Stratigraphy of the Badlands National Park
By Vic Bennett
The Badlands are located off interstate 90 north of the town of Interior in Pennington and Jackson counties in the high great plains of south west south Dakota . Named mako sica meaning badlands by the Lakota Indians and badlands by white settlers due to its rugged barren desolate appearance, and because the soil made poor farm land. The park was designated a national monument in 1929 by Franklin Roosevelt in a effort to protect the fossil rich terrestrial deposits of the white river group and then became a national park by act of congress in 1978. The park has in total 244,000 acres divided into three areas, the northern Sage Creek area containing 64,000 acres of wilderness area which is home to the endangered black footed ferret. In the south there are the two southern units, the Stronghold unit, and the smaller Palmer Creek unit, both are located in the Pine Ridge Indian reservation, and are managed by the Oglala Lakota Indians, and the National Park Service (fig 1).
Figure 1 The Badlands are best known for its scenic landscapes and rugged topography.
The Badlands were not even here until 500,000 years ago when erosion began to shape the landscape, before that it was a vast flat floodplain that has not been subjected to mountain building process. Climate is the main factor in molding the parks topography, with weather extremes of over 100ºF in the summer to subzero in the winter, and a annual rainfall of 16 inches, with most of the rain fall occurring at spring producing hot dry summers, and cold dry winters which lead to sparse vegetation, and an maximum erosional process (Stoffer, 2003). Erosion is still today changing the landscape, it is estimated that one inch per year is being removed; suggesting that in 500,000 more years the badlands will disappear.
Pierre Shale (fig. 2)
The visible landscape first began to form 75 million years ago during the cretaceous period when a shallow sea covered what is now the great basin. This sea may have persisted for 50 million years slowly depositing sediments thick with marine fossils such as ammonites and clams. This depositional period produced a formation known to geologists as the Pierre Shale (fig. 2), or strat column. The Pierre Shale is further subdivide into five members (formally) or facies (informally) in the badlands park area, with the Degrey as the oldest followed by Verendrye, Virgin Creek, Mobridge, Elk Butte as the uppermost and youngest of the Pierre Shale. The Degrey facies outcrops along the Cheyenne River valley, and along Indian creek, and is dark reddish-gray fissile shale with thin yellow bentonite beds with fossils of marine ammonites, and clams. Verendrye facies is gray shale with limestone concretions, and contains giant clam fossils, and is visible along Sage creek close to the Sage creek campground. Above the Verendrye is the Champanian-Maestrichtian unconformity which seems to be related to a global fall and rise in sea level, and suggests major changes to the ecology that occurred approximately 71 million years ago. Above the unconformity is the Virgin creek facies that is light gray shale with yellowish bentonite beds and limestone concretions that can be found in the north unit along the Sage creek valley. Mobridge facies is deposited on top of the Virgin creek facies, and can best be viewed in the hillsides along South fork, and middle fork valley’s in the Sage creek wilderness area. The Mobridge is calcareous shale, chalk, and marl with limestone concretions, and is light blue in color, containing a large straight shelled ammonite as an indicator fossil. The final and upper most facies of the Pierre shale is the Elk Butte facies this shale can be identified as being dark gray fissile and barren of fossils, best seen along middle fork in the Sage Creek wilderness area.Figure 2.
Fox Hills Formation (fig. 2)
Approximately 68 million years ago, at the end of the cretaceous period the Rocky Mountains, and the Black Hills were being uplifted, slowly changing the environment from marine to terrestrial in the Badlands area. During this time the Fox Hills formation was being deposited on top of the Pierre Shale (fig. 2) or strat column. This unit is not recognized on the USGS geological map of the badlands (Raymond and King 1976, but will be described here according to (Stoffer, O.F.R. 03-35, 2003), and has been recognized as part of the Badlands north unit. According to Gill and Cobban (1973) the Fox Hills Formation can be described as being shallow marine, and marginal terrestrial deposits usually in the form of massive cross bedded sandstone, but this feature is missing in the badlands park area. The formation contained four members, the lower Trail City, and Timber Lake members both being marine deposits, upper Colgate, and Iron Lighting members both being terrestrial deposits, and the Enning facies, also marine. Stoffer, 2003 added two other facies on top of the Fox Hills formations those being the disturbed zone, and the unnamed marine facies. The Trail City member can be found along the tops of the hills along the south and the middle fork of the Sage Creek. The Trail City member can be described as being pale gray mudstone or shale with large iron concretions, and containing ammonite fossils. The Timber Lake member sets above the Trail City member, and can be found in the Conata Creek area, and described as being brown to reddish brown sandstone, and contains one of the youngest ammonite fossils of the late cretaceous peorid (jeletzkeytes nebrascensis) (Stoffer, O.F.R. 03-35, 2003). The Enning facies this facies can be described as a green and red colored marl, with fossils of fish, clams and plant material, and more.
