sedimentary, wisconsin

Ripple Marks

If you’ve ever looked through clear waters at a beach or gentle flowing river to the sand below, you’ve likely seen ripple marks formed by the moving water.

The image above actually shows preserved “fossil” ripple marks in the 1.7 billion-year-old Baraboo (Wisconsin) quartzite. These ripple marks were formed when the marine sandstone was initially deposited and then were later metamorphosed. However, these ripple marks lie along a vertical rock face, meaning that these rock layers have nearly been overturned from their original horizontal position!

Ripple marks can be useful as paleocurrent indicators—sedimentary structures that help to determine the direction in which water flowed in the geologic past.

Symmetrical ripples are formed by the back and forth motion of waves, like at a beach. Asymmetrical ripples (which have a gentle up-current slope and a steeper down-current slope) can be formed in rivers and also in aeolian environments.

So although we’ll never actually be able to travel back to a Wisconsin beach nearly 2 billion years ago, we can still get pretty close!

Image by author

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s