Apatitic microspherules of unknown origin discovered above the Brazos River, Texas K/Pg impact bed

Huber, Brian T.¹*; MacLeod, Kenneth G.²

1. Smithsonian National Museum of Natural History, Washington, D.C., USA; 2. University of Missouri, Columbia, Columbia, Missouri, USA

Correspondent author*: huberb@si.edu

Abstract

The Cretaceous/Paleogene (K/Pg) boundary interval exposed at the River Bank South (RBS) outcrop along the Brazos River in Fall County, Texas yields one of the most complete and expanded records of post-impact microfossil recovery in the world. Spectacularly well-preserved foraminifera from strata bracketing the K/Pg impact bed along the Brazos River have been well documented for decades, but recent study of samples from the RBS section has revealed the presence of perfectly preserved earliest Danian biosiliceous microfossils, including diatoms and ebridians, as well as discovery of amber colored microspherules of unknown origin. The microspherules are perfectly round with a shiny surface, their diameter ranges from 72-112 microns, and their wall is thin, microcrystalline, and lacks any apertural opening. Energy dispersive X-ray spectroscopy reveals a wall composition with 10% phosphorous, 27% calcium, 31% oxygen, and 31% carbon weight percentages, suggesting an apatitic mineralogy. Their first appearance in the RBS section is within earliest Danian Zone P0 at 1.5 m above the impact bed, and they range into early Danian Zone P1a, up to 3.7 m above the impact bed. The appearance and elemental composition of the microspherules suggest a biogenic origin, and they bear closest similarity to calcispheres, which are considered as extinct dinoflagellate resting spores. However, the apatitic spheres are not assigned to that fossil group given the absence of an apertural opening, the significant amount of phosphorous in the shell, and their slightly larger size than typical calcispheres which range from 40-70 microns in diameter. Future X-ray diffraction and Raman analysis should reveal a more accurate mineral composition for these specimens, but how the microspherules formed may remain a mystery.

Keywords

apatitic, microspherules, early Danian

Reconciling model and proxy records in a Maastrichtian biologically-enabled ocean simulation

Tessler, Maya¹,², Coupe, Joshua ¹,³,⁴ Harrison, Cheryl S.¹*, Tabor, Clay⁵, Lovenduski, Nicole³,⁴, MacLeod, Kenneth⁶, Garza, Victoria¹, Markwick, Paul⁷, Hu, Shixiong⁵, Sepúlveda, Julio⁴,⁸, &  Mitra, Siddhartha⁹

1. Department of Ocean and Coastal Science & Center for Computation and Technology. Louisiana State University, Baton Rouge, Louisiana, USA; 2. Department of Geosciences, University of Arizona, Tucson, Arizona, USA;  Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, USA; 3. Institute of Arctic and Alpine Research, University of Colorado Boulder, USA; 4.Department of Earth Sciences, University of Connecticut, Storrs, CT 06269, USA; 5. Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA; 6. School of Geographical Sciences, University of Bristol; 7. Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA; 8. Virginia Institute of Marine Sciences, Gloucester Point, VA 23062, USA

Correspondent author*: cherylharrison@lsu.edu

Abstract

Reconstructions of Late Cretaceous ocean circulation rely heavily on geochemical proxy records, yet interpretations of these proxies often conflict. Here we use an isotope and ocean biogeochemistry enabled Earth system model to simulate Maastrichtian (~72–66 Ma) climate and compare modeled temperature and carbon isotope distributions to compilations of proxy data. The simulated ocean is warm (global mean sea surface temperature = 25.4 °C) and characterized by deep water formation in the North Pacific and intermediate water formation in the South Pacific. Simulated sea surface temperatures agree well with proxy reconstructions, particularly at mid-latitudes, supporting evidence for relatively high atmospheric CO₂ concentrations (~850 ppm) during the Maastrichtian. However, significant model–proxy mismatches occur in the deep ocean: simulated deep waters are colder and exhibit lower δ¹³C values than indicated by benthic foraminiferal records. We suggest that these discrepancies arise from sluggish ventilation and restricted circulation in the Atlantic and Southern Ocean basins in the model. Comparison with previous Late Cretaceous modeling studies indicates that plausible variations in paleogeography strongly influence deep water formation and may explain persistent cold deep ocean biases. These results demonstrate that isotope-enabled Earth system models provide a powerful framework for evaluating proxy interpretations while highlighting the sensitivity of Maastrichtian ocean circulation to paleogeographic boundary conditions.

Keywords

Maastrichtian; Earth system model; proxy

High-resolution records of mercury deposition across the Cretaceous-Paleogene transition from the North American Interior record a catastrophe

McMillan, Darby¹; Yanjie, Gong²; Beats, Kamaren¹; Bowersox, Mia¹; Hewett, Brittany¹; Knight, Marisa¹; Luksch, Corinne¹; Webster, Rachel¹; Wood, Rebecca¹; Barclay, Richard³; Bercovici, Antoine⁴; Bourque, Robert⁵; Gill, Benjamin⁶; Harris, M. Scott¹; Johnson, Kirk³; Sepúlveda, Julio⁵; Lyson, Tyler R.⁴; Them II, Theodore R.¹*

1. Department of Geology and Environmental Geosciences, College of Charleston, Charleston, USA; 2. PetroChina Research Institute of Petroleum Exploration and Development, Beijing, China; 3. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC, USA. 4. Department of Earth Sciences, Denver Museum of Nature and Science, Denver, USA; 5. Department of Geological Sciences and Institute of Arctic and Alpine Research (INSTAAR), University of Colorado Boulder, Boulder, USA; 6. Department of Geosciences, Virginia Tech, Blacksburg, USA

Correspondent author*: themtr@charleston.edu

AbstractAn asteroid impact triggered the end-Cretaceous mass extinction event (ECME) at the Cretaceous/Paleogene (K/Pg) boundary. It has also been hypothesized that contemporanous Deccan Traps volcanism destabilized the global environment, thus contributing to the ECME.  The mercury (Hg) record, a geochemical proxy for volcanism, has been predominantly applied to marine and coastal K/Pg boundary sections worldwide. These Hg data have been used to argue for increased Hg loading in sediments through enhanced atmospheric fallout of Deccan Traps-derived mercury. Because geologically catastrophic events that are transient in nature (e.g., an asteroid impact) require sedimentary environments that have high accumulation rates to preserve these signals, there may be issues with distinguishing between the sources of Hg from an impact or volcanic activity in most sites. Therefore, we have studied Hg concentrations and isotopes from terrestrial environments (representing floodplains, ponds/lakes, and swamps) during the latest Cretaceous and early Paleogene from a suite of study locations (outcrops and drill core) in western North America that span approximately 9° latitude.

