Conference Agenda

We have conducted a comprehensive study of calcareous nannofossils in numerous Cretaceous successions located at low and middle latitudes, including both land and oceanic sections. Through a rigorous review of existing literature and the incorporation of new findings, we have significantly revised previous zonal schemes. The proposed biozonation include the intercalibration of nannofossil events with planktonic foraminiferal biozones, magnetostratigraphy and chemostratigraphy. This enhancement includes a critical assessment of the reproducibility and reliability of individual nannofossil events, as well as a reevaluation of their ages in light of recent advancements in defining Cretaceous stage boundaries. Moreover, the new nannofossil biozonation is specifically applied to the characterization of oceanic anoxic events.

The Valanginian stage of the Early Cretaceous (~137.05–131.29 Ma) witnesses important geological, climatic, and biological events and is a key interval for global stratigraphic correlation. As precise radio-isotopic ages were scarce until recently, the chronology of events remained poorly understood, and comparing the Andean and Tethyan domains has been challenging due to differing depositional environments and tectonic settings.

Data on ammonoid biostratigraphy, calcareous nannofossil bioevents, astrochronology, and chemostratigraphy have significantly improved their temporal alignment. A pivotal event aiding correlation is the Valanginian carbon isotope excursion (Weissert CIE), a globally recognized positive δ¹³C shift, interpreted as linked to increased volcanic activity and carbon cycle perturbation. This excursion is recorded in both Andean and Tethyan sedimentary sequences, serving as a reliable chemostratigraphic marker.

The Vergol-Morénas (Vocontian Basin, France) and the Cerro La Parva (Neuquén Basin, Argentina) sections were studied recently. They are geographically remote, were deposited in different environments, and encompass the lower-upper Valanginian boundary. In both cases, the δ¹³ Corg correlates with the 405-ka eccentricity cycle, and both sections can be correlated based on these cycles with a precision in time of ca. 100 ka. This study adds the Cañada de Leiva section (Neuquén Basin), which spans the entire Valanginian with a precise ammonoid and nannofossil biostratigraphy.

By integrating fossil evidence provided by ammonites and calcareous nannofossils with astrochronological and chemostratigraphic data, it has been possible to strengthen the correlation between the Andes and Tethys during the Valanginian, clarifying global paleoenvironmental changes and refining the Early Cretaceous timescale.

The Lower Cretaceous (Barremian - Albian) interval is marked by complex stratigraphic correlations between the Boreal Realm and the Tethys, often hindered by biostratigraphic inconsistencies and regional variation. We present stable and radiogenic isotope data (δ¹³Ccarb, δ¹⁸O, ⁸⁷Sr/⁸⁶Sr) for the Lower Cretaceous (Barremian - Albian) based on new findings from northern Germany, contributing to a refined chemostratigraphic framework.

1) Geochemical analyses of eight well-preserved macrofossils (corals, oysters, gastropods, ammonites, belemnites), from a single level dated to the earliest Albian reveal notable variability. The δ¹³Ccarb values vary by up to 5‰, indicating organism-specific food sources and subsequent biofractionation. Due to diagenetic effects the ⁸⁷Sr/⁸⁶Sr signals also differ significantly among taxa by 0.000225, with belemnites providing the most reliable data. They are in closest agreement with existing Early Cretaceous Sr-isotope reference curves, and are thus considered the most stratigraphically reliable ones.

2) The belemnite-based Sr-isotope data enable correlation between the Boreal Realm and the Tethys independent of biostratigraphy. This chemostratigraphic approach addresses long-standing discrepancies within the Lower Cretaceous biostratigraphic framework. Several offsets in the current biostratigraphic scheme, are re-evalutated. The mid-Barremian warming event is mirrored by the highest Sr-isotope values recorded int the entire Early Cretaceous, which we link to intensified continental weathering and increased run-off. These environmental conditions likely contributed to the deposition of black shales in restricted Boreal basins.

Our data offer an independent temporal framework to support regional and interregional stratigraphic alignment, providing new insights on Early Cretaceous paleoceanography and climate dynamics.

