bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimation of measurement uncertainty for
in situ
borehole determinations using a geochemical logging tool
Authors: Ramsey M. H. , Watkins P. J. , Sams M. S. 
Published: April 2008

Abstract
Methods for the estimation of measurement uncertainty are discussed with particular reference to concentration measurements made by a geochenmical logging tool (GLT; Mark of Schlumberger) in a borehole penetrating a cyclothem sequence at Northumberland, UK. Two components of uncertainty have been quantified for 6 elements determined by the GLT over a wide range of concentrations. The random component was estimated from duplicated determinations within this borehole over a 120 m depth interval. These uncertainty values ranged from 2.7% for Si to 71% for S, expressed at the 95% confidence limit. The systematic component of the uncertainty was estimated by determinations made on corresponding core samples by inductively coupled plasma atomic emission spectrometry (ICP-AES) over a 40 m depth interval. The ultimate basis for this estimation of bias was the certified reference materials which were analysed during the ICP-AES determinations. The bias measured by this method was typically in the range + 5% to −14% for 5 out of the 6 elements determined.
This method assumes that the samples analysed by both techniques are physically comparable. By depth averaging the ICP-AES determinations it was possible to reduce errors due to differences in sample size. However, a possible source of bias that was recognised is that samples were dried before ICP-AES determinations, whereas this was not the case for in situ GLT measurements. Such variability in the size of the systematic component of the uncertainty prevents the effective correction of this term as is recommended by the International Standards Organisation. The large values of measurement uncertainty found for some elements (e.g. S) will exert limitations on the geochemical interpretations made from the GLT measurements, in terms of ‘fitness-for-purpose’ criteria.
Conjunctive interpretation of core and log data through association of the effective and total porosity models
Authors: Worthington P. F. 
Published: April 2008

Abstract
Traditionally, the deterministic open-hole petrophysical evaluation of non-Archie primary reservoirs has been undertaken exclusively within one or other of two intergranular systems, those of effective and total porosity. Yet, these interpretative models can be considered conjunctively with the object of inter-model validation of petrophysical interpretation. These considerations reveal ways of demonstrating the numerical compatibility of the two approaches. The compatibility is expressed in terms of equalities that contain core-calibrated, log-derived parameters and that are founded on the underlying petrophysics. The equalities must be satisfied if the petrophysical procedures are to be applied consistently and correctly. These inter-model algorithms constitute a basis for a proposed quality assurance scheme in well-log interpretation that goes beyond tying log data back to core. They suggest quality control points at which core-calibrated log data can be examined to assess the meaningfulness and performance of interpretation procedures at different stages of the petrophysical evaluation process. These assessments form a basis for the development of measures of confidence in the practice of open-hole well-log interpretation for porosity and hydrocarbon saturation, regardless of whether the interpretation is ultimately set in the context of the effective or the total porosity model. More generally, the subject matter forms part of a broader thrust to introduce a systematic quality assurance culture into open-hole petrophysical interpretation.
Permeability prediction in anisotropic shaly formations
Authors: Xu S. , White R. 
Published: April 2008

Abstract
We present a unified model for simulating the permeability and electrical conductivity of anisotropic shaly formations. The model is based on Willis’ formulae and the concept of a host medium, the selection of which is crucial in predicting these transport properties. Different rock components, including shales and mudrocks, are characterized by parameters typifying their pore geometry, namely the aspect ratio, size and orientation distribution of the pores. In this regard the model is an extension of the elastic model of Xu & White for predicting P- and S-wave velocities in siliciclastic rocks. The electrochemical effect of clay minerals on electrical conductivity is simulated by Waxman & Smits’ model. A novel feature of the permeability model is that its percolation factor is estimated by a nonlinear transformation of the percolation factor found from conductivity measurements.
The model was tested on the laboratory measurements published by Waxman & Smits. Comparison of the results with those from the Waxman & Smits, Dual-Water, and Kozeny-Carman models, and with multilinear and non-linear regression techniques, demonstrated that the unified model predicted conductivity and permeability more accurately than any of these models from the same number or fewer parameters. The improved prediction was most noticeable in samples containing a significant clay mineral fraction. Apart from Waxman & Smits’ data, we have found no published dataset that is comprehensive enough to test physical predictions of both conductivity and permeability.
High-resolution core-log integration techniques: examples from the Ocean Drilling Program
Authors: Major C. O. , Pirmez C. , Goldberg D. 
Published: April 2008

