62nd Annual Meteoritical Society Meeting 5088.pdf THE WORLD’S OLDEST MICROMETEORITES IN THE MESOPROTEROZOIC SATAKUNTA FORMATION, FINLAND - SEDIMENTOLOGY OF THE HOST ROCKS. D. Kettrup1, P. Pihlaja2, A. Deutsch1 and L. Pesonen2, 1Institut fuer Planetologie, University of Muenster, Wilhelm-Klemm-Strasse 10, D- 48149 Muenster, Germany (
[email protected]), 2Geological Survey of Finland, FIN-02150 Espoo, Fin- land. Problem and research concept: The approxi- sandy mudstone/siltstone. Main components are mately 1.4 Ga (Mesoproterozoic) old Satakunta For- quartz and K-feldspar (microcline), rock fragments, mation in SW Finland contains the world’s oldest muscovite, biotite and chlorite. Overall, the minera- micrometeorites [1,2]. So far, more than 50 fossil logical and chemical features of the Satakunta Forma- cosmic spherules have been recovered from the Sata- tion correspond to normal arkose suites of different kunta red beds. Mineralogical, textural and chemical geological ages [5]. features, amongst them Cr/Fe, Co/Fe, Ni/Fe, and Ir/Fe Lithification of the sandstones results mainly from ratios, indicate the presence of various spherule types two different effects. Most frequent are cements of and sub-types [2,3]. The spherules are unaltered and authigenetic quartz, micas and K-feldspar. Bounding match in their properties cosmic material from, e.g., of sand grains by clay minerals are the second type. the Greenland ice shield [3]. It is fundamental to un- The spherule-containing samples do not display derstand why the Satakunta micrometeorites are in specific sedimentological characteristics and appar- such an excellent state of preservation. Processes ently lack common features. which play a key role in this context are (i) sedimen- Discussion: The Satakunta Formation was depos- tation, and (ii) lithification.