The Aptian Working Group (AWG) of the International Commission on Stratigraphy (ICS), led by Elisabetta Erba and Helmut Weissert, has been working on the definition of the base of the Aptian stage over the last three decades. After considering the base of magnetic chron M0r, following research on ammonite biostratigraphy triggered further discussion and the need for another primary marker. Consequently, in 2024 the AWG decided to shift the base of the Aptian upwards into C34n and for the first time in Mesozoic stratigraphy, a chemostratigraphic event was selected as primary marker. A prominent “negative spike” in the C_org- and C_carb- isotope records was first identified by Menegatti et al. (1998) in Northern Italy (Cismon section) and later recognized in various land and marine sites across different paleolatitudes and settings (Erba et al., 2015; Leandro et al., 2022).

This distinctive C isotope negative spike was, therefore, selected by the AWG as the new marker for defining the base of the Aptian. Two potential sites were chosen for the final vote as candidate Global Boundary Stratotype Section (GSSP): Cismon (Italy) and Cau (Spain). The majority of AWG members favored the expanded hemipelagic shelf section at Cau for the Aptian GSSP.

This communication presents a review of available data for the Barremian/Aptian boundary interval at the proposed Cau locality in Spain, characterized both in an outcrop section and in a continuous core (Castro et al., 2021).

This study presents a high-resolution magnetostratigraphic framework for the Gorgo a Cerbara section near Piobbico (Umbria-Marche Basin, Central Italy), spanning the uppermost Hauterivian to lower Aptian. The new dataset includes directional paleomagnetic measurements from 41 oriented hand samples, with alternating field (AF) demagnetization used to isolate the characteristic remanent magnetization (ChRM). Based on inclination and polarity patterns, eight magnetozones were identified: four of normal polarity (N1 to N4) and three of reverse polarity (R1 to R3). Magnetozone N1, located near the top of the section and directly overlying the Selli Level (OAE1a), was correlated with Chron C34n, in agreement with literature associating this event with the onset of the Cretaceous Normal Superchron. Deeper intervals were correlated to M-sequence chrons: M0r (R1), M1n (N2), M1r (R2), M3n (N3), M3r (R3), and M5n (N4), establishing a coherent age model from Chron M5n (~127.0 Ma) to C34n (~120.9 Ma). We recognize and reconstruct a fault that challenges the continuity of the age model downward. These results refine the chronostratigraphic framework for a section proposed as candidate for the Global Stratotype Section and Point (GSSP) of the Aptian base. The comparison with biostratigraphic and palynostratigraphic data supports the accuracy of this interpretation, particularly regarding the position of the M1n/M1r boundary. New environmental magnetism, bulk mineralogy, and elemental geochemistry have also been produced. This integrated age model enhances our understanding of Early Cretaceous geochronology and provides an essential reference for correlating paleoenvironmental events, including the onset of the Selli Event.

The Albian was a major turning point for palaeoenvironmental change in the Cretaceous, with the opening of the Equatorial Atlantic Gateway leading to a reorganisation of surface and deep circulation, frequent occurrence of Oceanic Anoxic Events and significant increases in surface and deep water temperatures. Therefore, a radioisotopic-based age model for the Albian period is important, but has yet to be realized, because silicic tuffs are rarely interbedded in the representative Albian strata in Europe. The Yezo Group, Hokkaido, Japan, comprises forearc basin sequences accumulated on the active continental margin of the Eurasian continent in the northwestern Pacific Ocean. The strata yield abundant age-diagnostic macro and microfossils, and intercalate numerous silicic tuffs. We have compiled microfossil-, macrofossil- and carbon isotope stratigraphy for the Albian section of the Yezo Group, and obtained U-Pb zircon ages of tuffs from several stratigraphic levels. On the basis of integrated stratigraphic correlation with the sequence of the Vocontian Basin, we identified the levels of the Leenhardt of OAE1b, OAE1c, OAE1d and A/CB in the Yezo Group. U-Pb zircon ages of silicic tuffs intercalated in these levels, are 110.00 ± 0.60 (Leenhardt), 103.71 ± 0.82 Ma (OAE1c), 101.67 ± 0.81 Ma (OAE1d) and 100.74 ± 0.10 Ma (A/CB). The former three ages were obtained by LA-ICP-MS, the latter by ID-TIMS, so there is room for improvement. Further dating of the Yezo Group silicic tuffs is expected to make a significant contribution to improving the accuracy and precision of the global Albian age model.