Horncastle, United Kingdom
Horncastle, United Kingdom

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Hollis C.,University of Manchester | Bastesen E.,University of Bergen | Boyce A.,Scottish Universities Environmental Research Center | Corlett H.,University of Manchester | And 4 more authors.
Geology | Year: 2017

There are numerous examples of fault-controlled, so-called hydrothermal dolomite (HTD), many of which host economic mineral deposits or hydrocarbons, but there remains a lack of consensus as to how they form. In particular, multiple phases of diagenetic overprinting can obscure geochemical fingerprints. Study of a Cenozoic succession with a relatively simple burial history here provides new insights into the development of differentially dolomitized beds. The Hammam Faraun fault (HFF) block within the Suez Rift, Egypt, hosts both massive and stratabound dolostone bodies. Non-fabric-selective massive dolostone is limited to the damage zone of the fault, while fabric-selective stratabound dolostone bodies penetrate nearly 2 km into the footwall. Oligo-Miocene seawater is interpreted to have been drawn down discrete faults into a deep aquifer and convected upwards along the HFF. Escape of fluids from the incipient HFF into the lower Thebes Formation led to differential, stratabound dolomitization. Once the HFF breached the surface, fluid circulation focused along the fault plane to form younger, massive dolostone bodies. This study provides a snapshot of dolomi-tization during the earliest phases of extension, unobscured by subsequent recrystallization and geochemical modification. Contrary to many models, stratabound dolomitization preceded non-stratabound dolomitization. Fluids were hydrothermal, but with little evidence for rapid cooling and brecciation common to many HTD bodies. These results suggest that many of the features used to interpret and predict the geometry of HTD in the subsurface form during later phases of structural deformation, perhaps overprinting less structurally complex dolomite bodies. © 2017, Geological Society of America. All right reserved.


Haines T.J.,University of Aberdeen | Haines T.J.,Badley Ashton and Associates Ltd | Neilson J.E.,University of Aberdeen | Healy D.,University of Aberdeen | And 3 more authors.
Computers and Geosciences | Year: 2015

Image analysis is widely used to quantify porosity because, in addition to porosity, it can provide quantitative pore system information, such as pore sizes and shapes. Despite its wide use, no standard image analysis workflow exists. When employing image analysis, a workflow must be developed and evaluated to understand the methodological pitfalls and assumptions to enable accurate quantification of total porosity. This study presents an image analysis workflow that is used to quantify total porosity in a range of carbonate lithofacies. This study uses stitched BSE-SEM photomicrographs to construct greyscale pore system images, which are systematically thresholded to produce binary images composed of a pore phase and a rock phase. The ratio of the area of the pore phase to the total area of the pore system image defines the total porosity. Image analysis total porosity is compared with total porosity quantified by standard porosimetry techniques (He-porosimetry and mercury injection capillary pressure (MICP) porosimetry) to understand the systematics of the workflow. The impact of carbonate textures on image analysis porosity quantification is also assessed.A comparison between image analysis, He-porosimetry and MICP total porosity indicates that the image analysis workflow used in this study can accurately quantify or underestimate total porosity depending on the lithofacies textures and pore systems. The porosity of wackestone lithofacies tends to be significantly underestimated (i.e. greater than 10%) by image analysis, whereas packstone, grainstone, rudstone and floatstone lithofacies tend to be accurately estimated or slightly underestimated (i.e. 5% or less) by image analysis. The underestimation of image analysis porosity in the wackestone lithofacies is correlated to the quantity of matrix pore types and is thought to be caused by incomplete imaging of microporosity and by unrepresentative fields of view. Image analysis porosity, which is calculated from 2D areas, is comparable with 3D porosity volumes in lithofacies that lack or are weakly microporous; in such lithofacies, image analysis is assumed to be accurately measuring other 2D parameters, including pore sizes and shapes. © 2015 Elsevier Ltd.


