bluuebunny/crossref_metadata_2025_split huggingface dataset:
Use of palynofacies analysis to define Lower Jurassic (Sinemurian to Pliensbachian) genetic stratigraphic sequences in the Wessex Basin, England
Authors: Cole David C. , Harding Ian C. 
Published: April 2008

Abstract

Quantitative palynological and palynofacies analyses allow the Lower Jurassic succession of the Dorset coast (Wessex Basin, southern England, UK) to be placed within a genetic sequence stratigraphic framework. The multifaceted approach employed utilizes various palynological criteria adopted from previous publications (e.g. both relative and absolute particle abundance data, allochthonous versus autochthonous palynomorphs ratios, phytoclast type, etc.), and suggests new parameters which may be studied in this context (e.g. ratios of acritarch spine length). Interpretation of plynofacies trends within the studied succession enables the identification of eight genetic sequences informally described as Genetic Stratigraphic Sequences I–VIII. Genetic stratigraphic sequence boundaries are placed at the following horizons: Mongrel, Grey Ledge, Pavior, the Coinstone, Hummocky, the Belemnite Stone, Day’s Shell Bed and the
margaritatus
Stone. These results compare well with sequence stratigraphic frameworks for published for the British Lower Jurassic interval both in Dorset and elsewhere, suggesting that the maximum flooding events recognized are likely to have been of inter-regional extent.
The documentation of a latest Jurassic-earliest Cretaceous uplift throughout southern England and adjacent offshore areas
Authors: McMahon Neil A. , Turner Jonathan 
Published: April 2008

Abstract
The development of the Wessex Basin, Celtic Sea Basins and the Western Approaches Trough was initiated during the break-up of Pangea with active subsidence continuing throughout the Mesozoic until the basins were inverted in the Tertiary. The Mesozoic stratigraphy in these basins is characterized by a number of unconformities. In the Early Cretaceous two major erosional events can be identified, one in the Berriasian and the second in the Aptian. These unconformities have a significant bearing on both the Cretaceous stratigraphy and the hydrocarbon potential in the region.
Stratigraphic data from onshore exposures in the Wessex Basin, from over 100 boreholes, and seismic data document the evolution and erosion pattern of both unconformities. The Aptian unconformity has been well documented by previous authors, and may be related to uplift associated with commencement of sea-floor spreading in the Bay of Biscay. However, an older unconformity can be identified as Berriasian in age on the basis of tracing its correlative conformity using vertical and lateral facies changes and a rapid lateral increase in the thickness of the Wealden Group. This older unconformity is herein interpreted to have been formed by a latest Jurassic-earliest Cretaceous uplift event and can be recognized in all basins surrounding the Cornubian Platform. The areal extent of the unconformity implies that the interpreted uplift was of regional significance, centred on the Cornubian Platform, but unlike the younger Aptian event was unrelated to any specific intra-basinal extensional event or the Apto-Albian sea-floor spreading in the nearby Bay of Biscay. Its effects dominated Early Cretaceous sedimentation, the results of which are demonstrated in subsidence patterns within these basins.
The thermal maturity of the Lias (Early Jurassic), the main hydrocarbon source rock in the area, has also been affected by the latest Jurassic-earliest Cretaceous uplift, as well as Tertiary uplift and inversion. The latest Jurassic-earliest Cretaceous event resulted in the erosion of much of the Jurassic succession in the basins closest to the Cornubian Platform, and in many areas uplifted the Lias from the top of the oil window. Only on the flanks of the uplift, where high sedimentation rates occurred during the deposition of the Purbeck and Wealden Beds, were source rocks buried to depths sufficient to generate hydrocarbons. Only by understanding the tectonic evolution of the latest Jurassic-earliest Cretaceous uplift can accurate play risk modelling and prediction of the hydrocarbon fairway take place.
Biodegradation of seep oils in the Wessex Basin — a complication for correlation
Authors: Bigge M. Ashley , Farrimond Paul 
Published: April 2008

Abstract

A detailed organic geochemical investigation of seep oils from the Dorset coast has revealed notable variation in both the extent and pathways of biodegradation. All the seep samples analysed from Mupe Bay, Stair Hole (near Lulworth Cove) and Osmington Mills have had their
n
-alkanes and acyclic isoprenoid alkanes removed, but some samples are more extensively degraded, with partial loss of steranes and/or hopanes. At Mupe Bay (conglomerate matrix samples; see Parfitt & Farrimond 1977 this volume) the hopanes have been preferentially attacked, whilst at Stair Hole the steranes appear heavily degraded although there has been no alteration to the hopane distribution. 25-Norhopanes were not detected in any of the samples.

