Petit Jean and Mount Magazine Geological Tour - Arkansas ...

GuidebookAssociation ofDesk and Derrick Clubs________________________________________________Petit Jean and Mount MagazineGeological TourSept. 24 th and 26 th , 2007Prepared byAngela K. ChandlerArkansas Geological SurveyBekki White, State Geologist

GuidebookFor2007 ADDC Convention________________________________________________Petit Jean and Mount MagazineGeological TourSept. 24 th and 26 th , 2007Prepared byAngela K. ChandlerArkansas Geological SurveyBekki White, State Geologistii

Table of ContentsLocation………………………………………………………………………………………...…1Geologic History…………………………………………………………………………..……....1Description of Fieldtrip Stops……………………………………………………………………2.Stop 1 – Petit Jean State Park…………………………………………………………………....2Stop 1A – Cedar Falls Overlook………………………………………………………………....3Stop 1B – Turtle Rocks near Mather Lodge……………………………………………………4Stop 2 – Mount Magazine State Park………………………………………………………...…5Stop 2A – Mount Magazine Lodge/Lunch………………………………………………………7Stop 2B – Signal Hill………………………………………………………..………………….....8Stop 2C – Cameron Bluff Overlook Drive…………………………………………………...….8Stop 3 – Wiederkehr Village……………………………………………………………………..9Economic Geology………………………………………………………………………………..9References………………………………………………………………………………………..10FiguresFigure 1. Physiographic Provinces of Arkansas………………………………………….1Figure 2. Diagrams showing folded geologic structures………………………………. 2Figure 3. The Atoka Formation along Highway 154……………………………………. 2Figure 4. Columnar section showing sequence of rock formations within the park…… 3Figure 5. Hartshorne Sandstone capping Petit Jean Mountain…………………………...3Figure 6. View of Cedar Falls from overlook…………………………………………….3Figure 7. “Carpet rocks” along Cedar Creek Trail…………………………………… …4Figure 8. Box work near Cedar Falls Overlook……………………………………… …4Figure 9. Turtle rocks near Mather Lodge…………………………………………… ….4Figure 10. Turtle rocks near Rock House Cave………………………………………...…5Figure 11. Rock House Cave……………………………………………………………..5Figure 12. Columnar section showing rock formations within the park………………….5Figure 13. Shale in the Atoka Formation along Highway 309………………………… 6Figure 14. Contact between Hartshorne Sandstone and Atoka Formation……………….6Figure 15. Hartshorne Sandstone along Highway 309…………………………………...6Figure 16. McAlester Formation along Highway 309……………………………………7Figure 17. Savanna Formation along Highway 309……………………………………...7Figure 18. The Lodge at Mount Magazine State Park……………………………………7Figure 19. Rock wall made of Arkansas stone…………………………………………...8Figure 20. Signal Hill…………………………………………………………………….8Figure 21. The Savanna Formation along the bluff line of Overlook Drive……………...8Figure 22. Generalized stratigraphic column showing named coal beds.………………...9iii

Fieldtrip RouteRefer to the map below for the geological tour route. The tour route ismarked as a purple line with the field stops labeled in red. The physiographicregions are divided by a bold black line and labeled in black. The gray mapbase is a shaded relief map showing the topography of each region. Notice thedifference in each region and the rounded structures in the River Valley. Theseare the surface expressions of the anticlines and synclines we will be seeing onour tour.iv

