26 December 2013
Mississippian invertebrates from the Lodgepole Limestone
Posted by Callan Bentley
Last summer, after our summit of Sacagawea Peak in the Bridger Range, my students and I spent some pleasant time poking around among the lateral moraines and talus slopes of Sacagawea Cirque. We found some lovely fossils in the blocks of Mississippian Madison Limestone there.
Here, for example are a bunch of bryozoans, with a few brachiopods and crinoid columnals for good measure…
A big coral colony…
This next one is a double-feature: Trace fossils made in sediment that itself is a hash of body fossils…
You noted the linear burrows there, right? Okay, good. Now we can zoom in to see the “sand” that makes up this block of limestone…
Mostly crinoid stem segments, all positively weathering, popping out of the rock. Lovely stuff.
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.
Great photos, Callan. The coral in No. 2 is Syringopora a pretty common tabulate coral in Meramecian/Visean rocks like the St. Louis Limestone equivalents around the country; including the Hillsdale Limestone (Greenbrier Group) of southwestern Virginia and southern West Virginia.
If they made a documentary about the Mississippian it would be “Walking with Crinoids”
Thanks for the reminder of studying the Lodgepole – Mission Canyon years ago as field assistant, along with Mike McLane, to Ray Gutschick and Joe Rodriguez. The Bridger Range outside Bozeman was an important location for us.
Quite spectacular outcrop pictures. Bryozoans, Brachiopods, and Crinoids are not only well-preserved, also in some instances, displaying minute ornamentation details. I suppose it was the end of these marine invertebrates due to Permian extinction. I seem to remember seeing similar assemblages within the Madison Limestone outcropping in the Big Horn Mountains (Wyoming) and now Bridger Mountain discovery brings more prominence to this marine habitat. Excellent field reporting. Naz