Sunday, July 13, 2014

Ripple Marks at Cairns Australia

Have you ever seen a cross section of ripples similar to this in rocks exposed in a road cut along the side of a road?  When these kinds of structures are preserved in layered sedimentary rocks, geologists call them 'bed forms.'  By cataloging variations in the shape and size of these structures where they occur in modern active environments, researchers have come to understand the specific circumstances under which different variations form.  Through this work, they have become a useful tool in understanding the environment in which the sediments that have been preserved in ancient rocks were deposited.  Sedimentary geologists can recognize the difference between ripples produced by wind or water, can tell whether sand or clay was deposited in a river, a delta, or in the sea, can distinguish different speeds and directions of water flow, and can also tell whether water changed directions periodically or was influenced by significant wave activity on the surface.  In case you would like to learn more, here is a link to a youtube video of a typical flume experiment (a tank in which water flows over sediment in a controlled setting) in which you can see the formation and migration of ripples:  and here is a link to the Wikipedia page associated with bedforms:

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