Lovely sedimentary ripple marks and mud cracks.
Ripples form when a fluid, like water or air, flows over a fine-grained surface (sand, silt, or dust)-- you've probably seen these ripples in rivers, at the beach, or in a desert-- or maybe even with fine bits of dust in the bottom of a wash basin. If the ripples are covered by more sediments without being disturbed, they can become part of the rock record-- and can inform us about past environments.
Mudcracks have a similar origin-- when waterlogged fine-grained sediments dry out, the material contracts, and cracks in the process. If these cracks are filled in by new sediments, but not disturbed, they too can be preserved in the rock record.
This is a really neat specimen that preserves mudcracks on the bottom surface, and ripple marks on the top. What we learn from this is that fine sediments were deposited quite wet, then dried out-- and covered rapidly with new sediments; these new sediments preserved the mudcracks in the layer below as a cast, then were in turn buried rapidly-- but these didn't dry out, which we know because the sample has ripple marks on the top. This sample is a calcareous (carbonate-bearing) siltstone from the Tertiary Barstow formation, out of the Owl Canyon member, near Barstow, CA. The sample is marked Tboc-1-- for Tertiary Barstow Owl Canyon.
This would be a great gift for the budding geologist or scientist.
You will receive the specimen pictured.
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