High-resolution multiproxy cyclostratigraphic analysis of environmental and climatic events across the Cretaceous-Paleogene boundary in the classic pelagic succession of Gubbio (Italy)

Abstract

We studied a high-resolution multiproxy data set, including magnetic susceptibility (MS), CaCO 3 content, and stable isotopes (δ 18 O and δ 13 C), from the stratigraphic interval covering the uppermost Maastrichtian and the lower Danian, represented by the pelagic limestones of the Scaglia Rossa Formation continuously exposed in the classic sections of the Bottaccione Gorge and the Contessa Highway near Gubbio, Italy. Variations in all the proxy series are periodic and refl ect astronomically forced climate changes (i.e., Milankovitch cycles). In particular, the MS proxy refl ects variations in the terrigenous dust input in this pelagic, deep-marine environment. We speculate that the dust is mainly eolian in origin and that the availability and transport of dust are infl uenced by variations in the vegetation cover on the Maastrichtian-Paleocene African or Asian zone, which were respectively located at tropical to subtropical latitudes to the south or far to the east of the western Tethyan Umbria-Marche Basin, and were characterized by monsoonal circulation. The dynamics of monsoonal circulation are known to be strongly dependent on precession-driven and obliquity-driven changes in insolation. We propose that a threshold mechanism in the vegetation coverage may explain eccentricity-related periodicities in the terrigenous eolian dust input. Other mechanisms, both oceanic and terrestrial, that depend on the precession amplitude modulated by eccentricity, can be evoked together with the variation of dust infl ux in the western Tethys to explain the detected eccentricity periodicity in the δ 13 C record. Our interpretations of the δ 18 O and MS records suggest a warming event ~400 k.y. prior to the Cretaceous-Paleogene (K-Pg) boundary, and a period of climatic and environmental instability in the earliest Danian. Based on these multiproxy phase relationships, we propose an astronomical tuning for these sections; this leads us to an estimate of the timing and duration of several late Maastrichtian and Danian biostratigraphic and magnetostratigraphic events.

Astronomical component estimation (ACE v.1) by time-variant sinusoidal modeling

“…4j). However, this slight increase in SR was not reported by Sinnesael et al (2016). Interestingly, a similar increase in sedimentation rate has been described in a cyclostratigraphical study of a nearby coeval section in the Bottaccione Gorge, also in Gubbio, Italy (Galeotti et al, 2015).…”

“…tonic biostratigraphy (Luterbacher and Premoli Silva, 1964), magnetostratigraphy (Arthur and Fischer, 1977) and the Cretaceous-Palaeogene boundary (Alvarez et al, 1980). The MS record consists of a total of 1049 samples with a sample spacing of 1 cm for the lower half of the record and a sample spacing of 2 cm for the upper half (Sinnesael et al, 2016). The total length is 14 m and includes a large portion of the Danian including magnetochrons C29r (Paleogene part) to the top of C27n (Lowrie at al., 1982;Coccioni et al, 2012a, b).…”

“…The total length is 14 m and includes a large portion of the Danian including magnetochrons C29r (Paleogene part) to the top of C27n (Lowrie at al., 1982;Coccioni et al, 2012a, b). Sinnesael et al (2016) presented a cyclostratigrahic framework for this section, reporting the orbital imprint in this data set.…”

“…In the original publication, Sinnesael et al (2016) used a band-pass filter to extract the long eccentricity component, assuming a constant average sedimentation rate of 4.3 m Myr −1 . Subsequently, this filtered signal was used to tune the record to the eccentricity solution (Laskar et al, 2011a).…”

“…Thereafter, a first case study using an un-tuned Pliocene-Pleistocene benthic oxygen isotope (δ 18 O) record from Ocean Drilling Program (ODP) Site 846 (Mix et al, 1995;Shackleton et al, 1995) is tested. A second case study deals with a Danian magnetic susceptibility record from the pelagic carbonate Contessa Highway section in Gubbio, Italy (Sinnesael et al, 2016).…”