Rise of Modern Marine Fishes Captured in an Early Paleocene Lagerstätte

El-Sayed, Sanaa¹,²,³*; Friedman, Matt²,³; Salem, Belal S.¹,⁴,⁵,⁶; Gohar, Abdullah S.¹,⁷; Al-Ashqar, Shorouq F.¹; Amin, Mohamed¹; El-Saka, Hossam¹, Saad, Hadeel²,³; Speijer, Robert P.⁸; Sallam, Hesham M.¹

1. Mansoura University Vertebrate Paleontology Center (MUVP), Mansoura University, Mansoura, 35516, Egypt; 2. Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan, 48109-1079, USA; 3. Museum of Paleontology, University of Michigan; Ann Arbor, Michigan, 48109-1079, USA; 4. Department of Biological Sciences, Ohio University; Athens, Ohio, 45701, USA. 5. Ohio Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio, 45701, USA; 6. Department of Geology, Faculty of Science, Benha University, Benha, 13518, Egypt; 7. Department of Anatomy and Cell Biology, Oklahoma State University Center for Health Sciences, Tulsa, Oklahoma, 74107, USA; 8. Department of Earth and Environmental Sciences, KU Leuven, Celestijnenlaan, 3001 Heverlee, Belgium.

Correspondent author*: sanaael@umich.edu

Abstract

The Cretaceous–Paleogene (K-Pg) extinction reshaped Earth’s biodiversity, yet its impact on marine fishes remains debated due to gaps in the Paleocene record. Here we report a paleotropical assemblage from the early Paleocene (Danian) of Egypt that provides a window into this transition. The Qreiya 3 Lagerstätte (62.2 Ma) reveals an offshore marine ecosystem with at least 21 actinopterygian taxa across 9 orders, exceeding the diversity of all other Danian skeletal assemblages combined. Most fishes are percomorphs and include the oldest skeleton-based records for at least six ecologically divergent extant groups. These findings reinforce inferences of fish extinction linked to the K–Pg and the rapid establishment of compositionally modern communities, marked by the first occurrences of new lineages no later than ~4 Myr after the event. Comparisons across sites indicate that percomorphs appear more common at lower paleolatitudes in the Paleocene, expanding into higher paleolatitudes by the Eocene.

Keywords

K-Pg; Percomorpha, tropics

Mapping a greenhouse world: global Paleogene climates and their biotic consequences

Burgener, Landon¹*; Rhodes, Rebekah²; Krumperman, Ryan³; Hayes, Sebastian⁴; Morgan, McKay¹; Santibañez Pacheco, Santiago¹; Hafner, Zachary¹; Christensen, Michael³; Tay, Albert⁴; Reich, Brian⁵; Hyland, Ethan⁶

1. Department of Geological Sciences, Brigham Young University, Provo, USA; 2. Department of Earth and Planetary Sciences, University of California - Davis, Davis, USA; 3. Department of Statistics, Brigham Young University, Provo, USA; 4. Department of Electrical and Computer Engineering, Brigham Young University, Provo, USA; 5. Department of Statistics, North Carolina State University, Raleigh, USA; 6. Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, USA

Correspondent author*: landon.burgener@byu.edu

Abstract

The Paleogene (66–23 Ma) represents the most recent prolonged greenhouse interval of the Phanerozoic. The epoch was characterized by elevated atmospheric greenhouse gas concentrations, reduced equator-to-pole temperature gradients, and an intensified hydrological cycle, making it an important analogue for understanding climate dynamics and biotic responses under high greenhouse forcing. Here, we present high-resolution, proxy-based reconstructions of global terrestrial paleoclimate patterns across nine Paleogene stages (Danian–Chattian) and assess their implications for biotic change.

We are compiling a comprehensive database of quantitative and semi-quantitative temperature and precipitation proxies (currently n > 15,000 unique samples), integrating marine (e.g., foraminiferal δ¹⁸O, TEX₈₆) and terrestrial (e.g., leaf physiognomy, paleosol) records. These data are assimilated using Bayesian hierarchical models and Markov Chain Monte Carlo methods to generate spatially continuous estimates of mean annual temperature, warmest and coldest mean monthly temperatures, and mean annual precipitation. These interpolated paleoclimate datasets are translated into paleo-Köppen climate classifications, allowing direct comparison with modern climate systems and facilitating ecological interpretation.

Our reconstructions indicate that early Paleogene climates, particularly during the early Eocene, supported extensive tropical and paratropical zones extending into high latitudes. Precipitation patterns suggest an expanded and intensified hydrological cycle, with broadly humid conditions across much of the globe. Through the middle and late Eocene, progressive cooling and increased seasonality led to a contraction of tropical climates and the development of more distinct temperate zones. By the Oligocene, cooler and more heterogeneous climates were established, including the emergence of polar conditions.

Comparison with climate model simulations reveals persistent discrepancies, especially in high-latitude temperatures, with proxy data indicating warmer conditions than most models reproduce. These differences highlight uncertainties in greenhouse climate feedbacks and the need for improved data–model integration.

The spatial and temporal evolution of paleoclimate zones corresponds closely with major Paleogene biotic patterns, including the poleward expansion of thermophilic taxa during early warmth and subsequent range contractions during cooling. These results emphasize the strong coupling between climate and biotic change in greenhouse systems and provide a robust framework for evaluating Earth system sensitivity to elevated greenhouse gas concentrations in the future.

Keywords

paleoclimatology; Paleogene; proxies; spatial interpolation

A unique, high elevation record of Cretaceous-Paleogene terrestrial paleoclimate from the Sheep Pass Formation in central NV, USA

Snell, Kathryn E.¹*; Olsen-Valdez, Juliana.¹; Havranek, Rachel E.²; Widlansky, Sarah J.³; Trower, Elizabeth J.¹; Clyde, William C.⁴; Fricke, Henry C.⁵

1. Geological Sciences, University of Colorado Boulder, Boulder, USA; 2. Department, University of Utah, Salt Lake City, USA; 3. Earth Sciences, University of New Hampshire, Durham, USA. Now at: U.S. Geological Survey, Woods Hole, USA; 4. Earth Sciences, University of New Hampshire, Durham, USA; 5. Geology, Colorado College, Colorado Springs, USA.

Correspondent author*: kathryn.snell@colorado.edu

Abstract

Relative to marine records, the thermal evolution of land environments in response to global climate change is poorly constrained. The Sheep Pass Formation, in central Nevada, is a latest Cretaceous to mid-Eocene aged unit that contains a sequence of lacustrine, fluvial and palustrine sediments, dominantly carbonates, that preserves a record of the response of a high elevation lake basin to this important period of global warmth, and may preserve a record of large scale perturbations such as the end-Cretaceous extinction and the Paleocene-Eocene Thermal Maximum (PETM). Here we present the results of our sedimentological, geochemical and geochronological studies thus far on the Sheep Pass Formation and compare these records to other terrestrial paleoclimate records of similar age in the western US. Sheep Pass member B, which formed from carbonate precipitation in a shallow lake basin, preserves facies changes associated with lake level changes as well as waxing and waning intervals of microbial activity, reflected by variable stratigraphic thickness and lateral extent of distinctive thrombolite units. The middle portion of Sheep Pass member B contains the thickest and best developed thrombolite interval, but the reason for this expansion of microbialite development is unknown. Our current age constraints suggest that much of member B is Paleocene in age, and so preserves some part of the recovery interval after the end-Cretaceous extinction. One hypothesis is that this thick thrombolite interval preserves a very early stage of this recovery, but more work is needed to determine if the end-Cretaceous extinction is preserved and at which stratigraphic level. In addition, carbon isotope records show distinct offsets between the clots and matrix of the thrombolites, allowing us to differentiate between local carbon cycle effects and global carbon isotope shifts that can be used for chemostratigraphic correlations. Finally, clumped isotope temperatures through member B show resolvable temperature trends, with temperatures between 20-35° in the lowermost part of the member, cooling to between 10-20°C in the middle portion and warming back to 25-30°C in the uppermost part of member B. Generally, these temperatures are on par with other estimates of terrestrial temperatures in the region, except for the coolest phase in the middle of member B. The large magnitudes of temperature change (~10-15°C) are also consistent with other records from the western US for this general time period, including across warming events like Eocene hyperthermals (e.g. 12-15°C for the PETM in the Bighorn Basin, ~7-8°C for Eocene hyperthermals, ETM2 and H2), which are larger than most marine temperature trends (at long and short timescales) for this time. These results highlight the value of this new and evolving record of terrestrial climate during this globally warm time and suggest that the western US may have experienced amplified warming relative to global averages.

Keywords

microbialites; terrestrial; isotopes; hyperthermals; paleotemperature

Assessing Short-Term Climate Change Across the Cretaceous-Paleogene Boundary with an Earth System Model

Hu, Shixiong.¹*; Tabor, Clay R.¹

1. Department of Earth Science, University of Connecticut

Correspondent author*: shixiong.hu@uconn.edu

Abstract

Although most research points to the Chicxulub impact event as the primary driver of the end-Cretaceous mass extinction, the details remain uncertain. This is due, in part, to uncertainties surrounding impact-driven aerosol emission sources and amounts. To better understand the potential climate responses after the Chicxulub impact, we performed several impact emission simulations with a state-of-the-art Earth System model that resolves the evolution of multiple aerosols within a single modeling framework. Following the emissions scheme in Toon et al. (2016), we simulate a comprehensive full-emission Chicxulub impact scenario that includes soot, dust, and sulfur. We also perform a series of sensitivity tests including ‘no-soot’, ‘no-sulfur’, and ‘no-dust’ scenarios. In the full-emission scenario, we find that soot is the primary contributor to the post-impact climate and the only aerosol capable of inhibiting photosynthesis for several years. Among the sensitivity tests, the ‘no-soot’ case exhibits the weakest response, with the smallest surface-temperature reduction and the fewest months of low-light conditions; the ‘no-dust’ case shows an intermediate response, whereas the ‘no-sulfur’ case most closely resembles the full-emission simulation.

Keywords

K-Pg; Chicxulub; aerosols; climate; soot

Rapid KPg recovery and Paleogene variability of Southern Ocean siliceous phytoplankton from Seymour Island, Antarctic Peninsula

Coenen, Jason J.¹*, Harwood, David M.¹, Tobin, Tom S.²

1. Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln; 2. Department of Geological Sciences, University of Alabama

Correspondent author*: JCoenen3@unl.edu

Abstract

Seymour Island (James Ross Basin, NE Antarctic Peninsula) preserves a rare, near-continuous Southern Ocean marine succession that spans the Cretaceous-Paleogene extinction event and extends into key Paleogene intervals. This offers an opportunity to examine how high-latitude phytoplankton communities reorganized during greenhouse climates and following a major extinction event. We use museum-curated carbonate concretions with early-cemented microfossil archives to refine diatom and silicoflagellate records at a higher stratigraphic resolution than is typically possible in sediments with high diagenetic loss. Archived concretions from the Polar Rock Repository (Ohio State University) and the Burke Museum (University of Washington) were analyzed and correlated among multiple field collections to build a composite section (~100 m below and above the boundary). Five boundary-crossing transects were documented, including two key profiles collected by David Elliot in 1989, spanning ~4 m below the boundary through 6.8 and 15 m above the boundary. 

