bluuebunny/crossref_metadata_2025 huggingface dataset:
Displacement transfer between thick- and thin-skinned décollement systems in the central North American Cordillera
Authors: McClelland W. C. , Oldow J. S.
Published: April 2008

Late Cretaceous-Early Tertiary contractional deformation along the Cordilleran margin of North America is represented by two distinct styles of foreland deformation, thin-skinned and thick-skinned, that primarily differ in depth to their respective basal décollements. Given the coeval nature of contraction in regions experiencing different styles of deformation, displacement on deep-level detachments associated with thick-skinned basement-cored uplifts in the southern Rocky Mountains was kinematically linked with displacement along shallow-level detachments in the southern Canadian Rockies. In the central North American Cordillera, the transition in foreland décollement depth was accommodated by a NW-trending oblique ramp system. The oblique ramp extended from the basement-cored uplifts of Wyoming along the northern margin of the Idaho batholith to the Shuswap crustal duplex in southeastern British Columbia. While accommodating transfer between differing structural levels, the Late Cretaceous to Paleocene displacement on the oblique ramp produced uplift and exhumation of high-grade metamorphic and plutonic rocks of the Idaho batholith between the NW-striking Lewis and Clark line and the Orofino shear zone. This resulted in truncation of the transpressional western Idaho shear zone, and may have localized the site of Eocene extension in this portion of the Cordillera.
Isothermal decompression, partial melting and exhumation of deep continental crust
Authors: Whitney Donna L. , Teyssier Christian , Fayon Annia K.
Published: April 2008

Decompression of deep, hot continental crust is the primary mechanism of crustal melting, with major consequences for the geodynamics of orogens. Decompression within thickened continental crust may be initiated by processes driven from above (erosion, tectonic denudation) and/or below (crust/lithosphere thinning, buoyant rise of deep crust). On a larger scale, decompression of subducted continental crust may add material, including melt, to the overlying, non-subducting plate. This mechanism has the potential to produce large amounts of melt because fertile material is continually conveyed into the mantle, where it eventually buoyantly ascends and melts. Decompression-driven melting of continental crust may account for the high melt fractions (≥20 vol.%) and great thickness (20–30 km) inferred for the partially molten layer in orogenic crust. When high melt volumes are present in the crust and/or the thickness of the partially molten layer is large, the subsequent thermo-mechanical evolution of orogens is strongly influenced by lateral (channel) and vertical (buoyant) crustal flow. For both lateral and vertical flow, the presence of melt decouples deep crust from upper crust, and continental crust from mantle lithosphere.

A major consequence of vertical crustal flow is the generation of migmatite-cored gneiss domes that riddle most orogens. High-grade rocks in many domes record pressure-temperature-time (
P-T-t
) paths indicating near-isothermal decompression followed by cooling from
T
> 700 °C to
T
< 350 °C in <2–5 Ma. Diapiric ascent of partially molten crust accounts for the decompression rate and magnitude required to maintain a near-isothermal path. We propose that gneiss domes are a signature of decompression and crustal melting, and are therefore fundamental structures for understanding the thermo-mechanical evolution of continental crust during orogeny.
Recent and sub-recent microborings from the upwelling area off Mauritania (West Africa) and their implications for palaeoecology
Authors: Glaub Ingrid
Published: April 2008

Late Quaternary dead molluscan shells off Mauritania (West Africa) from the intertidal zone to 220–300 m water depth were studied for microborings. The study gives preliminary data on microborings in upwelling areas and their implications for the fossil record. In total 18 ichnotaxa are described. They are considered to be produced by cyanobacteria, green algae, red algae, fungi and foraminifera. The ichnotaxonomic composition shows minor differences relative to tropical/subtropical areas of investigation. No ichnotaxa are believed to be specific to upwelling areas. Bathymetrical distribution patterns revealed different depth ranges for individual ichnotaxa. Relative to areas with similar latitude but not influenced by upwelling, the absolute depth of the photic zone is shallower. The majority of ichnotaxa observed are already known from the fossil record (tropical and subtropical study areas) and should also be expected from ancient upwelling areas.
A new approach to the analysis and interpretation of tracks: examples from the dinosauria
Authors: Manning Phillip L.
Published: April 2008

Tracks can potentially offer unique sources of information, providing insight into the environments, gait and posture, locomotion and behaviour. Track preservation can yield important information on substrate consistency and enable the recognition of transmitted subsurface tracks. The ability to recognize transmitted tracks has broad implications for the understanding of palaeoenvironments and interpretation of ichnological assemblages. In order to gain an understanding of how tracks are formed in three dimensions, and of their variability of expression in different substrates, controlled laboratory simulations were undertaken. Experiments were designed to recover subsurface track layers, yielding for the first time detailed information on subsurface morphology that could be related to ‘true’ surface track features. It was found that subsurface track relief can be correlated with the magnitude and distribution (across a foot) of load acting on the surface sediment. This pressure is transmitted through the sediment, and deforms successive layers at depth, producing an undertrack. The most significant factor controlling track morphology, whether surface or subsurface, was found to be the moisture/density relationship within the substrate at the time of track formation. Variability in the dimensions of simulated tracks, relative to the ‘true’ surface track, indicates that caution should be exercised when using fossil tracks to calculate hip height, speed, age, and population dynamics. In addition, comparison of experimental tracks with dinosaur tracks from the Yorkshire coast suggests that many morphological differences between vertebrate ichnotaxa reflect sediment rheology and taphonomy rather than taxonomy of the track-maker.
Phanerozoic history of deep-sea trace fossils
Authors: Uchman Alfred
Published: April 2008

