Carbon isotope and biostratigraphic evidence for an expanded Paleocene–Eocene Thermal Maximum sedimentary record in the deep Gulf of Mexico

In this study, we present evidence of a Paleocene–Eocene Thermal Maximum (PETM) record within a 543-m-thick (1780 ft) deep-marine section in the Gulf of Mexico (GoM) using organic carbon stable isotopes and biostratigraphic constraints. We suggest that climate and tectonic perturbations in the upstream North American catchments can induce a substantial response in the downstream sectors of the Gulf Coastal Plain and ultimately in the GoM. This relationship is illustrated in the deep-water basin by (1) a high accommodation and deposition of a shale interval when coarse-grained terrigenous material was trapped upstream at the onset of the PETM, and (2) a considerable increase in sediment supply during the PETM, which is archived as a particularly thick sedimentary section in the deep-sea fans of the GoM basin. Despite other thick PETM sections being observed elsewhere in the world, the one described in this study links with a continentalscale paleo-drainage, which makes it of particular interest for paleoclimate and source-to-sink reconstructions

Cycles of Andean mountain building archived in the Amazon Fan

Cordilleran orogenic systems have complex, polycyclic magmatic and deformation histories, and the timescales and mechanisms of episodic orogenesis are still debated. Here, we show that detrital zircons (DZs) in terrigenous sediment from the late Pleistocene Amazon Fan, found at the terminus of the continent-scale Amazon River-fan system, record multiple, distinct modes of U-Pb crystallization ages and U-Th/He (ZHe) cooling ages that correlate to known South American magmatic and tectonic events. The youngest ZHe ages delineate two recent phases of Andean orogenesis; one in the Late Cretaceous – Paleogene, and another in theMiocene. Frequency analyses of the deep-time Phanerozoic record of DZ U-Pb and ZHe ages demonstrate a strong 72Myr period in magmatic events, and 92Myr and 57Myr periods in crustal cooling. We interpret these results as evidence of changes in upper and lower plate coupling, associated with multiple episodes of magmatism and crustal deformation along the subduction-dominated western margin of South America

Anatomy of an extinction revealed by molecular fossils spanning OAE2

The Cenomanian–Turonian mass extinction (Oceanic Anoxic Event 2-OAE2) was a period of profound ecological change that is recorded in the sedimentary record in many locations around the globe. In this study, we provide a new and detailed account of repetitive changes in water column ecology by analyzing the organic geochemical record preserved within the OAE2 section of the Greenhorn Formation, Western Interior Seaway (WIS) of North America. Results from this study provide evidence that OAE2 in the WIS was the result of the cumulative effect of reoccurring environmental stresses rather than a single massive event. During OAE2, extreme variations in biotic composition occurred erratically over periods of several thousands of years as revealed by molecular fossil (biomarker) abundances and distributions calibrated to sedimentation rates. These cycles of marine productivity decline almost certainly had follow-on effects through the ecosystem and likely contributed to the Cenomanian–Turonian mass extinction. While the causes behind organic productivity cycling are yet unproven, we postulate that they may have been linked to repeated episodes of volcanic activity. Catastrophic volcanism and related CO2 outgassing have been interpreted as main drivers for OAE2, though this study provides new evidence that repetitive, punctuated environmental stresses were also important episodes within the anatomy of OAE2. Following OAE2, these cycles of productivity decline disappeared, and the WIS returned to conditions comparable to pre-OAE2 levels

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