bluuebunny/crossref_metadata_2025 huggingface dataset:
Tertiary response to oblique subduction and indentation in Sumatra, Indonesia: new ideas for hydrocarbon exploration
Authors: Howells Chris
Published: April 2008

The Tertiary basins of Sumatra, which lie along the leading edge of the Eurasian Plate, comprise a mature hydrocarbon province whose origin and subsequent evolution are closely related to the processes of oblique subduction and indentation that have resulted from the collision of the Indo-Australian and Eurasian plates. The Sumatran basins exhibit a general rift-sag geometry with broad plate-margin parallel sag basins overlying a series of N-S-oriented grabens. It is these N-S-oriented grabens, whose origin and subsequent development are still debated despite extensive oil industry data, that control the distribution of the lacustrine sediments which are the primary source-rock for hydrocarbons in Sumatra. The Ombilin Basin provides high quality outcrops of sediments of equivalent age and depositional setting that may be studied, providing new insights into petroleum exploration of the basin itself that may be applied to the more mature areas of Sumatra.

The Ombilin Basin shows a three-fold evolution. Initial sedimentation in the Eocene appears to have been controlled by normal fault displacements and not strike-slip motions. This suggests a close genetic relationship with the N-S-oriented early Tertiary grabens currently located within the back-arc region (North, Central and South Sumatra Basins), and that the Ombilin Basin did not originate as a local pull-apart related to the Sumatra Fault Zone. Subsequent sedimentation in the basin (Oligocene) was dominated by fluvial deposition which is shown to have had a tectonic control at a time of active volcanism and strike-slip faulting. This is taken to indicate modification of the initial basin style by strike-slip activity along the Sumatra Fault Zone. The final phase of sedimentation in the basin (Early Miocene) is dominated by marine deposits which form the lower part of a transgressive-regressive wedge of regional extent. This wedge of sediments buries the earlier graben systems and is related to thermal subsidence. Uplift of the basin to its present intramontane setting and differentiation from the Central and South Sumatra Basins took place in the Mid-Miocene or later.

The model for the Ombilin Basin proposed here is that of a wrench-modified rift basin and is quite different from previous models giving the possibility for development of new play concepts. A similar genetic origin to the Central and South Sumatra Basins is clearly suggested, highlighting the applicability of the Ombilin Basin as an exploration model for the Sumatra graben and other analogous basins in SE Asia.
Identification and spatial distribution of fractures in porous, siliciclastic sediments
Authors: Gabrielsen Roy H. , Aarland Randi-Kristin , Alsaker Einar
Published: April 2008

Spatial and size distribution data of fractures provide essential information in statistical bulk strain estimates and in predictive fracture scaling models for sediments which have undergone brittle deformation. Most fracture populations in naturally deformed sediments include structures which originated at different stages, and in response to different conditions during the deformation history of the rock. Hence, the final fracture population may contain fractures which genetically are related to gravitational (near-surface) instabilities, burial, uplift and unroofing, thermal expansion and contraction, and regional tectonism. Furthermore, grain size, bed thickness and different rheological properties may strongly influence the fracture style and frequency.

Particularly when only well cores are available, identification of fractures of different genetic origin is difficult, and fracture classification and predictive modelling can only be accomplished with data acquired from careful fracture logging. In such logging, information on position of the well relative to major structures, the geometry of nearby faults, and the general geological (sedimentary and tectonic) environment need to be included. Also, fracture frequencies should be compared to, and normalized according to, lithology and bed thickness, and the fracture frequency diagrams should be corrected for eventual well deviation before predictive fracture frequency modelling is performed.
Potential contamination of groundwater by pulverized fuel ash
Authors: Lee S. , Spears D. A.
Published: April 2008