The Phanerozoic diversity of deep-sea trace fossils, based on 151 flysch formations, displays distinct, non-linear changes through the Phanerozoic, with peaks in the Ordovician-Early Silurian and Early Carboniferous, lowered in the Permian-older Late Jurassic, a peak in the Tithonian-Aptian, lowered in the Albian, and the maximum in the Eocene. The contribution of graphoglyptids in trace fossil assemblages rises gradually up to the end of the Cretaceous, shows a peak in the Palaeocene-Eocene but a depression in the Oligocene. All the changes were probably influenced by competition for food and food supply, bottom water temperatures and oxygenation, and frequency of flysch habitats. There is no clear influence of major biotic crises (Ordovician/Silurian, Cretaceous/Tertiary, Palaeocene/Eocene) on the diversity of deep trace fossils, except the Eocene/Oligocene crisis.
Ichnology of Carboniferous tide-influenced environments and tidal flat variability in the North American Midcontinent
Authors: Mángano M. Gabriela , Buatois Luis A.
Published: April 2008

Trace fossils are sensitive indicators of environmental fluctuations and, accordingly, ichnological studies have the potential to improve facies characterization of marginal-marine systems. Carboniferous intertidal deposits in eastern Kansas and western Missouri accumulated under contrasting palaeoenvironmental conditions, ranging from the open shoreline to fluvio-estuarine transitions. Comparative analysis of these exposures illustrates lateral variations in trace-fossil content and allows characterization of the intertidal ichnofaunas developed in three sub-environments: open marine, restricted bays and fluvio-estuarine transitions. Openmarine tidal flat ichnofaunas are characterized by (1) high ichnodiversity, (2) marine ichnotaxa produced by both euryhaline and stenohaline forms, (3) the presence of both infaunal and epifaunal traces, (4) the presence of simple and complex structures produced by presumed trophic generalists and specialists respectively, (5) dominance of horizontal trace fossils of the Cruziana ichnofacies, (6) presence of multispecific associations, (7) high density, and (8) wide size range. This ichnofauna is present in heterolithic deposits and reflects the activity of a biota that inhabited tidal flats dominated by normal-marine salinities and connected directly to the open sea. Restricted-bay ichnofaunas display (1) low ichnodiversity, (2) ichnotaxa commonly found in marine environments, but produced by euryhaline organisms, (3) dominance of infaunal traces rather than epifaunal trails, (4) simple structures produced by opportunistic trophic generalists, (5) a combination of vertical and horizontal trace fossils from the Skolithos and Cruziana ichnofacies, (6) the presence of monospecific associations, (7) variable density, and (8) small size. This assemblage occurs in heterolithic facies and records the activity of a brackish-water benthic fauna inhabiting intertidal areas of estuarine basins and embayments. Fluvio-estuarine ichnofaunas are characterized by (1) moderate to relatively high diversity, (2) forms typically present in continental environments, (3) the dominance of surface trails and absence of burrows, (4) temporary structures produced by a mobile deposit-feeding fauna, (5) a mixture of trace fossils belonging to the Scoyenia and Mermia ichnofacies, (6) moderate density of individual ichnotaxa, (7) absence of monospecific suites, and (8) small size. This assemblage occurs in tidal rhythmites and records the activity of a typical freshwater/terrestrial benthos inhabiting tidal flats that were developed in the most proximal zone of the inner estuary under freshwater conditions. Through integration of ichnological and sedimentological data, conventional sedimentological interpretations of marginal-marine depositional systems can be refined and enhanced.
Palaeoecology of the Bright Angel Shale in the eastern Grand Canyon, Arizona, USA, incorporating sedimentological, ichnological and palynological data
Authors: Baldwin Christopher T. , Strother P. K. , Beck J. H. , Rose Eben
Published: April 2008

The Middle Cambrian Bright Angel Shale in the eastern Grand Canyon contains a depauperate normal marine fauna, but trace fossils and palynomorphs are abundant throughout the formation. Conventional interpretations place the depositional setting of this shale below wavebase as the distal component of a shelfal transgression, but the palynological signature in the mudstones of the Bright Angel Shale indicates a freshwater source to these muds. Examination of several sections in the vicinity of Proterozoic monadnocks and the integration of sedimentological, ichnological and palynological observations yield a more robust model for the palaeoecology of the Bright Angel Shale. Initial correspondence between organic matter content in mudstones and feeding type and intensity (as indicated by traces) is consistent with an estuarine setting for this deposit. The level of organic activity preserved in these sediments indicates that the carbon flux into shallow marine settings due to terrestrial runoff was substantial by middle Cambrian (
Glossopleura
biozone) time.
An approach to the description and interpretation of ichnofabrics in palaeosols
Authors: Genise Jorge F. , Bellosi E. S. , Gonzalez M. G.
Published: April 2008

