United States Meteorite Impact Craters

Shatter cones are the only macroscopic (visible to the unaided eye) structures that serve as unambiguous diagnostic evidence that a geological structure is the result of a hypervelocity impact event (meaning a large meteorite impact).

In 1883, J. Collett described shatter cones at the Kentland impact structure as follows: "At the latter station the stone was a slightly crystalline, bluish-gray limestone, with great nodules of cone-in-cone one to two feet in diameter, indicating pressure of superimposed material while it was in a plastic condition."

A second very early description can be found in Gorby (1886), again discussing what is later known as the Kentland impact structure.

"In fact, it seems probable that the upheaval occurred while great masses of the Upper Silurian deposit were yet in a plastic condition, which is evidenced by frequent and large impressions termed cone-in-cone, caused probably by an upward pressure of the substrata. This cone-in-cone consists of a number of cone-shaped masses, having the appearance at times of one being within the other, hence the name. The apex of the cone is always vertical to the plane of the lines or seams of stratification; that is, where the stratum lies in a horizontal position the apex of the cone always points upward. These peculiar masses vary from a few inches across the base to eight or ten feet, and the hight generally equals or exceeds the diameter of the base. At Kentland, Ind., where the rocks lie in a horizontal position, the apex of the cone points upward, but where they dip to the east as much as 75° or 80°, as they do in Mr. John McKee's quarry, the apex of the cone points directly to the east. On another part of his farm, where the dip of the strata is 70° to 80° to the west, the cone-in-cone was observed to extend in the same direction."

In 1889, Maurice Thompson characterized shatter cones at Kentland, Indiana, as follows. "At McKee's quarry the cone-in-cone structure produced by points of pressure from below, are everywhere to be seen. The force causing these beautiful rosettes in the fiber of the stone has acted in a line exactly perpendicular to the original plane of deposit, showing that the strata were once horizontal, and have since assumed their distorted forms."  For students of science history, it is interesting to note that Thompson contextualizes his comments within the uniformitarianism versus catastrophism debate of his era.

Gorby and Thompson presage the later work of Dietz and others in several facets of their descriptions, as they attribute the cones to a sudden event, addresses the direction of applied force, and comment upon the original orientation of the shatter cone containing bedding relative to the force at the time of formation.

Kindle again briefly mentions shatter cones as cone-in-cone structures in a discussion of work at Kentland in 1903.

Shatter cones were described at Steinheim, in Germany, in 1905 (Branco and Fraas, 1905), as conical rayed structures in limestone (strahlenkalke).  Branco and Fraas coined the term cryptvolcanic in this article to describe the explosive geological structure at Steinheim, now the Steinheim impact crater.  Cryptovolcanism later emerged as a model that competed with the impact paradigm from the 1920s to the 1970s.  

McHone et al. (2012) notes that the term 'strahlenkalke' was still in use in German literature in the 1920s, citing Franz et al., 1924.

The term 'shatter cone' replaces the 'cone-in-cone' terminology in the United States in the early 1930s, and may have been coined by Dr. Walter H. Bucher, in 1932, when he used it to describe "Intense local shattering which produced “shatter cones,” such as have been described from the crypto volcanic Steinheim Basin, Germany, where the evidence for an explosive force is convincing."  (Bucher, 1932)  Dr. Bucher was a champion of the cryptovolcanic explanation, and was speaking of the Well's Creek, Tennessee, impact structure at the time.  Though he steadfastly advocated the cryptovolcanic model, Bucher contributed much to the early characterization of the complex crater population in the US.  In 1933 (published 1936), he listed shatter cones as one of the common characteristics of cryptovolcanic structures.

Shrock and Mallott (1933) describe shatter cones at 3 quarries at the Kentland impact structure, saying they had been described by earlier authors, as 'cone-in-cone' structures (a term now exclusively applied to a different and unrelated type of sedimentary structure), and then goes on to cite personal correspondance with Dr. Bucher, who considered them to be of cryptovolcanic origin.  "The curious cone-in-cone-like fracture pattern, which I like to refer to as 'shatter cones,' looks like that which I found in the central area of Well's Creek Basin in Tennessee."  Bucher then refers to the similar structures also reported at Steinheim Basin, in Germany.  Bucher's early description of shatter cones is "a sort of fracture cleavage representing inter-penetrating cones into which the rock could easily be split by gentle tapping with the hammer."

