Paleocene-Eocene Thermal Maximum Research Articles

Deciphering Paleocene‐Eocene Thermal Maximum Climatic Dynamics: Insights From Oxygen and Hydrogen Isotopes in Clay Minerals of Paleosols From the Southern Pyrenees

AbstractThis study focuses on the Paleocene‐Eocene Thermal Maximum (PETM), a hyperthermal event characterized by a rapid increase in global temperature (5–8°C) over 20 ka, in the Southern Pyrenean Foreland Basin. Although there is evidence of increased flood discharge and erosion in the Southern Pyrenees, how paleoclimatic conditions and weathering evolved remains to be assessed. This study focuses on the catchment scale climatological changes recorded in the clay minerals of floodplain paleosols, giving insights into how rainfall affected the weathering regime during and after the hyperthermal event. The oxygen (δ18O) and hydrogen (δD) isotope compositions were analyzed in two clay fractions in paleosols of the Esplugafreda continental section. The clay minerals comprise a dominant smectite‐rich assemblage, which indicates a predominantly seasonal, semi‐arid climate throughout the section. Two positive excursions in the δ18O record during the Pre‐Onset Excursion (POE) and the Syn‐PETM support an increase in air near‐surface temperature. Using the δD and δ18O smectite fractionation factors, we estimate a Mean Annual Air Temperature (MAAT) of 24.2 ± 1.0°C for the POE and 27.0 ± 0.8°C for the Syn‐PETM. The δD values show a relatively stable composition during the climatic disturbance, which suggests that this mid‐latitude catchment was overall characterized by low yearly rainfall, with a peak in extreme events during the body of the PETM and a trend toward aridification during the recovery phase of the PETM, supported by the paleosol morphotype. These climatic conditions suggest a kinetically controlled weathering regime, where physical transport of the sediments played a primary role as a denudation mechanism.

The Baroch Nala section (NE Pakistan): A new PETM standard for the eastern Tethys

We present an integrated, high-resolution, biostratigraphical, mineralogical, and geochemical characterization of the well-exposed Upper Paleocene - Lower Eocene stratigraphic succession of the Surghar Range (Baroch Nala section, NE Pakistan). The faunal assemblages from the Baroch Nala section, dominated by hyaline benthic foraminifera and green calcareous algae, along with the significant terrigenous fraction and the presence of terrestrially derived organic matter, testify to the deposition in a low-energy shallow-marine environment. Such environmental conditions, coupled with weak diagenetic effects, allow us to integrate a continuous record of carbon stable isotopes with a detailed account of the biotic response by carbonate-producing assemblages, paleoclimatic information based on clay-minerals, and information on volcanic activity based on mercury concentrations. The environmental evolution from the Late Paleocene up to the Paleocene Eocene Thermal Maximum (PETM) is clearly documented, including the weaker warm excursion that precedes the PETM (i.e. the Pre-Onset Excursion “POE”), and the evolution of large benthic foraminiferal assemblages. The overall record perfectly shows how the turnover in benthic carbonate producers started with the onset of the PETM and was completed by the time the excursion ended, highlighting how (geologically) brief environmental oscillations can have long lasting effects on the biosphere.

High-precision U–Pb geochronology of the Lundy igneous complex: implications for North Atlantic volcanism and the far-field Paleocene–Eocene ash record

The Lundy Island (Bristol Channel, UK) granite is a felsic expression of the southernmost igneous centre of the North Atlantic Igneous Province that emplaced millions of cubic kilometres of magma during the Paleogene. The granite's distinctive S-type, peraluminous, two-mica ± garnet ± tourmaline composition has led to the hypothesis that eruptions from the Lundy volcanic centre may be the source of thick felsic ash layers within the early Eocene Fur Formation (Denmark) that act as key marker horizons for the onset and duration of the Paleocene–Eocene Thermal Maximum. This paper presents high-precision zircon U–Pb emplacement ages of 57.24 ± 0.11/0.12/0.13 Ma for the granite and 55.970 ± 0.021/0.030/0.070 Ma for a felsic ‘lundyite’ dyke. Trace and rare earth element patterns indicate close similarities between late-stage Lundy activity and ash layer −33 in Denmark. This ash layer was deposited during the Paleocene–Eocene Thermal Maximum carbon isotope excursion, suggesting that the Lundy volcanic centre is likely to be the source of this key ash horizon and that magmatism at Lundy likely continued into the early Eocene.