Immediately above the K-Pg boundary, diatom assemblages are dominated by Stephanopyxis spp. and contain abundant resting spores (20-30%), consistent with stressed or strongly seasonal surface-water conditions following the extinction event. At ~3 m above the boundary (sample K-504), Stephanopyxis richness increases, and resting spores comprise 29%. Slightly higher 5-6.8 m above the boundary, overall diatom diversity increases while resting spore abundance declines to ~20%. A volcanic glass-bearing sample 15 m above the boundary contains exceptionally well-preserved siliceous microfossils and records high diatom diversity and abundance as well as silicoflagellate recovery, with the genus Corbisema diversifying. Correlation to Sr ages from adjacent sections suggests this interval represents ~42 kyr after the extinction event. Together, these observations indicate a rapid rebound of siliceous phytoplankton and near-continuous diatom productivity in the high-latitude Southern Ocean immediately following the K-Pg perturbation. 

To place recovery in a broader Paleogene context, we extend observations into younger stratigraphic intervals (Sobral Formation and La Meseta Formation) to assess longer-term changes in siliceous microfossil preservation and community structure through the Paleocene and Eocene. Preliminary analyses of a Polar Rock Repository sample from the La Meseta Formation further suggest that exceptional siliceous microfossil preservation may also occur at or near the Eocene-Oligocene transition, motivating targeted sampling to evaluate biotic and environmental change during the Paleogene.

Keywords

diatoms, silicoflagellates, KPg, recovery, Paleogene

New evidence for a K–Pg boundary fungal spore spike from West Bijou (Colorado, USA) supports primary productivity collapse at a global scale.

Bercovici, Antoine¹*; Dunn, Regan E.²; Vajda, Vivi³; Barclay, Richard S.⁴; Currano, Ellen D.⁵; Gill, Jacquelyn L.⁶,⁷; Pittermann, Jarmila⁸; Sessa, Emily⁹; Lyson, Tyler R.¹

1. Denver Museum of Nature & Science, 2001 Colorado Boulevard, Denver, CO 80205, USA.; 2. Samuel Oschin Global Center for Ice Age Research, La Brea Tar Pits, Natural History Museum of Los Angeles County, Los Angeles, CA, USA.; 3. Department of Palaeobiology, Swedish Museum of Natural History, P.O. Box 5007, Stockholm, Sweden.; 4. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C., 20013, USA.; 5.Departments of Botany and Geology & Geophysics, University of Wyoming, 1000 E. University Ave., Laramie, WY 82071, USA.; 6. School of Biology and Ecology, University of Maine, 100 Murray Hall, Orono, ME 04469, USA.; 7. Climate Change Institute, University of Maine, 5764 Sawyer Research Center, Orono, ME 04469, USA.; 8. Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA, 95060 USA.; 9. William and Lynda Steere Herbarium, New York Botanical Garden, 2900 Southern Blvd., Bronx, NY 10458, USA.

Correspondent author*: abercovici@dmns.org

Abstract

The Cretaceous–Paleogene (K–Pg) mass extinction (66.0 million years ago) is marked by a catastrophic disruption to Earth’s biosphere, coincident with the Chicxulub asteroid impact. Geophysical modelling has suggested that impact-generated dust and combustion-derived soot severely reduced incoming solar radiation, suppressing photosynthesis on a planetary scale. In addition to the immediate mass devastation to terrestrial plant ecosystems caused by the blast of the impact, wildfire ignited by the release of thermal energy, and acid rains from sulfate aerosols, the post K–Pg “impact winter” is hypotesized to have led to a collapse of primary productivity lasting several years. This hypothesis is supported by a unique occurrence of a fungal spike at the Moody Creek Mine K–Pg section in New Zealand, with >75% fungal spores within a 0.5 cm interval immediately following the K–Pg boundary.

We report the second discovery of a fungal spike at the Bowring Pit K–Pg section in West Bijou Creek, east of Denver, USA. From relative abundance counts of pollen and spores in 40 samples spanning ±30 cm across the K–Pg boundary, a spike of 31.9% fungal spores is observed within the topmost 3 cm of the boundary clay layer. While fungal spores are ubiquitous in the terrestrial rock record of the K–Pg boundary in North America, they usually are represented by amerospores (single-celled spores) and phragmospores (multi-celled spores) and are present in low numbers (< 1%). The West Bijou spike is remarkable as it shows, for the first time, a germinating succession unfolding in two distinctive phases. First, an abundance of septate hyphae are observed, growing in situ within the boundary clay which represents freshly deposited ejecta from the Chicxulub impact. This is followed by the proliferation of a single morphotype of didymospore (dual-celled spores). Most modern fungi producing didymospores are Ascomycetes and are saprophyte species found on dead wood, leaf litter, decomposing vegetation and in top soil (e.g., Didymella, Septonema, Trichothecium, etc.). This particular succession shows a completed asexual reproductive cycle of hyphal growth to mass sporulation, which has a duration of days to weeks in modern Ascomycetes. The fungal spike is immediately followed by a 20–40% Cyathidites spp. fern spore spike, indicating the recovery of devastated landscapes by pioneer plant recolonizers as photosynthesis resumed after post-impact darkness.

This new evidence of a fungal spike from Colorado underscores devastation of forests at the K–Pg boundary which provided a dramatic increase in available substrates for saprophytic organisms and that this response occurred at a global scale. The collapse of primary productivity during the years of post-impact darkness would have greatly affected higher trophic levels relying on disappearing resources, while food webs based on detritus and decomposing communities would have been more resilient to the K–Pg mass extinction event.

Keywords

extinction; recovery; palynology; fungi; Colorado

Prolonged terrestrial ecosystem instability following the Cretaceous-Paleogene (K/Pg) Boundary

Flynn, Andrew G.¹*; Milligan, Joseph N.²; Peppe, Daniel J.³; Gygi, Danielle³; Geng, Jie⁴; Secord, Ross⁵; Williamson, Thomas E.⁶; Brusatte, Steven L.⁷; Shelley, Sarah L.⁸

1. Department of Geological Sciences, New Mexico State University, Las Cruces, NM, USA; 2. Environmental Science and Studies Department, Washington College, Chestertown, MD, USA; 3. Department of Geosciences, Baylor University, Waco, TX, USA; Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA; 5. Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA; 6. New Mexico Museum of Nature and Science, Albuquerque, NM, USA; 7. School of GeoSciences, University of Edinburgh, Edinburgh, Scotland, UK; 8. School of Natural Sciences, University of Lincoln, Lincoln, UK

Correspondent author*: agflynn@nmsu.edu

Abstract

Early Paleocene floral and faunal communities were substantially restructured as a result of the end-Cretaceous mass extinction approximately 66.0 Ma. While events immediately adjacent to the Cretaceous-Paleogene (K-Pg) boundary have been widely studied, comparatively little research has looked at long-term patterns in terrestrial ecosystem recovery during the early Paleocene. The San Juan Basin (SJB), located in northwestern New Mexico, preserves exceptional, diverse, and geochronologically well-constrained early Paleocene floral and faunal records, making it an ideal location to investigate long-term recovery of early Paleocene terrestrial ecosystems. Here we present a high-resolution record of early Paleocene terrestrial ecosystem instability during the first ~1.5 Myr of the Paleocene using plant and vertebrate fossils coupled with bulk organic carbon δ¹³C from the SJB.

Plant and vertebrate macrofossils in the SJB were collected from the lower Paleocene Ojo Alamo Sandstone and lower Nacimiento Formation spanning the first ~1.5 Myr of the Paleocene. Floral extinction, origination, and net diversification rates were estimated using the Pradel capture-mark-recapture (CMR) model from 66.0-64.5 Ma with 100 Kyr timesteps. Two early Paleocene intervals of decreasing floral diversity were identified: a rapid interval of ~40% diversity decrease at ~65.5 Ma and a prolonged interval of decreasing diversity ~65.2 to 64.7 Ma. Two short intervals of rapid floral diversification were also identified at ~65.3 and ~64.6 Ma. The onset of both intervals of decreasing floral diversity are coeval with a -1.5 to -2.5 ‰ bulk organic carbon δ¹³C excursion and a decrease in forest canopy density reconstructed from paleo-leaf area index. The rapid floral diversification events at ~65.3 and 64.6 Ma are coeval with the first appearance the Puercan 3 (Pu3) and Torrejonian 1 (To1) mammalian faunas, respectively, in the SJB.

We also applied the Pradel CMR model to coeval macrofloras from the Denver Basin (DB), Colorado and the Williston Basin (WB), North Dakota and Montana, respectively. The floral diversity patterns estimated from the DB and WB indicate intervals of increasing and decreasing  floral diversity that are contemporaneous with the same intervals identified in the SJB. This suggests a regional driver in patterns of floral diversity change during the early Paleocene in western North America, reflecting prolonged terrestrial ecosystem instability following the K-Pg mass extinction.

Keywords

Cretaceous; Paleogene; K/Pg Boundary; Terrestrial

Mammals from the Hewett’s Foresight local fauna (Lance Formation, Bighorn Basin, Wyoming) suggest Laramide uplifts influenced terrestrial diversity patterns prior to the Cretaceous–Paleogene mass extinction

Sweedler, Rory E.¹,²*; Weaver, Lucas N.¹,²

1. University of Michigan Museum of Paleontology, Ann Arbor, MI; 2. University of Michigan Department of Earth and Environmental Sciences, Ann Arbor, MI

Correspondent author*: sweedler@umich.edu

Abstract

Studies of mammalian communities leading up to the Cretaceous–Paleogene (K–Pg) mass extinction have almost exclusively focused on fossils from coastal lowland paleoenvironments. Today, small mammals are species-poor in coastal lowlands; our current knowledge of pre-extinction mammalian communities may thus be missing ancient biodiversity hotspots. In modern continental basins, biodiversity is highest within and proximal to mountain uplifts and decreases in more distal lowlands, a pattern known as a topographic diversity gradient. Hewett’s Foresight is a latest Cretaceous (ca. 68–66 Ma) fossil locality in the Lance Formation of the Bighorn Basin, Wyoming, that is located ~15 km southwest of the Laramide Beartooth Uplift and thus offers an opportunity to study pre-extinction mammalian biodiversity in a mountain-proximal paleoenvironment. This study revises the taxonomy of mammals from the Hewett’s Foresight local fauna and compares updated taxonomic diversity data with the roughly coeval, mountain-distal Type Lance local fauna nearly 400 km to the east. Multituberculates, the most speciose and abundant mammals at that time, exhibit greater species richness at the mountain-proximal Hewett’s Foresight compared to the mountain-distal Type Lance, suggesting the presence of a topographic diversity gradient in the latest Cretaceous of western North America. Comparisons of faunal similarity among latest Cretaceous mammals across the continent indicate additional latitudinal and temporal factors influencing faunal composition, consistent with previous studies. Preliminary observations of the species richness and composition of leptictid and cimolestid eutherians suggest affinities between Hewett’s Foresight and the coeval Trochu assemblage from the Scollard Formation, proximal to the Sevier front in Alberta. Novel topographic patterns described here suggest the emergence of Laramide uplifts were important drivers of mammalian community assembly and spatial heterogeneity in the North American Western Interior just prior to the K–Pg mass extinction, which may have implications for geographic patterns of recovery post-extinction.

