We studied the feasibility of using laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) for U–Pb dating of fossils (vertebrate-invertebrate) and pedogenic calcite. U–Pb dating of hydrogenic and fossil material can be challenging because samples often contain low U levels and variable amounts of non-radiogenic Pb. Our improved processing methods (UtilChron) give accurate U–Pb ages for low U samples. Line scans using LA–ICPMS provide the widest range of ratios available for defining the radiogenic to common Pb mixing line, hence the best age estimate for calcite and fossil material. For example, the first accurate U–Pb age on fossilized soft tissue, yielded an age of 3.16 ± 0.08 Ma consistent with its late Pliocene stratigraphy while coexisting shark teeth are variably reset by late-diagenesis. U–Pb dating on a paleosol sample from the Katberg Formation, Karoo Basin, South Africa yielded an age of 252 ± 3 Ma, which overlaps with a previous high-precision U–Pb zircon date from a volcanic ash deposit 2 meters above the paleosol demonstrating, for the first time, the reliability of using LA–ICPMS dating on terrestrial pedogenic calcite. Processing LA–ICPMS data at the single cycle level allows more precise absolute dating of fossils and carbonates. In some cases, separate regression of totally reset and partially reset domains can resolve ages of early and late diagenesis. Apatite fossils such as teeth or bones contain high U content, but they are more susceptible to late diagenetic alteration whereas calcitic invertebrate fossils like belemnites or rugose corals seem to be more stable but usually show low U content. Our research has demonstrated that pedogenic carbonate nodules and fossils can potentially be dated with meaningful precision, providing another mechanism to constrain the age of sedimentary sequences and study events associated with fossil extinctions.

How to cite: Rochin-Banaga, H., Davis, D. W., and Kamo, S.: U-Pb Dating of Fossils and Calcite: dating the Sedimentary and Paleontological record, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20743, https://doi.org/10.5194/egusphere-egu25-20743, 2025.

The WaverideR  R package was initially developed to use the Continuous Wavelet Transform (CWT) to conduct cyclostratigraphic analyses. In the initial release of the R package, the functions mainly focussed on plotting wavelet scalograms, extracting astronomical cycles from the CWT and to create simple age-models. Over time the WaverideR R package has seen some major updates in capabilities regarding both functionality and visualisation of cyclostratigraphic results. Enhanced visualisation options now allow users to customise wavelet scalograms, with flexible plotting directions and an array colour palettes to create personalised outputs. Existing functions have also been updated, resulting in the elimination of bugs and enhanced computational efficiency.  New functionalities have also been added, including Monte-Carlo modelling functions that allow the use of multi-proxy datasets to create an astrochronology including uncertainty, calculate the duration of a hiatus and anchor an astrochronology to a single absolute age date. In conclusion the updated WaverideR package contains many new functionalities that are complementary to existing cyclostratigraphy R codes/packages. 

How to cite: Arts, M. and Da-Silva, A.-C.: The WaverideR Package: a tool for cyclostratigraphy, the updated version, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17106, https://doi.org/10.5194/egusphere-egu25-17106, 2025.

Variations in Earth's orbit and axial tilt induce climatic changes on its surface, which are recorded in sedimentary deposits. These cyclical variations are driven by the main secular frequencies of the solar system. Analyzing these cycles in sedimentary records can help establish an astronomical time scale for the geological record by correlating geological proxies with computed variations in insolation on the Earth's surface, in accordance with the laws of celestial mechanics. A critical aspect of this analysis is the estimation of the sedimentary deposition rate, which determines the time-depth transfer function, relating geological depth to relative or absolute time.

We propose a novel approach for constructing astronomical time scales for geological stratigraphic records. The AstroGeoFit method establishes a time-depth transfer function throughout the record, accommodating variable sedimentation rates, and extracts the primary astronomical signal from the geological sequence. This is achieved using a genetic algorithm that adapts to a wide range of sedimentation rate variations. This statistical analysis enables the reconstruction of an astronomical signal (e.g., eccentricity and/or precession) purely from the stratigraphic sequence with minimal personal bias. When this template is correlated with an astronomical solution, an absolute time scale is obtained for the entire record. In addition, we show that quantitative uncertainties can be estimated at each stage of the AstroGeoFit process with the Bayesian approach.

The publication of the AstroGeoFit approach will be associated to an open source python package that fully implement the AstroGeoFit algorithm.