LocationPetit Jean and Mount Magazine StateParks are located in the central portion of theArkansas River Valley. This region is a rathernarrow and typically low-lying areasurrounding the valley of the Arkansas Riverand its major tributaries. The Arkansas RiverValley is bordered to the north by the OzarkPlateaus and to the south by the OuachitaMountains. This region is characterized bygently tilted sedimentary rocks. In contrastare the flat-lying rocks of the Ozarks, and thesteeply tilted and folded rocks of the OuachitaMountains.Figure 1. Physiographic Provinces of ArkansasGeologic HistoryThe rocks exposed in Petit Jean and MountMagazine State Parks formed during thePennsylvanian Period around 315-290 millionyears ago. Underneath these sandstones andshales are older rocks, predominantlylimestones and dolostones that formed duringthe Cambrian through Mississippian Periods.The area known as the Arkansas River Valleyhas been above sea level and eroding since thebeginning of the Permian Period.During the Pennsylvanian Period, the areanow known as the Arkansas River Valley wasa basin sitting between the slightly upliftedOzarks to the north and the slowly risingOuachita Mountains to the south. Thesehigher areas from the surrounding regionssupplied sand, silt and clay that was carriedinto the basin by ancient river systems comingfrom the northeast creating deltas.Periodically, much of the basin was coveredby a deepening ocean. Swamplands populatedby ferns and trees unlike any today developedaround bays and inlets. Sea level fluctuatedduring this time and as sediment subsided inthe basin, sea water spread into the areacovering the bays and inlets burying theswamplands. Several cycles of depositioncreated layers of clay and sand whichcontained thin layers of plant material. Theselayers became buried and compressed byoverlying deposits to form shales andsandstones with an occasional thin coal bed.These layers of rock are known as the AtokaFormation.After deposition of the Atoka Formationa large river flowing from the east deposited asandstone called the Hartshorne Sandstone.This river was comparable to the present daysize of the Mississippi River and extendedfrom Conway, Arkansas to eastern Oklahoma.Following deposition of the HartshorneFormation were more delta systems creatingthe McAlester and the Savanna Formations,similar to the environment of deposition thatcreated the Atoka Formation.Continents CollideThe continents as we know them todaylooked much different in the past. SinceCambrian time they have been shifting andcolliding so that around 365 million years ago,North America was attached to the continentsnow known as Greenland and Europe to formone large landmass called Laurasia situatedalong the equator. South of the equator a1

larger continent called Gondwana, made up ofthe continents now known as South America,Africa, Antarctica and Australia, had formed.These two landmasses moved toward eachother and finally collided around 340 millionyears ago. During this collision some of thecontinental rocks of Gondwana becameattached to the southeastern portion ofLaurasia in what is now Arkansas.This collision first affected the sequenceof rocks in what is now known as the OuachitaMountains. These once flat-lying rocks werecompressed into tight folds, downwarps andupwarps, called synclines and anticlines.Eventually deformation spread to the flatlyingshales and sandstones of what is nowcalled the Arkansas River Valley. Theserocks were compressed into more gentle foldsthat extended far above the current landsurface. During the last 250 million yearsthese rocks have eroded to form the presentlandscapes within the Arkansas River ValleyThe area now known as Petit JeanMountain and Magazine Mountain werecompressed into a downwarp or syncline. Thelimbs and younger rocks that would haveexisted on top of the mountains have beeneroded. The lowest portion of each synclinehas been preserved as a mountain today.After a stop at the Visitors Center we willproceed to regular field trip stops.Directions: From Little Rock travel on I-40to exit 108 Highway 9. Travel south toOppelo and take a right on Highway 154 toPetit Jean State Park.Geologic formations present within thepark.Petit Jean Mountain is underlain by shalesand sandstones in the Atoka Formation andthe Hartshorne Sandstone. The AtokaFormation is divided into upper, middle andlower members based on regionally mappableshale or sandstone intervals. Only the uppermember is exposed in the park. In some areasfossiliferous beds containing mostlygastropods and bivalves are present. Theupper member of the Atoka Formation can beseen when beginning the climb to the top ofthe mountain from either direction onHighway 154. The best exposures are foundalong the highway on the east side of themountain beneath Stouts Point. At thislocation dark gray to black shales areinterbedded with thin layers of tan to graysandstone. Thicker sandstones appear alongthe road at the top of the mountain. Thesesandstones are part of a different rockformation called the Hartshorne Sandstone.Figure 2. Diagrams showing folded geologic structures.Description of Field Trip StopsSTOP 1 – Petit Jean State ParkFigure 3. The Atoka Formation along Highway154.2