Abstract
Cores offer the ability to describe lithological, physical, and chemical properties of rocks at the millimetre and smaller scale. However, continuous coring is expensive and only occasionally recovers 100% of the drilled interval. Microresistivity images of the borehole wall depict features down to the centimetre and smaller scale and can complement, or in some cases substitute for, core description as a means of geologic interpretation. This paper describes two techniques of integrating core data with borehole image and log data. Two case studies in carbonate rocks recovered during Ocean Drilling Program Legs 160 and 166 are presented.
Microresistivity log images, grey-scale reflectivity from core photographs, and gamma ray logs are correlated at the centimetre scale over up to 300-metre cored intervals. Direct visual correlation of core photographs with borehole images and correlation of gamma ray measurements on core with downhole logs are shown to be complementary techniques. High-resolution core-log depth matching may be best achieved by correlating multiple datasets to reduce the error inherent in each and more precisely constrain depth matching. Depth matching of individual features allows a more accurate and consistent depth scale for use in quantitative stratigraphic analysis.
Multi-scalar structure at DSDP/ODP Site 504, Costa Rica Rift, III: faulting and fluid circulation. Constraints from integration of FMS images, geophysical logs and core data
Authors: Ayadi M. , Pezard P. A. , Bronner G. , Tartarotti P. , Laverne C. 
Published: April 2008

Abstract
Downhole geophysical logs and high-resolution electrical images (FMS) from DSDP/ODP Hole 504B are analysed in combination with core data to obtain an integrated description of oceanic faults met in the hole. About 34 500 fractures were mapped from FMS images over 1672 m of basement. The fracture distribution from FMS confirms the presence of a main fault zone between 800 and 1100 mbsf (metres below sea floor), elsewhere detected from seismic data as well as magnetic, acoustic, and electrical resistivity measurements. The fracture density profile reveals the presence of two other highly fractured zones, (1) between 400 and 575 mbsf and (2) close to the bottom of Hole 504B (1700 to 2100 mbsf). Consequently, we infer that Site 504 was submitted first to an extensional stress regime near the ridge axis, with circulation of high-temperature fluids and pervasive alteration of the basalts. This initial phase is associated with the main fault met in Hole 504B. Similar but less developed deformation was generated off-axis, with lower-temperature parageneses, such as that cored between 400 and 575 mbsf. The present compressional to strike-slip stress regime is expressed in subhorizontal fracturing detected in discrete zones, such as within the main fault zone and the lower fracture zone (1700 to 2100 mbsf) in Hole 504B.
Multi-scalar structure at DSDP/ODP Site 504, Costa Rica Rift, II: fracturing and alteration. An integrated study from core, downhole measurements and borehole wall images
Authors: Tartarotti P. , Ayadi M. , Pezard P. A. , Laverne C. , De Larouziere F. D. 
Published: April 2008

