Monthly Archives: February 2010

Formations

The crust of the Earth is composed of a complex mix of rock types formed in specific depositional environments. Most of your everyday experience occurs in erosional environments, places where the surface of the Earth is being eroded away by physical or chemical processes. Rocks underfoot are being broken up then transported as sediments to other areas. The Grand Canyon is a good example of a river cutting through the layers of rock, exposing those layers, and transporting the rock away—piece by piece.

A cross section model of the Grand Canyon showing the rock layers and how they are broken into recognized formations.

A cross section model of the Grand Canyon showing the rock layers and how they are broken into recognized formations.

Where is that material going? It is transported to places where it is deposited, depositional environments, where the sediments accumulate. Given enough time and protection from further weathering, those newly deposited sediments can become the sedimentary rocks of the future. The deposition of sediment occurs in a wide variety of environments such as in oceans, rivers, ponds and the like.

If we look at the rocks on the surface of the Earth today, we can see differences in their color, texture, composition, and so on. We see layering as one rock type gives way to another. Geologists map these layers to trace out the history of the Earth, as each change in rock type represents a change in the environment that created it. So each outcropping of rock represents a time machine of sorts, transporting us back to the primeval environment of that spot.

A geologic formation is a formal unit, technically called a lithostratographic unit. That fancy word simply means that rocks are grouped by similar lithology, or rock type. For example, during the Late Cretaceous the last inland sea across the mid-continent of North America (a specific environment) deposited thick accumulations of chalk and shale. Today, we can lump specific sections of that collection of rock (lithology) into a single formation and call it the Niobrara Formation.

Each formation is described and named in a specific, formal way. There are rules that geologists should follow in designating specific formations (North American Commission on Stratigraphic Nomenclature, 2005). For example, each formation should have a type section designed. This type section is not unlike a type specimen mentioned in another post: it represents the standard for that formation to help others understand how it is unique.

In future posts we will explore more aspects of formations.

NORTH AMERICAN COMMISSION ON STRATIGRAPHIC NOMENCLATURE. 2005. North American Stratigraphic Code. American Association of Petroleum Geologists Bulletin, 89(11):1547-1591.

Related Post

Spending time in Purgatoire

Nature wallpaper for fun

Here at boneblogger we examine all things related to nature, including how you might celebrate nature in your own home. You can check out our recommendations for computer wallpaper. Here we explore nature wallpaper patterns that work well in your own private “den.”

Patterned papers

You can get a wide variety of papers with a nature theme. Patterned wallpaper has a regular, repeating theme, and care must be taken to match the pattern up on the wall during installation, so there is a bit of challenge with it. An example of a dinosaur-themed patterned paper is shown here:

A patterned dinosaur wall paper.


Perhaps you would like a more geology-based theme by having a “rock look” like this:

Or a travertine tile pattern like this (learn more about travertine):

Murals

Another popular choice for nature wallpaper is actually a giant wall mural. Such images can give a room an expansive feel by blowing out one wall of a room into a wider world. Such scenes include prehistoric themes like this:

Or space and astronomy themes such as this:

Or nature scenes like:

Borders

A slightly less overwhelming way to express your love of nature with a wall covering might be a simple border paper. Just the right nature image or the perfect accent colors on a border may be just the thing to personalize your space.

You could pick from rustic looks like these:

While it may be easy to find many choices of nature wallpaper for your home, choosing between them might prove to be a “dinosaur-sized” task. Have fun and express yourself.

Giant Short-Faced Bear: a Northern California Original

In 1878, James D. Richardson explored Potter Creek Cave in Shasta County, California. He found the skull of a bear beneath several inches of cave dirt, and he sent the specimen to Edward D. Cope, who determined that it was the type specimen for a new species of American “cave bear” (Cope, 1879).

Arctodus

Reconstruction of the Giant Short-faced Bear, Arctodus

When a scientist studies an animal and determines that it is something new to science, they set up a name for it and designate a type specimen. The type specimen, or type, holds a special significance as the “name bearer” for the entire species, and subsequent investigations of that species make reference to the type. They are often kept in special collections within the museums that hold them, or at least given special protection over other specimens. For example, they often are not loaned out as other specimens in the museum collection might be, so there is less risk of damage. (For a description of geologic type sections, see formations).

All too often the type specimens of fossil species have been based on fragmentary material or poor descriptions, making a full understanding of the species more difficult. A famous example of this is the story of the dinosaur Apatosaurus.

Apatosaurus was named by Cope’s rival, O. C. Marsh (Marsh, 1877). Both Cope and Marsh were rushing to describe more fossil species than the other, and their famous rivalry led to shoddy work by both men on occasion. Marsh said the type specimen of Apatosaurus was a “nearly complete specimen in excellent preservation.” However, he only briefly described the vertebrae of this new animal in his haste to publish the new name.