STOP 1A – Cedar Falls OverlookDirections: Turn right off of Highway 154into the parking area for Cedar FallsOverlook when heading east/southeasttoward Mather Lodge.This is a very short walk to a magnificentview of the canyon cut by Cedar Creek andCedar Creek Falls. Walk underneath thestairway and around to the left to see greatliesegang banding sometimes called box-workand “carpet rock”.Figure. 4. Columnar section showing sequence ofrock formations within the park.The Hartshorne Sandstone caps Petit JeanMountain and forms the near vertical ledgesand bluffs around the top of the mountain.This rock formation also contains most of thegeologic curiosities including Rock HouseCave and Bear Cave. The sandstone is brownto light gray, forms thick beds, and is usuallycross-bedded. Scenic exposures of thissandstone are found behind Mather Lodge andmany of the cabins. This formation is easilyviewed at any of the overlooks for Cedar Fallsand the canyon formed by Cedar Creek.Figure 5. Hartshorne Sandstone capping PetitJean Mountain.Figure 6. View of Cedar Falls from overlook.Carpet RocksBox-shaped and triangular patterns areabundant in the sandstones on top of Petit JeanMountain. These patterns form when ironpresent in the rock is oxidized. Iron exists asthe minerals siderite, magnetite, hematite andsome clay minerals that are present in theHartshorne Sandstone. At some point ingeologic history water filled the pore spaces ofthe rock formation and came into contact withminerals made up of iron. This caused theiron to go into solution. If the rock becomesexposed to air then oxygen is added to thesolution and causes the iron to oxidize andprecipitate out along exposed joints in the rockformation. Sometimes color bands result from3

the different oxidation states of iron. Thesebands are also referred to as Liesegangbanding or box work by the scientificcommunity. Often the joints form interestingtriangles referred to as “carpet rock” by thepark community.Figure 7. “Carpet rocks” along Cedar CreekTrail.STOP 1B – Turtle Rocks area near MatherLodgeDirections: Veer right off of Highway 154onto lane toward Mather Lodge. Stop nearfirst rock outcropping on right side of road.Turtle RocksSome of the most unique features seen aroundthe park are those called “turtle rocks”.Mounded polygonal structures resembling aturtle shell were carved in thick sandstones ofthe Hartshorne Sandstone. These features areunique to this sandstone but not to themountain itself. More turtle rocks can befound throughout the Arkansas River Valleywhere the Hartshorne Sandstone is exposed.Turtle rocks also exist on Pleasant ViewMountain and London Mountain nearRussellville and Cove Mountain south of PetitJean State Park.The exact processes that create “turtlerocks” are poorly understood. Oneexplanation involves spheroidal weathering.This process occurs when water percolatingthrough cracks and between individual grainsin the rock loosens and separates layers of therock. The weathering acts more rapidly on thecorners and edges of the rock producing arounded shape. Another theory concerns theamount of calcite present in the matrix of therock holding the grains together along with thesize of the grains that allow for this type ofweathering. Either way the weathering of therocks is strongly influenced by the polygonaljoint pattern seen in all “turtle rocks”.Figure 8. Box work near Cedar Falls overlook.Figure 9. Turtle rocks near Mather Lodge.4

Other areas of interestIf time allows we may walk down to RockHouse Cave. Start at the Rock House CaveTrail and walk down to a excellent exposureof “turtle rocks”. This is a good area toexamine the joints around each “turtle back”.Follow the trail off of the outcrop and down tothe rock shelter. See what Cedar Creek carvedout long ago!Figure 10. Turtle rocks near Rock House Caveto Danville. Take a right in Danvillecontinuing on Highway 10 pass the town ofBellville. The next town is Havana. Take aright in Havana on Highway 309. Proceednorth to Mount Magazine State Park.After a stop at the Visitors Center we willproceed to regular fieldtrip stops.Geologic formations present within thepark.Mount Magazine State Park is underlain bysandstones and shales in the Atoka Formation,Hartshorne Sandstone, McAlester Formationand the Savanna Formation. All of theseformations can be seen when beginning theclimb to the top of Magazine Mountain fromHavana on Highway 309. For purposes of thisfield trip, the geologic descriptions of the areawill start approximately 3 miles north ofHavana on Highway 309. At this locationgood exposures of the upper part of the AtokaFormation can be seen.Figure 11. Rock House CaveSTOP 2 – Mount Magazine State ParkDirections: From Petit Jean State Parktravel west on Highway 154 to Highway155. Travel south to Hwy 10. Take a righton Highway 10 and continue west to Ola.Continue on Highway 10 turning left in OlaFigure 12. Columnar section showing rockformations within the park.5