The notion that shatter cones and the 'cryptovolcanic' sites at which they were found could be related to meteorite impact was present in the late 1930s, but was treated with significant reservation. Boone and Albritton (1936) explicitely state "The meteorite hypothesis explains the occurrence of folds resembling damped waves, and evidences of violent explosion (breccias, shatter-cones, etc.) as well as does the cryptovolcanic hypothesis."  In 1937, Robert Shrock, a proponent of the crytpovolcanic explanation for the shatter cones at Kentland, which was still one of only 3 sites at which shatter cones had been observed, responded to and rejected Boone and Albritton's 1936 suggestion with solid, rational arguments.  He pointed out the scale of the upward displacement, the complete lack of meteorite remnants, a lack of significant heat indicators, and the overall scale of the structure. 

In a 1937 publication concerning the Kentland crater, Robert Shrock provides a beautiful photograph (plate 5) of shatter cones.  He also provides what appears to be the first generalized technical description of shatter cones as a class of small-scale geological structure and formalizes the 'shatter-cone' or 'shatter cone' name for the objects.  He incorrectly contradicts Bucher's 1886 assessment that the shatter cones are meaningfully oriented relative to stratigraphic bedding, but then goes on to accurately state "It appears that these unique structures are the result of some violent shock to which the rocks were subjected during the deformation, and it is significant that they characterize the so-called "cryptovolcanic" and closely related structures."  In literature up to this time, shatter cones had been referred to in a variety of ways, including cone-in-cone, cup-and-cone, shatter-cone, pressure-cone, and shear-cone structures, among others.  On the basis of Bucher's, Shrock's, and Dietz' early work at the site Gutschick (1976, 1983, and 1987) suggests that Kentland, Indiana, should be considered the shatter cone type location in the US. 

Boone and Albritton tentatively suggested an impact origin for Kentland and Wells Creek again in 1938, in the context of a catalog of possible meteorite impact sites.  They also listed several others at which it turned out shatter cones would soon be found, including Sierra Madera, Ries, Flynn Creek, and Vredefort.  It is possible that there are early observations of shatter cones that have been missed among the early descriptive work concerning these and others.

[author note to self - See Boon and Albritton 1938 for additional 1931-1938 references, by other authors, to Reis and Steinheim as impact craters.  Did they identify shatter cones as an indicator of similar sturctures?]

Few people have done more to further our early understanding of shatter cones and their relation to hypervelocity meteorite impacts than Robert S. Dietz.  Dietz started looking at impact craters in 1946, with two papers suggesting that the craters visible on the moon's surface were of impact origin, rather than volcanic.  He then turned his attention to fieldwork, focussed on identifying related structures on earth.

Approaching the shatter cone-bearing central uplift at Kentland with an impact paradigm already in mind, Dietz was able to see the evidence in a different way.  In 1947, R. S. Dietz published articles correctly postulating that the orientation of shatter cones and the nature of the displacement within them suggested a top-down force, and thus a meteorite impact origin, rather than a cryptovolcanic force applied from below.  He also introduced the term crytpoexplosive, to replace cryptovolcanic, in his work in 1946 allowing latitude in interpretation of cause.  At that time, shatter cones were still known from only 3 locations, Kentland, Well's Creek, and Steinheim (Dietz, 1947).

Shatter Cones were reported at Crooked Creek in 1954 (Hendricks, 1954), and by this time, Dietz' work had reframed the conversation.  Shatter cones were comfortably associated with impact rather than with cryptovolcanism.

