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Science 2 November 1984:
Vol. 226. no. 4674, pp. 539 - 542
DOI: 10.1126/science.226.4674.539
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Articles

Elemental Anomalies at the Cretaceous-Tertiary Boundary, Woodside Creek, New Zealand

ROBERT R. BROOKS 1, ROGER D. REEVES 1, XING-HUA YANG 2, DOUGLAS E. RYAN 3, JIRI HOLZBECHER 3, JOHN D. COLLEN 4, VINCENT E. NEALL 5, and JULIAN LEE 6

1 Department of Chemistry, Biochemistry, and Biophysics, Massey University, Palmerston North, New Zealand
2 Lanzhou Institute of Geology, Lanzhou, China
3 Trace Analysis Research Centre, Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J1
4 Department of Geology, Victoria University, Wellington, New Zealand
5 Department of Soil Science, Massey University
6 Applied Biochemistry Division, Department of Scientific and Industrial Research, Palmerston North, New Zealand

Iridium and 26 other elements were determined in shale from the Cretaceous-Tertiary boundary at the locus classicus (for iridium anomalies) at Woodside Creek, New Zealand. Iridium, gold, copper, cobalt, chromium, nickel, arsenic, molybdenum, and iron were enriched in the basal 2 millimeters of the 8-millimeter shale parting as compared with the rest of the stratigraphic column. No other shale partings in the column had anomalous concentrations of any element when the data were expressed on a carbonate-free basis. The boundary material showed striking compositional similarities with the Stevns Klint Danish boundary shale. Elemental concentrations were in general much higher in the New Zealand material than in nonboundary shales from elsewhere in the world. The high concentration of iridium (153 nanograms per gram) in the basal layer of the boundary, together with the enrichment of other siderophile elements supports the idea of an extraterrestrial source for much of the material. The iridium/gold ratio of 2.1 is also in accordance with such a source. The iridium content of the basal layer is higher than for any other marine boundary shale obtained on land. The integrated iridium value is 187 nanograms per square centimeter of boundary surface.

Submitted on May 3, 1984
Accepted on July 17, 1984


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Shocked Quartz in the Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution.
B. F. Bohor, B. F. BOHOR, P. J. MODRESKI, and E. E. FOORD (1987)
Science 236, 705-709
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