Early Eocene Climatic Research Articles

Time for speciation and niche conservatism explain the latitudinal diversity gradient in clupeiform fishes

AbstractAimThe latitudinal diversity gradient of increasing species richness from poles to equator is one of the most striking and pervasive spatial patterns of biodiversity. Climate appears to have been key to the formation of the latitudinal diversity gradient, but the processes through which climate shaped species richness remain unclear. We tested predictions of the time for speciation, carrying capacity and diversification rate latitudinal diversity gradient hypotheses in a trans‐marine/freshwater clade of fishes.LocationGlobal in marine and freshwater environments.TaxonClupeiformes (anchovies, herrings, sardines and relatives).MethodsWe tested predictions of latitudinal diversity gradient hypotheses using a molecular phylogeny, species distribution data and phylogenetic comparative approaches. To test the time for speciation hypothesis, we conducted ancestral state reconstructions to infer the ages of temperate, subtropical and tropical lineages and frequency of evolutionary transitions between climates. We tested the carry capacity hypothesis by characterizing changes in net diversification rates through time. To test the diversification rate hypothesis, we qualitatively compared the diversification rates of temperate, subtropical and tropical lineages and conducted statistical tests for associations between latitude and diversification rates.ResultsWe identified four transitions to temperate climates and two transitions out of temperate climates. We found no differences in diversification rates among temperate and tropical clupeiforms. Net diversification rates remained positive in crown Clupeiformes since their origin ~150 Ma in both tropical and temperate lineages. Climate niche characters exhibited strong phylogenetic signal. All temperate clupeiform lineages arose <50 Ma, after the Early Eocene Climatic Optimum.Main conclusionsOur results support the time for speciation hypothesis, which proposes that climate niche conservatism and fluctuations in the extent of temperate climates limited the time for species to accumulate in temperate climates, resulting in the latitudinal diversity gradient. We found no support for the carrying capacity or diversification rate hypotheses.

Eocene Paleoclimate Evolution under the Background of Warmhouse-Hothouse Conditions in the Continental Fushun Basin: Implications from Magnetic Susceptibility and Color Reflectance.

Paleocene–Eocene hyperthermal events are a current research focus in the fields of sedimentology and paleoclimatology. The Fushun Basin in northeast China contains continuous continental Eocene fine-grained rocks, and a series of Eocene hyperthermal events in the Fushun Basin have been identified. Because of the high cost of high-precision isotope data testing, it is necessary to find new and alternative paleoclimate parameters. In this study, Eocene coal and oil shale-bearing layers in the Fushun Basin are used as research objects. The high-precision data of magnetic susceptibility, color reflectance, rock composition, and cluster analyses are used to conduct a vertical comparison in the same category and compare that analysis with the identified Eocene hyperthermal events in the Fushun Basin. The preliminary results show that high-frequency-dependent susceptibility, high color reflectance a* (redness)/L* (lightness) values, and high kaolinite content in the study area have good correspondence with global hyperthermal events and can be used as effective parameters for the identification of continental basin hyperthermal events. The detailed magnetic susceptibility and color reflectance data also reveal that the Eocene strata in the Fushun Basin recorded the Late Lutetian Thermal Maximum (LLTM) and 13 short-term hyperthermal events during the Early Eocene Climatic Optimum (EECO). These results indicate that the parameters of rock physical properties can be used to study the evolution of the paleoclimate in geological history, and it has universal practicability in continental and marine fine-grained sedimentary rocks.

Phylogenomics Resolves the Phylogeny of Theaceae by Using Low-Copy and Multi-Copy Nuclear Gene Makers and Uncovers a Fast Radiation Event Contributing to Tea Plants Diversity