Expanded subsurface ocean anoxia in the Atlantic during the Paleocene-Eocene Thermal Maximum

The ocean has experienced substantial oxygen loss over recent decades, affecting marine ecosystems and fisheries. Investigating ocean deoxygenation during hyperthermal events, such as the Paleocene-Eocene Thermal Maximum (PETM), offers insights into its future dynamics. Here, sediment cores from the South Atlantic reveal a pronounced decline in foraminifera-bound δ15N, concurrent with an increase in marine barite δ34S and enhanced ocean productivity during the PETM. These findings suggest an expansion of oxygen-deficient zones (ODZs) from suboxia to anoxia in the thermocline, with ammonium and sulfide accumulation. Model simulations indicate “ammonium-type” ODZs were driven by Southern Ocean warming and elevated productivity. Intense fixed nitrogen loss at the upper boundary of these ODZs, along with increased oceanic phosphorus inventory, likely spurred a compensatory rise in N2 fixation. While the Pacific might experience different oxygenation conditions during the PETM, parts of the Atlantic thermocline became anoxic, highlighting potential spatial variabilities of ocean deoxygenation under global warming.

Crocodylian diversity during the early Eocene climatic optimum in the Golden Valley Formation of North Dakota, U.S.A.

ABSTRACT Rich bone beds from the lower Eocene strata of the Golden Valley Formation of Stark County, North Dakota reveal a speciose sympatric crocodylian fauna. However, analyses demonstrate limited phylogenetic diversity among these co-occurring taxa, and of the four species known for the locality, three are alligatorids and one is a crocodyloid. Phylogenetic hypotheses recover Chrysochampsa mylnarskii as a late lived member of Brachychampsini—a stem-based clade including Brachychampsa montana and all alligatorids more closely related to it than to Caiman crocodilus or Alligator mississippiensis—and a new genus and species, Ahdeskatanka russlanddeutsche groups with species of Allognathosuchus. The crocodylians, partitioned by body size and plan, would have occupied an array of ecological niches and feeding strategies. Whereas the large-bodied alligatorid Chrysochampsa mylnarskii preserves a generalist morphology, Ahdeskatanka russlanddeutsche bears a short, broad snout and globular distal teeth. Contemporaneous with a peak in alligatoroid diversity during this interval, Ahdeskatanka russlanddeutsche is an exemplar of a radiation of small-bodied alligatorids with crushing dentition and preserves the ancestral alligatorid feeding strategy. Trophic dynamics of the locality diverge from modern environments and the abundant crocodylians may have filled the ecological niche of large mammalian carnivores conspicuously absent here. This alligatorid-rich crocodylian fauna evolved in swampy lowlands and meandering streams flanked by subtropical forests during one of the hottest sustained intervals in Earth history. The lush, highly productive ecosystems preserved in the Golden Valley Formation inform the evolutionary history of North American alligatorids and preserve significant biodiversity following the Paleocene–Eocene Thermal Maximum.

Linking the PETM and North Atlantic volcanism using tellurium in sediments

The Paleocene – Eocene Thermal Maximum (PETM) was a short period (~170 kyr) of global temperature rise starting at 55.93 Ma, which occurred during the breakup of the North Atlantic and the emplacement of the North Atlantic Igneous Province (NAIP). Recently, mercury (Hg) concentrations in sediments have been used in an attempt to connect the eruptive history of the NAIP with environmental change during this period, at a higher resolution than possible using geochronology. Here we present sedimentary tellurium (Te) as a novel proxy to further reconstruct NAIP volcanism at high resolution. We measured 45 trace elements in 401 sediment samples from 3 sections across the PETM in the northern hemisphere. All study sites exhibit an increase in Te concentrations and Te/Th ratios close to the onset of the PETM and remain high until the end of the main North Atlantic ash phase about 1 Myr later. The trace element data indicate that changes in sediment lithology or in environmental conditions do not influence sedimentary Te concentrations suggesting a volcanic source instead. We used existing age models to remove the effect of changes in sedimentation rate and calculated volcanic Te fluxes. Our Te data suggest increased volcanism in the latest Paleocene and early Eocene. This fits existing radiometric ages of the NAIP, which demonstrate that a more than 5 km thickness of lava in eastern Greenland and the Faroes was erupted within about 1 Myr between ~56 to ~55 Ma. All our study sites show similar Te flux variations across the PETM. In contrast, sedimentary mercury (Hg) profiles from these and other sites are less consistent. Tellurium in sediments may represent a useful proxy to reconstruct NAIP volcanism.

