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Abstract\nKEY POINTSThe 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.The White Hills Gravel in central Victoria is dominated by conglomerate (∼61% of beds), with lesser sandstone (∼36% of beds) and rare mudstone (∼3% of beds).In valleys across the central Victorian Highlands, White Hills Gravel outcrops are characteristically elevated above the Calivil Formation, and in the Campaspe and Loddon valleys, the long profiles of both formations cross over downstream.There is no evidence of a tectonic origin for the formation; instead, the White Hills Gravel was most likely deposited in response to a sharp rise in precipitation.The very-coarse-grained base of the formation was deposited by major thunderstorm-generated paleofloods with discharges up to and exceeding 7200 m3 s−1 in small catchments.The White Hills Gravel may denote a significant fluvial response to climate modification across the Paleocene–Eocene Thermal Maximum. [ABSTRACT FROM AUTHOR]

Here we report on anguimorph lizards from the earliest Eocene (MP 7) of the Dormaal locality in Belgium, from the time of the warmest global climate of the past 66 million years. Several clades can be identified in this site: Glyptosauridae, Varanidae, and Palaeovaranidae. Our study focuses on glyptosaurid specimens previously reported from the site, some of which had been provisionally described as a new species,? Placosaurus ragei , and some assigned to an unnamed Placosauriops -like 'melanosaurine'. Our study presents data on new material, including an almost complete glyptosaurine frontal that has enabled us to assign much of the previously described material to a single genus and species. The specimens that had been assigned to both ? P ragei and the 'melanosaurine' share apomorphies (flat osteoderms and chevron-shaped osteoderms) with Gaultia , a glyptosaurid previously known from the earliest Eocene of Wyoming, USA. The Dormaal material represents the first record of this genus outside North America. In fact, the only potential evidence of the occurrence of 'Melanosaurinae' in Dormaal might be a single isolated vertebra described here. Here we also describe previously unfigured material of Saniwa and palaeovaranids from Dormaal. The presence of previously reported helodermatids cannot be supported in this Belgian site. [ABSTRACT FROM AUTHOR]

The Paleocene‐Eocene thermal maximum (PETM, 56 Ma) is an ancient global warming event closely coupled to the release of massive amounts of 13C‐depleted carbon into the ocean‐atmosphere system, making it an informative analogue for future climate change. However, uncertainty still exists regarding tropical sea‐surface temperatures (SSTs) in open ocean settings during the PETM. Here, we present the first paired δ13C:Mg/Ca record derived in situ from relatively well‐preserved subdomains inside individual planktic foraminifer shells taken from a PETM record recovered in the central Pacific Ocean at Ocean Drilling Program Site 865. The δ13C signature of each individual shell was used to confirm calcification during the PETM, thereby reducing the unwanted effects of sediment mixing that secondarily smooth paleoclimate signals constructed with fossil planktic foraminifer shells. This method of "isotopic screening" reveals that shells calcified during the PETM have elevated Mg/Ca ratios reflecting exceptionally warm tropical SSTs (∼33–34°C). The increase in Mg/Ca ratios suggests ∼6°C of warming, which is more congruent with SST estimates derived from organic biomarkers in PETM records at other tropical sites. These extremely warm SSTs exceed the maximum temperature tolerances of modern planktic foraminifers. Important corollaries to the findings of this study are (a) the global signature of PETM warmth was uniformly distributed across different latitudes, (b) our Mg/Ca‐based SST record may not capture peak PETM warming at tropical Site 865 due to the thermally‐induced ecological exclusion of planktic foraminifers, and (c) the record of such transitory ecological exclusion has been obfuscated by post‐depositional sediment mixing at Site 865. Plain Language Summary: The Paleocene‐Eocene thermal maximum (PETM, about 56 million years ago) is a global warming event that is widely regarded as an ancient analogue for climate change being driven by the current rise in atmospheric carbon dioxide (CO2) levels. Accurate measurements of PETM warmth in the tropical oceans are crucial to validating climate model simulations and gauging the effect of global warming on oceanic ecosystems. However, chemical analyses of marine microfossils (foraminifera) typically yield tropical sea surface temperatures (SSTs) for the PETM that are cooler than those computed by climate models. Primary reasons for this discrepancy are poor preservation of the foraminifer shells and displacement of shells from the cooler pre‐PETM interval into overlying PETM sediments via sediment mixing processes. Here, we use in situ microanalytical techniques to measure both the carbon isotope composition (δ13C) and Mg/Ca ratio within the same individual shells. The δ13C values of shells were used to identify displaced pre‐PETM specimens with higher, background δ13C ratios and exclude them from our Mg/Ca‐based temperature record. Our new "isotopically filtered" Mg/Ca‐based temperature record suggests ∼6°C of warming in the tropical Pacific, with SSTs (33–34°C) likely exceeding the maximum temperature tolerances of many calcifying plankton during the PETM. Key Points: Microanalytical techniques used to measure paired δ13C and Mg/Ca ratios in individual foraminifer shells from a pelagic Paleocene‐Eocene thermal maximum (PETM) recordδ13C values of individual foraminifers used to identify and exclude reworked non‐PETM specimens from Mg/Ca‐based sea‐surface temperature (SST) recordUnmixed Mg/Ca‐based temperature record indicates tropical SSTs increased by ∼6°C in central Pacific Ocean during PETM [ABSTRACT FROM AUTHOR]