Ventra D.,University Utrecht | Ventra D.,University of Geneva | Cartigny M.J.B.,UK National Oceanography Center | Bijkerk J.F.,British Geological Survey | Acikalin S.,Badley Ashton and Associates Ltd.
Geology | Year: 2015

Deposits of fluvial systems in highly seasonal tropical climates possess unique architectural and facies characters owing to a flood-prone regime alternating with lengthy periods of ineffective discharge. Distally linked deltaic successions should also feature distinctive attributes, with great potential to preserve the stratigraphic evidence of exceptional discharge events. We describe Late Carboniferous deltafront, valley-confined sandstones from the Pennine Basin (UK), originally deposited at paleoequatorial latitudes during final assembly of the Pangean megacontinent and characterized by giant sedimentary structures with repetitively sigmoidal geometry. Facies traits indicate geologically instantaneous deposition of a large sediment volume from a density current at sustained supercritical-flow conditions, leading to aggradation of cyclic steps, recently identified bedforms developing in high-energy flows and of which this is the first complete outcrop example. The lack of unconformable erosional surfaces and absence of different associated facies point to a single aggradational event during which the structures attained dimensions comparable to those indicated by seismic data sets from which they are remotely detected on modern seafloors. Cyclic-step formation in a deltaic setting suggests that Pangean megamonsoons could have triggered hydrologic events capable of imprinting sedimentologic signatures on shallow-marine deposits. © 2015 Geological Society of America.


Michie E.A.H.,University of Aberdeen | Michie E.A.H.,Badley Geoscience Ltd | Haines T.J.,University of Aberdeen | Haines T.J.,Badley Ashton and Associates Ltd
Petroleum Geoscience | Year: 2016

Selected carbonate-hosted normal fault zones on the island of Malta have been analysed to assess the potential impact of fault rocks on fluid flow (i.e. fault seal). Fault displacement ranging from <1 to 90 m has allowed systematic investigation of the evolution of fault-rock types, distribution and properties with increasing displacement. The focus has been on examining locations of fault-rock formation, because this significantly affects fluid-flow pathways across and along faults, and the types of fault rock formed. The location of fault rock is dependent on the fault-zone architecture. Fault zones on Malta have architectures with multiple slip surfaces within weaker carbonate layers, distributing fault rock onto several slip surfaces. This distribution prevents formation of a continuous fault core, particularly at lower displacements (<30 m). The discontinuous fault core causes these faults to be transmissive, allowing fluids to flow across the fault. The hydraulic behaviour is also a function of the deformation mechanisms active in the formation of fault rocks. Lithological heterogeneity in a faulted carbonate succession leads to a variety of deformation mechanisms, generating up to nine different fault-rocks types with a range of deformation microstructures along a single slip surface. The type of fault rock formed is a function of the host rock texture, juxtaposition, displacement and deformation conditions. Each deformation microstructure has different petrophysical properties, causing the porosity and permeability to vary along-strike and downdip on any slip surface, affecting the fault’s hydraulic behaviour. The extent of the poroperm variation depends on lithofacies juxtaposition and displacement: juxtaposition of similar lithofacies reduces poroperm variation and juxtaposing different lithofacies at higher displacements (>30 m) increases the range of poroperm. © 2016 The Author(s).


Cavailhes T.,Montpellier University | Cavailhes T.,Badley Ashton and Associates Ltd. | Sizun J.-P.,University of Franche Comte | Labaume P.,Montpellier University | And 8 more authors.
AAPG Bulletin | Year: 2013