There were still only 4 known sites at which shatter cones had been identified in 1959, when Robert Dietz designated the Steinheim Basin, in Germany, as their type location.  In the same article, Dietz tentatively suggested that shatter cones could be uniquely associated with cryptoexplosive structures of meteorite impact origin, and that they might serve as a criterion for their recognition (Dietz, 1959).  He immediately set out to use them in this way, and found shatter cones at 3 more crypto-explosion sites, consistent with his prediction, within the next year.  

In a 1960 article in the journal, Science, Dietz presented his fieldwork.  He explicitely proposed shatter cones as 'definitive evidence' of meteorite impact origin for cryptoexplosion structures, and added Sierra Madera, Flynn Creek, and Serpent Mound to the list of sites at which shatter cones had been clearly identified.  This increased the total number of known shatter cone sites to 7.  Shatter cones had become the second diagnostic indicator of an impact crater, after meteorite remnants.

Coesite, a high pressure polymorph of quartz, was first identified at an impact crater in the same year, 1960, in Coconino sandstone at Barringer Crater, Arizona (Chao et al., 1960).  Cohen et al. (1961) strengthened the connection between shatter cones and hypervelocity meteorite impact structures, with the report of coesite in the immediate environment of shatter cones at Kentland Crater, and associated with shatter cones from Serpent Mound Crater.  Subsequent research has clarified that, though shatter cones and coesite are both indicative of hypervelocity impact, they represent very different pressure regime zones within an impact crater.

Shoemaker et al. (1961) reported the production of small shatter cones in a laboratory, generated by firing aluminum pellets into dolomite at extremely high velocity.  Bucher (1963) attempted to produce shatter cones by impacting larger masses at lower velocity, but failed (Dietz, 1963).  It had become clear that shatter cones were produced by shock - waves traveling through the target rock at a rate faster than the speed of sound in the target material.  It had also become clear that shatter cones pointed towards the location of impact.  When the orientation of the rock units in which they occurred were rotated to account for subsequent changes, the apexes of the shatter cones at a site generally point upwards and inwards towards a point of initial contact.  This became an investigative tool by the 1960s (e.g.: Hargraves, 1961; Manton, 1965).

Dietz and others formalized and expanded upon the relationship between shatter cones and impact craters in later publications.  By 1968 (see Dietz article in French and Short volume, 1968), shatter cones were firmly recognized as shock indicators, and had been unequivocally associated with grain-scale deformation of quartz and other mineral grains, and with high pressure mineral polymorphs, as indicators of large hypervelocity meteorite impact scars.  A pivotal conference, in 1966, and associated volume, in 1968, brought all of this together.

It was also discovered, in the 1960s, that nuclear explosions could produce shatter cones (e.g. Bunch and Quaide, 1968).  Nuclear and high-explosive test sites and large meteorite impact craters remain the only known contexts in which shatter cones occur outside of laboratory experiments.  Additional studies reporting the production of shatter cones in explosive experiments were published by Roddy and Davis (1969, 1977) [note to self: read these].

Like other classes of impact evidence, shatter cones only occur within rocks subjected to a specific range of impact generated shock pressure.  Placing lower and upper limits on shatter cone formation required both a detailed look at where shatter cones were being found within known impact structures, and the integration of other lines of emerging impact evidence, more specifically, grain scale evidence from petrographic studies, both from field collected samples and from shock experiments in the laboratory. [Roddy and Davis 1969, 1977; Robertson, 1975; Dence, 1968; Dence et al., 1977; Horz, 1971] 

Killgore et al., 2011, and McHone et al., 2012, expanded the understanding of shatter cones when they described and presented shatter cones as records of impact in meteorites.

Constraints on the lower range of crater diameters at which shatter cones have been reported can be found in Beauford (dissertation), 2015.

Today, shatter cones are broadly accepted as sufficient stand-alone evidence of the impact origin of a structure, even when other evidence is lacking (eg. French and Koeberl, 2010).

Timing and Context of Shattercone Formation

Shatter cones form preferentially in fine grained rock, but it is not clear that there is any rock type in which they will not form.  Both shatter coned breccias and shatter cone fragments in breccia have occasionally been reported (e.g.: Bjornerud, 1998; Wilshire et al., 1971).  Wilshire et al. (1971) describes both shatter cone formation in monomict breccias, and shatter cone fragments included within polymict breccis, at Sierra Madera.

