by: Charles O’Dale
- EARTH HISTORY vs IMPACT
- IMPACT CRATER/STRUCTURE IDENTIFICATION – Geologic confirmation for an impact event.
- GEOMORPHOLOGY – One of the first indicators of a possible impact site is “circular geology”.
- SHATTER CONES/SLICKENSIDES – Shatter cones are distinctive striated conical fractures that are considered unequivocal evidence of impact events.
- BRECCIA – Breccias are extremely common in the central uplift, in crater-fill deposits, and in the ejecta blanket of meteorite impact craters.
- FRACTURED ROCK – While travelling toward impact sites I documented fractured rocks increasing in magnitude as we neared the crater site.
- GRAVITY ANOMALIES – Gravity contours illustrate anomalies caused by fractured country rock under an impact site.
- MAGNETIC ANOMALIES – Magnetic studies document the magnetic disturbances within impact structures.
- SHOCK METAMORPHOSIM – The extreme pressures and temperatures at hypervelocity impacts have caused shock metamorphic effects on target rocks.
- CRATER EJECTA – When the crater formation process ends, the resulting circular structure and the surrounding area is covered by an ejecta blanket.
- CRATER RIM – Documentation of surviving crater rims on this planet.
- CRATER SHAPE – Why are impact craters almost always round? (or polygonal)?
- CRATER FORMATION – Impact involves the transfer of massive amounts of energy to a relatively small area of the Earth’s surface, in an extremely short period of time (Kinetic energy). Three stages of crater formation:
- contact & compression;
- excavation; and
- CRATER CLASSIFICATION – On this planet, impact craters are divided into three basic morphologic subdivisions:
- simple craters;
- complex craters; and
- peak ring craters.
- PLANET VS CRATER SIZE – The primary factors governing the size and shape of impact craters are:
- impact energy;
- gravity; and
- properties of the target.
- GLOSSARY – IMPACT CRATER/STRUCTURE
- impact crater glossary; and
- meteorite types;
- dating meteorites;
- meteorite glossary; and
- CANADIAN CRATERS – Documented in 1967 & 1975.
Osinski G. The Geological Record of Meteorite Impacts Canadian Space Agency 2018