HR: 1340h
AN: GP33A-0105    [Abstracts]
TI: Paleomagentic Constraints on the Timing of the Decaturville Impact Structure, Southwest Missouri
AU: * Dulin, S A
EM: smyers@ou.edu
AF: University of Oklahoma School of Geology and Geophysics, 100 E. Boyd St. Suite 810, Norman, OK 73019 United States
AU: Elmore, R D
EM: delmore@ou.edu
AF: University of Oklahoma School of Geology and Geophysics, 100 E. Boyd St. Suite 810, Norman, OK 73019 United States
AU: Mulvany, P S
EM: patrick.mulvany@dnr.mo.gov
AF: Missouri Department of Natural Resources, P.O. Box 250, Rolla, MO 65402 United States
AU: O'Brien, V
EM: obrienvj@ou.edu
AF: University of Oklahoma School of Geology and Geophysics, 100 E. Boyd St. Suite 810, Norman, OK 73019 United States
AB: The Decaturville impact structure in southern Missouri is characterized by a 6km-diameter zone of intensely deformed strata and impact-related features such as shatter cones and shocked quartz. The age of this event is enigmatic because dating techniques have not produced an unambiguous result. A previous study constrained the timing as post-Pennsylvanian through Cretaceous. In this study we use the results of a modified conglomerate test on impact related breccias to further constrain the timing of the impact event. Two types of breccias are present in the impact structure: monolithologic breccias that are confined to a single bed and mixed breccias composed of clasts from numerous formations that are present throughout the impact structure. Samples of both breccia types within the Jefferson City dolomite were collected along state highway 5, on the southeast quadrant of the structure. All specimens of the mixed breccia contain the same characteristic remanent magnetization (ChRM) carried by magnetite that has southeasterly declinations and shallow inclinations. The stratigraphic breccias carry a weak, poorly defined remanent magnetization, and more analysis of these breccias is needed. Preliminary data from the Jefferson City dolomite outside the structure indicates it contains a component similar to the ChRM. The ChRM is post-depositional, and could be related to heat or chemical remagnetization processes that may or may not be related to the impact. The pole position for the ChRM is 50.6°N, 130.2°E, which lies close to the mid to late Permian segment of the apparent polar wander path for North America, and places a limit on the age of the impact. Geochemical and other studies are currently underway to determine the origin of the remagnetization in the mixed breccia. The ChRM is post-depositional and the Decaturville impact can be no younger than the late Permian, which constrains the age better than previous studies. It is interesting to note that deformed Mississippian limestones in the Weaubleau-Osceola structure, a supposed impact structure which lies approximately 60 miles to the west of Decaturville, contain a Mississippian post deformational ChRM which is older than the ChRM at Decaturville.
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1599 General or miscellaneous
DE: 5420 Impact phenomena, cratering (6022, 8136)
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005