Biological marker distributions of seep oils which have suffered no hopane or sterane biodegradation are compared with those of three reservoired oils from the area (Wytch Farm and Kimmeridge fields). Molecular parameters indicate significant variation in source rock facies and maturity within the oils of the Wessex Basin.
Reservoir architecture of the upper Sherwood Sandstone, Wytch Farm field, southern England
Authors: McKie T. , Aggett J. , Hogg A. J. C. 
Published: April 2008

Abstract

The Sherwood Sandstone Group reservoir in the Wytch Farm field comprises a
c.
150 m thick succession of arkosic sandstones deposited in a variety of fluvial, lacustrine and aeolian depositional systems. These systems show at least three orders of facies variability, which are interpreted to be the depositional response to climatic changes. These comprise a first-order evolutionary trend over the entire Sherwood Sandstone Group from perennial braidplain to ephemeral sheetflood systems to ephemeral lacustrine conditions. This trend culminated in deposition of the Mercia Mudstone Group, and reflects a long-term waning of sand supply and increasing ‘flashiness’ of the fluvial system. This trend is further subdivided into second-order cycles defined by five areally widespread floodplain and lacustrine deposits containing minimal development of fluvial sandstones. These represent widespread, episodic reductions in fluvial sediment supply and rising base level during more ‘humid’ climatic conditions. These horizons form the basis for the reservoir layering scheme. Each floodplain episode is increasingly more mud-rich upwards through the Sherwood section, and the sand-rich fluvial packages between become systematically more ephemeral in character. Third-order cycles are defined by thin (<2 m), but alreally widespread floodplain and lacustrine horizons which are most readily identifiable in the upper half of the Sherwood section. The sandstones between these cycles are composed of aeolian and sheetflood deposits, but are incised by coarse-grained multistorey-multilateral channel deposits. The incisions are interpreted to be the result of fluvial erosion during dry climatic conditions when lake levels fell and the alluvial plain was devegetated. These incised fluvial deposits form the principal producing intervals in the upper part of the reservoir, particularly in the eastern part of the field. Higher frequency stratigraphic cycles are locally expressed by variations in ephemeral lake levels, palaeosol development and episodic development of wind-blown sand patches. At outcrop, the stratigraphically equivalent Otter Sandstone Formation (
c.
100 km to the west) shows comparable evolutionary patterns, albeit with a subtly different facies make-up. The recognition of a hierarchy of climatically driven cycles within the reservoir permits high-resolution correlation and the recognition of subtle, but important, changes in sandbody geometry and connectivity within successive cycles.
Exhumation of UHP rocks by transtension in the Western Gneiss Region, Scandinavian Caledonides
Authors: Krabbendam Maarten , Dewey John F. 
Published: April 2008

Abstract

In the Western Gneiss Region (WGR) in the Scandinavian Caledonides, Scandian ecologites (
P
= 16 to >28 kbar) occur in a large area of reworked Proterozoic gneisses, structurally below a series of Scandian nappes. The top-to-the-west, extensional Nordfjord-Sogn Detachment (NSD) separates the WGR from allochthonous units, which include several late-orogenic Devonian basins. The allochthon has not experienced Scandian high-pressure (HP) metamorphism. Below the NSD, the WGR is intensely deformed under late-orogenic amphibolite-facies conditions. This deformation is bulk-constrictional, as indicated by a linear feldspar fabric within augen gneisses and tight to isoclinal, lineation-parallel folds within layered gneisses. In a later stage, the NSD, the WGR and the Devonian basins were folded by east-west trending folds, coeval with continuing movement along detachments.

To explain these features we propose a transtensional model for the late-orogenic evolution of the WGR. Transtension in West Norway had a sinistral sense and was partially partitioned with increasing transtensional angle towards the NE-SW trending Møre-Trøndelag Fault Zone in the NW. During transtension, there is a strong tendency for rejuvenation of detachments, because detachments fold and may lock as they move. In the WGR, the younger Hornelen Detachment developed above the older NSD. Transtension was the principal exhumation mechanism of the HP and ultra-high-pressure (UHP) rocks in the WGR and involved oblique plate divergence of Laurentia and Baltica during the Early Devonian.
The estimation of modal mineralogy: a problem of accuracy in core-log calibration
Authors: Harvey P. K. , Brewer T. S. , Lovell M. A. , Kerr S. A. 
Published: April 2008

