The Aptian was characterized by dramatic tectonic, oceanographic, climatic and biotic changes and its record is punctuated by Oceanic Anoxic Events (OAEs). The timing and duration of these events are still contentious, particularly the age of the Barremian-Aptian boundary. This study presents a cyclostratigraphic evaluation of a high-resolution multiproxy dataset (δ13C, δ18O, MS and ARM) from the Poggio le Guaine core. The identification of Milankovitch-band imprints allowed us to construct a 405-kyr astronomically-tuned age model that provides new constraints for the Aptian climato-chronostratigraphic framework. Based on the astronomical tuning, we propose: (i) a timespan of ~7.2 Myr for the Aptian; (ii) a timespan of ~420 kyr for the magnetic polarity Chron M0r and an age of ~120.2 Ma for the Barremian−Aptian boundary; and (iii) new age constraints on the onset and duration of Aptian OAEs and the ‘cold snap’. The new framework significantly impacts the Early Cretaceous geological timescale.

Orbital cycles are related to variations of Earth's orbit through time and exert profound control on glacial and interglacial climates due to changes in insolation. In this study, we aim to test whether orbital and millennial‐scale climate cycles conditioned the deposition of rhythmites in the southern Gondwana during the Late Paleozoic Ice Age (LPIA). We present the first cyclostratigraphic study based on X‐ray fluorescence records from a 27‐m‐thick interval of LPIA rhythmites in the southeastern border of the Paraná Basin, Brazil. TiO2 and Fe2O3 records display cycles in the Milankovitch and millennial bands. Among millennial‐scale variability, there are strong signals suggesting cycles with periods similar to the ~2.4‐kyr Hallstatt heliomagnetic and the ~1.5‐kyr Dansgaard‐Oeschger cycles. We estimated an average sediment accumulation rate of 5.94 cm/kyr, which suggests that the rhythmites were deposited in a relatively distal setting, during deglaciation episodes paced by millennial‐scale climate cycles. We interpret variations in concentrations of the terrigenous components TiO2 and Fe2O3 as indicative of glacial‐interglacial changes, reflected by advances and retreats of glaciers under drier and wetter climate conditions, respectively. Here we show that these high‐latitude glacial‐interglacial cycles were probably paced by short eccentricity, as previously suggested for Carboniferous cyclothems in low‐latitude deposits, and highlight the importance of millennial‐scale climate cycles at controlling glacially influenced deposition at high latitudes. Our results for the LPIA are similar to patterns seen in Pleistocene records.

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