The Geologic Story of Petit Jean State Park
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SPS-02 STATE OF ARKANSAS ARKANSAS GEOLOGICAL SURVEY Bekki White, State Geologist and Director STATE PARK SERIES 02 THE GEOLOGIC STORY OF PETIT JEAN STATE PARK by Angela Chandler Little Rock, Arkansas 2007 STATE OF ARKANSAS ARKANSAS GEOLOGICAL SURVEY Bekki White, State Geologist and Director STATE PARK SERIES 02 THE GEOLOGIC STORY OF PETIT JEAN STATE PARK by Angela Chandler Little Rock, Arkansas 2007 STATE OF ARKANSAS Mike Beebe, Governor ARKANSAS GEOLOGICAL SURVEY Bekki White, State Geologist and Director COMMISSIONERS Dr. Richard Cohoon, Chairman………………………………………....Russellville William Willis, Vice Chairman…………………………………...…….Hot Springs David J. Baumgardner………………………………………….………..Little Rock Brad DeVazier…………………………………………………………..Forrest City Keith DuPriest………………………………………………………….….Magnolia Becky Keogh……………………………………………………...……..Little Rock David Lumbert…………………………………………………...………Little Rock Little Rock, Arkansas 2007 i TABLE OF CONTENTS Introduction…………………………………………………………………………..................... 1 Geologic History……………………………………………………………………………………………. 1 Continents Collide………………………………………………………………...……...……… 2 Geologic Formations Present Within the Park………………………………………………..….. 3 Overlooks MA Richter and CCC Overlooks…..………………………………………………….....…….4 Stouts Point……..…...……………………………………………………………….....……... 4 Cedar Creek………………...……………………………...…………………………….….… 5 Interesting Features Within The Park Carpet Rocks…………………………………………………….…………………………..…6 Turtle Rocks………………………………………………………………………………..… 7 Ancient River Features…………………………………………………………………….…………………..….7 Fossils……………………………………………………………………...………………….….. 8 Trails………………………………………………………………………………………….…... 9 Figures Figure 1. Physiographic Provinces of Arkansas………………………………………................ 1 Figure 2 Geologic time scale showing rocks present at Petit Jean State Park………………..… 2 Figure 3 Diagrams showing folded geologic structures.…...……….................……………….. 3 Figure 4. Generalized cross-sections from Petit Jean Mtn to Adona.…..……………………… 3 Figure 5. The Atoka Formation along Hwy. 154 beneath Stouts Point…………………………. 3 Figure 6. Columnar section showing sequence of rock formations at Petit Jean State Park.…… 3 Figure 7. Hartshorne Sandstone capping the Mountain………………..……………………… 4 Figure 8. Topographic map showing the “nose” at Stouts Point…………………….………...…4 Figure 9. The Arkansas River and its flood plain as seen from Stouts Point………………...…..5 Figure 10. Liesegang banding in rocks used to build the CCC structure at Stouts Point……….. 5 Figure 11. Rock House Cave rock shelter…………………………………………………..…….5 Figure 12. Cedar Falls. Notice contact betweenHartshorne and Atoka Formations………..……6 Figure 13. Talus or rock fall slope near Cedar Falls Trail…………………………………..…….6 Figure 14. Carpet rocks along Cedar Creek Trail………………………………………..………..7 Figure 15. Turtle rocks above the Seven Hollows Trail……………………………………...…...7 Figure 16. Ripple marks in rock at the CCC overlook……………………………………..……..7 Figure 17. Diagram of ripple marks………………………………………………………..…….. 8 Figure 18. Cross-bedding in Hartshorne Sandstone……………………………….……………...8 Figure 19. Lycopod fossils………………………………………………………………………..8 Figure 20. Fossil snails, clams and sea anemone…………………………………………….…... 9 Maps (In pocket) Trail Map 1: Geologic Map of Rock House Cave and a portion of Boy Scout Trail Trail Map 2: Geologic Map of Cedar Creek Trail Trail Map 3: Geologic Map of Cedar Falls Trail, Bear Cave Trail and Boy Scout Trail Trail Map 4: Geologic Map of Rock House Cave-portion of Boy Scout Trail ii THE GEOLOGIC STORY OF PETIT JEAN STATE PARK by Angela Chandler Introduction produced curiosities called “turtle rocks” and “carpet rocks”, leaving an unforgettable The majority of Arkansas State Parks are imprint in the mind. These are just a few of developed around interesting geologic the features preserved as illustrations of the features. Arkansas’s first State Park, Petit geologic story seen in the rocks at Petit Jean Jean State Park, was built by the Civilian State Park. Conservation Corps (CCC) from 1933 until 1941 and contains some of the best Location preserved and most scenic geologic features in the state. It is noted in the Nature Center Petit Jean State Park is located in the that Petit Jean became the first state park central and southern portion of Petit Jean “because of the beauty and drama of the Mountain. The mountain is located in the geological features in Seven Hollows”. Arkansas River Valley Region, a rather narrow and typically low-lying region surrounding the valley of the Arkansas River and its major tributaries. This region is bordered to the north by the Ozark Plateaus and to the south by the Ouachita Mountains. The Arkansas River Valley is characterized by gently tilted sedimentary