bluuebunny/crossref_metadata_2025_split huggingface dataset:
An approach to the description and interpretation of ichnofabrics in palaeosols
Authors: Genise Jorge F. , Bellosi E. S. , Gonzalez M. G. 
Published: April 2008

Abstract
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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract
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

Abstract

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

Abstract

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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract

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

Abstract

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

Abstract

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.