Shatter cones in Illinois: Evidence for metoeritic impacts at Glasford and Des Plaines

Shatter cone fragments were recovered from rock cores at two previously suspected, but heretofore unverified, impact structures in Illinois. Both sites are buried features known from geophysical surveys and drill holes. Shatter cones are accepted widely as field criteria of meteoritic impact. Detection of these shock indicators in both the Glasford Structure and the Des Plains Disturbance upgrades these sites in Earth's inventory of known and suspected impact structures from possible impact sites with compatible structure and morphology to probable impact structures which possess also evidence of shock metamorphism

Sudbury Breccia and suevite as glacial indicators transported 800 km to Kentland Astrobleme, Indiana

A glacial erratic whose place of origin is known by direct comparison with bedrock is known as an indicator. In 1971, while visiting the known astrobleme at Kentland, Indiana, Peredery recognized and sampled in the overlying glacial drift deposits a distinctive boulder of Sudbury suevite (black member, Onaping Formation) that normally occurs within the Sudbury Basin as an impact fall-back or wash-in deposit. The rock was sampled (but later mislaid) from a farmer's cairn next to a cleared field. Informal reports of this discovery prompted the other authors to recently reconnoiter the Kentland locality in an attempt to relocate the original boulder. Several breccia blocks were sampled but laboratory examination proved most of these probably to be diamictites from the Precambrian Gowganda Formation, which outcrops extensively in the southern Ontario. However, one sample was confirmed as typical Sudbury Breccia, which outcrops in the country rock surrounding the Sudbury Basin. Thus two glacial indicators were transported by Pleistocene continental glaciers about 820 km over a tightly proscribed path and, curiously, from one astrobleme to another. Brecciated boulders in the Illinois/Indiana till plain are usually ascribed to the Gowganda or Mississagi formations in Ontario. But impact-generated rocks need not be confused. The carbonaceous matrix of the suevite, for example, was sufficiently distinctive to assign it to the upper portion of the black Onaping. The unique and restricted source area of these indicators provide an accurate and reliable control for estimating Pleistocene ice movement

Space shuttle observations of terrestrial impact structures using SIR-C and X-SAR radars

Ten terrestrial impact structures were imaged during two flights of the 1994 Space Radar Laboratory (SRL) experiment. These craters include Wolf Creek, Australia; Roter Kamm, Namibia; Zhamanshin, Kazakhstan; B.P. and Oasis, Libya; Aorounga, Chad; Amguid, Algeria; and Spider, Connolly Basin and Henbury, Australia. SRL contained two co-registered instruments; the United States SIR-C polarimetric radar system operating in L-band (lambda =24 cm) and C-band (lambda =5.6 cm), and the joint German/Italian X-SAR vertically-polarized radar operating in X-band (lambda =3 cm). Comparisons show SRL images to be complementary to, or in some cases superior to, corresponding optical images for evaluating size, location, and relative age of impact features. Regardless of wavelength or polarization, craters with significant relief appear prominently on radar as a result of slope and roughness effects. In desert regions, longer wavelengths penetrate dry sand mantles to reveal hidden crater dimensions or associated buried landforms. Radar polarities and wavelengths are particularly sensitive to vegetation, surface roughness, and soil moisture or electrical properties. In the more temperate environments of Kazakhstan and Australia, SRL images show detailed stream patterns that reveal the location and structure of otherwise obscured impact features.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202