Prairie Wanderings: Learning from fossils
By PAUL G. JANTZEN
Contributing writer
While hiking straight up the rocky east slope of Butterfly Hill at Konza Prairie, we cross the prominent horizontal outcropping of the Cottonwood Limestone. Cottonwood Limestone is one of the most easily recognized rocks in Kansas. Some of it is almost a solid mass of fusilinid shells from the now-extinct single-celled creatures that inhabited the shallow sea here during the Permian Period 240 million years ago. It is also known by its light gray to buff color, its rather uniform thickness of 3 to 6.5 feet wherever it is exposed, and the flint nodules it contains.
The flint probably originated in the shells of tiny floating organisms that died and fell to the sea floor, covering or intermingling with the limestone. Following the Permian Period, erosion has become a greater factor than deposition and the Cottonwood River has cut down through the limestone which often forms the rim of the Cottonwood River valley.
Cottonwood Limestone has been one of Kansas' most popular building stones. The house and barn of the Konza Prairie headquarters are built of Cottonwood Limestone. The courthouse in Chase County and most of the State House in Topeka are of this limestone quarried from Chase County.
Immediately above the Cottonwood Limestone is the Florena Shale. It formed as mud along the shoreline of the Permian sea and was compacted by the weight of later overlying sediments. In western Chase County, I have seen an abundance of fossilized sea animals in the Florena Shale: brachiopods (lamp shells), bryozoans, and fragments of sea urchins and sea lilies (crinoids). After rains, many of these fossils are exposed and lie loosely on the flat surface of Cottonwood Limestone. Many of these species have long been extinct.
Immediately below the Cottonwood Limestone is the Eskridge Shale. In the Neosho River watershed in western Lyon County during the summer of 1959, Jack Sensintaffar and I saw fossils in the shale fragments which had become detached and washed downstream in an unusually-dry creek bed which cut into the Eskridge Shale. Excavations at various upstream sites where the creek has eroded through several shaley layers revealed a rich supply of fossil plant material.
Because the shale was fragile, we exercised extreme care to collect intact leaf parts. Both compression and impression fossils were present. Compressions represented the actual remains of organisms converted into structureless carbon by the action of pressure and heat. Impressions were present as imprints of fossil remains in the entombing sediment.
The identification of fossil leaves was based largely upon shape, venation patterns, and mode of attachment of leaf units. Our specimens were compared to detailed photographs of fossils preserved from Permian and near Permian exposed in other states. All the plants identified displayed fernlike foliage and were either ferns or the now-extinct seed ferns.
True ferns bear no seeds but produce spores on their leaf surfaces. Paleobotanists have found specimens of leaf and stem structures with seeds attached. These were seed ferns. We found 27 species of ferns and seed ferns in this Kansas creek bed. Most of these are not extinct.
Back in the laboratory, we used microscopes to examine the shale in which these fossil leaves were found. Again, we discovered a rich supply of fossil material — spores of ferns and pollen of seed ferns. Before microscopic examination, we treated our shale samples with a series of procedures involving hydrofluoric and hydrochloric acids to dissolve mineral sediments without altering the spores and pollen grains.
Identification was done by reference to various journals containing photos and/or descriptions (in English, German, or Russian) of more than 4,000 species from various continents. We identified 18 species of ferns, seed ferns, and gymnosperms. Twenty of the microfossils were of doubtful identification.
Some of the roadcuts in Chase County expose alternating layers of limestone and shale. This sequencing suggested changes in the depth of the sea through time. And the appearance of ferns and seed ferns suggested that at least some of Kansas experience swamp conditions followed by the encroachment of sea waters. Confirming this suggestion is the coal extracted from strip and shaft mines in the deeper and older layers in southeast Kansas and the fossils we have seen associated with them.
And what does all this mean for us today?
While natural forces ultimately determine the shape of this land, human activities such as mining, road building, and daming scar its surface. Overgrazing had produced deserts. Modern use of fossil fuels is related to global warming which spawns hurricanes, tornadoes, droughts, floods, melting of glaciers, and rising sea levels.
And there are myriads of creatures that once lived on this planet but have since disappeared — forever. Human activities have increased the rate of extinctions. Is the human species immune from this danger?