The Paleocene‐Eocene Thermal Maximum (PETM) was a transient global warming event and is recognized in the geologic record by a prolonged negative carbon isotope excursion (CIE). The onset of the CIE was due to a rapid influx of 13C‐depleted carbon into the ocean‐atmosphere system. However, the mechanisms required to sustain the negative CIE remains unclear. Enhanced mobilization and oxidation of petrogenic organic carbon (OCpetro) has been invoked to explain elevated atmospheric carbon dioxide concentrations after the onset of the CIE. However, existing evidence is limited to the mid‐latitudes and subtropics. Here, we determine whether: (a) enhanced mobilization and subsequent burial of OCpetro in marine sediments was a global phenomenon; and (b) whether it occurred throughout the PETM. To achieve this, we utilize a lipid biomarker approach to trace and quantify OCpetro burial in a global compilation of PETM‐aged shallow marine sites (n = 7, including five new sites). Our results confirm that OCpetro mass accumulation rates (MARs) increased within the subtropics and mid‐latitudes during the PETM, consistent with evidence of higher physical erosion rates and intense episodic rainfall events. High‐latitude sites do not exhibit drastic changes in the source of organic carbon during the PETM and OCpetro MARs increase slightly or remain stable, perhaps due a more stable hydrological regime. Crucially, we also demonstrate that OCpetro MARs remained elevated during the recovery phase of the PETM. Although OCpetro oxidation was likely an important positive feedback mechanism throughout the PETM, we show that this feedback was both spatially and temporally variable. Plain Language Summary: The Paleocene‐Eocene Thermal Maximum (PETM) was the most severe global warming event of the last 66 million years and was caused by the rapid release of greenhouse gases into the atmosphere. However, scientists have been unable to determine why the PETM lasted for >100,000 years. Here, we test whether CO2 released from the erosion, transport, and oxidation of ancient rock‐derived (or petrogenic) organic carbon can explain the long duration of the PETM. We also aim to identify if this occurred globally and/or throughout the PETM. We achieve this by looking at biomarkers (molecular fossils) and use this approach to "fingerprint" the input of petrogenic organic carbon into the marine realm. Our results suggest enhanced transport of petrogenic organic carbon was restricted to the subtropics and mid‐latitudes, with limited changes in the high‐latitudes. We also find evidence for erosion and transport of petrogenic organic carbon throughout the PETM. Therefore, this process likely contributed to increasing atmospheric CO2 levels and may have been an important positive feedback mechanism in past and future warm climates. Key Points: We assess spatial and temporal patterns in petrogenic organic carbon (OCpetro) mobilization during the Paleocene‐Eocene Thermal MaximumEvidence for enhanced OCpetro mobilization in the subtropics and mid‐latitudes, likely due to an increase in extreme rainfall eventsOCpetro mobilization remained elevated during the recovery phase of the Paleocene‐Eocene Thermal Maximum [ABSTRACT FROM AUTHOR]

The Paleocene‐Eocene Thermal Maximum (PETM) and early Eocene hyperthermal events were characterized by a Hothouse climate state. Our understanding of the climatic impact of these hyperthermals is currently biased toward marine settings and the mid‐latitudes. Here we present organic geochemical data from Stenkul Fiord, Ellesmere Island, Arctic Canada. This organic rich formation was deposited in a high northern latitude wetland setting during the late Paleocene to early Eocene, spanning the PETM and subsequent ETM‐2 hyperthermals. Biomarker data (e.g., diterpenoids), combined with published palynological data from the site, indicate Cupressaceae‐dominated vegetation. Biomarkers suggest that land plant composition remained fairly unchanged across the two hyperthermal events. Increases in abundance and 13C‐depletion of hopanoid biomarkers (minima <−50‰ (VPDB)) highlight periods of enhanced bacterial methane consumption, particularly during the PETM. However, periods of low hopanoid δ13C values were also found outside the hyperthermal intervals. Relatively low δ2H values of higher plant n‐alkanes (average δ2H values of n‐C25, n‐C27, n‐C29 ∼ −230 to −270‰ (SMOW)) indicate that deposition formed during times with enhanced precipitation. The wettest intervals, as identified by the lowest δ2H n‐alkane values, contain high abundances of hopenes, indicating enhanced bacterial turnover. At Stenkul Fiord, high temperatures and CO2 concentrations likely fostered the growth of widespread wetland forests that became a CO2 sink and may have played an important role in carbon drawdown during the Early Paleogene. Key Points: First detailed biomarker study on high‐latitude terrestrial PETM settingBiomarkers and stable isotope signatures demonstrate cypress plant dominated setting with high methane cycling during hyperthermalsSwamp environment suggested and intense bacterial methane consumption not restricted to hyperthermals [ABSTRACT FROM AUTHOR]

To better understand the effect of the Paleocene‐Eocene Thermal Maximum (PETM) on continental ecosystems, we studied 40 new palynological samples from the Bighorn Basin (BHB), northwestern Wyoming, USA. We see palm and fern abundances increase in the last 20–40 ka of the Paleocene, then dramatically with the onset of the carbon isotope excursion (CIE) defining the base of the PETM. Palynomorphs of plant groups with modern temperate climate distributions are absent from the CIE body, and this is when tropical plants are most diverse and abundant. During the CIE recovery, pollen of mesophytic/wetland plants become more common while tropical taxa persist. In the post‐CIE early Eocene tropical taxa are rare and temperate forms abundant, similar to the late but not latest Paleocene. Changes in the palynoflora are more easily detected if reworked palynomorphs are removed from analyses. We interpret palynofloral changes to indicate warming in the latest Paleocene, rapid warming and drying with the CIE onset, dry tropical climates through the CIE body, a return to wetter floodplains during a very warm CIE recovery, and cooler wet conditions in the post‐PETM early Eocene. These inferences are consistent with geochemical and paleobotanical proxies. Strikingly similar patterns in the palynoflora and megaflora suggest changes in vegetation were a basin‐wide phenomenon. These rapid, climatically forced changes in floral composition occurred without major extinction, perhaps indicating nearby refugia in which plants adapted to cooler and wetter climates persisted through the PETM. Key Points: Bighorn Basin palynofloras began shifting toward hot/dry tolerant plants during the latest Paleocene "pre‐onset" carbon isotope excursionsPalynofloras from early in the carbon isotope excursion (CIE)‐body were dominated by ferns and palms indicating disturbance, then later by dry tropical lineagesWetland taxa regained abundance during the CIE recovery, indicating climate‐forced changes in plant distributions without major extinction [ABSTRACT FROM AUTHOR]