Keywords

Mammalia, Cretaceous, biogeography, paleoecology

Fluvial Fan Evolution in the San Juan Basin (New Mexico, USA) and its Association with the Paleocene-Eocene Thermal Maximum (PETM)

Fricke, Henry¹*; Zellman, Kristine²;  Beverly, Emily J.³;  Flynn, Andrew⁴; Korasidis, Vera ⁵; Plink-Björklund, Piret⁶; Snell, Katie⁷; Wing, Scott⁸; Williamson, Thomas⁹

1. Colorado College; 2. USGS, Denver; 3. University of Minnesota; 4. New Mexico State University; 5. University of Melbourne; 6. Colorado School of Mines; 7. University of Colorado Boulder; 8. Smithsonian Institution of Washington; 9. New Mexico Museum of Natural History and Science

Correspondent author*: hfricke@coloradocollege.edu

Abstract

Sedimentological and stratigraphic analyses of the Paleocene-Eocene uppermost Nacimiento and lower San Jose Formations of the San Juan Basin, New Mexico, document at least two episodes of fluvial fan progradation, with fan advance interpreted to reflect intensified inter- and intra-annual precipitation variability. The episodic nature of these fan dynamics raises a key question: do the hydroclimatic shifts recorded in the fluvial record correspond to discrete hyperthermal episodes? Changes in sedimentation patterns consistent with increased precipitation variability have been correlated with the Paleocene-Eocene Thermal Maximum (PETM) in other terrestrial basins, raising the possibility that the PETM had a similar impact in northern New Mexico.

To investigate this connection, we present a combination of paleontological, paleomagnetic, and carbon isotope data from the southern margin of the San Juan Basin. Mammalian biostratigraphic and magnetostratigraphic data constrain lower San Jose Formation deposition to the first ~3.5 Myr of the Eocene (magnetochrons C24r-C23r) during the early-middle Wasatchian North American Land Mammal Age. Negative carbon isotope excursions of -3.5‰ recorded in charcoal from lowermost San Jose Formation sandstones suggest a correlation with the PETM. Pollen data from the basal San Jose Formation units indicate that initial sandstone deposition was diachronous, however, and in some locations may have begun in the latest Paleocene, raising the possibility that the earliest fan progradation records a pre-onset precursor event identified in other basins.

Taken together, these data suggest that in the San Juan Basin the onset of the PETM was associated with immediate changes in precipitation patterns toward more frequent high-intensity events, driving the flooding and channel infilling that characterize fluvial fan progradation. Because channel migration during fan progradation was intermittent, basin infilling was spatially uneven and variable thicknesses of San Jose Formation rock record variable amounts of PETM time, depending on location. Future research will focus on stratigraphic correlation within the lower San Jose Formation, with the ultimate goal of characterizing PETM-driven sedimentologic, hydrological, and ecological change.

Keywords

PETM, chemostratigraphy, distributive fluvial systems

Hot before the hyperthermal? New terrestrial temperature constraints across the Late Paleocene–PETM transition

Allen, Matthew L.¹*; Wisniewski, Anna¹; Unruh-Friesen, Evan¹; Newman, Will¹; Passey, Benjamin H.¹

1. Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA

Correspondent author*: mattall@umich.edu

Abstract

The late Paleocene of the Bighorn Basin (Wyoming, USA) preserves one of the world’s most important terrestrial records of environmental and biotic change leading into the Paleocene-Eocene Thermal Maximum (PETM). Successions spanning the Tiffanian and Clarkforkian North American Land Mammal Ages (NALMAs) document major mammalian turnover events preceding the PETM and provide a critical archive for understanding long-term greenhouse climate evolution in continental interiors. Despite extensive paleontological and stratigraphic study in the basin, geochemical temperature reconstructions from the Tiffanian and early Clarkforkian remain comparatively limited. Existing carbonate clumped isotope records from the Bighorn Basin primarily focus on the PETM interval itself and younger early Eocene deposits, leaving late Paleocene climate conditions unexplored. Here we present new pedogenic carbonate clumped isotope data spanning the late Paleocene (Thanetian) and across the Paleocene-Eocene transition from stratigraphically constrained paleosol successions in the northern Bighorn Basin. Most reconstructed carbonate formation temperatures fall between ~20-40 °C and are broadly consistent with previous clumped isotope-based reconstructions of extreme summer warmth in the Bighorn Basin during the PETM and early Eocene (Snell et al., 2013; Havranek, 2023). Temperatures generally increase through the Clarkforkian and into the PETM interval, suggesting that substantial continental interior warming began prior to onset of the PETM carbon isotope excursion. In addition, several mid-Tiffanian samples yielded temperatures comparable to those observed during the PETM, implying that very warm continental conditions may have developed episodically well before peak PETM warming. Ongoing work is evaluating the extent to which reconstructed temperatures may reflect radiative heating effects, burial recrystallization, and/or solid-state isotopic reordering. Dual-clumped isotope measurements, replicate consistency, stratigraphic trends, and similarity to previously published early Eocene records from the Bighorn Basin suggest that many samples preserve primary environmental signals and are not strongly overprinted by secondary alteration. These findings provide important climatic context for late Paleocene mammalian turnover events in the Bighorn Basin and help constrain the timing and magnitude of terrestrial warming leading into the PETM. More broadly, the results suggest that continental interior environments in western North America may have been substantially warmer and more thermally variable during the late Paleocene than traditionally assumed.

Keywords

paleoclimate; PETM; paleotemperatures; Paleocene; Bighorn

Monsoonal extremes along the Tethys margin during the Paleocene-Eocene Thermal Maximum

Rush, William D.¹*; Crouse, Alexander S.¹

1. Department of Environmental Studies and Sciences, Santa Clara University, Santa Clara, CA, USA 95126

Correspondent author*: wrush@scu.edu

Abstract

The Paleocene–Eocene Thermal Maximum (PETM, ≈ 56 Ma) is argued to be the most rapid warming event prior to the modern day and provides a case study to explore how rapid increases in CO₂ can influence regional hydrology. Sedimentary records from the eastern Tethyan margins document abrupt lithologic changes across the Paleocene-Eocene boundary, which suggest hydrologic intensification on the margins of the Tethys Sea (modern-day region of northern India, southern China, Nepal, and Tibet). Using 25 km-resolution models incorporating both CO₂ and orbital forcing, we examined hydrologic changes along the boundaries of the Tethys. The study sites exhibit a distinct monsoonal climate despite the paleogeography of the late Paleocene differing dramatically from the modern day. CO₂ forcing primarily increases regional temperature and atmospheric moisture availability, whereas orbital maximum forcing more strongly reorganizes summer moisture convergence, low-level circulation and the seasonal distribution of rainfall. Rainfall intensification was spatially heterogeneous: orbital forcing generally enhances low-to-moderate and seasonal rainfall events, while elevated CO₂ becomes increasingly important for the highest intensity precipitation thresholds. The strongest storm responses commonly occur under combined CO₂ and orbital forcing, indicating that greenhouse moisture loading and orbital monsoon reorganization acted in tandem to intensify event-scale hydrology. Comparisons with lithologic records suggest that modeled changes in seasonal and extreme rainfall provide plausible mechanisms for increased runoff, sediment influx, carbonate platform disruption and terrigenous material delivery during the PETM. Together, these results indicate that PETM hydrologic intensification along the eastern Tethyan margin was produced by the interaction of greenhouse driven moisture loading and orbitally driven monsoon reorganization.

Keywords

monsoon, PETM, model-data, hydroclimate, sedimentology

Is the shape and duration of the PETM consistent with understanding of carbon cycle feedbacks?

Kirtland Turner, Sandra.¹*; Vervoort, Pam.²; Greene, Sarah E.²; Fantle, Matthew S.³; Waldeck, Anna R.³; Ridgwell, Andy.¹

1. Department of Earth and Planetary Sciences, University of California Riverside, Riverside, CA, USA; 2. School of Geography, Earth, and Environmental Science, University of Birmingham, Birmingham, UK; 3. Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania, USA

Correspondent author*: sandrakt@ucr.edu

Abstract

Improvements to cyclostratigraphic age models and correlation between terrestrial, shallow marine, and deep sea records has established a characteristic shape for the PETM d13C excursion. The PETM had an extremely abrupt onset, an extended ~100-kyr ‘body’ during which both d13C and deep sea sedimentary carbonate content remained suppressed, and a relatively rapid recovery in both d13C and deep sea carbonates. Multiple modeling strategies of varying degrees of complexity and comprehensiveness have been applied to simulate PETM carbon forcing and the resulting climate and environmental change. However, key discrepancies persist across models and data and in between various models, which likely reflects the significance of missing or incomplete feedbacks in models. In particular, the relative importance of inorganic and organic carbon burial feedbacks are significant in determining the duration of the ‘body’ and recovery phases of the PETM with respect to both d13C and the ocean carbonate system. However, experimental frameworks are lacking that incorporate mechanistic representation of both the silicate weathering feedback and geologic organic carbon cycle feedbacks relating to the weathering and burial of organic matter. Here we evaluate the differential impact of geologic inorganic and organic carbon cycle feedbacks on the shape of the PETM using the cGENIE Earth system model. We compare simulations including a temperature-dependent silicate weathering feedback against simulations including geologic organic carbon cycle feedbacks including productivity and oxygen sensitive burial of organic matter alongside the temperature sensitive weathering of kerogen. Our comparison indicates that the inclusion of geologic organic carbon feedbacks causes a much more rapid recovery of d13C and marine carbonate content compared to a silicate weathering feedback alone. Whether or not these feedbacks are considered has implications for reconstructions of carbon emissions required to explain the shape of the event.

Keywords

PETM, carbon cycle feedbacks, modeling

High-resolution sedimentary records imply biogeochemical, not volcanic, forcing of PETM mercury spike

Them II, Theodore R.¹*; Gong, Yanjie²; Meier, Clara¹; Sorrem, Natalie¹; Webster, Rachel¹; Bowen, Gabriel³; Foreman, Brady⁴; Self-Trail, Jean⁵; Wing, Scott L.⁶

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 Geology and Geophysics, University of Utah, Salt Lake City, USA; 4. Geology Department, Western Washington University, Bellingham, USA; 5. United States Geological Survey, Reston, USA; 6. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC, USA

Correspondent author*: themtr@charleston.edu

Abstract

The many hypothesized triggers of the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma), include extraterrestrial impact, submarine landslides, wildfires, methane production from wetlands, outgassing of methane from the oceans, volcanic activity, and a combination of several factors. In recent years, much focus has been placed on the possible role of the North Atlantic Igneous Province (NAIP), as its emplacement spans the PETM. The accumulation of mercury (Hg) in sediments has been identified as an important proxy to directly tie NAIP emplacement to global environmental change associated with the PETM. When volcanoes erupt, they inject Hg into the atmosphere, which can then be manifested as sedimentary Hg enrichments. Although this proxy has been used to confidently link NAIP emplacement to the PETM, other known processes can also yield sedimentary Hg enrichments. Currently, no high-resolution records of Hg accumulation from North America, where some of the best sedimentary archives of the PETM are found, exist. Here, we present new Hg accumulation data from both marine and terrestrial PETM deposits in North America, including the Atlantic Coastal Plain (ACP) and the North American Interior (NAI).

