Charlotte Prud'homme  Olivier Moine  Jerome Mathieu  Segolene Saulnier‐Copard  Pierre Antoine 《Boreas: An International Journal of Quaternary Research》2019,48(1):257-268

High concentrations of calcite fossil granules produced by earthworms (ECG) have been identified in most of the stratigraphical units along the loess‐palaeosol reference sequence of Nussloch (Germany). They are particularly abundant in interstadial brown soils and in tundra gley horizons, the latter reflecting short‐term phases of aggradation then degradation of permafrost. These granules are characterized by a radial crystalline structure produced in the earthworms by specific bio‐mineralization processes. In our study, we used this biological indicator combined with ¹⁴C and OSL dating, and sedimentological parameters to characterize millennial‐time scale climatic variations recorded in loess sequences. The approach is based on high‐resolution counts of ECG throughout a 17‐m‐thick loess sequence (332 samples). Strong increases in granule and mollusc concentrations suggest warmer climate conditions during palaeosol formation phases, associated with increasing biodiversity, biological activity and vegetation cover. Decreased granule concentrations occur within primary loess deposits, indicating a strong correlation with palaeoenvironmental conditions and demonstrating the reliability of ECG concentration variations as a new palaeoenvironmental proxy. Finally, this pattern is also recorded in loess sequences located about 600 km westward in northern France demonstrating the large‐scale validity of this new palaeoclimatic proxy.  相似文献   

    

Ximena Navarro‐Harris  Mario Pino  Pedro Guzmn‐Marín  María Paz Lira  Rafael Labarca  Alexandre Corgne 《Geoarchaeology》2019,34(5):592-612

In this study we used a multidisciplinary approach, coupling morphological, geological, geochemical, and statistical analyses to investigate the provenance of rhyodacitic and dacitic glass knapped at the Pilauco site (40°34′11” S, 73°06′17” W; 13,570 ± 70–12,540 ± 90 ¹⁴C year BP) in northwestern Chilean Patagonia. A morphotechnological analysis was performed on the entire lithic assemblage, which is composed of cores, retouched and unretouched unifacial flakes, and small pieces of debitage, some of them closely associated with Notiomastodon aff. N. platensis gomphothere bones. Sixty‐two archeological and geological samples were analyzed by inductively coupled plasma mass spectrometry revealing a wide range of basaltic to rhyodacitic compositions. The archeological knappable dacitic and rhyodacitic glasses were recovered from pebbles deposited mainly on a beach away from the site, as deduced by the presence of minute and dense crescentic percussion marks on the cortexes. Geochemical trace element analysis suggests that the Puyehue–Cordón Caulle Volcanic Complex is the most likely source for the volcanic glass artifacts at Pilauco. The new morphotechnological and provenance record and improved stratigraphic sequences highlight the Pilauco site as an important contribution for the diversity of the South American geoarchaeological context.  相似文献   

    

Arne P. Willner  Stuart N. Thomson  Johannes Glodny  Hans‐Joachim Massonne  Rolf L. Romer  Cees R. van Staal  Alexandre Zagorevski 《地学学报》2019,31(1):1-10

Following Appalachian orogenesis, metamorphic rocks in central Newfoundland were exhumed and reburied under Tournaisian strata. New zircon fission‐track (ZFT) ages of metamorphic rocks below the Tournaisian unconformity yield post‐depositionally reset ages of 212–235 Ma indicating regional fluid‐absent reheating to at least ≥220°C. Post‐Tournaisian sedimentary thicknesses in surrounding basins show that burial alone cannot explain such temperatures, thus requiring that palaeo‐geothermal gradients increased to ≥30–40°C/km before final late Triassic accelerated cooling. We attribute these elevated palaeo‐geothermal gradients to localized thermal blanketing by insulating sediments overlying radiogenic high‐heat‐producing granitoids. Late Triassic rifting and magmatism before break up of Pangaea likely also contributed to elevated heat flow, as well as uplift, triggering late Triassic accelerated cooling and exhumation. Thermochronological ages of 240–200 Ma are seen throughout Atlantic Canada, and record rifting and basaltic magmatism on the conjugate margins of the Central Atlantic Ocean preceding the onset of oceanic spreading at ~190 Ma.  相似文献   