Ref: J. Laskar, N. Hoang, N. Hara, Y. Wu, A.Sultanov, M. Sinnesael, T. Westerhold, P. Bujons, AstroGeoFit. A Genetic Algorithm and Bayesian approach for  the Astronomical Calibration of the Geological Timescale, 2025, in revision.

How to cite: Laskar, J., Hoang, N., Hara, N., Wu, Y., Sultanov, A., Sinnesael, M., Westerhold, T., and Bujons, P.: AstroGeoFit. A Genetic Algorithm and Bayesian approach for  the Astronomical Calibration of the Geological Timescale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13546, https://doi.org/10.5194/egusphere-egu25-13546, 2025.

The middle Cambrian was a critical period of Earth’s history, marked by explosive diversification of metazoans and several profound changes in Earth’s surface environments and global climate. A valid temporal framework for the middle Cambrian period and across the major bio-events is yet poorly constrained, and millennial-scale climate variability (MCV) are not fully addressed. Here, high-resolution spectral gamma-ray logs, of Potassium, Uranium, Thorium and magnetic susceptibility records are utilized to conduct a cyclostratigraphic analysis of the global stratotype section for the Wuliuan Stage in South China. A ∼1.1 Myr-long high-resolution astronomical time scale across the Wuliuan-Stage 4 is developed by astronomical tuning of gamma-ray logs to the ~100-kyr short-eccentricity cycles. We report semi-precession cycles of 11.7–7.9 kyr, which were probably associated with the twice-annual passage of the intertropical convergence zone across the intertropical zone, consistent with the paleogeographical location of South China near the equator during the middle Cambrian. Furthermore, our results suggest that MCV (with periods of 4-7 kyr) is modulated by eccentricity, obliquity, and precession cycles and can be directly generated by the harmonization between fundamental orbital cycles (e.g., obliquity and precession cycles). These results describe one of the oldest known geological candidates for solar-influenced climate change modulated by Milankovitch forcing.

How to cite: Zhang, Y., Fang, Q., Shi, M., Gai, C., Zhang, S., Yang, T., Li, H., and Wu, H.: Millennial-scale climate cycles detected in the middle Cambrian GSSP (ca. 509 Ma) of the basal Wuliuan Stage, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-351, https://doi.org/10.5194/egusphere-egu25-351, 2025.

In the central portion of the Orobic Basin (Trabuchello-Cabianca anticline), on the Valtellina side of the Orobic Alps, the Val D’Ambria (Sondrio, Italy) represents a site of exceptional paleontological richness, both for the high quality and quantity of data.

This sedimentary basin is renowned for its geological complexity and the preservation of a thick stratigraphic sequence dating back to the early Permian. The fossils found at the site belong to the Kungurian Pizzo del Diavolo Formation and are characterized by remarkable diversity, consisting primarily of tetrapod footprints, invertebrate traces, and sparse macroflora remains. The vertebrate footprints represent a diverse ichnofauna, with at least eight different ichnogenera identified, including Amphisauropus, Batrachichnus, Dimetropus, Dromopus, Erpetopus, Hyloidichnus, Limnopus, and Varanopus. Among these, Dromopus and Erpetopus are the most common, whereas footprints assigned to Dimetropus are the rarest and, therefore, of particular interest. These fossil tracks suggest that the area was frequented by a community of terrestrial animals, including reptiles, amphibians and rare synapsids.

In addition to the tetrapod footprints, the discovery of invertebrate traces and macroflora remains provides crucial data for interpreting the depositional environments, as well as the climatic and ecological conditions of the early Permian in the Southern Alps. The combination of these paleontological data, stratigraphic logs, and detailed descriptions of sedimentary facies will allow for a more precise reconstruction of the paleoenvironmental and palaeoecological evolution of the Orobic Basin during the time interval in which these biotas thrived.

Preliminary analyses suggest that the Orobic Basin, located in the paleoequatorial domain, may have hosted diverse depositional settings, under alternating semi-humid and dry seasonal conditions. These frequent changes are characteristic of specific present-day fluvial-lacustrine landscapes, which feature extensive alluvial sand-to-mud flats, playa and ephemeral lakes, situated not far from the basin margins. Further analyses of palynological data and other methodologies, such as C and O stable isotopic analyses as paleoenvironmental indicators on clay deposits and geochemical analyses on volcanic deposits, are expected to provide a better understanding of the climate change during this time interval in the studied area.