We describe the structure, microstructure, and petrophysical properties of fault rocks from two normal fault zones formed in low-porosity turbiditic arkosic sandstones, in deep diagenesis conditions similar to those of deeply buried reservoirs. These fault rocks are characterized by a foliated fabric and quartz-calcite sealed veins, which formation resulted from the combination of the (1) pressure solution of quartz, (2] intense fracturing sealed by quartz and calcite cements, and (3) neoformation of synkinematic white micas derived from the alteration of feldspars and chlorite. Fluid inclusion microthermometry in quartz and calcite cements demonstrates fault activity at temperatures of 195°C to 268°C. Permeability measurements on plugs oriented parallel with the principal axes of the finite strain ellipsoid show that the Y axis [parallel with the foliation and veins) is the direction of highest permeability in the foliated sandstone (10-2 md for Y against 10-3 md for X, Z, and the protolith, measured at a confining pressure of 20 bars). Microstructural observations document the localization of the preferential fluid path between the phyllosilicate particles forming the foliation. Hence, the direction of highest permeability in these fault rocks would be parallel with the fault and subhorizontal, that is, perpendicular to the slickenlines representing the local slip direction on the fault surface. We suggest that a similar relationship between kinematic markers and fault rock permeability anisotropy may be found in other fault zone types (reverse or strike-slip) affecting feldspar-rich lithologies in deep diagenesis conditions.


Cavailhes T.,Montpellier University | Cavailhes T.,Badley Ashton and Associates Ltd. | Soliva R.,Montpellier University | Labaume P.,Montpellier University | And 7 more authors.
Geophysical Research Letters | Year: 2013

Phyllosilicate content and related permeability of fault zones form primary controls on hydraulic and mechanical behavior of the brittle crust. Hence, understanding and predicting the localization of these ubiquitous minerals is a major issue for fundamental and applied geosciences. We describe normal fault zones cutting a foreland arkosic turbiditic formation suffering high-T diagenesis and formed under conditions (~200°C) typical of deeply buried reservoirs and common within the seismogenic interval. Microstructural analyses show a large proportion of phyllosilicates (up to 34%) in the fault rock, derived from near-complete feldspar alteration and disaggregation during deformation. This study shows that even faults with offsets (~20 cm) much lower than bed thickness can have such large feldspar-to-phyllosilicate transformation ratios, implying that the origin of the phyllosilicates is purely transformation related. These results imply that the potential sealing capacity and strength of faults could be predicted from the host rock feldspar content. Where sealing capacity and fault strength can be related to phyllosilicate content, these properties can then also be inferred from the predicted phyllosilicate content: this opens up new horizons concerning the hydraulic and the mechanical behavior of the upper crust. Key Points first quntification of phyllosilicates formation Shale Gouge ratio has to be modified in deeply buried reservoir Feldspar content of host rock as a predictive proxy. © 2013. American Geophysical Union. All Rights Reserved.


Dasgupta K.,Badley Ashton and Associates Ltd. | Kostic B.,Badley Ashton and Associates Ltd.
Society of Petroleum Engineers - European Unconventional Resources Conference and Exhibition 2014: Unlocking European Potential | Year: 2014

For a holistic characterisation of fine-grained unconventional reservoirs, our integrated approach utilises coherent, reproducible datasets and refined work practices carried out within a comprehensive quality management system. A typical reservoir characterisation includes integration of sedimentological, structural and pore-scale datasets, however, the specific work flow design depends entirely on the nature of the problem and the availability of appropriate data. This paper illustrates an example of unconventional reservoir characterisation of a fine-grained formation from the North Sea where the specific aims were to establish the depositional framework for recognising sedimentary environments, recommend sample locations to target specific queries within the sedimentological context for petrographical and geochemical analyses, to investigate what porosity types are present and to assess 'brittleness' of the rocks. First and foremost, high-resolution interpretative graphic core descriptions were carried out at 1:24 scale, utilising Badley Ashton's mudrock-specific lithotypes and depositional packages schemes. Lithotype characterisation uniquely captures very fine-scale attributes (bed to subbed scale), whilst upscaled depositional packages (bed-stack scale) provide a more holistic characterisation from core, as well as from wireline and image logs, where available. Plugs coded by the above descriptors were selected post-logging, for detailed petrographical and geochemical analysis including Rock-Eval pyrolysis within the sedimentological/structural context. Mineralogical data was acquired by whole-rock and clay-fraction XRD analysis, whilst pore-scale fabric/textural investigation were undertaken by conventional light microscopy and BS-SEM. A subset of the plugs was subjected to FIB SEM analysis to characterise any potentially organic matter associated pore system. All these different strands of data were then integrated to evaluate and link the depositional system/sedimentary environment, storage capacity and brittleness of the reservoir in order to assess the overall reservoir potential of the fine-grained formation.


