Iridium and Osmium as Tracers of Extraterrestrial Matter in Marine Sediments
Platinum group elements, specifically iridium and osmium, are the most sensitive non-volatile elemental tracers of extraterrestrial (meteoritic) matter in marine sediments. The budget of these elements in sediments can be considered a mixture of extraterrestrial, eolian (i.e., wind-blown dust), and hydrogenous (i.e., seawater-derived) sources. Differences in the osmium isotopic composition between these three sources allow quantification of the amount of extraterrestrial osmium in sediments. Osmium isotope data for about 30 pelagic sediments from the Atlantic and Pacific oceans, spanning the past 80 Myr, yield an average annual flux of extraterrestrial matter of 30,000 ± 15,000 metric tons. The only clear exception is the large impact at the Cretaceous-Tertiary boundary. Temporal resolution of these flux estimates is limited to at least several thousand years by the need to obtain statistically representative samples. The scatter in the flux estimates is large and secular variations in the flux of less than a factor of about three cannot be excluded. However, samples from individual cores indicate that the flux of extraterrestrial matter has varied by less than a factor of two, if the flux is averaged over the scale of temporal resolution in marine sediment samples.
KeywordsMarine Sediment Platinum Group Element Flux Estimate Mass Accumulation Rate Matter Flux
Unable to display preview. Download preview PDF.
- Goldschmidt, V M. Geochemistry. (Muir, A., Ed.), Clarendon Press, Oxford, 730 pp. (1954).Google Scholar
- Hirt, B., Tilton, G. R., Herr, W., and Hofmeister, W. The half life of l87Re. In Earth science meteoritics. (Geiss, J. and Goldberg, E., Eds.), North Holland Publ., 273–280 (1963).Google Scholar
- Hughes, D. W. Meteors. In Cosmic dust (McDonnell, J. A. M., Ed.), Wiley, Chichester, 123–185 (1978).Google Scholar
- Marcantonio, F., Turekian, K. K., Higgins, S., Anderson, R. F., Stute, M., and Schlosser, P. The accretion rate of extraterrestrial 3He based on oceanic 230Th flux and the relation to Os isotope variation over the past 200,000 years in an Indian Ocean core. Earth Planet. Sci. Lett. 170, 157–168 (1999).ADSCrossRefGoogle Scholar
- Peucker-Ehrenbrink, B. and Jahn, B. M. Platinum-group-element concentrations and osmium-isotopic ratios in loess: A proxy for the eroding upper continental crust? In Ninth annual V. M. Goldschmidt conference, LPI Contrib. No. 971, LPI, Houston, 224–225 (1999).Google Scholar
- Turekian, K. K. Potential of l87Os/l86Os as a cosmic versus terrestrial indicator in high iridium layers of sedimentary strata. Geol. Soc. Am., Spec. Pap. 190, 243–249 (1982).Google Scholar
- Turekian, K. K. and Pegram, W. J. Os isotope record in a Cenozoic deep-sea core: Its relation to global tectonics and climate. In Tectonic uplift and climate change (Ruddiman, W. F., Ed.), Plenum, New York, 384–397(1997).Google Scholar
- Wetherill G. W. and Shoemaker, E. M. Collision of astronomically observable bodies with the Earth. Geol. Soc. Am., Spec. Pap. 190, 1–24 (1982).Google Scholar
- Zhou, L. Characterization of chemical signatures in sediments: Application to selected problems. Ph.D. thesis, Univ. California, Los Angeles, 200 pp. (1990).Google Scholar