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Friday Field Foto #12: Combined-flow ripples

April 13, 2007

I realized today that I haven’t done a Friday Field Foto since early February…go here to see all the previous FFF posts.

Today, I decided to show a close-up instead of the usual landscape-scale views that I usually post. This is from the Cretaceous of central Utah (associated w/ these rocks) and shows some very nice ripple cross-laminated sandstone. In this case you can very nicely see some slightly climbing ripple-laminated sandstone toward the bottom overlain by some ripples heading the other way (apparently), and then some wavy laminae and smaller-scale ripples on top. Above and below this bed are abundant hummocky cross-stratified sandstones indicating that these ripple-laminated deposits are likely the product of combined flow (oscillatory + unidirectional) associated with storm waves (i.e., between storm- and fair weather-wave base).

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