Bottaccione Gorge, Gubbio

Assembled from 16 blocks · 1 evidence · 6 related

1. Story
2. A gorge cut through pelagic limestones just outside the town of Gubbio in Umbria, where a continuous section of deep-water Scaglia limestone spans the Cretaceous–Palaeogene boundary. Walter Alvarez was working on the palaeomagnetic stratigraphy of this section in the 1970s when he became interested in the two-centimetre clay layer at the boundary and in how much time it represented. The attempt to answer that question — using iridium delivered by cosmic dust as a clock for the deposition rate — produced instead an iridium concentration far too high to be explained by dust, and turned a stratigraphic side question into the impact hypothesis. The site is therefore an unusually clean example of a discovery arriving as the failure of a measurement rather than as the confirmation of a prediction. The boundary clay at Gubbio is still visible in outcrop and the section remains a reference locality.
3. Knowledge
4. The Cretaceous–Palaeogene iridium anomaly
5. Bottaccione Gorge, Gubbio
6. Connections
7. The Cretaceous–Palaeogene iridium anomaly
8. The Cretaceous–Palaeogene mass extinction
9. The Alvarez impact hypothesis is published
10. The Cretaceous–Palaeogene mass extinction
11. Bottaccione Gorge, Gubbio
12. The Cretaceous–Palaeogene mass extinction
13. The Alvarez impact hypothesis is published
14. Chicxulub is identified as the K–Pg impact crater
15. Evidence
16. Supports the iridium anomaly at Gubbio and Stevns Klint, the siderophile-depletion reasoning and the inference of an impactor about ten kilometres across. V55 verification basis: this session had no network access to any source — WebFetch was egress-blocked and the WebSearch budget was exhausted — so the cited work was not retrieved and its pagination was not re-checked. Volume and page range are quoted from standing knowledge and were not re-checked.