The Palaeocene–Eocene Thermal Maximum (PETM) was a global extreme climatic event, but it is relatively unknown from lower latitudes or equatorial regions in comparison to mid- and high latitudes. The present study provides the first clay mineralogical evidence of the PETM and subsequent hyperthermal events in a near-equatorial region represented by the Akli Formation in the Barmer Basin, India. The 32 m-thick succession of the Akli Formation shows abrupt changes in smectite and kaolin abundances preceding, during and succeeding the PETM event. Within the studied section, the kaolin content increases from 5–8% pre-PETM to 30–35% during the PETM, and then again decreases to 5–6% during the post-PETM period. The smectite, however, is marked by a corresponding decrease and its transformation into kaolin in acid weathering conditions. The transformation of the smectite is first marked by hydroxy interlayering and then transformation into kaolin during the PETM. The transformation of smectite into kaolin also resulted in extensive precipitation of iron oxide in sediments. The clay mineralogical changes in the Palaeocene–Eocene transition sediments of the Akli Formation were caused by 3–5°C warming and a 25–50% increase in rainfall during the hyperthermal events. Unusually high charcoal (∼20%) fragments during the Palaeocene–Eocene transition also suggest warming and widespread biomass burning during the PETM in the lower latitudes. [ABSTRACT FROM AUTHOR]

The Paleocene‐Eocene Thermal Maximum (PETM; ∼56 Ma)–a geologically rapid carbon‐release event similar to anthropogenic carbon emissions–is ideal for investigating weathering responses to rapid carbon release and associated climate change. Here, for the first time, we present high‐resolution lacustrine lithium isotope data that reflect basin‐scale silicate weathering across the PETM in the Nanyang Basin, eastern China. Our results reveal an ∼100% increase in regional silicate weathering intensity through the PETM relative to the pre‐PETM level. Synchronous variations between carbon isotope values and weathering intensity demonstrate a strong coupling between carbon cycle, climate, and chemical weathering on millennial timescales. These findings argue that strong negative weathering feedback and massive removal of CO2 maintained Earth's climate within a habitable range during the PETM. Plain Language Summary: The chemical breakdown of silicate minerals on continents is a major regulator of climate via atmospheric CO2 removal on million‐year timescales; however, on shorter timescales of greater relevance to understanding the fate of anthropogenic CO2, the link between silicate weathering and climate remains unclear. The Paleocene‐Eocene Thermal Maximum (PETM; ∼56 Ma)–a geologically rapid carbon‐release event similar to anthropogenic carbon emissions–represents an ideal interval for investigating weathering responses to rapid carbon release and climate change. Here, we measured the chemistry of lacustrine sediments that span the PETM in the Nanyang Basin, eastern China to reveal the link between silicate weathering and rapid carbon release. We find that regional silicate weathering increased by ∼100% through the PETM. Our results also demonstrate that carbon release, climate change, and silicate chemical weathering were closely coupled over millennial time scales. Strong negative silicate weathering feedback and massive removal of CO2 maintained Earth's climate within a habitable range across the PETM. Key Points: First lacustrine Li isotope measurements during the Paleocene‐Eocene Thermal Maximum (PETM)Lacustrine Li isotope compositions reflect regional silicate weathering processes across the PETMCarbon release, climate, and weathering were tightly coupled on millennial timescales [ABSTRACT FROM AUTHOR]

Benthic foraminiferal turnover during the Palaeocene–Eocene Thermal Maximum (PETM) has been extensively studied but numerous questions remained unresolved, question such as why some foraminiferal species went into extinction at a particular location but survive in another or why some species survive in extremely low oxygen environment. Because foraminiferal community interaction with the environment is driven by biological traits instead of taxonomic composition, this study has adopted trait-based approach to provide insight into the life strategies of foraminifera that enables them to survive in extreme environmental conditions. The result from this study shows that traits such as test composition, perforation, ornamentation and living habits play an important role in the ecological functioning and adaptability of foraminifera in the environment. The faunal assemblage in the studied site is dominantly cosmopolitan taxa suggesting the environment was perturbed during the PETM. Foraminiferal composition is characterised by faunal turnover indicated in extensive mortalities and extinction of both planktonic and benthic fauna. The ordination (non-metric dimensional scaling) of faunal composition also indicated ecological disturbance. The planktonic community was relatively stable before and after PETM but experienced a high level of ecological perturbation during the carbon isotopic excursion (CIE). The benthic community showed higher evidence of perturbation as the fauna assemblage ordination indicated that ecological stress started before the PETM with the disarray of samples in the ordination diagram. Only the recovery interval experienced some level of ecological stability. The environmental disturbance noticed in the fauna composition reflected on the trait. Benthic foraminiferal traits indicated instability throughout the studied section. The evidence of environmental disturbance in the benthic community suggests that the source of the light carbon that caused the PETM may have originated beneath sea floor in the Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Caldera-forming eruptions are amongst the most hazardous events in the Earth’s history, and understanding their formation is essential to forecasting activity at active calderas worldwide. In this study we present new field and geochronological evidence for a Paleocene-Eocene caldera from Skye, NW Scotland. Magma exploited a regional thrust fault as a conduit, and then ponded against intrusive igneous rocks emplaced against a regional extensional fault. Replenishment of silicic magma reservoirs with basaltic magma triggered eruptions. The eruptions typically deposited extremely coarse ignimbrites, demonstrating catastrophic collapse of the caldera, which occurred via an inner ring fault and a complexly faulted marginal zone. Collapse was followed by remobilisation of silicic magma and caldera resurgence. The magma consumed dolostone country rocks, causing significant release of CO2 and contributed to the Paleocene-Eocene Thermal Maximum. Our results demonstrate how tectonics localise magma and caldera development, and how this can cause cataclysmic volcanic and climatic hazards.

Pollen and spores were recovered from the Paleocene Fort Union Formation and Paleocene–Eocene Willwood Formation of the Bighorn Basin (BHB), northwestern Wyoming, USA. In many local stratigraphic sections in the BHB, the base of the Eocene has been identified by the characteristic negative carbon isotope excursion (CIE) that marks the beginning of the Paleocene–Eocene Thermal Maximum (PETM). The palynotaxa from outcrop samples were examined using light microscopy (LM) and scanning electron microscopy (SEM). Seven new species are formally described (Tricolpites vegrandis, Rousea spatium, Striatricolporites astutus, Striatopollis calidarius, Friedrichipollis geminus, Retistephanocolporites modicrassus and Retistephanocolporites pergrandis). The temporal and geographic distributions of many of these palynotaxa suggest that hotter and more seasonally dry climates facilitated their northward range shifts during the PETM from the tropics or subtropics of the USA. For the temperate palynotaxa, the hotter and seasonally dry conditions resulted in local extirpation. A re-evaluation of the palynostratigraphic schemes established for the Paleocene–Eocene boundary confirms that the first appearance of Platycarya platycaryoides denotes the Paleocene–Eocene boundary in the Rocky Mountains region. A new Striatopollis calidarius Subzone, associated with early Wasatchian (Wa) Wa-0 and Wa-R faunas, is also recognized for CIE body localities in the BHB. [ABSTRACT FROM AUTHOR]

