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211 Uppsatser om Record - Sida 15 av 15

Extraterrestrisk och terrestrisk kromrik spinell i fanerozoiska kondenserade sediment

This study aims to assess the normal inflow of extraterrestrial chromite to Earth. The results from the investigationare compared to earlier studies of middle Ordovician Orthoceratite Limestone in which 1 - 3 extraterrestrial chromitegrains ( >63 ?Êm ) per kilogram limestone were found. These values have been interpreted as evidence of a twoorders of magnitude increase in the flux of extraterrestrial matter to Earth during a part of middle Ordovician.From an early Paleocene marine sedimentary sequence with known sedimentation rate in Zumaia, northernSpain, 90,5 kilogram of condensed limestone, dated to about 63 Ma, was sampled. The limestone was dissolved inhydrochloric- and hydrofluoric acid and the residue was sieved and searched for opaque minerals under the binocularmicroscope.

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