock specimens, drew formation contacts and structures on the map, then handed it off to our cartography staff to digitize. Final layout and production of the maps was accomplished by the geologists, after which they were subjected to an extensive review and editing process by fellow staff.

The following images were taken during this year’s field season. Hopefully, they will provide a small glimpse into some of what we were privileged to experience in the field this year.  They are arranged in stratigraphic order from youngest to oldest:

Alluvium in War Eagle CreekDSCN1957[14]

Alluvium in War Eagle Creek (left). Landslide on Highway 23 above Dry Fork (right).

DSCN0110

Ball and pillow structures in the Atoka Formation in Drakes Creek.

Herringbone Crossbeds in AtokaDSCN1357DSCN1353

Sequence of photos zooming into herringbone cross-beds in the Greenland Member of the Atoka Formation.

DSCN0602

Large blocks of Kessler Limestone sliding into Lollar’s Creek.

DSCN2294DSCN2258DSCN2279

Sequence of photos zooming into oncolitic limestone of the Kessler Member of the Bloyd Formation. The oncolite pictured far right is nucleated on a tabulate coral.

DSCN1057

Lycopod (tree-like plant) fossil weathering out of the Dye Shale.

Top of the Parthenon sandstone in Lollar's CreekDSCN0491

Top of the Parthenon sandstone (Bloyd Formation) in Lollar’s Creek (left). Parthenon resting on the Brentwood Limestone (Bloyd Formation) with travertine precipitating at the drip line (right).

DSCN0319DSCN0773

Siltstone unit in the upper Brentwood Limestone. Cross-bedded (left) and bioturbated (right). 

DSCN0065

Biohermal mounds in the Brentwood Limestone in Jackson Creek.

DSCN3028

Massive bluff of limey sandstone in the Prairie Grove Member of the Hale Formation.

DSCN3307DSCN2742

Sandy limestone in the Prairie Grove. Stream abrasion has revealed cross-bedding (left) and an ammonoid (right).

DSCN1710DSCN1753

Typical thin-, ripple-bedded sandstone of the Cane Hill Member of the Hale Formation (left). A basal conglomerate in the Cane Hill contains fossiliferous and oolitic limestone pebbles and fossil fragments (right).  This unit probably rests on the Mississippian-Pennsylvanian unconformity.

DSCN1799

The Pitkin Limestone in War Eagle Creek.

This year we will be mapping the Weathers quadrangle which is just east of the Witter, and the Delaney quadrangle which is just south of the Durham (which we mapped two years ago). The Kings River flows through Weathers, so this should be a good place to start while river levels are low (and it’s so hot!). I will update you as I can, but until then, I’ll see you in the field!

Richard Hutto

Geo-pic of the week: Syringodendron

Syringodendron

The above picture is of a syringodendron, the fossilized trunk of a giant tree-like fern that lived in Arkansas in the Pennsylvanian Period (318 to 299 Million years ago).  The Pennsylvanian Period is a sub-division of the Carboniferous Period of geologic history which was so named due to the preponderance of lush vegetation that existed at the time.  Because there was so much vegetation , the geologic record for the Pennsylvanian period is coal-rich and also preserved a lot of plant fossils.  This syringodendron was rescued from an abandoned coal mine in Scott County Arkansas by the land’s owner prior to the land being reclaimed.

The syringodendron is a somewhat rare as a fossil.  It is actually from the same plant that produces another more common plant fossil called a Sigillaria.  Here is an artists representation of what that plant may have looked like:

sigillaria_by_unlobogris

Syringodendron is a Sigillaria trunk that has lost its bark prior to fossilization.  The double impressions that run vertically at regular intervals are called Parichnos scars, or “hare’s trails” colloquially.  Between the vertical impressions are slight linear protrusions called ribs.  If you examine the top edge of the fossil, the ribs give a wavy or undulating shape to the margin of the trunk.

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

 

DurhamStratColumn

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.

image

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:

DSCN6923

Liesegang boxworks–Greenland Sandstone.  Mapped into the Atoka Formation

DSCN7179

Asterosoma trace fossils–Trace Creek Shale of the Atoka Formation

DSCN6339

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

DSCN0706

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

DSCN7923

Mounded bioherms in the Brentwood Limestone

DSCN4331

Tabulate coral colony in the Brentwood Limestone

DSCN7482

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

DSCN5407

Goniatitic Ammonoids in calcareous sandstone–Prairie Grove

DSCN5535

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

DSCN5470

Soft-sediment deformation–Cane Hill

DSCN4033

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

DSCN8341

A cluster of solitary Rugose corals–Pitkin Limestone

DSCN4565

Wedington Sandstone of the Fayetteville Shale at West Fork

DSCN4403

Base of the Wedington–mapped into the upper Fayetteville Shale

DSCN0763

Large septarian concretion–lower Fayetteville Shale

Img0033DSCN5622

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

DSCN5822

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!

DSCN5534DSCN4657

Richard Hutto and Garry Hatzell

Geo-pic of the week: Slickensides

Slickensidedshale_edited

The grooved surface pictured above is a slickenside.  Slickensides indicate the relative direction of movement between fault blocks (hanging wall moved up, down, laterally, etc..).  

Slickensides form when fault blocks move against each other.  The natural irregularities on each scratches grooves into the other.  The grooves are parallel to movement;  for instance in this example, movement was either to the right or the left.  To tell whether it was right or left, you can rub your hand along the slickensides.  They feel smooth in the direction the fault moved and rough in the opposite direction – it’s like petting a dog from tail to head.  Slickensides are a valuable tool because determining fault movement can be a challenge when there are no easily-recognized beds that can be correlated across the fault to show the sense of offset.

The shale above was photographed in Big Rock Quarry, North Little Rock, AR.  It’s a part of the Jackfork Formation (Pennsylvanian).

Geo-pic of the week: Conostichus trace fossils

Conostichus topConostichus bottom

Above are two pictures of a trace fossil, Conostichus, from the Ozark Plateaus region of Arkansas.  Like other trace fossils, Conostichus are structures found in sedimentary rock that represent the spot where an animal lived, fed, or travelled.  Despite their abundance, especially in rocks of the Carboniferous period (299 to359 million years ago), it’s not certain what kind of animal made Conostichus, because the animal’s body wasn’t preserved. 

The upper picture is the top of the Conostichus and shows the hole through which the animal entered or exited the structure.  The lower picture is the same Conostichus with the top facing down.  As you can see, they taper and come to a rounded point at the base, vaguely resembling a badminton birdie.  

At present, the most widely accepted theory for their origin is that Conostichus are burrow traces left by Sea Anemone.

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).

DSCN0999

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.

DSCN0704

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.

DSCN2086

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.

DSCN2258

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.

DSCN2641

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.

 DSCN3153

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

  DSCN2275       

Richard Hutto