The temperature-precipitation duel and tropical greening during the Early Eocene Greenhouse episode

Under rising anthropogenic CO2, the future of the tropical climate states and the response of the biosphere, specifically the fate of the tropical rainforest (TRF), is uncertain. Therefore, deep-time climate proxy records and model simulations are being extensively utilized to understand the possible response of the TRF community during extreme climate states. However, comprehensive climate-TRF proxy data from the tropical/equatorial region for the paleo-global warming episodes, e.g., Late Paleocene – Early Eocene interval (~56 to 51 Ma, encompassing transient hyperthermal events like Paleocene-Eocene Thermal Maximum [PETM], Eocene Thermal Maximum2 [ETM2]/H1/ Eocene Layer of Mysterious Origin [ELMO], H2, I1, and I2), are very limited and create difficulties in the validation of simulated results. Here we present long-term land surface temperature and precipitation (δ2H and δ18O of pedogenic clay mineral-derived) and TRF diversity (palynology) data from a paleo-equatorial region, spanning the ~56 to 51 Ma interval. Present data suggest that the hydrological response to global warming was not temporally uniform in the paleo-equatorial land. While a significantly increased rainfall buffered the terrestrial temperature during the PETM, an insignificant increase in precipitation and negligible temperature lowering can be observed during the ETM2 hyperthermal event. However, the climate system's response during the other Early Eocene hyperthermals, i.e., H2, I1, and I2, was very similar to the PETM. Despite these small aberrations, the long-term average equatorial land surface temperature (27 ± 4 °C) during the Early Eocene greenhouse episode remained very similar to the modern equatorial temperature (28–30 °C). Rainfall proxy and plant diversity data suggest that the precipitation aided TRFs' resilience and proliferation, possibly through temperature buffering, during this paleo-greenhouse episode.

Multi‐Elemental Statistical Features of Early Paleogene Sediments From the Mid‐Latitude Eastern Indian Ocean

AbstractThe early Paleogene, including the Paleocene and Eocene, is characterized by Warmhouse and Hothouse climate states with superimposed transient warming events known as hyperthermals. While these paleoenvironmental changes are well‐documented in the Pacific and Atlantic Oceans, records of such changes in the Indian Ocean are limited. Here, we present a new data set of bulk chemical composition and stable isotopic ratios from the late Paleocene to middle Eocene sediments on the Exmouth Plateau in the mid‐latitude eastern Indian Ocean. The bulk δ13C and δ18O suggest a warming period called the Early Eocene Climatic Optimum (EECO) and cooling toward the middle Eocene in a long‐term perspective. In the short‐term, we identified at least six hyperthermals (Paleocene–Eocene Thermal Maximum, H2, I1, J, ETM3, and L) in the studied sections. By applying independent component (IC) analyses (ICA) to the bulk chemical composition data, we identified six ICs corresponding to sediment source materials and post‐depositional processes. The ICA result infers an increase in detrital materials or a decrease in carbonate rain flux, and an increased population of higher‐order consumers in the oceanic ecosystem during both long‐term (EECO) and short‐term (hyperthermal) warmings around the Exmouth Plateau. Furthermore, ICs representing diagenetic processes and post‐depositional remobilization of elements showed excursions across the hyperthermal horizons, indicating that changes in the redox state of pore or bottom water are associated with hyperthermals. This study provides critical insights into the paleoceanography of the Indian Ocean, highlighting the response of marine environments to both long‐term and short‐term climatic events during the early Paleogene.

