Stop 3: Tertiary Sediments
| At this stop we will examine the ground water capacity of the Tertiary sediments and explore what type of depositional environment may have produced such a unit. |
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 for Air Photo
Stop 3 topographic portion Modified from Topo II
To better orient yourself, take a look at the trip log page!
contour interval: 40 ft
How are the sediments different?
Looking south along River Road
At the last stop we learned that crystalline rock is a poor aquifer because it only carries water in fractures and often those fractures are not connected, making the rock impermeable. Now that we have moved "stratigraphically up section," meaning we are looking at younger rocks that were deposited on the basement (the gneiss) we find a very different rock type.
Tasks! |
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- Find yourself on the geologic map. What rock unit are you looking at?
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Alternative geologic maps? |
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- Write a geologic description of the rock unit. Be sure to include grain size, grain shape and a sketch of the rock unit.
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Depositional environment:
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| Because events in geologic history happen over long periods of time, it is often necessary to use our imagination to determine the historical environment that deposited old units. In Stop 1 we talked about the principle of uniformitarianism, we can use this principle and our imagination to determine a likely depositional environment for this sedimentary unit. |
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- Imagine you are standing on this very spot in the Tertiary age. Remember in Stop 1 we saw the river depositing a gravel unit with areas of silt and sand. Describe the depositional environment.
- Are your feet wet?
- If so, are you treading water or just standing in water?
- Are you near a river, lake, ocean?
- What else might you see in the area?
- How much energy is in the system?
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