Mercury concentrations are paired with total organic carbon (TOC) concentrations from nine locations spanning New Mexico, Colorado, South Dakota, North Dakota, Wyoming, and Montana to assess the chemostratigraphic morphology of Hg/TOC within this transect. This geographic distribution allows us to remove the possible effects of latitude on Hg accumulation in a single site. We also generated Hg isotopes from the John’s Nose (North Dakota) that contains the impact layer. Both Hg/TOC values and Hg isotopes (Δ¹⁹⁹Hg and δ²⁰²Hg) point to a rapid and catastrophic perturbation to the Hg cycle. Some sites in Montana (Iridium Hill, Nirvana) and North Dakota (Mud Buttes) display clear diagenetic processes that impacted the Hg record. Beyond the K/Pg sedimentary Hg enrichment interval, Hg concentrations tend to follow local depositional environment at each location, further supporting the notion that most deep-time sedimentary Hg records are controlled by local processes, not volcanic activity. The calculated amount of Hg entering Earth’s surface environments in the aftermath of the impact would have been deleterious to ecosystem health. We do not find any robust evidence for protracted Deccan volcanism as a significant source of Hg to sediments at the K/Pg boundary in North America.

Keywords

extinction; Chicxulub; Deccan Traps; metals

Insight from biogenic barium for reconstructing carbon export in the ocean

Griffith, Elizabeth M.¹*

1. School of Earth Sciences, The Ohio State University, Columbus, Ohio, USA

Correspondent author*: griffith.906@osu.edu

Abstract

As our oceans continue to warm in response to increased global temperatures, questions about the impact on nutrient cycling, primary productivity, and marine ecosystems remain. Looking to records of past change in deep sea sediment is critical to understand how the Earth system responded during other prior warm intervals. Proxy records reconstructing the carbon export in different regions in the ocean will be explored from three periods of interest including the Miocene Climate Optimum, Early Eocene, and Late Cretaceous. An emphasis will be on interpreting biogenic barium proxy records. Pacing and potential drivers of change during these warm intervals differ, but all highlight the dynamic nature of the response of the ocean-atmospheric system in different regions and the importance of constructing multi-proxy records. Special attention to assumptions and limitations of proxy records is necessary when comparing potentially conflicting records, which can ultimately provide invaluable insight into potential changes in carbon export at different depths in the ocean and nutrient cycling when thoughtfully combined.

Keywords

barium; carbon export; Miocene; Eocene

Evaluating Early Miocene hiatuses in the Atlantic deep-sea sedimentary record

Chan MacRae, Bella¹*; Freedman, Natalia²; Kasbohm, Jennifer³; Sibert, Elizabeth C.⁴; Antell, Gawain T.⁵; Auderset, Alexandra⁶; Browne, Imogen M.⁷; Farmer, Jesse R.⁸; Hess, Anya V.⁹; Lam, Adriane R.⁷; Matsuzaki, Kenji¹⁰; Smith, Jansen A.¹¹; Swain, Anshuman¹²; Woodhouse, Adam¹³

1. Department of Geology, Macalaster College, Saint Paul, MN, USA; 2. Department of Earth & Environmental Sciences, Vanderbilt University, Nashville, TN, USA; 3. Earth & Planets Laboratory, Carnegie Science, Washington, DC, USA; 4. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, USA; 5. Department of Geography, University of California, Los Angeles, Los Angeles, CA, USA; 6. School of Ocean and Earth Science, University of Southampton, Southampton, UK; 7. Department of Earth Science, Binghamton University, Binghamton, NY, USA; 8. School for the Environment, University of Massachusetts Boston, Boston, MA, USA; 9. Department of Atmospheric, Oceanic, and Earth Sciences, George Mason University, Fairfax, VA, USA; 10. Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan; 11. Department of Earth and Environmental Sciences, University of Minnesota Duluth, Duluth, MN, USA; 12. Department of Ecology and Evolutionary Biology & Museum of Paleontology, University of Michigan, Ann Arbor, MI, USA; 13. School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes, UK

Correspondent author*: bellachanmacrae@gmail.com

Abstract

While major climate perturbations and transitions have been studied extensively across the middle Miocene, the early Miocene (22–17 Ma) remains relatively understudied despite evidence of major marine biotic turnovers  (Sibert & Rubin, 2021; Swain & Woodhouse et al., 2024), nutrient cycle alterations (Auderset et al., 2022), and other potential Earth system changes. In addition to frequently poor recovery of early Miocene sediments from ocean drill cores, there appear to be widespread hiatuses in early Miocene sedimentary records (Keller & Barron, 1983) that create challenges in studying causes and consequences of early Miocene climate and biotic shifts.

Here we quantify the timing, duration, and bordering lithologies of depositional hiatuses in early Miocene deep-sea sedimentary records. We devised a system of classifying evidence for potential large-scale early Miocene depositional hiatuses based on both drilling recovery and  each site’s age model, and we applied this scheme to Atlantic Ocean deep sea sites. This system allowed us to differentiate between poor recovery and/or incomplete age model assessment versus the presence of an actual hiatus. To promote comparison among sites where we document hiatuses, we have re-calibrated the predominantly biostratigraphic age models to Geologic Time Scale 2020 ages.

Our preliminary results show that a number of Atlantic deep sea sites demonstrate conclusive hiatuses both within and encompassing the early Miocene, with durations spanning millions to tens of millions of years. Possible mechanisms that contribute to this pattern may include increased carbonate dissolution and/or intensified physical erosion attributed to known early Miocene events such as the opening of the Drake Passage (Dutkiewicz & Müller, 2022). However, as future work on this study will expand to include all ocean basins, better age models are necessary to further calibrate the precision with which we evaluate hiatus distribution, timing, duration, and cause. This work is part of a larger collaborative effort to more holistically evaluate the early Miocene Earth from a climate and biotic perspective.

Keywords

Early Miocene; stratigraphy; Atlantic Ocean

Leveraging high-resolution fossil records and novel AI workflows to study the effects of climate change on mammalian functional diversity across the PETM

Bloch, Jonathan I.¹*; Vitek, Natasha S.²; Porto, Arthur¹, Gordon, Caleb M.¹; Wing, Scott L.³; Morse, Paul E.⁴

1. Department of Natural History, Florida Museum of Natural History, University of Florida, Gainesville, FL, 32611, USA; 2. Department of Ecology & Evolution, Stony Brook University, Stony Brook, NY, 11794, USA; 3. Department of Paleobiology, P.O. Box 37012; National Museum of Natural History, Smithsonian Institution, Washington, D.C., USA; 4. Department of Cell & Developmental Biology, University of Colorado School of Medicine, Aurora, CO, 80045, USA

