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Investigating Atlantic Meridional Overturning Circulation in the Quaternary using Neodymium Isotopes
Get PDFAtlantic Meridional Overturning Circulation (AMOC) plays an important role in the global climate through its regulation of northward heat transport in the surface ocean and its
infl uence upon carbon storage in the deep ocean. Despite the efforts of both biological proxy reconstructions and modelling studies, exactly how this Atlantic overturning has evolved with past changes in the climate remains uncertain. In an effort to improve the understanding of how AMOC has varied during the Quaternary, this thesis presents measurements of neodymium (Nd) isotopes - a quasi-conservative water mass tracer - made on uncleaned foraminifera and fi sh debris from cores throughout the Atlantic Ocean covering time periods from 2.1 million years ago to the present day
Phase equilibria modelling of blueschist and eclogite from the Sanbagawa metamorphic belt of south-west Japan reveals along-strike consistency in tectonothermal architecture
No full textThe Sanbagawa metamorphic belt of southwest Japan is one of the type localities of subduction-related high-P metamorphism. However, variable pressure–temperature (P–T) paths and metabasic assemblages have been reported for eclogite units in the region, leading to uncertainty about the subduction zone paleo-thermal structure and associated tectonometamorphic conditions. To analyse this variation, phase equilibria modelling was applied to the three main high-P metabasic rock types documented in the region – glaucophane eclogite, barroisite eclogite and garnet blueschist – with modelling performed over a range of P, T, bulk rock H2O and bulk rock ferric iron conditions using thermocalc. All samples are calculated to share a common steep prograde P–T path to similar peak conditions of ∼16–20 kbar and 560–610 °C. The results establish that regional assemblage variation is systematic, with the alternation in peak amphibole phase due to peak conditions overlapping the glaucophane–barroisite solvus, and bulk composition effects stabilizing blueschist v. eclogite facies assemblages at similar P–T conditions. Furthermore, the results reveal that a steep prograde P–T path is common to all eclogite units in the Sanbagawa belt, indicating that metamorphic conditions were consistent along strike. All localities are compatible with predictions made by a ridge approach model, which attributes eclogite facies metamorphism and exhumation of the Sanbagawa belt to the approach of a spreading ridge
Evolution and dynamics of a fold-thrust belt: the Sulaiman Range of Pakistan
No full textWe present observations and models of the Sulaiman Range of western Pakistan that shed new light on the evolution and deformation of fold-thrust belts. Earthquake source inversions show that the seismic deformation in the range is concentrated in the thick pile of sediments overlying the underthrusting lithosphere of the Indian subcontinent. The slip vectors of the earthquakes vary in strike around the margin of the range, in tandem with the shape of the topography, suggesting that gravitational driving forces arising from the topography play an important role in governing the deformation of the region. Numerical models suggest that the active deformation, and the extreme plan-view curvature of the range, are governed by the presence of weak sediments in a pre-existing basin on the underthrusting Indian Plate. These sediments affect the stress-state in the over-riding mountain range and allow for the rapid propagation of the nose of the range and the development of extreme curvature and laterally varying surface gradients
The Runes of Evolution: How the Universe Became Self-Aware
No full textHow did human beings acquire imaginations that can conjure up untrue possibilities? How did the Universe become self-aware? In The Runes of Evolution, Simon Conway Morris revitalizes the study of evolution from the perspective of convergence, providing us with compelling new evidence to support the mounting scientific view that the history of life is far more predictable than once thought.
A leading evolutionary biologist at the University of Cambridge, Conway Morris came into international prominence for his work on the Cambrian explosion (especially fossils of the Burgess Shale) and evolutionary convergence, which is the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.
In The Runes of Evolution, he illustrates how the ubiquity of convergence hints at an underlying framework whereby many outcomes, not least brains and intelligence, are virtually guaranteed on any Earth-like planet. Conway Morris also emphasizes how much of the complexity of advanced biological systems is inherent in microbial forms.
By casting a wider net, The Runes of Evolution explores many neglected evolutionary questions. Some are remarkably general. Why, for example, are convergences such as parasitism, carnivory, and nitrogen fixation in plants concentrated in particular taxonomic hot spots? Why do certain groups have a particular propensity to evolve toward particular states?
