The palaeoenvironment of the middle Miocene pliopithecid locality in Damiao, Inner Mongolia, China

Damiao, Inner Mongolia, has three main fossil horizons representing the early, middle, and late Miocene. The middle Miocene locality DM01 is the only primate locality from the region and also represents the latest occurrence of pliopithecoids in northern China. The presence of pliopithecoid primates in central Asia after the middle Miocene climatic optimum seems to contradict the general trend of strengthening climatic zonality and increasing aridity. To investigate this enigma, we employ faunal similarity, ecometrics, and stable isotope analysis. Our results support previous inferences concerning the presence of locally humid environments within the increasingly arid surroundings that characterized central Asia. Hypsodonty, estimated mean annual precipitation (MAP), local sedimentology, and large mammal fossils suggest more humid and possibly more forested and wooded environments for the DM01 locality. We compared our results with the adjacent fossil-rich middle Miocene Tunggur localities. However, the small mammal fauna and isotope data are consistent with a mosaic of forest and grassland environment for all Damiao localities. Based on our results, Tunggur may have been too seasonal or not sufficiently humid for pliopithecids. This is supported by the higher mean hypsodonty and lower estimated MAP estimates, as well as slightly higher d13C values. We suggest that DM01, the driest known Asian pliopithecid locality, may have been a more humid refugium within a generally drier regional context.Peer reviewe

Calibration of the dolomite clumped isotope thermometer from 25 to 350°C, and implications for a universal calibration for all (Ca, Mg, Fe)CO_3 carbonates

Carbonate clumped isotope thermometry is based on the temperature-dependent formation of ^(13)C^(18)O^(16)O_2^(2-) ion groups within the lattice of solid carbonate minerals. At low temperatures the bonds between rare, heavy ^(13)C and ^(18)O isotopes are thermodynamically favored, and thus at equilibrium they are present in higher than random abundances. Here we calibrate the use of this temperature proxy in a previously uncalibrated carbonate phase — dolomite [CaMg(CO_3)_2] — over a temperature range that extends to conditions typical of shallow crustal environments, by determining the Δ_(47) values of CO_2 extracted from synthetic or natural (proto)dolomites grown at known temperatures from 25 to 350°C and analyzed in two different laboratories using different procedures for sample analysis, purification and post-measurement data treatment. We found that the Δ_(47) – 1/T^2 dependence for (proto)dolomite is linear between 25 and 350°C, independent of their Mg/Ca compositions or cation order (or the laboratory in which they were analyzed), and offset from, but parallel to, the theoretical predictions of the Δ_(63) dependence to temperature of the abundance of the ^(13)C^(18)O^(16)O_2 isotopologue inside the dolomite and calcite mineral lattices as expected from ab-initio calculations (Schauble et al., 2006). This suggests that neither the equilibrium constant for ^(13)C–^(18)O clumping in (proto)dolomite lattice, nor the experimental fractionation associated with acid digestion to produce CO_2, depend on their formation mechanism, degree of cation order and/or stoichiometry (ie., Mg/Ca ratio) and/or δ^(18)O and δ^(13)C compositions (at least over the range we explored). Thus, we suggest the following single Δ_(47) – 1/T^2 linear regression for describing all dolomite minerals: with T in kelvin and Δ_(47) in the Carbon Dioxide Equilibrium Scale (CDES) of Dennis et al. (2011) and referring to CO_2 extracted by phosphoric acid digestion at 90°C. The listed uncertainties on slope and intercept are 95% confidence intervals. The temperature sensitivity (slope) of this relation is lower than those based on low temperature acid digestion of carbonates, but comparable to most of those based on high temperature acid digestion (with however significantly better constraints on the slope and intercept values, notably due to the large range in temperature investigated and the large number of Δ_(47) measurements performed here, n = 67). We also use this dataset to empirically determine that the acid fractionation factor associated with phosphoric acid digestion of dolomite at 90°C (Δ∗_(dolomite90)) is about + 0.176‰. This is comparable to the Δ∗_(calcite90) experimentally obtained for calcite (Guo et al., 2009), suggesting that the acid fractionation Δ∗ for acid digestion of dolomite and calcite are the same within error of measurement, with apparently no influence of the cation identity. This hypothesis is also supported by the fact that our dolomite calibration data are indistinguishable from published calibration data for calcite, aragonite and siderite generated in similar analytical conditions (ie., carbonate digested at T ⩾ 70°C and directly referenced into CDES), demonstrating excellent consistency among the four (Ca,Mg,Fe)CO_3 mineral phases analyzed in seven different laboratories (this represents a total of 103 mean Δ_(47) values resulting from more than 331 Δ_(47) measurements). These data are used to calculate a composite Δ_(47)–T universal relation for those carbonate minerals of geological interest, for temperatures between -1 and 300°C, that is found to be statistically indistinguishable from the one described by dolomite only: Thus, in order to standardize the temperature estimates out of different laboratories running high temperature digestion of (Ca,Mg,Fe)CO_3 carbonate minerals, we recommend the use of this single Δ_(47)-T calibration to convert Δ_(47CDES) data into accurate and precise temperature estimates. More widely, this study extends the use of the Δ_(47) thermometry to studies of diagenesis and low-grade metamorphism of carbonates with unprecedented precision on temperature estimates based on Δ_(47) measurements — environments where many other thermometers are generally empirical or semi-quantitative