Simple SummaryThe Theaceae includes more than 300 species of great morphological diversity and has immense economic, cultural, and ornamental values. However, the evolutionary history of this family remains elusive. We integrated 91 genomes and transcriptome datasets of Theaceae and successfully resolved the phylogeny of Theaceae including relatives of cultivated tea plants from both extensive low-copy and multi-copy nuclear gene markers. Bayes-based molecular dating revealed that the ancestor of the tea family originated slightly earlier than the K-Pg boundary (Mass extinction events including the extinction of dinosaurs) with early diversification of three tribes associated with the Early Eocene Climatic Optimum. Further speciation analysis suggested a sole significant diversification shift rate in the common ancestor of Camellia associated with the Mid-Miocene Climatic Optimum. Collectively, polyploidy events, and key morphological innovation characters, such as pericarp with seed coat hardening, could possibly contribute to the Theaceae species diversity.Tea is one of the three most popular nonalcoholic beverages globally and has extremely high economic and cultural value. Currently, the classification, taxonomy, and evolutionary history of the tea family are largely elusive, including phylogeny, divergence, speciation, and diversity. For understanding the evolutionary history and dynamics of species diversity in Theaceae, a robust phylogenetic framework based on 1785 low-copy and 79,103 multi-copy nuclear genes from 91 tea plant genomes and transcriptome datasets had been reconstructed. Our results maximumly supported that the tribes Stewartieae and Gordonieae are successive sister groups to the tribe Theeae from both coalescent and super matrix ML tree analyses. Moreover, in the most evolved tribe, Theeae, the monophyletic genera Pyrenaria, Apterosperma, and Polyspora are the successive sister groups of Camellia. We also yield a well-resolved relationship of Camellia, which contains the vast majority of Theaceae species richness. Molecular dating suggests that Theaceae originated in the late L-Cretaceous, with subsequent early radiation under the Early Eocene Climatic Optimal (EECO) for the three tribes. A diversification rate shift was detected in the common ancestors of Camellia with subsequent acceleration in speciation rate under the climate optimum in the early Miocene. These results provide a phylogenetic framework and new insights into factors that likely have contributed to the survival of Theaceae, especially a successful radiation event of genus Camellia members to subtropic/tropic regions. These novel findings will facilitate the efficient conservation and utilization of germplasm resources for breeding cultivated tea and oil-tea. Collectively, these results provide a foundation for further morphological and functional evolutionary analyses across Theaceae.

Enhanced storm-induced turbiditic events during early Paleogene hyperthermals (Arabian continental margin, SW Iran)

Early Paleogene hyperthermal episodes including the Paleocene-Eocene Thermal Maximum (PETM) have long been viewed as analogues of the Anthropocene global warming. Few studies, however, have analyzed the environmental consequences of such climatic anomalies in deep-water turbidite-rich successions. This integrated sedimentological, biostratigraphic, and stable-isotope study of the Paleogene Pabdeh Formation, deposited along the Arabian continental margin of southwestern Iran, allowed us to document the geological response of hyperthermal events in deep Neo-Tethyan Ocean. The late Thanetian event (Pre-Onset Excursion or long-term late Paleocene climatic perturbation), the Early Eocene Climate Optimum, and the Middle Eocene Thermal Maximum were successfully identified within the Pabdeh Formation. The PETM event could not be documented because the Paleocene/Eocene boundary corresponds to a prolonged non-depositional hiatus marked by a glauco-phosphorite interval. Based on high-resolution microfacies analysis, three different processes in a carbonate slope to basin-margin environment were distinguished including pelagic settling, upwelling-condensation-reworking, and storm-induced turbiditic deposition. Detailed sedimentological analysis revealed an anomalous abundance of storm-induced proximal to distal turbidites represented by packstones with deep-water and reworked shallow-water bioclasts occurring during the hyperthermal intervals. A close causal link between climate warming and tropical storms during the early Paleogene hyperthermal events is thus envisaged. As a principal mechanism, we propose that rapid warming in response to massive carbon release triggered pronounced sedimentological changes along low-latitude tropical margins, leading to generation of storm-induced calciturbidite and re-deposition in the deep sea during hothouse stages.

