bluuebunny/crossref_metadata_2025_split huggingface dataset:
Animal-substrate interactions in freshwater environments: applications of ichnology in facies and sequence stratigraphic analysis of fluvio-lacustrine successions
Authors: Buatois Luis A. , Mángano M. Gabriela 
Published: April 2008

Abstract
At present, three continental archetypal ichnofacies are widely accepted: the Scoyenia, Mermia and Coprinisphaera ichnofacies. The last is present in palaeosols, and the first two occur in fluvio-lacustrine environments. Additionally, the Skolithos ichnofacies may be present in relatively high-energy fluvio-lacustrine deposits. The ichnofauna from active fluvial channels is characterised by low-diversity assemblages of simple vertical burrows and escape traces, referred to the Skolithos ichnofacies. Abandoned or inactive channel deposits characteristically contain low-diversity assemblages dominated by meniscate traces. Floodplain water bodies that experienced progressive drying (desiccated overbank deposits) may contain abundant arthropod and vertebrate trackways, backfilled meniscate traces, ornamented burrows and bilobate traces with scratch marks, which allow recognition of the Scoyenia ichnofacies. Floodplain water bodies that are filled by overbank vertical accretion without experiencing desiccation (overfilled overbank deposits) include simple grazing trails, locomotion trails and horizontal dwelling burrows, representing impoverished occurrences of the Mermia ichnofacies. Hydrologically closed lakes are very stressful environments in which subaqueous ichnofaunas are rare. The richest ichnofaunas in closed lakes are present at the lake margins, and record the activity of terrestrial rather than aquatic faunas (Scoyenia ichnofacies). Hydrologically open lakes host relatively diverse and abundant ichnofaunas, comprising the Scoyenia ichnofacies in low-energy, lake-margin areas, and the Mermia ichnofacies in permanent subaqueous lacustrine zones. Sediments deposited in relatively high-energy lacustrine environments, such as wave-dominated shorelines and delta mouth-bars, commonly are represented by the Skolithos ichnofacies. Although continental trace fossils have not been extensively used in sequence stratigraphy, they have potential for future integrated study. Softground trace fossils are commonly well developed in overfilled lake basins and are useful to delineate parasequences and parasequence sets. In balanced-fill and underfilled lake basins, softground ichnofaunas are poorly developed because of stressful conditions. In contrast, firmground suites are rare in overfilled lake basins, but widespread in lowstand deposits of balanced-fill and underfilled lake basins. Early lowstand amalgamated incised fluvial channels are usually unbioturbated, but palaeosol ichnofaunas (e.g. the Coprinisphaera ichnofacies) may delineate sequence boundaries in interfluve areas. Increasingly isolated fluvial channels encased in overbank deposits develop during late lowstand, and lacustrine deposits accumulate during transgressions, favouring preservation of biogenic structures.
Trace fossil distribution in lacustrine deltas: examples from the Triassic rift lakes of the Ischigualasto-Villa Unión basin, Argentina
Authors: Melchor Richardo N. 
Published: April 2008

