Alluvial record of an early Eocene hyperthermal within the Castissent Formation, the Pyrenees, Spain

The late Palaeocene to the middle Eocene (57.5 to 46.5 Ma) recorded a total of 39 hyperthermals – periods of rapid global warming documented by prominent negative carbon isotope excursions (CIEs) as well as peaks in iron content – have been recognized in marine cores. Documenting how the Earth system responded to rapid climatic shifts during hyperthermals provides fundamental information to constrain climatic models. However, while hyperthermals have been well documented in the marine sedimentary record, only a few have been recognized and described in continental deposits, thereby limiting our ability to understand the effect and record of global warming on terrestrial systems. Hyperthermals in the continental record could be a powerful correlation tool to help connect marine and continental deposits, addressing issues of environmental signal propagation from land to sea. In this study, we generate new stable carbon isotope data (δ13C values) across the well-exposed and time-constrained fluvial sedimentary succession of the early Eocene Castissent Formation in the south central Pyrenees (Spain). The δ13C values of pedogenic carbonate reveal – similarly to the global records – stepped CIEs, culminating in a minimum δ13C value that we correlate with the hyperthermal event “U” at ca. 50 Ma. This general trend towards more negative values is most probably linked to higher primary productivity leading to an overall higher respiration of soil organic matter during these climatic events. The relative enrichment in immobile elements (Zr, Ti, Al) and higher estimates of mean annual precipitation together with the occurrence of small iron oxide and iron hydroxide nodules during the CIEs suggest intensification of chemical weathering and/or longer exposure of soils in a highly seasonal climate. The results show that even relatively small-scale hyperthermals compared with their prominent counterparts, such as PETM, ETM2, and ETM3, can leave a recognizable signature in the terrestrial stratigraphic record, providing insights into the dynamics of the carbon cycle in continental environments during these events

Late Jurassic bimodal magmatism in the northern sea-floor remnant of the Rocas Verdes basin, southern Patagonian Andes

Magmatic and detrital zircon ages from the Rocas Verdes basin, a tectonically juxtaposed remnant of sea floor in the Magallanes fold and thrust belt (southern Patagonia, South America), indicates that a rifting phase of the Rocas Verdes basin occurred between 152 and 142 Ma, and was accompanied by bimodal magmatism. A dacite dyke cross-cutting pillow-basalt successions and a plagiogranite dyke in mixed maficfelsic terranes of the basal Sarmiento Ophiolite Complex contain 150 Ma zircon crystals, indicating that mafic submarine volcanism had started prior to or during the Late Jurassic, 10-15 Ma earlier than previously thought. The silicic pyroclastic rocks of the Tobifera Formation, with two samples dated at 148 and 142 Ma, were heralded by synrift sedimentation along fault-bounded grabens within Palaeozoic metasediments. No evidence for an active volcanic arc during the early formation of the Rocas Verdes basin was detected in detrital zircon grains of the lower sedimentary member of the Tobifera Formation. A minimum of 25 Ma of continuous sedimentation in the Rocas Verdes basin is suggested by detrital zircon grains in the upper member of the Zapata Formation. The Rocas Verdes basin was rimmed on the western side by an incipient and subaerial magmatic arc only in its later evolution