In 2018, we have discovered small impact craters 10-80 meters in diameter near Douglas, Wyoming, which are all in the same stratigraphic layer and are around 280 million years old. Two hypotheses were tested during the project: was this crater field formed by the fragmentation of one or more asteroids entering the atmosphere (scenario 1) or are the craters secondary craters formed by the ejection of ejecta from a large, previously unknown, primary crater (scenario 2).
In the course of the project, 42 small craters were detected as a result of shock effects in quartz in an area of 40 x 90 km. In addition, there is a large number of potential craters. The size of the crater field and the lack of meteoritic traces rule out scenario 1. On the basis of the often elliptical crater shapes and their arrangement in clusters and rays, it was possible to reconstruct the directions from where the impacting bodies came. The radial arrangement of the trajectories indicates that the craters are secondary craters that were formed by ejection from a primary crater, whose probable position and size could be reconstructed by the intersection of the ejection paths, thus confirming scenario 2. The primary crater is therefore located in the northern Denver Basin, where 280 million years old layers lie at a depth of approx. 3 km. The modelling of ballistic trajectories and numerical simulations of crater formation revealed that the impacts occurred at velocities of ~ 700-1000 m/s and generated peak pressures during impact, which can lead to shock effects.
The overarching question we are addressing in the continuation application is: Where exactly is the primary crater located and how large is it? Based on the trajectory intersections and an initial geophysical analysis, two potential locations for the primary crater, each characterized by a prominent gravity anomaly, will be investigated. The structure closer to the secondary crater field is 20-40 km in size, the more distant structure has a diameter of 80-120 km. We use aeromagnetic and gravity field data provided by the USGS, which are processed and analyzed. We have identified over 40 deep boreholes in the region that have drilled the relevant Permo-Carboniferous strata. These wells will be sampled at the relevant depth and analyzed for possible impact rocks and shock wave effects.
In addition, we want to use existing boreholes and seismic data to detect further secondary craters that are not exposed on the Earth’s surface. Finally, we intend to compare secondary crater formation on Earth with that on Mars and the Moon in order to better understand the effects of the atmosphere and gravity on secondary crater formation.