Abstract: Lithologic and Stratigraphic Evidence for the Impact Origin of a Buried Ordovician Age Crater and Reservoir Near Ames, Major County, Oklahoma

Kevin E. Nick

An anomalous circular depression present in the subsurface beneath the town of Ames, Major County, Oklahoma is the site of oil and gas production from around 9000 feet. Characteristics of the Ames crater correspond to criteria that identify meteor impact sites. The gross shape and details of the geomorphology of the crater are consistent with an impact origin. Details of the textures, mineralogies and stratigraphic relations of lithologies sampled by cuttings, drilled sidewall cores, and conventional cores also provide a weight of evidence supporting an impact origin. Six major lithologies are encountered inside the crater. Wells near the center of the crater are completed in uplifted, brecciated granite. Other wells are completed in fractured and karsted Arbuckle dolomite, distal to he crater center. Mixed granite-dolomite breccias and conglomerates are encountered between pure granite and dolomite units. In these breccias granite abundance decreases and dolomite content increases with depth and dolomite clasts are highly fractured. An altered tuff-like melt unit dominated by vesicular textures with microtektite shaped, siliceous grains is locally present above the Arbuckle material but is not continuous within the crater. Most of the crater is filled with a thin unit of water transported, dense, very poorly sorted arenite. The detrital grains in the arenite are dolomite, quartz, feldspar, accretionary peloids, and clay. Many quartz grains in this unit contain multiple sets of shock lamellae. Dark fossiliferous shales fill the remainder of the crater. Brecciated res rvoir facies are overlain by directly emplaced and reworked air fall material.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994