First Report of a Shatter - Coned Meteorite

Shatter Cones; history and significance: A distinct, striated conical rock failure occurs at many terrestrial impact structures. Conical limestone fragments with radiating surface grooves were first reported by Branco and Frass [1] at Steinheim Basin, Germany in 1905. They ascribed the 4 km wide depression to deeply buried explosive magma which failed to reach the surface during a ‘crypto volcanic’ event. Kranz [2] in 1924 suggested rocks at Steinheim became brittle by absorbing pressurized gases, then broke into delicately grooved cones which he termed ‘strahlenkalk’ or rayed limestone. Walter Bucher in 1931 began studying cryptovolcanic structures in North America and soon found strahlenkalken at Wells Creek, Tennessee. In his report [3] he coined the term shatter cones; the name now used worldwide. By 1933 Shrock and Malott [4] reported shatter cones at Kentland, Indiana. And in 1934 Rohleder [5] described ‘Druckfiguren’, or pressure figures, at Lake Bosumtwi which he compared to Steinheim rock fractures. In his 1936 summary of United States crytovolcanic structures, Bucher [6] included the association of shatter cones as indicators of an underlying blast event. In 1947 Dietz [7] demonstrated that shatter cone apices point toward the source of an advancing shock pulse, and at Kentland the majority pointed upward. Since the explosive force came from above, not below, he suggested the Kentland disturbance was due to explosion of a meteorite rather than a hidden volcano. Shatter cones were next found in 1954 at Crooked Creek, Missouri by Hendriks [8] who suggested an impact origin for the circular disturbance. In 1959 Dietz [9] introduced the genetically neutral term ‘cryptoexplosion’ rather than cryptovolcanic. By 1960 Dietz [10] had found shatter cones at Sierra Madera, Texas; Serpent Mound, Ohio; and Flynn Creek, Tennessee, and he proposed shatter cones as a field criterion of meteoritic impact. Today, properly identified shatter cones are widely accepted as reliable and diagnostic impact indicators [11]. The search continues with considerable success and shatter cones are now confirmed in target rocks at more than 70, of about 180, documented terrestrial impact structures [12,13].