Disposal sites containing pulverized fuel ash (PFA) generate leaches which could contaminate surface and groundwaters. PFA has elevated concentrations of soluble salts and trace elements, including As, B, Cd, Cr, Mo, Ni, Pb, Se, V and Zn, which are associated with the surfaces of PFA particles. Batch and column leaching tests in the laboratory have been used to predict the environmental impact of PFA. However, laboratory testing may not reproduce natural conditions in the field. The majority of the field-based studies have been concerned with the relatively rapid release of trace elements from the surfaces of the PFA particles. Less information is available on the longer-term leaching behaviour of field-disposed PFA, where elements may be originating from the silicate glass and minerals. Two recently completed field-based studies suggest that leachate from older PFA could potentially contaminate groundwater over a period of many years.
Investigation of point source pollution by chlorinated solvents in two different geologies: a multi-layered Carboniferous sandstone-mudstone sequence and the Chalk
Authors: Bishop P. K. , Lerner D. N. , Stuart M.
Published: April 2008

Two investigations of point source chlorinated solvent pollution of groundwater from very different settings are described: an industrial site in Coventry underlain by a multi-layered Carboniferous sandstone-mudstone sequence, and a village site (Sawston) underlain by Chalk in rural eastern England. The investigations are probably two of the most comprehensive studies of point source pollution by solvents in the UK. Both followed a phased approach with key elements being soil gas surveys, and definition of vertical pollution profiles through development of multi-level groundwater sampling and pore-water extraction techniques. The studies identified very significant contamination by chlorinated solvents, trichloroethene and 1,1,1-trichloroethane in the case of the Coventry site, and tetrachloroethene in the case of the Sawston site. The non-aqueous solvent phase was not detected at either site. The main similarities and differences between the studies are brought out, and the successes and failures of the studies discussed. The main successes are considered to be the development of effective soil gas and pore-water sampling methods, and sampling methods for determining vertical variations in groundwater quality. The main failures are considered to be the occurrence of cross-contamination at the Coventry site and the failure to accurately define pollution plumes. An ideal methodology is presented for future investigations, involving a phased approach maximizing the quality of information gained in each phase and preventing cross-contamination.
The retardation and attenuation of liquid radioactive wastes due to the geochemical properties of the zone of injection
Authors: Solodov Igor N.
Published: April 2008

Natural geochemical factors are of significant importance for the design of underground waste disposal systems and their subsequent operation. Analysis of geochemical similarities between liquid radioactive waste (LRW) disposal sites and sulphuric acid uranium-leaching mines in sandy aquifer horizons, has proved to be a productive approach, permitting predictive understanding of the hydrogeochemical processes which might develop in aquifer horizons subject to the injection of LRW. The approach allows the attenuative geochemical properties of terrigenous aquifers to be estimated. It is demonstrated that a number of geochemical processes (neutralization, reduction, sorption, precipitation, pore occlusion and radiolysis) in the injection zone of such aquifers may lead to attenuation, degradation and solid-phase immobilization of contaminants associated with LRW.
Turbidite flux, architecture and chemostratigraphy of the Herodotus Basin, Levantine Sea, SE Mediterranean
Authors: Reeder Mike , Rothwell Guy , Stow Dorrik A. V. , Kahler Gisela , Kenyon Neil H.
Published: April 2008

