Bridging the Gap Between the Foreland and Hinterland I: Geochronology and Plate Tectonic Geometry of Ordovician Magmatism and Terrane Accretion on the Laurentian Margin of New England

U-Pb dates on magmatic and detrital zircon from samples in the hinterland of the Taconic orogen place new constraints on the timing and plate tectonic geometry of terrane accretion and magmatic arc activity. The Moretown terrane, a Gondwanan-derived exotic block, extends from the Rowe Schist-Moretown Formation contact in the west to the Bronson Hill arc in the east. Arc-related plutonic and volcanic rocks formed above an east-dipping subduction zone under the western leading edge of the Moretown terrane from approximately 500 to 475 Ma, until collision with hyperextended distal fragments of Laurentia, represented by the Rowe Schist, at 475 Ma. Magmatic arc rocks formed during this interval are primarily located in the Shelburne Falls arc, although some are also located in the Bronson Hill arc to the east. Metasedimentary rocks in the Shelburne Falls arc contain detrital zircon derived from mixing of Gondwanan, Laurentian, and arc sources, suggesting that the Moretown terrane was proximal to Laurentia by 475 Ma. Explosive eruptions at 466 to 464 Ma preserved in the Barnard Volcanic Member of the Missisquoi Formation in Vermont and as ash beds in the Indian River Formation in the Taconic allochthons may record slab-breakoff of subducted lithosphere following collision of the Moretown terrane with distal Laurentian crustal fragments. Between 466 and 455 Ma a reversal in subduction polarity lead to a west-dipping subduction zone under Laurentia and the newly accreted Moretown terrane. Magmatic arc rocks in the Bronson Hill arc formed above this west-dipping subduction zone along the eastern trailing edge of the Moretown terrane at approximately 455 to 440 Ma. The western boundary of Ganderia in New England is east of the Bronson Hill arc, buried beneath Silurian and Devonian rocks deformed during the Acadian orogeny

One Diamictite and Two Rifts: Stratigraphy and Geochronology of the Gataga Mountain of Northern British Columbia

Neoproterozoic glacial diamictites and rift-related volcanics are preserved throughout the North American Cordillera, yet the nature and timing of both glaciation and rifting are poorly constrained. New geochronological, geochemical, and stratigraphic data from the Cryogenian Gataga volcanics and bounding units at Gataga Mountain, in the Kechika Trough of northern British Columbia, better constrain the age of these rift-related volcanics and suggest that they erupted during glaciation. At Gataga Mountain, three informal sequences are exposed; a basal quartzite, the Gataga volcanics, and an overlying mixed carbonate-siliciclastic succession. The basal quartzite is dominated by cross-bedded sandstone with an intertidal facies assemblage including bidirectional cross-stratification and mud-cracks, indicative of non-glacial deposition. The overlying Gataga volcanics are over one kilometer thick, comprising both mafic and felsic units, with volcaniclastic breccia and interbedded sedimentary units including iron formation and matrix-supported diamictite with exotic clasts. Magmatic ages in the upper Gataga volcanics span 696.2 0.2 to 690.1 0.2 Ma, and detrital zircon from the underlying non-glacial quartzite provide a maximum age constraint on the onset of glaciation \u3c735.8 0.6 Ma. We interpret interfingering beds of matrix-supported diamictite with exotic clasts within the Gataga volcanics to record sub-ice shelf sedimentation and volcanism during the Sturtian Glaciation. Although volcanic facies are consistent with eruption in a sub-ice to sub-aqueous (below ice shelf) environment, we acknowledge the difficulty of distinguishing sub-glacial from sub-aqueous explosive volcanic facies. Overlying the Gataga volcanics, a mixed carbonate-siliciclastic succession contains minor basalt flows that are geochemically distinct from the underlying volcanic rocks. Based on chemostratigraphic and lithostratigraphic similarities, we suggest that this sequence is correlative with Ediacaran strata to the north. Together, we suggest that the stratigraphy and geochemical signature of volcanic rocks at Gataga Mountain records two episodes of Neoproterozoic extensionrelated sedimentation and volcanism, the first indicated by the Cryogenian Gataga volcanics and interbedded sedimentary strata and the second by the overlying Ediacaran carbonate-siliciclastic succession with interfingering basalt

Exercise metabolism in non-obese patients with type 2 diabetes following the acute restoration of normoglycaemia