Correspondent author*: jbloch@flmnh.ufl.edu

Abstract

The Paleocene-Eocene Thermal Maximum (PETM) was an interval of rapid, millennial scale carbon release and global warming (~5 °C) ~56 million years ago that altered terrestrial ecology and permits testing of hypotheses related to modern biotic responses to future climate change. Despite intensive study of the PETM terrestrial vertebrate fossil record in North America, basic patterns such as the timing of species first and last appearances and temporal ranges are unresolved. Characterization of such fundamental faunal dynamics is limited by stratigraphic resolution and fossil sampling that is often biased towards recovery of larger taxa. Two decades of intensive fieldwork has yielded >20,000 vertebrate fossils from sections spanning the PETM, across tens of kilometers in the southeastern Bighorn Basin (BHB), Wyoming. Traditional surface collecting methods coupled with exhaustive screenwashing for smaller taxa from similar lithologies have reduced biases related to sampling and taphonomy. A stratigraphic framework that incorporates multi-proxy data from paleosols, fossil vertebrates and plants, and isotopes permits characterization of a shifting regional biome through the PETM across the field area. While the BHB is well known for paleontological and stratigraphic studies of the PETM, only in the past few years have fossil samples and contextual information from multiple horizons before, during, and after the PETM become complete enough to address fundamental questions about the links between climate and community assembly. Leveraging these large samples, our principal objective is to distinguish the effects of change in both climate and taxonomic composition on the functional diversity of mammalian communities. To this end, we are generating rich 3D datasets from micro-CT scans of mammalian molars, tarsal elements, and distal phalanges. A new set of AI tools is being trained on diverse pilot datasets to rapidly isolate, segment, and crop 3D surfaces of these elements for functional measurements. Measurements include molar dental topography, tarsal facet curvature, and linear measurements of distal phalanges from a stratigraphically-resolved fossil sample spanning the PETM. Measurement of functional diversity permits ecological characterization of the mammalian fauna without becoming mired in the many challenging and complex questions about taxonomic affiliations. It allows for direct tests of whether abiotic drivers such as temperature or biotic drivers such as plant community composition have a greater influence on mammalian functional diversity.

Supported by National Science Foundation Grants: EAR-0720268, EAR-0717892, EAR-0718740, EAR-0719941, EAR-0640076, EAR-2422839, EAR-2422838, EAR 2422840. Vertebrate fossils were collected under Bureau of Land Management permits to J.I.B. (PA04-WY-113, PA10-WY-185).

Keywords

fossil; mammal, AI; climate; PETM

Constraining the Evolution of N-fixing Symbioses in Alders

Grajales, Alexandra M.¹*; Johnson, Benjamin W.¹; Wing, Scott L.²

1. Department of The Earth, Atmosphere and Climate, Iowa State University, United States; 2. Smithsonian National Museum of Natural History, Washington DC

Correspondent author*: grajales@iastate.edu

Abstract

Several plant lineages, including legumes and Alnus, have evolved symbioses with diazotrophs that give them access to atmospheric nitrogen (N), needed to construct essential proteins and amino acids needed for photosynthesis. Leaves of such plants typically have lower carbon: nitrogen (C:N) ratios than those of other plants, and δ¹⁵N of -1‰, similar to atmospheric N2. Determining the time and place of origin of N-fixing symbiosis might shed light on the factors influencing its evolution. We hypothesize that the earliest fossil Alnus leaves found in the Eocene period would have lower C:N ratios than co-occurring non-N fixing plants and have δ¹⁵N closer to atmospheric N2. Geochemical analyses to date show fossil Alnus leaves from the Willwood Formation in the Bighorn Basin, WY to have significantly lower C:N ratios than co-occurring non-N fixing Platycarya (19.8 vs. 23.7, p=0.04). Although δ¹⁵N was significantly different between the two taxa (Alnus = 3.00‰, Platy. = 4.41‰, p=0.04), Alnus had a significantly higher mean than atmospheric N2. The cause of the distinction between the C:N between fossilized Alnus and Platycarya, but more enriched isotopic signatures of the fossilized Alnus is unknown and remains as an area of exploration of this research. Further analyses to test potential diagenetic and/or preservation alterations, and a larger sample set are also needed to confirm these findings and contextualize broader herbivory patterns during periods of changing atmospheric conditions.

Keywords

nitrogen fixation; symbioses; Alnus; isotopes

Disentangling Paleoclimate Signals Across the Paleocene-Eocene Thermal Maximum Using Individual Foraminiferal Analyses from IODP Site U1580, Agulhas Plateau

Kong, Tianshu¹*; Hupp, Brittany¹; Penman, Donald²; Burkett, Ashley³; Westerhold, Thomas⁴; Bohaty, Steve⁵; Thompson, Maya²; Foxall, Jake⁵

1. Department of Atmospheric, Oceanic and Earth Sciences, George Mason University, Fairfax, VA, 22030, USA; 2. Department of Geosciences, Utah State University, Logan, UT, 84322, USA; 3. Boone Pickens School of Geology, Oklahoma State University, Stillwater, OK, 74078, USA; 4. Center for Marine Environmental Sciences - MARUM, University Bremen, Bremen, Germany; 5. Institute of Earth Sciences, Heidelberg University, Heidelberg, Germany

Correspondent author*: tkong2@gmu.edu

Abstract

The Paleocene–Eocene Thermal Maximum (PETM; ~56 Ma) represents one of the most rapid and extreme global warming events in Earth history, marked by a pronounced negative carbon isotope excursion (CIE), pervasive ocean acidification, and hydrologic cycle disruption driven by large-scale carbon injection into the ocean–atmosphere system. Foraminiferal geochemistry has long formed the backbone of PETM paleoclimate reconstructions of ocean warming, carbon cycling, and circulation change. However, existing foraminiferal multi-shell geochemical records are compromised by two key biases: sediment mixing and seafloor carbonate dissolution, which together attenuate geochemical signals and erase foraminiferal material from the CIE onset. Here, we apply a high-resolution single-shell geochemical and morphological workflow to discrete intervals across the PETM record at IODP Expedition 392 Site U1580 (southern Agulhas Plateau, southwestern Indian Ocean; paleolatitude ~55°S; sedimentation rate ~1.2 cm/kyr) to potentially circumvent the interpretive impacts of these taphonomic processes. Uniquely among deep-sea PETM sites, the shallow paleodepth (~2.5 km) of U1580 largely shielded the seafloor from acidification-driven carbonate dissolution, maintaining wt.% CaCO3 above 70% and preserving abundant foraminifera across the CIE onset. We are in the process of applying a sequential individual foraminiferal analysis (IFA) workflow to 1,080 shells across 12 stratigraphic intervals spanning the pre-PETM through post-PETM, targeting 50 individuals of surface-dwelling Acarinina soldadoensis, 20 of thermocline-dwelling Subbotina spp., and 20 of epibenthic Nuttalides truempyi per interval. Each individual shell is processed sequentially via: (1) MicroCT to quantify shell wall thickness, density, porosity, and preservation state; (2) LA-ICP-MS to constrain individual shell trace element geochemistry, with particular focus on Mg/Ca; and (3) cryofocused continuous-flow IRMS for single-shell δ¹³C and δ¹⁸O values. Stable isotope measurements will distinguish in situ from reworked specimens, while integration with Mg/Ca-derived paleotemperatures will constrain the timing and magnitude of surface and deep seawater warming across the PETM onset. Comparison of δ¹³C and Mg/Ca will identify any lead-lag relationships between carbon release and warming. MicroCT of in situ vs. reworked shells (as identified by δ¹³C) will allow evaluation of MicroCT as a non-destructive pre-screening tool for multi-shell geochemical analyses. Preliminary single-shell δ¹³C-δ¹⁸O analyses of 20 A. soldadoensis identify two discrete isotopic populations (pre-PETM and PETM, ~1.9‰ offset in δ¹³C) within the same CIE-interval samples, providing evidence for bioturbation-driven vertical mixing. Preliminary results underscore the necessity of single-shell methodologies for recovering unbiased records of PETM onset dynamics.