Studies on ichnofabrics have focused mainly on marine environments. Attempts to apply the ichnofabric methodology and theoretical framework to continental deposits bearing palaeosols are few and poorly developed. Methodologies analysed in this contribution include the applicability of current ichnofabric indexes and diagrams, the assessment of the destruction of the original bedding by ichnofabrics and by other soil characters separately, and the relationships between different stages of palaeosol and ichnofabric development. Many soil features may be formed without the intervention of bioturbation, or may be the result of interactions of physical, chemical and biological processes, in which traces of organisms may have only a subsidiary role. Ichnofabrics can be well developed in palaeosols devoid of other soil characters and, conversely, palaeosols showing a well-developed soil structure can bear almost no trace fossils. This fact adds a third component to classical methods that normally consider only original bedding and ichnofabrics. Theoretical analysis includes the possibility of recording composite ichnofabrics in palaeosols, and the value of individual ichnotaxa as possible indicators of subaerial conditions and environmental changes. The ecological preferences and requirements of trace-makers provide the key to understanding composite ichnofabrics; however, only complex traces can be certainly attributed to particular modern taxa. Insect nests, pupal chambers and earthworm burrows are the most reliable indicators of subaerial exposure and, in many cases, very particular environmental conditions.
Development of early Palaeozoic ichnofabrics: evidence from shallow marine siliciclastics
Authors: Droser Mary L. , Jensen Søren , Gehlîng James G.
Published: April 2008

Earliest Cambrian fine-grained sediments appear to have been firm close to the sediment-water interface. As a result there was a high preservational potential of shallow tiers. There is limited evidence for a mixed layer at this time; rather, most of the preserved trace fossils were open burrows. Later in the Cambrian, depth of sediment mixing increased but firmground conditions are still found relatively close to the sediment-water interface. The development of the mixed layer and properties of Cambrian muddy sediments have numerous stratigraphic and ichnological consequences. These include secular trends in the preservation of event beds and shallow-tier trace fossils including
Rusophycus
and
Cruziana
.
Trace fossils in the aftermath of mass extinction events
Authors: Twitchett Richard J. , Barras Colin G.
Published: April 2008

Ichnology has great potential to advance our understanding of mass extinction events and yet is currently an underutilized resource in such studies. Here we review published ichnological studies for the Ordovician-Silurian, Permian-Triassic and Cretaceous-Tertiary extinction-recovery intervals. In addition, new information regarding the Triassic-Jurassic ichnological record from England, Austria and the western USA is presented. Trace fossils provide important information on the ecological response of the benthic community at such times. In the immediate post-extinction aftermath, the ichnodiversity, burrow size, depth of bioturbation, and ichnofabric index of the sediments are all much reduced. There is an increase in all these parameters through the post-extinction recovery period. In some cases, the stepwise reappearance of certain distinctive ichnotaxa (e.g.
Diplocraterion, Rhizocorallium
and
Thalassinoides
) may be of some stratigraphic use. Evidence from Permian-Triassic studies indicates that recovery took longer at low (tropical) palaeolatitudes than mid-high palaeolatitudes. Trace fossils also provide important information on palaeoenvironmental change through the extinction-recovery interval. The application of ichnology to mass extinction studies is in its infancy, but should prove a valuable tool in future research.
A stratigraphy of marine bioerosion
Authors: Bromley Richard G.
Published: April 2008

About 65 ichnogenera and a number of bioerosional trace fossils that are unnamed are catalogued with respect to their stratigraphic ranges. In most cases, corresponding stratigraphic studies of the trace-makers are not possible because (1) the rank of taxonomic ascription is too high to be meaningful and (2) not all members of a high taxon are bioeroders. For example, radulation traces of chitons are known from Jurassic to Recent, whereas chitons have a body fossil record back to the Early Palaeozoic. Similarly, whereas the round drill-hole
Oichnus paraboloides
is known from Cambrian to Recent, the only identified makers of this trace fossil, naticid gastropods, range from Cretaceous to Recent. The stratigraphic ranges of bioerosion ichnotaxa emphasize the two marine revolutions of the Phanerozoic: there is marked increase in diversification during the Ordovician-Devonian interval and since the Triassic.
Lower Cretaceous planktonic foraminiferal and nannofossil biostratigraphy of Ontong Java Plateau sites from DSDP Leg 30 and ODP Leg 192
Authors: Sikora P. J. , Bergen J. A.
Published: April 2008