Abstract
We used a database derived from the integration of core material and geophysical downhole measurements in order to investigate the relationships between fracturing and alteration in the volcanic section of DSDP/ODP Hole 504B. The studied crustal section (from top of the basement to 1000 mbsf (metres below sea floor)) consists of low resistivity/high porosity pillow lavas associated with breccias and rubble material, alternating with high resistivity/low porosity massive basalt flows. A positive correlation between DLL (Dual Laterolog)-derived porosity and occurrence of breccias in the core suggests that breccias more than fractures contribute to the electrical resistivity signal. A structural analysis performed from core suggests that most fractures and veins are steeply dipping, and may represent tectonic features or cracks due to contractional cooling of the crust, the latter being more abundant in pillows. Fractures and veins recorded on core tend to be clustered in massive units or thin flows. This result may derive from criteria adopted during structural measurements and must be taken with care. The natural radioactivity (GR) profile delineates two main alteration zones in the volcanic section: an oxidizing zone with increased potassium above, and a reducing one without K gain below. Most of the GR maxima are found to be correlated with celadonite-bearing alteration halos. GR minima are frequently located at the boundaries between domains of contrasting fracture orientation, where metasomatic reactions may have occurred due to contrasting permeability.
LISP-UK Littoral Investigation of Sediment Properties: an introduction
Authors: Black K. S. , Paterson D. M. 
Published: April 2008

Abstract
The Humber estuary on the east coast of England was selected as the study area by the UK Natural Environment Research Council (NERC) as the focus of the Land Ocean Interaction Study (LOIS) Community Research Programme. LISP-UK stands for Littoral Investigation of Sediment Properties, and is a Special Topic funded directly by LOIS. LISP-UK is concerned with the dynamics of sediment transport to and from the intertidal mudflats within the Humber estuary. This paper describes the historical, scientific and logistical basis of LISP, and provides the regional setting of the mudflat field area as a preface to LISP-related papers appearing in this volume.
The typology of intertidal mudflats
Authors: Dyer K. R. 
Published: April 2008

Abstract
A descriptive typology of intertidal mudflats is presented as the first stage of the development of a quantitative classification. This categorizes the various attributes of intertidal mudflats in terms of readily visible parameters. Mudflats are present in a wide range of tidal situations, and from exposed to sheltered from high wave energy. They can show morphological profiles indicative of erosion and deposition; concave upwards or convex upwards respectively. Their slopes can also vary widely, with some mudflats being several kilometres in width, and they possess characteristic bedforms. The sediments range from being comparatively hard to extremely soft, with complementary variations in their organic contents and biological assemblages. The relationships between these factors are shown to be distinctive of the mudflat type.
Pigment fingerprints as markers of erosion and changes in cohesive sediment surface properties in simulated and natural erosion events
Authors: Wiltshire K. H. , Tolhurst T. , Paterson D. M. , Davidson I. , Gust G. 
Published: April 2008

Abstract

The pollutant dynamics of estuaries is closely associated with the transport of particulate matter and one problematic area is the quantification of the erosion, deposition and transport of intertidal sediment. The primary event in sediment erosion is the resuspension of surficial layers which are often densely colonized by assemblages of microphytobenthos and bacteria. The dominant microphytobenthos (Bacillariophyceae or diatoms) contain characteristic marker pigments, chlorophyll c and fucoxanthin. To date, few marker compounds have been used to characterize particulate matter and to monitor its transport. This study identifies pigments as useful marker compounds in monitoring erosive events, particularly at low erosion rates. Erosion can either be considered as occurring when the stress at the surface exceeds the threshold strength of the bed or as one side of a deposition/entrainment equilibrium always occurring at the bed surface. The present analysis indicates that an erosion threshold exists and that pigments derived from surface biofilms appear in the water column before the general failure of the bed. The result is a lower yield stress (
U
*
crit
) for biofilm components than for the sediments themselves, supporting the contention that the ‘yield stress’ of natural sediments has a strong biological component, in addition to purely physical control. Pigment fingerprinting is shown to provide information on the origin of suspended matter, including the suspension and deposition of particles. The potential for using microphytobenthic pigments as indicators of erosion events in laboratory simulations (erosion and respiration chambers) and in the field is discussed.
The macrofaunal communities of the Skeffling muds (Humber estuary), with special reference to bioturbation
Authors: Davey J. T. , Partridge V. A. 
Published: April 2008

