GeoResJ最新文献

This work combines core-flood experiments with X-ray μ-computed tomography (μ-CT) to investigate the swelling of clay minerals and its impact on permeability of unconsolidated porous media. Both swelling (montmorillonite) and non-swelling (kaolinite) clay were added as coatings on soda lime beads and quartz grains. Clay content varied from 1.4 to 5.5 wt.% in the montmorillonite-coated samples and from 2.0 to 6.8 wt.% in the kaolinite-coated samples. Permeability changes were monitored as a function of time using pure water. Visualization of coated bead and grains columns by μ-CT provided quantitative information on morphological changes of clay grains/coatings among dry and water-saturated samples. All clay-coated samples showed a 10–40% decrease in permeability as compared to uncoated samples. In general, permeability decreases with increasing clay content. A 39% volume increase of montmorillonite particles was observed by μ-CT immediately after the sample was saturated with water, i.e. swelling occurred almost instantaneously after water–clay contact. In contrast, kaolinite particles had a 15% volume increase, which was primarily attributed to the hydration of clay pellets by water. The calculated porosity reduction associated with clay swelling ranged from 0.4% to 1.7% including both montmorillonite- and kaolinite-coated samples. This decrease in porosity was estimated to cause only a 2–5% reduction in permeability, primarily due to the high initial porosity and permeability of the selected samples. This study presents a baseline to estimate changes in permeability as a result of clay swelling for samples with variable clay content, grain size, and porosity.

The freezing temperatures of hundreds of water drops with radii 20–50 μm containing known average concentrations of suspended, mostly micron- to submicron-sized, volcanic ash particles composed of SiO₂-rich glass were recorded using optical microscopy. As expected, the ash suppresses supercooling, and in contrast to earlier studies of much larger ash particles, the median freezing temperature clearly scales with the available ash surface area per drop. The heterogeneous nucleation rate coefficient per unit mass of ash ($j_m$) increases exponentially with decreasing temperature (T) (increasing supercooling) with a possible change in the slope of a plot of $\log j_m$ against T at $T=245\pm 1\text{K}$. Although uncertainties in the ash surface area limit quantitative comparisons, we conclude that volcanic glass is a less effective ice-nucleating agent than feldspar crystals and more similar to other minerals previously studied.

This study presents bulk-rock major, trace, and platinum-group element data, as well as mineral chemistry for peridotites which form large enclaves (up to 500 × 1000 m) within Mesoarchaean orthogneisses of the Akia terrane in the Fiskefjord region, southern West Greenland. The largest peridotite body, known as Seqi, contains highly fosteritic olivine with a median Mg# of 92.6 and hosts extensive layers of chromitite, which can be traced for tens of metres with thicknesses of up to 30 cm. Thinner (<100 m thick), but extensive (up to 2000 m long) peridotite sheets are associated with coarse norite and orthopyroxenite with distinct cumulate textures in the Amikoq complex, located a few tens of kilometres south of Seqi. Intercalated amphibolites of tholeiitic basaltic composition show complementary geochemical evolution to the peridotites, consistent with igneous crystal fractionation trends. The U-shaped trace element patterns of the peridotites may either reflect the parental melt composition from which these olivine-rich rocks were derived, or alternatively this feature may be the result of melt-rock interaction. Overall, we interpret the Fiskefjord region peridotites to have formed as ultramafic cumulates derived from Archaean high-Mg, low Ca/Al magmas, although their geodynamic setting remains to be established.

The Curie depth is the depth at which the crust and uppermost mantle cease to be ferromagnetic or ferromagnetic, the main cause of crustal magnetism, due to the action of geothermal effects. One method to estimate the Curie depth for Australia is to map the base of magnetisation derived from observations of magnetic intensity. We have used a nonlinear direct sampling inverse technique to fully explore the parameter space of a fractal forward model of magnetisation. This produces an ensemble of models that allow us to produce maps of both the maximum depth of magnetisation and its uncertainty for Australia. The base of magnetisation varies significantly across the continent, between 10 and 70 km depth, with an uncertainty of 7–10 km. The variations in magnetisation depth conform with the boundaries of geological provinces due to their differing magnetic properties: In general, cratons and older provinces generally show a deeper base of magnetisation results and hence may be inferred to have deeper Curie depths, reflecting that these areas are on the whole cooler. We also find general agreement in our results with known geothermal anomalies.

Coccoliths contribute significantly to pelagic sediments formed over the last 200 million years, yet their geochemistry has been largely overlooked as a potential record of palaeoenvironmental information. Recently developed techniques have enabled successful extraction of coccolith-dominated sediment fractions. However, the reliability of palaeoenvironmental interpretations that can be drawn from coccolith analyses is still confounded by a poor understanding of the “vital effect” – the physiological component of the isotopic composition of biominerals. Here we demonstrate that oxygen isotope composition in core-top coccoliths is not only set by the temperature and isotopic composition of seawater, but appears to be controlled to first order by the environmental factors regulating algal growth rate. Partial registration of the isotopic signature of assimilated CO₂ (with a heavy isotopic composition relative to other dissolved inorganic carbon species) is confirmed to be the dominant mechanism behind the vital effect recorded in the Noelaerhabdaceae coccoliths. Our data point towards a strong role of growth irradiance on expression of the ¹⁸O and ¹³C vital effects, ranging from limited (near equilibrium composition) in low light regimes to 3‰ offset in oxygen isotopes at higher growth irradiances, such as those found under light-saturated conditions typically imposed in laboratory cultures. This highlights the importance of considering environmental controls when translating oxygen isotope composition of coccoliths into temperature estimates. Furthermore, our calibration suggests that the alkenone-based CO₂ palaeobarometer proxy may be refined by combining paired organic/calcite measurements during the Cenozoic.