Quantitative reconstruction of atmospheric pCO2 sources during Eocene hyperthermal events based on data from the Fushun Basin, Northeast China

Eocene hyperthermal events are thought to be closely linked to rapid increases in atmospheric CO2. It is important to better understand the atmospheric triggers of these extreme events; however, reconstruction of pCO2 from sedimentary records remains challenging. Eocene hyperthermal events (Eocene thermal maximum, ETM; Early Eocene Climatic Optimum, EECO; Mid-Eocene Climatic Optimum, MECO) are well documented in the Fushun Basin of northeast China, but the source of organic matter (OM) used as a pCO2 archive in previous studies includes land plants, algae, mixed land and aquatic organisms in the Ypresian, Lutetian and Bartonian intervals, respectively. In this paper, we calculate pCO2 concentrations using δ13CTOC and δ13C27–31 and discuss the factors influencing discrepancies based on various calculations. Results show that both δ13CTOC and δ13C27–31 from single OM sources are reliable proxies for pCO2. During the ETM2, ETM3, EECO and MECO intervals, pCO2 was 638–2277 ppm, and palaeotemperature was approximately 2.6–8.9 °C higher than present. The background and peak values of pCO2 during hyperthermal events were compared with those related to methane hydrate, OM oxidation and volcanic sources of pCO2 carbon. The comparison revealed that pCO2 values associated with the ETM2, ETM3, EECO and MECO events were more consistent with those calculated by OM oxidation and locally overlapped with volcanic sources. These results indicate that these pCO2 estimates of hyperthermal events are predominantly derived from terrestrial OM oxidation and were influenced by volcanism.

Plastid and mitochondrial phylogenomics reveal correlated substitution rate variation in Koenigia (Polygonoideae, Polygonaceae) and a reduced plastome for Koenigia delicatula including loss of all ndh genes

Koenigia, a genus proposed by Linnaeus, has a contentious taxonomic history. In particular, relationships among species and the circumscription of the genus relative to Aconogonon remain uncertain. To explore phylogenetic relationships of Koenigia with other members of tribe Persicarieae and to establish the timing of major evolutionary diversification events, genome skimming of organellar sequences was used to assemble plastomes and mitochondrial genes from 15 individuals representing 13 species. Most Persicarieae plastomes exhibit a conserved structure and content relative to other flowering plants. However, Koenigia delicatula has lost functional copies of all ndh genes and the intron from atpF. In addition, the rpl32 gene was relocated in the K. delicatula plastome, which likely occurred via overlapping inversions or differential expansion and contraction of the inverted repeat. The highly supported but conflicting relationships between plastome and mitochondrial trees and among gene trees complicates the circumscription of Koenigia, which could be caused by rapid diversification within a short period. Moreover, the plastome and mitochondrial trees revealed correlated variation in substitution rates among Persicarieae species, suggesting a shared underlying mechanism promoting evolutionary rate variation in both organellar genomes. The divergence of dwarf K. delicatula from other Koenigia species may be associated with the well-known Eocene Thermal Maximum 2 or Early Eocene Climatic Optimum event, while diversification of the core-Koenigia clade associates with the Mid-Miocene Climatic Optimum and the uplift of Qinghai-Tibetan Plateau and adjacent areas.

Hydroclimate variability in the United States continental interior during the early Eocene Climatic Optimum

The early Eocene (56.0 to 47.8 million years ago) was punctuated by a series of transient episodes of rapid global warming superimposed on the long-term early Cenozoic warming trend, culminating in the early Eocene Climatic Optimum (EECO; 53.3 to 49.1 million years ago). Details of the hydroclimate regime operating during the EECO are poorly constrained, especially for continental interior sites. The Green River Formation (GRF) of Utah and Colorado was deposited in a suite of large, unusually productive lakes that offer an ideal opportunity to study the hydrological response to warming. Here we report the hydrogen isotopic composition (δ 2 H) of leaf wax (long-chain n -alkanes) and algal (phytane) lipids preserved in the organic-rich Mahogany Zone (49.3 to 48.7 Ma) and use these data to reconstruct precipitation and lake water δ 2 H records, respectively. We observe large inter-site variations in algal and leaf wax δ 2 H values (~50 to 75‰), suggesting that additional local controls influence precipitation and/or lake water δ 2 H (e.g., salinity). Intriguingly, leaf wax and algal lipid δ 2 H values show little variation through the Mahogany Zone, implying a relatively stable hydrological regime during the latter phase of the EECO. This contrasts with the more variable hydrological regime that prevailed during early Eocene hyperthermals. Unlike the EECO, the early Eocene hyperthermals in the Uinta region do not coincide with the deposition of organic-rich sediments. This suggests that a stable hydrological regime during the EECO may enable the preservation of organic matter within continental-interior lake systems, potentially leading to an important negative climate feedback during the early Eocene and other greenhouse climates. • Gradual variations in leaf wax δ 2 H values indicate a stable hydrological cycle during the latter phase of theEECO. • However, leaf wax and algal δ 2 H values exhibit large lake inter-site variability (~50 to 75‰). • Stable hydroclimate may have promoted organic matter burial within the lake system. • High organic carbon burial may have acted as an important negative climate feedback.