Boix C.,Badley Ashton and Associates Ltd | Frijia G.,University of Potsdam | Vicedo V.,Autonomous University of Barcelona | Bernaus J.M.,Statoil | And 3 more authors.
Cretaceous Research | Year: 2011

The Upper Cretaceous La Cova limestones (southern Pyrenees, Spain) host a rich and diverse larger foraminiferal fauna, which represents the first diversification of K-strategists after the mass extinction at the Cenomanian-Turonian boundary.The stratigraphic distribution of the main taxa of larger foraminifera defines two assemblages. The first assemblage is characterised by the first appearance of lacazinids (Pseudolacazina loeblichi) and meandropsinids (Eofallotia simplex), by the large agglutinated Montsechiana montsechiensis, and by several species of complex rotalids (Rotorbinella campaniola, Iberorotalia reicheli, Orbitokhatina wondersmitti and Calcarinella schaubi). The second assemblage is defined by the appearance of Lacazina pyrenaica, Palandrosina taxyae and Martiguesia cyclamminiformis.A late Coniacian-early Santonian age was so far accepted for the La Cova limestones, based on indirect correlation with deep-water facies bearing planktic foraminifers of the Dicarinella concavata zone. Strontium isotope stratigraphy, based on many samples of pristine biotic calcite of rudists and ostreids, indicates that the La Cova limestones span from the early Coniacian to the early-middle Santonian boundary. The first assemblage of larger foraminifera appears very close to the early-middle Coniacian boundary and reaches its full diversity by the middle Coniacian. The originations defining the second assemblage are dated as earliest Santonian: they represent important bioevents to define the Coniacian-Santonian boundary in the shallow-water facies of the South Pyrenean province.By means of the calibration of strontium isotope stratigraphy to the Geological Time Scale, the larger foraminiferal assemblages of the La Cova limestones can be correlated to the standard biozonal scheme of ammonites, planktonic foraminifers and calcareous nannoplankton. This correlation is a first step toward a larger foraminifera standard biozonation for Upper Cretaceous carbonate platform facies. © 2011 Elsevier Ltd.


Di Staso A.,University of Naples Federico II | Perrone V.,Urbino University | Perrotta S.,Urbino University | Perrotta S.,Badley Ashton and Associates Ltd. | And 2 more authors.
Comptes Rendus - Geoscience | Year: 2010

