Badlands Background, part I: Soils Past and Present

After a not-insignificant hiatus, blog entries have resumed. For the record, I would personally not recommend starting up a blog before: (1) traveling overseas, (2) getting violently ill, (3) returning home to hurriedly prepare to move to another state, (4) starting a new job, and (5) trying to finalize a manuscript for publication, in that or any order. Regardless, I have recently assumed a seasonal position at Badlands National Park, South Dakota. Due to the literal backyard accessibility and extensive library collections, many of the posts in the near future will likely be focused on Badlands NP geology and paleontology. So, I figured it would be prudent to give a brief background.

The first question, even among practicing geologists, may be “What exactly are badlands?” Unfortunately, “badlands” has come to be defined by consensus rather than by strict criteria, referring to terrain dominated by steep, rugged hills of loose sediment with little to no vegetation. Their creation results from a combination of loose, sandy sediment, sparse vegetation, sudden and intense rainfall, strong winds, and aridity. Despite their nebulous definition, the badlands at Badlands NP have come to be seen as the archetypical badlands due to their size and extent (also thanks to a bit of good timing in their discovery by white men). Incidentally, the name “bad land” has no complicated etymology – that exact phrase, or a slight variation thereof, was historically applied to this terrain by Lakota, French trappers, and English-speaking explorers alike. The same properties that allow for the creation of badlands mean the land isn’t conducive to transport, farming, or habitation, and isn’t a good source of water or oil. Badlands are an excellent source for fossil exposure, however, and are highly valued by paleontologists. Badlands NP, in fact, is worthy of its designation not only for its natural beauty and geologic record, but also for its rich fossil fauna (but more on that later). 

In Badlands NP, the “loose sediment” is over 150 m of volcaniclastic sediment, blown into western South Dakota from eruptions in Nevada and Utah(see Larson and Evanoff, 1998), and fluvially transported into the park between 32 and 28 Ma (Oligocene). Collectively, this sediment composes the Brule Formation, which makes up the bulk of the rugged, colorful badlands seen in the park. As it turns out, the famous colors of the badlands are significant - color banding of rocks in places like Grand Canyon and Canyonlands National Parks are a result of sediment deposited in very different environments, representing different formations. The color banding in Badlands NP is largely confined to one formation, and is caused by paleosols, or fossilized soils (Retallack, 1983). In the picture to the left, for example, the different red, white, and grey bands, as well as the thinner bands sticking out as ledges, represent different paleosols (the brown stakes at the bottom left are 1 m tall, for scale). As can be seen in the picture below, these paleosols can be found ad nauseum in outcrops – in one area, Retallack (1983) found 87 separate paleosols in a 143 m stratigraphic section. Taphonomically, paleosols are great because they represent surface exposure, can indicate the paleoenvironment, and can even hint at whether fossils may be present. But that’s only if you know how to read them, which as I’m learning, is not at all easy (the banding you see on the surface of the badlands, for instance, may have little to do with the actual banding in the rock underneath). Anyways, much more to come…

 

REFS

Larson, E.E., and Evanoff, E. 1998. Tephrostratigraphy and sources of the tuffs of the White River sequence, in Terry, D.O., Jr., LaGarry, H.E., and Hunt, R.M., eds., Depositional environments, lithostratigraphy, and biostratigraphy of the White River and Arikaree Groups (Late Eocene to Early Miocene, North America): Geological Society of America Special Paper 325, p. 1-14).

Retallack, G.J. 1983. Late Eocene and Oligocene paleosols from Badlands National Park, South Dakota: Geological Society of America Special Paper 193, 82 p.