The GSSP for the base of the Campanian Stage is defined by the magnetic polarity reversal from Chron 34n (top of the Long Cretaceous Normal Polarity-Chron) to Chron C33r at the 221.53 m level in the Bottaccione Gorge section at Gubbio, Umbria-Marche Basin, Italy.
The GSSP section (geographic coordinates: 43°21'45.6"N, 12°34'58.2"E) is located 1.4 km NNE from the town of Gubbio (central Italy). It is continuously well exposed with a strike of 140° and a dip of 50° NE along the Regional Road 298 "Eugubina" that crosses the Bottaccione Gorge.
The GSSP section extends from 210.79 m to 233.63 m (following the study of Coccioni and Premoli Silva, 2015), it is 22.84 m thick, and consists of well-bedded, pink to red and white bioturbated limestones with bedding thickness ranging from 6 to 80 cm. Pink to reddish and grey to greenish-grey chert nodules and limestone beds with thickness ranging from 3 to 6 cm occur throughout. As a result, the limestone beds are frequently silicified. In particular, the occurrence of white limestone beds together with grey to greenish-grey chert nodules characterizes the interval that spans 228.94 m - 232.75 m. The upper Santonian-lower Campanian is positioned within the upper part of the stratigraphic member R1 (lower Turonian-lower Campanian) of the Scaglia Rossa Fm. (Alvarez and Montanari, 1988). The interval is devoid of turbidites and substantial internal structural deformation. Only a negligible fault with a displacement of a few dm occurs at 221.20 m (Maron and Muttoni 2021). The displaced strata can be easily reconnected and therefore the stratigraphy is regarded as continuous. Stylolites are common in the thicker beds.
The magnetic polarity reversal from Chron 34n (top of the Long Cretaceous Normal Polarity-Chron) to Chron C33r at 221.53 m.
Listed below from the stratigraphic bottom to the top (Abbreviations: FO= First Occurrence; LO= last occurrence; FCO= First Common Occurrence; CIE= Carbon Isotope Excursion)
Different age estimates are available for the Santonian/Campanian Boundary derived from bentonite layers (Western Interior, Montana: 84.19 ± 0.38 Ma, Sageman et al. 2014; Songliao Basin, China: 82.90 ± 0.18 Ma, He et al. 2012, Wang et al. 2016). Wu et al. (2022) suggested an age of 82.776 ± 0.22 Ma for the reversal and the base of the Campanian. Gale et al. (2020) placed the boundary at 83.65 Ma, based on a combination of data from radiometric dates, the oceanic magnetostratigraphic record and orbital tuning. All that can be said with certainty at present is that, according to the present array of proposed radiometric dates and their uncertainties, the boundary must lie between 82.7 and 84.5 Ma.
Chron C33r marks the base of the C-sequence of magnetozones, a fundamental boundary, which has been recognised globally in the magnetic anomaly record of oceanic crust. The high-resolution magnetostratigraphy recorded at Gubbio provides an unambiguous record, which can be calibrated to the calcareous micro- and nannoplankton and carbon isotope record. The C34n-C33r boundary has been identified in the auxiliary sections at Postalm in Austria (Wolfgring et al. 2018), Bocieniec in Poland (Dubicka et al. 2017), in the Smoky Hill Chalk in northern Kansas (Kita et al. 2017) and in the Aksu-Dere section in the Crimea (Guzhikov 2021).
Seaford Head, Sussex, England, UK (F50°45'47.25"N, 0°0.6'41.11"E): The sea cliff section in the English Channel at Seaford Head, provides a continuously exposed succession in white chalk facies across the Santonian-Campanian boundary with an excellent carbon-isotope curve (Thibault et al., 2016), which permits correlation of the crinoid zones to the GSSP Bottaccione section. The base of the Campanian falls between the higher peak of the Late Santonian Event and the FO of common Aspidolithus parcus parcus, a level immediately underlying the Blackrock Marl at 80.2 m.