This study investigated how acute restoration of normoglycaemia affected energy metabolism during exercise in nonobese patients with type 2 diabetes. Six subjects (mean ± SEM) aged 56.2 ± 2.7 years, with a BMI of 24.5 ± 1.5 kg/m2 and a VO2 peak of 28.7 ml/kg/min, attended the lab on two randomised occasions for a four-hour resting infusion of insulin or saline, followed by 30 minutes cycling at 50% VO2 peak. During the 4 h resting infusion, there was a greater (P < 0 0001) reduction in blood glucose in insulin treatment (INS) (from 11.2 ± 0.6 to 5.6 ± 0.1 mmol/l) than in saline treatment/control (CON) (from 11.5 ± 0.7 to 8.5 ± 0.6 mmol/l). This was associated with a lower (P < 0 05) resting metabolic rate in INS (3.87 ± 0.17) than in CON (4.39 ± 0.30 kJ/min). During subsequent exercise, blood glucose increased significantly in INS from 5.6 ± 0.1 at 0 min to 6.3 ± 0.3 mmol/l at 30 min (P < 0 01), which was accompanied by a lower blood lactate response (P < 0 05). Oxygen uptake, rates of substrate utilization, heart rate, and ratings of perceived exertion were not different between trials. Insulin-induced normoglycaemia increased blood glucose during subsequent exercise without altering overall substrate utilization

A Basin Redox Transect at the Dawn of Animal Life

Multiple eukaryotic clades make their first appearance in the fossil record between ~810 and 715 Ma. Molecular clock studies suggest that the origin of animal multicellularity may have been part of this broader eukaryotic radiation. Animals require oxygen to fuel their metabolism, and low oxygen levels have been hypothesized to account for the temporal lag between metazoan origins and the Cambrian radiation of large, ecologically diverse animals. Here, paleoredox conditions were investigated in the Fifteenmile Group, Ogilvie Mountains, Yukon, Canada, which hosts an 811 Ma ash horizon and spans the temporal window that captures the inferred origin and early evolution of animals. Iron-based redox proxies, redox-sensitive trace elements, organic carbon percentages and pyrite sulfur isotopes were analyzed in seven stratigraphic sections along two parallel basin transects. These data suggest that for this basin, oxygenated shelf waters overlay generally anoxic deeper waters. The anoxic water column was dominantly ferruginous, but brief periods of euxinia likely occurred. These oscillations coincide with changes in total organic carbon, suggesting euxinia was primarily driven by increased organic carbon loading. Overall, these data are consistent with proposed quantitative constraints on Proterozoic atmospheric oxygen being greater than 1% of modern levels, but less than present levels. Comparing these oxygen levels against the likely oxygen requirements of the earliest animals, both theoretical considerations and the ecology of modern oxygen-deficient settings suggest that the inferred oxygen levels in the mixed layer would not have been prohibitive to the presence of sponges, eumetazoans or bilaterians. Thus the evolution of the earliest animals was probably not limited by the low absolute oxygen levels that may have characterized Neoproterozoic oceans, although these inferred levels would constrain animals to very small sizes and low metabolic rates.Earth and Planetary SciencesOrganismic and Evolutionary Biolog

A Robust Age Model for the Cryogenian Pocatello Formation of Southeastern Idaho (Northwestern USA) from Tandem in situ and Isotope Dilution U-Pb Dating of Volcanic Tuffs and Epiclastic Detrital Zircons

Tandem in situ and isotope dilution U-Pb analysis of zircons from pyroclastic volcanic rocks and both glacial and non-glacial sedimentary strata of the Pocatello Formation (Idaho, northwestern USA) provides new age constraints on Cryogenian glaciation in the North American Cordillera. Two dacitic tuffs sampled within glacigenic strata of the lower diamictite interval of the Scout Mountain Member yield high-precision chemical abrasion isotope dilution U-Pb zircon eruption and depositional ages of 696.43 ± 0.21 and 695.17 ± 0.20 Ma. When supplemented by a new high-precision detrital zircon maximum depositional age of ≤ 670 Ma for shoreface and offshore sandstones unconformably overlying the lower diamictite, these data are consistent with correlation of the lower diamictite to the early Cryogenian (ca. 717–660 Ma) Sturtian glaciation. These 670–675 Ma zircons persist in beds above the upper diamictite and cap dolostone units, up to and including a purported “reworked fallout tuff,” which we instead conclude provides only a maximum depositional age of ≤ 673 Ma from epiclastic volcanic detritus. Rare detrital zircons as young as 658 Ma provide a maximum depositional age for the upper diamictite and overlying cap dolostone units. This new geochronological framework supports litho- and chemostratigraphic correlations of the lower and upper diamictite intervals of the Scout Mountain Member of the Pocatello Formation with the Sturtian (716–660 Ma) and Marinoan (≤ 650–635 Ma) low-latitude glaciations, respectively. The Pocatello Formation thus contains a more complete record of Cryogenian glaciations than previously postulated

