ALBERT

Description: The data of two sections studied in the Barremian (Early Cretaceous) of the Subbetic Domain (SE Spain) are shown here together with a detailed log showing the bed number and the biostratigraphic scheme. The samples were collected with a geologist hammer in May 2016. The average sample distance is 0.07 m and was kept as constant as possible using a Jacob's staff to ensure the detection of all the Milankovitch cycles applying Fast Fourier Transforms and related methods (e.g. multi-taper). The lithology is composed of marl-limestone alternations deposited in a (hemi-)pelagic setting. Observed fauna is composed of ammonites, radiolarians, foraminifera, calcareous nannofossils and scarce belemnites, bivalves, gastropods, brachiopods and irregular echinoids. The biostratigraphy scheme is provided in the detailed logs and is based on Tethyan ammonite and calcareous nannofossils. The interval studied of Barranco de Cavila section (38°3'10'' N; 1°53'20'' W) covers from the Late Barremian (Vandenheckii Zone) to the Early Aptian (Forbesi Zone). Carbon and oxygen isotope ratios were measured with a Wahlen VG Prism II mass spectrometer. The mass spectrometer was calibrated with three NBS standards, Nos. 18, 19 and 20

Description: These contain bulk-rock carbon and oxygen isotope ratios, CaCO3 content, magnetic susceptibility values and clay mineral assemblages from the Valanginian part of the Vergol-Morénas composite section, SE France. Two sequences have been analysed in this study. The lower sequence (Sequence 1 or S1) was analysed at the transition between the Pertransiens and the Campylotoxus zones. The sequence is located in the Vergol section. The upper sequence (Sequence 2 or S2) is located within the Verrucosum Zone and is located in the Morénas section. The data were measured from January 2018 to November 2019 at the Université de Rennes 1 and the Université de Bourgogne Franche-Comté.

Description: An integrated radio-astrochronological framework of the Agrio Formation in the Andean Neuquén Basin of west-central Argentina provides new constraints on the age and the duration of the late Valanginian through Hauterivian stratigraphic interval. A CA-ID TIMS U-Pb age of 126.97 ± 0.04(0.07)[0.15] Ma is presented here from the upper Hauterivian Agua de la Mula Member of the Agrio Formation. Biostratigraphic data from ammonoids and calcareous nannofossils and this high precision new radioisotopic age, together with three former ones from the same Agrio Formation are combined with new astrochronological data in the Andes. These are correlated with modern cyclostratigraphic studies in the classical sections of the Mediterranean Province of the Tethys, supporting detailed interhemispheric correlations for the Early Cretaceous. We also provide new δ13C data from the Agrio Formation which are compared with records from the classic Tethyan sections. According to our calibration, the minimum in the values in the mid-Hauterivian appears to be synchronous and, thus, another important stratigraphic marker for global correlation. A new duration of 5.21 ± 0.08 myr is calculated for the Hauterivian Stage, starting at 131.29 ± 0.19 Ma and ending at 126.08 ± 0.19 Ma. The difference between the duration of the Hauterivian in GTS2016 and in this study is 1.32 myr while the base and top of the GTS2016 Hauterivian differ respectively by 3.40 and 4.69 myr.

Description: An orbital floating time scale of the Hauterivian-Barremian transition (Early Cretaceous) is proposed using high-resolution magnetic susceptibility measurements. Orbital tuning was performed on the Río Argos section (southeast Spain), the candidate for a Global boundary Stratotype Section and Point (GSSP) for the Hauterivian-Barremian transition. Spectral analyses of MS variations, coupled with the frequency ratio method, allow the recognition of precession, obliquity and eccentricity frequency bands. Orbitally-tuned magnetic susceptibility provides minimum durations for ammonite biozones. The durations of well-constrained ammonite zones are assessed at 0.78 myr for Pseudothurmannia ohmi (Late Hauterivian) and 0.57 myr for Taveraidiscus hugii (Early Barremian). These results are consistent with previous estimates from the other reference section (Angles, southeast France) and tend to show that the Río Argos section displays a complete succession for this time interval. They differ significantly from those proposed in the Geologic Time Scale 2008 and may help to improve the next compilation. The Faraoni Oceanic Anoxic Event, a key Early Cretaceous oceanographic perturbation occurring at the P. ohmi/P. catulloi subzone boundary has a duration estimated at 0.10-0.15 myr, which is similar to previous assessments.