Abstract

The macrofaunal communities are described for the four transect stations of the April 1995 LISP-UK (Littoral Investigation of Sediment Properties) project. Cores of different sizes were taken to sample major bioturbating macrofauna (500 µm sieve) and smaller annelids (125 µm sieve). Three species, the small clam
Macoma balthica
and the polychaetes
Nereis diversicolor
and
Nephtys hombergii
, are discussed in detail because they have the greatest impact on sediment properties through disturbance by feeding, the construction and irrigation of burrow structures and sediment movement.
Macoma
was the only species present at all four stations, but whilst their population densities were similar, their calculated potential feeding areas varied by a factor of between 2 and 5. This affects the rate at which they disturb and re-cycle sediment by feeding.
Nereis
burrow walls at the two most shoreward stations were estimated to provide an additional sediment/water interface equivalent to 0.2–0.3 of the unburrowed area.
Nephtys
at the two most seaward stations may produce slow homogenization of surface sediments to a few centimetres depth. All macrofaunal populations were well below annual maxima that would be reached later in the year.
In situ
measurements of exopolymer production by intertidal epipelic diatom-dominated biofilms in the Humber estuary
Authors: Underwood Graham J. C. , Smith David J. 
Published: April 2008

Abstract

Epipelic diatoms are a major component of the microphytobenthos inhabiting fine cohesive sediments. Epipelic diatoms produce carbohydrate-rich exopolymers (EPS) during locomotion. By binding adjacent sediment particles and through the production of a smooth surface layer, EPS can result in biostabilization of intertidal sediments.
In situ
EPS production rates were measured during spring and neap tide periods as part of the LISP investigation carried out in the Humber Estuary, UK, in Spring 1995. There was a significant relationship between the biomass of diatoms (chl.
a
) and the concentrations of colloidal carbohydrate on the Skeffling mudflats, and the production of colloidal carbohydrate was closely linked to rates of primary production (c. 10% of photoassimilates present as colloidal-S carbohydrate). However, the production of EPS (the polymeric component of colloidal carbohydrate) was not tightly correlated with the rate of primary production, and ranged between 0.1–1.0% of net benthic primary production. Measurements of incorporation and utilization of
14
C labelled carbohydrate fractions indicated that diatoms utilized intracellular carbohydrate stores in EPS production, and that EPS production was higher during darkness and just before tidal cover.
The impact of fluid shear and the suspended sediment concentration on the mud floc size variation in the Dollard estuary, The Netherlands
Authors: Van Der Lee W. T. B. 
Published: April 2008

Abstract
Observations of floc sizes in the Dollard estuary in a tidal channel and above a tidal flat were used to obtain more insight into the contributions of fluid shear and suspended sediment concentration to flocculation. The suspended sediment concentration dominated the floc sizes in the tidal channel. There was no visible effect of fluid shear disrupting the larger flocs. The fluid shear dominated the floc sizes above the tidal flat. Measured fluid shear in both environments was, however, comparable. The close proximity of the bed above the tidal flat, with high fluid shear along this boundary, may have caused floc breakup and resuspension of the mud. This near-bed floc breakup probably decreased floc sizes over the whole water column above the tidal flat.
Seasonal variability of subtidal and intertidal sediment distributions in a muddy, macrotidal estuary: the Humber-Ouse, UK
Authors: Uncles R. J. , Stephens J. A. , Harris C. 
Published: April 2008

Abstract
Surveys of subtidal and intertidal sediment distributions were undertaken in the upper Humber and Ouse during autumn (fall) and winter. Within the Ouse, the great majority of sediment samples comprised a mixture of predominantly silt and clay (<63 µm) and very fine sand (>63 and <125 µm). A pronounced seasonal transport was observed both in subtidal lag sediments and intertidal bank sediments. The strongest difference between autumn and winter distributions of subtidal bed sediments resulted from the down-estuary movement of very fine sand from the upper reaches of the Ouse during winter. This feature was also evident in the intertidal sediments. Intertidal banks in the upper reaches of the Ouse utilized very fine sand to grow during summer and autumn, and were eroded back to stronger silt and clay substrates over the winter period. The down-channel redistribution of sand-sized sediment was a response to increased freshwater inflows over winter. This movement is approximately balanced in summer and autumn, during low freshwater inflows, by an up-channel sediment transport due to tidal velocity asymmetry and its associated flood dominance.
Spatial variability of tidal flats in response to wave exposure: examples from Strangford Lough, Co. Down, Northern Ireland
Authors: Ryan N. M. , Cooper J. A. G. 
Published: April 2008