Making Interdisciplinary Collaboration Work: Key Ideas, a Case Study and Lessons Learned

This article discusses the ‘lessons learned’ from an attempt to establish an interdisciplinary education research group. The growth, development and dissolution of the group are treated as an instrumental case study. Current literature on interdisciplinary collaboration is synthesized in order to provide a frame for analysis. Data was collected over several years and included three rounds of written participant reflections and documentation of group activities and meetings. Five major themes arose from the research, covering issues such as disciplinary diversity, common ground, interpersonal relationships, career pressures, and the need for concrete problems and tangible progress. Based on these themes, a number of ‘lessons learned’ are discussed which will likely be of great interest to those considering similar interdisciplinary initiatives.Cet article discute des «leçons apprises» d’une tentative visant l’établissement d’un groupe de recherche sur l’enseignement interdisciplinaire. La croissance, le développement et la dissolution du groupe sont présentés comme une étude de cas déterminante. Les ouvrages actuels portant sur la collaboration interdisciplinaire sont synthétisés de sorte à produire un cadre pour l’analyse. La collecte des données s’est étendue sur plusieurs années et a impliqué trois cycles de réflexions écrites par les participants et de documentation des activités de groupe et des réunions. Cinq grands thèmes ont découlé de la recherche, portant sur des questions comme la diversité disciplinaire, le terrain d’entente, les relations interpersonnelles, les pressions professionnelles, et le besoin de problèmes concrets et de progrès tangibles. À partir de ces thèmes, on discute de plusieurs «leçons apprises» qui intéresseront sans doute ceux qui envisagent des initiatives interdisciplinaires similaires

Early Neoproterozoic Basin Formation in Yukon, Canada: Implications for the make-up and break-up of Rodinia

SUMMARY: Geological mapping and stratigraphic anaylsis of the early Neoproterozoic Fifteenmile Group in the western Ogilvie Mountains of Yukon, Canada, has revealed large lateral facies changes in both carbonate and siliciclastic strata.  Syn-sedimentary NNW-side-down normal faulting during deposition of the lower Fifteenmile Group generated local topographic relief and wedge-shaped stratal geometries. These strata were eventually capped by platformal carbonate after the establishment of a NNW-facing stromatolitic reef complex that formed adjacent to the coeval Little Dal Group of the Mackenzie Mountains, Northwest Territories.  Correlations between specific formations within these groups are tested with carbon isotope chemostratigraphy.  As there are no known 830-780 Ma stratigraphic successions south of 62°N, the basin-forming event that accommodated the Fifteenmile and Little Dal Groups of the Ogilvie and Mackenzie Mountains and equivalent strata in the Shaler Supergroup of Victoria Island was restricted to the northwest margin of Laurentia. Therefore, this event does not represent widespread rifting of the entire western margin of Laurentia and instead we propose that these strata were accommodated in a failed rift generated by localized subsidence associated with the emplacement of the coeval Guibei (China) and Gairdner (Australia) large igneous provinces.  The northern margin of Laurentia was reactivated by renewed extension at ca. 720 Ma associated with the emplacement of the Franklin large igneous province.  Significant crustal thinning and generation of a thermally subsiding passive margin on the western margin of Laurentia may not have occurred until the late Ediacaran.RÉSUMÉLe cartographiage géologique et l’analyse stratigraphique du groupe néoprotézoïque Fifteenmile situé à l’ouest des montagnes Ogilvie du Yukon, Canada, ont révélé de grands changements latéraux de faciès à la fois pour les strates carbonatées et silicoclastiques. La mise en place des failles normales syn-sédimentaires inclinées vers le NNW au cours du dépôt du groupe Fifteenmile inférieur, a entrainé la formation locale d’un relief topographique et une prisme des strates. Ces dernières ont finalement été recouvertes de carbonates de plate-forme issus de la mise en place d’un complexe récifal stromatolitique exposé NNW contigu à la formation de même âge du groupe Little Dal des montagnes Ogilvie, en Territoires du Nord-Ouest. Les corrélations existant entre des formations spécifiques de chacun de ces groupes, sont testées grâce à la chimiostratigraphie des isotopes du carbone. Aucunes successions stratigraphiques agées de 830-780 Ma n’étant connues au sud de 62° N, la formation du bassin où sont accumulés les groupes Fifteenmile et Little Dal des massifs Ogilvie et Mackenzie, ainsi que les strates analogues du supergroupe Shaler de l’île Victoria, était restreinte à la bordure nord-ouest de la Laurentie. De ce fait, cet événement ne correspond pas au large rifting s’étendant sur l’entière bordure ouest de la Laurentie et nous proposons à la place, que ces strates ont été localisées au cours d’un rift avorté généré par la mise en place simultanée des larges provinces ignées Guibei (Chine) et Gairdner (Australie). La bordure nord de la Laurentie a été réactivée par une nouvelle phase d’extension à ca. 720 Ma associée à l’emplacement de la province ignée Franklin. L’amincissement crustal et la formation d’une marge passive thermiquement subsidente le long de la bordure ouest de la Laurentie ne se sont certainement pas produits avant l’Édiacarien supérieur

