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The Cambrian is the most poorly dated period of the past 541 million years. This hampers analysis of profound environmental and biological changes that took place during this period. Astronomically forced climate cycles recognized in sediments and anchored to radioisotopic ages provide a powerful geochronometer that has fundamentally refined Mesozoic–Cenozoic time scales but not yet the Palaeozoic. Here we report a continuous astronomical signal detected as geochemical variations (1 mm resolution) in the late Cambrian Alum Shale Formation that is used to establish a 16-Myr-long astronomical time scale, anchored by radioisotopic dates. The resulting time scale is biostratigraphically well-constrained, allowing correlation of the late Cambrian global stage boundaries with the 405-kyr astrochronological framework. This enables a first assessment, in numerical time, of the evolution of major biotic and abiotic changes, including the end-Marjuman extinctions and the Steptoean Positive Carbon Isotope Excursion, that characterized the late Cambrian Earth. The Cambrian is the most poorly dated period of the past 541 million years. Here, the authors present a new astronomical time scale, allowing for a first assessment, in numerical time, of the evolution of major biotic and abiotic changes that characterized the late Cambrian Earth. [ABSTRACT FROM AUTHOR]

Meso-Cenozoic evidence suggests links between changes in the expression of orbital changes and millennia-scale climatic- and biotic variations, but proof for such shifts in orbital cyclicity farther back in geological time is lacking. Here, we report a 469-million-year-old Palaeozoic energy transfer from precession to 405 kyr eccentricity cycles that coincides with the start of the Great Ordovician Biodiversification Event (GOBE). Based on an early Middle Ordovician astronomically calibrated cyclostratigraphic framework we find this orbital change to succeed the onset of icehouse conditions by 200,000 years, suggesting a climatic origin. Recently, this icehouse was postulated to be facilitated by extra-terrestrial dust associated with an asteroid breakup. Our timescale, however, shows the meteor bombardment to post-date the icehouse by 800,000 years, instead pausing the GOBE 600,000 years after its initiation. Resolving Milankovitch cyclicity in deep time thus suggests universal orbital control in modulating climate, and maybe even biodiversity accumulation, through geological time. The Middle Ordovician icehouse has been suggested to be sparked by extra-terrestrial dust associated with an asteroid break-up. Here, the authors use an astronomically calibrated timescale to decouple millennia-scale climate and biodiversity change from the meteorite shower 468.4 million years ago. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

An integrated study of magnetic mass susceptibility (MS), bulk stable isotopes and calcareous nannofossil paleoecological changes is undertaken on the late Maastrichtian of the Elles section, Tunisia, spanning the last ca. 1 Myr of the Cretaceous. A cyclostratigraphic analysis reveals the presence of Milankovitch frequencies and is used for proposal of two distinct orbital age models and to provide ages of important stratigraphic horizons, relative to the age of the Cretaceous-Paleogene boundary (K-PgB). Principal component analysis (PCA) performed on the nannofossil assemblage reveal two main factors, PCA1, mostly representing fluctuations of D. rotatorius, P. stoveri, Lithraphidites spp., Retecapsa spp., Staurolithites spp., Micula spp., and PCA2, mostly representing fluctuations of A. regularis, C. ehrenbergii, Micula spp., Rhagodiscus spp., W. barnesiae and Zeugrhabdotus spp. Variations in PCA1 and PCA2 match changes in bulk δC and δO, respectively, and suggest changes in surface-water fertility and temperatures and associated stress. The variations in abundances of high-latitude taxa and the warm-water species Micula murus and in bulk δO delineate fast changes in sea-surface paleotemperatures. As in many other sites, an end-Maastrichtian greenhouse warming is highlighted, followed by a short cooling and an additional warm pulse in the last 30 kyr of the Maastrichtian which has rarely been documented so far. Orbital tuning of the delineated climatic events is proposed following the two different age models. Calcareous nannofossil assemblages highlight a decrease in surface-water nutriency, but their species richness remains high through the latest Maastrichtian, indicating, in Tunisia, a weak impact of Deccan volcanism on calcareous nannoplankton diversity before the mass extinction. [ABSTRACT FROM AUTHOR]

The early Eocene (c. 56 - 48 million years ago) experienced some of the highest global temperatures in Earth's history since the Mesozoic, with no polar ice. Reports of contradictory ice-rafted erratics and cold water glendonites in the higher latitudes have been largely dismissed due to ambiguity of the significance of these purported cold-climate indicators. Here we apply clumped isotope paleothermometry to a traditionally qualitative abiotic proxy, glendonite calcite, to generate quantitative temperature estimates for northern mid-latitude bottom waters. Our data show that the glendonites of the Danish Basin formed in waters below 5 °C, at water depths of <300 m. Such near-freezing temperatures have not previously been reconstructed from proxy data for anywhere on the early Eocene Earth, and these data therefore suggest that regionalised cool episodes punctuated the background warmth of the early Eocene, likely linked to eruptive phases of the North Atlantic Igneous Province. The early Eocene was characterized by exceptionally high global temperatures and no polar ice. Here, clumped isotope paleothermometry of glendonite calcite from the Danish Basin shows that these were formed in waters below 5 °C, indicating that regionalised cool episodes punctuated the background warmth of the early Eocene. [ABSTRACT FROM AUTHOR]