Abstract

This paper reports six trace fossil assemblages from lacustrine deltas of the Triassic Ischigualasto-Villa Unión rift basin, northwest Argentina. They were recognized in three correlated stratigraphic sections separated by about 100 km, and come from river- and wave-influenced deltas developed in low- and high-accommodation lacustrine basins. Trace fossil assemblages correspond to delta front (six), delta plain (two) and marginal lacustrine (one) facies associations. Each trace fossil assemblage is described, together with a detailed lithofacies characterization of the trace fossil-bearing interval. They are analysed in conjunction with previously described ichnological assemblages from partially correlative sections of the same basin. Delta front facies contains a high-diversity assemblage (22 ichnotaxa), including
Cochlichnus
(a ubiquitous form),
Gordia, Helminthoidichnites, Helminthopsis, Didymaulichnus, Diplichnites, Stiaria, Cruziana, Bifurculapes, Protichnites, Diplopodichnus, Archaeonassa, Palaeophycus, Treptichnus, Rusophycus, Avolatichnium
, ‘rhomboidal traces’, ‘fusiform structures’ and ‘millimetre burrows’. Trace fossil assemblages from delta plain facies are much less diverse (seven ichnotaxa), but display representatives of a greater variety of ethological categories, including
Rhynchosauroides, Skolithos, Palaeophycus
, ‘horseshoeshaped structures’, escape trace and drab-haloed root traces. Marginal lacustrine deposits of a river-dominated delta yielded a monospecific assemblage consisting of
Cochlichnus anguineus
. Comparison of trace fossil assemblages in wave- and river-dominated lacustrine deltas from the basin (mainly those of the delta front facies) revealed important differences in ichnodiversity that can be useful in the discrimination between these lacustrine delta types. Lacustrine delta deposits contain trace fossils that can be ascribed to three different ichnofacies: a high-diversity occurrence of the Mermia ichnofacies in subaqueous delta front sediments, a low-diversity occurrence of Mermia ichnofacies in subaqueous marginal lacustrine facies, the Skolithos ichnofacies in high-energy upper delta front/lower delta plain facies, and the Scoyenia ichnofacies in intermittently exposed upper delta plain facies. The analysed trace fossil assemblages from delta front and marginal lacustrine settings suggest environmental gradients within the Mermia ichnofacies.
Modelled palaeolatitudes for the Louisville hot spot and the Ontong Java Plateau
Authors: Antretter Maria , Riisager Peter , Hall Stuart , Zhao Xixi , Steinberger Bernhard 
Published: April 2008

Abstract

Formation of the Ontong Java Plateau (OJP), a large igneous province in the western Pacific, has been attributed to a rising plume head in the initial stage of the Louisville hot spot, approximately 120–125 Ma ago. However, the Neal
et al.
plate reconstruction suggests that the plateau formed approximately 9° north of the current location of this hot spot at 51°S. The magnetization of the plateau’s basement records a palaeolatitude of approximately 25°S which further increases the discrepancy with the plume-head model. Modelling the motion of the Louisville hot spot for the last 120 Ma yields a possible southward motion of up to about 6°. True polar wander (TPW) models also shift the predicted palaeolatitudes of the plateau farther north. Taking into account both hot-spot motion and TPW, formation of the OJP by the Louisville not spot remains a possibility.
Early Cretaceous Pacific palaeomagnetic pole from Ontong Java Plateau basement rocks
Authors: Riisager Peter , Hall Stuart , Antretter Maria , Zhao Xixi 
Published: April 2008

Abstract

We present new palaeomagnetic data from Ocean Drilling Program Site 1184 on the eastern salient of the Ontong Java Plateau (OJP) where 337.7 m of Early Cretaceous (
c.
120 Ma) volcaniclastic rocks were drilled. Alternating field and thermal demagnetizations were equally effective in removing secondary components, allowing the characteristic remanent magnetization directions from a total of 173 samples (out of 183) to be defined. All samples have negative inclinations (normal polarity), and by treating each sample as an independent reading of the palaeomagnetic field a site-mean inclination of −53.9° (
N
= 173; α
95
= 1.0°,
k
= 109) was obtained. The corresponding palaeo-colatitude is in excellent accordance with previously published time-averaged palaeo-colatitudes from contemporaneous basalts drilled at OJP and the Nauru Basin. Based on the intersection of the seven palaeo-colatitudes a new Early Cretaceous (
c.
120 Ma) Pacific palaeomagnetic pole was obtained with co-ordinates 63.0°N, 10.1°E (95% confidence ellipse with a minor semi-axis of 2.9° with an azimuth of 32° and a major semi-axis of 47.7° with an azimuth of 122°). This pole is far more easterly than previously published Early Cretaceous Pacific palaeomagnetic poles. Based on published Pacific palaeogeographic reconstructions in the fixed hot-spot reference frame we were able to calculate different Pacific true polar wander (TPW) poles. All Pacific TPW poles are found to be statistically different from contemporaneous TPW poles obtained in the Indo-Atlantic realm, illustrating motion between the two groups of hot spots.
Rock magnetic results from Ocean Drilling Program Leg 192: implications for Ontong Java Plateau emplacement and tectonics of the Pacific
Authors: Zhao Xixi , Antretter Maria , Riisager Peter , Hall Stuart 
Published: April 2008

