Jim Buckman

Chemico‐structural evolution of linguloid brachiopod shells

Chemico-structures of shells representing all families presently assigned to the Linguloidea have undergone significant transformations since the Early Cambrian. Superficial hemispherical to hemi-ellipsoidal pits on the larval and/or mature shells are interpreted as casts of deformable, membrane-bound vesicles of mucus or rigid vesicles of glycoproteins or GAGs with thickened coats. Flat-bottomed, sub-circular imprints characterize acrotheloids and many acrotretides, and could be impressions of biconvex tablets of apatite like those exocytosed within the primary layer of the obolid ‘Lingulella’? antiquissima, whilst the rhomboidal imprints of the Paterula shell could have held tablets of proteinaceous silica like those of living discinid larvae. The ancestral fabric of the linguloid secondary layer was probably composed of rubbly and virgose sets, but trellised rods of apatite (baculation) are characteristic of most linguloids and also acrotheloids. This condition was suppressed in shells identified as ‘Lingula’ from at least the Early Carboniferous to the present day. In early Palaeozoic acrotretides and lingulellotretids, columnar and camerate fabrics evolved in place of baculation. Baculation in Discinisca tenuis and Glottidia pyramidata is associated with the amino acids glutamic acid, glycine, alanine, arginine and proline which may be components of an organic polymer axial to baculate accretion.

Archaeonassa Fenton and Fenton 1937 reviewed

Archaeonassa is a poorly known ichnogenus, originally described from the Cambrian of North America, which is a member of the Scolicia ’group’, but can be regarded as distinct from Scolicia. Archaeonassa was originally based on modern material, and therefore falls into a taxonomic grey zone concerning its availability, but as A. fossulata was erected on fossil material the ichnogenus is here retained. Although exhibiting a degree of morphological plasticity in its style of ornament, Archaeonassa is considered to be monospecific, with only the ichnospecies A. fossulata recognised. The ichnogenus appears to be restricted to the Paleozoic, although similar material is well documented from modern environments. Thus the ichnogenus is expected to be geographically and stratigraphically more widespread than it otherwise appears. Archaeonassa is a valuable tool for environmental reconstruction within the Paleozoic as it occurs within intertidal deposits. The ichnogenus is interpreted chiefly as the work of gastrop...

Wettability alteration in petroleum systems: the role of polar non-hydrocarbons

Compositional changes amongst surface active components of petroleum are brought about by crude oil/brine/rock interactions. The behaviour of petroleum components following simulated petroleum migration through an initially water-saturated continuous siltstone (89.7 cm × 5 cm) core was investigated. A suite of produced oils and core extract petroleum from the core-flood experiment were analysed by Iatroscan and Gas Chromatography-Mass Spectrometry (GC-MS). Dramatic changes were observed in the composition and distributions of polar non-hydrocarbons, namely, fluoren-9-ones, carbazoles, benzocarbazoles and C0–C3 phenols indicating varying degrees of surface activity within the core-flood system. Following flooding, environmental scanning electron microscopy (ESEM) was used to view water condensation behaviour on freshly exposed core chips. Samples prepared from the original unflooded core and core material sectioned towards the outlet of the core flood displayed surfaces exhibiting hydrophilic tendencies. Meanwhile, hydrophobic behaviour was observed in a sample from the core inlet. The ESEM descriptions of the interaction of water on core surfaces appear to be consistent with the compositional changes encountered in the core extract petroleum. Wettability was altered most strongly at the core inlet where surface active compounds are rapidly removed from the migrating petroleum. In particular, small hydrophilic moieties, such as alkylphenols, appear to rapidly precondition mineral surfaces, changing wettability and subsequently allowing larger hydrophobicmolecules to sorb. Hence, petroleum surface active compounds are capable of rapidly (days to months) facilitating wettability alteration in crude oil/brine/rock systems that are initially water wet.

Palaeoenvironment of a Lower Carboniferous sandstone succession northwest Ireland: ichnological and sedimentological studies

Abstract The shallow-marine deltaic sandstones and shales of the Lower Carboniferous Mullaghmore Sandstone, northwest Ireland, contain abundant trace fossils. A twenty-five metre thick measured section of Mullaghmore Sandstone from the northwest corner of Mullaghmore Head contains a minimum of twenty-eight ichnogenera and four informally named trace fossils. At least four coarsening-upward sequences occur within the measured section, with a possible total of six. Sedimentary structures and trace fossils indicate that each sequence represents deposition in a shallow-marine deltaic environment; prodelta-interdistributary bay passing upwards into a subaqueous channel environment. These represent a Cruziana-type ichnofacies, with an interbedded tempestite-associated Arenicolites ichnofacies, and a Skolithos-type ichnofacies respectively. The ichnogenus Neonereites, more typical of the Nereites ichnofacies, also occurs within the Cruziana ichnofacies, but only in limited numbers, and is atypical of the ichnofauna. Local lateral variation in ichnogenera and their sporadic occurrence along bedding planes indicates the need for extensive investigation, if trace fossils are to be used for detailed environmental reconstruction.

A comment on annulate forms of Palaeophycus Hall 1847: With particular reference to P. 'annulatus' sensu Pemberton and Frey 1982, and the erection of P. crenulatus ichnosp. nov.