Atoka FormationThe Atoka Formation is divided into upper,middle and lower members based onregionally mappable shale or sandstoneintervals. The upper part of the formationgenerally contains a higher proportion of grayblack shale than other parts of the AtokaFormation (Cohoon and Vere, 1988).Ironstone concretions and small coal seamsoccur in some intervals. Along Highway 309the Atoka consists of gray to black shales thatare less resistant than the overlyingHartshorne Sandstone. The contact betweenthe two formations is very sharp and wellexposed along the highway.Figure 14. Contact between HartshorneSandstone and Atoka Formationalong Highway 309.Figure. 13. Shale in the Atoka Formation alongHighway 309.Hartshorne SandstoneThe Hartshorne Sandstone is one of the mostpersistent sandstone units in Arkansas (Haley,1961). This unit is a prominent ledge formerin the area and consists of gray to brown finetomedium-grained sandstone. Sometimes anoccasional shale bed is interbedded within thesandstone and in some areas it has a thin coalbed at its base.Figure 15. Hartshorne Sandstone alongHighway 309.McAlester FormationThe McAlester Formation consists of mostly ashale sequence that can contain three or morecoal beds, in particular the Lower Hartshornecoal bed which is near the base of theformation (Haley, 1961). This unit is mostlycovered along Highway 309, but some shalewith interbedded thin sandstones is seenapproximately 4-5 miles north of Havana.6

STOP 2A – Mount Magazine Lodge/LunchDirections: Turn left off of Highway 309 infront of Visitor Center. Follow signs toLodge at Mount MagazineThe Lodge at Mount Magazine State ParkFigure 16. McAlester Formation alongHighway 309.Savanna FormationThe Savanna Formation consists of both shaleand sandstone, however the most notedportion of the unit is the sandstone capping themountain and forming the bluff line that isviewed at the overlooks.A good exposure of the Savanna Sandstoneoccurs at the last sharp curve climbing themountain just before the Petit Jean ValleyOverlook on Highway 309.This resort mountain lodge uses local stonework throughout the building and in thelandscaping on the grounds. Swartz StoneCompany in Paris, Arkansas provided a largesupply of ornamental stone especially thoseused for the rockwall in front of the lodge.Some stone also came from a quarry in theDanville area (Don Simonds, MountMagazine State Park, personalcommunication). Most likely the rock wasquarried from the Hartshorne Sandstone andthe Atoka Formation. Notice the decorativestone throughout the interior of the lodge aswell. Be sure to take a stroll on the backsideof the lodge and see the view of BlueMountain Lake. The large mountain beyondthe lake is Poteau Mountain and the axis of thePoteau Syncline.Figure 18. The Lodge at Mount MagazineState Park.Figure 17. Savanna Formation along Highway309.7

Figure. 19. Rock wall made of Arkansas stone.STOP 2B – Signal Hill – Highest Point inArkansasFigure 20. Signal Hill – Highest point inArkansas. Notice the rock monument.Signal HillThe highest point in Arkansas is located atMount Magazine State Park, specifically onSignal Hill with an elevation of 2,753 ft. Thehike to this point is a short one – only 15-20minutes one way and well worth it. There arethree different trails to this point. I suggesttaking either the one nearest the lodge whichis .6 miles or the trail starting at the entranceto Cameron Bluff Campground which is .4miles. Once you reach the summit, a rock“patio” (highpoint monument) in the shape orArkansas sits below a sign announcing thehighest point. Be sure to sign the guest book!STOP 2C – Cameron Bluff Overlook DriveCameron Bluff Drive provides spectacularviews north of the mountain into the rivervalley. Notice some of the structures typicalof the river valley called anticlines andsynclines. The Savanna formation is wellexposed creating a bluff line viewed at severalof the overlooks on this drive.Figure 21. The Savanna Formation along thebluff line of Overlook Drive.STOP 3 – Wiederkehr VillageDirections: From Magazine Mountainproceed north on Highway 309 to Paris.Take a left and travel west on Highway 369to Caulksville. Take a right onto Highway23 and travel to Ozark. Take a right andtravel east on Highway 64 to the town ofAltus. Turn left and travel north onHighway 186 for three miles to the village.8