Late early to early middle Eocene climate and vegetation change at Tastakh Lake (northern Yakutia, eastern Siberia)

The late early – early middle Eocene climate and vegetation evolution in northern Yakutia (Eastern Siberia) is quantitatively studied in detail for the first time, based on a palaeobotanical record. Palaeobotanical data for this time interval were obtained from 16 palynofloras from continental sediments on the southern shore of Tastakh Lake (the left bank of Indigirka River). In this first integrative study, we applied the Coexistence Approach for quantification of palaeoclimate, the Plant Functional Type (PFT) approach and Integrated Plant Record (IPR) vegetation analysis to quantify palaeovegetation. Our investigation documents the persistence of warm temperate and, at times, nearly tropical climate conditions in the earlier part of the record and the subsequent onset of a cooling trend. Overall humid climate conditions prevailed throughout the late early – early middle Eocene. Our reconstruction indicates low temperature seasonality and relatively strong seasonality in precipitation. Vegetation data as reconstructed are in good agreement with the climate evolution. PFT diversity spectra indicate the prevalence of mixed evergreen-deciduous forests of warm temperate character. The IPR method suggests that the mixed mesophytic forest biome persisted throughout the studied sedimentary succession. The presence of mangroves in our late early Eocene records (at the base of the section) is largely in line with our climate reconstruction and possibly can be related to the Early Eocene Climatic Optimum (EECO) hyperthermal event.

Paleoenvironmental evolution during the Early Eocene Climate Optimum in the Chicxulub impact crater

The Early Eocene represents the warmest climate during the Cenozoic Era punctuated by transient warming events. Here, we apply for the first time biomarker and stable isotope data to describe the depositional and environmental changes at the actual Chicxulub impact crater [International Ocean Discovery Program (IODP) Site M0077A] during the Early Eocene (∼56–48 Ma) including the Early Eocene Climate Optimum (EECO; ∼53–49 Ma). TEX86-based reconstructions indicate elevated sea surface temperature around 37°C for the entire succession, punctuated by warmer and cooler periods (37.8°C, 35.7°C, respectively). Biomarker and δ13C-org data of the core sediments reveal a shift from an organic-lean lower to an organic-rich upper section of the Early Eocene interval. Embedded in the lower section is a prominent organic-rich black shale layer. The lower section, directly overlying strata deposited upon the Paleocene-Eocene Thermal Maximum (PETM), is organically lean with low biomarker concentrations indicating low primary productivity. In the upper section, higher concentrations of algal and bacterial biomarkers are ascribed to high primary productivity and nitrogen fixation in an epipelagic zone, potentially supported by upwelling. The organic-rich black shale layer exhibits a negative δ13C-org isotope excursion ascribed to recycling of 13C-depleted organic matter via upwelling attributed to a transient hyperthermal event.

Assessing Nummulites geochemistry as a proxy for early Eocene palaeotemperature evolution in the North Sea Basin