Abstract
In the case study described here the quantitative modal mineralogy of a number of core samples was determined with the objective of using these modes to calibrate geochemical logs. Modal estimates were obtained for the core samples by quantitative X-ray diffraction, infrared spectroscopy, point counting of thin sections, and indirectly by calculation from a complete chemical analysis of the samples. In the case of calculated modes, three different algorithms were applied. A by-product of this particularly complete dataset is the possibility of evaluating the most accurate method of modal analysis, and although no certain conclusion is reached on this point the analysis of these data does demonstrate the difficulty of obtaining accurate modal estimates. The core samples, taken at regular intervals through a sand, sandy-shale sequence, capped by a carbonate unit, have a mineralogy which, although dominated by quartz, includes feldspars, carbonates, and clays (illite, kaolinite) together with minor phases. There was generally good agreement between methods in the estimation of quartz, total carbonate, albite, kaolinite, total clay and pyrite. The results for illite and K-feldspar were poor, a reflection of their relatively low concentrations (<10%), and problems of compositional co-linearity in the calculated modes.
Quantitative lithology: open and cased hole application derived from integrated core chemistry and mineralogy database
Authors: Herron M. M. , Herron S. L. 
Published: April 2008

Abstract
A new quantitative lithology interpretation is based on elemental concentrations of silicon, iron, calcium and sulfur available from logs. The lithology interpretation is founded on an integrated chemistry-mineralogy core database comprising over 400 samples from many wells of predominantly sand and shaly sand composition located on four continents. The lithological components include ‘clay’, which is the sum of all clay minerals; ‘carbonate’, which is the sum of calcite and dolomite; ‘anhydrite’, which is the sum of anhydrite plus gypsum; and ‘sand’ or ‘quartz-feldspar-mica’, which is the remainder of the formation essentially constituting the sand fraction. The new interpretation demonstrates that the elements aluminium alone or a combination of silicon, calcium, and iron provide a much more accurate estimation of clay than either gamma ray or its individual components potassium, thorium and uranium. Calcium alone or calcium and magnesium are used to determine carbonate concentrations. Calcium and sulfur can be used to estimate the anhydrite fraction. Having estimated the total clay, carbonate, and anhydrite fractions, the remainder of the formation is assumed to be composed quartz, feldspar, and mica minerals. Examples of the new lithology interpretation are provided for core data and also for geochemical log data from both open and cased hole environments.
Effects of water salinity, saturation and clay content on the complex resistivity of sandstone samples
Authors: Denicol P. S. , Jing X. D. 
Published: April 2008

Abstract
Complex resistivity measurements were made on sandstone samples in the frequency range from 10 Hz to 2 MHz. The main objective was to investigate the frequency response of complex resistivity and phase angle as a function of salinity, water saturation and clay content. The results showed the classical frequency dependence behaviour where the complex resistivity decreases with increasing frequency. The complex impedance behaviour in the intermediate frequency range (10–100 kHz) was used to relate the effect of frequency dispersion with interface polarization and, hence, pore geometry, specific surface area and permeability.
Both water saturation and salinity were found to influence the gradient and the relaxation frequency of the complex resistivity versus frequency relationship. A variation in water saturation from full to partial saturation resulted in a dramatic increase in the gradient and a clear shift of the relaxation frequency. Both the saturation and salinity dependence can be attributed to the polarization of both the rock-fluid and fluid-fluid interfaces within the pore space, which depend on the geometry and physical characteristics of the interfacial layers. The results presented in this paper can have important applications in identifying low resistivity and low contrast pay zones.
Sedimentation on a Humber saltmarsh
Authors: Brown Sue L. 
Published: April 2008

Abstract

Sediment deposition was measured on two transects down the profile of Skeffling marsh in four short term studies, ranging from two tidal covers to a spring tide cycle, and in longer term studies of four intervals over 18 months. Sedimentation in
Spartina
and bare areas at the same elevation at the marsh front was measured to determine the role of
Spartina
in accretion, and the effect of two levels of stem density on short term deposition was compared.

In terms of sediment deposition per number of tidal inundations at the different elevations, accretion was greatest on the upper parts of the marsh. At lower elevations, subjected to more frequent inundation, deposition generally increased with the number of tidal covers in three of the four short-term studies, although there was evidence of resuspension and/or bedload movement. During an autumn high spring tidal cycle, large amounts of sediment were deposited on the upper marsh (up to 4–5 mm), but very little sediment was retained on the lower marsh and erosion was observed on the bare mud at the marsh edge.
The longer term studies revealed accretion at all sites on the marsh compared with the initial baseline measurements, ranging between 3.2 and 6.3 cm after 18 months, depending upon the transect and elevation. At both transects, accretion was generally continuous at the upper levels, but deposition was more variable in the lower zones, particularly the bare mud at the marsh edge. This area accreted the most during the summer months, but lost material during the winter of 1996–1997 while the upper zones continued to build up.

