Geological History of Eau Claire WI
- This is a preview of the essay.
To view the full text you must login!
Geological History of Eau Claire
Event I Formation of Original Rock
The first event in the chronological sequence of history of the Eau Claire area is the formation of the original rock. When we say the original rock, we do not really mean original because there were certainly geological processes forming that rock and those processes were involving rocks that existed prior to that original rock. We say original, and it simply means that that is how far we are able to track the geological past of the area. The original rock was heterogeneous and was basalt and shale. Basalt and shale were found in inclusions at Small Falls (upstream of the Eau Claire River, North of Fall Creek). The relative age is determined by the inclusion principleinclusions are older.
Basalt is an igneous extrusive rock that has fine-grained (aphanitic) interlocking texture, mafic in composition, containing olivine, pyroxene and Ca-rich plagioclase feldspar. It is a sign of very explosive volcanic activity and abundant lava flows. Shale is a sedimentary rock that forms out of deposits on the oceanic floor. It is black, has a clastic texture, consists of well-sorted and well-rounded sediment, and breaks in sheets...