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Horncastle, United Kingdom

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

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. Source

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

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. Source

Bonin A.,Badley Ashton and Associates Ltd | Puceat E.,CNRS Biogeosciences Laboratory | Vennin E.,CNRS Biogeosciences Laboratory | Mattioli E.,CNRS Geological Laboratory of Lyon: earth, planets and environment | And 4 more authors.

The Early Aptian encountered several crises in neritic and pelagic carbonate production, major perturbations in the carbon cycle, and an oceanic anoxic event (OAE1a). Yet the causal links between these perturbations and climate changes remain poorly understood, partly because temperature records spanning the Early Aptian interval are still scant. We present new δ18O data from well-preserved bivalves from a carbonate platform of the Galve subbasin (Spain) that document a major cooling event postdating most of OAE1a. Our data show that cooling postdates the global platform demise and cannot have triggered this event that occurred during the warmest interval. The warmest temperatures coincide with the time equivalent of OAE1a and with platform biotic assemblages dominated by microbialites at Aliaga as well as on other Tethyan platforms. Coral-dominated assemblages then replace microbialites during the subsequent cooling. Nannoconids are absent during most of the time equivalent of the OAE1a, probably related to the well-known crisis affecting this group. Yet they present a transient recovery in the upper part of this interval with an increase in both size and abundance during the cool interval portion that postdates OAE1a. An evolution toward cooler and drier climatic conditions may have induced the regional change from microbial to coral assemblages as well as nannoconids size and abundance increase by limiting continent-derived input of nutrients. ©2015. American Geophysical Union. All Rights Reserved. Source

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

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. Source

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

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. Source

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