Since the late Pennsylvanian, the Palaeozoic was interested by global warming and progressive depletion of the Southern Pole glaciers, which culminated in the Artinskian Warming Event and the subsequent establishment of greenhouse-like-conditions that lasted for the rest of the Permian. Thanks to the different data gathered in the Val D’Ambria locality, its rich fossil record can highlight the consequence of the increased aridity and seasonality on the low-latitude biota during the Kungurian, and potentially provide information regarding the purported Olson’s Extinction (or Olson’s Gap).

The ongoing field research at this site will provide increasingly detailed insights into the biodiversity of this region during the early Permian, enriching our understanding of the dynamics of life and climate change at the end of the Paleozoic Era.

How to cite: Scarani, R., Marchetti, L., Dal Sasso, C., Cattaneo, M., Della Ferrera, E., Bonizzoni, S., Rossi, S., Merati, M., and Ronchi, A.: A new exceptionally preserved ichnofauna from the lower Permian of the Southern Alps: insights into the continental ecosystems after the Artinskian warming event, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7496, https://doi.org/10.5194/egusphere-egu25-7496, 2025.

Accurately estimating the duration of the Induan Stage (Early Triassic) is crucial for understanding biotic recovery and environmental upheavals following the Permian–Triassic Mass Extinction. However, considerable uncertainties remain due to discrepancies between astrochronological and radiometric dating methods. In this study, we present an integrated stratigraphic framework for the Induan Stage by combining cyclostratigraphy, magnetostratigraphy, radiometric dating, biostratigraphy, and chemostratigraphy. By analyzing gamma ray series from marine deposits at the Xiejiacao, Chaohu, and Daxiakou sections in South China, and correlating them with biostratigraphic, magnetostratigraphic, geochemical, and radiometric data, we establish a composite 405-kyr eccentricity cycle-calibrated time scale. Our results estimate the Induan duration at 1.55 ± 0.2 Myr. Anchoring this time scale to the Permian–Triassic boundary at 251.902 ± 0.024 Ma, we propose an estimated age of 250.35 ± 0.2 Ma for the Induan–Olenekian boundary. By reconciling discrepancies between astrochronology and radiometric dating, our results provide a robust temporal framework for stratigraphic correlations, carbon cycle perturbations, and biotic and environmental changes in the aftermath of the mass extinction.

How to cite: Zhang, H., Ji, K., Chen, Y., Ogg, J., Sun, Z., Wignall, P., Wang, M., Zhang, H., Zhang, X., Zhang, Y., Huang, K., and Li, M.: Astronomically calibrated integrated stratigraphy of the Induan Stage in the aftermath of the Permian–Triassic mass extinction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6527, https://doi.org/10.5194/egusphere-egu25-6527, 2025.

Paleotropical lacustrine strata of eastern North America are only known place where vertebrate and floral records of the end-Triassic extinction (ETE) (1) are directly interbedded with U-Pb zircon CA-TIMS-dated lavas of the CAMP (2) and a high-resolution, orbitally paced, lacustrine cyclostratigraphy (3, 4). New, continuous XRF elemental scans of Newark and Hartford rift basin cores (5) confirm previous work in showing expected climatic-precession-dominance modulated by eccentricity for most of the section (6, 7), but an emerging major surprise is that the 500 kyr interval around the Triassic-Jurassic transition is very strongly obliquity-dominated. Tied by sub-Milankovitch magnetic polarity stratigraphy [chron E23r (3)] to rich outcrop-based biostratigraphy, this new Mn/Fe, K/Al, Zr/Rb, S and Na chemostratigraphy requires a revision of environmental interpretations of the proximal cause of the continental ETE. We argue that despite the clear record of pulsed massive pCO₂ increases tied to CAMP emplacement, CAMP eruptions produced extreme, sulfur-driven, mega-volcanic winters that were proximal drivers of extinction on land (8) — not the giant hyperthermal itself. We hypothesize that these extreme cold events, superimposed on a background of polar latest Triassic-earliest Jurassic cooling (9) and wintertime freezing (10, 11), enhanced polar ice-albedo feedback and possibly glaciation (12). This amplified Earth System sensitivity to obliquity forcing, perhaps not unlike the initiation of the “40 kyr” world of the Late Neogene [e.g. (13)]. Onset of this Triassic-Jurassic obliquity pacing modality marked the continental phase of the ETE, but in light of these competing radiative balance forcings, interpretations of end-Triassic sea-level drop (12) and marine extinctions require reevaluation as well, considering factors beyond global warming alone (14).

