Cretaceous to Paleogene stratigraphic section of Bottaccione Gorge, Gubbio

The Bottaccione Gorge at Gubbio was the first major outcrop of pelagic limestone ever studied. Here the identification of planktonic foraminifera in thin section was first applied to hard rocks from which isolated foraminifera could not be extracted (Renz, 1936; Luterbacher and Premoli Silva, 1962). Anomalous levels of iridium were first reported from the K-Pg boundary at this and nearby localities (Alvarez et al., 1980). Iridium is present in meteorites but essentially absent in Earth’s sediments, which led to the theory that a large comet or asteroid impacted the Earth, triggering the K-Pg mass extinction. This theory was later confirmed by the discovery of the 150-km diameter Chicxulub structure in the subsurface of the Yucatán Peninsula of Mexico, the largest impact crater known from the last billion years of Earth history. Magnetic polarity reversal stratigraphy of limestones was first done in the Bottaccione Gorge, with the foraminiferal biostratigraphy making possible the dating of the magnetic polarity stripes on the ocean floor, and in turn the dating of the opening of the Atlantic Ocean by sea-floor spreading (Lowrie and Alvarez, 1981). Lately, a high-resolution cyclostratigraphic framework has been established at the section. For a review see e.g., Galeotti et al. (2015).