    

X.‐J. Wu  Y.‐F. Yuan 《Astronomische Nachrichten》2019,340(1-3):121-125

The two stars of stellar binaries can be tidally disrupted by supermassive black holes (SMBHs) or supermassive black hole binaries (SMBHBs) in sequence. In this contribution, we review our recent study about double tidal disruption events (DTDEs) with SMBHBs. With the help of scattering experiments, we find that the time interval between two successive tidal disruption events (TDEs) depend on the semimajor axis of incident stellar binaries. For stellar binaries with 1 M_⊙ for each companion star and a semimajor axis less than 100 au, the maximum time interval is about 150 days when the stellar binary is tidally disrupted by an SMBH. However, for an SMBHB, the time intervals can be very large, and the maximum can exceed 10,000 years. Moreover, we also compare the probabilities of a DTDE with the time interval larger than 150 days by the SMBHB and of two separate TDEs by the SMBH with the same time interval. We find that, for the time interval of 150 days to 15 years, the probability of DTDEs by the SMBHB with a large mass ratio (i.e., q_bhb ≳ 0.1 ) is larger than that of the SMBH scenario. Finally, according to our results, we suggest that DTDEs with the time interval of 150 days to 15 years could be useful tools for finding SMBHB candidates with the mass ratio q_bhb ≳ 0.1 at galactic centers.  相似文献   

    

Michal Zaja ek  B. Czerny  Mary Loli Martínez‐Aldama  Vladimir Karas 《Astronomische Nachrichten》2019,340(7):577-585

By applying different statistically robust methods, we analyze the time lag between the continuum and ionized line‐emission (Mg II line) light curves for the distant bright quasar CTS C30.10 (redshift z∼0.9 ). The data were obtained by the 10‐meter South African Large Telescope (SALT) telescope in South Africa. In detail, we demonstrate the application of several methods using the interpolated cross‐correlation function (ICCF), discrete correlation function (DCF), z‐transformed discrete correlation function (zDCF), von Neumann estimator, and the JAVELIN code package. In particular, we discuss the uncertainties of these methods. In conclusion, we find that the quasar lies on the broad‐line region (BLR) size—monochromatic luminosity power‐law scaling, , which was already confirmed for low‐redshift sources. In case, the BLR size–luminosity relation holds for other distant sources, quasars could be used to probe cosmological models as “standard candles” complementary to supernovae Ia.  相似文献   

    

C.‐P. Hu  C.‐Y. Ng 《Astronomische Nachrichten》2019,340(4):340-345

Magnetars are strongly magnetized pulsars and they occasionally show violent radiative outbursts. They also often exhibit glitches that are sudden changes in the spin frequency. It was found that some glitches were associated with outbursts but their connection remains unclear. We present a systematic study to identify possible correlations between them. We find that the glitch size of magnetars likely shows a bimodal distribution, different from the distribution of the Vela‐like recurrent glitches but consistent with the high‐end of that of normal pulsars. A glitch is likely a necessary condition for an outburst but not a sufficient condition because only 30% of glitches were associated with outbursts. In the outburst cases, the glitches tend to induce larger frequency changes compared to those unassociated ones. We argue that a larger glitch is more likely to trigger the outburst mechanism, either by reconfiguration of the magnetosphere or deformation of the crust. A more frequent and deeper monitoring of magnetars is necessary for further investigation of their connection.  相似文献   

    

G. Piccinelli  J. Jaber‐Urquiza  A. Snchez 《Astronomische Nachrichten》2019,340(1-3):230-233

The effect of a homogeneous weak magnetic field on the decay process of a neutral scalar particle to a pair of charged fermions is studied. The decay rate is calculated through the imaginary part of the self‐energy of the scalar particle interacting with the charged fermions, at one loop. The weak field approximation can be performed in different ways, depending on the hierarchy of scales. Here, we explore the regime where the progenitor particle has a high transverse momentum and we find that the process is favored by the increase of the magnetic field. We compare our results with recent findings for a different kinematical regime and briefly discuss the possible physical reasons for the different behaviors. The phenomenon can be relevant in early universe events or in high‐energy collisions.  相似文献   