The Palaeocene–Eocene Thermal Maximum (PETM) is one of the most important Cenozoic climatic events shaping modern biodiversity, yet reconstructions of its palaeobiomes remain controversial. Here we describe Gesomyrmex gallicus sp. nov., a new, extinct species of the ant genus Gesomyrmex Mayr, 1868, based on minor and major workers preserved in the early Eocene amber of Oise, France. Although there are only seven known extant species in the genus, all confined to warm and humid forests of SE Asia, the fossil record of Gesomyrmex indicates that the genus once radiated across Eurasia. The new species therefore provides direct evidence that this radiation likely co-occurred with the PETM. This observation constrains palaeoclimatic reconstructions of the Early Eocene by requiring the presence of an extensive, homogeneous and interconnected rainforest-like biome across palaeo-Eurasia, a scenario otherwise corroborated by pollen assemblages. The phases of regression of warm and humid forests and the widening of dry biomes probably occurred later during the Eocene, in between hyperthermals, and were probably less extensive than some computer models predicted. [ABSTRACT FROM AUTHOR]

Abstract The Paleocene‐Eocene Thermal Maximum (PETM; ∼56 Ma)–a geologically rapid carbon‐release event similar to anthropogenic carbon emissions–is ideal for investigating weathering responses to rapid carbon release and associated climate change. Here, for the first time, we present high‐resolution lacustrine lithium isotope data that reflect basin‐scale silicate weathering across the PETM in the Nanyang Basin, eastern China. Our results reveal an ∼100% increase in regional silicate weathering intensity through the PETM relative to the pre‐PETM level. Synchronous variations between carbon isotope values and weathering intensity demonstrate a strong coupling between carbon cycle, climate, and chemical weathering on millennial timescales. These findings argue that strong negative weathering feedback and massive removal of CO2 maintained Earth's climate within a habitable range during the PETM.

Seismic geomorphology and stratigraphic analysis can reveal how source-to-sink systems dynamically respond to climatic and tectonic forcing. This study uses seismic reflection data from the Norwegian Sea to investigate the stratigraphic response to a short-lived (0.2 Myr) period of climate change during the Paleocene-Eocene Thermal Maximum (PETM), superimposed on a long-lived (∼8 Myr) period of hinterland uplift. The data show that long-term uplift resulted in ∼300 m of relative sea-level fall, forced regression and formation of incised valleys during the latest Paleocene-earliest Eocene. The short-lived PETM climate perturbation at ∼56 Ma changed the transport dynamics of the system, allowing sediment to be bypassed to wide channel complexes on the basin floor, feeding a large mud-rich basin-floor fan more than 50 km into the basin. Our analysis also suggest that sediment supply was up to four times higher during the PETM compared to earlier and later periods. Maximum regression at ∼55.5 Ma resulted in the formation of a subaerial unconformity. The style of subaerial incision was dictated by shelf accommodation and proximity to the area of direct sediment input. Out-of-grade shelves and slopes sourced by littoral drift were prone to incision, but direct-fed and graded shelves and slopes were not. Despite maximum regression, sediments were not transported significantly beyond the toe-of-slope aprons, suggesting that rapid climate change was more efficient in bypassing sediment to the deep-water than low stands of sea level. As long-term accommodation increased after the PETM, deltas were still able to reach shelf edge, but periods of maximum regression were not associated with deep incisions along the outer shelf and only smaller canyons and gullies formed. The shelf-slope wedge was finally transgressed at ∼51 Ma. The age of deep valley incisions overlaps with the time of subaerial erosion in the East Shetland and Faroe-Shetland basins, suggesting a common mechanism for North Atlantic uplift around 55–56 Ma. Other seismic stratigraphic surfaces do not seem to be regionally time-equivalent, highlighting the importance of local controls on internal architecture of shelf-slope wedges. This study demonstrates the high-resolution stratigraphic response to long- and short-term external forcing together with intrinsic processes and can help identify similar relationships in other areas.

The Paleocene-Eocene Thermal Maximum (PETM) event, which represented a sudden and abnormal rise in temperature during the early Cenozoic Era, is regarded as one of the most important global geologic phenomena. Two important index microfossils (nannoplankton and Ostracoda) were utilised to understand and predict the paleoenvironment and describe the changes during this period. The basis of the study was 12 cutting samples taken from Aaliji and the lower part of Jaddala formations of a subsurface section of (Ba-8) borehole in central Iraq. Some geophysical data were used to determine the upper and lower contacts of the Aaliji Formation and define the shale rate in the studied formations. The micropaleontologic investigation reveals twenty-four nannoplankton species and twenty species belonging to seven genera of Ostracoda. The use of Nannoplankton fossils led to the identification of two types of biozones based on two species belonging to the genus Discoaster, which are ordered from bottom to top as follows; 1- Discoaster nobilis Interval Biozone (CP7) and 2- Discoaster multiraditus Interval Biozone (CP8). The biozones were compared locally and regionally with their equivalent biozones, which deduced the age of the Aaliji Formation as (Late Paleocene-Lower Early Eocene) whereas (Early Eocene) for the studied part of the Jaddala Formation. The determination of the upper and lower boundaries was determined by interpreting the geophysical logs. Ostracoda fossils were used to predict paleoecology and its changes in the area during the PETM episode. The transmutation of nanoplankton fossils from the Paleocene to the Eocene indicates an abnormal rise in global temperatures, flourishing and high diversity of some nanoplankton, such as some species gnigebleb to Discoster, especially those in the CP8 zone. [ABSTRACT FROM AUTHOR]

