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7. GEOLOGY

1

Sonia Ruth Anderson of Omaha, Nebraska, a winner in the Sixteenth Science Talent Search, wrote a report on seven years of "fooling around" with her fossil collection. It was called "The Collection, Study and Classification of Some Eastern Nebraska Fossils."

"In the autumn of 1950, I began to collect, study and clas­sify numerous eastern Nebraska fossils. My objective was to determine some of the organisms which existed here during prehistoric times and to learn something about them. I've gathered my entire collection, except for the Pliocene speci­mens, by myself.

Field Observations (See Map, Plate 42)

Most of my field work has been confined to the Pennsylvanian shales and limestones and to the Dakota Cretaceous sandstones in the eastern sections of both Cass and Sarpy counties.

Fossils in Cass and Sarpy Counties

Thin carbonaceous Pennsylvanian shale strata seem to con­tain comparatively few fossils. While cleaving these shales, I've found Calamites (Plate 40) and the impression of a ganoid (Frontispiece), which is quite rare.

I recognized the thick Pennsylvanian limestone strata by the presence of the index fossil Fusulina secalica (Plate I). These limestone exposures are often weathered, so that many nearly perfect fossil coelenterates, bryozoans, brachiopods, echinoderms and, occasionally, mollusks, trilobites and sharks' teeth may be collected from the residual debris.

Pennsylvanian strata seem to indicate the termination of the Paleozoic rocks in this locality, because the Permian deposits seem to be absent.

Between the Pennsylvanian and the overlying Dakota Cre­taceous formations, I observed the absence of Triassic and

Plate 1

CLASS SARCODINA ORDER FORAMINIFERA

Fusulina secalica
natural size

Locality: Plattsmouth, Nebraska

Period: Pennsylvania!!

Jurassic strata. During the Triassic and Jurassic periods, most of Nebraska was elevated, so that weathering and erosion obliterated all representative fossils and rock deposits except deep in the western portion of Nebraska.1

Dakota Cretaceous ferruginous sandstones and conglom­erates appear along the Missouri River bluffs near Plattsmouth and also near Louisville. These deposits seem to be nearly barren of fossils, except for Corbula hicksii (plate 22) and other mollusks.

Eocene, Oligocene, Miocene and Pliocene deposits are missing in this area.

A thin stratum of exposed Pleistocene glacial drift, con­sisting of granite and quartzite, overlies the Dakota Cretaceous formation near Cedar Creek. I've found no fossils either in this or in the loess and alluvial formations.

Transported Fossils in Sarpy County

Permian cephalopods (Plates 26-27) were found in chert railroad ballast, probably from Lancaster county.

Fossil bison teeth (Plate 37), petrified bones and petrified wood occur in the Platte River gravel at La Platte.

Fossils in Other Counties

I made a limited examination of an outcrop from the Cretaceous Greenhorn formation, consisting of large masses of Inoceramus labiatus (Plate 23), in a buff, chalky lime­stone near Ponca.

I found silicified wood in a Cretaceous outcrop near Niobrara.

The extensive Pleistocene glacial drift in Knox and Cedar counties has yielded no fossils.

My Procedure for Cleaning the Fossils

Many of my specimens were covered with limestone. The vise in which I placed each fossiliferous rock freed the fossils from their matrix. Immersion in hydrochloric acid or in vinegar removed any particles of limestone that I could not remove with a file.

1. Nebraska Geological Survey,  1903, vol. 1, p.  118.

Conclusions

Tropical, marine foraminiferans, corals, bryozoans, large numbers of brachiopods, sea urchins, crinoids and a few mol-lusks, trilobites, sharks and ganoids seem to have populated Cass and Sarpy counties during the Pennsylvanian period. A relative of the horsetails, Calamites, indicates that there probably was some elevated but swampy land.

Permian cephalopods and corals indicate that there probably was some sea in Lancaster county during the Permian period.

Many changes probably occurred in eastern Nebraska be­tween the Pennsylvanian and the Cretaceous periods. Pelecy-pods, which represent the only phylum from the Pennsylvanian period which I've also found represented in the Cretaceous system, seem to have occupied a more important position in the Cretaceous period than they did during the Pennsylvanian period. Silicified wood in the Cretaceous system indicates that there probably was some elevated land with forests.