1, Olsen+ 2002 Science 296:1305. 2, Blackburn+ 2013 Science 340:941–945. 3, Kent & Olsen 1999 JGR 104:12831-12841. 4, Olsen & Kent 1996 PPP 122:1-26. 5, Kinney+ 2002 Abstract PP25D-0899, AGU Fall Meeting. 6, Van Houten 1962 AJS 260:561. 7, Olsen 1986 Science 234:842. 8, Kent+ 2024 PNAS 121:e2415486121. 9, Judd+ 2024 Science 385:eadk3705. 10, Olsen+ 2022 Science Adv. 8:eabo6342. 11, Chang+ 2024 GSL Spec Pap. 538:114. 12, Schoene+ 2010 Geology 38:387. 13, Westerhold+ 2020 Science 369:1383-1387. 14, Funded by NSF & the Heising-Simons Foundation.

How to cite: Olsen, P., Kinney, S., Tibbits, D., Fang, Y., Chang, C., Schaller, M., Slibeck, B., Whiteside, J., and Kent, D.: Obliquity pacing of tropical lacustrine cyclostratigraphy of the great end-Triassic hyperthermal and mass extinction: competing radiative balance forcings induced by the Central Atlantic Magmatic Province (CAMP) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10277, https://doi.org/10.5194/egusphere-egu25-10277, 2025.

The end-Triassic mass extinction (ETME) and global climatic perturbation coincide with the onset of Central Atlantic Magmatic Province (CAMP) emplacement. The associated perturbation to the global carbon cycle is reflected by a ~ 3 – 6 ‰ negative carbon isotope excursion (CIE) coinciding with the ETME. The magnitude and duration of the negative CIE are however poorly constrained. Furthermore, the Early Jurassic Hettangian stage, marking the initial recovery phase following the end-Triassic mass extinction, has been the subject of significant debate over its precise timing and duration. Estimated Hettangian stage durations derived from cyclostratigraphic and U-Pb geochronological analyses vary between a ‘short Hettangian’ of 1.8 – 2.5 Myr, and a ‘long Hettangian’ of 3.9 – 4.4 Myr. Poor time constraints for the Triassic–Jurassic interval impact understanding of the timing and rate of biogeochemical cycling, environmental and biological recovery after the end-Triassic mass extinction, and global climatic perturbation.

We here conducted carbon isotopic and cyclostratigraphic analysis of the well-preserved, biostratigraphically complete, and expanded Hettangian succession in the Carnduff-2 core of the Larne Basin (Northern Ireland), nearby the Waterloo Bay outcrop. The studied sedimentary succession (~120 m in core) stratigraphically spans the upper Rhaetian (upper Triassic), including the end-Triassic mass extinction, Hettangian, and lower Sinemurian (lower Jurassic), and consists of predominantly mudstone, with varying degrees of limestone and silt throughout the succession. Cyclostratigraphic analyses of elemental and carbonate concentration data show a hierarchy of dominant frequencies, interpreted to reflect long and short eccentricity, obliquity, and precession. These observations suggest a total duration of ~2.2 Myr for the Hettangian Stage with a sedimentation rate of ~ 4.1 cm/kyr, confirming the ‘short-Hettangian’ hypothesis. The negative carbon isotope excursion (CIE) duration, which coincides with the ETME, is estimated at ~290 kyr. The first occurrence of the Jurassic ammonite Psiloceras tillmanni, marking the onset of Hettangian biotic recovery after the ETME across the British Isles, ~320 kyr after the end-Triassic negative CIE, suggesting a prolonged period of biotic demise in response to CAMP induced climatic and environmental upheaval at this time.

Key Words: end-Triassic mass extinction, Early Jurassic, Hettangian stage, Milankovitch cycles

How to cite: Perera, A., Ruhl, M., Xu, W., Silva, R. L., Raine, R., and Goodhue, R.: “Short” or “Long” Hettangian? Astronomical chronometry on the duration of lower Jurassic Hettangian stage and the recovery dynamics following the end – Triassic mass extinction. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13954, https://doi.org/10.5194/egusphere-egu25-13954, 2025.