The Lower Cretaceous sediments of the Ontong Java Plateau of the SW Pacific Ocean provide a depositional history for the period immediately following the termination of one of the largest extrusive igneous events of the Phanerozoic eon. A more complete stratigraphic record is formulated of this critical event in Earth’s history than previously available by integration of previous data and new analyses from DSDP Leg 30 sites combined with shipboard and post-cruise analyses from ODP Leg 192. The oldest sediment occurs within the upper part of the
Leupoldina cabri
planktonic foraminiferal zone, indicating equivalence with the last half of Oceanic Anoxic Event (OAE) 1a of which the Ontong Java eruption is a postulated cause. The remainder of the Aptian section is marked by major disconformities, with little section in common between central and marginal plateau sites. The Aptian-Albian boundary is conformable at both Leg 192 Sites 1183 and 1186 based on integration of biostratigraphy and preliminary δ
13
C data. However, the overall Albian interval is very incomplete, with regional distribution noted for only the lowermost and upper Albian sections.
Low-temperature alteration of submarine basalts from the Ontong Java Plateau
Authors: Banerjee Neil R. , Honnorez José , Muehlenbachs Karlis
Published: April 2008

We present a detailed mineralogical and petrological description of the low-temperature alteration patterns in basalts from four new sites drilled during ODP Leg 192 on the Early Cretaceous Ontong Java Plateau. Three main alteration types have been identified: pervasively altered dark grey basalt; black or dusky green halos; and brown halos. Dark grey basalts are the most common and represent the least intensive, but most pervasive, alteration phase. Early interaction of the basalts with low-temperature sea-water-derived hydrothermal fluids lead to the development of black and dusky green halos characterized by the replacement of groundmass and olivine phenocrysts by celadonitic phyllosilicates and smectite. Later interaction of basalts with cold oxidizing sea water produced brown halos characterized by replacement of primary phases and mesostasis by smectite and iron oxyhydroxides. Secondary minerals in order of decreasing abundance include phyllosilicates, calcite, iron oxyhydroxides, pyrite, chalcedony, quartz and zeolites. Veins, resulting from symmetrical infilling of open cracks, commonly contain phyllosilicates, iron oxyhydroxide or pyrite, and late calcite. Carbonate veins cross-cut all other alteration features and stable isotope analyses of vein carbonates indicate formation from marine bicarbonate below about 40°C. A positive correlation between vein density and overall degree of alteration is observed resulting in pervasive development of brown alteration halos in highly fractured rocks. Overall, alteration of basalts from the Ontong Java Plateau is similar to that observed from other DSDP/ODP sites throughout the oceans.
Opening histories of fractures in sandstone
Authors: Laubach S. E. , Lander R. H. , Bonnell L. M. , Olson J. E. , Reed R. M.
Published: April 2008

High-resolution scanning electron microscope (SEM)-based cathodoluminescence images were used to reconstruct incremental fracture opening in regional opening-mode fractures in sandstone. Opening is recorded by crack-seal texture in isolated mineral bridges that span opening-mode fractures
formed
in sandstone at moderate-great depth (
c.
1000–6000 m). We restored opening histories of nine representative fractures with apertures of millimetres in five sandstones from five sedimentary basins. Gaps created by fracture widening in 11 bridges range from less than 1 μm to more than 1 mm, but nearly all are less than 20 μm and most are less than 5 μm. These are the opening amounts that could be spanned by cement growth in these diagenetic environments. Our observations are the first evidence of opening amounts from mostly porous, opening-mode (joint-like) fractures formed in diagenetic environments. Patterns are consistent with a new structural diagenetic model of bridge growth that can use opening patterns to indicate rate of fracture opening as a function of time.
The feedback between joint-zone development and downward erosion of regularly spaced canyons in the Navajo Sandstone, Zion National Park, Utah
Authors: Rogers Christie M. , Engelder Terry
Published: April 2008

Large NNW-trending slot canyons cut into, but generally not entirely through, the approximately 600 m-thick Jurassic Navajo Sandstone at Zion National Park (ZNP). These canyons sit immediately above, and parallel to, joint zones and exhibit a regular spacing (
c.
450 m). The joint zones, in particular, consist of vertical and steeply dipping joints that tend to dip towards the axis of the canyon. These regularly spaced, joint-localized canyons are confined to the Navajo, suggesting a stress-shadow origin for their configuration; however, this explanation does not predict closely spaced joints in joint zones at each canyon. To explain the development of the joint zones, we treat the canyons themselves as cracks. Early, widely-spaced, NNW-trending joints propagated into the top of the Navajo, and later preferential erosion along these joints initiated the pattern of canyons with a cross-sectional profile consistent with blunt edge cracks spaced at about 450 m. Analogous to edge cracks, the canyons subsequently concentrated tensile stress at their tips while subjected to regional extension. Concentration of canyon-tip tensile stress was sufficient to drive steeply dipping secondary joints, reflecting principal stress rotation in a process zone ahead of the canyon tip. Joint density in each joint zone increases as a consequence of a gravity-induced shear traction that drives vertical wing cracks from the tips of steeply dipping secondary joints. Exfoliation jointing along canyon walls also contributes to the widening of canyons. The perferential erosion of slot canyons follows the joint zones, and thus, a feedback loop is set up between the growth of secondary jointing in the canyon-tip stress concentration and the downward erosion of the canyon.
Fracture-pattern variations around a major fold and their implications regarding fracture prediction using limited data: an example from the Bristol Channel Basin
Authors: Belayneh Mandefro , Cosgrove John W.
Published: April 2008

This chapter focuses on the evolution of fractures during the inversion of the Bristol Channel Basin, and examines the lateral and vertical consistency of the resulting fracture network within the alternating Liassic limestones and shales. The study has two principal aims. The first is to determine the reliability of fracture systems deduced using more limited data from less well-exposed regions or unexposed regions sampled only by drilling, and the second is to assess whether the fractures are linked to a regional stress field or are the result of a local stress field controlled by the geometry and mechanism of formation of a fold.