Keywords

foraminifera; geochemistry; PETM; paleoceanography

Foraminiferal carbon and oxygen isotopes reveal dynamic climate and carbon cycle behavior during the early PETM onset

Penman, Donald E.¹*; Burkett, Ashley²; Hupp, Brittany³; Bohaty, Steve⁴; Westerhold, Thomas⁵; Kong, Tianshu³; Thompson, Maya ¹; Newell, Dennis¹;  Foxall, Jake⁴

1. Department of Geosciences, Utah State University, Logan, UT, 84322, USA; 2. Boone Pickens School of Geology, Oklahoma State University, Stillwater, OK, 74078, USA; 3. Department of Atmospheric, Oceanic and Earth Sciences, George Mason University, Fairfax, VA, 22030, USA; 4. Institute of Earth Sciences, Heidelberg University, Heidelberg, Germany; 5. Center for Marine Environmental Sciences - MARUM, University Bremen, Bremen, Germany

Correspondent author*: donald.penman@usu.edu

Abstract

Foraminiferal geochemistry has proven an invaluable archive for studying the rapid climate and carbon-cycle perturbation that marks the Paleocene-Eocene boundary (the PETM, ~56 Ma). However, deep-sea foraminiferal records typically suffer from two significant drawbacks. First, vertical mixing (physical sediment reworking or bioturbation of near-surface sediments) mixes individual foraminifers 10’s of centimeters vertically, including across the P-E boundary. Thus, conventional foraminiferal geochemistry, which combines multiple foraminiferal shells for analysis, averages together tens of thousands of years into single datapoints. This smooths datasets, attenuating rapid paleoclimatic changes like the PETM onset. Second, ocean acidification drove massive seafloor carbonate dissolution, which truncates most deep-sea carbonate-hosted records at the onset – in the “clay layer” that so strikingly marks the PETM in most deep-sea records, representing tens of thousands of years of time from the earliest phases of the PETM that are missing from foraminiferal records.

IODP Expedition 392 (Agulhas Plateau) recently recovered a unique record of the PETM which is ideally suited to address these shortcomings. At Site U1580, carbonate contents remain high (>70%) throughout the PETM, presumably due to its shallow paleodepth. Abundant, well-preserved planktic foraminifers occur even within the PETM onset. Like many other sites, sediments across the PETM are vertically-mixed (with clear burrows visible in core section-half faces). This vertical mixing can be disentangled by measuring carbon and oxygen isotopes (δ¹³C/ δ¹⁸O) on individual shells of the mixed layer-dwelling Acaranina soldadoensis.

Preliminary single-shell δ¹³C/ δ¹⁸O results reveal two distinct populations. One population has higher δ¹³C and δ¹⁸O (interpreted as pre-PETM) and a second population has lower δ¹³C (by ~2 ‰) and δ¹⁸O (by ~1 ‰, implying 4-5 °C of warming), which we interpret to represent individuals that calcified during the PETM. The two populations are mixed stratigraphically, with pre-PETM individuals found up to a meter above the bulk δ¹³C CIE. Of particular interest are the single-shell stable isotope results from one sample taken from just below the bulk CIE onset, in an interval of light-colored (pre-PETM aged) sediments with distinct, darker Zoophycos burrows, which presumably represent early PETM-aged material reworked downwards by bioturbation. Some of the single A. soldadoensis shells analyzed from this sample have δ¹³C/ δ¹⁸O values that are intermediate between the pre-PETM and PETM populations. These are, to our knowledge, the first transitional single-shell stable isotope values found from the PETM onset. The frequency of these transitional-value shells along with the structure of that population (in δ¹³C/ δ¹⁸O space) may provide crucial, new insights into the pace and phasing (lead/lag relationships between temperature and δ¹³C) of the crucial PETM onset phase.

Keywords

PETM; foraminifera; stable isotopes; paleoclimate

Multi-proxy approach for assessing marine ecosystem turnover across early Eocene hyperthermals in the NW of Europe (UK and Belgium).

Kellner, Laura¹*; Speijer, Robert P.¹; Stassen, Peter¹; Vellekoop, Johan¹,²

1. Department of Earth & Environmental Sciences, KU Leuven, Leuven, Belgium; 2. Directorate Earth and History of Life, Royal Belgian Institute of Natural Sciences, Brussels, Belgium

Correspondent author*: laura.kellner@kuleuven.be

Abstract

As Earth faces an uncertain future characterised by rising anthropogenic climate change and other pressures, it is crucial to understand how its ecosystems respond to these factors. Geological reference intervals such as Eocene hyperthermals, provide insights on how severe biotic changes scale with rapid climate changes. Among all marine ecosystems, shallow marine ecosystems generally yield the highest biodiversity and play a crucial role in providing resources for our society. These ecosystems are already showing signs of profound disruption. Thus, it is relevant to constrain the scaling relationships between magnitude of climate change and ecosystem perturbations, and identify the tipping points of when ecosystem architectures change as a consequence of climate change. Therefore, a new research project at KU Leuven focusses on the Eocene hyperthermals in the NW European (Belgium and UK) shallow marine settings. Hyperthermals are being identified in selected cores and outcrops, through a combination of chemostratigraphy (bulk organic and foram δ¹³C), new biostratigraphic age constraints (dinoflagellate cysts and nannofossils), and stratigraphic intrabasinal comparison. Benthic foraminiferal δ¹⁸O and Mg/Ca ratios, supplemented by biomarker-based TEX86 paleotemperature analyses, will be used to reconstruct the relative temperature evolution across the selected of hyperthermals. Additionally, benthic foraminiferal and dinoflagellate cysts assemblages data will provide environmental proxies to assess secondary environmental changes (e.g., deoxygenation, eutrophication and freshwater influx). The expected outcomes of this project will allow us to potentially identify thresholds where climate change causes ecosystem structure to change. This will involve a bottom-up approach using marine phytoplankton as the base of the ecosystem, and a top-down approach using marine fish as indicator species. These innovative perspectives will reveal which components of shallow marine ecosystems are most vulnerable to climate change. Lastly, the detailed environmental and ecological records generated in this project will not only show when ecosystem changes occur, but will allow a prediction of the direction of change.