We examined several ACP drill cores recovered from Maryland and New Jersey that contain the PETM; they display synchronous, rapid, and transient sedimentary Hg enrichments in the basal Eocene Marlboro Clay. Mercury isotope data from these proximal marine sites indicate a terrestrial source of Hg to the ACP during the PETM interval. We also studied PETM outcrop locations from the NAI (Bighorn Basin, Hanna Basin, Piceance Creek Basin) to better understand Hg cycling in the terrestrial realm. Each NAI record is unique and does not display the expected sedimentary Hg enrichments if the NAIP was the dominant supplier of Hg to the atmosphere during the PETM. Based on our combined high-resolution records of Hg accumulation during the PETM, we find that the NAIP did not likely directly drive the observed sedimentary Hg enrichments. We posit that observed sedimentary Hg enrichments are instead driven by biogeochemical feedbacks to environmental change during the PETM.

Keywords

climate change; volcanism; extinction

A Pythonesque perspective of early Paleogene carbon cycling

Dickens, Gerald R.¹*

1. Trinity College Dublin, Discipline of Geology, Dublin, Ireland

Correspondent author*: dickensg@tcd.ie

Abstract

Stable carbon isotope (d13C) records, which were constructed from a variety of carbon-bearing substrates, show long-term (>1 Myr) trends and short-term (<100 kyr) aberrations in the Earth's exogenic carbon cycle. These relate to past variations in organic carbon fluxes to and from the ocean and atmosphere, but specific sources and causes remain enigmatic and debated. This has become particularly true for the early Paleogene (60 to 48 Ma) where negative d13C excursions of the PETM and other hyperthermal events are superimposed on the most prominent long-term d13C excursion in the last 80 Myr. In response to publications that divorce the PETM from surrounding time and suggest catastrophic carbon masses across this event, I present a Pythonesque view of the global carbon cycle. Following work from 25 years ago, a large and dynamic seafloor methane capacitor links to the exogenic carbon cycle. Here, though, some recent findings are incorporated, such as reverse weathering and return of d13C-rich carbon to the ocean during methane storage, and all is coded in Python so changes in the time domain can be assessed. Key findings for the early Paleogene interval include:

-- Long term d13C changes represent changes in seafloor methane storage.

-- The maximum storage occurred at about 56 Ma.

-- The minimum storage represents the Early Eocene Climatic Optimum.

-- Hyperthermal events depend on external forcing and the size of the capacitor.

-- Successive inputs of carbon affect each other and sequential d13C excursions.

-- Rapid recoveries of d13C arise from lower seafloor methane fluxes (recharge effect).

In principle, the Python capacitor can be connected to ocean models to arrive at good explanations for carbon cycling during the early Paleogene and other times.

Keywords

PETM; Paleocene; carbon cycling; gas hydrates

Southern Ocean CO₂ release during the Early Eocene Climate Optimum

Moretti, Simone¹*;  Fripiat, François²; Hain, Mathis³; Luciani, Valeria⁴; Lourens, Lucas⁵; Borucki, Paul⁶; Gerber, Lukas⁷; Agterhuis, Tobias⁵; Haynes, Laura⁸; Filippi Giulia⁴; Schiebel, Ralf¹; Haug, Gerald¹,⁹; Sigman, Daniel¹⁰; Martínez-García, Alfredo¹

1. MPIC Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany; 2. ULB Department Geosciences, Environment and Society, Université libre de Bruxelles, Brussels, Belgium; 3. EPS UCSC Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, United States; 4. UNIFE Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Ferrara, Italy; 5. UU Department of Earth Sciences, Utrecht University, Utrecht, Netherlands; 6. JGU Institut für Geowissenschaften, Johannes Gutenberg University, Mainz, Germany; 7. GEOW Institut für Geowissenschaften, University of Heidelberg, Heidelberg, Germany; 8. Department of Earth Science and Geography, Vassar College, Poughkeepsie, United States; 9. ETH Department of Earth Sciences, ETH Zurich, Zurich, Switzerland; 10. Department of Geosciences, Princeton University, Princeton, United States

Correspondent author*: simone.moretti@mpic.de

Abstract

During the Early Eocene Climatic Optimum (EECO) global temperatures and atmospheric CO₂ reached the heighest levels of the Cenozoic. Multiple carbon sources have been proposed to explain the EECO, but its origin is still not completely understood. The Southern Ocean, known to regulate atmospheric CO₂ during Quaternary glacial-interglacial cycles, may have exerted a similar influence much earlier in Earth history, but its role on million-year timescales remains poorly constrained.

Here we present foraminifera-bound nitrogen isotope records from four well-dated Ocean Drilling Program sites in the Atlantic and Indian sectors of the Southern Ocean spanning the EECO. The nitrogen isotope data indicate reduced nitrate consumption, and therefore increased surface nutrient availability, during peak warmth. Independent evidence suggests that the Southern Ocean already hosted major deep-water formation in the Paleogene; thus, higher preformed nutrient concentrations in this ventilating region imply a globally weaker biological pump.

This warming-driven reduction in biological pump efficiency, promoting CO₂ release to the atmosphere, mirrors the known Southern Ocean response observed during more recent glacial-interglacial cycles. The similarity across vastly different boundary conditions points to a persistent feedback linking Southern Ocean nutrient utilization and atmospheric CO₂ across a wide range of temporal timescales. The associated venting of CO₂ from the deep ocean to the atmosphere would have been amplified by the lower seawater pH buffering capacity of the Eocene. The low silicate rock weatherability during the Eocene may have weakened the “weathering thermostat”, allowing the reconstructed change in Southern Ocean biological pump efficiency to explain as much as 800ppm of the EECO atmospheric CO₂ increase.

Our results highlight the previously underexplored importance of the Southern Ocean in regulating the carbon cycle over million-year timescales and provide new insight into the origin and maintenance of the warmest climate state of the Cenozoic.

Keywords

Southern Ocean, Eocene, Nitrogen Isotopes

Latitudinal dependence of stability trends in Cenozoic marine plankton

Morrison, Maike L.¹*; Woodhouse, Adam²,³; Swain, Anshuman⁴,⁵

1. Santa Fe Institute, Santa Fe, New Mexico, USA; 2. School of Earth and Environmental Sciences, Cardiff University, Cardiff, UK; 3. School of Environment, Earth and Ecosystem Sciences, Open University, Milton Keynes, UK; 4. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA; 5. Museum of Paleontology, University of Michigan, Ann Arbor, Michigan, USA

Correspondent author*: answain@umich.edu

Abstract

The temporal stability and spatial heterogeneity of ecological communities are fundamental to their function and resilience, yet their deep-time evolution remains poorly understood. We reconstruct the stability landscape of Cenozoic planktonic foraminifera (66–0 Ma) using FAVA (FST-based Assessment of Variability across Abundances), which quantifies compositional variability across communities. Applied temporally, FAVA measures stability; applied spatially, it measures beta diversity.

Globally, planktonic foraminiferal communities exhibit a U-shaped trajectory of temporal instability: elevated instability characterizes post-K/Pg recovery and the late Neogene bipolar icehouse, with a stable interval spanning the Eocene through Miocene. Comparing FAVA across taxonomic (species), ecological (ecogroup), and morphological (morphogroup) classifications distinguishes functional redundancy from morphological or ecological disparity. Morphological disparity recurs at major climatic transitions—the PETM (~56 Ma), Late Eocene (~38 Ma), and early Miocene (~20.5 Ma)—underscoring morphogroup sensitivity to environmental forcing.

Spatially resolved analyses reveal that the global U-shaped signal masks a strong latitudinal divergence. Tropical communities were most unstable following the K/Pg extinction but have stabilized progressively. High-latitude communities, particularly in the Southern Ocean, show the opposite trajectory. Stability trajectories follow a robust quadratic relationship with paleolatitude and correlate significantly with paleotemperature proxies (δ¹⁸O: R = −0.74 for ecogroups, P < 0.001; SST: R = −0.60, P < 0.01), consistent with Cenozoic steepening of latitudinal temperature gradients.

Spatial FAVA reveals a complementary reorganization of beta diversity. Early Cenozoic tropical regions showed the highest spatial heterogeneity, reflecting patchy post-extinction recovery. By the late Neogene, this inverted: equatorial communities homogenized while polar communities, especially in the Southern Ocean, became increasingly heterogeneous. The past 30 million years exhibit a ""latitudinal seesaw""—high southern heterogeneity in the early Oligocene, a northern peak from ~15–10 Ma, and poleward volatility in the modern icehouse—consistent with asynchronous hemispheric cooling.

These findings demonstrate that modern tropical pelagic stability is a geologically recent phenomenon, while polar volatility reflects the late Neogene bipolar cryosphere transition. This deep-time framework illuminates how future warming may reverse 60 million years of tropical stabilization.

Keywords

planktonic foraminifera; community stability; paleotemperature

Morphological disparity and ecological resilience in Coccolithus across the Early Eocene Climatic Optimum

Asanbe, Joseph D.¹*; Henderiks, Jorijntje¹

1. Department of Earth Sciences, Uppsala University, Uppsala, Sweden

Correspondent author*: joseph.asanbe@geo.uu.se

Abstract

The Early Eocene Climatic Optimum (EECO; ~53–49 Ma) represents the warmest sustained interval of extreme greenhouse conditions in the Cenozoic and was associated with major reorganisations in marine phytoplankton communities. Calcareous nannoplankton turnover during this interval is well documented globally, but the most pronounced assemblage restructuring occurred in tropical settings. Yet, the impact of the prevailing environmental conditions on phenotypic variation and natural selection remains poorly constrained. The coccolithophore genus Coccolithus provides a valuable case study because, despite major tropical assemblage turnover across the EECO, this taxon remained consistently common throughout the EECO and subsequent cooling interval, suggesting ecological resilience during extreme warmth.

Here, we quantify intrageneric morphological variability by combining species-level assemblage counts with coccolith biometry in deep-sea sediment samples from ODP Site 1258 (Demerara Rise, equatorial Atlantic). This dataset provides an opportunity to better understand the adaptation and resilience of the Coccolithus lineage during the early Eocene. Our results reveal the highest morphological disparity during the EECO, characterised by a range of coccolith sizes and morphologies, including small forms with relatively wide central openings (such as C. latus). In contrast, the post-EECO cooling phase is marked by a reduction in disparity, with a shift toward larger coccoliths with narrower central openings mainly represented by C. pelagicus and C. formosus. This reduction in morphological diversity points to stronger environmental selection in the post-EECO cooling phase. Overall, these patterns indicate long-term community shifts in mean cell size, functional morphologies and associated physiological strategies under prolonged greenhouse conditions. Building on this, ongoing work explores how these patterns scale to broader phytoplankton communities using biogeochemical and plankton ecosystem modelling such as cGENIE and EcoGEnIE. Specifically, we aim to test how contrasting early Eocene Ocean states of strong stratification versus deeper mixed-layer conditions shaped phytoplankton size structure and community evenness. Model outputs will then be compared with observed morphological disparity in fossil coccoliths.