Bridging the Gap Between the Foreland and Hinterland II: Geochronology and Tectonic Setting of Ordovician Magmatism and Basin Formation on the Laurentian Margin of New England and Newfoundland

Ordovician strata of the Mohawk Valley and Taconic allochthon of New York and the Humber margin of Newfoundland record multiple magmatic and basin-forming episodes associated with the Taconic orogeny. Here we present new U-Pb zircon geochronology and whole rock geochemistry and neodymium isotopes from Early Paleozoic volcanic ashes and siliciclastic units on the northern Appalachian margin of Laurentia. Volcanic ashes in the Table Point Formation of Newfoundland and the Indian River Formation of the Taconic allochthon in New York yield dates between 466.16 ± 0.12 and 464.20 ± 0.13 Ma. Red, bioturbated slate of the Indian River Formation record a shift to more juvenile neodymium isotope values suggesting sedimentary contributions from the Taconic arc-system by 466 Ma. Eight ashes within the Trenton Group in the Mohawk Valley were dated between 452.63 ± 0.06 and 450.68 ± 0.12 Ma. These ashes contain zircon with Late Ordovician magmatic rims and 1.4 to 1.0 Ga xenocrystic cores that were inherited from Grenville basement, suggesting that the parent magmas erupted through the Laurentian margin. The new geochronological and geochemical data are integrated with a subsidence model and data from the hinterland to refine the tectonic model of the Taconic orogeny. Closure of the Iapetus Ocean by 475 Ma via collision of the peri-Gondwanan Moretown terrane with hyperextended distal fragments of the Laurentian margin is not clearly manifested on the autochthon or the Taconic allochthon other than an increase in sediment accumulation. Pro-foreland basins formed during the Middle Ordovician when these terranes were obducted onto the Laurentian margin. 466 to 464 Ma ashes on the Laurentian margin coincide with a late pulse of magmatism in both the Notre Dame arc in Newfoundland and the Shelburne Falls arc of New England that is potentially related to break-off of an east-dipping slab. Following slab reversal, by 455 Ma, the Bronson Hill arc was established on the new composite Laurentian margin. Thus, we conclude that Late Ordovician strata in the Mohawk Valley and Taconic allochthon of New York and on the Humber margin of Newfoundland were deposited in retro-foreland basins

Coulomb field of an accelerated charge: physical and mathematical aspects

The Maxwell field equations relative to a uniformly accelerated frame, and the variational principle from which they are obtained, are formulated in terms of the technique of geometrical gauge invariant potentials. They refer to the transverse magnetic (TM) and the transeverse electric (TE) modes. This gauge invariant "2+2" decomposition is used to see how the Coulomb field of a charge, static in an accelerated frame, has properties that suggest features of electromagnetism which are different from those in an inertial frame. In particular, (1) an illustrative calculation shows that the Larmor radiation reaction equals the electrostatic attraction between the accelerated charge and the charge induced on the surface whose history is the event horizon, and (2) a spectral decomposition of the Coulomb potential in the accelerated frame suggests the possibility that the distortive effects of this charge on the Rindler vacuum are akin to those of a charge on a crystal lattice.Comment: 27 pages, PlainTex. Related papers available at http://www.math.ohio-state.edu/~gerlac