Keywords

Eocene; Ecosystems; Biostratigraphy; Isotopes; Europe

Variation in Paleocene–Eocene moisture regimes between Wyoming basins

Keating, Katarina A.¹*, Sheldon, Nathan D.¹, Steeh, Kimberly.¹, Howard, Cecilia M.¹,², and Unruh-Friesen, Evan.¹

1. Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA; 2. Department of Environmental Sciences, University of Toledo, Toledo, OH, USA

Correspondent author*: kkeating@umich.edu

Abstract

In the terrestrial geologic record, paleoclimate reconstructions of warming events at single localities may be assumed representative of larger regions, but with potentially different responses between regions to common global drivers. Wyoming offers an opportunity to test this idea using strata and fossils from the penecontemporaneous Bighorn, Green River, and Hoback Basins. A drying trend during the Paleocene-Eocene Thermal Maximum (PETM) has been observed in the intensively-studied Bighorn Basin, WY, but it is unclear whether this is representative of the event’s effects on the moisture regime of the interior Rocky Mountain West region. The Hoback Basin is a small intermontane basin located ~200 km southwest of the Bighorn Basin and filled by Paleocene–Eocene strata. It is tectonically isolated from other nearby basins and may have been at a higher elevation at the time of deposition, providing an opportunity to investigate how global climate change may manifest differently in nearby but topographically distinct locations. Approximately 600 m of Hoback Basin strata has been identified as the Chappo Member of the Wasatch Formation based on its color-variegated paleosols and latest Paleocene and earliest Eocene (Clarkforkian and Wasatchian) vertebrate fauna. The Chappo Member recently yielded a potential PETM section in the Green River Basin to the south, but until this point there has not been thorough stratigraphic or geochemical investigation of the equivalent strata in the Hoback Basin. Here, we present stratigraphic and sedimentological observations paired with organic carbon isotope data from four outcrops in the Hoback Basin’s Chappo Member. We observe relatively low δ¹³C_org values, a lack of pedogenic carbonates, occasional lignites, and poorly-drained drab paleosols. We thus hypothesize that the paleoenvironment of the latest Paleocene-earliest Eocene Hoback Basin was less arid than that of nearby age-equivalent basins such as the Green River Basin and Bighorn Basin. We then discuss upcoming August 2026 fieldwork in the Hoback Basin, during which we plan to uncover old Clarkforkian fossil localities to improve biostratigraphic constraints, extend our carbon isotope record, and collect fossil teeth for isotopic analyses, including the novel Δ’17O proxy, which is sensitive to aridity. This will allow for direct quantitative comparisons of aridity near and/or across the PETM in the Hoback, Bighorn, and Green River basins.

Keywords

Paleocene, Eocene, Wyoming, aridity, Hoback

Two new cores through the Paleocene – Eocene Boundary in the Hanna Basin, Wyoming, USA

Dechesne, Marieke¹*;  Currano, Ellen D.²;  Dunn, Regan E.³; Foreman, Brady Z. ⁴; Diefendorf, Aaron F. ⁵;  Howard, Luke N. ⁵; Workman, Jeremiah B. ¹

1. Geosciences and Environmental Change Science Center, U.S. Geological Survey, Denver, Colorado, USA; USA; 2. Departments of Botany and Geology & Geophysics, University of Wyoming, Laramie, Wyoming, USA; 3. Samuel Oschin Global Center for Ice Age Research, La Brea Tar Pits, Natural History Museum of Los Angeles County, Los Angeles, CA, USA; 4. Department of Geology, Western Washington University, Bellingham, Washington, USA; 5. Department of Geosciences, University of Cincinnati, Cincinnati, Ohio, USA

Correspondent author*: mdechesne@usgs.gov

Abstract

The Paleogene upper Hanna Formation of the Hanna Basin in south-central Wyoming, USA, is made up of paludal to lacustrine carbonaceous shales, coals, and fluvial sandstones that include the Paleocene – Eocene Boundary. The location of the Paleocene-Eocene Thermal Maximum rapid warming event was identified using outcrop observations, leaf macrofossils, palynological analysis and a negative δ¹³C isotope excursion (CIE). The notable abundance of carbonaceous shales and coals in this basin, relative to nearby basins, together with its relatively rapid subsidence rate—suggesting an almost complete PETM record—makes this site particularly valuable for detailed geochemical and palynological analysis.

Sagebrush and colluvium obscure intervals critical to obtain a full and continuous record of the latest Paleocene, PETM, and post-PETM early Eocene. Therefore, two cores were drilled ~800 m behind a measured PETM outcrop section on Bureau of Land Management (BLM) land. Hanna Draw 1, drilled September – October 2023, extends to a depth of 828 ft (252 m), while Hanna Draw 2, drilled August – September 2025, covers a depth from 800 to 1236 ft (244 - 377 m). 

The cores are here correlated with the previously established outcrop-based stratigraphic framework for this area, enabling better constrained analysis of facies changes during the CIE, and are compared to overall Paleogene Hanna Basin sedimentation patterns. The excellent recovery of especially the organic rich sections in the cores will help refine spatial resolution of the δ¹³C isotope excursion, develop a more detailed palynological record, look at fire markers, and deepen our understanding of paleoenvironmental dynamics in the Hanna Basin during the rapid global climatic change of the PETM. We welcome collaboration on geochemical, palynological, or other analyses from these cores.

Keywords

PETM, Hanna Basin, stratigraphy, core

Weathering, provenance, and redox across the Paleocene-Eocene Thermal Maximum: Geochemical record from the Surprise Hill core, Salisbury Embayment, Virginia

Olaopa, Olabayo S.¹*; Hupp, Brittany N.¹;

1. Department of Atmospheric, Oceanic, and Earth Sciences, George Mason University, Fairfax, VA, USA

Correspondent author*: oolaopa@gmu.edu

Abstract

"The Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) was associated with major environmental reorganization on continental shelves. Along the U.S. Atlantic Coastal Plain (ACP), the event is marked by a shift to kaolinite-rich sedimentation, most prominently expressed by the Marlboro Clay (MC). This kaolinite pulse has been attributed to either intensified continental chemical weathering or physical remobilization of pre-weathered hinterland deposits. These mechanisms imply different roles for continental processes during the PETM CO₂ drawdown and recovery. Distinguishing between them requires evaluation of whether sediment source, transport, and weathering changed across the event. Previous work from the northern Salisbury Embayment suggests broadly stable detrital provenance during the PETM, but this has not been tested in sections farther south. The USGS Surprise Hill core (Virginia, USA) occupies a previously unstudied location within the North Atlantic Coastal plain compared to well-characterized Maryland and New Jersey sections.

This study employs high-resolution (~0.3 m sampling interval) portable X-ray fluorescence (pXRF) geochemistry on 95 samples across a 35 m section through the Aquia Formation, Marlboro Clay, and lower Nanjemoy Formation, anchored to δ¹³C data from the same core (Utsunomiya et al., 2025). Ti/Al remains stable across the Aquia-Marlboro transition, suggesting no first-order change in bulk detrital source composition. Notably, multiple weathering, transport, and redox-sensitive proxies begin to shift in the uppermost Aquia, several meters (~1 - 3m) below the recorded δ¹³C onset. This indicates that continental and shelf reorganization preceded the marine carbon perturbation. K/Al, Zr/Ti, and Si/Al then decrease sharply at the Aquia-Marlboro contact, recording abrupt kaolinite enrichment, reduced transport energy, and finer sediment delivery at the PETM onset. Ca/Al collapses across the same contact, indicating near-complete carbonate loss. Within the Marlboro Clay, Mn EF and Fe/Mn covary with δ¹³C and weathering-sensitive proxies, suggesting concurrent changes in shelf redox conditions during the body of the event.