The early Eocene climate is characterized by gradual warming towards the Early Eocene Climatic Optimum (EECO). Environmental changes related to this global long-term warming trend are recorded in Ypresian marine sediments in Belgium. The test geochemistry of Nummulites enables the reconstruction of palaeotemperature changes based on the incorporation of Mg into the calcite test without complications connected to other proxies. Early Eocene Nummulites occur in high abundances in the inner shelf deposits of the southern edge of the North Sea Basin, providing multiple sample locations. Because this palaeotemperature proxy has only recently been developed, we investigated a methodological approach. We assessed the relationship between test geochemistry and (1) preservation state, (2) test size and (3) a cleaning procedure to evaluate the use of this new proxy. We propose a simplified cleaning procedure (ethanol–methanol–peroxide) for well-preserved specimens within the smaller size range (radius <3 mm). Using this methodology, a long-term palaeotemperature increase of 7°C is reconstructed from the pre-EECO (±54 Ma) to the EECO (±51 Ma), with a mean EECO palaeotemperature of 28°C. This corresponds with previous studies, strengthening the use of Nummulites geochemistry as a proxy for reconstructing long-term climate change in the Southern North Sea Basin. Supplementary material: All geochemical data are available at https://doi.org/10.6084/m9.figshare.c.5811457

Evolution of Paleogene weathering intensity in the Qaidam Basin, northeastern Tibetan Plateau: Insights from clay geochemistry

An integrated multiproxy dataset involving both mineralogical and geochemical investigations of the northern Tibetan Plateau helps in assessing regional weathering processes linked to topographic evolution and environmental change. However, changes in landscape and drainage reorganizations caused by active tectonics and remarkable climate change during the Cenozoic characterize the basins in and around the Tibetan Plateau by frequent facies changes and coarse lithologies, which largely limit the reliability of bulk geochemical indicators for revealing the regional weathering history. Here, we present detailed geochemical investigations of clay-sized sediments collected from the Hongliugou section (54–26 Ma) in the northern Qaidam Basin to reconstruct high-resolution chemical weathering records of the northern Tibetan Plateau. To prevent chlorite bias when calculating the chemical index of alteration (CIA) in the clay-sized sediments, we propose a modified CIA formula (CIAMg+), in which Mg is added as a soluble cation that can be removed during weathering, similar to Na, K and Ca; thus, CIAMg+ = Al2O3/(Al2O3 + Na2O + K2O + CaO* + MgO) × 100. The CIAMg+ and illite chemistry indices are generally the highest values in the early Eocene Climate Optimum (∼52–49.5 Ma) and a long-term decreasing trend is present from ∼ 49.5–26 Ma; the Mg/Al ratios of the clay-sized sediments and hydrochloric acid leachates are the lowest during the EECO and present a long-term increasing trend in the following 49.5–26 Ma, thus collectively indicating a continuous decrease in the regional chemical weathering intensity. The weakening weathering process during the Paleogene is mainly attributed to the decreasing global temperature and decline in precipitation caused by global cooling. Our study suggests that the proposed geochemical index based on clay-sized sediments can serve as an efficient proxy for regional chemical weathering reconstruction, even in thick sedimentary sequences with frequently changing facies and lithology.

Eocene hyperthermal events in the terrestrial system: Geochronological and astrochronological constraints in the Fushun Basin, NE China

Frequent hyperthermal events during the Eocene (55-47 Ma), primarily characterised by carbon isotope excursions (CIEs), have been identified from marine records worldwide. However, only a few excursions have been recognised and described in continental deposits, thereby limiting the understanding of the effect of global warming on terrestrial systems. Thick, dark, organic-rich mudstone containing complete astronomical age information was deposited during the Palaeogene in the Fushun Basin. Based on U–Pb zircon dating and Milankovitch cycle analysis, the astronomical time scale (ATS) of the Fushun Basin was established. Based on the high-resolution chronostratigraphic framework, combined with the negative migration characteristics of organic carbon isotopes (δ13CTOC), three hyperthermal events were identified: Eocene Thermal Maximum 2 (ETM2), Eocene Thermal Maximum (ETM3) and long-term Early Eocene Climatic Optimum (EECO). In particular, several periods of short-term hyperthermal events were identified in the EECO period: L, M, N, O, P, Q, R, S, T, U, V, W, C22nH3, C22nH4, C22nH5, C21rH1, C21rH2, C21rH3, C21rH4, C21rH5, C21nH1 and C21nH2. The records of sea and land hyperthermal events show that the records corresponding to land basins are timelier and more sensitive.