Keywords

Coccolithus, early Eocene, morphological selection

Warm deep ocean temperatures from clumped isotopes suggest high climate sensitivity in early Cenozoic hothouse

Agterhuis, Tobias¹,ᵃ*; Ziegler, Martin¹; Oerlemans, Brendan¹,ᵇ; Ke, Sai¹,ᶜ; Koene, Bastiaan L. P.¹; de Vries, Lea¹,ᵈ; Kersten, Meya¹; Posthuma, Sanne¹; Roozendaal, Anne¹; Lourens, Lucas J.¹

1. Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, the Netherlands; a. Now at: School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, United Kingdom; b. Now at: Department of Earth Sciences, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands; c. Now at: Sorbonne Université, CNRS, EPHE, PSL, UMR METIS, Paris, France; d. Now at: Aeres University of Applied Sciences, Almere, the Netherlands

Correspondent author*: t.agterhuis@uu.nl

Abstract

The early Cenozoic was characterized by the warmest climates and highest atmospheric CO₂ levels of the past 85 Myrs. Reconstructions of deep ocean temperatures based on benthic foraminiferal oxygen isotope records are typically used to infer Earth’s global climate state during this hothouse world. However, this approach relies on uncertain assumptions about seawater isotope composition and species-specific vital effects. Here we use clumped isotope thermometry, a proxy not complicated by these non-thermal influences, to reconstruct early Cenozoic deep ocean temperatures on million-year timescales from the South Atlantic Ocean. Our measurements indicate systematically warmer temperatures than previously inferred from oxygen isotopes, consistent with clumped isotope reconstructions from the North Atlantic. This finding challenges the prevailing understanding of seawater isotope composition in an ice-free world and invokes potential pH effects on benthic oxygen isotopes. Deep ocean temperatures peaked at ~19 °C during the Early Eocene Climatic Optimum, more than 5 °C warmer than previous estimates. This implies a substantially higher climate sensitivity to pCO₂ forcing in these past warm climates (6–8 °C) than currently used in climate models that simulate future warming scenarios of the IPCC (2.5 to 4.0 °C).

Keywords

EECO; Δ47; deep ocean temperature

Strong climate control on Eocene benthic foraminiferal assemblages

Arreguín-Rodríguez, Gabriela J.¹,²,³*; Alvarado-Graef, Patricia³; Thomas, Ellen⁴,⁵; Fernández-Díaz, Violeta Z.³; Alegret, Laia¹,²

1. Departamento de Ciencias de la Tierra, Universidad de Zaragoza, Spain; 2. Instituto Universitario de Ciencias Ambientales de Aragón, Universidad de Zaragoza, Spain; 3. Facultad de Ciencias Marinas, Universidad Autónoma de Baja California, Mexico; 4. Department of Earth and Planetary Sciences, Yale University, USA; 5. Department of Earth and Environmental Sciences, Wesleyan University, USA

Correspondent author*: garreguin@unizar.es

Abstract

The gradual Paleogene transition from a global greenhouse to an icehouse world was punctuated by superimposed short-term rapid warming events. Global climate variability impacted deep-sea ecosystems, as evidenced by benthic foraminiferal faunas. Here we re-assess the effect of Eocene climate changes on faunas by calculating the accumulated heterogeneity (Haccum), and identifying biofacies in deep-sea benthic foraminiferal assemblages from Ocean Drilling Program Site 1263 (SE Atlantic). The studied intervals include geologically rapid warming events, including the Paleocene-Eocene Thermal Maximum (PETM), Eocene Thermal Maximum-2 (ETM2) and Eocene Thermal Maximum-3 (ETM3), as well as the Middle Eocene Climatic Optimum (MECO), the Ypresian-Lutetian boundary, and gradual cooling across the Eocene-Oligocene Transition (EOT). 

We recognize an abrupt change in biofacies at the beginning of the PETM, the most extreme, short-term warming event, in accordance with the Benthic Foraminiferal Extinction. The “PETM biofacies” extends above the event interval, indicating that conditions remained unfavourable for the deep-sea benthos for ~70 kyr (and/or recovery was very slow) after the end of the PETM. In contrast, during ETM2, there were multiple shifting biofacies. These reiterated changes suggest highly perturbed and unstable environmental conditions, but insufficient to cause a drastic drop in Haccum. Other events show a minor, negative impact on benthic foraminiferal assemblages. Across ETM3, two biofacies were recognized: the first indicates a slight decrease in Haccum, the second, starting at the middle of the event, an increasing trend in Haccum. This pattern is repeated during the MECO, with an enhanced decreasing trend in Haccum at the base of the event. Biofacies across the Ypresian-Lutetian boundary point to optimum environmental conditions towards and after the Early Eocene Climatic Optimum (EECO). However, a marked change in biofacies occurred across the EOT, reflecting a turnover in the Haccum trend, from increasing values during the late Eocene to decreasing ones into the Oligocene. 

These results allow us to identify patterns which are not always visible in the “simple heterogeneity”, i.e., heterogeneity calculated separately for each sample. By assessing Haccum, we identified a significant, strong correlation with benthic foraminiferal stable isotope values (δ¹³C and δ¹⁸O), not only across rapid warming events (hyperthermals) but also through more gradual climate changes (e.g., EECO and EOT), across which there is no significant correlation when looking at simple heterogeneity. Therefore, our findings suggest a stronger influence than previously documented of climate conditions on benthic foraminiferal assemblages on a variety of timescales, improving our understanding of the impact of Paleogene climate variability on deep-sea ecosystems.

Keywords

Eocene; hyperthermals; climate variability; foraminifera.

Machine learning for the detection of microfossils from the Late Paleocene and Early Eocene in North America: Exploring the full potential of palynology

Romero, Ingrid C.¹,²*; Barman, Arko.³; Shaikh, Abbas.³; Golden, Teon.³; Viswanathan, Aditya.³; Mayor, Praise.³; Ainlay-Vazquez, Patrick.³; Zhang, Eric.³; Yu, Tony.³; White, A.E.4 ; Rajakumar, Sanjeev.³; Vinay, Samhita.³; Nguyen, Anna.³;Diaz, Katelanny.³; Wing, Scott L.¹;  Shaw, Chad.³; Jaramillo, Carlos.²; Korasidis, Vera A.⁵; Punyasena, Surangi W.6

1. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution. Washington DC. USA; 2. Smithsonian Tropical Research Institute. Panama. Panama; 3. Data to Knowledge Lab, Rice University. Houston, TX. USA; 4. Smithsonian Office of Digital and Innovation, Washington, DC 20024, USA; 5. School of Geography, Earth and Atmospheric Sciences, University of Melbourne. Melbourne, Australia; 6. Department of Plant Biology. University of Illinois Urbana-Champaign. Urbana, IL. USA

Correspondent author*: incaromero@gmail.com

Abstract

The Paleocene-Eocene interval (60-49 Ma) is an excellent time period to study greenhouse climate because it includes examples of a relatively cool greenhouse climate (Mid to Late-Paleocene), the warmest period of the Cenozoic (Early Eocene Climatic Optimum or EECO), and short-lived hyperthermal events like the PETM and ETM2. Previous palaeobotanical studies suggest that plant ranges moved across North America in response to both long-term and short-term global warming, with thermophilic plants extending ranges northward during warming phases and retreating southward during cooling. Most of these studies, however, have used information from very few sites. Palynology has the potential to provide the most temporally continuous and geographically extensive record of terrestrial vegetation, but pollen identification is time-consuming, and palynological expertise is a scarce resource. 

Automatized methods have shown the potential to speed the workflow of palynological analyses by increasing the efficiency of pollen detection and classification, thus substantially increasing the data that can be collected. To have a better understanding of climate distribution across North America, we are comparing geographic patterns of floral composition between the Paleocene cool greenhouse (60- 56 Ma) and the EECO hot greenhouse (53-49 Ma). Our research relies on an extensive palynological sample set that is part of the US Geological Survey (USGS) Denver palynological collection (DPC). 

We are using a combination of two methods: a digital pathology slide scanning microscope, which allows the imaging of complete microscope palynological samples at more than 20 axial focal planes to capture the three-dimensional data from the whole samples; and machine learning models to detect the palynomorphs, including pollen, spores, fungi, dinoflagellates, and freshwater algae. We are developing a continental-scale proxy data set of palynofloral composition for which taxonomic categories have been standardized. The results of this study will be used to test paleoclimate simulations for the Paleocene and Eocene of North America from the Community Earth System model (CESM1.3).

Keywords

automatization; palynomorphs; Paleogene; digitization

The Paleogene and Neogene skeletal record of marine fishes in the Indo-West Pacific: implications for biogeographic hypotheses

Saad, Hadeel¹,²*; Sanaa, El-Sayed¹,²,³; Friedman, Matt¹,²

1. Department of Earth and Environmental Sciences, University of Michigan; Ann Arbor, Michigan, 48109-1079, USA; 2. Museum of Paleontology, University of Michigan; Ann Arbor, Michigan, 48109-1079, USA; 3. Mansoura University Vertebrate Paleontology Center (MUVP), Mansoura University; Mansoura, 35516, Egypt

Correspondent author*: hhsaad@umich.edu

Abstract

Biologists have long grappled with how marine groups dispersed into the Indo-Australian Archipelago (IAA) and why the highest concentration of marine species occurs in the broader Indo-West Pacific (IWP). This enduring problem in tropical marine biogeography lies at the center of efforts to explain not only how organisms reached the IAA, but also how subsequent diversification–and extinctions in other regions–produced the pattern of marine biodiversity recognized today. For many invertebrate groups, paleontological data support models of “hopping hotspots,” yet no comparable large-scale fossil research exists for marine fishes. It is widely assumed that  fishes followed the same biogeographic trajectories as invertebrates, especially reef-building corals. However, recent studies show that associations between reef-associated fishes and reefs are weaker than generally thought, and many “reef” fish lineages contain substantial proportions of species inhabiting non-reefal environments. Available molecular phylogenies suggest historical biogeographic patterns broadly mirroring those of invertebrates, with arrivals into the IAA during the Oligocene or Miocene and elevated diversification rates in lineages exploiting non-open-marine habitats. These tests, however, incorporate few fossil constraints, leading to an incomplete picture. Thus a major limitation in reconstructing the rise of the IWP region is the lack of any broad overview of Cenozoic tropical marine fossil fish faunas, either within the IWP or globally. Consequently, researchers working on extant tropical marine fishes rely disproportionately on the Eocene locality of Bolca, Italy, as a key source of data. This reliance has further ingrained a European perspective in discussions of  IWP marine biodiversity origins, despite the well-known spatial bias of the fossil record toward Europe and North America. Here, we review the fish skeletal fossil record of the IWP from the Paleogene to the Neogene (~66–2.6 Ma), drawing on a combination of museum collections, published data, and new fossils. Although the skeletal record is too patchily distributed to test the predictions of hotspot migration, we were able to quantitatively compare faunas to examine the relative paleoenvironmental, paleogeographic, and stratigraphic controls on ancient fish communities in and around the IWP. In aggregate, this survey considers 29 distinct localities with a total of ~250 teleost taxa represented by skeletal fossils, in many cases representing whole or partial fishes. Work to date suggests the early distinction between near- and offshore fish communities by the Eocene, with the establishment of assemblages similar to those found in nearshore settings in today’s modern IWP by the early Neogene.

Keywords

Tropical Marine Fishes, Cenozoic fishes

Early Eocene pollen and macrofossils from the Ghazij Formation, Balochistan, Pakistan: a test of long-standing biogeographic hypotheses

Spagnuolo, Edward J.¹*; Shaw, David²; Wilf, Peter¹; Przybylski, P. J.¹; Giraldo, L. Alejandro¹; ul-Haq, Munir³; Wing, Scott L.⁴; Clyde⁵, William C.; Korasidis, Vera A.⁴,⁶

1. Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania, 16802, USA; 2. Biostratigraphic Associates (UK) Ltd., Stoke-on-Trent, ST6 8NE, UK; 3. Geological Survey of Pakistan, Islamabad, Pakistan; 4. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC, 20560, USA; 5. Department of Earth Sciences, University of New Hampshire, Durham, New Hampshire, 03824, USA; 6. School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Parkville, Victoria, 3010, Australia.