Abstract
A rock magnetic study has been performed on rock samples recovered at Ocean Drilling Program Leg 192 sites on the Ontong Java Plateau in the western Pacific. Igneous rocks from the five Leg 192 sites displayed variable rock magnetic properties. The differences in the rock magnetic properties are a function of mineralogy and alteration. Titanomagnetite and titanomaghemite are present in the Ontong Java rocks. Samples with titanomagnetite exhibit Verwey transitions in the vicinity of 120K. Low-temperature curves for samples with multiple magnetic phases do not clearly show the Verwey transition. The inversion of titanomaghemite to a strongly magnetized magnetite is shown by the irreversible thermomagnetic-cooling curve. Despite the geographically widespread locations of the drill sites, variations in rock magnetic properties closely resemble each other, consistent with the fundamental results of the leg that the basement rocks were derived from homogeneous Kwaimbaita-type magma with a single age of approximately 120 Ma. The rock magnetic investigation provides constraints to evaluate the fidelity of the natural magnetic memory in the basalt rocks and corroborates the palaeomagnetic palaeolatitudes determinations for the Ontong Java Plateau. The generally good quality of rock magnetic data exhibited by Leg 192 rocks supports the inference that the characteristic directions of magnetization isolated from the Cretaceous Ontong Java Plateau sites were acquired near the onset of the Cretaceous Long Normal Superchron about 120 Ma. The portion of the Pacific plate containing the Leg 192 sites was in the southern hemisphere during the mid-Cretaceous volcanism.
Experimental petrology of basement lavas from Ocean Drilling Program Leg 192: implications for differentiation processes in Ontong Java Plateau magmas
Authors: Sano Takashi , Yamashita Shigeru 
Published: April 2008

Abstract

Melting relations of the basement lavas drilled from the Ontong Java Plateau during ODP Leg 192 were experimentally determined at 1150–1250°C and 0.1–190 MPa under the oxygen fugacity along the fayalite-magnetite-quartz (FMQ) and cobalt-cobalt oxide (CCO) buffers. The basement lavas were classified into two types according to phenocryst assemblage and whole-rock composition: one type is low in MgO (<8 wt%) and olivine + plagioclase + augite-phyric (Kwaimbaita type); and the other is rich in MgO (>8 wt%) and olivine-phyric (Kroenke type). One sample was chosen from each type as a starting material of the melting experiments. The experimental results demonstrate that the variations in phenocryst assemblage and whole-rock composition in the basement lavas can be modelled adequately by fractional crystallization processes in a shallow magma chamber (<6 km in depth). The experimentally determined mineral-melt equilibria, in combination with detailed petrographical investigation, revealed that the vast majority of phenocrysts are in equilibrium with their host magma composition, but some are not. The latter include unusually An-rich parts of plagioclase phenocrysts in the Kwaimbaita-type lavas. These An-rich parts probably crystallized in a mushy boundary layer along the wall of the magma chamber where the melt was relatively rich in H
2
O. Some olivine phenocrysts in the Kroenke-type lavas show reverse zoning, with core compositions that can be in equilibrium with the Kwaimbaita-type magmas. The cores of these olivine phenocrysts were most probably assimilated from a solidified pile of the Kwaimbaita-type lavas when the Kroenke-type magmas ascended through it.
Geochemistry of Cretaceous volcaniclastic sediments in the Nauru and East Mariana basins provides insights into the mantle sources of giant oceanic plateaus
Authors: Castillo Paterno R. 
Published: April 2008