These preliminary results indicate that the Surprise Hill PETM succession records linked changes in weathering intensity, sediment transport, carbonate preservation, and shelf geochemistry, and support a multi-stage reorganization of the source-to-sink system during Marlboro Clay deposition. Ongoing analyses will integrate mineralogical, weathering-index, and additional provenance constraints to further test these interpretations. This work fills a critical geographic gap in the ACP PETM transect and provides new constraints on continental-to-shelf response to rapid greenhouse forcing."

Keywords

PETM; geochemistry; chemical weathering; Marlboro

Paleomagnetic Record of the Paleocene - Eocene and PETM Zone in the Upper Hanna Formation, Wyoming, USA

Scaccia, Sophia L.¹*; Dechesne, Marieke²; Currano, Ellen D.³; Clyde, William C.¹

1. Department of Earth Sciences, University of New Hampshire, Durham, NH 03824; 2. U.S. Geological Survey, Geosciences and Environmental Change Science Center, Denver, CO 80225; 3. Departments of Botany and Geology & Geophysics, University of Wyoming, Laramie, Wyoming, 82071

Correspondent author*: sscaccia26@aol.com

Abstract

The Paleocene - Eocene Thermal Maximum (PETM; ~56 Ma) represents one of Earth history’s strongest analogues for abrupt global warming and provides invaluable insight for understanding the future of anthropogenic climate change. During the ~170 kyr duration of the PETM, the climate underwent 5-8℃ of warming and is best identified by its negative carbon isotope excursion (CIE) where isotopically light carbon was ejected rapidly into the earth system, triggering a cascade of effects including a warming climate, benthic foraminiferal extinction, remarkable mammalian dispersal, and hydrologic cycle intensification. Limited terrestrial records of this short-term climatic anomaly exist, but a recent discovery in the Hanna Basin in Wyoming, USA, presents a rare, near-complete sedimentological record of this event. The PETM in the Hanna Formation is constrained by a 𝛿¹³C isotope record, the occurrence of the index pollen Platycarya, and plant macro fossil assemblages. Applying magnetostratigraphy to the late Paleocene - early Eocene interval of the Hanna Basin provides an additional method to develop a temporal framework that spans beyond the PETM interval only. This study presents results from 35 paleomagnetically analyzed sample sites (135 samples) in the Hanna Basin. The magnetic polarity reversal from chron C25N to chron C24R has been clearly identified in the Hanna Draw section, but the next youngest reversal to C24N was not observed within the uppermost part of the section. By combining these new chronostratigraphic constraints with the existing record, sediment accumulation rates were calculated for the Hanna Basin for comparison to other PETM sections worldwide. This study's comparison indicates that the Hanna Basin has the most stratigraphically expanded PETM record in the world. The new age constraints and exceptional amount of sediment accumulation in the Hanna Basin provide a promising record for further studies on not only the paleomagnetism of the region, but also importantly the floral and faunal responses to the PETM which can help provide perspective on the current and impending anthropogenic climate change the earth faces.

Keywords

PETM, Paleogene, paleomagnetism, magnetostratigraphy, Wyoming

Leaf epidermal cells record the canopy response to changing climate during the late Paleocene to early Eocene in the Bighorn Basin, WY

Michel, Nathan¹*; Morgen, Rachel¹; Milligan, Joseph N.¹,²; Burke, Lula³; Barclay, Richard S.,²; Dunn, Regan E.⁴; Wing, Scott L²

1. Department of Environmental Science & Studies, Washington College, Chestertown, MD, USA; 2. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA; 3. Department of Earth & Environmental Science, Denison University, Granville, OH, USA; 4. Natural History Museums of Los Angeles County, La Brea Tar Pits, Los Angeles, CA, USA

Correspondent author*: nmichel2@washcoll.edu

Abstract

Canopy structure—the openness of a canopy—is a critical component of ecosystems. Changes in canopy structure play a role in ecological interactions (e.g., productivity, landscape stability, the composition of faunal communities, and mammal evolution) and can influence the Earth’s climate (e.g., albedo, hydrological and carbon cycling). Despite being a vital component of terrestrial ecosystems, deficiencies in existing proxy methods have necessitated higher-resolution analyses of canopy structure throughout deep time. Here, we study the relationship between canopy structure and climate change during the late Paleocene-early Eocene (~59-53 Ma) in the Bighorn Basin, Wyoming. This interval may provide good analogs for future climate change as Earth transitioned from a ‘warmhouse’ to a ‘hothouse’ punctuated by several hyperthermals with elevated atmospheric CO₂ levels. We used a new canopy structure proxy based on leaf epidermal cell morphology to reconstruct leaf area index, a measure of canopy density (LAI; foliage area (m²)/area of ground(m²)). Our preliminary results find a ~54% decrease in LAI from the late Paleocene to the Paleocene-Eocene Thermal Maximum (PETM) hyperthermal (Paleocene, 2.73 m²/m²; PETM, 1.29 m²/m²) and an increase in LAI to 4.07 m²/m² within the PETM recovery interval. LAI is variable during the Early Eocene Climatic Optimum ranging from 1.79 to 5.08 m²/m² depending on locality (EECO, average 3.44 m²/m²). A decrease in LAI during the PETM coincides with evidence of increased mean annual temperature and increased water stress within the BHB. Importantly, our results provide a new lens to evaluate the changes in flora and fauna and may provide insight into current and future ecosystem change. Future work will focus on reconstructing LAI in the Bighorn Basin during ETM2 and the early Eocene cool period to provide a more complete analysis of the impact of climate change on forest canopy structure.

Keywords

Bighorn Basin; PETM: Canopy structure

Terrestrial and marine palynology tracks shifts in vegetation and hydrology across Arctic Eocene hyperthermals

Willard, Debra A.¹*, Brinkhuis, Henk²,³, Craddock, William H.⁴, Lease, Richard O.⁵, Wycech, Jody B.⁶, Dreier, Mark⁶, Mohr, Michael⁷

1. U.S. Geological Survey, Florence Bascom Geoscience Center, Reston, Virginia, USA; 2. Department of Ocean Systems (OCS), NIOZ Royal Netherlands Institute for Sea Research, Texel, The Netherlands; 3. Department of Earth Sciences, Marine Palynology and Paleoceanography, Laboratory of Palaeobotany and Palynology, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands;  4. U.S. Geological Survey, Geology, Energy, & Minerals Science Center, Reston, Virginia, USA; 5. U.S. Geological Survey, Alaska Science Center, Anchorage, Alaska, USA; 6. U.S. Geological Survey, Central Energy Resources Science Center, Denver, Colorado, USA; 7. Boise State University, Isotope Geology Laboratory, Department of Geosciences, Boise, Idaho, USA