There was no evidence to suggest that
Spartina
enhances deposition in the pioneer zone at Skeffling. The tide advances rapidly across the expanse of mudflats and scours channels around the vegetation at the marsh edge.
Spartina
is probably more effective as a sediment stabilizer during periods of erosion and any resulting net accretion is likely to be apparent only when measured over longer time scales.
Temporal variation in sediment erodibility and suspended sediment dynamics in the Dollard estuary
Authors: Kornman Bart A. , Deckere Eric M. G. T. De 
Published: April 2008

Abstract

The influence of biological activity on sediment erodibility was studied in the Dollard estuary, The Netherlands. The sediment erodibility was measured with an
in situ
flume on an intertidal flat. The hydrodynamics and suspended sediment concentrations above the flat were monitored from a measuring-bridge and in the tidal channel from a platform, using conventional instrumentation. The data from the flume, bridge and platform show that erosion resistance varied considerably from March until August 1996. A diatom bloom at the beginning of April appears to have resulted in an increase in resistance. Currents and waves were no longer able to resuspend sediment from the flat. This resulted in very low mean suspended sediment concentrations. The increase in erosion resistance did not only occur at the research site but on all flats in the Dollard. At the beginning of June, sediment erodibility increased and consequently the suspended sediment concentrations increased. This coincided with the disappearance of diatoms in May and with an increasing density of the amphipod
Corophium volutator
on the flat in June.
100 years of environmental change in a coastal wetland, Augusta Bay, southeast Sicily: evidence from geochemical and palaeoecological studies
Authors: Cundy Andrew B. , Collins Philip E. F. , Turner Simon D. , Croudace Ian W. , Horne David 
Published: April 2008

Abstract

Recent (post-1950
ad
), industrial development in southeast Sicily has resulted in extensive modification of the coastline (port construction) and a potential for persistent, chronic pollution (oil refinery and petrochemical developments). High resolution radio-metric dating (
210
Pb and
137
Cs) and palaeoenvironmental analysis of a short saltmarsh core from the Mulinello estuary (Augusta Bay) provides a record of change over the period 1880–1995
ad
. Palynological data indicate expansion of halophytic vegetation across the study area between
c
. 1880 and 1945
ad
. An increase in sediment accumulation occurred between 1945–1965
ad
, with an associated rapid change in saltmarsh vegetation occurring at the beginning of this period. Palynological and geochemical data indicate that this increase in sediment accretion is probably due to an enhanced input of catchment-area derived material. This ante-dates the main period of industrial activity in the area, and probably reflects fluvial/catchment processes rather than local anthropogenic changes. Port and industrial developments, in comparison, have had a less significant impact on marsh vegetation and sediment supply, despite large-scale disturbance at the rear of the marsh. Trace element analyses show little input of industrial effluent to the Mulinello despite its location in a heavily-industrialized area. This, combined with preliminary diatom studies, indicates that the Mulinello receives most of its sediment from inland and local sources. The rapidity of local environmental change revealed in this sequence illustrates the dynamic nature of wetlands in microtidal settings and emphasizes their potential sensitivity to both local and regional disturbance. This study also demonstrates the use of combining palaeoecological with geochemical analyses to reconstruct environmental change in fluvial and estuarine wetland settings.
Microscale biogeotechnical differences in intertidal sedimentary ecosystems
Authors: Meadows Peter S. , Murray John M. H. , Meadows Azra , Wood David Muir , West Fraser J. C. 
Published: April 2008

Abstract

Intertidal sediments are inhabited by organisms that can modify the geotechnical and sedimentological properties of the sediment. We have analysed small scale differences in these properties at four closely adjacent sites on Ardmore Bay, Clyde Estuary, Scotland. The sites were an
Enteromorpha
algal mat site (EAM), a
Corophium volutator
site (CV), the head shafts of
Arenicola marina
(AMHS) and the tail shafts of
Arenicola marina
(AMTS) burrows. Three replicate cores were taken from each site. We measured load resistance, particle size parameters of mean particle size, sorting, skewness and kurtosis, and total organic matter (TOM) and carbonate. Load resistance was measured with a newly developed microscale load resistance penetrometer which measured load resistance of the sediment at 1 mm intervals through the sediment core from the surface to 100 mm. Sediment cores were then sectioned every 10 mm and particle size, total organic matter and carbonate content measured.
In situ
shear strength measurements were also taken at the four sites. The data were analysed by bivariate correlation analysis and multivariate cluster analysis. There was a number of significant positive and negative correlations between the parameters at the four sites. Significant down-core changes in the sediment parameters and their correlations were noted. These differed between the four sites. The CV site had the largest number of significant correlations, the EAM site had the least. Cluster analyses of the sites showed that in general the sites clustered separately, although there were a number of overlaps. The EAM site showed distinct clusters for its three separate replicate cores, while the CV site clustered into a top part and a bottom part of the core. Cluster analyses of the depths across all the sites identified a break in the data at depths of between 40 and 70 mm. There was a linear relationship between field shear strength and laboratory penetration resistance. The results are discussed in relation to the fine-scale geotechnical and sedimentological heterogeneity of intertidal sediments, and the effects of biological activity.