Wabash Reef EarthCache

This Earthcache will bring you to what is nationally recognized as one of the finest examples of a Silurian Coral Reef. It can be viewed from Paradise Springs Park in Wabash, Indiana. The famous Wabash Reef is located in the railroad cut northeast of the Big Four Railroad Station. The railroad cut bisects the reef and exposes a section of reef core, reef flank, and normal inter-reef rock about 900 feet long .However, neither the top nor the bottom of the reef can be seen in this exposure.

In 1898 , with the aid of dynamite, mules and strong backs, Railroad workers began cutting thru the ancient reef, thus creating the “Big Four Cut”.

The Wabash Reef is about 400 million years old. The reef is a remnant of the Silurian Sea that at one time covered part of Indiana and the Great Lakes Region. These reefs were exposed and modified by the rise and fall of the Wabash River.

The massive reef core, about 250 feet across, is composed of unstratified gray and tan dolomite which is splotched by small pockets of calcite and is cut by curved joint planes. The original reef-building material has been altered extensively, and few fossils can be recognized in it. Stromatoporoids stand out on the weathered surface on the back of the isolated spur east of the tracks, and Bryozoa are plentiful in shale pockets. Few corals are present in this reef.

The reef flank is composed of highly inclined tan and gray dolomite beds which wedge out away from the core and interfinger with normal interreef rock.. Some of the dips are as high as 65 degrees. The flank beds thin and thicken rapidly and probably represent talus slopes made from reef sands and stony organic fragments. The beds are more fossiliferous than the reef core. The normal inter-reef rock in this section is the Mississinewa shale. It occurs on both sides of the reef and has normal bedding within a few feet from the reef flank.

The coordinates listed above will take you to park signage that describes the Reef, and from which you can observe the Cut.

In order to log this cache, you must:

1. Post a picture of yourself, including your face, with your GPSr in hand next to the Sign.

2. Email the cache owner with an estimate of the depth of the Cut that exposes the layers of the Reef. In order to view the reef, you may want to move a little beyond the sign, but stay in the park.

Much of the limestone was laid down in large reef systems or bioherms in similar environments to the huge coral barrier reefs of today. After the end of the Ordovician, sea levels rose - probably due to release of water from the melting ice caps. The shallow water conditions over wide areas in Europe and North America provided ideal conditions for reef development. The other conditions - clear mud-free water and warmth were also largely present. Made up primarily of Calcium Carbonate (CaCO3) but sometimes dolomite [Calcium Magnesium Carbonate (CaMg(CO3)2)], limestone is the byproduct of organisms. In the earliest formations, bacteria and single-celled plants produced the lime by extracting the minerals from sea-water. At the start of the Cambrian System many different groups of animals started depositing their shelly skeletons into rocks. The vast quantities of skeletons then formed lime muds that under heat, pressure and vast periods of time turned into limestone rock. The reefs are formed by a whole collection of different organisms performing different tasks in the reef building process. The principles of the reef building process are the same today as in the Silurian 400 million years ago.