Calumet Geological History

This post is about the geologic history of the Calumet Area.  The Calumet Area is found at the southern tip of Lake Michigan.  Despite the fact that I have lived in this area my entire life, I have learned many new things about it from my science class.

Geological Time is a timescale used to describe the growth and development of the Earth over time.  I have learned about the formation of the Calumet Area over time and how it has come to be what it is now.

The bedrock of the Calumet Area give us information about the environment at the time they were developed.  For example, nearly all the layers of bedrock in this area are horizontal, except for the bedrock in Porter and LaPorte Counties.  There, they incline down toward the northeast.  They return near Niagara Falls.  Hard layers of dolomite and limestone are found next to the Lake Michigan shore in Wisconsin and Illinois.  These may have restricted glacial advances, helping create a concave area for Lake Michigan (Schoon, 12).

The top layer of rock in Porter, LaPorte, and Lake Counties is formed with Devonian rocks.  Scientists are able to tell that seawater covered this area during this period.  The top layer of rock in Cook and western Lake Counties is formed with Silurian rocks.  This shows that during this period, there was accumulation of limestone that was later transformed to dolomite.  Ordovician rocks form the next layer.  During this time the continent rose and fell.  This let the sea recede and advance time and time again.  When it advanced, it eroded the sediment and when it receded, it left sediment.  Cambrian rock is the next layer down.  Fossils in this layer show that the area was at the bottom of a shallow sea during this time (Schoon, 13). 

Many rocks were carried here by glaciers.  One such example is the boulder next to the Revelli Bandshell at Festival Park on the banks of Lake George in Hobart.  This boulder is an erratic, which is a rock that is different from surrounding rock and was brought here by glaciers.  These rocks are originally from Canada and upper Michigan.  They were carried here by glaciers (Schoon, 12).

Erratic

(http://en.wikipedia.org/wiki/File:Angular_glacial_erratic_on_Lambert_Dome-750px.jpg)

There is evidence in the Calumet Area that an ice age, perhaps several of them, occurred in this area.  One piece of evidence is till, a blend of different types of sediment that have been placed by glaciers.  Erratics are another type of material that glaciers have carried to this area and then melted, leaving them here.  Kettle lakes and moraines also give evidence to the glaciers that have been here.  These are ridges in the ground, caused by glaciers hauling these huge boulders.  The effects of glaciers can be seen near Lake Huron.  In some areas, dolomite rock is near the surface and the ground appears higher.  In other areas, the ground appears lower and shale is at the surface.  This is because shale is more easily worn by the glaciers passing through (Schoon, 14).

 Kettle Lakes

(http://en.wikipedia.org/wiki/File:PotholeLakes.Siberia.L7.20010910.jpg)

Sources:

Schoon, Kenneth J.. Calumet beginnings: ancient shorelines and settlements at the south end of Lake Michigan. Bloomington, Ind.: Quarry Books, an imprint of Indiana University Press, 2003. Print.