rocks. In contrast are the flat-lying rocks of the Ozarks, and the steeply tilted and folded rocks of the Ouachita Mountains. Geologic History The rocks exposed in Petit Jean State Fig. 1. Physiographic Provinces of Arkansas Park formed during the Pennsylvanian Period of geologic time around 315 million Petit Jean Mountain contains many years ago. Underneath these sandstones and exceptional geological landscapes as a result shales are older rocks, predominantly of weathering and erosion that has taken limestones and dolostones that formed place during the last 250 million years. during the Cambrian through Mississippian Drainage from this bowl-shaped mountain Periods. The area known as the Arkansas formed scenic Cedar Falls, that carved a River Valley has been above sea level and steep canyon that is considered the eroding since the beginning of the Permian centerpiece of the park. Surrounding the Period. Therefore, no rocks were preserved canyon are numerous overlooks and trails until the Quaternary Period when the containing rock shelters and passageways Arkansas River deposited sediment in the cut by Cedar Creek long ago. Weathering form of terraces close to the mountain. 1 During the Pennsylvanian Period, the and later became buried when the river area now known as the Arkansas River meandered and changed its course. This Valley was a basin sitting between the river deposited sandy sediment that became slightly uplifted Ozarks to the north and the buried and compressed to form sandstone slowly rising Ouachita Mountains to the sequences that in some areas contain plant south. These higher areas from the fragments. This is the Hartshorne Sandstone surrounding regions supplied sand, silt and seen today on Petit Jean Mountain. clay that was carried into the basin by ancient river systems. Periodically, much of Continents Collide the basin was covered by a deepening ocean. Swamplands populated by ferns and trees The continents as we know them today unlike any today developed around bays and looked much different in the past. Since inlets. Sea level fluctuated during this time Cambrian time they have been shifting and and as sediment subsided in the basin, sea colliding so that around 365 million years water spread into the area covering the bays ago, North America was attached to the and inlets burying the swamplands. Several continents now known as Greenland and cycles of deposition created layers of clay Europe to form one large landmass called and sand which contained thin layers of Laurasia situated along the equator. South plant material. These layers became buried of the equator a larger continent called and compressed by overlying deposits to Gondwana, made up of the continents now form shales and sandstones with an known as South America, Africa, Antarctica occasional thin coal bed. These layers of and Australia had formed. These two rock are known as the Atoka Formation. landmasses moved toward each other and finally collided around 340 million years ago. During this collision some of the continental rocks of Gondwana became attached to the southeastern portion of Laurasia in what is now Arkansas. This collision first affected the sequence of rocks in what is now known as the Ouachita Mountains. These once flat-lying rocks were compressed into tight folds, downwarps and upwarps, called synclines and anticlines. Eventually deformation spread to the flat-lying shales and sandstones of what is now called the Arkansas River Valley. These rocks were compressed into more gentle folds that extended far above the current land surface. Fig. 2. Geologic time scale showing rocks During the last 250 million years these rocks present at Petit Jean State Park. have eroded to form the present landscapes within the Arkansas River Valley and Petit Eventually the ocean retreated west and Jean State Park. the in-filled basin became exposed. A large river system flowing east to west developed The area now known as Petit Jean in the low-lying area. Swamplands Mountain was compressed into a downwarp developed on adjacent flood plain deposits or syncline. The limbs and younger rocks 2 that would have existed on top of the along the highway on the east side of the mountain have been eroded. The lowest mountain beneath Stouts Point. At this portion of the syncline has been preserved as location dark gray to black shales are a mountain today. interbedded with thin layers of tan to gray sandstone. Thicker sandstones appear along the road at the top of the mountain. These sandstones are part of a different rock formation called the Hartshorne Sandstone. Fig. 3. Diagrams showing folded geologic structures. Fig. 5 The Atoka Formation along Highway 154 beneath Stouts Point. Fig. 4. Generalized cross-section from Petit Jean Mountain to Adona. Geologic formations present within the park.