Stratigraphy of Pleistocene glaciations in the St Elias Mountains,southwest Yukon,Canada

At least five Middle to Late Pleistocene advances of the northern Cordilleran Ice Sheet are preserved at Silver Creek, on the northeastern edge of the St Elias Mountains in southwest Yukon, Canada. Silver Creek is located 100 km up‐ice of the Marine Isotope Stage (MIS) 2 McConnell glacial limit of the St Elias lobe. This site contains ~3 km of nearly continuous lateral exposure of glacial and non‐glacial sediments, including multiple tills separated by thick gravel, loess and tilted lake beds. Infrared‐stimulated luminescence (IRSL) and AMS radiocarbon dating constrain the glacial deposits to MIS 2, 4, either MIS 6 or mid‐MIS 7, and two older Middle Pleistocene advances. This chronology and the tilt of the lake beds suggest Pleistocene uplift rates of up to 1.9 mm a^?1 along the Denali Fault since MIS 7. The non‐glacial sediment consists of sand, gravel, loess and organic beds from MIS 7, MIS 3 and the early Holocene. The MIS 3 deposits date to between 30–36 ¹⁴C ka BP, making Silver Creek one of the few well‐constrained MIS 3‐aged sites in Yukon. This confirms that ice receded close to modern limits in MIS 3. Pollen and macrofossil analyses show that a meadow‐tundra to steppe‐tundra mosaic with abundant herbs and forbs and few shrubs or trees, dominated the environment at this time. The stratigraphy at Silver Creek provides a palaeoclimatic record since at least MIS 8 and comprises the oldest direct record of Pleistocene glaciation in southwest Yukon.     

Hominins without fellow travellers? First appearances and inferred dispersals of Afro-Eurasian large-mammals in the Plio-Pleistocene

Discoveries of fossil Homo outside Africa predating 1.0 Ma have generated much discussion about hominin dispersal routes. However, tool-using bipeds were only one element of the inter-continental mammalian dispersals that occurred during the climatic changes of the Pliocene and Pleistocene. This paper will place hominin movements in the context of those of the wider mammalian fauna, which includes carnivores, bovids and non-human primates. The distribution of these different taxa suggests that species moved individually when the environmental conditions were right for them, rather than in multi-species waves of dispersal, and allows evaluation of the contextual evidence for the newly emerging ‘Out of Asia’ paradigm as well as the established ‘Out of Africa’ model.     

Distribution and Characteristics of Dinosaur Eggs in China

正China is one of the most prolific countries for dinosaur material in the world,from skeletons to footprints and eggs.At present,China has documented more than 160kinds of dinosaur,35 genera and 39 ichnospecies of dinosaur footprints,and 17 genera and 44 oospecies of dinosaur eggs.The dinosaur eggs in China are mainly distributed in Xinjiang,Inner Mongolia,Ningxia,Gansu,     

Influence of the Mississippi River on <Emphasis Type="Italic">Pseudo-nitzschia</Emphasis> spp. Abundance and Toxicity in Louisiana Coastal Waters

The presence of domoic acid (DA) toxin from multiple species of Pseudo-nitzschia is a concern in the highly productive food webs of the northern Gulf of Mexico. We documented the Pseudo-nitzschia presence, abundance, blooms, and toxicity over three years along a transect ～100 km west of the Mississippi River Delta on the continental shelf. Pseudo-nitzschia were present throughout the year and occurred in high abundances (>10⁴ cells l^?1) in the early spring months during high Mississippi River (MSR) flow (～20,000 m³ s^?1) but were most abundant (>10⁶ cells l^?1) when MSR discharge was relatively lower among the spring months. A high particulate toxin production (maximum reaching 13 μg DA l^?1) was associated with the high cell abundances and exceeded, by an order of magnitude, prior reports of particulate DA concentrations in Louisiana coastal waters. Differences in Pseudo-nitzschia peak times and its toxicity were correlated mainly with the timing and magnitude of MSR discharge and changes in associated parameters such as nutrient stoichiometry and salinity. A negative relationship between high MSR discharge and Pseudo-nitzschia and particulate DA concentrations was documented. These riverine dynamics have the potential to influence DA contamination in pelagic and benthic food webs in the coastal waters of the northern Gulf of Mexico.     

Quantitative Analysis of Paleoatmospheric CO2 Level Based on Stomatal Characters of Fossil Ginkgo from Jurassic to Cretaceous in China

A better theoretical and practical understanding of the linkage between paleo-CO2 and climate during geological history is important to enhance the sustainable development of modern human society. Development in plant physiology since the 1980s has led to the realization that fossil plants can serve as a proxy for paleoatmosphere and paleobiosphere. As a relict gymnosperm with evolutionary stasis, Ginkgo is well suited for paleoenvironmental reconstruction. This paper analyzes fossil Ginkgo species from integrated strata in the north of China using anatomic data of plant physiology. Using stomatal parameters, a trend for the paleo-CO2 level during the Early-Middle Jurassic and the Early Cretaceous was obtained, which is consistent with the estimates by GEOCARB. The trend is also similar to that of Mean Global Surface Temperature in geological time. Compared with three other atmospheric CO2 concentration parameters, the trend of paleo-CO2 level based on the stomatal parameter of the fossil Ginkgo specimens from three contiguous strata is more exact.     