Abstract
Strangford Lough is a shallow marine embayment, whose present form resulted from the late Glacial and Holocene marine erosion of a drumlinized coastal lowland platform. Constriction at the Lough mouth means that most waves are generated by wind blowing over restricted fetches. Tidal flats in the northern parts of Strangford Lough show variable morphology and sediment composition. Tidal flats on the up-wind margin are muddominated and located in an intact drowned drumlin landscape. Those on the downwind margins are sandy and exist in partly or wholly eroded former drumlin topography. Our preliminary results indicate strong control by wave exposure (mediated by fetch distance) over tidal flat sediments and morphology which has led to the formation of a series of spatially variable tidal flats within a single depositional basin.
At the time scale of the Holocene, exposure to wave action appears to exert a major influence on tidal flat morphology in this sediment-limited setting though its long-term control of topographical change (seen here as variable extent of drumlin erosion) and the consequent and subsequent role of this topography in determining exposure to contemporary wave action.
Relating erosion shear stress to tidal flat surface colour
Authors: Riethmüller R. , Hakvoort J. H. M. , Heineke M. , Heymann K. , Kühl H. , Witte G. 
Published: April 2008

Abstract

The relationships between erosion shear stress and bio-geochemical parameters, and between the optical reflectance spectra and bio-geochemical parameters of different tidal flats were investigated in the North Frisian part of the Wadden Sea. Erosion shear stress shows clear dependencies both on fine-grain fraction <63 µm and on the benthic diatom chlorophyll
a
concentration present in the uppermost 1 mm sediment layer. The strongest dependence of erosion shear stress on the benthic diatom chlorophyll
a
surface concentration was found for muddy areas. This dependence vanishes for sandy surface sediments. The reflectance spectra show two main classes. The first class contains information on the fine-grain fraction <63 µm of areas not covered by phytobenthos. The second class corresponds to the phytobenthos which can be subdivided into benthic diatoms and other macrophytes. A significant correlation was found between reflectance spectra and the amount of the fine-grain fraction <63 µm present and also between reflectance spectra and the benthic diatom chlorophyll
a
concentration. Thus, erosion shear stress can be related to tidal flat surface colour yielding a basis to map the erodibility of tidal flats using optical remote sensing.
Biological control of avalanching and slope stability in the intertidal zone
Authors: Shaikh Masroor A. , Meadows Azra , Meadows Peter S. 
Published: April 2008

Abstract

Sediment structure and stability are important features of soils and sedimentary environments, and are of great importance for the maintenance of estuarine, and intertidal banks and channels. Avalanching and slope stability are critical factors controlling the shape of intertidal dunes. The role of biological activity in these processes, either in the form of vegetation and roots, animal burrows, algal mats or microbial glues, is now a forefront area of research. The objective of our research has been to quantify the effects of biological activity on the avalanching of intertidal sediments. Natural microbial and meiofaunal communities and particularly burrowing infauna such as
Corophium volutator
and
Nereis diversicolor
dramatically increase angles of avalanche and factors of safety. They do not significantly alter angles of repose. Factors of safety, duration of avalanches, and percentage increase in sediment volume, all increase with increasing angles of avalanche. Video analysis of the avalanching process shows that different slope failure mechanisms are associated with the different types of biological activity, and probably reflect specific chemical and mechanical stabilizing effects produced by the different types of biological activity. These latter include tubes, extracellular polymeric materials, and a small element of compaction. These mechanisms include rotational failure, block and wedge failure and translational failure. The significance of our results for the stability of slopes under field conditions is discussed, and it is concluded that field seeding experiments in the intertidal zone with the species that we have used would be very productive.