Cenozoic Carbon Dioxide: The 66 Ma Solution

The trend in partial pressure of atmospheric CO2, P(CO2), across the 66 MYr of the Cenozoic requires elucidation and explanation. The Null Hypothesis sets sea surface temperature (SST) as the baseline driver for Cenozoic P(CO2). The crystallization and cooling of flood basalt magmas is proposed to have heated the ocean, producing the Paleocene–Eocene Thermal Maximum (PETM). Heat of fusion and heat capacity were used to calculate flood basalt magmatic Joule heating of the ocean. Each 1 million km3 of oceanic flood basaltic magma liberates ~5.4 × 1024 J, able to heat the global ocean by ~0.97 °C. Henry’s Law for CO2 plus seawater (HS) was calculated using δ18O proxy-estimated Cenozoic SSTs. HS closely parallels Cenozoic SST and predicts the gas solute partition across the sea surface. The fractional change of Henry’s Law constants, Hn−HiHn−H0 is proportional to ΔP(CO2)i, and Hn−HiHn−H0×∆P(CO2)+P(CO2)min, where ΔP(CO2) = P(CO2)max − P(CO2)min, closely reconstructs the proxy estimate of Cenozoic P(CO2) and is most consistent with a 35 °C PETM ocean. Disparities are assigned to carbonate drawdown and organic carbon sedimentation. The Null Hypothesis recovers the glacial/interglacial P(CO2) over the VOSTOK 420 ka ice core record, including the rise to the Holocene. The success of the Null Hypothesis implies that P(CO2) has been a molecular spectator of the Cenozoic climate. A generalizing conclusion is that the notion of atmospheric CO2 as the predominant driver of Cenozoic global surface temperature should be set aside.

Recognition of a cryptic maximum flooding surface in shallow marine carbonate sequences using geochemical (Y/Ho) proxy data

ABSTRACTSince diagnostic primary depositional sedimentary structures and depth‐dependent grain‐size trends are rarely preserved, building a comprehensive sequence stratigraphic framework for the vast majority of the Phanerozoic carbonate platform sequences is pending. Among the two most important sequence stratigraphic surfaces, while the subaerial unconformity can be reliably identified by either karst development or the appearance of siliciclastic materials, the demarcation of the maximum flooding surface remains difficult in lithologically uniform shallow marine carbonate sequences. The present study attempts to identify the globally documented maximum flooding surface within the body of the negative carbon isotope excursion of the Palaeocene–Eocene Thermal Maximum recorded in the shallow marine carbonate platform sequences. The results show that, along with the carbonate microfacies, the yttrium to holmium ratio (Y/Ho ratio) of the carbonate fraction reliably records the sea‐level changes. A Y/Ho ratio between 70 and 80 demarcates the stratigraphic position of the maximum sea‐level state (the most open marine condition in the studied interval) and maximum flooding surface in the studied sections. Since the Y/Ho ratios remain relatively stable throughout diagenesis, they can be used for maximum flooding surface identification in shallow marine carbonate platform sequences. The possibility exists that the same method can also be applied to the mixed siliciclastic–carbonate systems.

Long- and short-term coupling of sea surface temperature and atmospheric CO2 during the late Paleocene and early Eocene

The late Paleocene and early Eocene (LPEE) are characterized by long-term (million years, Myr) global warming and by transient, abrupt (kiloyears, kyr) warming events, termed hyperthermals. Although both have been attributed to greenhouse (CO2) forcing, the longer-term trend in climate was likely influenced by additional forcing factors (i.e., tectonics) and the extent to which warming was driven by atmospheric CO2 remains unclear. Here, we use a suite of new and existing observations from planktic foraminifera collected at Pacific Ocean Drilling Program Sites 1209 and 1210 and inversion of a multiproxy Bayesian hierarchical model to quantify sea surface temperature (SST) and atmospheric CO2 over a 6-Myr interval. Our reconstructions span the initiation of long-term LPEE warming (~58 Ma), and the two largest Paleogene hyperthermals, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) and Eocene Thermal Maximum 2 (ETM-2, ~54 Ma). Our results show strong coupling between CO2 and temperature over the long- (LPEE) and short-term (PETM and ETM-2) but differing Pacific climate sensitivities over the two timescales. Combined CO2 and carbon isotope trends imply the carbon source driving CO2 increase was likely methanogenic, organic, or mixed for the PETM and organic for ETM-2, whereas a source with higher δ13C values (e.g., volcanic degassing) is associated with the long-term LPEE. Reconstructed emissions for the PETM (5,800 Gt C) and ETM-2 (3,800 Gt C) are comparable in mass to future emission scenarios, reinforcing the value of these events as analogs of anthropogenic change.