Correspondent author*: spagnuolo@psu.edu

Abstract

The Eocene collision of the Indo-Pakistan tectonic plate into Asia and resulting biotic exchanges contributed to the immense biodiversity of Southeast Asia. However, pollen and macrofossil data with robust age constraints from pre-interchange Indo-Pakistan are rare, limiting constraints for testing these hypotheses. Previously, mammal assemblages from the early Eocene (ca. 54–50 Ma) Ghazij Formation in Balochistan, Pakistan showed an into-India dispersal pattern. Here, we present a preliminary report on the first plant macrofossils (primarily leaf compressions), insect damage, and palynofloras from the same well-constrained strata of the Ghazij Formation that produced the mammal fossils. The 39 palynological samples were collected from the lower, middle, and upper Ghazij. The macrofossils (15 sites, ca. 420 specimens) are nearly all from the upper Ghazij. The palynofloras indicate an environmental transition from coastal marine settings (lower Ghazij), to freshwater and coastal palm swamps (middle Ghazij), and to increasingly terrestrial ecosystems that retained marine influence (upper Ghazij). Diverse dinocysts reaffirm the early Eocene age. We found palynomorphs typical of modern SE Asian forests in the lower and middle Ghazij, including Podocarpus, Dacrydium, Casuarinaceae, Nypa, Barringtonia, Euphorbiaceae, Fabaceae, Meliaceae, Moraceae, Dipterocarpaceae, and Alangium. Additional pollen taxa from the upper Ghazij include Croton, Malvaceae, Polygonaceae, and Onagraceae. The macroflora is dominated by Pometia-like Sapindaceae leaflets and multiple Fabaceae and Arecaceae morphotypes. Rarer morphotypes include possible Menispermaceae, Rhamnaceae, Calophyllum, and Araceae, and the ferns Acrostichum and Salvinia, also preserved as spores. Insect-feeding damage is diverse and abundant, totaling 42 damage types—some of the highest richness of insect herbivory in the fossil record, when adjusted for sample size using rarefaction. Our key finding is the presence of many significant extant Asian taxa as palynomorphs in the lower and middle Ghazij Formation, from the same strata that showed limited mammalian interchange with Asia. This is consistent with established hypotheses that these plant taxa were present in Indo-Pakistan before the main phases of India-Asia interchange, and our review of the published tropical Asian pollen record suggests that many of the tree lineages found in the Ghazij Formation were present elsewhere on the subcontinent before or during the India-Asia collision. However, the limited pre-collision deposits in other areas of South and Southeast Asia are too sparse to entirely rule out their prior presence on the mainland. The abundant, well-preserved, and stratigraphically constrained macrofossil and microfossil records from the early Eocene Ghazij Formation highlight its importance as a benchmark for biogeographic and paleontological studies of the Asian tropics.

Keywords

pollen; leaves; Eocene; India-Asia; biogeography

More equable past and future warm climates in unprecedented high-resolution simulations

Zhu, Jiang¹*; Otto-Bliesner, Bette L.¹; Tierney, Jessica E.²; Brady, Esther C.¹; Simpson, Isla R.¹; Bonan, David B.³; Lunt, Daniel J.⁴

1. NSF National Center for Atmospheric Research, Boulder, CO, USA; 2. Department of Geosciences, The University of Arizona, Tucson, AZ, USA; 3. Department of Atmospheric and Climate Science, University of Washington, WA, USA; 4. School of Geographical Sciences, University of Bristol, Bristol, UK.

Correspondent author*: jiangzhu@ucar.edu

Abstract

Understanding Earth’s past warm climates is crucial for improving climate modeling and future projections. We revisit the early Eocene "Equable Climate Problem", the longstanding mismatch between proxy-inferred weak meridional and seasonal temperature contrasts at ~50 Ma and the steeper gradients simulated by climate models, using one of the first fully coupled, high-resolution (HR) Eocene simulations. Our simulation employs ~10x finer spatial resolution in both the atmosphere and ocean than conventional low-resolution (LR) models at ~1–2°. The HR simulation produces a more equable Eocene climate, with over 5℃ warmer temperatures in continental interiors during winter and oceanic western boundary current regions. These temperatures align closer with paleoclimate proxies, reducing the model-proxy discrepancy by ~20–30% relative to LR simulations. The improvements arise from stronger wintertime atmospheric synoptic- and mesoscale storminess at high latitudes, enhancing atmospheric heat transport and downward cloud longwave radiation, along with differences in oceanic eddy heat transport. Parallel HR simulations of future climate change similarly show additional regional and seasonal warming relative to LR. These findings indicate that traditional LR models may systematically underestimate extreme warming in past and future warm climates, underscoring the need for HR simulations in climate research and projections.

Keywords

Eocene climate; high-resolution modeling

Sensitivity of simulated atmospheric rivers to model resolution and atmospheric CO₂ during the early Eocene

Macarewich, Sophia¹*;  Otto-Bliesner, Bette¹; Zhu, Jiang¹; Esther Brady¹; Lora, Juan²

1. Climate and Global Dynamics Laboratory, NSF National Center for Atmospheric Research, Boulder, USA; 2. Department of Earth and Planetary Sciences, Yale University, New Haven, USA

Correspondent author*: macarew@ucar.edu

Abstract

Geologic evidence indicates intense flooding and enhanced hydrologic cycling during the early Eocene, likely driven by atmospheric rivers (ARs) in the extratropics. However, understanding paleo-ARs has been limited by the coarse resolution and/or atmosphere-only configuration of previous simulations. Recent work shows that low-resolution models severely underestimate AR strength and precipitation, while higher resolution improves representation of integrated vapor transport and orographic effects. Here we present high- and low-resolution Community Earth System Model (CESM1.3) simulations of the early Eocene (~56 Ma) with 857 and 1,714 ppm CO₂, including water isotopes, to isolate the impacts of grid resolution and atmospheric CO₂ on simulated AR activity. Our high-resolution coupled configuration (~0.25° atmosphere/land, ~0.1° ocean) reveals that both elevated CO₂ and higher resolution enhance global AR activity. Notably, intensified ARs drive extreme precipitation increases over western Australia, Iberia, and northwestern North America. We also assess sensitivity to AR detection methodology, finding substantial uncertainty in AR characteristics and precipitation impacts, highlighting detection method as a critical source of uncertainty in paleo-AR studies.

Keywords

Eocene, atmospheric rivers, climate model

The Austral Antarctic Forest during the Early Eocene Climatic Optimum – biogeography, diversity, ecology, and the fate of polar lineages.

Slodownik, Miriam¹*; McElwain, Jennifer¹; Hill, Robert S.²

1. Trinity College Dublin, Dublin, Ireland; 2. Department of Ecology and Evolution, University of Adelaide, Adelaide SA 5005 Australia

Correspondent author*: miriam.slodownik@tcd.ie

Abstract

The Early Eocene Climatic Optimum (EECO; c.53–49 Ma) is one of Earth’s hottest times marked by high global temperatures that allowed tropical-like forests to extend beyond the polar circles. These polar forests are ecosystems without modern equivalent, thriving under vastly different light environments than today’s tropical forests.

The fossil plant assemblage of the Macquarie Harbour Formation (MHF) in Tasmania, southeastern Australia, offers a unique window into this extinct biome. Situated at polar palaeolatitudes (65–70°S), and dating back approximately 53–50 Ma to the EECO, it represents one of the oldest post-Cretaceous plant assemblages in Australia. During this time, Tasmania, represented the last landbridge between Australia and Antarctica, thus it is important for understanding the biogeographic patterns in the Southern Hemisphere and the ecology of polar forests.

We present new data from a near-polar forest, including systematics, diversity, and adaptations to the high latitudes. Furthermore, we revealed taxon- and ecosystem-scale biogeographic patterns across the Southern Hemisphere.

Intriguingly, many lineages present at the fossil site survive today only as relicts with limited populations in Australasia (especially tropical Oceania) and South America (primarily the Neotropics), where they are often restricted to high-altitude and/or humid habitats. The presence of these lineages in the early Eocene assemblages of South America and Australia, as well as the Paleocene of Antarctica, demonstrates the continuous extent of the Austral Antarctic Forest, thus favouring the vicariance hypothesis for many taxa that are today shared between these land masses.

Furthermore, the assemblage contains extinct lineages, Mesozoic relicts, such as Araucarioides and Komlopteris, that appear to have had a Gondwana-wide distribution. We correlate their extinction with the northward continental migration, and the rise of the Andes in South America, which led to significant aridification, changes in insolation and an increased competition with angiosperms.

Keywords

Palaeobotany, Palaeoforest, Greenhouse Climate, South

Paleogene reptiles of North America demonstrate body size – climate correlations over deep time intervals

ElShafie, Sara J.¹*

1. UC Museum of Paleontology, University of California, Berkeley, USA; Milken Institute, Washington, DC, USA

Correspondent author*: selshafie@berkeley.edu

Abstract

Extant reptiles are particularly susceptible to changes in temperature and precipitation. But this relationship is poorly understood over geologic time spans. Metabolic theory for ectothermic vertebrates predicts that maximum body size should correlate with environmental temperature over ecological time scales. To test this theory on an evolutionary time scale, the Paleogene record of the North American Interior is an ideal study system given its rich, nearly continuous fossil record and abundance of paleoclimate proxy data. Here, I hypothesize that maximum snout-vent length (SVL) in two higher order reptile groups occupying different habitats—terrestrial lizards and semiaquatic crocodyliforms—tracks both temperature and precipitation over deep time intervals, and that these patterns emerge across both regional and local geographic scales. 

I measured 283 lizard and 280 crocodyliform fossil specimens from intermontane basins across the Western Interior of North America through the warming, cooling and aridification events of the Paleogene (66-23 Mya). I used extant regressions to reconstruct body size from isolated cranial or limb bones for both groups. I also collected over 100 estimates each for mean annual paleotemperature (MAPT) and paleoprecipitation (MAPP) from literature and tested for correlation between these variables and maximum SVL in lizards and crocodyliforms.

My results indicate that during the warmest interval in the early Eocene, maximum lizard SVL (about 1 meter) had a modest positive correlation with paleotemperatures averaged across the Western Interior. The limited intrabasinal sample sizes available reflect the same relationship. In contrast to the lizards, maximum crocodyliform SVL (about 2 meters) was consistently high across the intermontane basins through the Paleogene and indicated a strong linear relationship to paleoprecipitation rather than temperature. Large-bodied crocodyliforms were most abundant in localities that hosted large bodies of water at the time of deposition. Maximum body size and diversity decreased for both lizards and crocodyliforms in the early Oligocene, when the Western Interior experienced cooling and aridification. Neontological studies of lizard and crocodylian ecology and physiology corroborate these paleontological observations. These results offer new evidence that climate variables affect body size in ectothermic reptiles on evolutionary time scales, which deepens our understanding of these dynamics on ecological time scales.

Keywords

Reptiles, climate, body size, America

Foraminiferal-Algal Assemblage and Palaeoenvironmental Reconstruction of Early Eocene Umlatodoh Limestone Form South Shillong Shelf: Signature of ETM2?