The joint patterns were studied using a combination of scanline and window sampling, and the results indicate that there are considerable variations in the fracture systems between adjacent limestone beds and also lateral variation within the same bed. Although there is little doubt that the independent development of fracture patterns in adjacent limestone beds is facilitated by the intervening shale horizons, which allow them to become mechanically decoupled, the reasons for these variations are still unclear.
Arrest and aperture variation of hydrofractures in layered reservoirs
Authors: Brenner Sonja L. , Gudmundsson Agust
Published: April 2008

Hydrofractures are extension fractures generated by internal fluid overpressure (net or driving pressure): they include dykes, veins and many joints. The growth of a hydrofracture depends primarily on the mechanical properties of the host rock and the overpressure of the hydrofracture. Field observations show that in heterogeneous and anisotropic rocks, many hydrofractures change their apertures on passing through layers with different mechanical properties. Alternatively, hydrofractures may become arrested at contacts (and other discontinuities) between layers. We present boundary-element models on hydrofracture arrest and aperture variation that focus on the effects of abrupt changes in Young’s modulus in layered reservoirs. The results show that, for internal fluid pressure as the only loading, high tensile stresses concentrate in the stiff layers. When approaching a stiff layer, the hydrofracture tip becomes sharp and narrow, and would normally continue its propagation through that layer. By contrast, soft layers suppress the tensile stresses associated with the hydrofracture tip and blunt the tip itself. Without a nearby weak, subvertical discontinuity that could open up, the hydrofracture tends to become arrested on meeting with a soft layer. When fluid over-pressure is the only loading, the aperture of a hydrofracture is normally larger in soft layers than that in stiff layers, which may lead to flow channelling in a layered reservoir.
Probabilistic-mechanistic simulation of bed-normal joint patterns
Authors: Hoffmann Wendy , Dunne William M. , Mauldon Matthew
Published: April 2008

Mechanistic and probabilistic methods are individually used to characterize and predict joint networks. Combining these two approaches yields a method where the mechanical controls are honoured and implemented probabilistically in order to efficiently model joint development at the scale of the entire network with a useful ease of implementation. For this approach, bed-normal joints are characterized not with fracture trace geometries, but rather with intersection geometries to bedding. T-intersections represent joint termination at bedding, X-intersections represent joints crossing bedding and E-intersections are those intersections at the sample window edge. Using the intersection counts as input, a new computer program was developed that uses mechanically constrained probabilities to simulate and predict the spatial distribution of bed-normal joints in profiles across bedding. Initially, simulations are compared to ideal joint geometries for one or two lithologies with one or two bed thickness values, and found to match well. Simulations are then compared to joint geometries in four natural profiles from Llantwit Major, Wales, UK and Huntingdon, PA, USA. Simulations visually resemble the natural profiles and reasonably match the natural values of the joint network for density and mean joint height. We also extend the methodology to predicting joint networks beyond sample windows by investigating the minimum count of intersections needed to produce a representative result. Based on the five natural profiles with typical joint geometries, a sample size about 50–100 intersection counts is sufficient to produce a reasonable prediction of the expected count and, hence, the joint geometry in a rock volume.
Forensic geology: yesterday, today and tomorrow
Authors: Murray Raymond C.
Published: April 2008

Sir Arthur Conan Doyle and Hans Gross suggested the possibility of using soil and related material as physical evidence. Edmond Locard provided the intellectual basis for the use of the evidence. High-visibility cases, such as the work of the Federal Bureau of Investigation (FBI) in the Camarena case, the laboratory of the Garda Siochana in the Lord Mountbatten case and G. Lombardi in the Aldo Moro case, contributed to the general recognition that geological evidence could make an important contribution to justice. The value of geological evidence results from the almost unlimited number of rock, mineral, soil and related kinds of material combined with our ability to use instruments that characterize these materials. Forensic examinations involve identification of earth materials, comparison of samples to determine common source, studies that aid an investigation and intelligence studies. The future will see increased use of the evidence, new automated methods of examination, improved training of those who collect samples, and research on the diversity of soils and how, when and what parts of soils are transferred during various types of contact. The microscope will remain important because it allows the examiner to find the rare and unusual particle.
Geophysics and burials: field experience and software development
Authors: Watters M. , Hunter J. R.
Published: April 2008

