¹Dominik Loroch, ^1,2Alexander Deutsch, ¹Jasper Berndt,³André Bornemann
Meteoritics & Planetary Science (in Press)    Link to Article [DOI: 10.1111/maps.12667]
¹Institut für Mineralogie, Westfälische Wilhelms-Universität Münster (WWU), Muenster, Germany
²Institut für Planetologie, WWU Münster, Muenster, Germany
³Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Hannover, Germany
Published by arrangement with John Wiley & Sons

We present results of an in-situ geochemical study using laser-ablation inductively coupled plasma–mass spectrometry (LA-ICP-MS) analyses along a ~4.3 cm long section across the K-Pg event bed, drilled during IODP Expedition 342 at J Anomaly Ridge south of St. John’s, Newfoundland. This section comprises the Maastrichtian with a sharp boundary to the graded, between 1.5 and 1.8 cm thick ejecta layer with totally altered impact glass spherules, which in turn is topped by Danian sediments. The porous and clayey material required elaborate preparation in order to yield reliable data. The ejecta bed shows a highly variable depletion in rare earth elements that even results in strongly subchondritic concentrations. The Ce/Ce* varies strongly (0.81–34), Ni/Cr ranges from 0.38 to 2.79. The maximum platinum group elements (PGE) concentrations are located in one LA-spot exactly at the basis of the ejecta layer; they amount (in μg g−1) to 0.35 (Rh), 1.64 (Pd), 2.79 (Pt), and 0.86 (Au). The Nb/Ta ratio increases in the Ma from ~10 to 35.9 toward the ejecta horizon, which itself has higher Nb, Ta, Zr, and Hf concentrations than the background sedimentation, combined with low Nb/Ta (~5–10), and low Zr/Hf (~20–30). The overall result is that alteration processes changed totally the original geochemical characteristics of this K-Pg spherule bed. To explain the exorbitant element mobility at distances of hundreds of μm, we discuss a combination of mostly reducing redox processes and interaction with organic compounds. This study demonstrates the high potential of in-situ analyses with high spatial resolution at complex geological materials. Moreover, our results indicate that some caution is necessary in determining the projectile type in impactites via PGE ratios.

¹Joseph A. Nuth,²Natasha M. Johnson,^2,3Frank T. Ferguson,²Alicia Carayon
Meteoritics & Planetary Science (in Press)   Link to Article [DOI: 10.1111/maps.12666]
¹Solar System Exploration Division, Code 690, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
²Astrochemistry Laboratory, Code 691, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
³Chemistry Department, The Catholic University of America, Washington, D.C. 20064, USA
⁴International Space University, Strasbourg Central Campus, France
Published by arrangement with John Wiley & Sons

We report the ratio of the initial carbon available as CO that forms gas-phase compounds compared to the fraction that deposits as a carbonaceous solid (the gas/solid branching ratio) as a function of time and temperature for iron, magnetite, and amorphous iron silicate smoke catalysts during surface-mediated reactions in an excess of hydrogen and in the presence of N2. This fraction varies from more than 99% for an amorphous iron silicate smoke at 673 K to less than 40% for a magnetite catalyst at 873 K. The CO not converted into solids primarily forms methane, ethane, water, and CO2, as well as a very wide range of organic molecules at very low concentration. Carbon deposits do not form continuous coatings on the catalytic surfaces, but instead form extremely high surface area per unit volume “filamentous” structures. While these structures will likely form more slowly but over much longer times in protostellar nebulae than in our experiments due to the much lower partial pressure of CO, such fluffy coatings on the surfaces of chondrules or calcium aluminum inclusions could promote grain–grain sticking during low-velocity collisions.