Global perturbations to the Jurassic environment have been extensively documented over the last decades, notably those that were associated with major events such as mass extinctions, global environmental crisis and hyperthermal events that often mark stage boundaries. However, much less attention has been given to background times and to lesser palaeoenvironmental and palaeoclimatic events. As such, the long-term secular evolution in the Jurassic carbon cycle and palaeoenvironmental response, that provide the broader context, is very poorly understood. One such understudied time interval is the Bathonian-Callovian transition (Middle Jurassic). Although at first it may appear as a relatively stable time, there is evidence for biotic turnover, climate warming, dramatic sea-level rise, and carbon cycle disturbance. A positive excursion in the carbon isotope ratio (CIE) has been documented in Europe and Greenland, but the current state of records does not yet allow determination of the exact causes and nature of the isotope shift and the environmental changes across the Bathonian-Callovian boundary. As for other Mesozoic positive CIEs, it has been proposed that increased burial of organic matter due to elevated primary productivity might have generated the positive shift. The lack of continuous well-dated records with robust stable carbon isotope chemostratigraphy and environmental context complicate the attribution of a Global Boundary Stratotype Section and Point for the Bathonian-Callovian.

This study aims to tackle this lack of empirical data by providing a multi-proxy dataset combining sedimentological observations, nannofossil biostratigraphy, mineralogical and geochemical analyses. The Ravin des Vas section in SE France has been selected because it encompasses the Bathonian-Callovian boundary and comprises an extended 100 m-thick homogeneous succession of dark marls, with little lithological change, which is an advantage for geochemical analysis. Organic carbon isotope analysis reveals a pronounced positive excursion at the base of the Callovian, associated with an increase in organic carbon content. This excursion can be correlated to other coeval sites, confirming the likely global nature of this carbon cycle perturbation. Whole-rock and clay mineralogy will be used to determine the climatic and weathering conditions, and phosphorus content will inform on the nutrient availability. Altogether, the new dataset from France will give new insights into our understanding of the palaeoclimatic and palaeoenvironmental conditions across the Bathonian-Callovian boundary, and hence provide a reference framework for further studies on this yet poorly known time interval.

How to cite: Fantasia, A., Gavillet, L., Bodin, S., Hesselbo, S. P., Mattioli, E., and Adatte, T.: Unravelling the base Bathonian-Callovian boundary event: New insights from the SE France Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15198, https://doi.org/10.5194/egusphere-egu25-15198, 2025.

The early Aptian OAE 1a is one of the most prominent hyperthermal events in Earth’s history. This event is associated with global environmental and biotic perturbations, including global rise in temperatures, ocean oxygen depletion, and widespread deposition of organic-rich marine sediments.

The onset of OAE 1a coincided with a major disturbance of the global carbon cycle, recorded with a marked negative spike in the C-isotope record. A complex response of the environmental and biotic system occurred, ultimately triggered by volcanism of the Ontong-Java Plateau.

In this study, we present two expanded records of OAE 1a from the Southern Iberian Palaeomargin (SIP, Western Tethys): the Carbonero and Cau sections, which comprise high-resolution C-isotope records that have served as the basis for a precise stratigraphic correlation.

The Carbonero section is composed of black shales, radiolarites and marls, deposited on a fault-bounded, highly subsiding sector of the pelagic basin of the SIP. The Cau section (also studied in a core), consists of an alternance of hemipelagic marls and marly limestones deposited in the distal platform settings of the SIP. Previous studies have provided with multiproxy evidence, including stratigraphy and sedimentology, biostratigraphy (ammonites, planktonic foraminifera, calcareous nannofossils and radiolaria), C-O and Re-Os isotope stratigraphy, elemental composition and biomarker distributions. The time model has been based on a combination of biostratigraphy and cyclostratigraphy. Atmospheric CO₂ concentrations records across OAE 1a have been derived from bulk and compound-specific C-isotope data from the Cau section. The high-resolution C-isotope stratigraphy from the Cau core has been used to refine the previously defined C-isotope segments of the Aptian, and to correlate the succession with other records worldwide.

The onset of the OAE 1a has been studied at ultrahigh-resolution scale (0.2–0.5 kyr spacing) revealing a succession of sharp C-isotope negative spikes, interpreted as a record of pulses of volcanism and methane emissions. The largest spike was rapid (<10 kyr) and marks the base of OAE 1a, which occurs within a longer-term falling C-isotope trend. The C-isotope profile across OAE 1a records the negative (C3/Ap3), positive (C4/Ap4), steady (C5/Ap5), and positive (C6/Ap6) segments that were defined from Cismon (Italy) and subsequently recognized worldwide.