 

Shatter Cone from Beaverhead crater.  Thanks to Steve and Qynne Arnold.

Hargraves et al., 1990; Hargraves et al., 1994.

Shatter Cone from Crooked Creek Crater. 

Shatter cone from Glover Bluff crater.  Thanks to Steve and Qynne Arnold.

Shatter cone from Kentland Crater.

Shatter cone from Santa Fe crater.

Shatter cone from Sierra Madera crater.

Shatter cone from Wells Creek crater.

Shatter cone in NWA meteorite.

Bibliography and References:

Baratoux D, Melosh H J (2003) The formation of shatter cones by shock wave interference during impacting. Earth and Planetary Science Letters 216, pages 43-54.

Bjørnerud M. G. 1998. Superimposed Deformation in Seconds: Breccias from the Impact Structure at Kentland, Indiana (USA), Tectonophysics v. 290, issue 3-4, pp. 259-269.

http://www.sciencedirect.com/science/article/pii/S0040195198000237

[Distinguishes 3 types of breccia, and examines timing and process of emplacement.  The author suggests different breccia units may form simulataneous with shatter cone formation vs. afterwards, and that these can be distinguished by the entrainment of shatter cone fragments as clasts.]

Boon J. D., Albritton C. C. 1936. Meteorite Craters and Their Possible Relationship to “Cryptovolcanic Structures”. Field and Laboratory, Volume 5, No. 1, pp. 1-9.

Boon J. D., Albritton C. C. (1938) Established and supposed examples of meteoritic craters and structures. Field and Laboratory, Volume 6, No. 2, pp. 44-56.

Branco W., Fraas E. 1905. Das kryptovulkanische Becken von Steinheim. In Abhandlungen der königl. preuß. Akademie der Wissenschaften. Berlin 1905.

[Described shatter cones at Steinheim, Germany, in 1905.  Coined the term 'cryptovolcanic.']

Bucher W. H. 1932. Wells Creek Basin, Tennessee, a typical cryptovolcanic structure [abstracts]. Proceedings of the Forty-fourth Annual Meeting of the Geological Society of America, Tulsa, Oklahoma, December, 1931, in Bulletin of the Geological Society of America, Volume 43, Part 1, pages 147-148.



[Possibly the first use of the term 'shatter cone' in print.]

Bucher, W. H. 1936. Cryptovolcanic structures in the United States (with discussion) Report XVI. 16th International Geological Congress (Washington), 1933, Proceedings, Volume 2, pages 1055-1084.

no link found

[Also occasionally cited as 1933 or 1935.]

Chao, E. C. T., Shoemaker, E. M., and Madsen  B. M. First Natural Occurence of Coesite. Science 22 July 1960, Volume 132, Issue 3421, pages 220-222.

[Coesite first found in nature, at Barringer Crater, Arizona.]

Cohen A. J., Bunch T. E., Reid A. M. 1961. Coesite Discoveries Establish Cryptovolcanics as Fossil Meterorite Craters. Science, 17 Nov 1961, Volume 134, Issue 3490, pages 1624-1625.



[Associates shatter cones with coesite at Kentland and Serpent Mound.]

Collett, J. 1883. Geological survey of Newton County. Indiana Department of Geology and Natural History, 12th Annual Report, pages 58-59.



Dence M. R. (1968) Shock zoning at Canadian craters: Petrography and structural implications, In Shock Metamorphism of Natural Materials, B. M. French and N. M. Short, eds., Mono. Baltimore. pages 169-184.

Dence M. R., Grieve R. A. F., Robertson P. B. (1977) Terrestrial impact structures: Principle characteristics, and energy considerations. In Impact and Explosion Cratering (D. J. Roddy, R. O. Pepin, and R. B. Merrill, eds.) pages 247-275, Pergamon Press, New York.