The Herodotus Basin is the deepest part of the SE Mediterranean and receives allochthonous sediments as turbidity currents and debris flows from around its margin. During the late Quaternary, characteristic supply has been from at least four sources. These are (1) dark coloured, calcium carbonate-poor fine-grained turbidites derived from the Nile Cone to the south and south-east, (2) lighter coloured, calcium carbonate-rich, slightly coarser-grained turbidites derived from the Libyan-Egyptian shelf to the south, (3) small, light brown foraminifer-rich, muddy-silty turbidites derived from the Cyprus-Eratosthenes seamount (Anatolian Rise) carbonate shelf to the east, and (4) small localized debris flow deposits derived from the Mediterranean Ridge to the north. During the late Quaternary (0–60 ka), and specifically the period of 0–27 ka, the basin has filled predominantly with allochthonous material derived from the Nile Cone, although one megaturbidite of basinwide extent was derived from the Libyan-Egyptian shelf. Turbidites have been correlated across the Herodotus Basin using the technique of chemostratigraphy. Matching the results of geochemical analysis may show whether or not the beds in different cores were deposited by the same mass-wasting event, for individual turbidites commonly have diagnostic and unique geochemical ‘fingerprints’ in terms of major, minor and trace element composition. Sediment budgets for the three main turbidite sources are calculated. The cumulative volume of the sedimentary input for the Nile Cone- derived turbidites over the last 27 ka is
c.
500 km
3
, giving an average sedimentation rate of
c.
45 cm ka
−1
, and a volume per unit time of 18 km
3
ka
−1
. A megaturbidite, derived from the Libyan-Egyptian shelf, is of basinwide extent and has a volume of
c.
400 km
3
.
The British Nuclear Fuels Drigg low-level waste site characterization programme
Authors: Sears Rob
Published: April 2008

Site characterization work is being undertaken to underpin the post-closure radiological assessment of the UK’s Drigg low-level radioactive waste disposal site. This work is providing high-quality data on the geology, hydrology and hydrogeology of the site, thus ensuring that both the monitoring programme and predictions of the radiological impact are based on a good understanding of the hydrogeology.

The programme has two phases. The first addresses the surface water balance of the site; this has been achieved by constructing a surface water balance model which has been combined with a forest interception model to determine the hydrologically effective rainfall. This model has been calibrated using extensive soil moisture data gathered on-site. The second phase is concerned with improving knowledge of the site geology and hydrogeology. Continuously cored rotary boreholes are being drilled across the site to recover geological data. Additionally, a complementary geophysical programme and trial trench studies have been undertaken. Hydrogeological data are being provided by a series of borehole clusters, drilled using cable percussion rigs, centred around the rotary boreholes. During the drilling of the cable percussion boreholes, extensive hydrogeological and hydrogeochemical data are being acquired. These data, in conjunction with data from weirs on the site streams, will provide the data required to complete the hydrogeological water balance.
Groundwater resource development and protection considerations for the Ogallala Formation in Ogallala, Nebraska
Authors: Gabriel William J. , Mason John M. , Gottler Paul F.
Published: April 2008

The Ogallala Formation is the primary stratigraphic unit of the High Plains Aquifer which comprises the largest fresh-water aquifer in the United States. The Ogallala Formation covers approximately 450 500 km
2
extending from South Dakota to west Texas and eastern New Mexico. This study focuses on the hydrogeological characteristics and resource management of the Ogallala Formation in the type locality of Ogallala, Nebraska. For this study, the geology of the Ogallala Formation was evaluated using outcrops and sub-surface data. The hydrogeological and geochemical properties of the aquifer were also characterized to assess groundwater flow and analyte distributions. The study revealed two distinct hydrostratigraphic units separated by an aquitard. Groundwater analyses indicated that the upper unit contained high concentrations of sulphate which would preclude its use as a potable water source, but that it could be used for industrial or agricultural purposes. In contrast, water in the lower unit was of high quality, and it is currently used for drinking water supply. However, water supply well construction allowed the hydraulic connection of these two units. The study concluded that adequate aquifer characterization prior to developing this groundwater resource is essential for proper development. Specifically, the proper design of pumping wells to limit the potential for mixing of non-potable water from the upper zone with high quality water within the lower unit should be considered.
Estimation of groundwater recharge on Jersey
Authors: Blackie J. R. , Houghton-Carr H. A. , McCartney M. P. , Moores J. P.
Published: April 2008

