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Besides providing unique information on early mammal evolution, the UNESCO World Heritage Site “Messel Fossil Pit” (Hesse, Germany) yields detailed insight into short-term climate variability during the early to middle Eocene due to its annually laminated oil-shale sequence. Here, we constrain the chronostratigraphy of the sediments from the Messel paleolake to allow precise correlation with other marine and terrestrial archives from that time period. This study utilizes a suite of geochemical proxy data (gamma ray, total organic carbon and carbon isotopes of organic matter) obtained from a scientific drillcore (FB2001) from the depocenter of the Messel paleolake. The drillcore comprises the full succession of the lacustrine sediments of the Lower (LMF) and ~60% of the Middle Messel (MMF) Formations, including all marker beds that are used to stratigraphically correlate excavated fossil remains across the lake basin. Based on the proposed astronomical tuning, we infer that the LMF and MMF obtained in core FB2001 cover in total c. 840 kyr and were deposited between 48.06 Ma and 47.22 Ma. More specifically, our tuning yields a duration of c. 130 kyr and c. 430 kyr for the annually laminated oil shale of the LMF and MMF, respectively. Our results imply a slightly longer deposition of the LMF than previously proposed based on the same core. By contrast, the deposition of the MMF occurred over a slightly shorter time interval. As a result of our tuning approach, and considering the revision of a previously published 40Ar/39Ar age for the base of the LMF, the top of the MMF in core FB2001 has an age of 47.22 ± 0.21 Ma and is thus ~200 kyr younger than suggested previously. We also find that the average sedimentation rate (~20 cm/kyr) for the oil-shale intervals is slightly higher than previously estimated. In line with previously published palynological records our geochemical data point to a strongly variable climate during deposition of the LMF and MMF, with humidity changes being paced by orbital precession and eccentricity. The synchronicity of negative excursions in the organic matter-derived carbon-isotope signals for the LMF and MMF as presented in our study to those registered in quasi-global carbon-isotope compilations further corroborates the robustness of our age model. As these quasi-global carbon-isotope anomalies represent disturbances of the global carbon cycle and are often associated with abrupt warming events (“hyperthermals”), the organic-rich sediments recovered at Messel provide the opportunity to study the response of aquatic and terrestrial ecosystems to climate disturbances in un­precedented temporal resolution.

The mid-Cretaceous period was one of the warmest intervals of the past 140 million years1–5, driven by atmospheric carbon dioxide levels of around 1,000 parts per million by volume6. In the near absence of proximal geological records from south of the Antarctic Circle, it is disputed whether polar ice could exist under such environmental conditions. Here we use a sedimentary sequence recovered from the West Antarctic shelf—the southernmost Cretaceous record reported so far—and show that a temperate lowland rainforest environment existed at a palaeolatitude of about 82° S during the Turonian–Santonian age (92 to 83 million years ago). This record contains an intact 3-metre-long network of in situ fossil roots embedded in a mudstone matrix containing diverse pollen and spores. A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric carbon dioxide concentrations of 1,120–1,680 parts per million by volume and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo under high levels of atmospheric carbon dioxide.

Magnetic mineral diagenesis is an important process in sediments that is responsible for the partial or total destruction of records of Earth's magnetic field variations and also plays an important part in iron and sulfur cycling. A rock magnetic study has been carried out at International Ocean Discovery Program Expedition 350 Site U1437 in the Izu Bonin rear arc to investigate magnetic mineral diagenesis in deeply buried sediments from ~775 to ~1,002 m below sea floor (mbsf) with burial temperatures ranging from ~67 to 85 °C. Nonsteady state geochemical environments occur within an unusual deep methanic zone (below 850 mbsf) because of a release of sulfate below the shallow sulfate reduction zone. A drastic decline in magnetic susceptibility and remanence is observed at ~850 mbsf due to a decrease in ferrimagnetic iron oxide contents. Reduction of (titano)‐magnetite and pyritization occur at this inferred deep sulfate‐methane transition zone. Below ~850 mbsf, lower magnetic mineral contents coincide with further methane release. Geochemical analyses support a change in redox conditions and secondary precipitation of iron sulfides and carbonates in the methane‐rich zone. Magnetic mineral alteration is enhanced in zones where methane accumulates underneath low porosity intervals that act as seals. Although geochemical processes due to methane occurrence are likely dominant, more than one mechanism, possibly involving microbial activity, is probably responsible for the observed magnetic mineral assemblage changes. Dissolution of magnetic iron oxides is observed in an unusual deep methanic zoneMagnetic mineral alteration is enhanced in methane‐rich intervals below lower porosity seal‐like sedimentsGeochemical reactions involving methane, and possible microbiological processes, are likely responsible for the observed diagenetic alteration