Some questions lead to unexpected evolutionary insights: If bees sleep (as they do), do they dream? Why is that insect copulating with an orchid? Why have sponges evolved a system of fiber optics? What do mantis shrimps and submarines have in common? If dinosaurs had not gone extinct what would have happened next? Will a saber-toothed cat ever re-evolve?
Conway Morris observes: “Even amongst the mammals, let alone the entire tree of life, humans represent one minute twig of a vast (and largely fossilized) arborescence. Every living species is a linear descendant of an immense string of now-vanished ancestors, but evolution itself is the very reverse of linear. Rather it is endlessly exploratory, probing the vast spaces of biological hyperspace. Indeed this book is a celebration of how our world is (and was) populated by a riot of forms, a coruscating tapestry of life.”
The Runes of Evolution is the most definitive synthesis of evolutionary convergence to be published to date
Extensional salt tectonics in the partially inverted Cotiella post-rift basin (south-central Pyrenees): structure and evolution
No full textThe Cotiella Massif in the south-central Pyrenees hosts upper Cretaceous gravity-driven extensional faults which were developed in the Bay of Biscay–Pyrenean paleorift margin of the Atlantic Ocean. They accommodate up to 6 km of post-rift carbonates above relict upper Triassic salt. Subsequent Pyrenean contractional deformation preserved the main extensional features, but most of the upper Triassic salt was expulsed and then dissolved, leaving little indications of the original salt volume. Nonetheless, several distinctive salt-related features are still recognizable both at outcrop and at basin scale, providing an exposed analogue for salt-floored extensional basins developed on passive margins. Based on field research, we re-interpret the tectonic evolution of the area and suggest that passive diapirs were coeval with gravity-driven extension during the development of the Cotiella basin. The given interpretations are supported with detailed geological maps, original structural data, cross sections and outcrop photographs. The discovery of previously unknown post-rift salt structures in the Cotiella Massif is an extra element to consider in the paleogeographic reconstructions of the upper Cretaceous passive margin of the Bay of Biscay–Pyrenean realm and consequently helps in our understanding of the evolution of current Atlantic-type margins
Triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke
No full textLarge earthquakes can generate small changes in static stress: increases that trigger aftershock swarms, or reductions that create a region of reduced seismicity—a stress shadow. However, seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity. This makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks. Dyke intrusions do not generate dynamic stresses, so provide an unambiguous test of the stress shadow hypothesis. Here we use GPS and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath Bárðarbunga Volcano, central Iceland, in August 2014. We find that during dyke emplacement, bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano. We calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke. Our results imply that static stress changes help control earthquake clustering. Similar small static stress changes may be important for triggering seismicity near geothermal areas, regions being hydrofractured and deflating oil and gas fields
Geological relationships in northwestern Fogo Island and their implications for the timing of orogenic events. Newfoundland Department of Natural Resources, Geological Survey, Report 2015-1, 27-42.
No full textSedimentary and volcanic rocks in northwestern Fogo Island are traditionally assigned to the Silurian Botwood Group,
and are subdivided into the Fogo Harbour Formation (dominated by siliciclastic sedimentary rocks) and the Brimstone Head
Formation (dominated by pyroclastic rocks). These two formations have long been considered to form a continuous, con-
formable, homoclinal sequence. Detailed mapping shows that the contact between the Fogo Harbour and Brimstone Head
formations exhibits a complex geometry and that the volcanic rocks sit upon different lithostratigraphic units within the under
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lying sedimentary rocks in different places. New observations also indicate that sandstones sitting beneath the basal contact
of the Brimstone Head Formation are locally downward-facing. These results suggest that the contact between the two for-
mations is a cryptic angular unconformity across which there could be a significant time gap. It appears that the Fogo Har-
bour Formation experienced recumbent folding, uplift and erosion prior to the extrusion and deposition of the Brimstone Head
Formation. The Brimstone Head and Fogo Harbour formations are juxtaposed locally by reverse faults associated with sig-
nificant penetrative deformation.
