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Geologic significance of Isle LaMotte

A side view through a part of the reef, specifically at a stromatoporoid, shows the texture of the rock at Isle LaMotte. (Submitted photo) A side view through a part of the reef, specifically at a stromatoporoid, shows the texture of the rock at Isle LaMotte.
Many Vermont Catholics know of Isle LaMotte for its religious and historic significance, but it also has geologic significance that is threatened by development.
 
Charlotte Mehrtens, a University of Vermont professor of geology, has been studying “The Chazy Reef" for about 30 years, and she is concerned about development of the landscape where the fossil reef is exposed.
 
"The Chazy Reef" is the name given to a fossiliferous portion of the Chazy group, an approximately 500-foot thick sequence of limestone rocks of middle-Ordovician age (470-450 million years old). Rock exposures of the reef can be found throughout the Champlain Valley of southern Quebec, New York and Vermont. 
 
“It is a fabulous educational resource,” Mehrtens said. “It can be used for hands-on instruction in biology, ecology and geology by teachers from elementary to university level.”
 
Edmundite Father Brian J. Cummings, spiritual director of St. Anne’s Shrine in Isle LaMotte, said the Lake Champlain island – site of the first Mass celebrated in what is now Vermont -- is an example of the beauty of God’s creation in many respects. “The peacefulness of the island and the deep green of the summer season with stunning sunsets over the Adirondacks are simply breathtaking. The expansive night skies display a light show with shooting stars and a full moon lights up the shrine’s holy grounds on clear nights. There is nothing more prayerful than to see God’s presence in such creation,” he said, adding that the natural beauty of the shrine calls to mind the words of the psalmist: “Near restful waters he leads me, to refresh my soul.”
 
Many people are familiar with coral reefs. “The environment that we call a ‘reef’ is one where a group of organisms live together in shallow, warm marine water in a complex food web,” she explained. Today, reefs are constructed by coral, sponges and algae, but this was not the case in the geologic past; different plants and animals constructed reefs.
 
“The Chazy Reef is the oldest example of a fully developed reef ecosystem, with organisms that changed composition over time. In other words, it exhibits ecological succession,” the professor explained. This means that the oldest reef horizons were built by one group of organisms (bryozoa) and then the middle reef horizons were built by stromatoporoids (a relative of the sponges), algae and coral and finally, the upper reef horizons were built by stromatoporoids, sponges, coral and algae.    
 
Coral first appear in The Chazy Reef but are not the dominant reef-builders as they are on modern reefs.  
 
When studying the reef, Mehrtens and her students ask questions like, “Why did the primary reef-builders change over time?"  "What are the associations of plants and animals that co-exist?” “Is the increase in marine biodiversity at this time in Earth’s history the explanation for the appearance of ecological succession?"  
 
Much of her work has been in documenting the organisms that occur, what layers they occur in and what other plants/animals occur in the same layers. Early work studied the rocks themselves in order to determine physical controls on the environment such as water level and wave and current activity. “We need to know this so we know what environmental conditions the reef organisms are living in,” she said.
 
Mehrtens encourages support of local land trust organizations that identify places deserving of preservation. “The Isle LaMotte Land Trust and Goodsell Preserve have been critical in saving some of the best exposures from second home/vacation home development,” she said.


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Originally published in the 2017 spring issue of Vermont Catholic Magazine.
 
Last modified onMonday, 27 March 2017 13:55
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