Welcome to Postcard Friendship Friday, hosted by
Marie at the French Fractrice.
This week’s geology postcard is the bedrock geology map of Indiana. It is published by the Department of Natural Resources, Indiana Geological Survey at Indiana University, 611 North Walnut Grove, Bloomington In 47405
The state of Indiana is underlain by Paleozoic sedimentary rocks, Ordovician to Pennsylvanian in age. Note that the older rocks are in the east, and younger rocks in the west. These rocks are shale, siltstone, limestone and dolomite, indicating they were deposited in ocean water.
From The Tectonic Features of Indiana webpage:
“The younger sedimentary rocks that were deposited on top of this basement complex were formed in a setting of quiet marine and river waters. Much of this time the craton was covered by a large shallow sea, a so-called "epicratonic sea" (meaning literally "on" the craton). Sometimes land masses or mountain chains rose up on the distant edges of the craton and then eroded down, shedding their sand across Indiana. These sediments whether deposited in rivers or seas eventually compacted into the sedimentary rocks that cover the state today.”
See the bright pink pattern in central Indiana, looking like a tree branch, or perhaps a river valley with tributaries? It is indeed an old river system, the Teays River system. More on this below.
Covering the bedrock in most of Northern Indiana are glacial sediments, laid down by the Ice Ages.
From Freeze Frame: The Ice Age in Indiana by Anthony Fleming:
“As it crossed the landscape this first glacier completely changed the surface drainage that had taken millions of years to develop, damming up river valleys into lakes, diverting stream channels to the south, and in some cases completely filling up large valleys with sediment, leaving little record of their existence. The giant Teays bedrock valley system was one such victim. This valley system was the premier drainage way in eastern North America prior to glaciation, extending from its headwaters in the western mountains of North Carolina and Virginia to the Mississippi River in western Illinois. The gorge-like valley of this river was as much as 200 to 400 feet deep and crossed north-central Indiana between about Berne (Adams County) and Lafayette (Tippecanoe County). Today, there is virtually no trace at the modern land surface of the once giant river—only a deeply buried valley on the bedrock surface defined by various wells and test borings.”
Near Bloomington are many limestone quarries, most disused now. Indiana Limestone (or Bedford limestone) has been used as exterior stone of many US government buildings, college campus buildings, and the Empire State Building.
If you have seen the movie Breaking Away then you have seen the quarries, and Bloomington Indiana.
I think I am at the end of my geology postcard series. I have you have enjoyed it.
