Wednesday, December 31, 2014

What a Geologist Sees - Part 17

I am generally a "mountains and desert" person, but when I do go to the beach, I always like to get some photos of ripple marks and other "sedimentary structures".

Ripple marks and the raindrop impressions are actually termed "external sedimentary structures", as this is what we see when we see the top of a sedimentary layer.

I have seen numerous examples of ripple marks preserved in the "rock record" in sandstones, but I have not seem them combined with raindrop impressions. Usually, when we see symmetrical ripples in a sandstone, it is indicative of a beach environment, where the ripples and raindrops can be obscured by the next storm tides or the next heavy rains, while the sand was still soft and unconsolidated.

I have seen ripples with rain-drop impressions in red siltstones (finer-grained than the sandstones), which were deposited in a tidal flat setting. Sometimes in those cases, after the exposed layer had dried and hardened somewhat, it was covered over and preserved by the next layer.

[So while I may look at the pretty girls, I am taking photos of clouds, waves, ripple marks, and sand dunes, so as not to be labeled a "dirty old man".]

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