Continental shelf sediments along the northeast continental margin of North America contain a magnetofossil‐rich interval deposited during the Paleocene‐Eocene Thermal Maximum (PETM), an abrupt global warming event that occurred ∼56 Ma. These magnetofossils were produced by magnetotactic bacteria and unidentified, iron‐biomineralizing organisms. Previous work shows three distinct magnetofossil endmembers identified from principal component analysis of first‐order reversal curves (FORC‐PCA). The relative proportions of these magnetofossil endmembers varied over time during the PETM. Benthic foraminiferal species associations from the same sediments also vary during the PETM. Here, we compare the variability in magnetofossils and benthic foraminifera and statistically test, for the first time, whether they are significantly correlated. We find that changes in the type of magnetofossils present within the sediment correspond to changes in benthic foraminiferal assemblages, thus reflecting syndepositional conditions such as changes in oxygen, nutrients, and organic carbon concentrations, rather than diagenetic processes. We also find that magnetofossil‐producing organisms may respond to specific environmental pressures differently than benthic foraminifera, and in some cases, may better record these environmental signals. Therefore, FORC‐PCA on magnetofossil‐rich sediments can be used to understand discrete changes in ocean and/or early sediment chemistry over episodes of climate change. These environmental responses are inferred from non‐destructive, reproducible magnetic measurements, adding an independent environmental proxy to more commonly studied microfossil and geochemical proxies. Notably, these measurements only require small bulk sediment samples and do not need to contain calcium carbonate, making this approach ideal where sample material is limited and the record is affected by ocean acidification. Plain Language Summary: Magnetic measurements of sediments containing iron‐rich magnetic particles are sensitive to the shape and size of those particles. Magnetofossils are iron oxide or iron sulfide mineral grains made by bacteria and some unicellular eukaryotes. Living forms of iron‐biomineralizing bacteria are sensitive to the oxygen, food, and nutrient supply in the watery environments in which they live. Here, we study marine shelf sediments deposited along the northeast continental margin of North America during a period of abrupt and extreme global warming 56 million years ago. We quantitatively compare specific magnetofossil groups with assemblages of benthic, unicellular, eukaryotic organisms (foraminifera) from the same sediment layers. The magnetofossil assemblages correspond to distinct benthic foraminiferal populations whose environmental significance has been studied in more detail. In some cases, the magnetofossils better record environmental signals than the foraminifera. Our results highlight the promise of using non‐destructive, reproducible magnetic measurements to quantify magnetofossil assemblage variability, which leads to a better understanding of environmental change in the oceans triggered by climate change. Key Points: Changes in magnetofossil disparity correspond to changes in benthic foraminiferal species associationsMagnetofossil disparity can be used to understand changes in oxygen, nutrients, and organic matter over episodes of climate change [ABSTRACT FROM AUTHOR]

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. • In 56 Ma SE Australia, 5 m sealevels flooded >55,000km2 of near-coastal environments. • PETM megathermal biota are found at localities down to ∼65°S paleolatitude. • The PETM is identified in the Gippsland, Bass, Otway and Sorell basins. • The PETM contains mangrove Nypa palm pollen (Spinizonocolpites prominatus). • Thermophylic marine dinoflagellates include Apectodinium hyperacanthum. [ABSTRACT FROM AUTHOR]

Marine settings provide major carbon sinks for organic carbon, and act as a key reservoir that can sequester excess carbon during times of high CO 2 and global warming. Organic carbon burial in lake sediments also plays an important, but perhaps less appreciated, role in the global carbon cycle. However, the fate of organic carbon burial during times of increasing CO 2 and rapid global warming in lacustrine settings is still unclear. This study investigates organic carbon accumulation and its mechanism during the globally significant Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma) hyperthermal event in the Jianghan Basin, China, based on organic and element geochemistry data. The PETM is identified in our studied rocks based on their broad age constraints and the presence of a 4.3‰ negative excursion in organic carbon isotope. Our study shows that organic carbon accumulation during the PETM in the Jianghan Basin might be mainly controlled by preservation conditions and sediment accumulation rates (SAR), which responded to changing hydrology/climate. A hot and humid climate during the PETM could lead to an increase in terrestrial input and SAR, which might dilute the overall organic matter concentration. Also, enhanced rainfall could contribute to the ventilation of the lake water and expedite the oxidation of organic matter, thus, contributing to relatively low organic matter concentration in the Jianghan Basin. In contrast, an arid and relatively low oxygen environment during the post-PETM interval of our studied section created conditions conducive to the retention of organic matter, resulting in high organic matter content. An examination of other terrestrial PETM records reveals that the poor preservation condition of the organic matter and higher SAR might also have been the primary factors for the low organic matter concentrations in PETM terrestrial sections at other subtropical and mid-latitude locations. Compared to marine settings, terrestrial settings may exhibit lower efficiency in sequestering excess CO 2 from the atmosphere through organic carbon burial during the PETM. • Elucidating the impact of climate fluctuations on organic matter preservation during the PETM in the Jianghan Basin. • Oxidation and elevated clastic flux hindered organic matter preservation in terrestrial deposits during the PETM. • Terrestrial settings may be less effective than ocean in sequestering excessive atmospheric CO 2 during the PETM. [ABSTRACT FROM AUTHOR]

We present a model of calcareous nannoplankton response of the global warming at the PETM, based on studies of Bulgarian sections. New data acquired from forams'carbon and oxygen isotopes, as well as high-resolution quantitative study of calcareous nannofossils suggest 3 phases of the event: pre-PETM, core of PETM and recovery phase. During the core phase, a significant increase in warm-water nannofossil species was registered, as well as signs of acidification and higher salinity of the surface waters (dissolution of carbonate skeletons of nannofossils). In the recovery phase, the cold-water species from pre-event conditions gradually return, however g. Fasciculithus completely disappears. [ABSTRACT FROM AUTHOR]

