Animikie Basin
The Animikie basin started forming about 2.3 billion years ago in what is now northern Wisconsin and the Upper Peninsula of Michigan and continued forming until about 1.86 billion years ago. 

 
The stratigraphic column for the basin is as follows, from oldest to youngest rocks. 

Mesnard Quartzite—Basal 
Kona Dolomite 
WeWe Slate 
((Angular Unconformity—signs of basin deformation)) 
Ajibik Quartzite 
Siamo Slate 
Iron Formation 
((Unconformity)) 
Goodrich Formation—Present in Marquette and Goegebic Range in the Upper Peninsula only 
Greywacke/Slate (Michigamme in the Upper Peninsula of Michigan) 
((Unconformity)) 
 

 
Outcrop of the Kona Dolomite showing stromatolites.  Pencil for scale.  Stromatolites are formed in shallow marine environments by sediments deposited on algal mats.

 
The Mesnard is dated at about 2300 million years old.  The unconformity between the Ajibik and the WeWe indicates tilting within the basin. The Siamo slate is often missing in the sequence, but is present in the Marquette area of the Upper Peninsula of Michigan. 
Road cut near Negaunee, UP,showing the angular unconformity between the Ajibik Quartzite and the WeWe slate.  Quartzite is on left and slate is on right.
The Iron Formations are distributed throughout Northern Wisconsin and the Upper Peninsula as well as parts of Minnesota.  There are differences in the composition of  the formation which may be evidence of the presence of several sub-basins in the area. 

The Iron Formation is found only in rocks dated as 2 billion years old or older.  This is considered to be evidence of a change in the atmosphere at around this time, as organisms are putting oxygen into the air, and in turn causing the iron to precipitate out of the water.  This increase in oxygen levels not only causes the iron present to precipitate out of solution but prevents iron from being dissolved in the waters at the previous quantities. 
 
Tilden hematite and magnetite mine in the Marquette Iron Range near Ishpeming, UP. 

 
The unconformity after deposition of the Iron Formation represents a missing 300 million years.  During this time, there was a change from passive to convergent tectonics in the area.  The top of the succession is the Michigamee greywacke/ slate which is found in most places in the Lake Superior region but is called by several different names.  The Michigamee is dated at about 1860 million years old.