Haokip T. N.¹*, Sarkar U.²

1. Department geology, Rajiv Gandhi University, Rono Hills, AP, India; 2. Department of Earth Science, Indian Institute of Engineering Science and Technology (IIEST), Shibpur, WB, India

Correspondent author*: tngamlengin.haokip@gmail.com

Abstract

Microfacies analysis of Early Eocene shallow-marine carbonate successions are sampled from the outcrop of Thangskai, Jaintia Hills, Meghalaya, India and the subsequent integration with sedimentology has been used to produce a detailed palaeoenvironmental reconstruction.  From the forty-one meters high outcrop, nine microfacies types, viz., quartz abundant wackestone (U-MFT1), rotaliid grainstone (U-MFT2), sandy foraminiferal packstone (U-MFT3), Oolitic grainstone (U-MFT4), fossiliferous dolomitic grainstone (U-MFT5), Ovulites grainstone (U-MFT6), alveolinid miliolid grainstone (U-MFT7), fossiliferous wackestone (U-MFT8), and glauconitic mudstone (MFT9), are identified. Larger benthic foraminiferal and coralline algal assemblages are the dominating constituents here and larger benthic foraminifera indicates the age as SBZ 6 to SBZ 9. Four facies belts have been inferred associated with specific facies, for example, the facies U-MFT1, U-MFT3, U-MFT8, and U-MFT9 are located in the sheltered lagoon (SL); U-MFT4 indicate the facies belt shoal setting (SS); U-MFT2, U-MFT6, U-MFT7 indicate deposition in the high-energy back shoal (BS); and U-MFT5 is designated to be deposited in the fore shoal (FS). Overall, two types of faunal associations are identified: perforate foraminifera (Nummulites sp. and Discocyclina sp.) and porcelaneous forams and green algae (Rotaliid-Alveolinid-Miliolid-Ovulites-Halimeda). The faunas are dominated by both r- and k-strategists in an oligotrophic nutrient regime during this time. Dominant foraminiferal species are Alveolina sp., Glomalveolina sp., Quinqueloculina sp., Biloculina sp., Idalina sp., Periloculina sp., Lockhartia sp., Nummulites sp., Orbitoclypeus sp., Discocyclina sp., Bolivina sp., and Textularia sp. Subordinate constituents of bivalve and ostracods are observed. The algal components include Ovulites sp., Halimeda sp., and Dasycladalean (Salpingoporella sp.) represent green algae, and Distichoplax sp. represent the non-geniculate coralline-red algae. Also, sutured type horizontal and parallel stylolite present in the MFT8 indicates the upper part is subjected to dissolution, and underwent tectonic stress during diagenesis.  Thus, variable energy above the fair-weather wave base influences the depositional architecture of the Umlatodoh Limestone Member, which ranges from hypersaline lagoonal to normal marine within the inner shelf of shallow marine carbonate settings. Concurrently, the foraminiferal diversity and subsidiary abundance of rectilinear benthic foraminifera (biserial forams) and the majority of the stunted larger benthic foraminifera may indicate the stress that can be correlated with the transient climatic Eocene Thermal Maximum -2 (ETM -2) (SBZ 8; 54.1 Ma) event.

Keywords

Early-Eocene; Neo-Tethys; Umlatodoh Limestone; ETM-2; Larger Benthic Foraminifera

The Bartonian: A time of transition for cetaceans

Uhen, Mark D.¹*

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

Correspondent author*: muhen@gmu.edu

Abstract

Understanding the geological, paleoclimatological, paleoceanographical, and biological aspects of the Bartonian (Late Middle Eocene) is becoming increasingly crucial to understanding the origin of Pelagiceti (fully aquatic whales) due to several factors. First, updates to ages of several stratigraphic units, particularly the Gehannam Formation of Egypt, have pushed many occurrences of basilosaurine archaeocetes from the Bartonian into the Priabonian (Late Eocene). Second, several finds of the basilosaurid subfamily Pachycetinae have added many fossils to the Bartonian that greatly increase our anatomical understanding of this previously enigmatic group. These new fossils (along with those previously described) show that these animals have craniodental features that have been previously associated with the basilosaurine basilosaurids including, cheek teeth with multiple accessory denticles and the loss of the upper third molar. At the same time, pachycetines appear to retain vertebral regional counts like those of protocetids, while also having autapomorphies of somewhat elongate trunk vertebrae with anteroposteriorly long vertebral processes, along with pock-marked bone texture. New fossils from Peru also show that pachycetines have well-developed hind limbs and innominata unlike either protocetids or basilosaurids. All together these observations show that the time of transition from semi-aquatic to fully aquatic whales likely took place during the Bartonian. Additional characterization of this time period will help to contextualize this transition even further.

Keywords

Bartonian; Cetacea; Basilosauridae; Pachycetinae; Pelagiceti

Change in the Larger Benthic Foraminiferal Assemblages across the Eocene-Oligocene Transition Event, Eastern Neo-Tethys (Pakistan)

Kamran, Muhammad¹*; Xi, DangPeng¹; Frontalini, Fabrizio²; Khameiss, Belkasim³; Wan, Xiao-Qiao¹

1. State Key Laboratory of Geomicrobiology and Environmental Changes, Frontiers Science Center for Deep-time Digital Earth, China University of Geosciences, Beijing, China; 2. Dipartimento di Scienze Pure e Applicate, Università degli Studi di Urbino “Carlo Bo,” Campus Scientifico, Località Crocicchia, Urbino 61029, Italy; 3. Oklahoma Geological Survey, Sarkeys Energy Center, Norman, Oklahoma, United States"

Correspondent author*: kamran@email.cugb.edu.cn

Abstract

The Earliest Oligocene transition (EOT) event is part of the global climate changes that occurred during the Eocene–Oligocene boundary, with a profound impact on marine biota. Until now, the shallow-sea response to the EOT has been poorly known. Shallow-marine sediments from the Baluchistan Basin in the Eastern Neo-Tethys offer an opportunity to investigate the EOT and its impact on shallow-marine biota. This study examines the response of larger benthic foraminifera (LBF) of the Nisai Formation. During this interval, compositional changes in the LBF assemblages resulted from a glacio-eustatic sea-level fall induced by an Antarctic glaciation pulse. A replacement of mid-ramp sediments by inner-ramp ones was observed. This also involved a major LBF extinction, characterized by the complete disappearance of typical Eocene LBF taxa such as Nummulites fabianii, Chapmanina sp., and Orthophragminids. Simultaneously, the appearance and proliferation of typical Oligocene LBF taxa such as Nummulites fichteli, N. vascus, Operculina complanata, and Sivasina egribucakensis were noted. We hypothesize that climate changes likely triggered the LBF turnover during the global sea-level fall. These changes may have led to enhanced nutrient levels induced by a pulse of Antarctic glaciation, which was, in turn, driven by the sea-level fall at the onset of the EOT event.

Keywords

EOT, LBF, Extinction, sea-level fall

Paleoproductivity and ocean gateway openings drove planktic foraminifera community changes from the late middle Eocene to early Oligocene in the western South Atlantic Ocean

Standring, Patricia¹,²*; Lowery, Christopher M.¹; Borrelli, Chiara³; Routledge, Claire M.⁴; McIntyre, Andrew⁵; Villa, Alexandra⁶; Robustelli Test, Claudio⁷; Matt, Lily³, Martindale, Rowan C.⁸; and the Exp.³⁹⁰/³⁹³ Science Party⁹

1. Institute for Geophysics, University of Texas at Austin, United States; 2. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C; 3. Department of Earth and Environmental Sciences, University of Rochester, United States; 4. Institute of Geosciences, Christian-Albrechts-University of Kiel, Germany; 5. School of Geography, Geology and the Environment, University of Leicester, United Kingdom; 6. MARUM – Center for Marine Environmental Sciences, University of Bremen, Germany; 7. Dipartimento di Scienze della Terra, Università degli Studi di Torino; 8. Department of Earth and Planetary Sciences, University of Texas at Austin, United States; 9. The affiliations for Exp 390/393 are listed here: https://iodp.tamu.edu/scienceops/expeditions/south_atlantic_transect.html

Correspondent author*: StandringP@si.edu

Abstract

The Eocene-Oligocene Transition, ~34 Ma, is associated with more vigorous thermohaline circulation and the initial establishment of akin to modern current patterns. The South Atlantic Ocean sits at an important juncture where modern North Atlantic Deep Water and Antarctic Bottom Water bathe the seafloor, Antarctic Intermediate Water flows northward, and surface currents are dominated by the subtropical gyre; thus, it is the ideal location to determine how Eocene and Oligocene deep water currents and surface circulation developed as the climate cooled and ocean gateways changed. Here we present planktic and benthic foraminifera population analysis spanning the late middle Eocene to early Oligocene (40 Ma to 32 Ma) at International Ocean Discovery Program Site U1558 (Holes A and F) in the western South Atlantic. Late Eocene dissolution of foraminifera, including high percentage of foraminifera test fragments and a low relative abundance of planktic to benthic foraminifera, provides evidence for the influx of a corrosive water mass, potentially from the Pacific Ocean, following the opening of the Drake Passage in the late middle Eocene. Dissolution obscures most of the Eocene planktic foraminiferal assemblage, but a well-preserved interval in the late middle Eocene was dominated by mixed layer symbiont-bearing planktic foraminifera species, including species of Acarinina, Catapsydrax, Dentoglobigerina, Globigerinatheka, Paragloborotalia, Subbotina, and Turborotalita. Carbonate preservation improved shortly after the Eocene/Oligocene boundary, and the Oligocene assemblage was dominated by non-symbiotic mixed layer taxa, including species of Tenuitella, Chiloguembelina, and Pseudohastigerina, many of which were small microperforates. Minor components of the Oligocene assemblages included Catapsydrax, Subbotina, Globorotaloides, Dentoglobigerina, and rare Turborotalia. This is indicative of cooler water temperatures and higher nutrient conditions, resulting from global cooling, reorganization of ocean circulation, expansion of the Antarctic Ice Sheet, and the equatorward expansion of the subantarctic front. The dominance of opportunistic taxa in the Oligocene indicates increased primary productivity in the South Atlantic Gyre, which we suggest results from increased nutrient delivery due to a combination of more vigorous overturning circulation and the deepening of the Drake Passage. We speculate that carbonate dissolution in the late Eocene corresponds to a corrosive Pacific water mass moving into the region following the opening of the Drake Passage that was subsequently displaced by a younger North Atlantic deep water mass in the Oligocene.

Keywords

paleoceanography; paleoecology; foraminifera; Eocene/Oligocene

Mid-Oligocene Braarudosphaera chalk in the South Atlantic Ocean: new insights into paleoceanographic changes from multi-proxy analysis

Sander, Victória H.¹*; Trentin, Franciele A.¹; Fenske, Brenda B.¹; Aumond, Gustavo N.¹; Luft-Souza, Fernanda¹; Lucca, Ana Maria S. T.¹; Strohschoen Junior, O.¹; Cruz, Jenifer S.¹; Lopes, Fernando M.¹; Barreto, Diana R. L.¹; Panera, Juan P. P.²; Tokutake, Lucio R.³; Anjos-Zerfass, Geise S.³; Ferreira, Elizabete P.³; Michelon, Mateus F.⁴; Fauth, Gerson¹; Rodrigues, Ana Natália G.⁵; Bruno, Mauro D. R.¹.

