Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.501m&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 501-502
Astronomy and Astrophysics
Astrophysics
Carbonates, Chemical Composition, Cretaceous-Tertiary Boundary, Sea Water, Strontium Isotopes, Clays, Geochemistry, Radioactive Age Determination, Radioactive Decay, Weathering
Scientific paper
Studies on the Sr isotopic composition of ocean water through time have shown that anomalously high Sr-87/Sr-86 ratios occur at the time of the KT boundary (KTB) event. Studies on the Os isotopic composition of the KTB section of Sumbar, Turkmenistan, are consistent with enhanced weathering of continental crust. To see if there is any correlation between these two isotopic systems, the Sr isotopic composition (IC) was studied on splits of the same samples analyzed for the Os-IC. The sediments were leached with 5M CH3COOH to dissolve only the carbonate component. Because the radiogenic ingrowth of Sr-87 through the decay of Rb is insignificant, the leachates should represent the isotopic composition of seawater at the time of deposition. The abrupt increase of the Sr-87/Sr-86 ratio at the KTB and the smooth decrease of the ratio with stratigraphic height is in agreement with published data. The sudden increase toward a more radiogenic Sr signature is consistent with a catastrophic event. The last two Maastrichtian samples show slightly elevated Sr-87/Sr-86. But these two values are consistent with literature data of samples below the KTB. These ratios are indistinguishable from the 5.5-6.5 cm interval above the boundary clay. The slight increase of the Sr isotopic ratio before the KTB is in contradiction to a catastrophic event. Elemental mobilization could be the cause, but the increase in the Sr-87/Sr-86 goes parallel with a change of the Ir concentration and the Os IC in the last centimeter of the Maastrichtian. Since mobilization of Ir and Os are most unlikely, the possibility of a slight mechanical mixing of the enriched KTB clay with the underlying deposits has to be discussed.
Meisel Th.
Pettke Thomas
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