Thermal, chemical, alternating field (AF) and two‐stage (AF followed by thermal) experiments were performed on 18 sites (217 specimens) of three sedimentary units (groups A, B and C) of the Mascarene Group of southwestern New Brunswick. Groups A and B of Pembroke age (late Late Silurian) apparently carry a dual polarity initial remanence yielding a pole at 087°E, 05°S. Group C of probably Waweig age (older than Pembroke) carries a magnetite remanence and a hematite remanence with the former probably being the initial and yielding a pole at 085°E, 28°N. This would indicate a pole shift of some 30° southwards relative to the sampling area during the Upper Silurian, in agreement with the hypothesis that considerable polar shift took place during the Siluro‐Devonian period. The extensive experimental work (over 4000 treatments) demonstrates the need to use several techniques in the pursuit of the magnetic history of the rock. For example, if the work had been limited to thermal treatment up to 650°C, an overprinted or more likely an apparent remanence could conceivably have been mistaken for the initial remanence. Conversely, the considerable information gathered through the use of different techniques allows one to advance and model the most probable scenario of remanence acquisition while contributing additional knowledge about the magnetic characteristics of sedimentary units. Results from this investigation, including those of a Mascarene Group intrusion also reported here, are discussed in the context of Siluro‐Devonian poles of North America. Different options are open to the interpreter attesting to the difficulties in establishing both the rock and remanence ages. It is concluded that more data from detailed investigations are needed before the evolution of the eastern seaboard and the Appalachians can be retraced by paleomagnetic means.
The Newry Igneous Complex (NIC) in Northern Ireland comprises three largely granodioritic plutons, together with an intermediate-ultramafic body at its northeast end. Geochronology shows that the NIC becomes broadly younger to the southwest and towards the centres of individual plutons. Geophysical results from the recent Tellus Survey of Northern Ireland have been combined with petrology and geochemistry to establish 17 distinct zones within the NIC, which are interpreted to represent separately intruded magma pulses. A combination of Anisotropy of Magnetic Susceptibility (AMS), petrographical and field data shows that the NIC was emplaced as a series of laccoliths into a tension-releasing bend on a strike-slip fault. This regime is proposed to have been facilitated by two deep-seated crustal lineaments. Inflation is suggested to have occurred due to magma pressure during emplacement of each individual zone. At least five constituent parts of the NIC are interpreted to have been emplaced separately at successively higher crustal levels. Thus the intrusion is thought to represent a series of stacked laccoliths, produced by a southwestward migrating source.
The Tellus high-resolution airborne magnetic and radiometric maps define previously unmapped zones within the Newry Igneous Complex, County Down.High-precision uranium-lead zircon dating of nine rock samples from different parts of the complex provides a robust set of age constraints (c.414-407 Ma), which confirm that the different plutons of the complex young towards the south-west.Combined, these new data allow an innovative model of intrusion to be developed, with intrusion beginning in the north-east and progressing towards the south-west.
Marine dinoflagellates produce a diversity of polyketide toxins that are accumulated in marine food webs and are responsible for a variety of seafood poisonings. Reef-associated dinoflagellates of the genus Gambierdiscus produce toxins responsible for ciguatera poisoning (CP), which causes over 50,000 cases of illness annually worldwide. The biosynthetic machinery for dinoflagellate polyketides remains poorly understood. Recent transcriptomic and genomic sequencing projects have revealed the presence of Type I modular polyketide synthases in dinoflagellates, as well as a plethora of single domain transcripts with Type I sequence homology. The current transcriptome analysis compares polyketide synthase (PKS) gene transcripts expressed in two species of Gambierdiscus from French Polynesia: a highly toxic ciguatoxin producer, G. polynesiensis, versus a non-ciguatoxic species G. pacificus, each assembled from approximately 180 million Illumina 125 nt reads using Trinity, and compares their PKS content with previously published data from other Gambierdiscus species and more distantly related dinoflagellates. Both modular and single-domain PKS transcripts were present. Single domain β-ketoacyl synthase (KS) transcripts were highly amplified in both species (98 in G. polynesiensis, 99 in G. pacificus), with smaller numbers of standalone acyl transferase (AT), ketoacyl reductase (KR), dehydratase (DH), enoyl reductase (ER), and thioesterase (TE) domains. G. polynesiensis expressed both a larger number of multidomain PKSs, and larger numbers of modules per transcript, than the non-ciguatoxic G. pacificus. The largest PKS transcript in G. polynesiensis encoded a 10,516 aa, 7 module protein, predicted to synthesize part of the polyether backbone. Transcripts and gene models representing portions of this PKS are present in other species, suggesting that its function may be performed in those species by multiple interacting proteins. This study contributes to the building consensus that dinoflagellates utilize a combination of Type I modular and single domain PKS proteins, in an as yet undefined manner, to synthesize polyketides.
In light of global reef decline new methods to accurately, cheaply, and quickly evaluate coral metabolic states are needed to assess reef health. Metabolomic profiling can describe the response of individuals to disturbance (i.e., shifts in environmental conditions) across biological models and is a powerful approach for characterizing and comparing coral metabolism. For the first time, we assess the utility of a proton-nuclear magnetic resonance spectroscopy (1H-NMR)-based metabolomics approach in characterizing coral metabolite profiles by 1) investigating technical, intra-, and inter-sample variation, 2) evaluating the ability to recover targeted metabolite spikes, and 3) assessing the potential for this method to differentiate among coral species. Our results indicate 1H-NMR profiling of Porites compressa corals is highly reproducible and exhibits low levels of variability within and among colonies. The spiking experiments validate the sensitivity of our methods and showcase the capacity of orthogonal partial least squares discriminate analysis (OPLS-DA) to distinguish between profiles spiked with varying metabolite concentrations (0 mM, 0.1 mM, and 10 mM). Finally, 1H-NMR metabolomics coupled with OPLS-DA, revealed species-specific patterns in metabolite profiles among four reef-building corals (Pocillopora damicornis, Porites lobata, Montipora aequituberculata, and Seriatopora hystrix). Collectively, these data indicate that 1H-NMR metabolomic techniques can profile reef-building coral metabolomes and have the potential to provide an integrated picture of the coral phenotype in response to environmental change.
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