There has been growing concern that groundwater abstraction on the island of Jersey may exceed recharge, with the consequent depletion of the island’s finite water resources. A three-year study to determine groundwater recharge through hydrological modelling is nearing completion. A daily model has been developed which predicts evapotranspiration, soil moisture, recharge and streamflow from inputs of rainfall and potential evapotranspiration. Preliminary calibration of the model has used data collected from a small, intensively instrumented catchment around Trinity, Jersey, between April 1993 and December 1994. Subsequent validation, for the pre-study period January 1990 to December 1992, has shown estimated net recharge for the catchment as a whole to be 50 mm, with an initial depletion of groundwater reserves in 1990 followed by two years of positive recharge. Net recharge under a grass site was estimated to be slightly more than under arable land. Model calibration and validation will be reworked following collation of the 1995/96 dataset. The model will then be run on 25 years of catchment rainfall and potential evapotranspiration data to estimate recharge patterns over the period 1968–92, and to assess the impact of different abstraction rates.
Methods used to delineate groundwater source protection zones in England and Wales
Authors: Burgess D. B. , Fletcher S. W.
Published: April 2008

Groundwater source protection zones (GPZs) are an integral part of land surface zoning within the Environment Agency’s Policy and Practice for the Protection of Groundwater. The methods and experience gained in delineating GPZs around 1000 groundwater sources in England and Wales are reviewed. The methods include: manual calculations, hydrogeological mapping, analytical and semi- analytical modelling and numerical modelling. The large numbers of sources within a diverse number of hydrogeological settings has led to a structured approach to selecting the GPZ method appropriate to each groundwater source. This includes consideration of the protected yield, data acquisition and formulation of a conceptual flow model. The GPZ methods also include consideration of parameter uncertainty. Further developments in GPZ delineation methods are required to cope with fissured/fractured groundwater flow and to exploit the results of transient groundwater models.
Lower Palaeozoic reservoirs of North Africa
Authors: Crossley Rob , McDougall Neil
Published: April 2008

This paper provides an overview of features considered significant in the exploration and development of Lower Palaeozoic reservoirs of North Africa. Information is derived from a review of literature on the Lower Palaeozoic successions of north Africa, combined with outcrop observations from the Anti Atlas mountains of Morocco. The focus of the exploration-oriented part of the review is on identification of potential traps other than two-way structural dip closure. Stratigraphic elements described include depositional models of reservoir facies, tectonic unconformities and possible eustatic unconformities. Cases of established or potential trapping by post-depositional faulting, by diagenesis and by hydrodynamic flow are examined. Development-related topics highlighted include the impact on reservoir matrix quality of burial diagenesis and of palaeo-weathering at the Hercynian unconformity. Other issues discussed which additionally affect producibility from the reservoir matrix include tectonic fracturing, palaeotopography and unloading fracturing at the Hercynian unconformity, and induced fracturing within the present stress regimes.
The lithostratigraphy of the latest Triassic to earliest Cretaceous of the English Channel and its adjacent areas
Authors: Ainsworth Nigel R. , Braham William , Gregory F. John , Johnson Ben , King Christopher
Published: April 2008

The stratigraphy of the latest Triassic through to the earliest Cretaceous of the Portland-Wight Basin and its adjacent areas may be subdivided using petrophysical (gamma-ray and interval transit time) criteria, in association with gross lithology to allow a total of 50 lithological units to be recognized. Three units occur within the latest Triassic, 46 in the Jurassic and one in the earliest Cretaceous. The lithostratigraphy can be integrated into a biostratigraphic template using published data and subsequent observations based on micropalaeontology (ostracods, foraminiferids) and palynology (dinocysts, miospores). Throughout the study area recognition of major lithostratigraphic and biostratigraphic events enables the chronostratigraphic framework of the basin to be determined, which has aided identification of regional stratigraphic breaks throughout much of the Portland Wight Basin, including haitii in proximity to the Pliensbachian-Toarcian and the Aalenian-Bajocian boundaries, and also within the Late Oxfordian. Although the majority of the lithostratigraphic events have been deduced to be isochronous, a number of lithological units exhibit significant diachroneity. These specifically include the Frome Clay and the Great Oolite, the Kellaways Sand Member and Clay Member, and the Sandsfoot Grit Formation and the Ampthill Clay Equivalent.
Tectonic accentuation of sequence boundaries: evidence from the Lower Cretaceous of southern England
Authors: Ruffell A.
Published: April 2008

