edge formed an outer ring 8 to 10 mi [13 to 16 km] in diameter and 1 to 2 mi [1.5 to 3 km] wide consisting of fractured and brecciated Arbuckle dolomite. The bottom of the crater filled with melt brec- cias—mixtures of granite, carbonate and dolo- mite in a spherulitic matrix—that had been ejected then fell back in. Tsunamis deposited diamictites, poorly sorted clastic breccias, atop the melt breccias.22
These crater-fill rocks con-
tained abundant shock-metamorphosed minerals and impact glass. The crater formed a closed lacustrine or
marine depression 300 to 600 ft [90 to 180 m] deep in which anoxic conditions prevailed, filling with black organic-rich shales that acted as
17. Carpenter BN and Carlson R: “The Ames Meteorite- Impact Crater,” in Johnson KS and Campbell JA (eds): Ames Structure in Northwest Oklahoma and Similar Features: Origin and Petroleum Production (1995 Symposium). Norman, Oklahoma: Oklahoma Geological Survey, Circular 100 (1997): 104–119.
18. Roberts C and Sandridge B: “The Ames Hole,” Shale Shaker (March–April 1992): 203–206.
19. Ahern JL: “Gravity and Magnetic Investigation of the Ames Structure, North-Central Oklahoma,” in Johnson KS and Campbell JA (eds): Ames Structure in Northwest Oklahoma and Similar Features: Origin and Petroleum Production (1995 Symposium). Norman, Oklahoma: Oklahoma Geological Survey, Circular 100 (1997): 330–333.
20. Sandridge R and Ainsworth K: “The Ames Structure Reservoirs and Three-Dimensional Seismic Development,” in Johnson KS and Campbell JA (eds): Ames Structure in Northwest Oklahoma and Similar Features: Origin and Petroleum Production (1995 Symposium). Norman, Oklahoma: Oklahoma Geological Survey, Circular 100 (1997): 120–132.
21. Koeberl C, Reimold WU, Brandt D, Dallmeyer RD and Powell RA: “Target Rocks and Breccias from the Ames Impact Structure, Oklahoma: Petrology, Mineralogy, Geochemistry, and Age,” in Johnson KS and Campbell JA (eds): Ames Structure in Northwest Oklahoma and Similar Features: Origin and Petroleum Production (1995 Symposium). Norman, Oklahoma: Oklahoma Geological Survey, Circular 100 (1997): 169–198.
Koeberl C, Reimold WU and Kelley SP: “Petrography, Geochemistry, and Argon-40/Argon-39 Ages of Impact-Melt Rocks and Breccias from the Ames Impact Structure, Oklahoma: The Nicor Chestnut 18-4 Drill Core,” Meteoritics & Planetary Science 36, no. 5 (2001): 651–669.
Fischer JF: “The Nicor No. 18-4 Chestnut Core, Ames Structure, Oklahoma: Description and Petrography,” in Johnson KS and Campbell JA (eds): Ames Structure in Northwest Oklahoma and Similar Features: Origin and Petroleum Production (1995 Symposium). Norman, Oklahoma: Oklahoma Geological Survey, Circular 100 (1997): 223–239.
22. Fischer, reference 21.
Mescher PK and Schultz DJ: “Gamma-Ray Marker in Arbuckle Dolomite, Wilburton Field, Oklahoma—A Widespread Event Associated with the Ames Impact Structure,” in Johnson KS and Campbell JA (eds): Ames Structure in Northwest Oklahoma and Similar Features: Origin and Petroleum Production (1995 Symposium). Norman, Oklahoma: Oklahoma Geological Survey, Circular 100 (1997): 379–384.
For more on tsunamis: Bunting T, Chapman C, Christie P, Singh SC and Sledzik J: “The Science of Tsunamis,” Oilfield Review 19, no. 3 (Autumn 2007): 4–19.
Karst
> Creation and preservation of the complex impact crater at Ames. About 470 million years ago a high-velocity asteroid plunged into the shallow sea that covered Oklahoma (A). Impact (B) created a transient crater and also brecciated and melted the carbonate target rock. Rebound of the deepest portion of the crater resulted in a high central uplift of target rock and underlying granitic basement (C). The outer walls of the crater collapsed from instability. The central uplift collapsed and formed a central ring of fractured target rock surrounding fractured basement rock (D). Deposition of shale (E) and other sediments buried the crater, and the region underwent tilting.
Oilfield Review Autumn 09 Impact Fig. 12
ORAUT09-Impact Fig. 12 B Impact melt Ejecta
Approximately 10 mi Ground zero
A Arbuckle group dolomite Kindblade Formation marker Basement (granodiorite)
Ejecta C Collapse
Central uplift D
Suevite and cavern system impact melt
Brecciated/fractured megablocks (fallback)
Ejecta
McLish sandstone
Winter 2009/2010
23
E
McLish shales
1,700 ft
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