Middle Devonian palynomorphs and carbon isotope stratigraphy of borehole cores in the Dounreay area, Caithness

This preliminary report describes progress in the use of fossil palynomorph assemblages and δ13C org stratigraphy in correlating cores of Devonian strata from the Dounreay Site area. A total of 134 samples from Nirex BH 2, SHIP-2, SHIP-8, SHIP-9, SWB-6, SWB-8 and SWB-9. boreholes have been analysed for palynology, while a further 94 samples from Nirex BH 2 and SHIP-2 boreholes were analysed for bulk δ13C org. A list of samples and sampling intervals is given in Section 13. The objectives of the study were to: 1. determine the age of spore assemblages in the cores, using standard Devonian biozonation schemes; 2. test the presently accepted lithological and geophysical correlations between the boreholes, using standard palynostratigraphical methods; 3. characterise cycles 21 and 26 within the Nirex BH 2 and SHIP-2 boreholes using palynology and δ13C org; 4. correlate the most complete cored reference sequences in the Nirex BH 2 and SHIP-2 boreholes using characterised cycles, and thus test traditional correlation based on the lithological character of cycles and cycle position. Overall, the organic yield of the samples is high. The organic residue is dominated by yellow brown amorphous organic material (AOM), and palynomorphs (land plant spores, fungal spores and ?spores of unknown affinity) are usually rare. A small number of samples, notably within cycles 21 and 26 (Nirex BH 2 and SHIP-2) contain significant quantities of land-derived phytoclasts (resistant particles of plant material) and very poorly preserved spores of vascular plant origin. Spore colour indicates that thermal maturity is low (TAI value 2 to 2+) and comparable to that recorded in other studies from the Dounreay area (Stephenson 2003, Auton 2004). Spores-pergramme yields vary between 0 and approximately 1200. The detailed trends of palynofacies, palynology and yields-per-gramme of spores within the boreholes are shown in Figures 1-7. The scarcity of age-diagnostic palynomorphs makes age determination of these sequences difficult. However, most of the sections contain spores similar to Rhabdosporites langii and zonate spores similar to Grandispora velata, and none contain the distinctive spore Geminospora lemurata. This indicates a probable early Eifelian to earliest Givetian age for the sampled sections (Stephenson 2003, Richardson & McGregor 1986, Marshall 2000). Conventional palynostratigraphic correlation between the boreholes using the ranges of palynomorph taxa is difficult to apply because the assemblages are dominated by long ranging taxa, which are commonly poorly preserved. In addition, the sparse nature of assemblages prevents reliable correlation, because presence or absence of significant palynomorphs is probably as much a matter of chance as evolution and phylogeny. In order to improve the precision of correlation between the cores and to improve knowledge of Dounreay Middle Devonian palaeoecology and palaeoenvironment, a new correlation method has been employed. This involves determining the palynological, palynofacies and δ13C org characteristics of certain groups of strata in order to ‘fingerprint’ them. Using this approach it has been possible to fingerprint lacustrine cycles 21 and 26 in Nirex BH 2, and match these to fingerprints of corresponding cycles previously identified by lithological logging in SHIP-2 (Figures 9 and 10). Thus, the presently accepted correlations (JacobsGIBB 2002) based on down-hole geophysical logs (notably natural gamma) and lithological correlations based on ‘cycle-counting’ between Nirex BH 2 and SHIP-2 are now also supported by palynological, palynofacies and δ13C org evidence. This is crucial independent evidence required for the development of an accurate 3D model of the geology of the Dounreay site area and should provide firm constraints on the estimates of the cumulative throw of faults between the 2 borehole sites, c. 1 km apart. The presence of abundant AOM, which has been shown throughout the Orcadian Basin to be of lacustrine algal origin, indicates that the sediments in the Dounreay site area were deposited in a lake that was occupied by algae. The scarcity of terrestrially-sourced phytoclasts, as well as the low spores-per-gramme values throughout the sections, even in facies indicating a relatively proximal depositional position, could indicate a relatively sparse flora occupied the hinterland of the Dounreay during the mid-Devonian. This may have been due to aridity or to plant assemblages reflecting only early stages of colonisation. The low ratio of phytoclasts to spores, which is unlike that seen in younger sediments (for example of the Carboniferous or Permian), probably indicates the lack of supportive plant tissues in the hinterland plants, which were likely to have been small and herbaceous in character. This joint palynological, palynofacies and δ13C org analysis has the potential to provide a better broad correlation between the cored sequences than palynology alone can achieve and may allow better correlation between units mapped at the surface and those recognised in the cores. Consequently, the next phase of work, which mainly consists of collection and analysis of surface samples from across the area will use a similar methodology to that developed here. The aim of this new work will be to link the surface exposures in the Site Area to the cores, put the Dounreay sequence in its regional context, and also allow (in conjunction with petrological studies) correlation of the Baligill and Achanarras fish bed maker horizons across the district. An understanding will also be gained of how the Dounreay sequence differs from younger Orcadian successions farther east

