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USGS CMG InfoBank: Ridge Basin

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Comment: 18:37 - 20:06 (01:29)
Source: Annenberg/CPB Resources - Earth Revealed - 17. Sedimentary Rocks: The Key to Past Environments
Keywords: "Cathy Busby-Spera", "sedimentary rock", "clastic sediment", "sedimentary structure", "Ridge Basin", sedimentologist, lake, "fine grained sediment", "thin bed", water, "depositional environment", "river channel", continuity, limestone, microfossil, "fresh water", "mud crack", "ripple mark"

Our transcription: To determine how the Ridge Basin formed, sedimentologists like Cathy Busby-Spera attempt to find out what the Ridge Basin once looked like.
Here we're looking at a very thick succession of fine grained deposits that we can interpret as lake deposits.
There are several lines of evidence that we can use to determine that this was deposited in a lake.
First of all, the fine grain size and the thinness of the beds indicates slow deposition by fine grain sediment settling through a water column.
Another thing is that the beds are very laterally continuous, as you can see it its outcrop, which would suggest deposition in a big feature like a lake rather than a small feature like a river channel.
The third thing, that we can't really see from here, is that some of the thinner beds in this succession are limestones, and they bear microfossils that indicate deposition in fresh water.
Another feature that we can use to identify a lake is mud cracks and wave ripples.
These features all taken together: the wave ripples, the mud cracks, the fresh water fossils, and the fine grain nature of the deposit give us real convincing arguments that this is a lake setting.

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