Bocieniec, Warsaw, Poland (50°16'21.21"N, 19°56'1.09"W): The section is located in an old quarry in the village of Laski Dworski, 25 km north of Krakow and exposes 5.5 m of Upper Cretaceous sediments, unconformably overlying Jurassic limestones (Dubicka et al. 2017). The succession is thin, but has provided important data on magnetostratigraphy, biostratigraphy (nannofossils, planktonic and benthic foraminifera, crinoids and palynomorphs), and a detailed carbon isotope curve. The base of the Campanian is taken at ca. 4.45 m where Dubicka et al. (2017) positioned the base of Chron 33r, within the upper part of the Stensioeina pommerana Zone, slightly below the FO of true Bolivinoides culverensis.Bocieniec, Warsaw, Poland (50°16'21.21"N, 19°56'1.09"W): The section is located in an old quarry in the village of Laski Dworski, 25 km north of Krakow and exposes 5.5 m of Upper Cretaceous sediments, unconformably overlying Jurassic limestones (Dubicka et al. 2017). The succession is thin, but has provided important data on magnetostratigraphy, biostratigraphy (nannofossils, planktonic and benthic foraminifera, crinoids and palynomorphs), and a detailed carbon isotope curve. The base of the Campanian is taken at ca. 4.45 m where Dubicka et al. (2017) positioned the base of Chron 33r, within the upper part of the Stensioeina pommerana Zone, slightly below the FO of true Bolivinoides culverensis.
Postalm, Austria (47°36'37.8"N, 13°23'07.5"E): The Santonian-Campanian boundary interval of the Postalm section within the Gosau Group of the Northern Calcareous Alps of Austria is 20 m thick and was proposed as a Campanian reference section for the NW Tethys (Wolfgring et al. 2018, 2020). Palaeomagnetic data allow recognition of the top of the Long Cretaceous Normal Polarity-Chron 34n and the following reversal Chron C33r. Biostratigraphic events (nannofossils, planktonic and benthic foraminifera) have been correlated to the magnetostratigraphic primary marker. The base of the Campanian corresponds to a Sr isotope value of 0.707534 (± 0.000005, mean of four analyses around the boundary interval).
Smoky Hill, Kansas, USA: The stratigraphy, sedimentology and palaeoecology of the Smoky Hill Chalk Member of the Niobrara Formation of Kansas was described by Hattin (1982). Locality 24 of Hattin (1982, p. 25) has been selected as an auxiliary reference section. Kita et al. (2017) studied a composite section of the Smoky Hill Member of the Niobrara Formation across Logan, Gove and Trego counties in north Kansas, including locality 24, where the base of Chron 33r was recorded at 174 m. Kita et al. (2017) provided a detailed nannofossil distribution within the section, showing that Aspidolithus parcus parcus first occurs at 166.3 m and A. parcus constrictus at 193.15 m.
Tepeyac, Coahuila, Mexico (28°54'45"N, 100°44'29"W): The section is located ca. 5 km south of the small village Tepeyac, about 40 km north of Piedras Negras and 15 km SSW of Jiménez, Coahuila. The section exposes 28.9 m of rhythmically bedded grey to light yellow-coloured layers of limestone, and intercalated units of marl (Ifrim and Stinnesbeck, 2021; Ifrim et al., 2021). The ammonite assemblage documented from Tepeyac consists of about 220 specimens and permits identification of a succession of zones originally identified in the Gulf Coast states of the USA and from the Atlantic seaboard. The inoceramids provide the most abundant and detailed record of this group known across the Santonian-Campanian boundary. The 13C record is suitable for long-distance correlation. The carbon-isotope succession demonstrates that the correlated GSSP marker falls between the Late Santonian Event and the Pilula Event and corresponds approximately with the base of the Menabites (Delawarella) delawarensis Zone.
Andy Gale, Sietske Batenburg, Rodolfo Coccioni, Zofia Dubicka, Elisabetta Erba, Francesca Falzoni, Jim Haggart, Takishi Hasegawa, Christina Ifrim, Ian Jarvis, Hugh Jenkyns, Agata Jurowska, Jim Kennedy, Matteo Maron, Giovanni Muttoni, Martin Pearce, Maria Rose Petrizzo, Isabella Premoli-Silva, Nicolas Thibault, Silke Voigt, Michael Wagreich, and Irek Walaszczyk (2023). The Global Boundary Stratotype Section and Point (GSSP) of the Campanian Stage at Bottaccione (Gubbio, Italy) and its Auxiliary Sections: Seaford Head (UK), Bocieniec (Poland), Postalm (Austria), Smoky Hill, Kansas (U.S.A), Tepayac (Mexico). Episodes 2023; published on line 1 February 2023. DOI: 10.18814/epiiugs/2022/022048