1997 Physical Geology Field Trip
Below are 5 images from our 1997 field trip, which visited some of the major geologic units exposed in two quarries in the Omaha area. Without a doubt the best place to learn geology is in the field! Many things can be understood at many levels. As you read and look through the below virtual field trip one major conclusion can be that the Omaha area has seen some major changes throughout it's geologic history.
The above image is of a small quarry wall cut into small bluffs along the N side of the Platte River flood plain, just E of where Route 50 crosses the river. The dashed blue line represents a major disconformity (time gap) between sediments less than several million years old above and Mesozoic sediments below.
In the quarry wall weakly cemented conglomerates and sandstones display features instructive as to the conditions at the time these sediments were deposited. Cross beds give an indication of the direction the water current carrying the sediment was traveling, while clay and conglomerate layers indicate times of quiet water deposition alternating with vigorous currents.
Here a discussion by students on the nature of the geology at this quarry is being led by Dr. Engelmann.
A second large commercial quarry was also visited to investigate the older deeper bedrock seen in the the cliff here. These are limestones and shales of Paleozoic age. Certain layers show an abundance of marine fossils, including shark teeth, fish scales, corals, brachiopods, and much more. Clearly conditions where quite different when these sediments were being deposited in comparison to the present.
Some modern processes were also evident. Well developed mudcracks have formed in the fine lime muds of the quarry. Such mudcracks preserved in older sediments indicate conditions were somewhat similar.
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