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Near‐Future pCO 2 During the Hot Miocene Climatic Optimum
No full textTo improve future predictions of anthropogenic climate change, a better understanding of the relationship between global temperature and atmospheric concentrations of CO2 (pCO2), or climate sensitivity, is urgently required. Analyzing proxy data from climate change episodes in the past is necessary to achieve this goal, with certain geologic periods, such as the Miocene climatic optimum (MCO), a transient period of global warming with global temperatures up to ~7°C higher than today, increasingly viewed as good analogues to future climate under present emission scenarios. However, a problem remains that climate models cannot reproduce MCO temperatures with less than ~800 ppm pCO2, while most previously published proxies record pCO2 < 450 ppm. Here, we reconstructed MCO pCO2 with a multitaxon fossil leaf database from the well‐dated MCO Lagerstätte deposits of Clarkia, Idaho, USA, using four current methods of pCO2 reconstructions. The methods are principally based on either stomatal densities, carbon isotopes, or a combination of both—thus offering independent results. The total of six reconstructions mostly record pCO2 of ~450–550 ppm. Although slightly higher than previously reconstructed pCO2, the discrepancy with the ~800 ppm required by climate models remains. We conclude that climate sensitivity was heightened during MCO, indicating that highly elevated temperatures can occur at relatively moderate pCO2. Ever higher climate sensitivity with rising temperatures should be very seriously considered in future predictions of climate change
Determination of the microscopic mineralogy ofinclusions in an amygdaloidal pillow basalt by LIMS
No full textWe present chemical depth profiling studies on mineralogical inclusions embedded in amygdale calcium carbonate by our Laser Ablation Ionisation Mass Spectrometer designed for in situ space research. An IRfemtosecond laser ablation is employed to generate ions that are recorded by a miniature time-of-flightmass spectrometer. The mass spectra were measured at several locations on the sample surface and yield chemical depth profiles along the depth length of about 30 mm. The presence of oxides and sulphides within inclusion material allows us to derive elemental abundance calibration factors (relative sensitivity coefficients, RSCs) for major and minor elements. These are obtained from the atomic intensity correlations performed on the depth profiling data. With the RSCs corrections the quantitative analysis of more complex mineralogical phases within the inclusion is conducted by correlating atomic abundance fractions in ternary diagrams, typically used in geology. The spatial resolution of the depth profiles was sufficient to study chemically distinct micrometre-sized objects, such as mineralogical grains and thin layers of minerals including micrometre-sized filamentous structures. The method presented here is well-suited for the quantitative chemical analyses of highly heterogeneous materials where the ablation condition can vary locally with the material composition making the application of standard reference materials less accurate. The presented method is developed to distinguish between abiotic and biological material while searching for micrometre-sized extinct or extent life forms on the surfaces of Solar System bodies
Assessing the utility of barium isotopes to trace Eurasian riverine freshwater inputs to the Arctic Ocean
No full textTracing riverine freshwater transport pathways within the Arctic Ocean is key to understanding changes in Arctic Ocean freshwater inventories. Dissolved Ba concentrations have been used in this capacity but are compromised by non-conservative processes. To assess the potential for Ba isotopes to provide insights into the impact of such processes on Arctic Ocean dissolved Ba inventories, Ba concentration and isotope data for surface seawater samples from the Siberian Shelf and Bering Sea/Strait are presented. These samples capture the mixing of riverine freshwater discharged by the rivers Yenisey, Lena and Ob, with Atlantic and Pacific derived seawater, which are traced by relationships between salinity, Ba concentration and δ138/134Ba. The δ138/134Ba of net river inputs, following modification by estuarine processes, are constrained to be 0.31 ± 0.04‰, 0.20 ± 0.06‰ and 0.23 ± 0.04‰, for the rivers Yenisey, Lena and Ob respectively. These values are used to estimate an average δ138/134Ba for Eurasian river freshwater input to the Arctic Ocean of 0.23 ± 0.04‰. The Ba concentration and δ138/134Ba of Lena River freshwater transported across the Laptev Sea are modified by non-conservative processes. These non-conservative processes do not result in distinctive modification of dissolved Ba concentration-δ138/134Ba mixing relationships between Eurasian riverine freshwater and Arctic seawater, which unfortunately limits the potential of Ba isotopes to improve tracing riverine freshwater sources in the central Arctic Ocean basins using dissolved Ba inventories. More generally the results of this study help advance understanding of Ba isotope cycling in the environment and their development as an emerging tracer of marine processes