Vineyard GeologyWiederkehr Wine Cellars is located in theArkansas River Valley on top of St. MarysMountain. According to the history of thewinery, the microclimate atop the mountainresembles the grape-growing climates inEurope’s finest wine regions. The winery andvineyards are located on the HartshorneSandstone.natural gas fields which contain approximately53 wells in Sebastian County. These wells areproducing from the Lower Hartshorne Coal inthe McAlester Formation.Annual coal bed natural gas production isestimated at 1.8 billion cubic feet as of 2006.Economic GeologyCoalThere are coal beds present in each of theformations exposed at Petit Jean and MountMagazine State Parks but not in the parkthemselves. The coal seams occur in variousplaces in the River Valley, averaging fromtwo inches to 6 feet thick. Major coal bedsoccur in the McAlester Formation and theSavanna Formation. Coal production inArkansas started in the late 1800’s mostlyfrom underground mines. In the 1950’ssurface mining began and became thedominant form of mining well into the 1970’s(Haley, 1978). The only coal mined inArkansas at this time is from the LowerHartshorne Coal in the McAlester Formation.There are two active mines in SebastianCounty. The coal has several uses: in acoating for pipelines; as charcoal briquettes;as a heat source for blacksmiths; and cokingused in steel-making and power generation.Coal Bed Natural GasThere is the potential for some of the coalbeds in Arkansas to produce gas. Methane isabsorbed on the internal surface of the coalitself and can be produced from the coal bed.This potential has not yet been quantified andis dependent upon many factors. However,coal bed production began in Arkansas in2002 and currently there are four coal bedFigure 22. Generalized stratigraphic columnshowing named coal beds.Natural GasCommercial development of natural gas inArkansas began in 1902 in Sebastian County.The principal gas producing formation in theArkoma Basin is the Atoka Formation thatcontains numerous sandstone beds (reservoirs)throughout the unit. The HartshorneSandstone was exploited prior to the 1930’sbut because of low pressure and low9

production this unit is of little commercialinterest (Storm, 1998). There is only one wellin Arkansas producing gas from theHartshorne Sandstone in Arkansas. TheMcAlester and Savanna Formations are notconsidered gas producers in Arkansas becausethey are present only at the surface or if buriedwould be too shallow and provide nooverburden pressure for gas production.The Arkoma Basin contains 104 gas fields butonly 99 of the fields are actively producinggas. Annual production is estimated at 150million cubic feet as of October 2006.Building Stone and AggregateMost of the sandstone quarried in Arkansas iscrushed and used for aggregate in concreteand asphalt. Large blocks (riprap) are used forfill and in dike and jetty construction. Rough,weathered sandstone blocks and boulders(fieldstone) have been used for years as facingstone on homes and other buildings, and tobuild other structures such as fireplaces, walls,and walkways. Much flaggy sandstone hasbeen produced from the Hartshorne Sandstone(Pennsylvanian) near Midway in LoganCounty. Other counties in west-centralArkansas that occasionally produce this typeof material are Logan, Sebastian, andFranklin. A substantial tonnage of thinflagstone and dimension stone has beenproduced in the state since the early 1950’s.References:Cohoon, Richard R., and Vere, Victor K., 1988, Blue Mountain Dam and Magazine Mountain,Arkansas: Geological Society of America Centennial Field Guide, South-Central Section.Haley, Boyd R., 1961. Geology of Paris Quadrangle, Logan County, Arkansas: ArkansasGeological Commission Information Circular 20-B.Haley, Boyd R., 1978, Resources of low-volatile bituminous coal and semianthracite in westcentralArkansas, 1978: U.S. Geological Survey Bulletin 1632.Storm, Taylor, 1988, The Hartshorne Formation of Arkansas in The Hartshorne Play insoutheastern Oklahoma: Regional and detailed sandstone reservoir analysis andcoalbed-methane resources: Oklahoma Geological Survey Special Publication 98-7.For more information contact:Arkansas Geological Survey3815 W Roosevelt RoadLittle Rock, Arkansasagc@arkansas.gov501-296-187710

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