When
3:30 p.m., May 5, 2009
Where
Kuiper Space Sciences 308
Professor Paul Knauth of Arizona State University is the scheduled speaker.
Layered sediments at both MER landing sites on Mars have sedimentary structures and other features almost identical to those observed in base surge deposits produced around terrestrial volcanic and nuclear explosions. The terrestrial base surges are roiling, dilute, ground-hugging, multiphase, turbulent clouds that spread out for many crater radii around large explosions. Impacts on objects with atmospheres and volatiles in the target area are expected to also produce base surges. Accretionary lapilli that form like hailstones in colossal numbers in the turbulent clouds in volcanic base surges are observed in severely eroded and altered impact deposits from the Chicxulub, Sudbury, and S. African Archean impacts. The Meridiani spherules are utterly dissimilar to any known terrestrial concretions but are similar in abundance, size, shape, and sorting to terrestrial examples of known accretionary lapilli. The geochemistry of Meridiani sediments cannot be explained in terms of aqueous processes without resorting to problematical diagenetic scenarios far more complicated than any ever proposed for terrestrial rocks but is easily explained in terms of geochemical maturation of an impact surge deposit exposed to water vapor and ice over long times. Home Plate at the Spirit site has sedimentary structures mostly indistinguishable from those at Meridiani but has been interpreted as a pyroclastic deposit completely overlying an invisible volcanic vent amidst coarsely-layered impact debris. Instead, Home Plate and numerous other layered deposits now observed all over Mars may simply be examples of impact surge deposits. Like their terrestrial volcanic and nuclear explosion counterparts, any base surge deposits around ancient terrestrial impact craters have been largely eroded away or misinterpreted as aqueous or eolian deposits. Because of its cold, dry history, Mars is therefore probably the best place in the Solar System to observe preserved impact surge deposits.
Layered sediments at both MER landing sites on Mars have sedimentary structures and other features almost identical to those observed in base surge deposits produced around terrestrial volcanic and nuclear explosions. The terrestrial base surges are roiling, dilute, ground-hugging, multiphase, turbulent clouds that spread out for many crater radii around large explosions. Impacts on objects with atmospheres and volatiles in the target area are expected to also produce base surges. Accretionary lapilli that form like hailstones in colossal numbers in the turbulent clouds in volcanic base surges are observed in severely eroded and altered impact deposits from the Chicxulub, Sudbury, and S. African Archean impacts. The Meridiani spherules are utterly dissimilar to any known terrestrial concretions but are similar in abundance, size, shape, and sorting to terrestrial examples of known accretionary lapilli. The geochemistry of Meridiani sediments cannot be explained in terms of aqueous processes without resorting to problematical diagenetic scenarios far more complicated than any ever proposed for terrestrial rocks but is easily explained in terms of geochemical maturation of an impact surge deposit exposed to water vapor and ice over long times. Home Plate at the Spirit site has sedimentary structures mostly indistinguishable from those at Meridiani but has been interpreted as a pyroclastic deposit completely overlying an invisible volcanic vent amidst coarsely-layered impact debris. Instead, Home Plate and numerous other layered deposits now observed all over Mars may simply be examples of impact surge deposits. Like their terrestrial volcanic and nuclear explosion counterparts, any base surge deposits around ancient terrestrial impact craters have been largely eroded away or misinterpreted as aqueous or eolian deposits. Because of its cold, dry history, Mars is therefore probably the best place in the Solar System to observe preserved impact surge deposits.
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