Platteville fossils in Cottage Grove

Cottage Grove, Minnesota is not noted as a geological wonderland, although Cottage Grove Ravine Regional Park certainly has its charms if you are willing to put in a little shoe leather. There are also scattered outcrops of the St. Peter Sandstone. However, persistence may be rewarded. Back in November I came across a couple of small fossiliferous blocks in town.

The first thing to do was to figure out the stratigraphy. The rocks were not in situ, but they were not heavily worn, either; in other words, they hadn't fallen off a glacier. The rocks of the area included outcrops of the St. Peter, and initially I wondered if I'd stumbled on a stray carbonate lens in the upper part of the formation. A rather more likely identity, though, is as erosional lag from the Platteville. In fact, the rocks look not unlike the occasional poorly dolomitized intervals I've seen in the Mifflin, and the fossils are certainly appropriate.

A (relatively) large brachiopod shell, among numerous teeny-tiny crinoid columnals and other fragments.

They include a mix of the BBC (brachiopods, bryozoans, and crinoids). There is also one object that looks like a whorl of a small Phragmolites sticking out. A couple of notable features include the small size of the fossils, particularly the crinoids; and the density of small fossil fragments and elements.

A different relatively large brachiopod shell among numerous teeny-tiny crinoid columnals and other fragments; note some nice bryozoan fragments on the left.

A hash of tiny fragments.

See what looks like tire tread near the center? That's what reminds me of Phragmolites.

Before we sign off for the year, I'd like to note that for some reason, over the past few weeks the "Fossil Felids of the National Park Service" post has been attracting a few dozen views a week. (Considering I don't do any external promotion and have reduced my social media presence from "negligible" to "zero", this is a lot!) I have no idea where this is coming from (probably picked up by a group somewhere that doesn't register in stats) or why it should have attracted interest (well, felines, I suppose, or maybe Pleistocene megafauna or predators in general), but I'm not complaining! Someone who actually knows something about cats could probably make an interesting and well-attended series like "Your Friends The Titanosaurs".