In the Beni Issef Massif, nearly 30 km west of Chefchaouen (Morocco), the thickest post-nappe succession within the Rifian sector of the Maghrebian Chain seals the tectonic contact between the Intrarifian External Tanger and Loukkos Units, related to the Rifian External Domain. This succession is very important for the reconstruction of the deformation timing of the Rifian Maghrebids. The age of its base, in fact, is an important constraint for defining an upper boundary to the stacking of both the Intrarifian and Maghrebian Flysch Basin Units, because clasts fed by the Melloussa and Numidian Flysch Nappes are abundant in the conglomerate layers. Field and biostratigraphic analyses pointed out the presence of a Lower Beni Issef Fm, unconformable on the Intrarifian External Tanger and Loukkos Units, and an Upper Beni Issef Fm, unconformable on both the Intrarifian Units and the Lower Beni Issef Fm. The Lower Beni Issef Fm, 150 m thick, consists of lenticular conglomerates with huge blocks in a marly-clayey matrix, followed by marls and minor sandstones. It deposited in a siliciclastic platform, shows a fining upward trend and is affected by metre- to hectometre-sized, locally reversed, folds. Samples collected 45-50 m above the base of the formation resulted not older than Late Tortonian in age, but an older age for the base of the formation cannot be excluded. The Upper Beni Issef Fm, up to 550 m thick, starts with coarse conglomerates followed by medium- to coarse-grained well-bedded sandstones and by grey-blue marls and mudrocks. It indicates deposition in a channelized marine delta, with evolution towards pro-delta pelites, and shows sub-horizontal or gently dipping beds towards the east. Biostratigraphic data indicate a probable Messinian age for this formation. The composition of the arenites of both Lower Beni Issef and Upper Beni Issef Fms is quartzolithic and all samples show a notable content of monocrystalline well-rounded quartz and sedimentary lithic fragments. Detrital modes, all falling in the Quartzose Recycled and Transitional Recycled fields, suggest a provenance from recycling of sedimentary successions, easily recognizable in the Flysch Basin and External Units, mainly the Numidian Nappe sandstones. A Tortonian age of the Lower Beni Issef Fm would agree with the Late Serravallian age of the uppermost beds of the External Tanger Unit and indicate that the most probable age for the stacking of the Intrarifian Units falls in the Late Serravallian-Middle Tortonian time span. The Lower Beni Issef Fm was involved in a compressive tectonic phase testified by north-south striking folds. Later, probably during Messinian, the Upper Beni Issef Fm deposited in a younger intramontane basin, resting on both the Intrarifian Units and the Lower Beni Issef Fm. Successively, the Upper Beni Issef Fm was passively transported piggyback on top of the fold and thrust belt during later tectonic evolution of the Rifian Maghrebids. This tectonic evolution results quite similar to that recognized in the Tellian and Sicilian Maghrebids and also in the southern Apennines. © 2010 Académie des sciences.


Perrone V.,Urbino University | Perrotta S.,Badley Ashton and Associates Ltd. | Marsaglia K.,California State University, Northridge | Di Staso A.,Urbino University | Tiberi V.,Urbino University
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2014

Ophiolite-derived debrites, microbreccias and olistoliths are interbedded in the Monte Morello and Argille Varicolori Formations of the Val Marecchia Nappe, constituting the highest tectonic unit of the north-eastern Apennines and usually considered as having originated from the External Ligurian Domain.The ophiolite-derived clastic rocks were supplied exclusively by an oceanic sequence, consisting of peridotite, gabbro, basalt, radiolarite, pelagic limestone and shale. They are interbedded within a succession made up of fine-grained carbonate and siliciclastic turbidites, and of pelagic claystones.Petrographic and sedimentological features of the ophiolite-derived breccia and sandstone units testify to an intrabasinal source area for these clastic rocks rather than an extrabasinal origin from subaerially exposed oceanic crust, forming the inner flank of the basin, as previously suggested. Due to their Oligocene-earliest Miocene age, the deposits in which debrites and olistoliths occur, are related to Early Neo-Alpine tectonic events that caused reactivation and/or inversion of old normal/transform faults. Unstable fault escarpments provided a preferential path for submarine landslide and turbidite emplacement. Debrites, microbreccias and olistoliths, therefore, were added to the basin fill of fine-grained turbidite and pelagic deposits.This study suggests that the Val Marecchia Nappe succession was deposited on an oceanic substratum. Stratigraphy and age of the succession of this nappe can be well framed only in the evolution of the Sub-ligurian Domain, whereas they conflict with the interpretation of the Val Marecchia Nappe as a nappe originated from the External Ligurian Domain, as suggested previously by most authors. This interpretation also requires an oceanic substratum for the Sub-ligurian Domain, i.e. the existence of an oceanic belt external to the Ligurian Domain, which was deformed only in the Early Miocene. The Sub-ligurian Domain, therefore, would be an eastern branch of the Central Tethys and would represent the extension in the Northern Apennines of the Maghrebian-Lucanian oceanic realm, as recognized in the Betic Cordillera, Maghrebian Chain and Southern Apennines. © 2013 Elsevier B.V.

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