{"id":35216,"date":"2024-02-03T10:38:38","date_gmt":"2024-02-03T09:38:38","guid":{"rendered":"https:\/\/karmaka.de\/?p=35216"},"modified":"2024-02-03T10:44:18","modified_gmt":"2024-02-03T09:44:18","slug":"unusual-sources-of-fossil-micrometeorites-deduced-from-relict-chromite-in-the-small-size-fraction-in-467%e2%80%89ma-old-limestone","status":"publish","type":"post","link":"https:\/\/karmaka.de\/?p=35216","title":{"rendered":"Unusual sources of fossil micrometeorites deduced from relict chromite in the small size fraction in ~467\u2009Ma old limestone<span class=\"badge-status\" style=\"background:#787878\">OPEN ACCESS<\/span>&nbsp;"},"content":{"rendered":"\n<p>Philipp R. Heck, Birger Schmitz, Xenia Ritter, Surya S. Rout, Noriko T. Kita, C\u00e9line Defouilloy, Katarina Keating, Kevin Eisenstein, Fredrik Terfelt<\/p>\n\n\n\n<p>MAPS, Version of Record online: 02 February 2024<\/p>\n\n\n\n<p><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/10.1111\/maps.14133\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>LINK (OPEN ACCESS)<\/strong><\/a><br><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/epdf\/10.1111\/maps.14133\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>PDF (OPEN ACCESS)<\/strong><\/a><\/p>\n\n\n\n<p class=\"justify-text\">&#8220;Extraterrestrial chrome spinel and chromite extracted from the sedimentary rock record are relicts from coarse micrometeorites and rarely meteorites. They are studied to reconstruct the paleoflux of meteorites to the Earth and the collisional history of the asteroid belt. Minor element concentrations of Ti and V, and oxygen isotopic compositions of these relict minerals were used to classify the meteorite type they stem from, and thus to determine the relative meteorite group abundances through time. While coarse sediment-dispersed extraterrestrial chrome-spinel (SEC) grains from ordinary chondrites dominate through the studied time windows in the Phanerozoic, there are exceptions: We have shown that ~467\u2009Ma ago, 1\u2009Ma before the breakup of the L chondrite parent body (LCPB), more than half of the largest (&gt;63\u2009\u03bcm diameter) grains were achondritic and originated from differentiated asteroids in contrast to ordinary chondrites which dominated the meteorite flux throughout most of the past 500\u2009Ma. Here, we present a new data set of oxygen isotopic compositions and elemental compositions of 136 grains of a smaller size fraction (32\u201363\u2009\u03bcm) in ~467\u2009Ma\u2009old pre-LCPB limestone from the Lynna River section in western Russia, that was previously studied by elemental analysis. Our study constitutes the most comprehensive oxygen isotopic data set of sediment-dispersed extraterrestrial chrome spinel to date. We also introduce a Raman spectroscopy-based method to identify SEC grains and distinguish them from terrestrial chrome spinel with ~97% reliability. We calibrated the Raman method with the established approach using titanium and vanadium concentrations and oxygen isotopic compositions. We find that ordinary chondrites are approximately three times more abundant in the 32\u201363\u2009\u03bcm\u2009fraction than achondrites. While abundances of achondrites compared to ordinary chondrites are lower in the 32\u201363\u2009\u03bcm\u2009size fraction than in the &gt;63\u2009\u03bcm one, achondrites are approximately three times more abundant in the 32\u201362\u2009\u03bcm fraction than they are in the present flux. We find that the sources of SEC grains vary for different grain sizes, mainly as a result of parent body thermal metamorphism. We conclude that the meteorite flux composition ~467\u2009Ma ago ~1\u2009Ma before the breakup of the LCPB was fundamentally different from today and from other time windows studied in the Phanerozoic, but that in contrast to the large size fraction ordinary chondrites dominated the flux in the small size fraction. The high abundance of ordinary chondrites in the studied samples is consistent with the findings based on coarse extraterrestrial chrome-spinel from other time windows.&#8221;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Philipp R. Heck, Birger Schmitz, Xenia Ritter, Surya S. Rout, Noriko T. Kita, C\u00e9line Defouilloy, Katarina Keating, Kevin Eisenstein, Fredrik Terfelt MAPS, Version of Record online: 02 February 2024 LINK (OPEN ACCESS)PDF (OPEN ACCESS) &#8220;Extraterrestrial&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[28,208,23,3157,7,337],"tags":[320,4285,4802,325,490,2457,3548,1807,4191,2036],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/35216"}],"collection":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=35216"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/35216\/revisions"}],"predecessor-version":[{"id":35217,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/35216\/revisions\/35217"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=35216"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=35216"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=35216"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}