Most studies of the response of terrestrial vegetation to climate change during the Paleocene‐Eocene Thermal Maximum (PETM) have focused on individual sites and sections. To get a broader perspective we compiled published records of terrestrial pollen and spores across the Paleocene‐Eocene transition at 38 sites around the globe. For the 10 sites with quantitative data PETM palynofloras were largely distinct in composition from those in the latest Paleocene or post‐PETM early Eocene. We also inferred paleoclimatic conditions at each site from the distributions of nearest living relatives (NLRs) of fossil pollen taxa among present‐day Köppen climate types. The NLRs of Paleocene high‐paleolatitude palynotaxa are most diverse in cooler climates, whereas the NLRs of PETM taxa are more diverse in warmer, wetter climates. At middle‐paleolatitudes NLRs of Paleocene palynotaxa are most diverse in warm, wet climates, whereas NLRs of PETM palynotaxa are most diverse in warm, seasonally dry climates. In the tropics there is little change from Paleocene to PETM in the climate distributions of NLRs. We compared changes in paleoclimate reconstructed from the Köppen distributions of the NLRs with those simulated from the Community Earth System Model (version CESM1.2). Paleoclimatic changes during the PETM inferred from palynological proxies are mostly consistent with modeled climate changes, including the expansion of temperate climates at the expense of cold climate types at high‐paleolatitudes and the expansion of temperate and tropical climates in middle‐paleolatitudes. Despite this concordance, modeled winter temperatures in continental interiors and high‐paleolatitudes remain colder than those reconstructed from NLR distributions. Key Points: We assess how terrestrial vegetation and climate changed globally during the Paleocene‐Eocene Thermal Maximum (PETM) using published records of spores and pollenPalynofloral data and models agree on the expansion poleward of temperate and tropical climates at high and middle latitudes during the PETMProxy reconstructions are generally warmer at high latitudes and in mid‐latitude continental interiors, particularly in the pre‐PETM [ABSTRACT FROM AUTHOR]

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. • New insights into Esh-ElMellaha stratigraphy were achieved. • Reference section of the Dib Formation was introduced for the first time. • El-Dababiya Quarry Member, which marks the PETM, was defined. • Unconformity surfaces (Paleosol and irregular surfaces) were observed. • Two major syn-sedimentary tectonic events (K/Pg & P/E) were documented. [ABSTRACT FROM AUTHOR]

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. • Paleocene-Eocene foraminifera and corals biodiversity is affected by warming events. • The response of foraminifera and corals to the same warming events is different. • Foraminiferal diversity is more susceptible to rapid warming events. • Coral diversity appears less influenced by warming events. • Generally, both groups exhibit quite high resilience to warming events. [ABSTRACT FROM AUTHOR]

Ocean warming and acidification driven by anthropogenic carbon emissions pose an existential threat to marine calcifying communities. A similar perturbation to global carbon cycling and ocean chemistry occurred ∼56 Ma during the Paleocene–Eocene thermal maximum (PETM), but microfossil records of the marine biotic response are distorted by sediment mixing. Here, we use the carbon isotope excursion marking the PETM to distinguish planktic foraminifer shells calcified during the PETM from those calcified prior to the event and then isotopically filter anachronous specimens from the PETM microfossil assemblages. We find that nearly one-half of foraminifer shells in a deep-sea PETM record from the central Pacific (Ocean Drilling Program Site 865) are reworked contaminants. Contrary to previous interpretations, corrected assemblages reveal a transient but significant decrease in tropical planktic foraminifer diversity at this open-ocean site during the PETM. The decrease in local diversity was caused by extirpation of shallow- and deepdwelling taxa as they underwent extratropical migrations in response to heat stress, with one prominent lineage showing signs of impaired calcification possibly due to ocean acidification. An absence of subbotinids in the corrected assemblages suggests that ocean deoxygenation may have rendered thermocline depths uninhabitable for some deeper-dwelling taxa. Latitudinal range shifts provided a rapid-response survival mechanism for tropical planktic foraminifers during the PETM, but the rapidity of ocean warming and acidification projected for the coming centuries will likely strain the adaptability of these resilient calcifiers. [ABSTRACT FROM AUTHOR]

[Display omitted] • A transient south subtropical forest existed in central China during the PETM. • Quantitative estimates indicates an warm and humid south subtropical climate. • Response of rainfall and terrestrial ecosystem change to the warming is remarkable. Rapid global warming during the Paleocene-Eocene Thermal Maximum (PETM) profoundly affected the marine and terrestrial environments. However, details of the climate and vegetation of subtropical and arid regions of central China during the hyperthermal event are poorly understood. Here, we report a palynological record from the black shale of the lowermost Yangxi Formation exposed in Songzi city, western Jianghan Basin, central China. Biostratigraphy, magnetostratigraphy and isotope stratigraphy indicate a PETM age for the sedimentary succession. The palynological assemblage was characterized by high abundances of diverse tropical and subtropical broadleaved tree pollen, providing strong evidence of a dense south subtropical forest ecosystem that once existed in the arid belt of central China during the PETM. The reconstructed climatic parameters indicate an extremely warm and humid south subtropical climate, with mean annual temperatures (MAT) ranging from 21 to 24 °C and mean annual precipitation (MAP) ranging from 1396 to 1997 mm. The reconstructed precipitation was surprisingly high for such an arid setting that widespread arid climate prevailed in central China at that time. These findings demonstrate that rapid global warming during the PETM significantly increased precipitation, leading to the growth of dense forest ecosystems as well as increasing lake eutrophication in central China. The changes to precipitation and terrestrial ecosystems during this warming event are considerably more significant than previously reported in other mid-latitude regions, and highlighting the need to consider regional geographic characteristics to fully understand how the environment responds to rapid global warming. [ABSTRACT FROM AUTHOR]

As an episode of rapid global warming associated with the release of massive quantities of carbon to the atmosphere and oceans, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) is considered a potential analog for modern anthropogenic carbon emissions. However, the prevailing order of magnitude uncertainty in the rate of carbon release during the PETM precludes any straightforward comparison between the paleo-record and the modern. Similar barriers exist to the interpretation of many other carbon isotope excursions in the geological record. Here we use the Earth system model cGENIE to quantify the consequences of differing carbon emissions rates on the isotopic record of different carbon reservoirs. We explore the consequences of a range of emissions scenarios - from durations of carbon input of years to millennia and constant versus pulsed emissions rates, and trace how the isotopic signal is imprinted on the different carbon reservoirs. From this, we identify a characteristic relationship between the difference in carbon isotope excursion sizes between atmospheric CO2 and dissolved inorganic carbon (DIC) and the duration of carbon emissions. To the extent that available isotopic data spanning the PETM constrain the size of the marine and atmospheric carbon isotopic excursions, applying this empirical relationship suggests the duration of the component of carbon emissions that dominates the isotopic signal could be less than 3000 yr. However, utilizing the ratio of excursion size in the atmosphere to ocean as a metric to constrain duration of carbon emissions highlights the necessity to strengthen estimates for these two measurements across the PETM. Our general interpretive framework could be equally applied in assessing rates of carbon emissions for other geological events.

