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USGS CMG InfoBank: Evidence of Rivers

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Comment: 20:06 - 21:02 (00:56)
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", lake, river, "depositional environment", "fine grained sediment", mud, delta, thickening, "coarsening upward sequence", bed, "thin bedded sandstone", "medium bedded sandstone", sand, "coarse grained sediment"

Our transcription: In places the edges of the ancient lake can be seen in the rocks.
The rivers, which once poured into this lake, have also left evidence of their previous existence.
This lake was the site of deposition of fine grained sediments or muds, but periodically rivers spilled into this lake.
What we're looking at here then are the deposits of a river that built out into a lake.
This is referred to as a delta, and what we see is a thickening and coarsening upward sequence of beds.
The initial deposits of the river are thin to medium bedded sandstones, and these represent sands that jutted out into the lake from the mouth of river.
The relatively coarse grained river deposits stand in contrast to the finer grained, thinly bedded lake deposits.

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