Our results illustrate a complex evolution of environmental and biotic changes throughout the OAE 1a event, with an estimated duration of ca. 1.47 Ma. Moreover, the unprecedented resolution of the study of the onset of the event reveals rapid environmental and biotic changes at the scale of the thousands of years, providing valuable insights on the mechanisms acting at shorter time intervals and enabling comparisons with more recent hyperthermal events.

How to cite: Castro, J. M., de Gea, G. A., Quijano, M. L., Sequero, C., Ruiz-Ortiz, P. A., O'Dogherty, L., Froehner, S., Martinez-Rodriguez, R., Batenburg, S., Naafs, D., and Pancost, R.: Records of the early Aptian OAE 1a  (Southern Iberian Paleomargin, Western Tethys): multiproxy evidence from expanded successions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20508, https://doi.org/10.5194/egusphere-egu25-20508, 2025.

Late Maastrichtian to Early Eocene sediments from Wadi Nukhul, Egypt (67–55.5 Ma) were deposited during the eruptions of the Deccan Traps and the North Atlantic Igneous Province (NAIP). Using tellurium (Te) and mercury (Hg) as proxies for volcanic activity, we investigate the timing of flood basalt volcanism relative to environmental changes and extinction events. Te enrichments are observed during the latest Maastrichtian, earliest Danian, and Late Paleocene to Early Eocene, indicating increased volcanic inputs. In the Late Maastrichtian, a Te peak aligns with the Maastrichtian Warming Event, while a larger Te peak begins 120–80 kyr before the Cretaceous/Paleogene boundary (KPB), continuing into the Danian. The highest Te values (70–30 kyr before the KPB) suggest association with eruptions of the Deccan Wai Subgroup, independent of the Chicxulub impact. This suggests that Deccan volcanism caused climate instability, amplifying the environmental effects of the impact. A 6 Myr period of low Te during the Paleocene is followed by a sharp increase beginning at 57.5 Ma, peaking at the Paleocene-Eocene boundary (PEB, 56 Ma), coinciding with NAIP’s highest eruptive rates. In contrast, Hg variations during this period are less consistent. Our findings highlight Te as a robust proxy, complementing Hg, for tracking large volcanic events in Earth’s history.

How to cite: Adatte, T., Baumann, N., Regelous, M., Khozyem, H., Regelous, A., and Haase, K.: Tracing Volcanic Activity in the Deccan and North Atlantic Igneous Provinces Using Tellurium and Mercury Proxies (Late Cretaceous–Early Eocene), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10073, https://doi.org/10.5194/egusphere-egu25-10073, 2025.

Extreme climate warmth (hyperthermal) events occur throughout the geologic record. In particular, several transient events are well documented for the early Eocene with the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) standing as the major star. Yet, earlier short-lived (10⁴–10⁵ years) warming events, correlated with abrupt negative carbon isotope excursions (CIEs), also struck in the Paleocene producing noticeable environmental disturbances (e.g., DAN-C2 event in the Danian, ~65.2 Ma and the ELPE event in the early late Paleocene, ~59 Ma). The Early Late Paleocene Hyperthermal Event (ELPE), also known as the mid-Paleocene biotic event (MPBE), was first discovered during ODP Leg 178 Shatsky Rise in the northern Atlantic as a prominent clay-rich ooze close to the first occurrence (FO) of the nannofossil Heliolithus kleinpellii, a marker for the base of nannofossil Zone CNP8 (=NP6), and the base of chron C26n. It was interpreted as an abrupt warming that possibly caused a brief switch in the source of deep waters at Shatsky Rise.The base of C26n marks the Selandian/Thanetian stage boundary as defined in the Selandian GSSP in the hemipelagic relatively expanded section at Zumaia that provides an astronomical template including the first documented ELPE event from a land section.

Here, a conspicuous ~40 cm clay-rich layer occurring at Hole U1556A (located ~1250 km west of the Mid-Atlantic Ridge at a 5002 m water depth) in interval 390-U1556A-29X-5, 70-110 cm (270.7 to 271.1 m CSF-B) (also occurring in Holes U1556C and U1557B) is investigated at high resolution. Paleomagnetic directional data is presented from four U-channel samples from sections 390-U1556A-29X3 to 390-U1556A-29X6 that confirm the presence of chron C26n, also in agreement with the FO of H. kleinpellii. Rockmagnetic and bulk rock stable isotope (d¹³C and d¹⁸O) measurements (155 samples) along with calcareous nannofossil determinations (80 samples) and XRD bulk mineral analysis (51 samples) were achieved spanning cores 390-U1556A-29X and 390-U1556A-30X at variable resolution (average 9 cm but 1.5–3 cm along critical intervals, shipboard age model indicating 0.49 cm/ky).

