Brief Description: This cache is located on the ledges trail at Fitzgerald Park. There are many different trails at Fitzgerald Park; you will need to park and walk from the parking lot. The ledges trail starts with a staircase leading down to the bank of the Grand River and continues for about .33 miles along its’ edge. As you walk, the river will be on your left and the ledges will be on your right. You are looking for a cast of ripple marks in the rock about 20 feet above the ground. (see figure 1 below)
Figure 1. Ripple marks in rock about 20 feet above the trail. Photograph by: L. Smith
Cache Description: The ledges were formed relatively recently by the Grand River. As the river flowed towards Lake Michigan it has eroded away at the bedrock and formed sheer cliffs of ancient rock. This process of erosion has uncovered sandstone rock layers from the Pennsylvanian period which was 299 – 318 million years ago. It is believed that during this time period there were many fluctuations in sea level and much of Michigan was covered by costal swamps and small bodies of marine water.
Among the uncovered layers of sandstone there is a cast of ripple marks. Cast meaning that the original ripple marks have eroded away and what you are looking at is the sediment that settled into the ripple marks and turned into rock.
There are two different kinds of ripple marks, asymmetrical and symmetrical. Asymmetrical ripple marks are formed by water moving with a current (such as rivers or streams). Symmetrical ripple marks are formed by waves or oscillating water. Below in figure 2 is a diagram of what these two different ripple marks look like.
Use the information and pictures given to answer the three questions below and enjoy your time at Fitzgerald Park.
Logging Your Visit:
To obtain credit for visiting this EarthCache, please email me the response to the following questions.
Logging Question 1: Are the ripple marks seen at this location asymmetrical or symmetrical ripple marks? Explain your reasoning.
Logging Question 2: Based on your answer to question number one, what type of water body do you believe formed these ripple marks?
Logging Question 3: Can you tell what direction was the water flowing? Why or Why not?
Earth Science Literacy Principals:
1. Big Idea 5.6 – Water Shapes landscapes: There are two main ways that water has shaped the landscape at this site. First is the Grand River eroding away the bedrock as it flows toward Lake Michigan. Second is the ripple marks formed millions of years ago from a water source and left in the rock record for us to view today.
2. Big Idea 4.9 – Shorelines move back and forth across continents, depositing sediments that become the surface rock of the land: This relates directly to what is being seen at Fitzgerald Park. As the sea level on earth changed, the ripple marks were left behind. Sediments deposited into the ripple marks and it became rock.
· The mountains and valleys we see today have always been on earth. – This misconception is shown to be incorrect at the Fitzgerald Park Ledges. If the valley that the Grand River runs through had always been there, then we wouldn’t be able to see ripple marks 20 feet up formed by a different body of water millions of years ago. If this misconception were true, there would have been no surface rock up there for the water to flow along.
Levin, Harold L. "The Earth Through Time 8th Edition." Chapter Tutorials. N.p., 10 Mar. 2006. Web. 23 July 2012. <1.http://higheredbcs.wiley.com/legacy/college/levin/0471697435/chap_tut/chaps/chapter05-07.html>.
Schaetzl, Randall, Joe Darden, and Danita Brandt. "Chapter 4/ Paleozoic Environments and Life." Michigan Geography and Geology. N.p.: Custom, 2009. 54-58. Print