A thyasirid-dominated methane-seep deposit from Montañita, southwestern Ecuador, from the Oligocene-Miocene boundary
No full textA mass occurrence of the thyasirid bivalve Thyasira montanita in a limestone bed, exposed at Punta Montañita on the northern side of the Santa Elena peninsula in southeastern Ecuador, is here identified as an ancient methane-seep deposit. The massive to nodular limestone shows carbonate phases and microfabrics typical of seep limestones, such as banded and botryoidal cements. Its δ13 Ccarbonate values, as low as −52.6‰, suggest a biogenic methane source. Furthermore, the carbonate microfabrics and biomarkers typical of ANME-2 archaea indicate high seepage rates. Tubular fossils previously interpreted as worm tubes show cone-shaped projections and an internal structure consistent with that of crustacean cuticle and are here interpreted as crustacean fragments. Seep deposits with mass occurrences of thyasirid bivalves have so far only been reported from the Cretaceous, making the Montañita seep deposit the first such example from the Cenozoic. The faunal and biomarker inventories of this deposit indicate deposition on an open shelf; the oysters on the upper surface of the limestone are likely secondary encrusters that arrived only after the emergence of this deposit in shallower water
Brattforsite, Mn19(AsO3)12Cl2, a new arsenite mineral relatedto magnussonite, from Brattforsgruvan, Nordmark,Värmland, Sweden
No full textBrattforsite is an approved mineral (IMA2019-127), with ideal formula Mn19(AsO3)12Cl2. Associated minerals in the type specimen from the Brattfors mine, Nordmark (Värmland, Sweden) include jacobsite, alleghanyite, phlogopite, calcite anddolomite. Brattforsite, forming subhedral, mostly equant crystals up to 0.5 mm across, is orange to reddish-brown with a white streak, and translucent with a resinous to vitreous lustre. The fracture is uneven to subconchoidal, and no cleavage is observed. It is very weakly pleochroic in yellow, optically biaxial (–) with 2V = 44(5)° and has calculated mean refractive index of 1.981. Measured and calculated density values are 4.49(1) and 4.54(1) g·cm−3, respectively. Chemical analyses yields (in wt%): MgO 0.62, CaO 1.26, MnO 48.66, FeO 0.13, As2O3 46.72, Cl 2.61, H2Ocalc 0.07, O ≡ Cl –0.59, sum 99.49, corresponding to the empirical formula (Mn17.67Ca0.58Mg0.40Fe0.05)Σ18.70As12.17O35.90Cl1.90(OH)0.20, based on 38 (O + Cl + OH) atoms per formula unit. The five strongest Bragg peaks in the powder X-ray diffraction pattern are [d (Å), I (%), (hkl)]: 2.843,100, (-444)); 2.828, 99,(444); 1.731, 32, (880); 2.448, 28, (800); 1.739, 25, (088). Brattforsite is monoclinic and pseudotetragonal, space group I2/a, with unit-cell parameters a = 19.5806(7), b = 19.5763(7), c = 19.7595(7) Å, β = 90.393(3)°, V = 7573.9(5) Å3 and Z = 8. The crystal structure was solved and refined to an R1 index of 3.4% for 7445 reflections [Fo > 4σ(Fo)]. Brattforsite has the same overall structural topology as magnussonite (i.e., the species can be considered as homeotypic), but with 12 independent tetrahedrally coordinated As sites and 21 Mn sites with varying (4–8) coordination. The Mn-centered polyhedra, bonded through edge- and face-sharing, give rise to a three-dimensional framework. The (AsO3)3− groups are bonded to this framework through corner- and edge-sharing. Spectroscopic measurements (optical absorption, Raman, FTIR) carried out support the interpretation of the compositional and structural data
Bianchiniite, Ba2(Ti4+V3+)(As2O5)2OF, a new diarsenite mineral fromthe Monte Arsiccio mine, Apuan Alps, Tuscany, Italy
No full textThe new mineral bianchiniite, Ba2(Ti4+V3+)(As2O5)2OF, has been discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as brown {001} tabular crystals, up to 1 mm across, with a vitreous lustre. It is brittle, with a perfect {001} cleavage. Streak is brownish. In reflected light, bianchiniite is grey, with orange–yellow internal reflections. It is weakly bireflectant, with a very weak anisotropy in shades of grey. Minimum and maximum reflectance data for COM wavelengths [Rmin/Rmax (%), (λ, nm)] are: 5.0/5.8 (470),5.7/6.5 (546), 5.7/7.0 (589) and 5.2/6.3 (650). Electron microprobe analyses gave (wt.