An Explosive Discovery
Ka-boom! Explosives blasted a hole completely through the Big Manitou Rock signaling the birth of a new gateway. The year was 1892, and the Missouri-Kansas-Texas railroad endeavored to extend their line through the small town of Rocheport, Missouri. Unwittingly, new veins for exploration into the town's geologic history were also opened.
Like much of the Missouri River valley, the exposed rock surfaces in Rocheport are from the Mississippian period approximately 359 to 329 million years ago. Examples of lower and upper Burlington Limestone are easy to spot due to their fossiliferous nature. Crinoids, a marine organism with remains that mostly resemble segmented straws or discs, are plentiful. What makes the Rocheport tunnel unique is the presence of early calcareous (calcium carbonate) foraminifers.
Fora-What?
Foraminifers, colloquially referred to as "forams", are single-celled protists. As they grow, a mineral rich, multi-chambered shell, called a "test", forms around the core organism much like a mollusk. Their pseudopods, projections from the cellular membrane, can stretch up to twenty-five times their test size to gather nutrients and relocate. An abundant ocean species, they either live on the sea floor (benthic) or in the higher reaches of the water column (planktonic).
Five hundred and forty two million years ago, forams developed in Earth's oceans. Tests were initially tubular in shape and formed through agglutination (the gluing together of materials). The Mississippian and following Pensylvanian periods (also known as the Carboniferous period) marked a change where forams evolved to secrete porous tests comprised of calcium carbonate. Some became planktonic 159 million years after their inception migrating to the upper ocean. Today, four thousand different species still thrive in our oceans one percent of which are planktonic.
Geological Bookmarks
Sensitivity and a large variance give the foraminifer an edge in geologic observation. To date, there have been over forty thousand species of foram in the fossil record. Most are short lived and only exist in particular environments. A given species will indicate specific water temperature ranges, salinity and depth providing a very precise glimpse into the past. The remains of these organisms have become a reliable source for indicating likely locations of oil as a result.
The Rocheport foraminifers are rare in that they still exist. Surrounding the foram layers, or lenses, is Burlington limestone containing calcite crystals. These spars grow over time and usually overprint more fragile calcium sources such as the thinner and porous foram tests. This fate has not been completely escaped; the lenses containing our protist friends are also composed of calcite spars that may originate from the fossils themselves.
A Funny Thing Happened On the Way to the Foram
Are you ready to find some foraminifers? Start at the posted coordinates on the tunnel's east side. Walk to the tunnel. Look to the right (north) and three to four feet up from the ground just at the entrance. You will see the cross-cut of a foram lens in the rough shape of a capital letter "I".
A few observations can be made at this point. The pigmentation of the foram rock is distinctly different from the surrounding rough grey Burlington limestone and smooth, round white chert nodules. Oxidation of the organic components is to blame for the differing coloration. Shining a direct light on the exposure reveals crystalline calcite that sparkles. Incredibly tiny, rounder nodules can be seen intermixed with the spars; these are the foram fossils. Please do not touch this or any other foraminifer exposures; they are very fragile and easily broken.
1) What color, roughly, is the foraminifer lens? (hint: not grey or white)
2) From where do the calcite spars in the lens originate?
3) Measure the length and height of the capital letter "i". Which is longer?
Now, turn to the opposing (south) side. Seek the presence of further foram layers; you shouldn't have to go more than twenty-five feet into the tunnel. A flashlight may or may not be required depending on the time of day. Also note crinoid fossils; these are a staple of Burlington limestone.
4) How many foraminifer layers are on the south side of the tunnel?
5) Are crinoid fossils found within the foram lenses?
Continue through the tunnel to the other entrance. Watch out for pigeons! Exiting the western aperture, proceed to mile marker 179 (N 38° 58.668 W 092° 34.377). Keep your previous observations in mind, and locate foraminifer layers on the north side of the trail.
6) How do the exposed foram lenses differ from those inside the tunnel?
7) Why are foraminifers good indicators of geologic history?
Excellent! Now that you've answered these questions, please send your responses to Unitzoid by clicking here. Your find won't count otherwise!
Consulted Sources
First and foremost, this EarthCache wouldn't be possible without the help of Howard Loftis and Steven Stanton of the University of Missouri Department of Geological Sciences. Both dedicated time, equipment, and, most importantly, their expertise to this EarthCache. Seeing foraminifers magnified was simply incredible and revealed the amazing diversity of these creatures.
Alden, Andrew. Foraminifers or Forams - Fossil Picture Gallery. http://geology.about.com/od/fossilstimeevolution/ig/fossil-pictures/fossil-foram.htm
Febo, Lawrence, Lubinski, David, Korsun, Sergei, and Polyak, Leonid. What are Foraminifera? http://bprc.osu.edu/geo/projects/foram/whatarefor.htm
Olney, Matthew. Foraminifera. http://www.ucl.ac.uk/GeolSci/micropal/foram.html
Wetmore, Karen L. Fossil Record of Foraminifera. http://www.ucmp.berkeley.edu/foram/foramfr.html
Permission to place this EarthCache was provided by Jim Gast, regional manager of the Katy Trail.