    

Zhi‐Fu Gao  Fang‐Kun Peng  Na Wang 《Astronomische Nachrichten》2019,340(9-10):1023-1029

Here, we summarize our recent work on the evolution of magnetic field and spin‐down of young pulsars including high‐B pulsars and magnetars. Our work includes the following three parts: (a) Based on the estimated ages of their potentially associated supernova remnants (SNRs), we estimate the values of the mean braking indices of eight magnetars with SNRs and find that five magnetars have smaller mean braking indices of 1 < n < 3, and we interpret them within a combination of magnetodipole radiation and wind‐aided braking. (b) The low braking index of n = 0.9(2) for PSR J1734‐3333 could undergo a supercritical accretion soon after its formation in a supernova explosion. The buried multipole magnetic fields will merge into a dipole magnetic field. Retaining the current field growth index ϵ = 1.34, this pulsar will become a magnetar with dB_p∼6.2(2) × 10¹⁴ G and dB_p∼1.06(4) × 10¹⁵ G after 50 kyrs and 100 kys, respectively. (c) By introducing a mean rotation energy conversion coefficient and combining the pulsar's high‐energy and timing observations with a reliable nuclear equation of state, we estimate the initial spin period, initial dipole magnetic field, and true age of PSR J1640‐4631. For this source, its measured high braking index n = 3.15(3) is attributed to a long‐term dipole magnetic field decay, and its soft X‐ray emission is attributed to anisotropic heating.  相似文献   

    

Samuel Ebert  Addi Bischoff  Dennis Harries  Sarah Lentfort  Jean‐Alix Barrat  Andreas Pack  Jrme Gattacceca  Robbin Visser  Peter Schmid‐Beurmann  Stephan Kimpel 《Meteoritics & planetary science》2019,54(2):328-356

Based on the high abundance of fine‐grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite–cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe‐rich olivine during a heating event without changing the textural appearance. A peak temperature of 400–600 °C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot‐like inclusions (UCLIs) within fine‐grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine‐grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice‐rich first‐generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.  相似文献   

    

M. B. Biren  J.‐A. Wartho  M. C. VAN Soest  K. V. Hodges  H. Cathey  B. P. Glass  C. Koeberl  J. W. Horton  W. Hale 《Meteoritics & planetary science》2019,54(8):1840-1852

Single crystal (U‐Th)/He dating has been undertaken on 21 detrital zircon grains extracted from a core sample from Ocean Drilling Project (ODP) site 1073, which is located ~390 km northeast of the center of the Chesapeake Bay impact structure. Optical and electron imaging in combination with energy dispersive X‐ray microanalysis (EDS) of zircon grains from this late Eocene sediment shows clear evidence of shock metamorphism in some zircon grains, which suggests that these shocked zircon crystals are distal ejecta from the formation of the ~40 km diameter Chesapeake Bay impact structure. (U‐Th/He) dates for zircon crystals from this sediment range from 33.49 ± 0.94 to 305.1 ± 8.6 Ma (2σ), implying crystal‐to‐crystal variability in the degree of impact‐related resetting of (U‐Th)/He systematics and a range of different possible sources. The two youngest zircon grains yield an inverse‐variance weighted mean (U‐Th)/He age of 33.99 ± 0.71 Ma (2σ uncertainties n = 2; mean square weighted deviation = 2.6; probability [P] = 11%), which is interpreted to be the (U‐Th)/He age of formation of the Chesapeake Bay impact structure. This age is in agreement with K/Ar, ⁴⁰Ar/³⁹Ar, and fission track dates for tektites from the North American strewn field, which have been interpreted as associated with the Chesapeake Bay impact event.  相似文献