% – average of 10 spot analyses): TiO2 10.34, V2O33.77, Fe2O3 3.76,As2O3 44.36, Sb2O3 0.22, SrO 0.45, BaO 34.79, PbO 0.28, F 1.77, sum 99.74, –O=F–0.75, total 98.99. On the basis of 12 anions per formula unit, the empirical formula of bianchiniite is (Ba2.00Sr0.04Pb0.02)Σ2.06(Ti4+1.14V3+0.44Fe3+0.42)Σ2.00[(As3.96Sb0.02)Σ3.98O10](O1.18F0.82)Σ2.00. Bianchiniite is tetragonal, space group I4/mcm, with unit-cell parameters a = 8.7266(4), c = 15.6777(7) Å, V = 1193.91(12) Å3 and Z = 8. Its crystal structure was refined from single-crystal X-ray diffraction data to R1 = 0.0134 on the basis of 555 unique reflections with Fo > 4σ(Fo)and 34 refined parameters. The crystal structure shows columns of corner-sharing [Ti/(V,Fe)]-centred octahedra running along c, connected along a and b through (As2O5) dimers. A {001} layer of Ba-centred [10+2]-coordinated polyhedra is intercalated between (As2O5) dimers. Bianchiniite has structural relations with fresnoite- and melilite-group minerals. The name honours the two mineral collectors Andrea Bianchini (b. 1959) and Mario Bianchini (b. 1962) for their contribution to the knowledge of the mineralogy of pyrite ± baryte ± iron-oxide ore deposits from the Apuan Alps
Pace, magnitude, and nature of terrestrial climate change through the end-Permian extinction in southeastern Gondwana
No full textRapid climate change was a major contributor to the end-Permian extinction (EPE). Although well constrained for the marine realm, relatively few records document the pace, nature, and magnitude of climate change across the EPE in terrestrial environments. We generated proxy records for chemical weathering and land surface temperature from continental margin deposits of the high-latitude southeastern margin of Gondwana. Regional climate simulations provide additional context. Results show that Glossopteris forest-mire ecosystems collapsed during a pulse of intense chemical weathering and peak warmth, which capped ∼1 m.y. of gradual warming and intensification of seasonality. Erosion resulting from loss of vegetation was short lived in the low-relief landscape. Earliest Triassic climate was∼10–14 °C warmer than the late Lopingian and landscapes were no longer persistently wet. Aridification, commonly linked to the EPE, developed gradually, facilitating the persistence of refugia for moisture-loving terrestrial groups.This research was also funded by U.S. National Science Foundation (NSF) grants EAR-1636625 (C.R. Fielding and D. Frank) and EAR-1636629 (A.M.E. Winguth and C. Winguth), and the Royal Swedish Academy of Sciences. We acknowledge NSF-sponsored high-performance computing support from Cheyenne provided by the U.S. National Center for Atmospheric Research (NCAR) Computational and Information Systems Laboratory.</p
Thermal evolution behavior of the organic matter and a ray of light on the origin of vitrinite-like maceral in the Mesoproterozoic and Lower Cambrian black shales: Insights from artificial maturation
No full textThe overmature Precambrian to Lower Paleozoic marine shales from China contain relatively simple organic matter (OM) composition, which is dominated by in-source solid bitumen (i.e., solid bitumen in the hydrocarbon source rocks). The thermal evolution behavior of the original OM and the determination of thermal maturity in the Precambrian to Cambrian marine shales have been challenging for decades. The vitrinite-like maceral (VLM) is widely present in these marine shales, and its origin is still unknown. To address these issues, the immature Proterozoic Xiamaling shales from China and the immature Cambrian Alum shales from Sweden, and a Chinese immature Carboniferous coal were heat-treated at temperature range of 300 ◦C to 550 ◦C. The carbonized residue of the artificially matured samples was examined for their morphological and reflectance variation, and the results were compared with data on the other overmature natural shales from China and Sweden. OM components are similar in the Xiamaling and Alum immature oil shales, consisting of filamentous algae, matrix bituminite, bituminite, VLM and liptodetrinite, and rare thucholites are present in the Xiamaling shales. The algal-derived OM decomposed gradually due to hydrocarbon generation at 300–350 ◦C. OM is mainly composed of the in-source solid bitumen in the artificially heated shales after 350 ◦C, similar to the overmature Precambrian to Cambrian natural shales, and the in-source solid bitumen gradually loses its mass with increasing thermal maturity. The in-source solid bitumen is derived from the thermal cracking of the retained oil or the direct conversion of algal-derived liptinite macerals (e.g., the bituminite) or their mixture. VLM in the Xiamaling oil shales can not be observed after 350 ◦C, but VLM is still present in the Alum oil shales. It can be inferred that there is a different source of VLM in these shales, and VLM in the Xiamaling oil shales contains more volatile material. The VLM in