WABASH
REEF
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.
GAG PHOTOS WILL NOT BE ACCEPTED