Formation of the large impact crater field in Wyoming, USA: secondary cratering or asteroid breakup?

• Applicant: Professor Dr. Thomas Kenkmann
• Subject Area: Geology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 470678063

In 2018, a large number of small impact craters, 10-120 m in diameter, was discovered in Wyoming. Shock effects were detected in many of these craters. The size of this so-called Douglas impact crater strewn field is 12.8 x 6.9 km. All craters occur stratiform in the uppermost layer of the Permo-Carboniferous Casper Formation and have a uniform age of about 280 Myr. Preliminary work now shows that additional craters are located outside the reported crater field in the same stratigraphic horizon, further increasing the size of the crater field. The size and age of the crater field are extremely unusual. The objective of this proposal is to survey the entire extent of the Wyoming impact crater field, characterize the craters, and interpret the origin of the crater field. Two basic hypotheses will be tested: Scenario 1 - The Wyoming crater field was caused by fragmentation of one or more asteroids as they entered the atmosphere.Scenario 2 - The craters of the Wyoming crater field represent secondary craters formed by ejection of large blocks from around a large, as yet unknown, primary crater. If this hypothesis proves true, the immediate question is the size and location of the causative primary impact crater. Scenario 1 can be verified by evidence of traces of the meteoritic projectile, parallel impact trajectories, and by a distribution of craters in the form of a strewn field ellipse. Scenario 2, on the other hand, can be characterized by the absence of traces of meteoritic projectile material, radial impact trajectories, and a large-scale distribution of secondary craters. The location of the primary crater would be determined by intersecting the reconstructed trajectories.To assess the size of the crater field, remote sensing methods will be used to examine the stratigraphic horizon of the Casper Formation in southeastern Wyoming for additional crater structures. Detected craters will be characterized morphometrically, structurally, and petrographically, with crater ellipticity and asymmetry of ejecta distribution providing information on impact trajectory. The detection of shock effects plays a central role. Equally important is the geochemical identification of potential projectile traces using isotopic signatures and siderophile elements. The favored formation scenario will be quantitatively analyzed by numerical methods. Simulation of meteoroid fragmentation (Scenario 1) is performed by the "Pancake" and "Separated Fragments" models. In the case of secondary crater formation (Scenario 2), numerical simulation using iSALE will first determine the impact energy and velocity of the secondary craters, then model the ballistic path taking into account the atmosphere, and finally model the primary crater itself. The backward modeling is validated by forward modeling of the entire impact process. Environmental disturbances such as heat radiation from the ejecta plume or the atmospheric shock wave will be also simulated.

• DFG Programme: Research Grants
• International Connection: Belgium, USA
• Cooperation Partners: Dr. Natalia Artemieva; Professor Dr. Steven Goderis; Dr. Kent Sundell