the Xiamaling shales may be biodegradation products of liptinites under anoxic environments. The origin of VLM in the Cambrian Alum shales requires further study to be verified, although it is certain that graptolites are not its sources. The reflectance of in-source solid bitumen (SBRo) increases with heat-treated temperature in both the Xiamaling shales and the Alum shales, but at different rates, which may be due to the difference of the original kerogen composition in these shales. VLM reflectance (VLMRo) and SBRo in sections perpendicular to bedding can be used to determine the maturation level of the Precambrian-Cambrian sediments. Their relation to equivalent vitrinite reflectance (EqVRo) can be expressed by the following equations: EqVRo = 1.07 × VLMRo – 0.18, EqVRo = 0.87 × SBRo + 0.25 (in the Precambrian sediments) and EqVRo = 1.15 × SBRo + 0.01 (in the Cambrian sediments).This work was supported by the National Natural Science Foundation of China (No. 41773031), the National Key Research and Development Program of China (No. 2017YFC0603102) and the Science Foundation of China University of Petroleum, Beijing (No. 2462020YXZZ021 and 2462021QNXZ001). One of the co-authors (V.S.) wishes to acknowledge the support of OP RDE, MEYS Czech Republic (Reg. No. CZ.02.1.01/0.0/0.0/16_019/0000728), which enabled him to contribute to this study</p
The Miocene: The Future of the Past
No full textThe Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned toward modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval—the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO2, and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO2 (∼400–600 ppm), the MCO has been suggested as a particularly appropriate analog for future climate scenarios, and for assessing the predictive accuracy of numerical climate models—the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re-interpretation of proxies, which might mitigate the model-data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here, we review the state-of-the-art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modeling studies.The initial workshops that catalyzed this project were supported by The Bolin Center for Climate Research, Stockholm University, and the Swedish Research Council (Conference Grant nr. 2018–06,618 to M. Steinthorsdottir). The authors acknowledge funding from: the Swedish Research Council (VR starting grant nr. NT7-2016 04,905 to M. Steinthorsdottir; VR grants nr. 2016–03,912 to A. M. de Boer and nr. 2016–04,434 to J. Henderiks); the United States National Science Foundation (NSF), through the P2C2 program grant nr. 1602905 to M. Huber, the Atmospheric and Geospace Sciences program grant nr. to N.J.B (who is also supported by the Alfred P. Sloan Foundation as a Research Fellow), and the Global Change, Sedimentary Geology & Paleobiology, and Geobiology and Low-temperature Geochemistry programs grant nrs. 1349749 and1561027 to M. J. Kohn; and the UK Natural Environment Research Council (grant NE/P019102) to C. H. Lear. E. Gasson acknowledges funding from a Royal Society fellowship. Clara Bolton, Peter Bijl, Daniel Breecker, Jeremy Caves Rugenstein, Florence Collioni, Mikael Fortelius, David Lazarus, Eelco Rohling, Francesca Sangiorgi, Maria Seton, Erik Skovbjerg Rasmussen, Appy Sluijs, Lars Werdelin, and Zhongshi Zhang are thanked for their useful comments with respect to Figure 1. M. Huber acknowledges assistance in Miocene work from Nick Herold and Ashley Dicks. No new data were created for this study, and all reviewed data sets are available through the cited original papers. The authors declare no conflict of interest.</p
Genomic signatures of rapid adaptive divergence in a tropical montane species
No full textMountain regions contain extraordinary biodiversity. The environmental heterogeneity and glacial cycles often accelerate speciation and adaptation ofmontane species, but how these processes influence the genomic differentiation of these species is largely unknown. Using a novel chromosomelevel genome and population genomic comparisons, we study allopatricdivergence and selection in an iconic bird living in a tropical mountainregion in New Guinea, Archbold’s bowerbird (Amblyornis papuensis). Ourresults show that the two populations inhabiting the eastern and western Central Range became isolated ca 11 800 years ago, probably because the suitablehabitats for this cold-tolerating bird decreased when the climate got warmer.Our genomic scans detect that genes in highly divergent genomic regions areover-represented in developmental processes, which is probably associatedwith the observed differences in body size between the populations. Overall,our results suggest that environmental differences between the eastern andwestern Central Range probably drive adaptive divergence between them