Description: The Valanginian positive carbon isotope excursion and associated environmental changes, known as the Weissert Event, is the first in the series of Cretaceous Earth system perturbations. Here, we develop a multiproxy cyclostratigraphy from a 31.2-m-thick Upper Valanginian to lowermost Hauterivian section of the Bersek Marl Formation in Gerecse Mountains, Hungary, comprising alternating marlstone layers of varying clay and carbonate content. The bulk carbonate d13C signal shows sustained, elevated values (up to 2.7 per mil) up to 19.2 m, followed by a decreasing trend upsection. Together with biostratigraphic data, this suggests that the lower part of the section was deposited during the plateau phase of the Valanginian Weissert Event. Spectral analyses of the multiproxy dataset, including magnetic susceptibility measurements and gamma-ray spectroscopy on the lower part of the section led to the identification of precession, obliquity, long and short eccentricity signals. A mean sedimentation rate of 14 m/Myr was calculated based on astronomical tuning. The cyclicity in the proxy signals reflects dilution cycles by detrital inputs in the basin, which supports the idea that orbitally-forced humid-arid cycles controlled the pelagic alternating sedimentation during the Early Cretaceous throughout the Tethyan area.

Description: Spectral analysis is a key tool for identifying periodic patterns in sedimentary sequences, including astronomically related orbital signals. While most spectral analysis methods require equally spaced samples, this condition is rarely achieved either in the field or when sampling sediment core. Here, we propose a method to assess the impact of the uncertainty or error made in the measurement of the sample stratigraphic position on the resulting power spectra. We apply a Monte Carlo procedure to randomise the sample steps of depth series using a gamma distribution. Such a distribution preserves the stratigraphic order of samples and allows controlling the average and the variance of the distribution of sample distances after randomisation. We apply the Monte Carlo procedure on two geological datasets and find that gamma distribution of sample distances completely smooths the spectrum at high frequencies and decreases the power and significance levels of the spectral peaks in an important proportion of the spectrum. At 5 % of stratigraphic uncertainty, a small portion of the spectrum is completely smoothed. Taking at least three samples per thinnest cycle of interest should allow this cycle to be still observed in the spectrum, while taking at least four samples per thinnest cycle of interest should allow its significance levels to be preserved in the spectrum. At 10 and 15 % uncertainty, these thresholds increase, and taking at least four samples per thinnest cycle of interest should allow the targeted cycles to be still observed in the spectrum. In addition, taking at least 10 samples per thinnest cycle of interest should allow their significance levels to be preserved. For robust applications of the power spectrum in further studies, we suggest providing a strong control of the measurement of the sample position. A density of 10 samples per putative precession cycle is a safe sampling density for preserving spectral power and significance level in the Milankovitch band. For lower sampling density, the use of gamma-law simulations should help in assessing the impact of stratigraphic uncertainty in the power spectrum in the Milankovitch band. Gamma-law simulations can also model the distortions of the Milankovitch record in sedimentary series due to variations in the sedimentation rate.

Description: The data of two sections studied in the Barremian (Early Cretaceous) of the Subbetic Domain (SE Spain) are shown here together with a detailed log showing the bed number and the biostratigraphic scheme. The samples were collected with a geologist hammer in May 2016. The average sample distance is 0.07 m and was kept as constant as possible using a Jacob's staff to ensure the detection of all the Milankovitch cycles applying Fast Fourier Transforms and related methods (e.g. multi-taper). The lithology is composed of marl-limestone alternations deposited in a (hemi-)pelagic setting. Observed fauna is composed of ammonites, radiolarians, foraminifera, calcareous nannofossils and scarce belemnites, bivalves, gastropods, brachiopods and irregular echinoids. The biostratigraphy scheme is provided in the detailed logs and is based on Tethyan ammonite and calcareous nannofossils. The two sections studied are Arroyo Gilico section (38°9'35'' N; 1°40'41'' W; the interval studied covers from the Late Hauterivian (Balearis Zone) to the Late Barremian (Vandenheckii Zone)) and Barranco de Cavila section (38°3'10'' N; 1°53'20'' W; the interval studied covers from the Late Barremian (Vandenheckii Zone) to the Early Aptian (Forbesi Zone)).Magnetic susceptibility was measured with a KLY-3 and calcium carbonate content was measured following the volumetric method using the automatic calcimeter Dream Electronique