asymmetrical ripple marks in siltstone from the Moenkopi Formation - teaching hand specimen
Back in stock soon. Inquire.
Asymmetrical ripple marks are caused by a current in wind or water. Unlike oscillation ripples with symmetrical ripples, asymmetrical ripples have one side steeper than the other, though this may be subtle. Careful observation by your students will let them discover that the distance from the bottom of a "valley" to the top of the ripple is greater on one side than on the other. The field photo shows obviously asymmetrical ripples forming on the surface of a dune, where sand is being pushed in one direction by the wind. In these ripples, the steeper side is downstream.
The mudstones, siltstones and sandstones of the early to middle Triassic Moenkopi Formation were deposited nearshore and on the floodplains of a broad coastal plain, in tidal flats and slow-moving rivers.
Here's an interesting article on ripples from MIT News, with an embedded video that shows ripples forming and adjusting to differing conditions: https://news.mit.edu/2018/beach-sand-ripples-ancient-weather-0928
These ripples are subtly asymmetrical, with one side steeper than the other. A little tricky, since weathering has removed the ripple tops. You can challenge your students or just use this specimen as an example of ripples in general.
Select a specimen: If there is more than one specimen shown, you can select a particular specimen by telling us what is in the photo with it, a blue or black and silver pen, a black mechanical pencil or one of those plus some number of coins, or you can let us make the selection.
Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. A link in that invoice will bring you back to checkout, no hassle.
Shipping: Priority Mail small flat rate box unless combined with other purchases. Click > shipping < for shipping rates. Use back button to return to this page