Dimethyl fumarate in patients admitted to hospital with COVID-19 (RECOVERY): a randomised, controlled, open-label, platform trial

Dimethyl fumarate (DMF) inhibits inflammasome-mediated inflammation and has been proposed as a treatment for patients hospitalised with COVID-19. This randomised, controlled, open-label platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]), is assessing multiple treatments in patients hospitalised for COVID-19 (NCT04381936, ISRCTN50189673). In this assessment of DMF performed at 27 UK hospitals, adults were randomly allocated (1:1) to either usual standard of care alone or usual standard of care plus DMF. The primary outcome was clinical status on day 5 measured on a seven-point ordinal scale. Secondary outcomes were time to sustained improvement in clinical status, time to discharge, day 5 peripheral blood oxygenation, day 5 C-reactive protein, and improvement in day 10 clinical status. Between 2 March 2021 and 18 November 2021, 713 patients were enroled in the DMF evaluation, of whom 356 were randomly allocated to receive usual care plus DMF, and 357 to usual care alone. 95% of patients received corticosteroids as part of routine care. There was no evidence of a beneficial effect of DMF on clinical status at day 5 (common odds ratio of unfavourable outcome 1.12; 95% CI 0.86-1.47; p = 0.40). There was no significant effect of DMF on any secondary outcome

Clumped isotope data and raw and normalized triple oxygen isotope data for samples from the K-Pg boundary of Site M0077 in the Chicxulub Crater

The newly formed Chicxulub crater was rapidly filled by seawater then disturbed by tsunami and seiche waves. Sedimentary layers deposited as wave energy declined provide a unique window into the environment of the nascent crater in the months and years to millennia after the impact. Geochemical data show temperatures in hotter regions of the crater in excess of 70°C for the first few years with heat derived from the underlying melt sheet via hydrothermal circulation. Cooler regions of the crater became habitats soon after impact with a suite of fossils indicating diverse life on the seafloor and sea surface, ranging from microbes to marine arthropods, and possibly fish. We suggest that this community was sustained by nutrients and heat from the hydrothermal system. The rapid early recovery in the Chicxulub crater and ocean above demonstrates the resiliency of life under extraordinarily harsh conditions, which has important ramifications for early life on Earth and life on other planets

P-24 Stable Isotope Analysis of Incisor Enamel in Thirteen-lined Ground Squirrels (Ictidomys tridecemlineatus)

We investigated stable-isotope profiles of incisor enamel from 8, well-referenced thirteen-lined ground squirrels (Ictidomys tridecemlineatus), using laser ablation coupled with gas chromatography–mass spectrometry. Stable isotope profiles were referenced to real time (cumulative dental growth record from mid-August to early May) based on known dates of events reflected in incremental dentin structure (entry into and exit from the hibernation season, fall injections of oxytetracycline). During late summer and fall, ∂13C of incisor enamel peaked between late August and mid September (individual peak values ranged from -3.7 to -1.9 ‰), with lower values before and after. Values of ∂13C were relatively low but variable during hibernation (≤ -9.6 ‰) and in the spring immediately after hibernation (≤ -11.0 ‰). Fall values of ∂18O were significantly and positively correlated with ∂13C for 5 of 8 squirrels. The roughly coordinated peak in ∂13C values in late summer across squirrels may indicate transient increase in the proportion of C4 plants (directly or indirectly via insects that feed on C4 plants), although this interpretation must be tested. Overall, our results indicate that fine-scale seasonal variation in paleo-diet and perhaps other paleoecological attributes might be reconstructed from incisors of fossil rodents

Formation of dolomite at 40–80 °C in the Latemar carbonate buildup, Dolomites, Italy, from clumped isotope thermometry

