With the larger perspective of the Cretaceous formations recently opened out to the west of us, between the Missouri River and the Rocky Mountains, the depositional relationships of our Iowa terranes take on new aspect. Above the basal Dakota sandstone, so well represented in our state, all of the great black-shale sequence, including the Benton, Pierre, Masuk and other similar divisions, is now regarded as a single provincial deposit, comprised under the title of Assiniboian series. Into this great body of black-shales extend from the shoreward margins huge wedges of terriginous clastics; while from our side, the seaward side,· appear limestones and chalks. lnstead, then, of our being on the eastern shore of the one-time, broad, mediterranean sea, the present Iowa border of these deposits is really originally situated near the middle, and the Cretaceous waters extend far to the eastward, to the present Hudson Bay, and the far shore of present Lake Superior. Thus a large proportion of our Cretaceous deposits, and especially our chalks, present itself in a new sedimental role.
Proceedings of the Iowa Academy of Science
©1926 Iowa Academy of Science, Inc.
"Terranal Affinities of Iowa Chalks,"
Proceedings of the Iowa Academy of Science, 33(1), 219-220.
Available at: https://scholarworks.uni.edu/pias/vol33/iss1/44