Trouble Identifying Rock Formations

[Clanjones]

I am an aspiring fossil collector from Minnesota. I have gone on multiple fossil hunting trips, but had trouble finding the layer I was looking for. Can anyone provide me with more detailed descriptions of Minnesota's fossiliferous rock layers? I have checked the guide to Minnesota fossil hunting and I am still having trouble distinguishing between rock layers. Any tips from more experienced fossil hunters?

[JimB88]

this map will tell you what age the rock is and if you click on the area it will tell you the formation and what kind of rock is present.

http://mrdata.usgs.gov/sgmc/mn.html

[ashcraft]

Telling rock formations apart can be quite difficult. My friend and I disagree over a particular outcrop of sandstone. Nobody would consider us experts, but we aren't rookies either. There are no fossils in the outcrop, so we are relying on color, bedding, knowledge of surrounding formations...........even experts often conflict, we have a formation that is either St. Peter or Everton, depending on which expert you talk to.

The best way to learn is find a type section for a formation, and go look it over personally. Take pictures, collect fossils, note the color, bedding, even the smell. You will get the feel for them.

fkaa

[Clanjones]

Thank you all very much.

[Bev]

Clanjones, where are you in Minnesota? I'm in the southeast portion - Ordovician. On my website there is a photograph of the different formations here taken by Caleb of Midwestpaleo. On my blog I have links to formation maps by county and these will tell you which layers are fossiliferous and may even tell you what fossils may be found.

If you have any questions, please feel free to contact me at bcfossillady at gmail dot com or you can private message me too.

I am far from an expert, but am an enthused hunter. I also have fossil hunting ground locations in Fillmore and Winona Counties on my blog.

Bev

[erose]

Geologic maps alone are helpful but what you need to study are the written descriptions that accompany the sheets. You may also want to pick up a dictionary of geologic terms. Learning the difference between a packstone and a micrite could be the difference between one limestone unit and another. I also find that paying close attention to the descriptions of how the unit weathers is important. Combine that with index fossils and you will be well on your way.

And don't be surprised when different geologists or other "experts" disagree on what formation is present at a site. And things get revised as further study is done. Formations and members get redefined and re-grouped over time. So you sometimes need to know that before, say 1960, it was called the XXX formation and now it is considered the YYY member of the ZZZ formation. That is where finding geologic society field trip guides or other technical publications come in handy as they often include correlation charts showing the name changes for rock units.

Bottom line: Keep good location notes and be ready to revise as you know more.

[Uncle Siphuncle]

many paleozoic formations are divided or identified by discrete horizons of brachiopods or other index fossils. i'd suggest channeling some portion of your research time this direction.