Dietz R. S. 1946. Geological structures possibly related to lunar craters. Popular Astronomy, Volume 54, pages 465-467

[introduces the term 'crypto-explosion structure', and describes the basic morphology of complex impact craters]

Dietz R. S. 1947. Meteorite impact suggested by the orientation of shatter-cones at the Kentland, Indiana disturbance. Science 105: 42-43.  DOI: 10.1126/science.105.2715.42

http://www.sciencemag.org/content/105/2715/42.extract

[correctly points out that shatter cones indicate a top-down application of force, contradicting the crypto-volcanic model of complex crater origin]

Dietz R. S. 1959. Shatter Cones in Cryptoexplosion Structures (Meteorite Impact?). The Journal of Geology, Volume 67, No. 5, pages 496-505.



Dietz R. S. 1960. Meteorite impact suggested by shatter cones in rock. Science, Volume 131, No. 3416, pages 1781-1784.

Dietz R. S. 1963. Astroblemes: Ancient Meteorite-Impact Structures on the Earth, in The Solar System, Volume 4, The Moon Meteorites and Comets, Edited by Gerard P. Kuiper, and Barbarra Middlehurst. The University of Chicago Press, Chicago, Ill. page 285



Dietz R. S. 1968. Shatter cones in cryptoexplosion structures. In Shock Metamorphism of Natural Materials, B. M. French and N. M. Short, eds., The Mono Book Corp., Baltimore. pages 267-285

Dietz R. S. 1972. Shatter cones (shock fractures) in astroblemes. Proceedings of the 24th International Geological Congress, Section 15, pages 112-118. 

French B. M., Koeberl C. 2010. The convincing identification of terrestrial meteorite impact structures: What works, what doesn't, and why, Earth-Science Reviews, Volume 98, Issues 1–2, Pages 123-170.



Killgore M., Killgore K., McHone J. F., Shoemaker C. 2011. First report of a shatter-coned meteorite (abstract #1112). Abstracts of the 2nd Planetary Crater Consortium.

[Reported shatter cones in meteorites.]

Kranz W., Berz K. C., Berckhemer F. 1924. Begleitworte Zur Geognostischen Spezialkarte von Wurttemberg, Atlasblatt Heidenheim, 2 Auflage.

Gash P. J. S. 1971. Dynamic mechanism for the formation of shatter cones, Nature - Physical Science (London), Volume 230, pages 32-35.

Gibson H M, Spray J G (1998) Shock-induced melting and vaporization of shatter cone surfaces: Evidence from the Sudbury impact structure. Meteoritics and Planetary Science 33, pages 329-336

Gorby S. S. 1886. The Wabash Arch. Geological survey of Newton County. Indiana Department of Geology and Natural History, 15th Annual Report, pages 228-241.



Hargraves R. B. (1961) Shatter cones in the rocks of the Vredefort ring. Transactions of the Geological Society of South Africa, Volume 64, pages 147-161. 

Hargraves, R.B., Cullicott, C.E., Deffeyes, K.S., Hougen, S.B., Christiansen, P.P., and Fiske, P.S., 1990, Shatter cones and shocked rocks in southwestern Montana: The Beaverhead impact structure: Geology, v. 18, p. 832-834.

Hargraves, R.B., Kellogg, K.S., Fiske, P.S., and Hougen, S.B., 1994, Allochthonous impact-shocked rocks and superposed deformations at the Beaverhead site, southwest Montana—possible crater roots buried in southcentral Idaho, in Dressler, B.O., Grieve, R.A.F., and Sharpton, V.L., eds., Large Meteorite Impacts and Planetary Evolution: Boulder, Colorado, Geological Society of America Special Paper 293, p. 225-236

Hendriks, H. E., 1954, Geology of the Steelville Quadrangle, Missouri. Missouri Geological Survey and Water Resources, Volume 36, Second Series, 88 pp. (with 2 geological maps)

no link found

Kindle E. M and Breger C. L. 1903. The Stratigraphy and Paleontology of the Niagara of Northern Indiana. Indiana Department of Geology and Natural Resources, 28th Annual Report, pages 43, 397-486.