The most interesting facies in the Fox Hills formation is without a doubt the disturbed zone. This zone sets on the Enning facies, and has been dated to 66.3 milloin years ago by radiometric dating of 87Sr/86Sr using belemnite fossils, and correlates to the time of the great extinction between the cretaceous and tertiary boundry (Stoffer 2001). The disturbed zone is a brightly colored mudrock that contains roll structures that is similar to hurricane deformation, but on a larger scale in the badlands (fig. 3). Other evidence that the disturbed zone is related to the k-t boundary is that the deposits below the disturbed zone contain cretaceous marine fossils such as the mosasaur, and the disturbed zone contains charcoal fragment, and fragments of plant materials. Also the Unnamed Marine facies above the disturbed zone are horizontal, and contain no cretaceous fossils, but does have Paleocene ichnofossils of Skolithos/Cruziana, representative of an intertidal zone of a shallow sea, but also contains modern fish fossils such as the shark, and barracuda.
Chadron Formation (fig 4)
After the deposition of the Fox Hills formation 66.3 million years ago the uplift of the Rocky Mountains continued to increase the local elevation of the badlands area. This changed the environment, at first the conditions were hot and humid, inland seas and lakes existed, but as the land continued to rise the badlands became a river system. Deposited in this river system about 35 million years ago during the Eocene period is a formation of poorly consolidated mudrocks collectively called the Chadron formation. The Chadron Formation was named after the town of Chadron Nebraska where similar rock are found, and has three members, beginning with the youngest to the oldest Peanut Peak Member, Ahearn Member, and the Crazy Johnson Member (fig 4) or strat column. The rocks of the Chadron are gray to olive-gray sandy clay with a conglomerate at its base, and white fresh water limestone lenses in the middle member. The upper member consists of sandy clay mud with lots of bentonictic clay that makes the hill side slick when wet and thus no vegetation can take hold. The Chadron was originally named the titanotherium beds by Meek and Hayden in 1862 due to finding the fossil bones of a large rhinoceros mammal that lived there (Stoffer, 2003). Retallack 1983 reproduced the environmental conditions of the badlands area from the fossils found there. The fossil record produced a picture of a forested flood plain with scattered meadow’s with ponds and lakes. Some of the animal fossils found there were alligators, rabbit like, squirrel like, fox like, saber-tooth cat, horses, and more
.Figure 5Brule Formation (fig 4)
As more time past in the badlands the climate began to become a drier and cool environment, and the forests began to disappear. The Brule formation was the result of deposition in a floodplain, and stream environment during the Oligocene Epoch 32-26 million years ago. There are two members in the Brule Formation the older Scenic Member, and the upper Poleslide Member. The Scenic member sits conformably on the Chadron formation, and is rusty-red and gray-white layers of an ancient soil, and sandstone respectively. The Poleslide Member points to a change in the environment to an even drier and arid place then the early Brule, with massive sandstone deposits as it’s dominate feature. Meeks and Hayden in the 1850 have called the Brule Member the turtle, and oreodon beds. The Scenic Member holds turtle and oreodon fossils which is a sheep-like animal that lived in burrows. The Scenic Member was also home to a water rhinoceros called Metamynodon. The Poleslide Member was also home to oreodons, but of a different variety, and fossils of a sheep-like herbivore called Proteroceras
Sharps Formation (fig 4)
The Sharps formation was essentially the last major preserved depositional
event to take place in the badlands. Major changes took place in the late oligocene.26-28
million years ago, when the climate became dryer, possibly desert like conditions
(Harkenson, 1961). During this time the basal Rockyford Ash Member was deposited
due to wide spread volcanism that may have been related to the uplift of the
Black Hills. The Rockyford Ash is 3-7 m thick, white, and columnar jointed,
and is the ledge forming cap rock that can be seen at pinnacles overlook (Stoffer,
2003). The upper part of the Sharps contains light colored siltstone, and dark
brown shale, with a dozen paleosols identified (Retallack, 1983). It is thought
the environment was stream or open floodplain, in a semi-arid climate that had
seasonal droughts. After the Sharps Formation there is no record of deposition
taking place in the Badlands, the only exception is what is called the Medicine
Root Gravels, which are gravels thought to have came from fast flowing stream
out of the Black Hills two million years ago. .
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Raymond, W. and King, R. (1976). Geologic Map Of The Badlands National Monument And Vicinity, West-Central South Dakota. U.S. Geological Survey, Map-I-934, 1:62,500
Stoffer, P. (2003). Geology of Badlands National Park: A Preliminary Report. U.S. Geological Survey, O.F.R. 03-35.Retallack, J. (1983), Late Eocene and Oligocene paleosols from Badlands National Park, South Dakota: Geological Society of America Special Paper, 193, 82 p.
Gill, and Cobban. (1973), Stratigraphy and Geologic History the Montana Group and Equivalent Rocks, Montana, Wyoming, South Dakota, USGS Professional Paper 776.
National Park Service: http;//www.nsp.gov/badl