Low reproductive success for copepods during a bloom of the non‐aldehyde‐producing diatom Cerataulina pelagica in the North Adriatic Sea

Egg production rates and/or hatching success in the copepods Acartia clausi, Calanus helgolandicus and Temora longicornis were negatively affected by a late spring (May–June 2003) phytoplankton bloom in the North Adriatic Sea, dominated mainly by the large diatom Cerataulina pelagica. Highest total concentrations of 3.3·10⁴ cells·ml^?1 were located in the vicinity of the Po River, which also corresponded to the area where the highest numbers of phaeophorbides were measured (0.779, 0.528 and 0.419 μg·l^?1, respectively, compared to an average of the remaining stations of 0.183 ± 0.049 SD), suggesting some grazing on the bloom. Phytoplankton biomass in terms of carbon was dominated by diatoms, representing on average 42% of total phytoplankton carbon and more than 80% at several stations. Cerataulina pelagica, Cyclotella spp., Chaetoceros spp. and small unidentified centric diatoms dominated the diatom community numerically but C. pelagica was by far the dominant diatom in terms of carbon due to its large cell size. This species represented more than 60% of the diatom biomass at nine of the 14 stations sampled, and was absent only at one station, which was the most offshore station sampled during the cruise. Although polyunsaturated aldehydes (PUAs) were not detected, other oxylipins which are hydroxy and keto derivatives of eicosapentaenoic and docosahexaenoic acids that affect copepod reproduction were found in these samples. Hence, we can attribute the negative impact of diatoms not only to PUAs, as previously believed, but also to these compounds. This is the first direct evidence of the presence of oxylipins other than PUAs in marine blooms dominated by diatoms.     

Carbon isotopic change at the base of the upper permian zechstein sequence

Fluctuation of the carbon isotope composition of marine carbonates has recently been developed as a powerful tool for the identification of ocean-wide anoxic conditions and changes in the world budget of carbon and oxygen. A change in δ¹³ from the normal marine values (0 to + 2%) to values highly enriched in ¹³C (+3·5 to 4·5%) is recorded at the base of the Zechstein sequence both in central Germany and northeastern England. The change occurred over a relatively short period of time indicating a rapid and pronounced change in the organic carbon/carbonate budget. Evidence from other Permian basins show similar highly enriched δ¹³C values. This change may correspond to that in carbon balance distinguished by the Garrels and Perry (1975) model and based on the change in sulphur isotopic composition during the Permian.     

Experimental impact cratering: A summary of the major results of the MEMIN research unit

This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two-stage light-gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane-driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high-temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters.     

Creating an isotopically similar Earth–Moon system with correct angular momentum from a giant impact

The giant impact hypothesis is the dominant theory explaining the formation of our Moon. However, the inability to produce an isotopically similar Earth–Moon system with correct angular momentum has cast a shadow on its validity. Computer-generated impacts have been successful in producing virtual systems that possess many of the observed physical properties. However, addressing the isotopic similarities between the Earth and Moon coupled with correct angular momentum has proven to be challenging. Equilibration and evection resonance have been proposed as means of reconciling the models. In the summer of 2013, the Royal Society called a meeting solely to discuss the formation of the Moon. In this meeting, evection resonance and equilibration were both questioned as viable means of removing the deficiencies from giant impact models. The main concerns were that models were multi-staged and too complex. We present here initial impact conditions that produce an isotopically similar Earth–Moon system with correct angular momentum. This is done in a single-staged simulation. The initial parameters are straightforward and the results evolve solely from the impact. This was accomplished by colliding two roughly half-Earth-sized impactors, rotating in approximately the same plane in a high-energy, off-centered impact, where both impactors spin into the collision.     

High‐pressure phase transitions of α‐quartz under nonhydrostatic dynamic conditions: A reconnaissance study at PETRA III

Hypervelocity collisions of solid bodies occur frequently in the solar system and affect rocks by shock waves and dynamic loading. A range of shock metamorphic effects and high‐pressure polymorphs in rock‐forming minerals are known from meteorites and terrestrial impact craters. Here, we investigate the formation of high‐pressure polymorphs of α‐quartz under dynamic and nonhydrostatic conditions and compare these disequilibrium states with those predicted by phase diagrams derived from static experiments under equilibrium conditions. We create highly dynamic conditions utilizing a mDAC and study the phase transformations in α‐quartz in situ by synchrotron powder X‐ray diffraction. Phase transitions of α‐quartz are studied at pressures up to 66.1 and different loading rates. At compression rates between 0.14 and 1.96 GPa s^?1, experiments reveal that α‐quartz is amorphized and partially converted to stishovite between 20.7 GPa and 28.0 GPa. Therefore, coesite is not formed as would be expected from equilibrium conditions. With the increasing compression rate, a slight increase in the transition pressure occurs. The experiments show that dynamic compression causes an instantaneous formation of structures consisting only of SiO₆ octahedra rather than the rearrangement of the SiO₄ tetrahedra to form a coesite. Although shock compression rates are orders of magnitude faster, a similar mechanism could operate in impact events.