1. Itt Oceaneon, Unisinos University, Brazil; 2. La Plata University, Argentina; 3. CENPES/PDIEP/GEO/BPA/Petrobras, Brazil; 4. EXP/GEO/TGEO/STGEO/Petrobras, Brazil; 5. CENPES/PDIEP/GEO/GEM/Petrobras, Brazil

Correspondent author*: victoriaherdersander@gmail.com

Abstract

The Oligocene Epoch (33.9–23.04 Ma) included significant cooling events driven by the Tasmanian and Drake gateways opening and a decline in atmospheric CO₂. These cooling events, leading to complex oceanographic changes that influenced the formation of enigmatic calcareous nannofossil-rich deposits known as Braarudosphaera chalk. These deposits constitute an important regional stratigraphic level in the southeastern Atlantic Ocean, recorded in the Brazilian sedimentary basins as a marker in the seismic profile. Similarly, a previous study at Walvis Ridge (African Margin) identified seven Braarudosphaera acmes. The mechanisms triggering these calcareous nannofossil acmes remain controversial and may include isolation forcing, water-column stratification, and monsoonal rainfall. We conducted a multiproxy study based on calcareous nannofossils, foraminifera, microbiofacies, geochemical, and cyclostratigraphic data to elucidate the impact of Oligocene paleoceanographic changes on marine biota. These analyses were performed on 91 samples from a 30 m-thick drill core section from the Campos Basin. Thin sections analysis reveals mudstones and shales containing abundant and well-preserved coccospheres of Braarudosphaera and calcareous dinoflagellate cysts. In addition, planktonic foraminifera were recovered, including Dentoglobigerina baroemoenensis, D. venezuelana, Gyroidinoides girardanus and Paragloborotalia mayeri, as well as benthic taxa such as Uvigerina sp. and Ammodiscus glabratus. In the Campos Basin, seven Braarudosphaera acmes are associated with increases in CaO/Fe2O3 ratios. Three acme intervals within Zone

CP18 and four within CP19a (?). Integration with cyclostratigraphic data enable to assign the deposition of the studied section to an interval between 30 and ~27 Ma. Carbon and oxygen isotopic data of bulk carbonate (δ¹³Cbulk; δ¹⁸Obulk) show positive excursions from ~30 to ~29.15 Ma, followed by negative excursions to 28.1 Ma. The isotopic values of δ¹³Cbulk range from −0.07 to 1.72%, and those of δ¹⁸Obulk range from −3.99 to −0.24%, although the peaks of the positive excursions of δ¹³Cbulk and δ¹⁸Obulk are recognized in the same sample and possibly related to the Oi-2* event (~29.15 Ma). Finally, carbon isotope bulk values observed in this study show similar excursions to those recorded at Walvis Ridge, suggesting a significant regional connection between the Brazilian and African margins during the mid-Oligocene. [Financial Support Petrobras/ANP Project: Cicloestratigrafia Multiproxy do Eoceno–Mioceno do Atlantico Sul].

Keywords

Geochemistry; Biostratigraphy; Cyclostratigraphy;

Eccentricity versus obliquity worlds: Modeling the state-dependent response of deep ocean temperature to orbital forcing

Mishra, Gayatri.¹*; Vervoort, Pam.²; Lin, Ying.¹;  Kirtland Turner, Sandra.¹; Ridgwell, Andy.¹

1. Dept. of Earth and Planetary Sciences, University of California, Riverside, USA; 2. School of Geography, Earth and Environmental Sciences, University of Birmingham, UK

Correspondent author*: gayatri.mishra@email.ucr.edu

Abstract

Imprints of astronomical forcing are widely present in deep-sea benthic foraminiferal climate proxy records across the entire Cenozoic Era. The Hothouse and Warmhouse climates of the Paleogene Period predominately display the influence of eccentricity while obliquity power only significantly emerges following the middle Miocene Climate Transition (~13.9 Ma). The emergence of obliquity power in benthic foraminiferal oxygen isotope records is widely interpreted as a consequence of the increasing influence of high-latitude processes on global climate associated with the increase in polar ice. However, the mechanisms leading to strong eccentricity power in the Paleogene and the overall feedbacks governing this state-dependent orbital sensitivity remain poorly understood.

Here we use the intermediate-complexity Earth system model cGENIE to investigate how climate, particularly ocean temperature, responds to time-varying orbital forcing under contrasting background climate states. We simulated both a Hothouse climate state driven by high-CO₂ (800 ppm) and a Coolhouse climate state with lower-CO₂ (400 ppm). We ran a suite of ~1.3 Myr simulations using a Miocene configuration of the model and analyzed the model response to orbital forcing in ocean temperature. Our results show that global annual mean sea-surface temperature predominately reflects an obliquity (~41 Kyr) signal under both scenarios. Global annual mean benthic temperatures, however, show a markedly different spectral response to orbital forcing: precession power dominates benthic temperature in both experiments, but the high-CO₂ scenario additionally exhibits strong eccentricity power, whereas the low-CO₂ world instead shows obliquity power. This differential response in benthic temperature accompanies distinct differences in the meridional overturning circulation between the high- and low-CO₂ experiments, with intensified Southern Ocean deep-water formation under high-CO₂. We hypothesize that the enhanced sensitivity of overturning circulation to temperature at high-CO₂ modulates the sensitivity of overturning to orbital forcing, and that the power spectra of benthic ocean temperature reflects these different ocean circulation responses. Our results demonstrate a mechanism by which background climate state, though differences in ocean circulation, influences how orbital forcing influences deep ocean temperature. Moreover, our results point to a mechanism to explain the Miocene shift from an eccentricity to an obliquity world that does not rely on the emergence of significant polar ice.

Keywords

Orbital forcing, climate sensitivity, ocean-circulation

Did deep-sea methane release contribute to the warm Miocene?

Auderset, Alexandra¹,²*; Inglis, Gordon N.¹; Farmer, Jesse R.³; Evans, Aled D.¹; Holbourn, Ann⁴; Martínez-García, Alfredo²

1. School of Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK; 2. Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz, 55128, Germany; 3. School for the Environment, University of Massachusetts Boston, Boston MA 02125, USA; 4. Institute of Geosciences, Christian-Albrechts-University, Kiel D-24118, Germany

Correspondent author*: a.auderset@soton.ac.uk

Abstract

The Miocene Climate Optimum (MCO) was an interval of elevated surface temperatures (~8-15°C higher than preindustrial) and atmospheric CO₂ concentrations (pCO₂ ~150-300 ppmv higher than preindustrial). However, global temperatures appear higher than expected based on pCO₂ estimates, and the drivers of elevated MCO CO₂ remain debated. Methane (CH₄) is a trace greenhouse gas that can enhance planetary warming both directly and indirectly via its oxidation to CO₂. Here, we use globally distributed archaeal biomarker records to quantify seafloor CH₄ release during the past 23 million years. Our data reveal persistently elevated deep-ocean CH₄ fluxes (~10 times higher than present) during the MCO, especially in core sites along active plate boundaries like (I)ODP Sites U1337, 1168, 704, 667 and 608. The close link observed between CH₄ fluxes and reconstructed oceanic crust production rates suggest that the deep-sea CH₄ release was driven by increased tectonic activity. Our results demonstrate that deep-sea CH₄ release could have directly or indirectly reinforced MCO greenhouse warmth, helping to explain its longevity as well as various hyperthermal events. Furthermore, the proposed enhanced CH₄ release could also resolve the apparent mismatch between global warming and modestly elevated CO₂ during the MCO, given modern estimates of climate sensitivity.

Keywords

Miocene, methane, GDGTs, seafloor spreading

Middle Miocene Hadley Cell Dynamics May Influence Marine Plankton Evolution and Antarctic Ice Sheet Growth

Lam, Adriane R.¹*; Patterson, Molly O.¹; Agnini, Claudia.²; Dallanave, Edoardo.³; Pekar, Stephen F.⁴; Westerhold, Thomas.⁵; King, Gretl.¹; Swain, Anshuman.⁶; Koorapati, Ravi Kiran.¹; Acosta, R. Paul.⁷; Browne, Imogen.¹; Doiron, Oliff.¹; Halberstadt, Anna Ruth.⁸; Kraus, Emily.⁸

1. Earth Sciences Department, Binghamton University, Binghamton, U. S. A; 2. Department of Geosciences, University of Padova, Padua, Italy; 3. Department of Earth Sciences, University of Milan, Milan, Italy; 4. School of Earth and Environmental Sciences, Queens College, Queens, U.S.A.; 5. Center for Marine and Environmental Sciences, University of Bremen, Bremen, Germany; 6. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, U.S.A.; 7. Atmospheric, Oceanic and Earth Sciences Department, George Mason University, Fairfax, U.S.A.; 8. Department of Earth and Planetary Sciences, The University of Texas at Austin, Austin, U.S.A.

Correspondent author*: alam@binghamton.edu

Abstract

During the Miocene Climatic Optimum (17–14.7 Ma) the Antarctic ice sheet (AIS) became sensitive to obliquity. Cessation of obliquity sensitivity occurred in the Middle Miocene Climate Transition (14.7–13.8 Ma) when the AIS expanded. Concurrently planktic foraminifera increased in global diversity with temperate-water lineages evolving first in the Southern Hemisphere. These processes suggest a coupling between mid-latitude atmospheric and surface ocean processes, ice sheet development and sensitivities, and influence on plankton evolution. Here, we provide a regional view of the southwest (SW) Pacific and Atlantic to infer how these processes interact. We use geochemical and paleontological analyses on SW Pacific IODP Site U1510, SW Atlantic Site U1560 and U1583, coupled with modeling. Site U1510 X-ray fluorescence (XRF) data show obliquity dominates the record, except for ~15–14.4 Ma, when obliquity disappears from the mid-latitude record and is apparent in the benthic foraminiferal 𝛅¹⁸O record. These results indicate that when obliquity disappears from the U1510 record, the Hadley Cell was expanded with pole-shifted westerlies, making AIS more sensitive to obliquity. Times when obliquity dominates the U1510 record, the Hadley Cell was contracted and the westerlies shifted equatorward, leading to persistence of AIS. Spectral analyses on the Sites U1560 and U1583 XRF data were conducted from 23–8 Ma to test for the same signal and timing in an adjacent ocean basin. Results are less clear, with the record dominated by eccentricity until ~17 Ma, where obliquity and precession become more apparent for the remainder of the Middle Miocene. This result could indicate a less pronounced Hadley Cell behavior in the Atlantic. Bulk grain size analyses were conducted on sediments from Site U1510 to infer how orbital cyclicity influenced plasticity of planktic foraminifera. Spectral analyses of grain-size data indicate a strong obliquity signal at ~14.9–14.4 Ma, matching the interval of AIS obliquity sensitivity. Foraminiferal test sizes generally decreased across the MCO, before increasing through the MMCT, although breakpoint analyses suggest that natural breaks in the data do not align with a 14.7 Ma boundary. Following natural breaks, average size decreases until 14.9 Ma, stays relatively constant until 14.4 Ma, before decreasing again. As foraminiferal test sizes are influenced by temperature, it appears that surface ocean water masses were still partly dominated by obliquity pacing. 

Climate, ice-sheet, and plankton seasonality modeling studies are underway to determine which factors are necessary to drive Hadley Cell expansion during the MCO and whether this process is important for moisture transport leading to AIS growth. Geochemical analyses from additional Southwest Pacific sites will be coupled with prior data and modeling studies to provide a more holistic view of these atmospheric and oceanic processes during a critical analogue climate event.

Keywords

foraminifera; Southwest Pacific; Southwest Atlantic