Quantitative analyses on calcareous nannofossils are carried out following the random settling technique to obtain the relative (%) and absolute abundance (coccoliths*gr^-1) data. The relative nannofossil fragmentation was also determined. Calcareous nannofossil assemblages are well to moderate preserved and diversified, and allowed determination of key biostratigraphic datums, and the main calcareous nannofossil dissolution events. During the ELPE, the total clay content reached up to 70 wt.%. Additionally, increased quartz and feldspar contents during this period suggests wind-driven sediment transport. Orbital chronology and paleoclimatic/paleoceanographic proxy data encompassing the ELPE event will be examined.

How to cite: Dinarès-Turell, J., Bonomo, S., Kim, S., and Yang, K.: Decoding the ELPE hyperthermal: a new biotic and paleoclimate record from South Atlantic IODP Sites U1556/U1557, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4546, https://doi.org/10.5194/egusphere-egu25-4546, 2025.

Due to their environmental sensitivity, planktic foraminifera are important proxies for reconstructing past climatic and oceanographic shifts, offering critical insights into marine ecosystem responses during intervals of rapid warming. Early Eocene hyperthermal (~50-200kyrs) episodes provide a unique opportunity to explore the effects of extreme heat on planktic foraminifera, a group of marine calcifiers highly sensitive to temperature, pH, and nutrient levels changes that may induce evolutionary modifications and variations in abundance and test size. Here we disentangle the global-scale impacts of Eocene Climatic Optimum (EECO,~53-49 Ma) hyperthermals on planktic foraminiferal communities, offering insights into their adaptability or loss of resilience under climatically related environmental stress.

We reveal significant modifications in PF assemblages during two major hyperthermals of the EECO, the J event (53.26 Ma), which marks the beginning of the EECO, and the K/X event (52.86 Ma). Following the J event, the symbiont-bearing genus Morozovella experienced a permanent decline in abundance and diversity at low-latitude locations while Acarinina thrived globally. At the same time, size in another symbiont bearing taxon Acarinina exhibits a reduction at tropical Pacific sites while Morozovella is becoming larger. Our stable isotope analyses reveal that Acarinina displays lower δ¹³C values than Morozovella, a feature likely linked to a reduction in photosymbiotic activity or change in symbiont and habitat deepening. This ecological strategy probably enabled Acarinina to succeed under the EECO environmental conditions.

Approximately 400kyr later, during the K/X event, a switch in Morozovella coiling direction – a dominance clockwise (dextral) or counterclockwise (sinistral) morphotypes- from dextral to sinistral was observed in the Atlantic, Pacific and Indian Oceans. This coiling shift represents a valuable biostratigraphic tool. It is   linked to an evolutionary turnover in Morozovella species, with M. crater and M. aragonensis becoming dominant. These two morphotypes may represent cryptic species, akin to living taxa, and their change can be interpreted as a further evolutionary change in the taxon. The K/X event is characterized by the disappearance of the Oxygen Deficient Zone (ODZ)-dwelling genus Chiloguembelina, indicating ODZ contraction during the EECO, as also supported by published Foraminifera-bound nitrogen isotope data from the Atlantic and tropical Pacific.

The J and K/X events appear to represent turning points for foraminiferal assemblages. δ¹³C records distinct long-term decrease (J) and increase (K/X), consistent with respectively enhanced and lowered fluxes in carbon inputs

Across the studied hyperthermals PF communities shifted to a new configuration that was never fully recovered, reflecting loss of resilience.

The environmental impacts of these relatively slow, compared to modern warming events underscore the potential for more severe and rapid ecosystem consequences in the modern context.  Our findings provide critical insights into the mechanisms and limits of marine ecosystem resilience.

How to cite: Luciani, V., Filippi, G., Sigismondi, S., and Schmidt, D.: Impact of EECO Hyperthermals on Planktic Foraminiferal Communities, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19492, https://doi.org/10.5194/egusphere-egu25-19492, 2025.

