|
FORMATIONS
Simply put, a formation is a certain amount of rock strata with similar features, whether that be appearance, texture, physical property, etc, or all of the above. You can replicate this on the small scale at home; fill a clear bottle with some sand, and then some dirt, then some pebbles. That is essentially how formations act, except on a much longer geological scale spanning billions of years. The study of formations, called stratigraphy, is important because it enables palaeontologists and geologists to understand how old certain rocks or fossils are, how they were deposited, what environment they were laid down in, etc. There are three formations found at FCSNA: New Richmond Sandstone: This is our oldest formation, approx. 485 million years old. It is composed of (you guessed it) sandstone! A mineral called dolomite is interwoven, as is chert. Chert is hard sedimentary rock composed of quartz, and forms grains so small, you'd need a microscope to see them in any detail. Shakopee Dolomite: About 480 million years old, the Shakopee is composed primarily of fine-grained dolomite. You might also notice intermixed sandstone, green to light gray shale, and siltstone. Fossils are prevalent in the Shakopee. St. Peter Sandstone: This is our youngest formation, at the youthful age of 458-453 million years old. The St. Peter is made up by extremely fine quartz sand that is relatively pure, free from clay and other minerals. As such, it has been popular with glassmakers for centuries, and is still actively quarried in other locations. It largely lacks fossils, asides from scolecodonts (explained below) and some burrows. |
Whipple's Cave reveals all three formations, with the New Richmond lying on bottom, topped by the Shakopee, and then overlaid by the St. Peter Sandstone.
|
|
FOSSILS
Fossils are the basis of palaeontology, and the most popular attraction of geology. You can find some at FCSNA, but please don't take any as these are state lands! Given the age and makeup of the rocks here, you won't be finding any dinosaurs. Instead, you'll find much, much older denizens of a shallow sea. Shells belonging to marine snails are likely the most common find here. But you might also take note of trilobites. Trilobites are an extinct group of arthropods that have been found all over the world, dating from 521-252 million years old. They had hard, segmented exoskeletons made of calcite, and for this reason - as well as their propensity to be bottom feeders - they tend to fossilize well. Occasionally, the remains of a cephalopod might turn up. These relatives of squid include orthocones, cephalopods with ice cream cone shells. Some of these orthocone species could grow to 20ft! Brachiopods (clam-shaped invertebrates) and bivalves, such as clams and scallops, might also be found. You may also find some scolecodonts. Scolecodonts are not a type of animal. Instead, they are the jaws of ancient polychaete worms. Lined by chitinous teeth, the scolecodonts are typically the only body part of these worms to fossilize. Lastly, you might notice trace fossils. Trace fossils are the fossilized traces of an animal, rather than the actual animal itself. They come in multiple forms, including the tiny, tiny footprints of trilobites or other extinct arthropods. Or perhaps you'll find the burrows of long-gone worms. Even poop can sometimes turn up as a trace fossil! GEOLOGY HOTSPOTS AT FCSNA
There are several places to check out if you're interested in geology. These include:
Check out our geology brochure!
|
Snail shells peek out from the rocks.
An ancient trilobite lays exposed for perhaps the first time in 480 million years.
Aqueous cross-bedding in the rock, produced by waves beating an ancient shore.
Crystalline structures called dendrites branch their way through the rock.
|