Ungulates seem to have been important during the Pliocene epoch. Oreodons, gigantic turtles, camels, prongbuck-like animals and rhinoceroses existed near Ainsworth.

Bison were in existence in the Pleistocene epoch, during which glaciation was taking place in Nebraska."

2

James Maxwell Bardeen of Champaign, Illinois, combined his two prime interests—geology and solid-state physics—in a project on thermoluminescence that helped him to become one of the forty winners of the Fifteenth Science Talent Search. He was able to use some of the specimens from his own rock collection in the experiments that led to his report on "The Thermoluminescence of Rocks and Minerals."

"Thermoluminescence has long been known to scientists, but it was only recently that a theory was developed by physicists to explain this phenomenon. When radiation of suf­ficiently high energy strikes a crystal, some of the electrons are freed from the valence bonds. Some of these freed elec­trons may become trapped by impurities or crystal defects at an energy level intermediate between that of valence electrons and that of free electrons. If these traps have a low energy level, the electrons cannot be freed unless considerable energy is imparted to them by something such as heat. Then the elec­trons may go to luminescent centers, where their excess energy is released as light. The trapped electrons are released at different temperatures, depending on the energy level of the trap. Thus the light is emitted in bursts as the crystal is heated up.

Much work has been done on the thermoluminescence of rocks and minerals by a research group at the University of Wisconsin under the direction of Farrington Daniels. Their final report, The Thermoluminescence of Crystals, is my main source of information on the subject. They conducted a gen­eral survey of the thermoluminescence of rocks and minerals and found limestone and granite to exhibit natural thermo­luminescence in almost all cases. Artificial thermoluminescence occurs when the traps are filled by irradiation in the labora­tory. Extremely small amounts of radioactivity acting over millions of years produce natural thermoluminescence. Glow curves, showing the amount of light corresponding to a given temperature as the specimen is heated at a uniform rate, were obtained for hundreds of samples by the Daniels group. No natural thermoluminescence was observed at temperatures much below 150° C, since ground heat acting over long periods of time evacuates the traps whose electrons require relatively little energy to be freed. The uses of thermolumines­cence in correlating rock strata, in determining relative ages of limestones and in finding the ages of intrusions were among the special topics which received a good deal of attention.

Apparatus

... A cone-shaped 600-watt electric heating element in a flowerpot serves as a "furnace" for heating my samples. The flowerpot rests on the porcelain socket with the cone coming up through an enlarged hole in the bottom of the flowerpot Granular insulation was put around the cone to screen out glow from the heater and hold in the heat. The samples are placed on a metal plate which rests on top of the cone. . . .

An IP-28 photomultiplier tube is being used to obtain curves of light emission (glow curves). The voltage required comes from old 90-volt "B" batteries. ... In order to increase the sensitivity of the apparatus, a condensing lens with a short focal length is placed between the specimen and the photo-multiplier tube. ...

Results and Future Plans

Since I am just getting started in the actual recording of glow curves, the quantity of my results is not very great as yet. Through the cooperation of Herbert D. Glass of the Illinois State Geological Survey I have received some fifteen specimens of limestone, most of which come from Illinois. In geological age they range from Pre-Cambrian to Penn-sylvanian. With these specimens I hope to be able to establish some relation between glow curve shapes and ages. It seems most likely that this will be in connection with the heights of the lower temperature peaks of the glow curve. . . .

Interesting anomalies have arisen with two specimens which have been tested for thermoluminescence. Both specimens are from my collection. Calcite in a matrix of Galena limestone, which I found near Mineral Point, Wisconsin, was observed to thermoluminesce quite brightly. Generally the light came only from regions adjacent to the matrix. The matrix itself, a yellowish, crumbly limestone, didn't thermoluminesce notice­ably. Perhaps the matrix has the radioactivity and the calcite the crystal structure required for thermoluminescence. A glow curve run on a piece of this calcite shows peaks at 190°, 250° and 340° C.

A specimen of La Salle limestone collected near Fairbury, Illinois, thermoluminesces quite brightly also. A fossil brachio-pod from this limestone, however, exhibited no thermolumi­nescence; and the thermoluminescence that had been observed was spotty.

Along with investigating these phenomena I am planning to check on the thermoluminescence of different kinds of fluorite—particularly to see if there is a relationship between color and glow curve peaks. . . ."

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