This photo displays a pretty spectacular unconformity—an erosional/non-depositional surface where rock units deposited during different intervals of time appear to be continuous. In the bottom half of the image, you can see Paleoproterozoic pink quartzite ~1.7 Ga in age, while in the top half of the image—directly overlying the quartzite—is Cambrian sandstone conglomerate ~540 Ma… Continue reading Can you spot the unconformity?
Here’s some lovely cross bedding in the ~1.7 Ga quartzite from Baraboo, WI!
Had a great day out at my field site with my professors! Spent a bit of time in the quarry and most of the afternoon trekking through the forest in search of outcrops. Here’s a photo of some lovely, smooth glaciated breccia we found!
Get to know BIFs. Get to love BIFs. HERE are some more absolutely beautiful BIFs that I saw while in northeastern Minnesota. Image by author
Some absolutely gorgeous ~2.7 Ga Banded Iron Formation (BIF) from Soudan, Minnesota. The rotating silver and reddish layers are hematite and jasper respectively, and these BIFs differ from their Proterozoic counterparts in that they were chemically precipitated. The outcrop is intensely folded and shows numerous interference patterns, meaning that there are folds that have been… Continue reading Banded Iron Formation, Soudan
See these thin little squiggly gray lines in the rock in the photo above? These are what you call stylolites. Stylolites are caused by pressure dissolution, meaning that a large amount of stress was applied to the rock in a direction perpendicular to which to stylolites are formed. Because of this pressure applied, there’s a dissolving… Continue reading What are these things? — Stylolites
Limestone with ooids and shells, viewed through a hand lens