Over geological time, climatic fluctuations and hyperthermal events profoundly influenced carbonate systems and the related marine ecosystems. During the Eocene, approximately 40.1 Ma, a significant warming phase, the Middle Eocene Climatic Optimum (MECO), occurred persisting for around 500,000 years. Within this context, the composition and calcification rates of marine organisms, such as corals and larger benthic foraminifera (LBF), were shaped by variations in global CO2 levels and oceanographic conditions, exerting a profound influence on photic-zone carbonate factories.

The Middle Eocene Monte Saraceno sequence (Gargano Promontory) and the San Domino Formation (Tremiti Islands), cropping out along the eastern margin of the Apulia Carbonate Platform (southern Italy), represent case studies to explore the carbonate factory responses to climatic variations as the MECO event. In this areas, Middle Eocene deposits are mainly characterized by two distinct intervals with different modes of carbonate production. In particular, a well-exposed section belonged to the Monte Saraceno sequence reveals a lower interval with clinostratified, thick beds of rudstone to floatstone, predominantly formed by LBF belonging to the genus Nummulites, indicating an early Bartonian age (Shallow Benthic Zone 17). The upper interval, separated from the lower by a sharp boundary, is characterized by branching coral floatstone to rudstone with a packstone matrix associated with bivalve, gastropods, and rare, small LBF. Here, the Heterostegina sp. and Glomalveolina ungaroi occurrences define a late Bartonian age (Shallow Benthic Zone 18). Likewise, in the Tremiti Islands, the San Domino Fm is characterized by abundant LBF in the lower intervals covered by coral-rich facies exhibiting a great diversity in coral species and morphologies.

Integration of biostratigraphy, stable-isotope, and sedimentological evidences of the Monte Saraceno sequence indicates that the lower clinostratified interval, featuring abundant Nummulites and an absence of corals, corresponds to the MECO event. Conversely, the abrupt transition in the late Bartonian to a coral-dominated carbonate factory, accompanied by a marked decline in LBF abundance and size, is likely attributable to a temperature drop that fostered conditions more favorable for coral growth. Analogously, the coral factory flourishing, occurred within upper interval of the San Domino Fm, is associated to colder environments probably reaching the late Bartonian-Priabonian ages.

Therefore, this study provides compelling evidence of how the environmental changes can impact on marine carbonate production, highlighting how these studies can be a powerful tool in understanding the relationship between climate dynamics and carbonate systems across geological timescales, including the past, present, and future.

How to cite: Morabito, C. and Morsilli, M.: Impact of the MECO (Middle Eocene Climatic Optimum) on shallow-water carbonate systems: a case study from the Apulia Carbonate Platform (Gargano Promontory and Tremiti Islands, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21136, https://doi.org/10.5194/egusphere-egu25-21136, 2025.

Conventional neo-Darwinian theory views organisms as responsive to their environments on neontological timescales, and able to readily change size or shape due to selection pressures (as exemplified by the famous case of Galápagos finches). But since 1863, it has been well established that Pleistocene animals and plants show limited morphologic change in response to the glacial-interglacial cycles. Rancho La Brea tar pits in Los Angeles, California, preserves a large and diverse fauna from many well-dated deposits, spanning 37,000 years. Pollen evidence shows that climate changed from oak-chaparral about 37 ka to snowy piñon-juniper-ponderosa pine forests during the peak glacial about 18 ka, then returned to the modern chaparral since the glacial-interglacial transition. We have studied all the sufficiently abundant mammals (dire wolves, saber-toothed cats, giant lions, Harlan’s ground sloths, camels, bison, and horses) and all the common birds (28 species, ranging from eagles, hawks, vultures, condors, owls, to yellow-billed magpies, ravens, and Western meadowlarks). We found complete stasis in size and robustness as measured by the major limb bones in all 28 species. There was no significant response even at 20 ka to 18 ka, during the peak glacial period, when climate and vegetation were very different at La Brea. The larger species might be so wide-ranging and versatile that they would not respond to environmental changes, but this is inadequate to explain stasis in even the smallest birds, such as meadowlarks and burrowing owls. While the Galápagos finch model suggests rapid morphological change in response to environmental change, the fossil record shows that such small-scale changes are transient and do not accumulate to result in speciation.

How to cite: Prothero, D. R.: Patterns of Evolution in late Pleistocene Mammals and Birds from La Brea Tar Pits, California, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21959, https://doi.org/10.5194/egusphere-egu25-21959, 2025.