Correspondent author*: correspondent

Abstract

The Franklin Bluffs locality, on the North Slope of Alaska, contains a continuous outcrop exposure of hundreds of meters of Eocene strata. Measurement of bulk organic carbon isotopes, U-Pb dating of zircons, and integrated palynological analysis of sporomorphs and organic walled dinoflagellate cyst assemblages provide both robust age control and new evidence for environmental changes associated with hyperthermal events of the early to middle Eocene. Initial palynological analyses focus on an interval within the Early Eocene Climatic Optimum (EECO: 54.0  - 48.2 Ma),  from a thick shallow marine section that preserves two carbon isotope excursions (CIEs). These excursions lie above a horizon dated by U-Pb at 52.2 Ma by chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) analyses of volcanic zircons. Before the initial CIE of  ~-1 ‰, pollen assemblages are dominated by Pinaceae grains, with low abundances of Cupressaceae and angiosperm pollen. Directly below the negative CIE, assemblages shifted to pteridophyte dominance, halving of Pinaceae abundance, and first occurrence of Platycarya. Dominance of Cupressaceae pollen began at the onset of the CIE, along with increased abundance of castaneoid angiosperms and occurrence of (sub-) tropical taxa such as palms and the Bombacoideae. Dinocysts are present throughout the CIE, including Apectodinium hyperacanthum and A. homomorphum. The presence of reworked Cretaceous and Carboniferous palynomorphs are suggestive of upstream erosion and, potentially, enhanced hydrologic transport to the site. A subsequent, shorter-lived CIE exhibited similar patterns, with increased pteridophyte abundance directly below the CIE, followed by greater abundance of Cupressaceae.

An earlier, larger CIE (~-4 ‰) is preserved in a thinner delta plain sequence that predates the 52.2 Ma tephra. This CIE likely represents one of the first three Eocene hyperthermal events, referred to as Eocene Thermal Maxima ( ETM1 [also referred to as the PETM: ~55.9 Ma], and subsequent ETM2, or ETM3), based on previous analyses. Pollen concentrations are low (<4,000 grains/gram) below the CIE, and pteridophyte spores are more abundant than in the later CIEs, further increasing in abundance during the CIE. Gymnosperms (both Cupressaceae and Pinaceae) strongly dominate assemblages above this early CIE.

Collectively, these records suggest that even minor and relatively short-lived hyperthermal events of the early to middle Eocene Arctic are correlated with shifts in vegetation and hydrology that are consistent with warmer conditions and enhanced hydrology that follow a similar pattern to those of the PETM in the Arctic and elsewhere. At least nine CIEs have been identified in the Franklin Bluffs locality, and further analysis of terrestrial and marine palynomorphs from these hyperthermal events would clarify the variability of terrestrial and marine ecosystems during the Eocene greenhouse world.

Keywords

Eocene, hyperthermal, Arctic, palynology

The Late Lutetian Thermal Maximum (41.52 Ma): response of planktic

foraminiferal assemblages at the Atlantic Ocean

Sigismondi, Silvia¹*; Filippi, Giulia¹; Westerhold, Thomas²; Ferrando, Florencia¹; Luciani, Valeria¹

1. Dipartimento di Fisica e Scienze della Terra, University of Ferrara, Italy; 2. MARUM, University of Bremen, Bremen, Germany

Correspondent author*: sgsslv@unife.it

Abstract

"Understanding the marine biota response and their resilience to past warming

events is essential in perspective of future climate changes. The Late Lutetian Thermal Maximum (LLTM) is a short-lived (~30 Kyr) hyperthermal centered at 41.52 Ma ago that temporarily interrupted the cooling trend started after the Early Eocene Climatic Optimum (EECO, ~53-49 Ma). Like most Eocene hyperthermals, this event is characterized by sharp negative excursions in the oxygen and carbon isotopic records that relate to temperature increase of ~2-3°C. The LLTM has been so far explored only for the benthic foraminiferal response. However, planktic foraminifera have a crucial role to evaluate how global warming affects marine ecosystems as being are extremely sensitive to ocean variations. We present here the impact on planktic foraminiferal communities to this event, at the south Atlantic sites 1263 and 702. Planktic

foraminiferal communities record pronounced variations despite the moderate

temperature increase of this event. At both sites the cold-index Subbotina declines in abundance. In the mixed-layer, only the warm-index genera Globigerinatheka and Morozovelloides increase their abundance. Stable isotopes performed on species occupying diverse ecological niches show that mixed-layer taxa moved deeper to escape the warming and upper water-column records a destratification. Conversely, at Site 702, is the genus Acarinina that dominated the assemblages. Interestingly, the genus Chiloguembelina, known as proliferating in the oxygen deficient zone (ODZ), markedly declined its abundance indicating a ODZ contraction, differently from observation in the current climate warming but in agreement with other Cenozoic global warmings. Return to the previous community state documents resilience to the LLTM at

the studied sites. Ecological competition and different flexibility allowed to challenge the new environmental conditions."

Keywords

LLTM; planktic foraminifera; ocean warming

Preliminary results of Paleogene palynomorph assemblages processed using two different methods

Gardner, Kristina¹* and Carriker, Diana¹

1. US Geological Survey, Florence Bascom Geoscience Center, Reston VA, USA

Correspondent author*: kgardner@USGS.gov

Abstract

Many palynomorph extraction techniques involve the use of corrosive acids. Hydrochloric acid (HCl) is commonly used to digest carbonates, followed by Hydrofluoric acid (HF) for the removal of silicate material. Safer acid-free techniques rely on agitation of disaggregated samples in a deflocculant solution followed by multiple rounds of rinsing with water and centrifuging to manually remove clays. Heavy minerals are removed via decanting to retain only suspended particles and/or heavy density liquid separation. This study aims to 1) outline the process of acid-free sample processing for dinocysts and other palynomorphs, 2) determine if, and to what extent, microfossil assemblage recovery and specimen preservation are impacted by the use of techniques involving strong acids compared to an acid-free methodology, 3) observe which lithologies are more suitable for each method and 4) determine if age has an impact on recovery with differing methods. 

A variety of sands, silts, muds, and shales from marine environments from the Paleogene and Cretaceous periods were processed to compare results from both methods. Samples include lower Eocene sand and clay from the Manasquan Formation and Marlboro Clay from the Sandtown core (Delaware), lower Eocene mudstones and silts from the Bolado Park Formation at the Tres Pinos outcrop near Hollister, California, and shales from the English Ridge greywacke outcrop on the Eel River, California. Paired samples processed in two separate laboratories were spiked with the same batch of Lycopodium tracer prior to processing to calculate final palynomorph concentrations, and none underwent acetolysis. Tres Pinos samples only underwent acid-free processing. Samples processed using acid-free methods were swirled to manually remove sands. All samples were treated with potassium hydroxide, and sodium poly-tungstate was used as a heavy density medium to float fossiliferous residue.  Recovered microfossils include fungal spores, pollen, foraminiferal linings, and dinoflagellate cysts. Calcareous nannoplankton specimens were also preserved in the Sandtown core samples. Preliminary analysis shows that acid-free processing preserves a greater variety of microfossil groups, may be better for removing the clay-sized sediments from shales and mudstones, and decreases risks for laboratory personnel. Optimizing processing methods for fossil preservation will result in easier identification and more complete assemblage data for paleoclimate analyses.

