Evolution of a lake and its sedimentary record

Below is a series of frames showing sediments being deposited in a lake basin with time. Use it to explore the following questions and to gain a better understanding of shifting depositional environments and the nature of the sedimentary record.

First, try to predict what some of the traits of the 3 sedimentary facies (river delta sands, lake bottom muds, and shoreline silts) might be. Which one is more likely to preserve bird tracks? Which one more likely has oscillation ripple marks preserved? Which sediment will be unaffected by waves?

Review the frames 1-7. How did the shorelines on the left and right sides shift position with time? Why did they shift? Are any abrupt changes in lake level evident? From a larger perspective you can ask, what was the history of this lake with time, and what might have influenced that history?

Note that if you trace sediments all of the same age, you pass from sandstones to shales to siltstones as you travel from left to right, and that different parts of a sandstone body (perhaps a stratigraphic unit such as a formation) formed at different times.

You can take this same approach with reef complexes, barrier island shorelines, different types of deltas, glacial systems, and many other depositional systems.


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