In the UK, geophysical survey methods have been increasingly applied in the search for clandestine burials and in the elimination of land from murder enquiries as part of a broader spectrum of systematic search techniques. This paper considers recent forensic search work and stresses the general resources and intelligence needed for a successful search, and the role played by geophysics. The main emphasis, however, is to discuss the applicability of ground-penetrating radar (GPR) in grave detection and to review recent developments in software, particularly the importance of high-resolution mapping. The paper also discusses the use of image analysis of both planes through blocks of buried landscape, together with predictive modelling and the value of 3-D analysis for data manipulation.
Rapid quantitative mineral and phase analysis using automated scanning electron microscopy (QemSCAN); potential applications in forensic geoscience
Authors: Pirrie Duncan , Butcher Alan R. , Power Matthew R. , Gottlieb Paul , Miller Gavin L.
Published: April 2008

QemSCAN is a scanning electron microscope (SEM) system, initially designed to support the mining industry by providing rapid automated quantitative mineral analyses. The system is based upon Carl Zeiss SEMs fitted with up to four light-element energy dispersive X-ray spectrometers. Representative subsamples are mounted into either resin or wax blocks and polished prior to analysis, or can be mounted onto carbon tape. During analysis, X-ray spectra are collected at a user-defined pixel spacing and are acquired very rapidly (
c.
10 ms per pixel). The measured spectra are automatically compared against a database of known spectra and a mineral or phase name is assigned to each measurement point by the QemSCAN computer software programs. In this way the near-surface qualitative elemental composition of each particle is systematically mapped, assigned to a mineral name or chemical compound/species, and digital pixel maps of each particle are created. Depending upon a range of parameters, including the particle size and the user-defined pixel spacing (which can vary between 0.20 μm and 25 μm), approximately 1000 particles, each 1–10 μm in size, can be measured per hour using a 1 μm pixel spacing. In addition to providing a qualitative elemental analysis and mineralogical or phase assignment for each particle, data relating to particle size, shape and calculated specific density are also generated. In this study, the potential application of this automated SEM system in forensic geoscience was evaluated by the analysis of: (1) a series of soil samples, and (2) a series of dust samples from an industrial complex. In both case studies, the mine-ralogy/phase composition of each sample analysed was found to be distinctive. In addition, textural data for the soil samples and particle shape data for the dust samples show that they can be clearly distinguished. Automated SEM using QemSCAN has clear potential application in the analysis of soil or other trace evidence in forensic case work.
Bayesian sediment fingerprinting provides a robust tool for environmental forensic geoscience applications
Authors: Small Ingrid F. , Rowan John S. , Franks Stewart W. , Wyatt Adam , Duck Robert W.
Published: April 2008

Sediment fingerprinting is an approach for the quantitative determination of sediment provenance (both spatial sources and types of sediment supply) over a range of temporal and spatial scales. Though widely adopted, studies often vary in their attention to the underlying assumptions and in their treatment of modelling uncertainty. A Bayesian approach to the multivariate problem of ‘unmixing’ sediment sources is reported, showing the significance of source group variability and source group sampling density to the accuracy of model output. The model produces results as median source group contributory coefficients (and associated 95% quantiles). The model was applied to environmental data obtained from selected soil erosion studies reported within the peer-reviewed literature. Good correspondence (r
2
=0.89) between reported mean source group contributory coefficients and median values were found when recalculated using the Bayesian analysis. However, confidence levels are highly variable, ranging from 2% to 97%. The robustness of any unmixing solution depends on factors such as the number of samples, the number of source groups and the variance of source group properties. It is concluded that ‘forensic-style’ investigations must recognize these uncertainties and be appropriately resourced to achieve tolerable accuracy and precision. The discussion considers additional confounding factors such as non-conservative tracer behaviour and enrichment/depletion during the sediment delivery process.
Stable carbon and nitrogen isotope variations in soils: forensic applications
Authors: Croft Debra J. , Pye Kenneth
Published: April 2008

A study has been undertaken to assess the significance of carbon and nitrogen content and stable isotopic variation in soils in relation to their practical use as a tool in forensic soil investigations. It forms part of a wider study to assess a range of techniques in a forensic context. Carbon and nitrogen abundance and δ
13
C and δ
15
N values have been determined in soil samples from six locations, using continuous flow-isotopic ratio mass spectrometry, to quantify: (1) stability over short time periods up to 2 years, (2) variation over short-scale distances, and (3) variability during primary transfer and mixing. Over a 2-year time period, variation was found to be largest in the elemental abundance, with the isotopic ratios being more stable. Used in combination, stable isotope analysis can be diagnostic and useful for discriminating between sites. No statistically significant differences at the 95% confidence level (using analysis of variance, ANOVA) were found for one-stage primary transfer in three of the four soils tested; the fourth sediment from an estuarine environment did show statistically significant difference at the 95% confidence level.
The right way and the wrong way of presenting statistical and geological evidence in a court of law (a little knowledge is a dangerous thing!)
Authors: Isphording Wayne C.
Published: April 2008

On 21 March 1981 a young black male was abducted in Mobile, Alabama, and taken to a site across Mobile Bay where he was beaten and murdered. The act was in apparent revenge for the mis-trial of a black man accused of killing a white police officer from Birmingham, Alabama. Three members of the notorious Ku Klux Klan were apprehended and charged with murder. All were found guilty and the ringleader was executed in 1997; the others are now serving life sentences.