Historical bedrock field observations have potential for significant value to the scientific community and the public if they can be rescued from physical records stored in archives of scientific research institutions. A set of historical records from ‘Operation Norman’, a bedrock mapping activity conducted in northwestern Canada by the Geological Survey of Canada (GSC) from 1968 to 1970, was identified as suitable for data rescue and incorporation into a GIS geodatabase. These observational data, including field stations, lithology descriptions, structural measurements, measured section locations, and fossil localities, were digitized as geospatial features with attributes assigned according to the observation records. Over 90% of the original observations were successfully rescued in this manner, allowing for effective incorporation with newer observations. Lack of reliable location information for field observations was the primary impediment to effective data rescue. Access to original participants in Operation Norman was particularly helpful in ensuring successful data rescue, as was the excellent state in which research materials had been curated. The resulting dataset of combined historical and recent observations provides improved distribution of observations to constrain geological analysis and map interpretation. Rescued data from Operation Norman have been incorporated in new bedrock map compilations and other scientific publications.

Geological models, as structural representations of the subsurface, are increasingly used for regional scale geological analyses and research studies. In this context, it is often essential to use geological legacy data, for example in the form of printed well logs, seismic sections, or maps and interpreted cross-sections from previous reports. A problem when using this type of data is that standard modeling methods and workflows are optimized towards applications in hydrocarbon and mineral exploration where data are usually newly acquired and of a high quality. Although recent developments address the modeling side for regional models with novel concepts and ideas, the possibility to change the workflow on a conceptual level has, to date, not been addressed.

We examine here how we can use legacy data more efficiently and sustainably, in a model construction workflow that leaves the typical sequential path of model development. In the common approach, a single best-fit model is continuously updated or refined when additional data become available. We test here the application of a parallel type of model construction where multiple models can be generated on the basis of different input data sets. Geological data and models are strictly separated, and this allows us to (a) use geological models to test quickly the spatial consistency of different geological data sets, and (b) to allow for an approach where we finally obtain multiple geological models as different hypotheses about the subsurface structural setting. Both aspects are especially important for the application of legacy data, as the data quality is always difficult to assess.

The concept is applied to a geological model project of the Perth Basin, Australia, where we show how it enables us to quickly revise and update the (previously constructed) model with additional data (e.g. newly available digitized legacy data), to evaluate the spatial consistency between different legacy data sets and interpretations, and to test different hypotheses. In our point of view, this is an important aspect towards a sustainable approach for geological modeling as it allows a very flexible and transparent use of different data sets for model construction – and therefore a more sustainable use of legacy data itself in the increasing use of subsurface representations using 3D geological models.

State geological surveys are home to legacy geological data that holds value in the present. Early legislation of geological surveys often included requirements that state surveys have a museum or cabinet to house their physical collections. These collections currently include data such as cores, cuttings, thin sections and fossils. State geological surveys maintain these collections to support scientific research that has value to those in government, industry, academia and the public. Survey collections and other similar science data collections, are in danger of being lost due to various risks such as poor curation, few access points, lack of funding, and space considerations. Efforts to preserve these collections have increased, beginning with a National Research Council report in 2002 highlighting this plight, and the founding of the National Geological and Geophysical Data Preservation Program by the United States Geological Survey (USGS) in 2005. Currently, programs like EarthCube address this problem by focusing on cyberinfrastructure needs that will ease discovery and access to specimen datasets. Even with these efforts, there is still much work to be done.

Increasing preservation and ease of access requires training in data curation and preservation as well as a better understanding of the users of geological data. This paper will introduce geological collections, provide examples of preservation challenges surrounding these types of collections, and suggest future research directions. This includes collaborations with library and information scientists, archivists, museums curators, as well as cross training of domain scientists. Future management systems for these collections should provide increased discovery and access to geological data.

Seismic shothole drillers’ logs, record the near-surface (avg. 18.6 m deep) lithostratigraphy encountered when drilling holes to place explosive charges. These records offer a largely unrecognized wealth of geoscience information in areas for which little may be otherwise known. Stored in the Basic Files archives of petroleum exploration and seismic acquisition companies, this study first convinced companies of the potential utility of this data, then recovered the hard copy and digitally scanned records (paper, fiche, microfilm) and rendered these into a digital database and GIS. The final database of 343,989 records provides the largest source of geoscience information of its kind in northwestern Canada, and in many cases contains unique and original records on a host of subjects including surficial-, bedrock-, and hydro-geology, permafrost, and geohazards. The drillers’ log records have further been used to create geospatial models of drift, till, muskeg, massive ice and ground ice thicknesses, and continue to be applied to new avenues of research such as temporal variations of bottomfast ice extents in offshore shallow marine environments. Published in freely downloadable Geological Survey of Canada Open File reports and providing commonly used database and GIS file formats, this data rescue exercise preserves and greatly enhances what was becoming an increasingly discarded corporate data set of unrecognized potential.