The temperature of formation of replacement dolomite and δ^(18)O(H_(2)O) of dolomitizing fluid in the Latemar carbonate buildup, Dolomites, Italy, were estimated independently from carbonate clumped isotope thermometry. Dolomite formed at 42–72 ± 9–11 °C (±2 standard deviations, SD) from fluid with δ^(18)O(H_(2)O) that averages –0.3‰ ± 3.3‰ (Vienna standard mean ocean water; ±2 SD). The estimated temperature and δ^(18)O(H_(2)O) are similar to those of modern diffuse flow fluids at mid-ocean ridges, the kind of fluid that has been proposed previously as the dolomitizing fluid in the Latemar buildup, based on the trace element compositions of dolomite. Calcite in limestone preserves original δ^(18)O, but records clumped isotope temperatures, 44−76 ± 9−11 °C (±2 SD), that are higher than those at which the limestone formed. Temperature recorded by calcite, but not δ^(18)O, was likely reset during dolomitization. Clumped isotope thermometry has great potential for application to studies of burial and diagenesis by retrieving independent estimates of temperature and δ^(18)O(H_(2)O) with uncertainties as low as ±5 °C (±2 standard errors, SE) and ± 0.75‰ (±2 SE), respectively, from a single stable isotope analysis of a carbonate mineral

Clumped‐Isotope Geothermometry and Carbonate U–Pb Geochronology of the Alta Stock Metamorphic Aureole, Utah, USA: Insights on the Kinetics of Metamorphism in Carbonates

To assess thermal and kinetic influences on atomic mobility and mineral (neo)crystallization, clumped‐isotope abundances of calcite and dolomite were measured alongside dolomite cation ordering and U–Pb dates, across metamorphic grade within the c. 35–30 Ma Alta stock contact metamorphic aureole, Utah, USA. Average Δ47 values of dolomite inside the metamorphic aureole reflect the blocking temperature of dolomite (300°C–350°C) during cooling from peak temperatures. Dolomite Δ47 values outside the metamorphic aureole record a temperature of ∼160°C. At the talc isograd, dolomite Δ47 values abruptly change, corresponding to a decrease of ∼180°C over <50 m in the down‐temperature direction. This observed step in dolomite Δ47 values does not correlate with cation ordering in dolomite or U–Pb dates, neither of which correlate well with metamorphic grade. The short distance over which dolomite Δ47 values change indicates strong temperature sensitivity in the kinetics of dolomite clumped‐isotope reordering, and is consistent with a wide range of clumped‐isotope reequilibration modeling results. We hypothesize that clumped‐isotope reordering in dolomite precedes more extensive recrystallization or metamorphic reaction, such as the formation of talc. Dolomite U–Pb analyses from inside and outside the metamorphic aureole populate a single discordia ∼60 Myr younger than depositional age (Mississippian), recording resetting in response to some older postdepositional, but premetamorphic process.Key Points:Dolomite clumped isotopes record an abrupt ∼180°C decrease, over <50 m, at the talc isograd of the Alta contact metamorphic aureoleThis step feature suggests strong thermal sensitivity in clumped‐isotope reordering that precedes talc neocrystallizationClumped‐isotope geothermometry may provide new insights into processes controlling metamorphism and reaction kinetics in carbonatesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/167127/1/ggge22474.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167127/2/2020GC009238-sup-0001-Supporting_Information_SI-S01.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167127/3/ggge22474_am.pd

Terrestrial cooling and changes in hydroclimate in the continental interior of the United States across the Eocene-Oligocene boundary

WOS:000437009200002International audienceOne of the most pronounced climate transitions in Earth's history occurred at the Eocene-Oligocene transition, similar to 34.0-33.6 m.y. ago. Marine sedimentary records indicate a dramatic decline in pCO(2) coeval with global cooling during the transition. However, terrestrial records are relatively sparse, with conflicting interpretations of hydroclimate in continental interiors. Here, we provide quantitative constraints on the response of the continental hydroclimate in the western United States across the Eocene-Oligocene boundary by studying clumped isotope temperatures [T(Delta(47))], delta C-13 and delta O-18 values of vadose carbonates, and delta C-13 values of bulk organic matter (delta C-13(org)) in eastern Wyoming. Our results show that T(Delta(47)) dropped from similar to 28 degrees C to similar to 21 degrees C, indicating similar to 7 degrees C cooling in air temperature, which occurred parallel to the decrease in atmospheric pCO(2) during the latest Eocene-early Oligocene. We find that aridity and the biome were stable, and ice-volume-corrected precipitation PO decreased similar to 1.6 parts per thousand across the Eocene-Oligocene boundary, attributable to reduced vapor condensation temperatures. These new quantitative data add to the growing body of evidence suggesting a marked terrestrial response in temperature and hydroclimate across the Eocene-Oligocene transition. Our findings indicate a pattern of greenhouse-gas- induced global temperature change in the continental interior of the United States that was roughly 1.5-2x the magnitude of cooling in the global ocean