Keywords

micropaleontology, methods, processing, palynomorphs

Shallow-marine benthic ecosystem responses to increasing global temperatures: insights from early-Eocene minor hyperthermals in North Atlantic records.

Steenhuyse-Vandevelde, Michael¹*; Doubrawa, Monika²; Vellekoop, Johan¹,³

1. Department of Earth & Environmental Sciences, KU Leuven, Leuven, Belgium; 2. Natural History Museum Basel, Basel, Switzerland; 3. Directorate Earth and History of Life, Belgian Institute of Natural Sciences, Brussels, Belgium

Correspondent author*: michael.steenhuyse-vandevelde@kuleuven.be

Abstract

The Early Eocene Climatic Optimum (EECO, 56–48 Ma) represents one of the warmest intervals of the Cenozoic, with global mean sea-surface temperatures up to 14 °C higher than today. This interval was punctuated by numerous short-lived warming events, or hyperthermals, each characterized by rapid carbon-cycle perturbations and significant environmental change. Hyperthermals offer valuable analogues for assessing ecosystem responses to different magnitudes of future global warming because most major modern marine clades were already established during the early Eocene,.

Shallow-marine ecosystems — among the most diverse on Earth — remain comparatively understudied in the context of early Eocene warming. To address this gap, we examine benthic foraminiferal communities from both sides of the early Eocene North Atlantic: the eastern margin (North Sea Basin) and the western margin (U.S. Atlantic Coastal Plain). This approach enables evaluation of whether ecological responses to hyperthermals were globally coherent or regionally distinct, how these systems responded to varying intensities of warming, and whether ecological change was gradual or marked by threshold behavior.

Our study focuses on several sediment cores that capture expanded early Eocene sections of the Nanjemoy and Manasquan formations in Virginia, Maryland, Delaware, and New Jersey. We apply integrated chemo- and biostratigraphic methods, including stable isotope analysis (δ¹³C, δ¹⁸O) of bulk sediment and benthic foraminifera, Mg/Ca ratios obtained by Laser Ablation‑ICP‑MS, and quantitative analysis of benthic foraminiferal assemblages. Negative carbon isotope excursions) identify hyperthermals, while δ¹⁸O, Mg/Ca — complementary to TEX₈₆ data — quantify associated temperature changes. 

We present preliminary results and ongoing research from the Loretto (Virginia) and Woodland Beach (Delaware) cores, as well as other relevant sites from the region. These findings offer new insights into the magnitude and ecological consequences of early Eocene hyperthermals in shallow-marine environments. By refining the nature of ecological thresholds and responses to warming, this work contributes to improving predictive models of ecosystem sensitivity under future climate change scenarios.

Keywords

Eocene, Atlantic, foraminifera, isotopes, hyperthermals

Microfossil analysis and paleoceanographic interpretation of the lower Eocene Bolado Park Formation, Tres Pinos section, California

Self-Trail, Jean M.¹*; McDougall, K.²; Gardner, Kristina F.¹

1. U.S. Geological Survey; Florence Bascomb Geoscience Center, Reston, VA; 2. U.S. Geological Survey; Geology, Minerals, Energy, and Geophysics Science Center, Flagstaff, AZ

Correspondent author*: jstrail@usgs.gov

Abstract

In recent years, interest in lower Eocene sediments has increased, because these sediments were deposited during the peak global Cenozoic warming that may be analogous to projected future conditions.  Modern taxonomic concepts and sedimentology are applied to thirty-seven samples from the ~90 m thick Bolado Park Formation, located along Tres Pinos Creek near Hollister, California, to better understand the global nature of Eocene hyperthermal events. These samples were examined for calcareous nannofossils and foraminifers and paired with grain-size analyses using laser ablation techniques. Based on nannofossil analyses and on the occurrence of Discoaster lodoensis with Tribrachiatus orthostylus, these assemblages are assigned to calcareous nannofossil Zone NP12 (~53-51 Ma) and were deposited during the Ypresian. The Toweius/Reticulofenestra turnover event, which occurs near the top of Zone NP12, is not recorded. This further restricts the age of the Bolado Park sediments and suggests that deposition occurred at ~53 Ma in the Eocene Thermal Maximum 3 (ETM3). The calcareous nannofossil assemblage from the bottom 10 m of the section is dominated by genera known to be associated with warm, oligotrophic settings as evidenced by the high percent abundance of Zygrhablithus bijugatus and Sphenolithus spp., with moderate abundances (~5%) of Discoaster kuepperi. An increase in the sand component above 10 m coincides with a gradual decline in the abundance of D. kuepperi and Sphenolithus spp. Abundances of Z. bijugatus decrease from a high of 30-40% in the lower 10 m section, to ~10-15% at 30 m and coincide with a steady decrease in Sphenolithus spp.  Abundances of D. kuepperi decrease to

Keywords

Microfossils; lower Eocene; ETM3

An overview of the late Paleogene and Neogene crocodylian fauna of the Siwaliks of South Asia

Jukar, Advait M.¹,²,³*; Burke, Paul M.J.⁴; Patnaik, Rajeev⁵, Mannion, Phillip D.⁶

1. Department of Natural History, Florida Museum of Natural History, University of Florida, Gainesville, FL, USA; 2. Division of Vertebrate Paleontology, Yale Peabody Museum, New Haven, CT, USA; 3. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC, USA; 4. Department of Palaeobiology, Naturhistoriska riksmuseet, Stockholm, Sweden; 5. Center for Advanced Study in Geology, Panjab University, Chandigarh, India; 6. Department of Earth Sciences, University College London, London, United Kingdom

Correspondent author*: advaitjukar@floridamuseum.ufl.edu

Abstract

The Siwaliks and co-eval sediments of South Asia preserve a rich record of terrestrial vertebrates from the Late Oligocene to the Pleistocene. While best known for its mammalian fossil record, these sediments preserve a diverse assemblage of crocodylians, including giant species of both long-snouted and broad-snouted animals. Late Oligocene faunas are characterised by co-existing large-bodied crocodyloids, such as Astorgosuchus bugtiensis, gavialoids such as Pseudogavialis curvirostris, and possibly species of the giant, long-snouted gavialoid Rhamphosuchus. By the Early Miocene, Astorgosuchus disappears in the record, whereas the latter two taxa persist. Gavialis is present throughout the Miocene–Pleistocene and is represented by several species. Gavialis and possibly other gavialoid taxa co-occur with a large unnamed tomistomine around 13 Ma, and with the smaller broad-snouted crocodyloid, Crocodylus palaeindicus, from 12.4 Ma. Rhamphosuchus re-appears in the record in the Late Pliocene, producing a ghost lineage spanning much of the Late Miocene to Early Pliocene. The earliest fossil occurrence of the extant mugger crocodile, Crocodylus palustris, is not until the Pleistocene, and there is some evidence to suggest that it is either the descendant of Crocodylus palaeindicus or originated via budding cladogenesis.

Keywords

Siwaliks, Crocodylia, South Asia