Abstract
Cretaceous volcaniclastic sediments sampled at the Nauru and East Mariana basins were chemically and isotopically analysed in order to learn more about the formation and mantle source of the Ontong Java Plateau, an oceanic large igneous province. Despite their variably altered state, the volcanogenic sedimentary components still contain petrogenetic tracers (e.g. high field strength elements, and Nd- and Pb-isotopes) that can be used to constrain the composition of their respective mantle sources. The Nauru volcaniclastics have incompatible trace-element and Nd- and Pb-isotope compositions typical of the Kwaimbaita-type tholeiitic lavas of the Ontong Java Plateau. Combined with the results of recent investigations, the presence of Kwaimbaita-type volcaniclastics in the Nauru Basin reinforces the proposal that the Kwaimbaita-type lavas comprise the bulk of the giant plateau. On the other hand, the East Mariana volcaniclastics have high incompatible trace-element concentrations and Nd- and Pb-isotope ratios typical of alkalic ocean island basalts. Their source is either the Limalok Guyot in the Ratak seamount chain of the Marshall-Gilbert Islands or the ancestral Manihiki-Hikurangi Plateau. Other geological data argue for the Manihiki-Hikurangi Plateau as the source. This implies that the mid-Cretaceous Pacific upper mantle was dominated by the sources of lavas that formed giant oceanic plateaus.
Growth of ductile opening-mode fractures in geomaterials
Authors: Eichhubl Peter 
Published: April 2008

Abstract
Opening-mode fractures in clinker and opal-CT chert spheroids form by growth and coalescence of pores, and are associated with extensive textural and compositional changes in the host material. Extensive inelastic deformation outside the immediate vicinity of fracture tips characterizes these fracture processes as ductile. Fracture formation in clinker is concurrent with high-temperature combustion alteration of diatomaceous mudstone. Fracture formation in chert spheroids is associated with the opal-CT to quartz transition in the same host material during early marine diagenesis. In both cases, growth of elongate pores is attributed to the combined effects of diffusive-fracture growth and flow by solution-precipitation creep. Pore growth and coalescence occur preferentially ahead of fracture tips along two directions oblique to the mean macroscopic fracture direction. This growth process, referred to as side-lobe damage, is interpreted to reflect the shear-stress dependence of pore growth by solution-precipitation creep. The tendency for oblique fracture growth is suppressed by global stress and strain-boundary conditions forcing the fracture along a characteristic zig-zag propagation path that is macroscopically perpendicular to the loading direction. These examples of ductile fracture demonstrate that macroscopic fracture formation is not uniquely associated with damage processes by microfracture at low-temperature ‘brittle’ subsurface conditions. Instead, fracture is a deformation process that can occur due to various inelastic-deformation mechanisms under diverse crustal environments, which include high-temperature conditions.
The index of hackle raggedness on joint fringes
Authors: Bahat Dov , Bankwitz Peter , Bankwitz Elfriede 
Published: April 2008

Abstract
In a previous laborious study we showed that considerably more new area is formed in hackle sections than in en echelon section per given nominal area of fringe. In the present study we resort to an alternative quantitative method that would enable a relatively rapid correlation between the fracture mode of secondary fractures on joint fringes and their change in fracture morphology. We introduce a set of seven criteria that enable a geologist to place every fringe on the ‘index of hackle raggedness’ (IHR) along a scale between 1 and 10. This method is applied to the ‘Mrákotin joint set’ from a granite quarry in the Bohemian Massif of the Czech Republic. The results show an IHR range between 1.4 ± 0.7 and 6.8 ± 0.7. The gap between the top value of the scale, 10, and the value 6.8 probably suggests that the joints in this study did not form under the most dynamic conditions. Experimental results carried out on polymers show that dynamic fracture is better correlated with the dynamic stress intensity and additional fracture mechanics parameters than with fracture velocity. The demonstration that en echelon segmentation may be obtained at maximum fracture velocity, if mechanical constraints are imposed on the system by crystal anisotropy, possibly suggests that similar results may be obtained under other constraints that need to be elucidated.
Preferential jointing of Upper Devonian black shale, Appalachian Plateau, USA: evidence supporting hydrocarbon generation as a joint-driving mechanism
Authors: Lash Gary , Loewy Staci , Engelder Terry 
Published: April 2008