Ironically, the perpetrators were successful in having evidence tying them to the crime scene completely discredited. Statistical evidence purporting to show similarities in soil chemistry from samples taken from the victim, the defendants, and the crime scene was totally invalidated because improper statistical analyses were used. Following completion of the trial, the defence’s expert witness was contacted by the district attorney and asked to describe the appropriate statistical tests that should have been offered and that would have supported his case. He was further able to take solace by learning that strong mineralogical evidence could also have been used. It simply had not been reviewed by anyone who possessed the proper expertise.
Using geological information to identify apparent ‘misrepresentation’ of facts in a litigious situation
Authors: Isphording Wayne C.
Published: April 2008

On 7 November 1980, a motorcyclist entered a curve in a fog-shrouded, marshy area. The cyclist subsequently stated that his helmet visor suddenly ‘fogged up’, and that he was unable to raise the visor. The motorcycle slid out of control, throwing the rider into the path of an oncoming car; the impact led to the surgical removal of his left leg. The victim sued the local motorcycle dealer and the motorcycle visor manufacturer, alleging that he had not been advised that the visor could not be raised.

A number of lines of evidence argued against the plaintiff’s version of the events. Index of refraction, X-ray diffraction and fluorescence analyses clearly showed that the visor on the plaintiff’s helmet was not of the same material as visors sold by the defendants. Furthermore, although the plaintiff claimed he had purchased the visor the night before the accident, the visor had a curvature that could have been acquired only from being attached to the helmet for a number of weeks. Scanning electron microscopy (SEM) disclosed scratches that were found to contain orthoclase feldspar. The accident site, however, was on the Plio-Pleistocene Citronelle Formation, which is completely devoid of feldspar. Each of these points was used to show that the visor had not been purchased the night before the accident. The outcome of the trial, however, showed that nothing is certain in a court of law.
The nature of, and approaches to, teaching forensic geoscience on forensic science and earth science courses
Authors: Lee C. W.
Published: April 2008

Whereas geoscience depends in part on the classical nomological method of the environmental sciences, it is also distinguished by a discrete set of logical procedures that lend themselves to forensic analysis. It has been argued that, as geology is a derivative science, it only partially lives up to the classical model of scientific reasoning. It does, however, provide a model of scientific reasoning based on interpretive techniques and its historical nature. Reasoning in geoscience offers a method that is applicable to the uncertainties and complexities of real-life situations because we are seldom in possession of all the data that we would like in order to make an unbiased or objective decision. The ‘geological’ method, in which we fill the gaps in our knowledge with interpretation and reasonable assumptions, is exemplified by the pragmatism of geological and geomorphological analysis and is herein considered analogous to that undertaken by forensic practitioners. A problem-based learning situation based on a past geological/forensic case study is included to illustrate the approach advocated.
A review of natural CO
2
accumulations in Europe as analogues for geological sequestration
Authors: Pearce J. , Czernichowski-Lauriol I. , Lombardi S. , Brune S. , Nador A. , Baker J. , Pauwels H. , Hatziyannis G. , Beaubien S. , Faber E.
Published: April 2008

Natural geological accumulations of carbon dioxide occur widely throughout Europe, often close to population centres. Some of these CO
2
deposits leak, whereas others are sealed. Understanding these deposits is critical for selecting and designing underground storage sites for anthropogenic CO
2
. To provide confidence that the potential risks of geological CO
2
storage are understood, geologists are required to predict how CO
2
may behave once stored underground. Natural CO
2
accumulations provide a unique opportunity to study long-term geochemical and geomechanical processes that may occur following geological storage of anthropogenic CO
2
. In addition, natural CO
2
springs and gas vents can provide information on the mechanisms of gas migration and the potential effects of CO
2
leakage to the surface. This paper provides a description of some natural, European CO
2
occurrences.

CO
2
accumulations occur in many basins across Europe. In addition, volcanic areas and seismically active areas allow CO
2
-rich fluids to migrate to the near surface. Many of these occur in areas that have been populated for hundreds and thousands of years.

Stratigraphic traps have allowed CO
2
to accumulate below evaporite, limestone and mudstone caprocks. Comparisons between reservoir sandstone and equivalent nearby sandstones that contain no CO
2
indicate that reservoir sandstones may experience increased secondary porosity development through feldspar dissolution. Where fracture reactivation allows CO
2
-rich fluids to migrate, limited self-sealing may take place through calcite precipitation. Gas migration experiments indicate that, due to geochemical interactions, fine-grained seals would be able to trap smaller volumes of CO
2
compared to, for example CH
4
. In natural systems most leakage from depth occurs along fractures and is typically extremely localized on a metre-scale.
The role of hydrogeological and geochemical trapping in sedimentary basins for secure geological storage of carbon dioxide
Authors: Gunter William D. , Bachu Stefan , Benson Sally
Published: April 2008