Enhanced Terrestrial Carbon Export From East Antarctica During the Early Eocene

AbstractTerrestrial organic carbon (TerrOC) acts as an important CO2 sink when transported via rivers to the ocean and sequestered in coastal marine sediments. This mechanism might help to modulate atmospheric CO2 levels over short‐ and long‐ timescales (103–106 years), but its importance during past warm climates remains unknown. Here we use terrestrial biomarkers preserved in coastal marine sediment samples from Wilkes Land, East Antarctica (∼67°S) to quantify TerrOC burial during the early Eocene (∼54.4–51.5 Ma). Terrestrial biomarker distributions indicate the delivery of plant‐, soil‐, and peat‐derived organic carbon (OC) into the marine realm. Mass accumulation rates of plant‐ (long‐chain n‐alkane) and soil‐derived (hopane) biomarkers dramatically increase between the earliest Eocene (∼54 Ma) and the early Eocene Climatic Optimum (EECO; ∼53 Ma). This coincides with increased OC mass accumulation rates and indicates enhanced TerrOC burial during the EECO. Leaf wax δ2H values indicate that the EECO was characterized by wetter conditions relative to the earliest Eocene, suggesting that hydroclimate exerts a first‐order control on TerrOC export. Our results indicate that TerrOC burial in coastal marine sediments could have acted as an important negative feedback mechanism during the early Eocene, but also during other warm climate intervals.

Rise and fall of rotaliid foraminifera across the Paleocene and Eocene times

Rotaliids are one of the groups of larger foraminifera that quickly recolonized the shallow-water environments after the mass extinction at the end of the Cretaceous. Here we present a summary of the state of the art about their stratigraphic distribution and diversity across the Paleocene and Eocene epochs. Our data suggest that their differentiation at the genus level was very rapid and reached its maximum in the upper Danian SBZ2. Specific diversification, instead, culminated in the upper Thanetian SBZ4, with a second peak during the Cuisian (=upper Ypresian). Successively, the rotaliid diversity definitely declined, whereas other groups of larger foraminifera, and especially Alveolina and Nummulites, became more widespread and flourished with a large amount of species, up to the lower Bartonian SBZ17, when a final drop in rotaliid diversity is recorded. These major changes appear strictly linked to climate warming events such as Late Danian Event (LDE, generic diversification of rotaliids), Paleocene-Eocene Thermal Maximum (PETM, faunal turnover followed by abrupt decrease in both generic and specific diversity), Early Eocene Climatic Optimum (EECO, increase in number of K-strategists under oligotrophic conditions) and Middle Eocene Climatic Optimum (MECO, ultimate drop in diversity and competition with other larger foraminifera).

Advances of driving mechanisms of the Early Eocene Climatic Optimum (EECO): Constraints from the Linzizong volcanic rocks in southern Tibet

Advances of driving mechanisms of the Early Eocene Climatic Optimum (EECO): Constraints from the Linzizong volcanic rocks in southern Tibet

Climate and ecology in the Rocky Mountain interior after the early Eocene Climatic Optimum

