-
Difficulty:
-
-
Terrain:
-
Size: 
(not chosen)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
The spillway at Clinton Lake provides an excellent introduction to the geology of Eastern Kansas. The dam here was constructed on the Wakarusa River in the 1970's and the spillway is a means by which water can move out of the lake during times of extremely high water levels.The bike path along this region was added in the 1990's and provides an excellent view of the geologic history.
Ground Zero will provide you with an excellent view of a cross section of the rock layers that are typical of this area. There are interbedded limestones and shales, all deposited during the Pennsylvanian Period of geologic history. During this period, Kansas was near the equator, the climate was warmer, and a shallow sea repeatedly advanced and retreated across the region. The rock layers here are fairly slim, but these formations extend vast distances across Kansas and adjacent states. Geologists have given each of these rock layers a name, based on the location where it was first described.
The limestones and shales here are part of two formations, the Oread Limestone and the Lawrence Formation. The Oread Limestone is named after nearby Mount Oread, home of the University of Kansas, where the formation was first described by geologist Erasmus Haworth in 1894. In spite of its name, the Oread Limestone, like many other formations, contains rocks other than limestones. The Lawrence Formation, which lies below the Oread (and is thus older), is named for the city of Lawrence.
Geologists have divided the rock layers in the Oread and the Lawrence down into smaller units called members. The rock layer at the bottom of the spillway is called the Amazonia Limestone Member, named for the small town of Amazonia, north of St. Joseph in Andrew County, Missouri. Above the Amazonia are shales that are also part of the Lawrence Formation. This part of the Lawrence Formation includes a thin coal layer called the Williamsburg coal bed, named for the small town of Williamsburg, Kansas. This coal layer is barely visible at the spillway. Above the Lawrence Formation is the Toronto Limestone Member of the Oread Limestone. The Toronto is a thick, light-gray to brown limestone that contains a few fossils. Above the Toronto is the Snyderville Shale Member, which is gray, and above that is the Leavenworth Limestone. The Leavenworth is a thin layer of gray to brown limestone that was first described from exposures near the town of Leavenworth. The next unit up is the Heebner Shale Member, one of the most recognizable rock layers in the spillway. The Heebner is very different from the Snyderville Shale and shales in the Lawrence Formation. The Heebner is dark-black. It is fragile and thinly bedded, deposited in layers so thin that they resemble pages in a book. In places, the Heebner contains phosphate nodules, marble-sized rocks that are high in phosphate and are slightly radioactive. Above the Heebner Shale is the Plattsmouth Limestone Member of the Oread Limestone. The Plattsmouth is a wavy-bedded, gray to brown limestone. In places it contains chert (or flint) and fossils such as crinoids, corals, or single-celled, wheat-grain-shaped animals called fusulinids. One obvious characteristic of these rock layers, as they are exposed here at the spillway, is their cyclicity. That is, the rocks here are deposited in a regular vertical sequence of limestone, shale, limestone, shale, etc.
This sequence of rocks, which geologists call a "cyclothem," is found not only in the Oread Limestone and Lawrence Formation, but is repeated in Pennsylvanian rocks above and below these formations. Geologists believe that this regular sequence of deposition is probably the result of fluctuations in sea level. As the sea levels deepened (in the range of tens of feet deep), limestone was deposited. As the seas shallowed, shale was deposited. Geologists disagree, however, about the reasons for the change in those Pennsylvanian sea levels. The changing sea levels may represent times when polar ice caps were shrinking or growing. When the ice caps melted, sea levels rose, resulting in limestone deposition. At other times, when ice caps grew, sea levels went down and shale was deposited.
There are other theories about the reasons behind the sea level change. Still, it is possible to look at the rock layers in the spillway as hard evidence of sea-level fluctuations in this long-ago ocean.
To Log This Cache 1) Estimate the thickness of the Heebner Shale layer. 2) Estimate the thickness of the Toronto Limestone layer. 3) What is the elevation at GZ?
Additional Hints
(No hints available.)