Sedimentary basins throughout the world are thick piles of lithified sediments that, in many cases, are the hosts for fossil fuel resources. They may become even more important in the future if they are used for the storage of anthropogenic carbon dioxide. The efficiency of CO
2
geological storage is determined by the structure of the sedimentary basins, which have an intricate plumbing system defined by the location of high and low permeability strata that control the flow of fluids throughout the basin and define ‘hydrogeological’ traps. The most secure type of hydrogeological trapping is found in ‘stratigraphic’ and ‘structural’ traps in oil and gas reservoirs that have held oil and gas for millions of years. Another form of hydrogeological trapping is ‘hydrodynamic’ trapping which has been recognized in saline aquifers of sedimentary basins that have extremely slow flow rates. A volume of carbon dioxide injected into a deep hydrodynamic trap may take millions of years to travel by buoyancy forces updip to reach the surface before it leaks back into the atmosphere. Moreover, as the carbon dioxide migrates towards the surface, it dissolves in the surrounding brine (‘solubility’ trapping) and may react geochemically with rock minerals to become permanently trapped in the sedimentary basin by ‘ionic’ or ‘mineral’ trapping. The efficiency of the CO
2
geological storage in sedimentary basins depends on many factors, among the most important being CO
2
buoyancy, formation water density, lithological heterogeneity and mineralogy. A risk analysis must be completed for each site chosen for the geological storage of CO
2
to evaluate the trapping security.
Seismic monitoring at the Sleipner underground CO
2
storage site (North Sea)
Authors: Arts Rob , Eiken Ola , Chadwick Andy , Zweigel Peter , van der Meer Bert , Kirby Gary
Published: April 2008

The growing emissions of greenhouse gases, especially CO
2
, are seen worldwide as one of the major causes of climate change. International treaties like the Kyoto Protocol are supposed to contribute to reducing the emission of greenhouse gases. Underground sequestration has the potential to play an important role in keeping large volumes of CO
2
from escaping into the atmosphere in the short term. The first case of industrial scale CO
2
storage in the world (close to one million tonnes per year since 1996) is taking place at the Sleipner underground CO
2
storage site in the North Sea offshore Norway. Careful monitoring of the behaviour of the storage facility is required to establish its safety. To this end, two time-lapse seismic surveys have been acquired; the first repeat survey was completed in October 1999 and the second in October 2001. The presence of CO
2
beneath thin intra-shale layers within the reservoir has caused significant changes both in reflection amplitudes (up to a factor 10) and in travel time (more than 40ms) through the CO
2
plume (the velocity push-down effect). Some aspects of the interpretation of these time-lapse seismic surveys will be presented here.
The Neogene to Recent Rallier-du-Baty nested ring complex, Kerguelen Archipelago (TAAF, Indian Ocean): stratigraphy revisited, implications for cauldron subsidence mechanisms
Authors: Bonin B. , Ethien R. , Gerbe M. C. , Cottin J. Y. , Féraud G. , Gagnevin D. , Giret A. , Michon G. , Moine B.
Published: April 2008

The Kerguelen Archipelago is made up of a stack of thick piles of Tertiary flood basalts intruded by transitional to alkaline igneous centres at various times since 30 Ma ago. In the SW, the Rallier-du-Baty Peninsula is mostly occupied by two silicic ring complexes, each with an average diameter of 15 km, comprising dissected calderas cross-cut by subvolcanic cupolas. Previous radiometric determinations yield ages ranging from 15.4 to 7.4 Ma in the southern centre, and 6.2 to 4.9 Ma in the northern one. The felsic ring dykes were injected by coeval mafic magmas, forming, successively, swarms of early mafic enclaves, disrupted synplutonic cone sheets, and late cone-sheets. After the emplacement and subsequent unroofing of the plutonic ring complexes, abundant and thick trachytic pyroclastic flows and falls were emitted from the younger caldera volcanoes, while hawaiite and mugearite lava flows were erupted from marginal maars and cones. Huge trachyte ignimbritic flows filled the glacial valleys in the central Peninsula, and capped lacustrine deposits and older lava flows, while related pumice falls are widespread throughout the archipelago. This powerful plinian eruption took place after the network of glacial valleys was established, but before the Little Ice Age that occurred during the last centuries. In the south of the peninsula, even younger trachytic formations are exposed, and fumarolic vents are still active.

The growth mechanisms of a caldera-related ring complex can be explained as a repetitive sequence of two eruptive episodes. The first episode of hydrofracturing, induced by volatile exsolution within the evolving magma chamber, creates a vertical circular fracture zone, along which highly vesiculated magmas are emitted during explosive eruptive events occurring at the surface in a caldera volcano. It is followed by a second episode of cauldron-subsidence of a crustal block down to the degassed magma chamber, induced by pressure release. Downward movement of the crustal block favours the emplacement at shallow depths within the older caldera-filling formations, of discrete magmatic sheets characterized by a 16-km mean diameter and a 1-km mean thickness, corresponding to an average unit volume of 200 km
3
. Actually, the estimated volumes of the different igneous episodes within the Rallier-du-Baty nested ring complex vary from 60 to 900 km
3
, and correspond to the production during 15 Ma of about 2800 ± 850 km
3
of new materials and a net crustal growth of about 100 ± 30 × 10
3
m
3
per year.