As an episode of rapid global warming associated with the release of massive quantities of carbon to the atmosphere and oceans, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) is considered a potential analog for modern anthropogenic carbon emissions. However, the prevailing order of magnitude uncertainty in the rate of carbon release during the PETM precludes any straightforward comparison between the paleo-record and the modern. Similar barriers exist to the interpretation of many other carbon isotope excursions in the geological record. Here we use the Earth system model cGENIE to quantify the consequences of differing carbon emissions rates on the isotopic record of different carbon reservoirs. We explore the consequences of a range of emissions scenarios - from durations of carbon input of years to millennia and constant versus pulsed emissions rates, and trace how the isotopic signal is imprinted on the different carbon reservoirs. From this, we identify a characteristic relationship between the difference in carbon isotope excursion sizes between atmospheric CO2 and dissolved inorganic carbon (DIC) and the duration of carbon emissions. To the extent that available isotopic data spanning the PETM constrain the size of the marine and atmospheric carbon isotopic excursions, applying this empirical relationship suggests the duration of the component of carbon emissions that dominates the isotopic signal could be less than 3000 yr. However, utilizing the ratio of excursion size in the atmosphere to ocean as a metric to constrain duration of carbon emissions highlights the necessity to strengthen estimates for these two measurements across the PETM. Our general interpretive framework could be equally applied in assessing rates of carbon emissions for other geological events.

Relevance. Diatomites and their transitional differences formed in the Paleocene–Eocene marine basin are one of the most widespread in the near-surface occurrence of sedimentary rocks in the vast territory of the Trans-Urals. At the same time, with regard to the genetic aspects of such rocks, the discussion on the fundamental sources of silica for formation remains still relevant. An urgent task is to analyze the role of each of two factors in the origin of rocks – continental weathering and upwelling activities. The ratio of Ge to Si can potentially be considered as a tool for deciphering the source of silica in biogenic siliceous rocks, since germanium is delivered to the rock by incorporation into biogenic opal; Ge introduction into the rock from other sources during the diagenesis is not significant, which makes the results indicatively valuable. The main aim is estimation of the chemical weathering intensity at the boundary of the Paleocene and Eocene in the Trans-Urals based on the study of the ratio of Ge and Si in diatomites of different ages. The methods: field studies, X-ray fluorescence analysis, inductively coupled plasma mass spectrometry, scanning electron microscopy. The results. The paper contains the first results of estimation of chemical weathering intensity at the boundary of the Paleocene and Eocene in the Trans-Urals by analyzing the ratios of germanium and silicon in bulk diatomite samples and bioclastic preparations, where clay material was removed. The Ge/Si ratios in bioclastic preparations from the Paleocene (Brusyana section) and Eocene (Irbit deposit) differ almost twofold. The obtained values ​​should be considered as mark that the intensity of chemical weathering undergoes serious changes at this boundary: intensive chemical weathering, strengthening of the hydrological cycle during the PETM period determined an increase in the supply of dissolved silica to the marine basin during the accumulation of biosiliceous rocks in the territory of modern Trans-Urals. The weakening of tectonic movements and land peneplenisation within the East Ural contributed to the weathering intensification. This provided an additional transfer of siliceous matter in the form of true and colloidal solutions to the sedimentation basin for the biosiliceous rocks accumulation. The amount of silica influx from land over a relatively short period of time became more noticeable in the overall balance of silica supplied to the sedimentation basin. For the same reason, i. e. the presence of an additional source of silicic acid, the gross SiO2 content in the Paleocene diatomites is slightly higher than in the Eocene.

The upper Paleocene to lower Eocene Margaret Formation exposed at Stenkul Fiord on southern Ellesmere Island, Nunavut, Canada, represents a nearly continuous terrestrial succession of microfossil-rich clastic sediments and coal. These strata were deposited at a time of extensive tectonic activity associated with Eurekan deformation. The precise chronology of the Eurekan deformation is poorly known. Prior studies at Stenkul Fiord provided a stratigraphic overview and relative age estimates for exposed strata but lack the absolute age control required to investigate the timing of deformation events. Strata at Stenkul Fiord preserve evidence of Arctic forests that may have grown during hyperthermal events that characterized the Paleogene, namely, the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM2). A quantitative palynological approach is herein used to define a new higher-resolution biostratigraphic framework for the Margaret Formation strata at Stenkul Fiord. This resulting improved biostratigraphic framework is integrated with new absolute age control of 53.7 ± 0.06 Ma provided by U-Pb ID-TIMS of zircon preserved in an ash bed within the studied succession. Nine pollen zones are defined based on cluster analysis, NMDS ordination, first- and last occurrences of taxa, and angiosperm pollen taxa diversity (H′). The presence of thermophilic pollen taxa at Stenkul Fiord provides evidence of climates related to the globally warm climates during the early Paleogene. [ABSTRACT FROM AUTHOR]

Palynological analysis of Site M0077A in the Chicxulub impact crater has yielded a record of the immediate Cretaceous/Paleogene (K/Pg) recovery from ground zero of the end-Cretaceous mass extinction, followed by a record of the Paleocene–Eocene Thermal Maximum (PETM) and later Ypresian (Eocene), including the Early Eocene Climatic Optimum (EECO). Eight specimens of the dinoflagellate cyst Trithyrodinium evittii have been observed near the base of the K/Pg transitional unit; these likely represent a post-impact dinoflagellate disaster recovery assemblage deposited within several days following the impact, although the possibility that some or all of the T. evittii specimens are reworked Maastrichtian cysts cannot be fully excluded. Despite high-resolution sampling of the lowermost Paleocene successions, the oldest identifiable terrestrial palynomorphs observed in the Site M0077A core, two specimens of Deltoidospora fern spores, occur at least ∼200,000 years after the impact. Other than these occurrences, the Paleocene section is nearly barren in terms of palynomorphs, likely a result of poor preservation of organic material combined with a long recovery time for vegetation in the vicinity of the crater. Pollen and fungal spore concentrations spike in an anoxic dark shale deposited during the PETM around 56 Ma, with a diverse pollen assemblage indicating the presence of a coastal shrubby tropical forest in the geographic vicinity, likely in the Yucatán Peninsula to the south. In the marine realm, this interval is characterized by thermophilic assemblages of dinoflagellate cysts. Stratigraphically constrained cluster analysis identified four statistically robust sample clusters in the lower Eocene successions, with Malvacipollis spp. and Milfordia spp. abundances driving the highest average dissimilarity between clusters. A second notable spike in palynological concentrations above the PETM section may represent another early Eocene hyperthermal event. Pollen and plant spore concentrations generally increased during the EECO, associated with increases in terrestrial input during basin infilling. [ABSTRACT FROM AUTHOR]