The lowermost volcanic formation of the Botwood Group (the Lawrenceton Formation) has previously been reported to
sit unconformably upon folded rocks of the older Badger Group on nearby Change Islands. The new information from Fogo
Island suggests that there may also be a second unconformity within the sequence assigned as part of the Botwood Group,
unless the Fogo Harbour Formation is actually an unrecognized part of the older Badger Group. In either interpretation,
geochronological studies in northwestern Fogo Island could provide important constraints on the timing of Silurian and
Devonian orogenic events in the Newfoundland Appalachians
The FEniCS Project Version 1.5
Get PDFThe FEniCS Project is a collaborative project for the development of innovative concepts and tools for automated scientific computing, with a particular focus on the solution of differential equations by finite element methods. The FEniCS Projects software consists of a
collection of interoperable software components, including DOLFIN, FFC, FIAT, Instant, UFC, UFL, and mshr. This note describes the new features and changes introduced in the release of FEniCS version 1.5
Temperature dependence of oxygen- and clumped isotope fractionation in carbonates: a study of travertines and tufas in the 6-95°C temperature range
No full textConventional carbonate–water oxygen isotope thermometry and the more recently developed clumped isotope thermometer have been widely used for the reconstruction of paleotemperatures from a variety of carbonate materials. In spite of a large number of studies, however, there are still large uncertainties in both δ18O- and Δ47-based temperature calibrations. For this reason there is a need to better understand the controls on isotope fractionation especially on natural carbonates. In this study we analyzed oxygen, carbon and clumped isotopes of a unique set of modern calcitic and aragonitic travertines, tufa and cave deposits from natural springs and wells. Together these samples cover a temperature range from 6 to 95 °C. Travertine samples were collected close to the vents of the springs and from pools, and tufa samples were collected from karstic creeks and a cave. The majority of our vent and pool travertines and tufa samples show a carbonate–water oxygen isotope fractionation comparable to the one of Tremaine et al. (2011) with some samples showing higher fractionations. No significant difference between the calcite–water and aragonite–water oxygen isotope fractionation could be observed. The Δ47 data from the travertines show a strong relationship with temperature and define the regression Δ47 = (0.044 ± 0.005 × 106)/T2 + (0.205 ± 0.047). The pH of the parent solution, mineralogy and precipitation rate do not appear to significantly affect the Δ47-signature of carbonates, compared to the temperature effect and the analytical error. The tufa samples and three biogenic calcites show an excellent fit with the travertine calibration, indicating that this regression can be used for other carbonates as well. This work extends the calibration range of the clumped isotope thermometer to travertine and tufa deposits in the temperature range from 6 °C to 95 °C
Antarctic Intermediate Water properties since 400 ka recorded in infaunal (Uvigerina peregrina) and epifaunal (Planulina wuellerstorfi) benthic foraminifera
No full textReconstruction of intermediate water properties is important for understanding feedbacks within the ocean-climate system, particularly since these water masses are capable of driving high–low latitude teleconnections. Nevertheless, information about intermediate water mass evolution through the late Pleistocene remains limited. This paper examines changes in Antarctic Intermediate Water (AAIW), the most extensive intermediate water mass in the modern ocean through the last 400 kyr using the stable isotopic composition (δ18O and δ13C) and trace element concentration (Mg/Ca and B/Ca) of two benthic foraminiferal species from the same samples: epifaunal Planulina wuellerstorfi and infaunal Uvigerina peregrina. Our results confirm that the most reasonable estimates of AAIW temperature and Δ[CO2−3] are generated by Mg/CaU. peregrina and B/CaP. wuellerstorfi, respectively. We present a 400 kyr record of intermediate water temperature and Δ[CO2−3] from a sediment core from the Southwest Pacific (DSDP site 593; 40°30′S, 167°41′E, 1068 m water depth), which lies within the core of modern AAIW. Our results suggest that a combination of geochemical analyses on both infaunal and epifaunal benthic foraminiferal species yields important information about this critical water mass through the late Pleistocene. When combined with two nearby records of water properties from deeper depths, our data demonstrate that during interglacial stages of the late Pleistocene, AAIW and Circumpolar Deep Water (CPDW) have more similar water mass properties (temperature and δ13C), while glacial stages are typified by dissimilar properties between AAIW and CPDW in the Southwest Pacific. Our new Δ[CO2−3] record shows short time-scale variations, but a lack of coherent glacial–interglacial variability indicating that large quantities of carbon were not stored in intermediate waters during recent glacial periods