Three sequence boundaries (SB1, SB2 and SB3) are documented in the Upper Aptian
martinioides
to
jacobi
zones of the Lower Greensand Group of southern England. Correlation shows how folding affects only the strata of the lowest depositional sequence, indicating a discrete phase of tectonism in the
nutfieldiensis
zone/subzone (SB2). No similar tectonic deformation occurs at the sequence boundaries above or below. The regional features of this unconformity surface demonstrate that tectonically enhanced sequence boundaries may be discerned from those of eustatic/global tectonic origin. The tectonically enhanced sequence boundary (SB2) was initially interpreted as a transgressive surface at individual outcrops, but the regional pattern of truncation indicates that the transgressive surface is amalgamated onto a sequence boundary. Comparison of the geometry of each sequence on a regional (basin-wide) scale shows clearly the structural origin to truncation. Correlation of the three depositional sequences is made using their bounding surfaces, and the variable deposits of fuller’s earth bentonite, estuarine sand and lagoonal muds between SB1 and SB2 are resolved as time-equivalent facies deposited at the turn-around from sealevel lowstand to transgression. This correlation can be compared to that achieved by two conflicting ammonite zonal/subzonal schemes: the older biostratigraphy suggests diachroneity of the deformed lower sequence, whilst a new zonation shows this same sequence to be approximately synchronous.
Basal Wealden of Mupe Bay: a new model
Authors: Hesselbo Stephen P.
Published: April 2008

Angular stratal relationships associated with the Mupe Bay palaeo-oilseep in the Lower Cretaceous Wealden Group of South Dorset have previously been viewed as evidence of angular unconformity. An alternative (preferred) interpretation is that the succession represents rotational channel-bank collapse at the margin of a large Early Cretaceous fluvial channel. The new interpretation explains observed bedding-plane orientations and palaeocurrent directions.
The Mupe Bay oil seep: a detailed organic geochemical study of a controversial outcrop
Authors: Parfitt M. A. , Farrimond P.
Published: April 2008

The oil seep in an intraformational conglomerate at Mupe Bay has attracted much interest as providing possible evidence of oil generation in the Wessex Basin by the early Cretaceous (Wealden). Previous organic geochemical studies investigating whether oils of different maturity exist in the clasts and matrix of the conglomerate have been complicated by the effects of heavy biodegradation of the oil. In this work, we present detailed molecular organic geochemical data from a significantly larger suite of samples than has been previously studied. These have been screened using a multivariate statistical approach to identify those samples which have been least influenced by biodegradation. Conventional molecular maturity parameters applied to the subset of samples which have suffered no detectable modification to their biological marker (hopane and sterane) distributions indicate that the oil in the clasts is of exactly the same maturity as that in the matrix. However, this observation does not preclude two phases of staining, although it remains to be proven that the clasts contained oil at the time of their deposition.
Contractional and extensional structures in the transpressive ‘Big Bend’ of the San Andreas fault, southern California
Authors: Rust Derek
Published: April 2008

The San Andreas Big Bend is well known as a restraining bend producing transpressional conditions. However, field mapping in the southern part of the bend reveals a very wide (10 km) zone of active San Andreas faulting displaying a marked structural asymmetry on either side of the conspicuous central main fault trace, a result unexpected in the context of theoretical and model studies. The southern half of the fault zone is dominated by contraction and uplift in a strike-slip duplex, whereas the adjacent northern half displays a much greater number of probably older faults, particularly a succession of apparent P-shears as well as left-lateral probable R
1
-shears, producing extension and subsidence. It is proposed that these two halves of the fault zone represent mirror images of each other as a result of their positions relative to the most restraining section of the Big Bend, the shortening in the southern half being initiated as this section is approached, and the extension and complex faulting history of the northern half occurring as this terrain moves away from the most restraining section. These asymmetrical structural relationships, as well as their history of development, may be more generally applicable to major strike-slip fault zones in transpressional and, by analogy, transtensional situations. Clearly, the two halves of such fault zones are, structurally, remarkably discrete.
Salar Grande pull-apart basin, Atacama Fault System, northern Chile
Authors: Reijs Jurriaan , McClay Ken
Published: April 2008

