WEAUBLEAU IMPACT VIRTUAL CORE LIBRARY

The Weaubleau structure of west-central Missouri formed during a mid-Mississippian (latest Osagean or earliest Meramecian Series) marine impact. The structure is slightly elliptical in shape and unusual because of its eccentric inner and outer rings. The inner ring is approximately 8 km in diameter and is interpreted as the “central” uplift area. The outer ring is approximately 19 km in diameter; it constitutes the tectonic rim, within which rocks are mildly to intensively deformed. The eccentricity of the rings is interpreted as a result of low-angle impact on a heterogeneous target rock succession of carbonate and shale with varying material strengths. The structure is remarkably well preserved because subsequent Mississippian and Pennsylvanian sedimentary cover prevented deep erosion. We recognize six types of breccia associated with the impact: megabreccia block, resurge, fracture, injection, dilation, and crystalline basement facies. Shocked quartz grains have been recovered from the resurge breccia facies. The total depth of the breccia is unknown but is at least 1,800 ft (550 m), the depth to basement in a nearby borehole.

Our understanding of the three-dimensional framework of the impact is somewhat limited. From 2003–2007, the Missouri Department of Transportation drilled ten cores around the Weaubleau impact structure to depths ranging from 60–320 ft (18–98 m). The drill sites were located in the central uplift and at various locations around its periphery. These cores are housed in the Missouri State University Core Lab, which was established in 2008. Cores are accessible to the meteorite impacts community for examination and limited sub-sampling for qualified scientific studies. The cores are also available to investigators, educators, and the public for viewing as a virtual core library at http://impacts.missouristate.edu. Seismic investigation and deeper core drilling will be needed to further elucidate our understanding of this unusual impact.