Abstract. As atmospheric carbon dioxide (CO2) and temperatures increase with modern climate change, ancient hothouse periods become a focal point for understanding ecosystem function under similar conditions. The early Eocene exhibited high temperatures, high CO2 levels, and similar tectonic plate configuration as today, so it has been invoked as an analog to modern climate change. During the early Eocene, the greater Green River Basin (GGRB) of southwestern Wyoming was covered by an ancient hypersaline lake (Lake Gosiute; Green River Formation) and associated fluvial and floodplain systems (Wasatch and Bridger formations). The volcaniclastic Bridger Formation was deposited by an inland delta that drained from the northwest into freshwater Lake Gosiute and is known for its vast paleontological assemblages. Using this well-preserved basin deposited during a period of tectonic and paleoclimatic interest, we employ multiple proxies to study trends in provenance, parent material, weathering, and climate throughout 1 million years. The Blue Rim escarpment exposes approximately 100 m of the lower Bridger Formation, which includes plant and mammal fossils, solitary paleosol profiles, and organic remains suitable for geochemical analyses, as well as ash beds and volcaniclastic sandstone beds suitable for radioisotopic dating. New 40Ar / 39Ar ages from the middle and top of the Blue Rim escarpment constrain the age of its strata to ∼ 49.5–48.5 Myr ago during the “falling limb” of the early Eocene Climatic Optimum. We used several geochemical tools to study provenance and parent material in both the paleosols and the associated sediments and found no change in sediment input source despite significant variation in sedimentary facies and organic carbon burial. We also reconstructed environmental conditions, including temperature, precipitation (both from paleosols), and the isotopic composition of atmospheric CO2 from plants found in the floral assemblages. Results from paleosol-based reconstructions were compared to semi-co-temporal reconstructions made using leaf physiognomic techniques and marine proxies. The paleosol-based reconstructions (near the base of the section) of precipitation (608–1167 mm yr−1) and temperature (10.4 to 12.0 ∘C) were within error of, although lower than, those based on floral assemblages, which were stratigraphically higher in the section and represented a highly preserved event later in time. Geochemistry and detrital feldspar geochronology indicate a consistent provenance for Blue Rim sediments, sourcing predominantly from the Idaho paleoriver, which drained the active Challis volcanic field. Thus, because there was neither significant climatic change nor significant provenance change, variation in sedimentary facies and organic carbon burial likely reflected localized geomorphic controls and the relative height of the water table. The ecosystem can be characterized as a wet, subtropical-like forest (i.e., paratropical) throughout the interval based upon the floral humidity province and Holdridge life zone schemes. Given the mid-paleolatitude position of the Blue Rim escarpment, those results are consistent with marine proxies that indicate that globally warm climatic conditions continued beyond the peak warm conditions of the early Eocene Climatic Optimum. The reconstructed atmospheric δ13C value (−5.3 ‰ to −5.8 ‰) closely matches the independently reconstructed value from marine microfossils (−5.4 ‰), which provides confidence in this reconstruction. Likewise, the isotopic composition reconstructed matches the mantle most closely (−5.4 ‰), agreeing with other postulations that warming was maintained by volcanic outgassing rather than a much more isotopically depleted source, such as methane hydrates.

Dextral to sinistral coiling switch in planktic foraminifer Morozovella during the Early Eocene Climatic Optimum

Coiling direction is a basic characteristic of trochospiral planktic foraminifera. Modifications in the coiling direction within ancient planktic foraminiferal populations may reflect important changes in evolution or environment, yet they remain scarcely discussed. Here we investigate fluctuations in the coiling direction within Morozovella assemblages from sections that span the interval of peak Cenozoic warmth, the Early Eocene Climatic Optimum (EECO; ~53–49 million years ago, Ma), at Atlantic Ocean Drilling Program (ODP) sites 1051, 1258 and 1263. The surface-dwelling genus Morozovella is of particular interest because it dominated tropical-subtropical early Paleogene assemblages then suffered an abrupt and permanent decline in abundance and taxonomic diversity at the start of the EECO. At all ODP sites, morozovellids display a dominant dextral coiling preference during the interval preceding the EECO. However, all the Morozovella species at all sites modify their coiling from preferentially dextral to sinistral coiling within the EECO, <200 kyr after the K/X event (~52.8 Ma), providing a new biostratigraphic tool for correlation. We also document that before the major shift in morozovellid coiling, transient excursions to higher abundances of sinistral tests occurred in conjunction with negative carbon isotope excursions. Significantly, carbon isotope data reveal that sinistral morphotypes belonging to the same morphospecies typically have lower δ 13 C values. The dominance of sinistral morphotypes, at the expense of dextral forms within the EECO, coupled with the lower δ 13 C signatures of the former, suggests that the sinistral forms were less dependent on their photosymbiotic partnerships and thus able to adapt more readily to paleoceanographic change at the EECO. The observed sinistral and dextral coiling of morozovellids can be a genetically heritable characteristic that lies within cryptic speciation across multiple morphologically defined species. Alternatively the coiling changes were exclusively ecophenotypic responses whereby different species were able to preferentially adopt sinistral coiling in reaction to the changed conditions in the mixed-layer during the EECO. Previous interpretations of coiling flips in planktic foraminifera in the early Eocene, especially including morozovellids, have favoured a genetic explanation rather than an ecological response. Our present data cannot validate or disprove this idea, but should stimulate renewed thought on the matter. • Coiling data on Morozovella species are presented from three widely separated Atlantic Ocean Drilling Program sites. • Morozovella switch from dextral to sinistral coiling direction across the Early Eocene Climatic Optimum. • Changes in coiling direction occurred in multiple morphologically distinct species. • Carbon isotopes indicate dextral and sinistral morphotypes differ in their ecology. • Sinistral morphotypes were less dependent on photosymbiosis and thus able to adapt more readily to paleoceanographic change.