Carbon isotope (δ13C) records from marine sediments and sedimentary rocks have been extensively used in Cenozoic chemostratigraphy. The early Paleogene interval in particular has received exceptional attention because negative carbon isotope excursions (CIEs) documented in the sedimentary record, for example, at the Paleocene Eocene Thermal Maximum (PETM), ca ∼56 Ma, are believed to reflect significant global carbon cycle perturbations during the warmest interval of the Cenozoic era. However, while bulk carbonate δ13C values exhibit robust correlations across widely separated marine sedimentary basins, their absolute values and magnitude of CIEs vary spatially, especially over time intervals characterized by major deviations in global carbon cycling. Moreover, bulk carbonates in open‐marine environments are an ensemble of different components, each with a distinct isotope composition. Consequently, a comprehensive interpretation of the bulk‐δ13C record requires an understanding of co‐evolution of these components. In this study, we dissect sediments, from the late Paleocene‐early Eocene interval, at ODP Site 1209 (Shatsky Rise, Pacific Ocean) to investigate how a temporally varying bulk carbonate ensemble influences the overall carbon isotope record. A set of 45 samples were examined for δ13C and δ18O compositions, as bulk and individual size fractions. We find a significant increase in coarse‐fraction abundance across the PETM, driven by a changing community structure of calcifiers, modulating the size of the CIE at Site 1209 and thus making it distinct from those recorded at other open‐marine sites. These results highlight the importance of biogeography in the marine stable isotope record, especially when isotope excursions are driven by climate‐ and/or carbon cycle changes. In addition, community composition changes will alter the interpretation of weight percent coarse fraction as proxy for carbonate dissolution. Plain Language Summary: Bulk carbonate stable isotope records are extensively used for chemostratigraphic correlation and reconstruction of past global changes. However, bulk carbonates in open marine settings being an ensemble of various calcareous components, with individually distinct isotope composition are enigmatic in terms of their usage and interpretations. Our study dissects bulk carbonates of early Paleogene age (58–50 Ma) from ODP Site 1209, at Shatsky Rise in north‐central Pacific Ocean, and attempts to interpret bulk carbonate stable isotope records in regard to how individual components co‐evolved. Documenting the size‐fraction‐specific isotope variations within the bulk carbonate records helps us understand how varying abundances of individual group of marine calcifying organisms can affect the resultant bulk isotope compositions. Size‐fraction‐specific isotope variations also have implications on the magnitude of prominent carbon isotope excursions, for example, the Paleocene Eocene Thermal Maximum, ca. ∼56 Ma. Key Points: Co‐evolution of different components within pelagic carbonate systems drive spatial variations within bulk carbonate stable isotope recordsAn increase in coarse fraction abundance caused by change in abundance of calcifying organims across the Paleocene Eocene Thermal Maximum (PETM) at Shatsky Rise affects its utility as a proxy for carbonate dissolutionSize‐fraction‐specific isotope variations can significantly alter the magnitude of carbon isotope excursions in bulk sediments [ABSTRACT FROM AUTHOR]

The Paleocene‐Eocene Thermal Maximum (PETM; 56 Ma) is considered to be one of the best analogs for future climate change. The carbon isotope composition (δ13C) of n‐alkanes derived from leaf waxes of terrestrial plants and marine algae can provide important insights into the carbon cycle perturbation during the PETM. Here, we present new organic geochemical data and compound‐specific δ13C data from sediments recovered from an early Cenozoic basin‐margin succession from Spitsbergen. These samples represent one of the most expanded PETM sites and provide new insights into the high Arctic response to the PETM. Our results reveal a synchronous ∼−6.5‰ carbon isotope excursion (CIE) in short‐chain n‐alkanes (nC19; marine algae/bacteria) with a ∼−5‰ CIE in long‐chain n‐alkanes (nC29 and nC31; plant waxes) during the peak of the PETM. Although δ13Cn‐alkanes values were potentially affected via a modest thermal effect (1‰–2‰), the relative changes in the δ13Cn‐alkanes remain robust. A simple carbon cycle modeling suggests peak carbon emission rate could be ∼3 times faster than previously suggested using δ13CTOC records. The CIE magnitude of both δ13C n‐C19 and δ13Cn‐C29 can be explained by the elevated influence of 13C‐depleted respired CO2 in the water column and increased water availability on land, elevated pCO2 in the atmosphere, and changes in vegetation type during the PETM. The synchronous decline in δ13C of both leaf waxes and marine algae/bacteria argues against a significant contribution to the sedimentary organic carbon pool from the weathering delivery of fossil n‐alkanes in the Arctic region. Plain Language Summary: The Paleocene‐Eocene Thermal Maximum (PETM), a rapid global warming event that occurred nearly 56 million years ago, is associated with large negative carbon isotope excursions (CIEs) in both marine and terrestrial sedimentary archives with varying magnitudes. New geochemical data from sediments collected in a stratigraphically thick and potentially high temporal resolution PETM site suggest synchronous carbon cycle perturbation in ocean and on land. In the ocean, we hypothesize that greater water column stratification from high salinity gradient in the ocean led to the −6.5‰ CIE. On the land, higher atmospheric pCO2 and increased water availability led to the −5.3‰ CIE. The similar profiles of carbon isotopes from both leaf wax and algal biomarkers suggest that weathering and redeposition of fossil n‐alkanes in sedimentary organic matter are not important in the studied site across the PETM. Key Points: Compound‐specific carbon isotope analyses reveal that carbon cycle perturbation occurred synchronously in ocean and land across the Paleocene‐Eocene Thermal MaximumThe magnitude of carbon isotope excursion in marine sections is amplified by 1.5‰ relative to terrestrial biomarkersThere is minimum reworking of the terrestrial n‐alkanes at the studied site [ABSTRACT FROM AUTHOR]