|2012 GSA Annual Meeting in Charlotte|
|Paper No. 270-13|
|Presentation Time: 5:05 PM-5:20 PM|
PROXIMAL TO DISTAL DEFORMATION IN THE WEAUBLEAU IMPACT STRUCTURE, MISSOURI
EVANS, Kevin, Geography, Geology, and Planning Department, Missouri State University, 901 S. National Ave, Springfield, MO 65804-0089, KevinEvans@MissouriState.edu, MICKUS, Kevin L., Geosciences, Missouri State Univ, 901 S National Ave, Springfield, MO 65804-0087, MILLER, James F., Geography, Geology, & Planning Dept, Missouri State University, Springfield, MO 655897, and DAVIS, George H., Missouri Department of Transportation, 1617 Missouri Blvd, Jefferson City, MO 65102|
The Weaubleau structure of west-central Missouri formed from a mid-Mississippian (latest Osagean or earliest Meramecian) low-angle, marine impact that generated a circular area (8 km dia.) of intense brecciation and a fan-shaped area (19 km dia.) of intense to gentle deformation directed toward the present-day northeast. The limits of these deformational domains roughly are outlined by two ring-like stream drainages that are eccentric to one another.
The main impact area constitutes the inner ring. Bouguer gravity anomaly maps show that this feature includes a small uplift that is centrally located. Exploratory core drilling around the structure has not penetrated deeper than 100 m, but from available data the main impact area is full of breccias that include six facies: crystalline basement breccia (only found in the eastern side), dilation breccia, megabreccia, injection breccia, fracture breccia, and resurge breccia. Post-impact middle Mississippian carbonates buried part of the structure. These strata were exposed subaerially and mostly removed below the sub-Pennsylvanian unconformity. Early to middle Pennsylvanian clastics re-buried the structure and partly have been exhumed by subsequent gentle uplift and erosion during the Ouachita orogeny. This mid-Mississippian impact is remarkably well preserved.
The distribution of strain in the outer ring is related both to the heterogenous material strengths of the target rocks and to the trajectory of the impactor. Proximal to the impact in the northeast, chaotic blocks of Mississippian rocks show brittle brecciation over ductily folded and faulted blocks associated with material flow. Injection breccias fill interstitial areas between megabreccia blocks. Resurge breccia caps this succession. To the northwest, thick to massive beds of brittle carbonates in the lower Burlington-Keokuk limestones (undivided) generally behaved as thin thrust sheets where siltstone of the lower Mississippian (Kinderhookian) Northview Formation served as a décollement. Thrust faulting also is exposed distally to the north and northeast at road cuts near Brush Creek and Weaubleau Creek on Highway 82. Resurge breccia is gradational with the sediments of the upper Burlington-Keokuk limestones in the northeasternmost exposures beyond the tectonic rim.
2012 GSA Annual Meeting in Charlotte
General Information for this Meeting
|Session No. 270|
Shock Processes and Shock Attenuation Associated with Hypervelocity Impact Events
Charlotte Convention Center: 213A
1:30 PM-5:30 PM, Wednesday, 7 November 2012
Geological Society of America Abstracts with Programs, Vol. 44, No. 7, p. 630
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