A delayed response of the trace fossil community at the Cretaceous-Paleogene boundary in the Bottaccione section, Gubbio, Central Italy

A bed-by-bed ichnological analysis at the classic Bottaccione section (Gubbio area, Italy), reveals an unusual response of ichnofauna to the environmental changes associated with the Cretaceous-Paleogene (K-Pg) boundary event. The trace fossil assemblage, consisting of Chondrites isp., Planolites isp., Thalassinoides isp., Trichichnus isp., and Zoophycos isp., is similar to that registered during Cenomanian and Turonian times, showing persistence of the same community for a long time interval in deep-sea carbonate deposits. Absence of significant changes through the K-Pg boundary confirms that the extinction did not touch the ichnofauna. The decline of trace fossils occurs at 6 cm above the K-Pg boundary, with the total absence of biogenic structures in a 3 cm-thick layer showing parallel laminations. A gradual record of Zoophycos and Planolites resumes in the overlying layers. This suggests a progression of inhospitable conditions for the macrobenthos, followed by a delayed response of ichnofauna to drastic diminution of available food starting about 15 k.y. after the K-Pg boundary event, and then a gradual recovery leading to pre-event environmental conditions.