The White Hills Gravel of central Victoria: an anomalous Paleogene very coarse-grained fluvial deposit

The White Hills Gravel is the coarsest fluvial gravel within Victoria, southeastern Australia, and outcrops discontinuously across a substantial part (>35 000 km2) of this region. It overlies a major regional unconformity representing >300 Ma, and is dominated by conglomerate (61% of beds), with less abundant sandy lithofacies (36% of beds) and rare mudstones (3% of beds). The sedimentary characteristics of the basal conglomerates (e.g. thick bedding, common boulders, very poor sorting and in places chaotic appearance) indicate deposition by significant paleofloods, including debris floods, within braided streams that had similar flow directions to the modern drainage. Paleohydraulic calculations estimate that the paleofloods had discharges exceeding >7200 m3 s−1, over 25 times the largest recorded floods in the same valleys. These paleofloods were probably caused by exceptionally severe storm systems, consisting of many individual thunderstorms. Deposition of the White Hills Gravel has previously been attributed to the mid-Cretaceous uplift that affected southeastern Australia, but the maximum possible age of the formation (early Paleocene) is too young for this to be a viable explanation. Instead, the White Hills Gravel may have been deposited during a period of increased precipitation at the Paleocene–Eocene Thermal Maximum (ca 56 Ma), when an intensification of the hydrological system generated significant sediment responses within fluvial systems around the world. Modelling indicates that this climatic event had a substantial impact in Victoria, where increases in mean annual precipitation (50–60%) and the most extreme rainfall rates achieved by the strongest storms (60–70%) were some of the largest globally, and frequent and intense Atmospheric Rivers were an important part of the hydrological system. These factors, together with a period of disturbed vegetation cover, resulted in major paleofloods that could have deposited the coarse-grained conglomerates of the White Hills Gravel.

New insights on the stratigraphy of the Upper Cretaceous-lower Paleogene successions at Esh-ElMellaha half-graben, Gulf of Suez, Egypt

Detailed field and stratigraphic (lithostratigraphy & biostratigraphy) studies were carried out on the Upper Cretaceous–lower Paleogene successions at Esh-ElMellaha half-graben, Gulf of Suez, Egypt. Four stratigraphic sections were investigated and arranged in a geologic profile extends from south to north as follow: Gabal El-Mellaha, Wadi Abu Had, Wadi Dib and Gabal Tarbul. The field work led to recognize four lithostratigraphic units (formations): Sudr (upper part), Dib, Esna and Thebes (top). The distinctive Dababiya Quarry Member (DQM) which characterizes the Paleocene Eocene Thermal Maximum (PETM) was initially recorded at Esh-ElMellaha region. Sudr Formation is stratigraphically differentiated into two distinctive informal rock units, argillaceous bedded limestone unit and calcareous shale unit. The Dib Formation is here reviewed and correlates with the Dakhla Formation (upper part) in the different geographic neighborhoods of Egypt. It consists of glauconitic carbonate rocks (bioclastic limestone) embracing reworked gravelly and pebbly extra-clasts and broken exhumed mega-fossils (e.g. cephalopods, gastropods and bivalves, corals). Dib Formation is assigned to thelower Paleocene (Danian Stage) according to the occurrence of praemuricids taxa (e.g. Praemurica inconstans and P. uncinata) index fossils. Esna and Thebes formations are assigned to the Ypresian Stage. Dib Formation is bounded by two regional unconformity surfaces (erosional surfaces) as a result of two tectonic events (I and II) linked to Syrian Tectonic Event.

Response of coastal California hydroclimate to the Paleocene–Eocene Thermal Maximum

Response of coastal California hydroclimate to the Paleocene–Eocene Thermal Maximum

Unparallel resilience of shallow-water tropical calcifiers (foraminifera and scleractinian reef corals) during the early Paleogene global warming intervals

Investigating the fossil record to provide evidence about the response of shallow-water tropical calcifiers to past warming events is crucial considering that they are severely threatened by current global warming. We thus focused our attention on scleractinian reef corals (SRC) and shallow-water foraminifera (SWF), both mainly symbiont-bearing organisms, analysing and comparing their diversity patterns during the Paleocene and Eocene from datasets of the Neothetyan circum-Mediterranean region. In particular, at both genus and species level, we analysed changes in diversity, together with origination and extinction rates.Despite some biases related to biostratigraphic resolution of SRC and SWF data, our results show that they reacted differently to the major warming events of the Early Paleogene. The K/Pg mass extinction caused the disappearance of almost all SWF, whereas several corals passed this crisis and persisted up to the end of Paleocene, when the Paleocene-Eocene Thermal Maximum (PETM) caused a relatively small decrease of coral diversity together with a global collapse of coral reefs. On the other hand, a rapid radiation of nummulitids and alveolinids occurred at species level. The impact of the Early Eocene Climatic Optimum (EECO) was apparently more severe for SWF than for SRC. After the Middle Eocene Climatic Optimum (MECO), the general cooling trend led to the fading of Eocene SWF genera and species, whereas SRC began their rapid diversification from Bartonian to Priabonian and culminating in the Chattian.Our results suggest that rapid warming events favoured speciation in SWF, whereas the slow cooling trend (e.g., after the MECO) favoured diversification of SRC. Our data also underline that SWF reacted differently to warming events as compared to deep-sea smaller benthic foraminifera and that the same events in the planktonic realm are not strictly coeval with those occurring in shallow-water environments.On a wider perspective, we observe that shallow-water calcifiers demonstrate a good degree of resilience to global temperature increases, even if undergoing to more or less marked reduction of biodiversity. We provide evidences for the recovery of past ecosystems from both short and long stressors.

