Computer Science
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001m%26ps...36..651k&link_type=abstract
Meteoritics & Planetary Science, vol. 36, no. 5, p. 651-669
Computer Science
4
Scientific paper
The 15-km-diameter Ames structure in northwestern Oklahoma is located 2.75 km below surface in Cambro-Ordovician Arbuckle dolomite, which is overlain by Middle Ordovician Oil Creek Formation shale. The feature is marked by two concentric ring structures, with the inner ring of about 5 km diameter probably representing the collapsed remnant of a structural uplift composed of brecciated Precambrian granite and Arbuckle dolomite. Wells from both the crater rim and the central uplift are oil- and gas-producing, making Ames one of the economically important impact structures. Petrographic, geochemical, and age data were obtained on samples from the Nicor Chestnut 18-4 drill core, off the NW flank of the central uplift. These samples represent the largest and best examples of impact melt breccia obtained so far from the Ames structure. They contain carbonate rocks which, therefore, are derived from the target sequence. The chemical composition of the impact melt breccias is similar to that of target granite, with variable carbonate admixture. Some impact melt rocks are enriched in siderophile elements indicating the possible presence of a meteoritic component. Based on stratigraphic arguments, the age of the crater was estimated at 470 Ma. Previous 40Ar-39Ar dating attempts of impact melt breccias from the Dorothy 1-19 core yielded plateau ages of about 285 Ma, which is in conflict with the stratigraphic age. The new 40Ar-39Ar age data obtained on the melt breccias from the Nicor Chestnut core by UV laser spot analysis, resulted in a range of ages with maxima around 300 Ma. These data could reflect processes related either the regional Nemaha Uplift or resetting due to hot brines active on a midcontinent-wide scale, perhaps in related to the Alleghenian and Ouachita orogenies. The age data indicate an extended burial phase associated with thermal overprint during Late Pennsylvanian-Permian.
Kelley Simon P.
Koeberl Christian
Reimold Wolf Uwe
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