Short-term climate and vegetation dynamics in Lena River Delta (northern Yakutia, Eastern Siberia) during early Eocene

Early Eocene climate and vegetation evolution in northern Yakutia (Eastern Siberia) are quantitatively studied for the first time based on paleobotanical records, using the coexistence approach (CA) for paleoclimate, the plant functional type approach (PFT) and the integrated plant record method (IPR). Paleobotanical data of this time-interval were obtained from 18 palynofloras of the coal beds outcropping on the bank of the Bykovskaya Channel in the area of Bulunkan Bay (Lena River Delta). The results indicate the persistence of warm temperate and at times possibly nearly tropical, overall humid climate conditions throughout the early Eocene, and a relatively strong seasonality in precipitation. The vegetation reconstructed is in agreement with the climate conditions determined by the CA. Analyses of the PFT diversity spectra indicate the prevalence of mixed warm temperate evergreen-deciduous forests. Based on the IPR method, plant biomes varied from mixed mesophytic forests during warmer intervals to broadleaved deciduous forest/mixed mesophytic forest ecotone during cooler episodes. The presence of mangroves in our early Eocene records is possibly related to hyperthermal events such as the Paleocene–Eocene Thermal Maximum.

Attenborough's beauty: exceptional pattern preservation in a frog‐legged leaf beetle from the Eocene Green River Formation, Colorado (Coleoptera, Chrysomelidae, Sagrinae)

AbstractA new fossil leaf beetle species, Pulchritudo attenboroughi (Chrysomelidae, Sagrinae), is described from the Eocene Green River Formation in Colorado and is the second known fossil representative of this subfamily from North America. The fossil stands out by its remarkable preservation of elytral patterns. Such sharp and high‐contrast preservation of exoskeletal colouration is extremely rare in the fossil record of beetles and unique in its definition and fidelity. Sagrinae currently do not occur in North America, but two extant species are present in tropical and subtropical South America, one of which is similar in several aspects to the new fossil. Many extant Sagrinae live in a warm, humid climate similar to that suggested for the Early Eocene Climatic Optimum of the Green River Formation.

Biotic Response to Early Eocene Warming Events: Integrated Record From Offshore Zealandia, North Tasman Sea

AbstractEnvironmental and biotic responses to early Eocene hyperthermal events in the southwest Pacific are critical for global paleoclimate reconstructions during Cenozoic greenhouse intervals, but detailed multidisciplinary studies are generally missing from this time and location. Eocene carbonate sediments were recovered during International Ocean Discovery Program Expedition 371 at Site U1510 on southern Lord Howe Rise in the Tasman Sea. Part of the Early Eocene Climatic Optimum (EECO; 53.26–49.14 Ma) and superimposed hyperthermal events have been identified based on refined calcareous nannofossil biostratigraphic data and carbon stable isotope records on bulk sediment and benthic foraminifera. Four negative carbon isotope excursions (CIEs) associated with negative oxygen isotope excursions are recognized within the EECO. Comparison with a global compilation of sites indicates these CIEs correlate to the K event (Eocene Thermal Maximum 3), and tentatively to the S, T, and U events. Sediments with a high carbonate content throughout the EECO provide an excellent opportunity to examine these CIEs, as carbonate dissolution often impacts correlative records elsewhere. Benthic foraminifera and calcareous nannoplankton taxa indicative of warm waters are most abundant during the K event, the most prominent hyperthermal of the EECO. Eutrophication of surface waters during the K event did not lead to increased trophic conditions at the seafloor, whereas a coupled response is observed during smaller hyperthermals. The biotic turnover sheds new light on the paleoenvironmental consequences of hyperthermal events.