The Manson Impact Structure: A Late Cretaceous Meteor Crater in the Iowa Subsurface The area of north-central Iowa around the town of Manson (about 80 miles northwest of Des Moines) has been known as a region of anomalous geology since the early part of the century, when samples collected during the drilling of a Manson town water well proved to be unlike other rocks in the area. The nature of the anomalous geology remained a mystery until 1953, when a joint Iowa Geological Survey-U.S. Geological Survey investigation led to its interpretation as a cryptovolcanic feature (a crater created by a blast of volcanic gas). In 1966, evidence was discovered proving the Manson Structure to be of meteor impact origin. In the late 1980s the Manson Impact Structure was linked to one of the Earth's greatest extinctions of life (including dinosaurs) at the end of a period of geologic time called the Cretaceous (about 65 million years ago). To test this relationship and learn more about the Manson crater, in 1991 and 1992 the Iowa Department of Natural Resources, Geological Survey Bureau and U.S. Geological Survey drilled 12 research cores in the structure (totalling over 4,000 feet). Impact rocks recovered during this drilling have been subjected to numerous investigations to develop a better understanding of the structure. One of the most significant discoveries resulting from this work was a new date for the Manson impact, about 74 million years ago. For a discussion of recent investigations of the Manson Structure, click here. Abstracts: Deposition of Crow Creek Member, Campanian, South Dakota and Nebraska (Abstract) The Drilling of the 1991-1992 GSB/USGS Manson Impact Structure Research Cores (Abstract) A Brief History of Investigations of the Manson Impact Structure (Abstract) Preliminary Investigation of the Clay Mineralogy of Sedimentary Clast Breccias Recovered by Core Drilling in the Manson Impact Structure (Abstract) Petrography of Crystalline Clast Breccias From the Manson M-1 Core (Abstract) Manson and Company: Impact Structures in the United States (Abstract) Preferential Feldspar Comminution in Impact Melt Breccias from the M-1 core of the Manson Impact Structure (Abstract) Sedimentary-Clast Breccias of the Manson Impact Structure, Iowa (Abstract) Asymmetry of the Manson Impact Structure: Evidence for Impact Angle and Direction (Abstract) First Round of Research on the Manson Impact Structure Answers Many Questions...Raises Many More (Abstract) Preliminary Investigation of Shocked Grains (Manson Ejecta?), Paleontology, and Depositional Features in the Crow Creek Member, Pierre Shale (Upper Cretaceous) of Southeastern South Dakota and Northeastern Nebraska, and its Effect on Upper Cretaceous Biota (Abstract) The Crow Creek Member, Pierre Shale (Upper Cretaceous) of Southeastern South Dakota and Northeastern Nebraska: Impact Tsunamite or Basal Transgressive Deposit? (Field Trip Abstract) The Crow Creek Member, Pierre Shale (Upper Cretaceous) of Southeastern South Dakota and Northeastern Nebraska: Impact Tsunamite or Basal Transgressive Deposit? (Abstract) Impact Materials Recovered by Research Core Drilling in the Manson Impact Structure (Abstract) Preliminary Results of U.S. Geological Survey - Iowa DNR Geological Survey Bureau Manson Core Drilling Project (Abstract) Phanerozoic Clast Breccia in the Manson Impact Structure (Iowa): Evidence for Impact into a Shallow Marine Environment? (Abstract) New Interpretations Suggest a Manson Impact into a Shallow Marine Environment (Abstract) Compositions of Minerals in Polymict and Suevitic Breccias from the Manson M-1 Core (Abstract) Core Drilling in the Manson Impact Structure Provides Abundant Research Materials and New Insights into the Geology of a Well-Preserved Complex Impact Crater (Abstract) Geophysical Logs and Lithology from Manson Impact Structure (Abstract) The Manson Impact Structure Research Program: A Summary of Results (Abstract) The Terminal Cretaceous Manson Impact Structure in North-Central Iowa: A Window into the Late Cretaceous History of the Eastern Margin of the Western Cretaceous Seaway (Abstract) The Manson Impact Structure Research Program: New Results (Abstract) Bunte Breccia-Like Deposits within the Manson Impact Structure (Iowa), Evidence for Impact into a Shallow Marine Environment? (Abstract) Research Core Drilling in the Manson Impact Structure: Preliminary Descriptions of Lithologic Units (Abstract) Preliminary Descriptions of Impact Rocks Recovered by Recent Core Drilling in the Manson Impact Structure (Abstract) New Research Core Drilling in the Manson Impact Structure: A Description of the Rocks Recovered and Preliminary Interpretations (Abstract) The Terminal Cretaceous Manson Impact Structure of Iowa and Its Possible Influence on K-T Boundary Events in the Western Interior (Abstract) Descriptions and Preliminary Interpretations of Cores Recovered from the Manson Impact Structure (Iowa) (Abstract) Petrography of the Crystalline Breccias from the Manson M-1 Core: Compositional Correlation to Target Lithologies (Abstract) Preliminary Observations from New Research Cores, Manson Impact Structure, North-Central Iowa (Abstract) The Manson Impact Structure Core-Drilling Project: An Exciting Look into Iowa's Cretaceous-Tertiary Impact Structure (Abstract) Preliminary Observations and Interpretations from the Manson M-1 Core (Abstract)