Image: Decorah area geology

Description: (a) Location of Decorah in the NE of the State of Iowa, USA. (b) Geological map of Winneshiek and Allamakee counties in the northeastern corner of Iowa State, bounded to the east by the Mississippi River and the State of Wisconsin. From the map Bedrock Geology of Northeast Iowa; Witzke et al. (1998). (c) Geological cross-section through the western part of the Decorah impact structure. The gently dipping Cambrian and Ordovician formations are disrupted by the impact basin, which is filled with breccia, conglomerate and sandstone (unnamed), overlain by the Winneshiek Shale. Much of the impact basin is overlain by the St Peter Sandstone, which varies in thickness due to the erosional contact at its base. Based on Wolter et al. (2011) and French et al. (2018).
Title: Decorah area geology
Credit: The Winneshiek biota: exceptionally well-preserved fossils in a Middle Ordovician impact crater. Journal of the Geological Society (2018) 175 (6): 865–874. https://doi.org/10.1144/jgs2018-101
Author: Derek E.G. Briggs; Huaibao P. Liu; Robert M. McKay; Brian J. Witzke
Usage Terms: Creative Commons Attribution 3.0
License: CC BY 3.0
License Link: https://creativecommons.org/licenses/by/3.0
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