[Briefly mentions shatter cones as cone-in-cone structures at McKee quarry, Kentland, Indiana.]

Manton W. I. (1965) The orientation and origin of shatter cones in the Vredefort ring. Annals of the New York Academy of Sciences, Volume 123, pages 1017–1048. doi:10.1111/j.1749-6632.1965.tb20415.x

McHone J. F., Shoemaker C., Killgore M, Killgore K. 2012. Two shatter-coned NWA meteorites. Abstracts of the 43rd Lunar and Planetary Science Conference.

[Reports shatter cones in meteorites.]

Milton D. J. 1977. Shatter cones - An outstanding problem in shock mechanics. In Impact and explosion cratering (D. J. Roddy, R. O. Pepin, and R. B. Merrill, eds.), Pergamon, New York, pages 703-714.

http://adsabs.harvard.edu/full/1977iecp.symp..703M

Nicolaysen L O, Reimold W U (1999) Vredefort shatter cones revisited. Journal of Geophysical Research 104, pages 4911-4930.

Osinski G. R. (2007) Meteoritics & Planetary Science, 42, 1945-1960.

Osinski, G. R., & Ferrière, L. (2016). Shatter cones: (Mis)understood? Science Advances, 2(8), e1600616. http://doi.org/10.1126/sciadv.1600616

Robertson P. B. (1975) Zones of shock metamorphism at the Charlevoix impact structure, Quebec, Bulletin of the Geological Society of America, Volume 86, pages 1630-1638.

Roddy D. J. and Davis L. K. 1969. Shatter cones at TNT explosion craters (abstract). In EOS Transactions of the American Geophysical Union. Volume 50, page 220.

Roddy D. J. and Davis L. K. 1977. Shatter cones formed in large-scale experimental explosion craters. D. J. Roddy, R. O. Pepin, and R. B. Merrill (Eds.), Impact and Explosion Cratering, Pergamon, Oxford, New York, pages 715-750.

Shoemaker E. M., Gault D. E., Lugn R. V. 1961. Shatter cones formed by high speed impact in dolomite: U.S. Geological Survey Professional Paper 424-D, pages 365-368.

[Reports first formation of shatter cones in a laboratory setting.]

Shrock R. R. 1937. Stratigraphy and structure of the area of disturbed Ordovician rocks near Kentland, Indiana. American Midland Naturalist, Volume 18, No. 4 (July, 1937), pages 471-531.



[Provides a detailed description and photograph of shatter cones (plate 5) and formalizes the name of this class of small-scale geological structure as 'shatter cones' or 'shatter-cones', within the context of a discussion of structural clues to the origin of the Kentland uplift.]

Shrock R. R., Malott C. A., The Kentland area of disturbed Ordovician rocks in northwestern Indiana. Journal of Geology, v. 41, pp. 337-370. 1933.

http://www.jstor.org/stable/30058967?seq=1#page_scan_tab_contents Shrock, R. R.,

Simon P. Y., Dachille F. (1965) Shock damage of minerals in shattercones (abstract). Geological Society of America Special Papers, Volume 87, pages 156-157.

Stratigraphy and structure of the area of disturbed Ordovician rocks near Kentland, Indiana. American Midland Naturalist, v. 18, pp. 471-531. 1937.

http://www.jstor.org/stable/2420651?seq=1#page_scan_tab_contents

Thompson M. 1889. The Wabash Arch. Geological survey of Newton County. Indiana Department of Geology and Natural History, 16th Annual Report, pages 41-53.



Wilshire H. Howard K. Offield T. (1971) Impact breccias in carbonate rocks, Sierra Madera, Texas. Geological Society of America Bulletin, Volume 82, pages 1009-1018.

[Thompson attributes cone-in-cone structures at Kentland, Indiana, to the abrupt application of force from below, and accurately identifies the fact that the bedding was perpendicular to the applied force at the time the cones formed, and that disruption followed.]