Today’s field trip examines the geology and fossils at Edgerton Road and K-10 Highway, which are located in the uplands south of the Kansas River near DeSoto in Johnson County, Kansas. Rocks and unconsolidated materials are Pleistocene Epoch glacial deposits (also known as the “Ice Age”) and late Carboniferous System rocks (also known as the “Coal Age”).

Overlying the Carboniferous rocks are unconsolidated Pleistocene Epoch or “Ice Age” glacial deposits. The Pleistocene spans a period about 1.8 million to 10,000 years before present. The period saw many glacial events and warm and cool climates. Sediment deposits on the hills in this area are fluvial (stream or river deposit), lacustrine (lake deposit) or till (direct glacier deposit) associated with an ice sheet that advanced into north east corner of the state some 700,000 years ago (fig. 1).

The Carboniferous rocks exposed in the road cuts at this location are predominantly in the Stanton Limestone Formation. The Carboniferous spans a period of about 300 to 360 million years before present. Although each rock layer here is only a few feet thick, these formations extend extremely long distances across Kansas and into adjacent states. Geologists have given each of these rock layers a name, based on the location where it was first described (fig. 2).

During the Carboniferous, Kansas was near the equator and the climate was warmer. The land was flat and near sea level. Shallow seas repeatedly advanced and retreated across eastern Kansas (figs. 3 and 4). Generally, where the water was deepest, limestone was deposited. As the sea became shallower, shale and then sandstone were deposited. These limestone and shale sequences occur in regular patterns or cycles that correspond to the depth of water as the oceans rose and fell. Geologists call these repeated patterns of rocks “cyclothems.”

Occasionally, when the sea was at its lowest, the area was at or slightly above sea level and river channels, estuaries, and river deltas deposited sands (now sandstone). At other times, sluggish rivers deposited mud, which eventually formed mudrocks, the softer, thinly layered rocks between limestones. Coal formed from the remains of plants that lived in brackish swamps. When the sea returned to the region, these plants were buried and compacted by new sediments. Although there are many coal layers in eastern Kansas, and a thriving coal industry once existed in southeastern Kansas, most are too thin or contain too much sulfur for fuel; nearly all of the electricity generated in the state comes from coal supplies in Wyoming.

The interbedded limestones and mudrocks at K-10 and Edgerton Road contain well-preserved remains of numerous invertebrates that lived in these Carboniferous seas. Invertebrates, or animals without backbones, flourished in the clear, warm water when it was high. Vertebrates, or animals with backbones, typically are not found in these rocks, although sharks teeth are found in some Carboniferous rock in Kansas. These rocks are much too old to contain any well known vertebrate fossils, such as the great dinosaurs. Those animals would not yet flourish until the Cretaceous and Jurassic Periods, some 100 to 150 million years later. The fossils at this location include crinoids, bryozoans, fusulinids, foraminifers, bivalves, brachiopods, corals, sponges, echinoderms, gastropods, and maybe even a stray trilobite (fig. 5).

References

Buchanan, R. C., and Maples, C. G., 1992, R. C. Moore and concepts of sea-level change in the midcontinent, p. 73–81; in, Eustasy—The Historical Ups and Downs of a Major Geological Concept, R. H.

Buchanan R. C., West, R., Suchy, D., and Enos, P., 2003, Geology and fossils of northeastern Kansas—a fi eld trip for the 7th International Conference on Coelenterate Biology, 9 July 2003: Kansas Geological Survey, Open-file Report 2003–39, 9 p.

Crouch, B. W., 1996, Internal stratigraphy of the Plattsmouth Limestone Member, Oread Limestone (Pennsylvanian, Upper Stephanian), Osage and Coffey counties, Kansas: M.S. thesis, Department of Geology, Kansas State University, Manhattan, 438 p.

McCauley, J., Brosius, L., Buchanan, R., and Sawin, B., 2000, Geology of northeastern Kansas field trip—public field trip in celebration of Earth Science Week, October 7, 2000: Kansas Geological Survey, Open-file Report 2000–55, 11p.

Scotese, C. R., and Golonka, J., 1992, PALEOMAP paleogeographic atlas: Department of Geology, University of Texas at Arlington, PALEOMAP Progress Report No. 20, 34p.

Tarbuck, E. J., and Lutgens, F. K., 2000, Earth science (9th ed.): Upper Saddle River, New Jersey, Prentice Hall, 672 p.

Zeller, D. E., ed., 1968, The stratigraphic succesion in Kansas: Kansas Geological Survey, Bulletin 189, 1 pl., 81 p.