The Cretaceous to Eocene: a biostratigraphical review and a new detailed palynostratigraphy of Greenland and adjacent areas

The present paper compile and correlate for the first time Cretaceous to Eocene palynostratigraphies across the Arctic. It focus on Greenland and adjacent areas, including the Labrador–Baffin Seaway, onshore Nuussuaq Basin in central West Greenland, onshore southern East Greenland, central East Greenland, North-East Greenland, eastern North Greenland and the Danmarkshavn Basin, but also extends to Canadian Arctic Archipelago and the Barents Sea region off Norway. The paper compile data from more than three decades of detailed Arctic palynological analyses, based mainly on dinoflagellate cysts. The paper gives a historical overview of the Cretaceous to Palaeogene paleontological studies of Greenland and presents an overview of 85 palynological intervals and numerous events. The palynological assemblages from the Labrador–Baffin Seaway, Nuussuaq Basin and north-east Baffin Bay reflect the opening of the Labrador–Baffin Seaway from brackish to freshwater environment in a large embayment in the Early Cretaceous to an open marine seaway in the Late Cretaceous. Assemblages reveal in dinoflagellate cyst provincialism between the opening stages of the Labrador–Baffin Seaway and the already opened Greenland–Norwegian–Barents seaway. The Upper Cretaceous global Oceanic Anoxic Event 2 (OAE2) spanning the Cenomanian/Turonian boundary is recognised from Arctic Canada, north-east Baffin Bay, Nuussuaq Basin in central West Greenland, and North-East Greenland, and is mapped and correlated based on dinoflagellate cyst stratigraphy and carbon isotope (δ13Corg) curves. The dinoflagellate cysts assemblages of the Cretaceous/Palaeogene boundary are correlated from the Labrador Sea across to the Nuussuaq Basin in central West Greenland; in both areas the earliest Danian palynological assemblage is represented by incoming warm-water species. The presence of the global Paleocene–Eocene Thermal Maximum (PETM) in the Palaeogene successions in North-East Greenland and in exploration wells in the Labrador–Baffin Seaway is indicated by the incoming of the warm-water dinoflagellate cyst species Axiodinium augustum.

Unique functional diversity during early Cenozoic mammal radiation of North America.

Mammals influence nearly all aspects of energy flow and habitat structure in modern terrestrial ecosystems. However, anthropogenic effects have probably altered mammalian community structure, raising the question of how past perturbations have done so. We used functional diversity (FD) to describe how the structure of North American mammal palaeocommunities changed over the past 66 Ma, an interval spanning the radiation following the K/Pg and several subsequent environmental disruptions including the Palaeocene-Eocene Thermal Maximum (PETM), the expansion of grassland, and the onset of Pleistocene glaciation. For 264 fossil communities, we examined three aspects of ecological function: functional evenness, functional richness and functional divergence. We found that shifts in FD were associated with major ecological and environmental transitions. All three measures of FD increased immediately following the extinction of the non-avian dinosaurs, suggesting that high degrees of ecological disturbance can lead to synchronous responses both locally and continentally. Otherwise, the components of FD were decoupled and responded differently to environmental changes over the last ~56 Myr.

Interactive Effects of Temperature, Aridity, and Plant Stoichiometry on Insect Herbivory: Past and Present.