Geochemistry, and carbon, oxygen and strontium isotope composition of brachiopods from the Khuff Formation of Oman and Saudi Arabia GeoArabia

Brachiopods are abundant in the Oman Khuff Formation and similar brachiopod faunas are present at a few horizons in the same formation in Central Saudi Arabia. Following extensive systematic and biostratigraphic studies of these faunas, specimens from the base of the Midhnab Member of the Khuff Formation of Saudi Arabia (Buraydah Quadrangle), and from Member 3 of the Khuff Formation of the Huqf outcrop of Oman were assessed for isotope geochemistry (Sr, O and C). Dating using 87Sr/86Sr alone is not conclusive. Five pristine Oman brachiopods from biostratigraphically well-constrained lower Wordian horizons record a range of 87Sr/86Sr values that form a separate cluster offset from the current Sr isotope seawater curve, which defines the Early Permian and earliest Mid-Permian. The 87Sr/86Sr of the pristine Saudi Arabian brachiopod sits in an area which corresponds to a wide scatter of 87Sr/86Sr in the seawater curve data. However, the Saudi Arabian data does indicate that the Midhnab Member is likely younger than Member 3 of the Khuff Formation of the Huqf outcrop. The well-preserved brachiopod carbonate allows deductions to be made about the palaeotemperature of the Oman Khuff Formation Member 3 seawater using its oxygen isotope composition (\u3b418O). Assuming \u3b418O of seawater < \u20130.5\u2030, then palaeotemperature derived from brachiopods in the Oman horizons would be +25\ub0C, +22\ub0C and +17\ub0C respectively. This is consistent with the trend of shallowing within Member 3, suggested by facie

Role of Subsurface Geo-Energy Pilot and Demonstration Sites in Delivering Net Zero

Recent research suggests that the effects of climate change are already tangible, making the requirement for net zero more pressing than ever. New emissions targets have been announced in April 2021 by various governments, including by the United Kingdom, United States, and China, prior to the Conference of the Parties (COP26) in Glasgow. Part of the solution for net zero will be geo-energy technologies in the subsurface, these include: mine water geothermal, aquifer thermal energy storage (ATES), enhanced geothermal systems and other thermal storage options, compressed air energy storage (CAES), and carbon dioxide capture and storage (CCS) including bioenergy CCS (BECCS). Subsurface net zero technologies have been studied by geologists at laboratory scale and with models, but also require testing at greater-than laboratory scale and in representative conditions not reproducible in laboratories and models. Test, pilot and demonstration facilities aid rock characterisation process understanding and up-scaling, and thereby provide a bridge between laboratory testing and computer modelling and full-scale operation. Examples of test sites that have progressed technology development include the Otway International Test Centre (Australia, CCS) and the Äspö Hard Rock Laboratory (Sweden, geological radioactive waste disposal). These sites have provided scale up for key research questions allowing science issues of relevance to regulation, licencing and permitting to be examined at scale in controlled environments. Successful operations at such sites allow research to be seen at first hand to inform the public, regulators, supply chain companies and investors that such technologies can work safely and economically. A Geological Society conference on the “Role of subsurface research labs in delivering net zero” in February 2021 considered the value of test sites and gaps in their capability. Gaps were identified in two areas: 1) test facilities to aid the design of low cost, high resolution, unobtrusive seismic and other monitoring for a seismically noisy urban environment with a sensitive human population, for example for ATES in urban areas; and 2) a dedicated through-fault zone test site to understand fault transmissivity and reactivation. Conference participants also recommended investment and development in test sites, shared facilities and risk, joint strategies, data interoperability and international collaboration

Seasonality fluctuations recorded in fossil bivalves during the early Pleistocene: implications for climate change

