What is Riprap?
Riprap consists of rock that is used to protect riverbanks from erosion. It is human-placed material that prevents water from disturbing and removing sediment. At Leach Park, riprap consists of sandstone.
St. Peter Sandstone:
St. Peter sandstone is a particular type of sedimentary rock found in several states, including Iowa. It consists of poorly cemented quartz, although there are trace amounts of feldspar. St. Peter sandstone was created in a marine depositional environment many years ago due to tidal fluctuations and storms when much of North America was covered in a shallow sea. As a result, many geologists have found rare fossils of prehistoric marine life. The most common types of fossils found in this sandstone are conodonts and crinoids.
Image 1: Location of St. Peter sandstone
What are conodonts?
Conodonts were eel-like animals. They are distantly related to the hagfish. Conodont fossils commonly preserve the animal’s teeth and/or vertebrae; they are relatively small. Conodonts have been preserved in a myriad of sedimentary rocks, including shales, siltstone, sandstone, and chert. Conodont fossils are extremely important discoveries for geologists when dating rocks as they existed from the Late Cambrian to the Late Triassic Period.
Image 2: Conodont fossil
What are crinoids?
Crinoids are echinoderms and are similar to organisms such as sea stars and sea urchins. Crinoid fossils are believed to be from the Paleozoic and Mesozoic eras. These fossils have been found in limestone and sandstone.
Image 3: Crinoid fossil
Parts of a Crinoid:
Image 4: Parts of a Crinoid
Logging Tasks:
- Study the riprap at the GZ and search for crinoid fossils embedded in the rock. What is the average size of the crinoids?
- Based on your observations and studying Image 4, what part of a crinoid animal is found in the fossils?
- Compare the crinoids to the conodont fossils. What are some differences and similarities between the two?
- As of June 2019, earthcaches contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
Sources:
https://www.ayresassociates.com/what-is-riprap-and-why-it-rocks/
https://en.wikipedia.org/wiki/St._Peter_Sandstone
https://australian.museum/learn/australia-over-time/fossils/what-are-conodonts/
https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/crinoids/#geologist
https://www.fossils-facts-and-finds.com/crinoid.html
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