Later, Marsh published the name Brontosaurus, with a few comments on the pelvis and vertebrae of that type (Marsh, 1879). Brontosaurus soon became widely known to the public, and to many, represented the quintessential dinosaur. However, by 1903 Elmer Riggs recognized that Apatosaurus and Brontosaurus were in fact the same species of dinosaur, and since Apatosaurus was named two years before Brontosaurus, that name had priority and was the name that should be used (Riggs, 1903). However, the old name Brontosaurus was in such popular usage that it took many decades for the public to catch on. Now, it seems that every young dinosaur buff knows of this name change and is comfortable with it.

Since the first Short-faced Bear fossil to be recognized in North America was from Northern California, the type specimen, and the name of the bear, Arctodus simus, will be forever linked to the region. This “American Cave Bear” is now known from over 100 localities from Alaska to Mexico, east coast to west (Richards et al., 1996). It was a wide-spread species of the late Pleistocene Ice Age.

What is perhaps most striking about this bear is its size. Arctodus is the largest mammalian carnivore ever discovered. It is larger than any of the modern bears, tigers, or lions by a significant degree. An estimate for the largest Arctodus found to date suggests that if the individual was “lean” it weighed from 1,300 to 1,400 pounds (Nelson and Madsen, 1983). In contrast, a male lion weighs about 450 pounds. (See How big was the GSFB?)

So this imposing carnivore of the Ice Age roamed across North America, and the North State can forever claim it as its own. A full skeletal mount of this beast can be seen in the new Gateway Science Museum at Chico State.

COPE, E. D. 1879. The cave bear of California. American Naturalist, 13:791.

MARSH, O. C. 1877. Notice of new dinosaurian reptiles from the Jurassic Formation. American Journal of Science, 14:514-516.

MARSH, O. C. 1879. Notice of new Jurassic reptiles. American Journal of Science, 18:501-505.

NELSON, M. E., AND J. H. MADSEN, JR. 1983. A giant short-faced bear (Arctodus simus) from the Pleistocene of northern Utah. Transactions of the Kansas Academy of Science, 86(1):1-9.

RICHARDS, R. L., C. S. CHURCHER, AND W. D. TURNBULL. 1996. Distribution and size variation in North American short-faced bears, Arctodus simus, p. 191-246. In K. M. Stewart and K. L. Seymour (eds.), Palaeoecology and Palaeoenvironments of Late Cenozoic Mammals: Tributes to the Career of C.S. Churcher. University of Toronto Press, Toronto.

RIGGS, E. S. 1903. Structure and relationships of opisthocoelian dinosaurs. Part
1: Apatosaurus Marsh. Field Columbian Museum, Geological Series, 2:165-196.

Related Posts:
How big was the GSFB?
Denning behavior
GSFB reexamined

New species are still being uncovered at the Gray Fossil Site

Dr. Steven Wallace holds the beaver tooth recently discovered at the Gray fossil site. (Brian Bishop / Johnson City Press)

The Gray Fossil Site near Johnson City, Tennessee is full of surprises. The site dates to the late Miocene in age, and preserves a diverse fauna of critters. It is highly unusual to have deposits of this age preserved in the Appalachian region as most of the sediments have been stripped away from the underlying crystalline bedrock. But in this unusual setting, sediments that filled a sinkhole were preserved, along with a lot of evidence of past life from the region.

Researchers have not yet “scratched the surface” of the deposit despite several years of excavation. Core samples indicate that the deposit covers several acres and is over 100 feet thick (Wallace et al., 2002). Many species have been identified from the site including: fish; alligator; snakes; turtles; amphibians; a proboscidean; the world’s largest single collection of tapirs; rhinos; a short-faced bear; ground sloth; a saber-toothed cat; and a red panda.

They have recently added beaver to the list.

Steven Wallace and his team have identified the specimen as Dipoides, a member of an extinct line of beavers which includes the giant beaver Castoroides. Dipoides has a stratigraphic range extending from the Hemphillian to the late Blancan (Kurten and Anderson, 1980), or approximately 9 million to 3 million years ago (Prothero, 1998).

Today, you can visit a large interpretive center at the site, and watch summer excavations. It is expected that an annex will be started soon to provide even more space for visitor activities. Check it out on line at www.grayfossilmuseum.com, and watch for continued news coming from Johnson City, Tennessee in paleontology.

References:

KURTEN, B., AND E. ANDERSON. 1980. Pleistocene Mammals of North America. Columbia University Press, New York, 443 p.

PROTHERO, D. R. 1998. The chronological, climatic, and paleogeographic background to North American mammalian evolution, p. 9-36. In C. M. Janis, K. M. Scott, and L. L. Jacobs (eds.), Evolution of Tertiary Mammals of North America. Cambridge University Press, New York.

WALLACE, S. C., J. NAVE, AND K. BURDICK. 2002. Preliminary report on the recently discovered Gray Fossil Site (Miocene), Washington Co., Tennessee: with comments on observed paleopathologies and the advantages of a large sample. Journal of Vertebrate Paleontology, 22(Supplement to Number 3):117A.