The present paper reviews the position of annulate Palaeophycus, and erects the new ichnospecies Palaeophycus crenulatus for forms of the ichnogenus with distinct axially continuous annulations. With the exception of Palaeophycus alternat us, previously described annulate ichnospecies of Palaeophycus can be considered as nomina dubia (these include Palaeophycus annulatus Badve 1987; Palaeophycus anulatus McCann and Pickcrill 1988; and Palaeophycus serratus McCann 1993). P. crenulatus is recorded from the Carboniferous of northwest Ireland and the Jurassic of Greenland, where it occurs within shallow‐water marine environments. The ichnospecies is the product of an annelid, and may have been constructed for either the purpose of sediment or suspension feeding.

An Environmental-Scanning-Electron- Microscope Investigation Into the Effect of Biofilm on the Wettability of Quartz

SummaryThe wettability relationships between oil, brine, gas, and rock are important in understanding reservoir dynamics. Chemical surfac-tants, scale inhibitors, and microbes introduced during exploration and production are all known to affect reservoir wettabilty. However, little thought has been given to the possibility of microbial con-tamination of cores during core preservation, handling, storage, or analysis and the effect that this may have on measuring parameters such as wettability. In an attempt to understand how wettability analysis of sandstone cores may be altered by the presence of micro-bial contamination, this paper examines the effect on wettability of bacterial/fungal biofilms on quartz. Wettability data for quartz and quartz colonized by bacterial/fungal biofilms were collected using an environmental scanning electron microscope (ESEM). The results illustrate that the introduction of bacteria and fungi to such systems can change wettability from hydrophilic to hydrophobic. These find-ings have important implications within the oil industry.Introduction

Charge contrast imaging of fine-scale microstructure and compositional variation in garnet using the environmental scanning electron microscope

Abstract Gaseous secondary electron (GSE) imaging of eclogite garnets under the environmental scanning electron microscope (ESEM) at low chamber gas pressures reveals detailed image contrast patterns (charge-contrast images, CCI) that are not present in back-scattered or secondary electron images. Image intensity is a function of the amount of surface charge accumulation. Successful acquisition of CCI depends on frame size and beam scan rate at a given chamber gas pressure and beam current. Images are obtained in a few seconds, and are stable and reproducible. CCI patterns do not correlate with cracks or grain boundaries, but do correspond closely to variations in major-element composition, both in the form of concentric (growth) zoning, and branching, linear features interpreted as cracks that have been healed by new garnet growth. Causes of CCI are not yet well understood, but may be related to variations in lattice defect density and their influence on charge-trapping and dissipation. These in turn influence the rate of charge build-up at or very close to the specimen surface. One interesting possibility is that CCI images detect vacancies related to non-homovalent coupled substitutions involving, for example, REE and hydroxyl, so the method offers a way of imaging the distribution of these trace species in garnets. The CCI images are rich in microstructural detail and offer the potential for rapid, high-resolution, low-noise reconnaissance mapping of intragranular microstructure and compositional variation in both natural and synthetic garnets.

Traditional cob wall: response to flooding

Purpose – The influence of flood conditions upon traditional cob construction is little understood. This paper aims to investigate the ability of cob materials to resist flood situations and documents basic failure mechanisms. This work also seeks to investigate the wettability characteristics of cob materials utilising environmental scanning electron microscopy.Design/methodology/approach – This paper takes the form of a literature review and case study underpinning laboratory experiments.Findings – Cob walls that are suitably compacted, straw reinforced and are composed and manufactured of the correct materials appear to have the ability to resist total failure when subjected to initial flood conditions, however, the duration to which these structures will remain intact has still to be ascertained, and testing is ongoing. A correlation appears to exist between the rate of cob materials compaction and the duration to which the structural integrity of the walls was retained when the samples were submerge...

Parataenidium, a new Taenidium-like ichnogenus from the Carboniferous of Ireland

The new ichnogenus Parataenidium is erected for backfilled tubular trace fossils that can appear superficially similar to Taenidium, but are divided horizontally into two distinct levels. Two ichnospecies are recognised: Parataenidium mullaghmorensis isp. nov. and Parataenidium moniliformis (Tate 1859). The latter ichnospecies is transferred from Eione Tate 1859, which is a junior homonym of Eione Rafinesque 1814, and therefore unavailable for Tates ichnotaxon. The ichnogenus is an important component of late Paleozoic shallow‐water siliciclastic sediments, and can be considered as a “guide”; indicator for the Carboniferous.

Heimdallia from the Lower Carboniferous of Ireland: H. mullaghmori a new ichnospecies, and re‐evaluation of the three‐dimensional format of the ichnogenus

Heimdallia is recorded for the first time from the Carboniferous, and the new ichnospecies Heimdallia mullaghmori is erected for material from the Lower Carboniferous of northwest Ireland. The latter ichnospecies is the first recorded branched representative of Heimdallia. Examination of well‐exposed examples of H. mullaghmori indicates the need to emend the diagnosis of Heimdallia, to allow for the concept of a horizontal basal tube, overlain by a vertical spreite‐like structure comprising inclined sediment packets, with the latter marking the former positions of upwardly inclined sections of distal tube. H. mullaghmori resembles Phycodes circinatus, as well as Teichichnus, but can nevertheless be distinguished on the basis of the discordant relationship between the inclined packets of sediment, that form the ‘spreite’, and its basal tube. H. mullaghmori is at present only recorded from the Mullaghmore Sandstone Formation, within shallow‐water deltaic siliciclastic facies, where it occurs in parallel‐lam...