sedimentary, wisconsin

Can you spot the unconformity?

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?

sedimentary, structure

Banded Iron Formation, Soudan

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

mineralogy, sedimentary

What are these things? — Stylolites

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