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– modification.
- 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– reference.
– introduction– meteorite types;– dating meteorites;– meteorite glossary; and– reference.
- CANADIAN CRATERS – Documented in 1967 & 1975.
Osinski G. The Geological Record of Meteorite Impacts Canadian Space Agency 2018