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Structural study of Cactus Crater

Vizgirda, Joana and Ahrens, Thomas J. (1982) Structural study of Cactus Crater. In: Proceedings of the Lunar and Planetary Science Conference. Geochimica et cosmochimica acta. Supplement ; 16. No.12. Pergamon Press , New York, NY, pp. 1623-1639. ISBN 0080280749.

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The detailed structure of Cactus Crater, a 105 m diameter nuclear explosion crater formed in water-saturated carbonate rock of Eniwetok Atoll, is delineated using the high to low Mg calcite diagenetic transition as a stratigraphic tracer. Outside Cactus, this transition is observed as a discontinuous horizon which appears to be depressed, possibly as a result of the cratering event, near the crater. Beneath the crater, this transition occurs gradually over a 4.5 ± 0.5 m interval, leading to the following conclusions: material inside Cactus Crater underwent primarily in situ brecciation and mixing, the maximum depth of the excavation cavity is 20 m below sea level, and a fallback breccia lens, if it exists, has a maximum thickness of l m. A central uplift of 4.5 ± 0.5 m is inferred from the observation that the transition interval occurs at a 4 to 5 m greater depth at 1/2 crater radius than in the center. The excavation process, deduced from the Mg calcite transition as well as gamma well log data, involves high velocity injection of strongly shocked material to form the excavation cavity lining. The in situ brecciation and mixing appears to be a turbulent process, probably facilitated by fluidization of the carbonate rock. Based on the Mg calcite transition patterns beneath the crater floor, dynamic rebound is inferred as the modification mechanism for Cactus Crater. Using the Melosh Bingham model for dynamic rebound, a maximum strength of ~1 bar is inferred for the cratered carbonate medium. This strength value is representative of clays, such as those in which Snowball, a chemical explosion crater having dimensions and features similar to Cactus', was formed. Comparisons between Cactus and meteorite impact craters are also presented.

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Additional Information:© 1982 Lunar and Planetary Institute. Provided by the NASA Astrophysics Data System. Discussions with B. Ristvet and J. Melosh are gratefully acknowledged. This research was supported under DNA contract 001-79-C-0252. Contribution No. 3615, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
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Defense Nuclear Agency (DNA)001-79-C-0252
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Caltech Division of Geological and Planetary Sciences3615
Series Name:Geochimica et cosmochimica acta. Supplement ; 16
Issue or Number:12
Record Number:CaltechAUTHORS:20150128-083525276
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Official Citation:Structural study of Cactus Crater Vizgirda, J.; Ahrens, T. J. Lunar and Planetary Science Conference, 12th, Houston, TX, March 16-20, 1981, Proceedings. Section 2. (A82-31677 15-91) New York and Oxford, Pergamon Press, 1982, p. 1623-1639.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54167
Deposited By: Ruth Sustaita
Deposited On:28 Jan 2015 17:54
Last Modified:03 Oct 2019 07:55

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