Abstract

The Catskill Delta Complex of western New York State contains fractured Upper Devonian black shales throughout a 300 km-transect from the more distal, somewhat shallower, deposits of the western region of the state eastward to more proximal and more deeply buried deposits. Each black shale unit grades upward into organically lean grey shale and abruptly overlies another grey shale unit. Within each black shale-grey shale sequence, ENE-trending vertical joints, interpreted to be hydraulic fractures, are best developed (i.e. more closely and uniformly spaced) in the organic-rich shale. Moreover, the density of ENE joints diminishes up-section through each black shale unit, as does the total organic carbon (TOC) content. While ENE joints are less well developed outside the black shale intervals, joints that formed during the Alleghanian orogeny (NW-trending) are found throughout the Upper Devonian shale sequence. Both sets are best developed in black shales in the distal delta sequence, whereas in more proximal deposits the Alleghanian joint sets are best developed in grey shales. Moreover, the density of ENE joints within each stratigraphic level of the black shale exceeds that of Alleghanian joints at the same level, except in the deepest black shale where Alleghanian joints are locally best developed at the top of the black shale interval. The preferential jointing of black shale units in the Appalachian Plateau reflects an extended hydrocarbon generation history. In the distal delta, hydrocarbon generation began when black shale was close to or at maximum burial depth (
c.
2.3 km) during the Alleghanian orogeny with the propagation of a NW joint set and continued through post-Alleghanian uplift of the Appalachian Plateau when the ENE joints propagated. In the proximal delta deposits ENE joints propagated before the onset of Alleghanian deformation suggesting that the base of the Upper Devonian section was buried to thermal maturity by progradation of the Catskill Delta Complex before the advent of Alleghanian sedimentation.
Eight distinct fault-joint geometric/genetic relationships in the Beer Sheva syncline, Israel
Authors: Bahat Dov 
Published: April 2008

Abstract
Extended research over two decades reveals more than 20 distinct fracture episodes in the Beer Sheva syncline. This paper focuses on eight fault-joint systems that differ from each other in their genetic affiliation and/or their geometric relationship and fracture properties. Two systems are linked to burial, whereas six others relate to various syntectonic-uplift associations. Joint sets within these systems are categorized into three, pre-, syn- and post-fault groups. Correspondingly, synfault early uplift and post-fault early uplift events can be distinguished from prefault and synfault late uplift events. Water drainage may be considerably improved along certain fault-joint systems. Accordingly, in formulating fracture-network models the particular distribution of fault-joint systems and their properties need to be taken into consideration.
Environmental influences on resistivity mapping for the location of clandestine graves
Authors: Scott J. , Hunter J. R. 
Published: April 2008

Abstract
Geophysical surveys are being increasingly applied for the detection of clandestine burials. Ground-penetrating radar has been used successfully but is not appropriate for many sites. For this reason, other techniques such as resistivity mapping are being tested. Resistivity is sensitive to many different changes in the ground that can be caused by a grave; however, the small physical extent of the target makes location extremely difficult. Other environmentally caused variations in resistivity may be of the same magnitude as those caused by a grave, and it is important to consider whether the resistivity anomaly caused by a grave can be detected over this background variation. This paper provides a summary of the method and discusses two case studies in which resistivity mapping was employed to locate a clandestine grave. The resistivity results of a survey over moorland were dominated by the thickness of the peat coverage while the resistivity of a survey in a river valley was dominated by various environmental variations, including a medieval furrow system. Both sites were eliminated from enquiries after extensive cadaver dog searches and some excavation, although it was considered that the environmentally caused resistivity variations at both sites would have made location of a grave by resistivity alone extremely difficult. However, the success of resistivity for landfill locations suggests that resistivity may be more appropriate for the location and delineation of larger features such as mass graves.
Colour theory and the evaluation of an instrumental method of measurement using geological samples for forensic applications
Authors: Croft Debra J. , Pye Kenneth 
Published: April 2008

Abstract

Colour is a fundamental characteristic of many materials, including soils and sediments, and has been much used in geological, pedological and Quaternary science research. Traditionally, colour has been described qualitatively by visual comparison with standard charts, such as the
Munsell Soil Color Charts
or the Geological Society of America
Rock Color Chart
. Instrumental colour determination has been developed and used in industry for a variety of applications, including quality testing of paints, dyes and foodstuffs. In this paper, colour theory is outlined, and the Minolta® CM-2002® hand-held spectrophotometer is tested on geological samples to investigate reproducibility, discriminatory power, and accuracy in analysis. Standard methods for calibration, presentation and testing of a variety of (often small) samples have been developed. Examples are provided for the use of the method in forensic geoscience casework.