The Salar Grande basin is a ‘poly-history’ strike-slip basin along the north-trending Atacama Fault System in northern Chile (21°S, 70°W). It exhibits a range of structures that indicate a complex evolution with multiple deformation styles. This paper presents a new interpretation of Salar Grande as a strike-slip pull-apart basin with three stages of evolution. In the first stage (Oligocene to Early Miocene), the basin opened as a sinistral strike-slip pull-apart structure at a left-stepping releasing jog of the Atacama Fault System. At the end of this stage, the basin had a rhomboidal geometry with dimensions of about 35 km length and 10 km width, bounded by a series of linked oblique-extensional basin-sidewall faults. The western sidewall faults linked to the northern fault strand of the Atacama Fault System whereas the eastern sidewall faults linked to the southern strand. The basin interior was a series of tilted fault blocks forming half-grabens. During the second stage (Oligocene to Early Miocene) a NNW-SSE basin short-cut fault developed, dissecting the basin with 6 km of sinistral offset. In the third stage (Pleistocene-Recent), NNW-SSE strike-slip faults were dextrally reactivated with displacements of up to 1 km. The understanding of field examples such as Salar Grande provides new insights into the geometries and evolution of complex multi-phase strike-slip terranes. The geometries recognized in Salar Grande compare well with analogue modelling studies of strike-slip fault systems.
Quaternary tectonics of the Pollino Ridge, Calabria-Lucania boundary, southern Italy
Authors: Schiattarella Marcello
Published: April 2008

The Pollino Ridge is a N120° trending morpho-structure, formed by Meso-Cenozoic carbonate rocks, that marks the boundary between Calabria and Lucania (southern Italy). It is bordered by Quaternary basins filled by both marine and continental sediments. A detailed geological survey and structural analysis in an area elongated perpendicular to the axis of the chain, ranging from the Morano Calabro basin to Mount Madonna del Pollino, was carried out. Data show that the entire mountain ridge and nearby Quaternary basins experienced several deformations in recent times, after the Mio-Pliocene thrust tectonics. Moreover, data are also consistent with numerous observations along the Calabria-Lucania boundary, from the Lauria Mountains to the Castrovillari basin. The present structure derives from reorganization of the pre-existing tectonogenetic configuration by Plio-Quaternary brittle tectonics. Mapping and kinematic analysis of a thrust along the northern (Lucanian) side of the Pollino Chain was performed for the first time. This thrust brings both the Cretaceous platform limestones and the Cerchiara Formation (lower Miocene age) over the Bifurto Formation (middle Miocene age). Low-angle transtensional faults along the southern (Calabrian) side were also mapped and analysed. These faults have created ‘younger-on-older’ type tectonic contacts. The present structure of the ridge is due to the effects of two different Quaternary tectonic stages. The first, lower Pleistocene in age, was characterized by strike-slip tectonics. It truncated ramp folds, producing new contractional and extensional features on the opposite sides of the carbonate ridge. The second stage occurred during middle Pleistocene times and was a purely extensional regime with a counter-Apenninic tensional axis, which reactivated the pre-existing structural pattern with different kinematics. However, both tectonic stages should be interpreted as a consequence of the continuous reorganization of the local stress fields as a result of a rotational field acting along the Pollino shear zone. The best explanation of this phenomenon seems to be a counter-clockwise block rotation of the carbonate ridge in an unchanging regional stress field.
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.