Manson Impact Structure Crow Creek Impact Ejecta

Manson Impact Structure: A Hidden Giant

Discover one of the largest intact impact structures in North America, completely buried under the verdant cornfields of north-central Iowa, near the town of Manson. This colossal crater spans approximately 23 miles in diameter, making it about 30 times larger than the famous Meteor Crater in Arizona. The impact occurred during the Cretaceous Period, 74 Ma, caused by a chondritic meteorite.

Why Crow Creek Impact Material is Important

The Crow Creek material contains "shocked quartz grains," produced when a high-energy shock wave from an impact passes through quartz grains, creating planar deformation features. Scientists believe that the special layer of sediment known as "Crow Creek," found in isolated patches in South Dakota and Nebraska, is linked to the Manson Impact Structure as impact ejecta. This sediment contains tell-tale shocked quartz and feldspar fragments from the Manson meteorite impact. Since the impact structure is buried and no impact rock is available at the surface, Crow Creek material is the only available signature remnant of this large impact event, besides drill cores.

Lithology of Crow Creek

Crow Creek consists of two distinct units: marlstone and a basal coarse layer. The material can contain light-gray, silty quartz sand with gravel-sized particles of pink and white quartz and detrital carbonate. Rip-up clasts from the Sharon Springs Member appear as rounded, black, noncalcareous mudstone clasts. Inoceramid shells mixed with detrital and skeletal carbonate, silt, and fine quartz sand in a wackestone to packstone fabric can also be found. Smectite is the dominant clay mineral, with minor kaolinite and illite. Black mudstone rip-up clasts may also be present. Quartz grains contain planar deformation features (PDF), which are only created by impacts.

Meteorite Impact Sizes in the USA

1. Chesapeake Bay impact structure, Virginia: Diameter: Approximately 85 kilometers (53 miles) Features: This structure, formed by an asteroid or comet impact around 35 million years ago, includes a deep, filled central crater, an annular trough, and a peak ring. The impact event vaporized and displaced rocks and sediments, creating glassy particles from solidified melt rock.

2. Beaverhead impact structure in Idaho and Montana: Diameter: Roughly 60 kilometers (37 miles) Features: Dating back about 600 million years, this structure is known for shatter cones, pseudotachylites, and planar deformation features in quartz. Although much of its original shape has been eroded, these geological features provide evidence of the impact.

3. Manson impact structure in Iowa: Diameter: About 35 kilometers (22 miles) Features: Formed by a stony meteorite impact around 74 million years ago, the Manson structure includes a central uplift and shocked quartz within the granitic central uplift. The impact disrupted various rock layers, including granite, gneiss, and shales. Additionally, the Crow Creek Member of the Pierre Shale in South Dakota and Nebraska contains ejecta from the Manson impact, which includes shocked mineral grains and other impact-related materials.

Product Specifications

• Disc size: 45mm diameter x 15mm depth
• Crow Creek Manson Ejecta Material size: 23mm length x 15mm width x 10mm height
• Ejecta weight: 2.5 grams

This specimen ships with a Certificate of Authenticity and information about the Manson Impact and the ejecta material. Tag and tag stand are included. Plexiglass base and photo cube are not included.

Have a World Impacts Collection?

This unique specimen makes an important addition to any world impacts collection. This impact structure is significantly larger the many impact structures on Earth! Don't miss out on an opportunity to add this rare, scientifically validated material to your collection today.

This scientific material is Guaranteed Authentic. It was professionally and legally collected and arrives with a Certificate of Authenticity and information about the Manson Impact Structure.