MAGNETIC/ISOTOPIC CHARACTERISTIC OF THE SPHERULE-RICH IMPACT EJECTA BLANKET FROM THE CHICXULUB CRATER: ANALOG FOR ROBOTIC EXPLORATION OF SIMILAR DEPOSITS ON MARS

Impact cratering events produce specific transient energy events, capable of leaving large spectrum of impact related physical characteristics of impacted material. In this study we report on magnetic characteristic. A major focus in the search for fossil life on Mars is on recognition of the proper material on the surface. Heavily cratered surface implies fluidized ejecta deposits. Robots can measure magnetism of rocks remotely. We collected samples of ejecta blanket deposits in southern Mexico and throughout Belize as a Martian analog. The ejecta layer that blankets the preexisting Cretaceous dolomite units consists of green glassy fragments, pink and white spheroids, and darker fragments of limestone. The spheroid bed is overlain by a coarse unit of pebbles, cobbles, and boulders, which in more distal locations is composed of a pebble conglomerate. Clasts in the conglomerate (Pooks Pebbles) have striated features consistent with hypervelocity collisions during impact.

We examined the magnetic/isotopic properties of individual fragments within the spheroid bed. Green glassy fragments are paramagnetic (0.2 - 0.3 Am2/kg at 2 T field) with no ferromagnetic component detected. Pink spheroids are less paramagnetic (0.001-0.04 Am2/kg at 2 T field) and with soft ferromagnetic component (saturation magnetization (Ms) = 0.02-0.03 Am2/kg). White spheroids have equal amount of paramagnetic and diamagnetic components (from-0.08 to 0.03 Am2/kg at 2 T field) and no apparent ferromagnetism. Darker fragments are diamagnetic (-0.05 to -0.02 Am2/kg at 2 T field) with absence of ferromagnetism. Intense paramagnetic properties of the glass allow distinction of glass containing samples. Pink spheroids appear to contain the most of ferromagnetic particles. Diamagnetic dark grains are most likely fragments of limestone.

Conglomerate unit is dolomite and consequently diamagnetic. The diamagnetism was established with portable magnetic susceptibility measurements. Pebbles have small natural magnetization. Thermal remanent magnetization (TRM) acquisition in laboratory field (0.04 mT) indicates TRM potential. Absence of large natural magnetization indicates that pebbles were not heated above the Currie point of hematite and/or magnetite (680 C and 570 C respectively) consistent with isotope measurement.