Sedimentary record of Early Permian deglaciation in southern Gondwana from the Falkland Islands

The deglaciation of southern Gondwana during the Early Permian was preceded by waxing and waning of the south polar ice sheet. The fluctuations in ice extent are recorded in the sedimentary record by strata separating thick deposits of glacial diamictite from post-glacial mudrock. These deposits span across all of the major Gondwana fragments, now recognized as South Africa, South America, India, Antarctica and Australia, and also occur on the Falklands and Ellsworth Mountains microplates created during break-up of the supercontinent in the Mesozoic. We present sedimentary evidence for the progression of deglaciation from the Falkland Islands microplate using a series of borehole core runs acquired during onshore mineral exploration. Glacial advance and retreat phases are inferred from the Hells Kitchen Member of the Port Sussex Formation; the rock succession that conformably overlies the main body of glacial diamictite known locally as the Fitzroy Tillite Formation. The pulsated nature of the transition to fully post-glacial conditions was accompanied by an intricate interplay of sedimentary processes, including soft sediment deformation, meltwater pulses and turbidity currents. The Falkland Islands core data lend insight into the evolving Early Permian environment and offer an unusually complete view of continental margin deglaciation preserved in the ancient sedimentary record. Supplementary material: Borehole core photographs from the Fitzroy Tillite Formation, Hells Kitchen Member and Black Rock Member for cores DD029 and DD090 are available at https://doi.org/10.6084/m9.figshare.c.4031119.v

The Marine Isotope Stage 19 in the mid-latitude North Atlantic Ocean: astronomical signature and intra-interglacial variability

n/

Eccentricity signal in the nannofossil time-series across the Mid-Pleistocene Transition in the northwestern Pacific Ocean (ODP Site 1209)

The Mid-Pleistocene Transition (MPT; 1.25–0.6 million years ago, Ma) is one of the most important and still debated climate reorganizations during which the glacial/interglacial cycles switched from a 41-thousand years (kyr) cycle (i.e. obliquity) to a quasi-periodic 100-kyr cycle (associated with orbital eccentricity). Variations in the orbital geometry can affect the abundance and distribution of certain marine biota such as the coccolithophores, a group of unicellular calcifying phytoplankton, whose skeletal remains – called nannofossils – represent a valid tool within the geological archives to infer change in surface water conditions and/or coccolithophore productivity and how orbital variations may have impacted them. Here, we apply for the first time various time series analytical techniques to the nannofossil dataset from mid-latitudinal Ocean Drilling Program (ODP) Site 1209 in the northwest Pacific Ocean for the interval spanning the last 1.6 Myr. To better interpret the orbital signal recorded by different nannofossil species we used time series analyses (i.e. wavelet, autocorrelation and cross correlation) to identify the main periodicities by single nannofossil species during the MPT, and to investigate further their response timings to those orbital drivers. In addition, we investigated how the recorded periodicities can improve understanding of the paleoecological preferences of particular species. The combination of multiple time series analyses allowed identification of the 100-kyr periodicity as the main cyclicity recorded in most analyzed species at Site 1209, documenting the predominance of the eccentricity-related signal at mid-latitudes and a reduced or absent influence of the obliquity response. Thus, our data highlight how orbital influence varies by latitude impacting the nannofossil species. The lag between eccentricity and species abundance fluctuations was also investigated, identifying a fast response ranging between 20 and 40 kyr for the taxa Calcidiscus leptoporus subspecies leptoporus, Gephyrocapsa caribbeanica small, and Reticulofenestra spp. (>5 μm). This study corroborates the potential of nannofossils to deepen understanding of the dynamics and effects of variations in orbital geometry through time. It also underlines the need to extend the study of the responses of specific species through the use of different time series analysis techniques in order to return complementary information and detect clearer orbital signals

“Natural” stress patterns and dependencies between edge alignment and quantity sensitivity

We conducted an artificial language learning experiment to study learning asymmetries that might reveal latent preferences relating to, and any dependencies between, the edge alignment and quantity sensitivity (QS) parameters in stress patterning. We used a poverty of the stimulus approach to teach American English speakers an unbounded QS stress rule (stress a single CV: syllable) and either a left- or right-aligning QI rule if only light syllables were present. Forms with two CV: syllables were withheld in the learning phase and added in the test phase, forcing participants to choose between left- and right-aligning options for the QS rule. Participants learned the left- and right-edge QI rules equally well, and also the basic QS rule. Response patterns for words with two CV: syllables suggest biases favoring a left-aligning QS rule with a left-edge QI default. Our results also suggest that a left-aligning QS pattern with a rightedge QI default was least favored. We argue that stress patterns shown to be preferred based on evidence from ease-of-learning and participants’ untrained generalizations can be considered more natural than less favored opposing patterns. We suggest that cognitive biases revealed by artificial stress learning studies may have contributed to shaping stress typology.publishedVersio

Thermal equation of state of cubic boron nitride: Implications for a high-temperature pressure scale

The equation of state of cubic boron nitride (cBN) has been determined to a maximum temperature of 3300 K at a simultaneous static pressure of up to more than 70 GPa. Ab initio calculations to 80 GPa and 2000 K have also been performed. Our experimental data can be reconciled with theoretical results and with the known thermal expansion at 1 bar if we assume a small increase in pressure during heating relative to that measured at ambient temperature. The present data combined with the Raman measurements we presented earlier form the basis of a high-temperature pressure scale that is good to at least 3300 K

Observation of off-Hugoniot shocked states with ultrafast time resolution

We apply ultrafast single shot interferometry to determine the pressure and density of argon shocked from up to 7.8 GPa static initial pressure in a diamond anvil cell. This method enables the observation of thermodynamic states distinct from those observed in either single shock or isothermal compression experiments, and the observation of ultrafast dynamics in shocked materials. We also present a straightforward method for interpreting ultrafast shock wave data which determines the index of refraction at the shock front, and the particle and shock velocities for shock waves in transparent materials. Based on these methods, we observe shocked thermodynamic states between the room temperature isotherm of argon and the shock adiabat of cryogenic argon at final shock pressures up to 28 GPa

Ultrafast high strain rate acoustic wave measurements at high static pressure in a diamond anvil cell

We have used sub-picosecond laser pulses to launch ultra-high strain rate ({approx} 10{sup 9} s{sup -1}) nonlinear acoustic waves into a 4:1 methanol-ethanol pressure medium which has been precompressed in a standard diamond anvil cell. Using ultrafast interferometry, we have characterized acoustic wave propagation into the pressure medium at static compression up to 24 GPa. We find that the velocity is dependent on the incident laser fluence, demonstrating a nonlinear acoustic response which may result in shock wave behavior. We compare our results with low strain, low strain-rate acoustic data. This technique provides controlled access to regions of thermodynamic phase space that are otherwise difficult to obtain

Thermodynamic ground states of platinum metal nitrides

We have systematically studied the thermodynamic stabilities of various phases of the nitrides of the platinum metal elements using density functional theory. We show that for the nitrides of Rh, Pd, Ir and Pt two new crystal structures, in which the metal ions occupy simple tetragonal lattice sites, have lower formation enthalpies at ambient conditions than any previously proposed structures. The region of stability can extend up to 17 GPa for PtN{sub 2}. Furthermore, we show that according to calculations using the local density approximation, these new compounds are also thermodynamically stable at ambient pressure and thus may be the ground state phases for these materials. We further discuss the fact that the local density and generalized gradient approximations predict different values of the absolute formation enthalpies as well different relative stabilities between simple tetragonal and the pyrite or marcasite structures