Geochemical anomalies near the Eocene/Oligocene and Permian/Triassic boundaries
As a test of the asteroid-impact theory, which predicts that extinctions of taxa and geochemical anomalies similar to those found near the Cretaceous/Tertiary boundary should occur with a frequency of about 100 million years (m.y.), geochemical studies have been made near the Permian/Triassic and Eocene/Oligocene boundaries. An extensive clay layer, which had previously been assigned to the P/T boundary, was found to be chemically and mineralogically very different from the clays above and below, and it probably originated as an ash. As no iridium (Ir) anomaly (<0.055 ppb) was detected in the layer, it probably had a volcanic rather than an impact origin. The latter possibility, however, cannot be ruled out, as high-speed comets could have the necessary explosive force and still have very little Ir. An Ir anomaly (0.4 ppb) was found near the Eocene/Oligocene boundary in a deep-sea core from the Caribbean Sea (DSDP Site 149, Core 31, Section 1, Intervals 1-2 and 3-4 cm) at exactly the same position that microtektites and extinctions of five species of radiolaria had been previously detected. Thus, the Ir anomaly, the microtektite data, and the radiolarian extinctions are all supportive of a major bolide impact 34 m.y. ago. A worldwide distribution of the Ir anomaly is strongly suggested by very recent studies made in collaboration with Billy P. Glass in which Ir anomalies associated with microtektites in late Eocene sediments have been found in the Gulf of Mexico (DSDP Site 94), the Central Pacific Ocean, (DSDP Hole 69A and DSDP Site 166), and the Indian Ocean (DSDP Site 216).
- Research Organization:
- Lawrence Berkeley Lab., CA
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6239284
- Journal Information:
- Geol. Soc. Am., Spec. Pap.; (United States), Journal Name: Geol. Soc. Am., Spec. Pap.; (United States) Vol. 190:190; ISSN GSAPA
- Country of Publication:
- United States
- Language:
- English
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Iridium anomaly approximately synchronous with terminal eocene extinctions
Current status of the impact theory for the terminal Cretaceous extinction