AbstractThe influence of climate on deep-time plant-insect interactions is becoming increasingly well known, with temperature, CO2 increases (and associated stoichiometric changes in plants), and aridity likely playing a critical role. In our modern climate, all three factors are shifting at an unprecedented rate, with uncertain consequences for biodiversity. To investigate effects of temperature, stoichiometry (specifically that of nitrogen), and aridity on insect herbivory, we explored insect herbivory in three modern floral assemblages and in 39 fossil floras, especially focusing on eight floras around a past hyperthermal event (the Paleocene-Eocene Thermal Maximum) from Bighorn Basin (BB). We find that higher temperatures were associated with increased herbivory in the past, especially among BB sites. In these BB sites, non-N2-fixing plants experienced a lower richness but higher frequency of herbivory damage than N2-fixing plants. Herbivory frequency but not richness was greater in BB sites compared with contemporaneous, nearby, but less arid sites from Hanna Basin. Compared with deep-time environments, herbivory frequency and richness are higher in modern sites, suggesting that current accelerated warming uniquely impacts plant-insect interactions. Overall, our work addresses multiple aspects of climate change using fossil data while also contextualizing the impact of modern anthropogenic change on Earth's most diverse interactions.

The Paleocene - Eocene mangroves of southeastern Australia: spatial and temporal occurrences across four geological basins

The advent of the Paleocene-Eocene Thermal Maximum (PETM), a ∼ 200 kyr period of global warming ca. 56 Ma, caused sea-levels to rise, transgressing near-coastal environments in southeastern (SE) Australia over >55,000 km2. During the PETM, warming tropical climates may have extended south to ≥60°S paleolatitude. The PETM in SE Australia is corroborated primarily by stable carbon isotope chemostratigraphy and detailed palynology records in four geological basins. Previous work showed that, in addition to the globally recognised carbon isotope excursion, the PETM interval in coastal SE Australia can be identified using the dual occurrence of the tropical mangrove Nypa palm pollen (Spinizonocolpites prominatus) accompanied by thermophilic marine dinoflagellate cysts (mainly Apectodinium hyperacanthum). We here document a total of twenty-six Gippsland Basin wells that record this Nypa-A.hyperacanthum association in the earliest Eocene Kingfish Formation (Lower Malvacipollis diversus Zone). In the Bass Basin, eight wells record Nypa-A.hyperacanthum association within the Eastern View Group basal Koorkah Formation, or lower part of the Lower M. diversus Zone (earliest Eocene). In the Bass Basin a further thirteen wells with Nypa occurrences near the top of the Cormorant Formation are found, which might be associated with the longer-term warmth of the Early Eocene Climatic Optimum (EECO, ∼53–49 Ma). Government bores and petroleum wells across the Otway Basin record the Nypa-A. hyperacanthum PETM association within the Pember Mudstone Lower M. diversus Zone in twenty-one bores. Nine horizons with Nypa occurrences occur within the Burrungule Member (EECO) at the top of the Dilwyn Formation. In western Tasmania, Nypa occurs in the Sorell Basin and Macquarie Harbour area within the Lower M. diversus Zone. Together, these observations show the remarkable extent of the mangrove-coasts that were established across the mid-high paleolatitudes in SE Australia during the warmest intervals of the Cenozoic, the PETM and EECO.

Fingerprinting enhanced floodplain reworking during the Paleocene–Eocene Thermal Maximum in the Southern Pyrenees (Spain): Implications for channel dynamics and carbon burial

Abstract The sedimentary record of the Paleocene–Eocene Thermal Maximum (PETM, ca. 56 Ma) allows the study of feedback mechanisms over the entire duration of a climatic event, from carbon release to the subsequent recovery phase. Clay sedimentation increase in the oceans during the PETM is linked to enhanced terrestrial erosion. Fluvial channel mobility has been invoked to explain this increase in fine sediment export based on more frequent transitional avulsions. In this study, we test whether the reworking of Microcodium (prismatic calcite concretions) from the floodplain to marine environments can serve to fingerprint floodplain reworking due to channel mobility. We quantified the abundance of floodplain-sourced Microcodium grains reworked in fluvial to marine sandstones pre-dating and coeval to the PETM in the Southern Pyrenees (Tremp Basin, Spain). Laser ablation–inductively coupled plasma–mass spectrometry U-Pb ages on calcite confirm the Thanetian age of the Microcodium grains. Our data show a four-fold increase in the export of floodplain sediments to the marine domain during the PETM. Moreover, we show that this is predominantly due to enhanced channel mobility, reworking channel banks and interfluves, with increased erosion in the hinterland as a secondary factor. This increase in floodplain reworking would correspond to an increase in biospheric carbon burial flux by a factor of 2.2. Therefore, enhanced channel mobility and fine-grain sediment transport to the oceans during a climatic perturbation such as the PETM may constitute an important negative feedback mechanism.