Understanding the transformations of the climate system may help to predict and reduce the effects of global climate change. The geological record provides a unique archive that documents the long-term fluctuations of environmental variables, such as seasonal change. Here, we investigate how seasonal variation in seawater temperatures varied in the Mediterranean Sea during the early Pleistocene, approaching the Early-Middle Pleistocene Transition (EMPT) and the beginning of precession-driven Quaternary-style glacial–interglacial cycles. We performed whole-shell and sclerochemical stable isotope analyses (δ18O, δ13C) on bivalves, collected from the lower Pleistocene Arda River marine succession (northern Italy), after checking shell preservation. Our results indicate that seawater temperature seasonality was the main variable of climate change in the Mediterranean area during the early Pleistocene, with the Northern Hemisphere Glaciation (NHG) exerting a control on the Mediterranean climate. We show that strong seasonality (14.4–16.0 °C range) and low winter paleotemperatures (0.8–1.6 °C) were likely the triggers leading to the establishment of widespread populations of so called “northern guests” (i.e., cold water taxa) in the Mediterranean Sea around 1.80 Ma. The shells postdating the arrival of the “northern guests” record a return to lower seasonal variations and higher seawater paleotemperatures, with seasonality increasing again approaching the EMPT; the latter, however, is not associated with a corresponding cooling of mean seawater paleotemperatures, showing that the observed seasonality variation represents a clear signal of progressive climate change in the Mediterranean Sea

Distribution and density of the partition function zeros for the diamond-decorated Ising model

Exact renormalization map of temperature between two successive decorated lattices is given, and the distribution of the partition function zeros in the complex temperature plane is obtained for any decoration-level. The rule governing the variation of the distribution pattern as the decoration-level changes is given. The densities of the zeros for the first two decoration-levels are calculated explicitly, and the qualitative features about the densities of higher decoration-levels are given by conjecture. The Julia set associated with the renormalization map is contained in the distribution of the zeros in the limit of infinite decoration level, and the formation of the Julia set in the course of increasing the decoration-level is given in terms of the variations of the zero density.Comment: 8 pages,8figure

Analysing the Coupled Effects of Compressive and Diffusion Induced Stresses on the Nucleation and Propagation of Circular Coating Blisters in the Presence of Micro-cracks

This paper presents the delamination of coating with micro-cracks under compressive residual stress coupled with diffusion induced stress. Micro-cracks in coating provide a passage for corrosive species towards the coating-substrate interface which in turn produces diffusion induced stress in the coating. Micro-cracks contract gradually with increasing compressive residual stress in coating due to thermal expansion mismatch which blocks the species diffusion towards the interface. This behaviour reduces the diffusion induced stress in the coating while the compressive residual stress increases. With further increase in compressive residual stress, micro-cracks reach to the point, where they cannot be constricted any further and a high compressive residual stress causes the coating to buckle away from the substrate resulting in delamination and therefore initiating blistering. Blistering causes the contracted micro-cracks to wide open again which increases diffusion induced stress along with high compressive residual stress. The high resultant stress in coating causes the blister to propagate in an axis-symmetric circular pattern. A two-part theoretical approach has been utilised coupling the thermodynamic concepts with the mechanics concepts. The thermodynamic concepts involve the corrosive species transportation through micro-cracks under increasing compression, eventually causing blistering, while the fracture mechanics concepts are used to treat the blister growth as circular defect propagation. The influences of moduli ratio, thickness ratio, thermal mismatch ratio, poisson’s ratio and interface roughness on blister growth are discussed. Experiment is reported for blistering to allow visualisation of interface and to permit coupled (diffusion and residual) stresses in the coating over a full range of interest. The predictions from model show excellent, quantitative agreement with the experimental results

The randomised uterine septum transsection trial (TRUST): Design and protocol

Background: A septate uterus is a uterine anomaly that may affect reproductive outcome, and is associated with an increased risk for miscarriage, subfertility and preterm birth. Resection of the septum is subject of debate. There is no convincing evidence concerning its effectiveness and safety. This study aims to assess whether hysteroscopic septum resection improves reproductive outcome in women with a septate uterus. Methods/design: A multi-centre randomised contr

Gaia Early Data Release 3: The celestial reference frame (Gaia-CRF3)

Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13-21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 μas yr-1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution