Physics
Scientific paper
Nov 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989georl..16.1301g&link_type=abstract
Geophysical Research Letters (ISSN 0094-8276), vol. 16, Nov. 1989, p. 1301-1304. Research supported by the Mellon Foundation, NS
Physics
3
Cretaceous-Tertiary Boundary, Iridium, Lead Isotopes, Meteoritic Composition, Tracers, Sediments, Stony Meteorites
Scientific paper
The global excess of Ir in sediments at the K-T boundary has been attributed to either a meteorite impact or enhanced volcanism. The isotopic composition of Pb associated with this Ir provides a test of these hypotheses because meteoritic Pb is isotopically quite distinct from Pb of volcanic or continental origin. Pb abundances and isotopic compositions of pelagic oozes from DSDP Site 577A (Shatsky Rise, NW Pacific) measured in this study show little change over the deposition interval of Ir-rich sediment (about 10 cm). However, a Pb-enriched layer with a more radiogenic isotopic composition is found in the basal 0.5 cm of the Tertiary. These observations appear to preclude the Ir excess in these sediments originating as impact fallout from a stony meteorite, although an iron meteorite impactor cannot be excluded. Any Pb flux accompanying Ir in volcanogenic aerosols from the Deccan Traps should be considerable. However, the boundary Pb 'spike' does not isotopically resemble known Deccan Trap lavas. Overall, any wind pattern changes following the K-T 'event' were apparently short-lived, as neither airborne sources of Pb nor their magnitude to the then central Pacific were affected while the Ir-enriched sediments were being laid down.
Erickson David J. III
Galer Stephen J. G.
Macdougall Douglas J.
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