Sorry for the lack of posts the past couple of weeks. I've been working, traveling, conferencing, and more -- busy busy! Things will be getting back to normal (whatever that is) so look for some new posts in the coming days.
In the meantime, above is a Friday Field Photo from the Ainsa Basin of Spain. These sedimentary rocks are from the Eocene (55-35 million years ago) Escanilla Formation and interpreted to be river (fluvial) deposits.
Note the inclined surfaces within the coarse-grained bed just above the camera bag. The photo below has some very quick scribblings to highlight this cross bedding.
This type of sedimentary structure develops as the sand and gravel rolls and bounces along the bottom of the bed forming dunes. As the dune migrates with the flow, the lee side is buried preserving the structure. If you start searching around the internet you can find tons of great explanations and visualizations of how cross bedding forms. In fact, I'd like to hear from readers about some of their favorite websites -- feel free to comment below.
Happy Friday!
Image: Cross-bedded pebbly sandstone / from my Flickr collection
