A total of eleven brachiopod genera were collected from the Decorah Formation (Upper Ordovician, Sandbian) exposed in southeastern Minnesota and northeastern Iowa as part of a paleoecological study. The Decorah Formation -part of the Galena Group- is divided into four members: the Carimona, the Spechts Ferry, the Guttenberg and the Ion. The brachiopods in this study were collected from six field sites, five in Minnesota and one in Iowa. At the time of deposition, the Decorah sediments were submerged within the Hollandale Embayment in the Galena Basin. The Decorah sediments were deposited in a tropical to subtropical shallow eperic sea. The primary composition of the Decorah Formation is green-grey shale interbedded with yellowish-brown limestone. All the brachiopods collected are articulate, eight of which lived attached by the pedicle to a hard substrate and three of which lived freely on the seafloor. Diorthelasma was found in only one locality and was the least widespread; Rostricellula was the most widespread, found at all six localities. In general, Zygospira and Sowerbyella were the most abundant brachiopods collected. The most diverse locality was C/W-733 Wangs Corner where eight genera were collected, compared to C/W-732 Golden Hill where only two genera were collected.


Wilson, Mark




Geology | Paleontology | Sedimentology


Geology, sedimentology, paleontology

Publication Date


Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis



© Copyright 2017 Dominique B. Bell